ID: 36267332
Title: NOS1AP is a novel molecular target and critical factor in TDP-43 pathology.
Abstract: Many lines of evidence have highlighted the role played by heterogeneous nuclear ribonucleoproteins in amyotrophic lateral sclerosis. In this study, we have aimed to identify transcripts co-regulated by TAR DNA-binding protein 43 kDa and highly conserved heterogeneous nuclear ribonucleoproteins which have been previously shown to regulate TAR DNA-binding protein 43 kDa toxicity (deleted in azoospermia-associated protein 1, heterogeneous nuclear ribonucleoprotein -Q, -D, -K and -U). Using the transcriptome analyses, we have uncovered that Nitric Oxide Synthase 1 Adaptor Protein mRNA is a direct TAR DNA-binding protein 43 kDa target, and in flies, its modulation alone can rescue TAR DNA-binding protein 43 kDa pathology. In primary mouse cortical neurons, we show that TAR DNA-binding protein 43 kDa mediated downregulation of Nitric Oxide Synthase 1 Adaptor Protein expression strongly affects the NMDA-receptor signalling pathway. In human patients, the downregulation of Nitric Oxide Synthase 1 Adaptor Protein mRNA strongly correlates with TAR DNA-binding protein 43 kDa proteinopathy as measured by cryptic Stathmin-2 and Unc-13 homolog A cryptic exon inclusion. Overall, our results demonstrate that Nitric Oxide Synthase 1 Adaptor Protein may represent a novel disease-relevant gene, potentially suitable for the development of new therapeutic strategies.

ID: 36922834
Title: The era of cryptic exons: implications for ALS-FTD.
Abstract: TDP-43 is an RNA-binding protein with a crucial nuclear role in splicing, and mislocalises from the nucleus to the cytoplasm in a range of neurodegenerative disorders. TDP-43 proteinopathy spans a spectrum of incurable, heterogeneous, and increasingly prevalent neurodegenerative diseases, including the amyotrophic lateral sclerosis and frontotemporal dementia disease spectrum and a significant fraction of Alzheimer's disease. There are currently no directed disease-modifying therapies for TDP-43 proteinopathies, and no way to distinguish who is affected before death. It is now clear that TDP-43 proteinopathy leads to a number of molecular changes, including the de-repression and inclusion of cryptic exons. Importantly, some of these cryptic exons lead to the loss of crucial neuronal proteins and have been shown to be key pathogenic players in disease pathogenesis (e.g., STMN2), as well as being able to modify disease progression (e.g., UNC13A). Thus, these aberrant splicing events make promising novel therapeutic targets to restore functional gene expression. Moreover, presence of these cryptic exons is highly specific to patients and areas of the brain affected by TDP-43 proteinopathy, offering the potential to develop biomarkers for early detection and stratification of patients. In summary, the discovery of cryptic exons gives hope for novel diagnostics and therapeutics on the horizon for TDP-43 proteinopathies.

ID: 36927019
Title: Mechanism of STMN2 cryptic splice-polyadenylation and its correction for TDP-43 proteinopathies.
Abstract: Loss of nuclear TDP-43 is a hallmark of neurodegeneration in TDP-43 proteinopathies, including amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). TDP-43 mislocalization results in cryptic splicing and polyadenylation of pre-messenger RNAs (pre-mRNAs) encoding stathmin-2 (also known as SCG10), a protein that is required for axonal regeneration. We found that TDP-43 binding to a GU-rich region sterically blocked recognition of the cryptic 3' splice site in STMN2 pre-mRNA. Targeting dCasRx or antisense oligonucleotides (ASOs) suppressed cryptic splicing, which restored axonal regeneration and stathmin-2-dependent lysosome trafficking in TDP-43-deficient human motor neurons. In mice that were gene-edited to contain human STMN2 cryptic splice-polyadenylation sequences, ASO injection into cerebral spinal fluid successfully corrected Stmn2 pre-mRNA misprocessing and restored stathmin-2 expression levels independently of TDP-43 binding.

ID: 37466726
Title: Cryptic exon detection and transcriptomic changes revealed in single-nuclei RNA sequencing of C9ORF72 patients spanning the ALS-FTD spectrum.
Abstract: The C9ORF72-linked diseases amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) are characterized by the nuclear depletion and cytoplasmic accumulation of TAR DNA-binding protein 43 (TDP-43). Recent studies have shown that the loss of TDP-43 function leads to the inclusion of cryptic exons (CE) in several RNA transcript targets of TDP-43. Here, we show for the first time the detection of CEs in a single-nuclei RNA sequencing (snRNA-seq) dataset obtained from frontal and occipital cortices of C9ORF72 patients that phenotypically span the ALS-FTD disease spectrum. We assessed each cellular cluster for detection of recently described TDP-43-induced CEs. Transcripts containing CEs in the genes STMN2 and KALRN were detected in the frontal cortex of all C9ORF72 disease groups with the highest frequency in excitatory neurons in the C9ORF72-FTD group. Within the excitatory neurons, the cluster with the highest proportion of cells containing a CE had transcriptomic similarities to von Economo neurons, which are known to be vulnerable to TDP-43 pathology and selectively lost in C9ORF72-FTD. Differential gene expression and pathway analysis of CE-containing neurons revealed multiple dysregulated metabolic processes. Our findings reveal novel insights into the transcriptomic changes of neurons vulnerable to TDP-43 pathology.

ID: 37605276
Title: TDP-43-regulated cryptic RNAs accumulate in Alzheimer's disease brains.
Abstract: Inclusions of TAR DNA-binding protein 43 kDa (TDP-43) has been designated limbic-predominant, age-related TDP-43 encephalopathy (LATE), with or without co-occurrence of Alzheimer's disease (AD). Approximately, 30-70% AD cases present TDP-43 proteinopathy (AD-TDP), and a greater disease severity compared to AD patients without TDP-43 pathology. However, it remains unclear to what extent TDP-43 dysfunction is involved in AD pathogenesis. To investigate whether TDP-43 dysfunction is a prominent feature in AD-TDP cases, we evaluated whether non-conserved cryptic exons, which serve as a marker of TDP-43 dysfunction in amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD-TDP), accumulate in AD-TDP brains. We assessed a cohort of 192 post-mortem brains from three different brain regions: amygdala, hippocampus, and frontal cortex. Following RNA and protein extraction, qRT-PCR and immunoassays were performed to quantify the accumulation of cryptic RNA targets and phosphorylated TDP-43 pathology, respectively. We detected the accumulation of misspliced cryptic or skiptic RNAs of STMN2, KCNQ2, UNC13A, CAMK2B, and SYT7 in the amygdala and hippocampus of AD-TDP cases. The topographic distribution of cryptic RNA accumulation mimicked that of phosphorylated TDP-43, regardless of TDP-43 subtype classification. Further, cryptic RNAs efficiently discriminated AD-TDP cases from controls. Overall, our results indicate that cryptic RNAs may represent an intriguing new therapeutic and diagnostic target in AD, and that methods aimed at detecting and measuring these species in patient biofluids could be used as a reliable tool to assess TDP-43 pathology in AD. Our work also raises the possibility that TDP-43 dysfunction and related changes in cryptic splicing could represent a common molecular mechanism shared between AD-TDP and FTLD-TDP.

ID: 38175301
Title: Cryptic splicing of stathmin-2 and UNC13A mRNAs is a pathological hallmark of TDP-43-associated Alzheimer's disease.
Abstract: Nuclear clearance and cytoplasmic accumulations of the RNA-binding protein TDP-43 are pathological hallmarks in almost all patients with amyotrophic lateral sclerosis (ALS) and up to 50% of patients with frontotemporal dementia (FTD) and Alzheimer's disease. In Alzheimer's disease, TDP-43 pathology is predominantly observed in the limbic system and correlates with cognitive decline and reduced hippocampal volume. Disruption of nuclear TDP-43 function leads to abnormal RNA splicing and incorporation of erroneous cryptic exons in numerous transcripts including Stathmin-2 (STMN2, also known as SCG10) and UNC13A, recently reported in tissues from patients with ALS and FTD. Here, we identify both STMN2 and UNC13A cryptic exons in Alzheimer's disease patients, that correlate with TDP-43 pathology burden, but not with amyloid-β or tau deposits. We also demonstrate that processing of the STMN2 pre-mRNA is more sensitive to TDP-43 loss of function than UNC13A. In addition, full-length RNAs encoding STMN2 and UNC13A are suppressed in large RNA-seq datasets generated from Alzheimer's disease post-mortem brain tissue. Collectively, these results open exciting new avenues to use STMN2 and UNC13A as potential therapeutic targets in a broad range of neurodegenerative conditions with TDP-43 proteinopathy including Alzheimer's disease.

ID: 38443601
Title: RNA aptamer reveals nuclear TDP-43 pathology is an early aggregation event that coincides with STMN-2 cryptic splicing and precedes clinical manifestation in ALS.
Abstract: TDP-43 is an aggregation-prone protein which accumulates in the hallmark pathological inclusions of amyotrophic lateral sclerosis (ALS). However, the analysis of deeply phenotyped human post-mortem samples has shown that TDP-43 aggregation, revealed by standard antibody methods, correlates poorly with symptom manifestation. Recent identification of cryptic-splicing events, such as the detection of Stathmin-2 (STMN-2) cryptic exons, are providing evidence implicating TDP-43 loss-of-function as a potential driving pathomechanism but the temporal nature of TDP-43 loss and its relation to the disease process and clinical phenotype is not known. To address these outstanding questions, we used a novel RNA aptamer, TDP-43APT, to detect TDP-43 pathology and used single molecule in situ hybridization to sensitively reveal TDP-43 loss-of-function and applied these in a deeply phenotyped human post-mortem tissue cohort. We demonstrate that TDP-43APT identifies pathological TDP-43, detecting aggregation events that cannot be detected by classical antibody stains. We show that nuclear TDP-43 pathology is an early event, occurring prior to cytoplasmic accumulation and is associated with loss-of-function measured by coincident STMN-2 cryptic splicing pathology. Crucially, we show that these pathological features of TDP-43 loss-of-function precede the clinical inflection point and are not required for region specific clinical manifestation. Furthermore, we demonstrate that gain-of-function in the form of extensive cytoplasmic accumulation, but not loss-of-function, is the primary molecular correlate of clinical manifestation. Taken together, our findings demonstrate implications for early diagnostics as the presence of STMN-2 cryptic exons and early TDP-43 aggregation events could be detected prior to symptom onset, holding promise for early intervention in ALS.

ID: 39114608
Title: Abnormal Splicing Events due to Loss of Nuclear Function of TDP-43: Pathophysiology and Perspectives.
Abstract: Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) are neurodegenerative diseases with a progressive and fatal course. They are often comorbid and share the same molecular spectrum. Their key pathological features are the formation of the aggregation of TDP-43, an RNA-binding protein, in the cytoplasm and its depletion from the nucleus in the central nervous system. In the nucleus, TDP-43 regulates several aspects of RNA metabolism, ranging from RNA transcription and alternative splicing to RNA transport. Suppressing the aberrant splicing events during RNA processing is one of the significant functions of TDP-43. This function is impaired when TDP-43 becomes depleted from the nucleus. Several critical cryptic splicing targets of TDP-43 have recently emerged, such as STMN2, UNC13A, and others. UNC13A is an important ALS/FTD risk gene, and the genetic variations, single nucleotide polymorphisms, cause disease via the increased susceptibility for cryptic exon inclusion under the TDP-43 dysfunction. Moreover, TDP-43 has an autoregulatory mechanism that regulates the splicing of its mRNA (TARDBP mRNA) in the healthy state. This study provides recent findings on the splicing regulatory function of TDP-43 and discusses the prospects of using these aberrant splicing events as efficient biomarkers.

ID: 39788898
Title: TDP-43 Cryptic RNAs in Perry Syndrome: Differences across Brain Regions and TDP-43 Proteinopathies.
Abstract: Perry syndrome (PS) is a rare and fatal hereditary autosomal dominant neurodegenerative disorder caused by mutations in dynactin (DCTN1). PS brains accumulate inclusions positive for ubiquitin, transactive-response DNA-binding protein of 43 kDa (TDP-43), and to a lesser extent dynactin. Little is known regarding the contributions of TDP-43, an RNA binding protein that represses cryptic exon inclusion, in PS. Therefore, we sought to identify the degree of TDP-43 dysfunction in two regions of PS brains. We evaluated the levels of insoluble pTDP-43 and TDP-43-regulated cryptic RNAs and protein in the caudate nucleus and substantia nigra of 7 PS cases, 12 cases of frontotemporal lobar degeneration (FTLD) with TDP-43 pathology, and 11 cognitively healthy controls without TDP-43 pathology. Insoluble pTDP-43 protein levels were detected in PS brains to a similar extent in the caudate nucleus and substantia nigra but lower than those in FTLD brains. The caudate nucleus of PS showed accumulation of eight TDP-43-regulated cryptic RNAs (ACTL6B, CAMK2B, STMN2, UNC13A, KCNQ2, ATG4B, GPSM2, and HDGFL2) and cryptic protein (HDGFL2) characteristic of FTLD. Conversely, only one cryptic target, UNC13A, reached significance in the substantia nigra despite similar pTDP-43 levels. We detected TDP-43 cryptic RNAs and protein in PS caudate nucleus. Given the importance of cryptic exon biology in the development of biomarkers, and the identification of novel targets for therapeutic intervention, it is imperative we understand the consequences of TDP-43 dysfunction across different brain regions and determine the targets that are specific and common to TDP-43 proteinopathies. © 2025 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

ID: 40275359
Title: Multi-region brain transcriptomic analysis of amyotrophic lateral sclerosis reveals widespread RNA alterations and substantial cerebellum involvement.
Abstract: Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease that primarily affects the motor neurons, causing progressive muscle weakness and paralysis. While research has focused on understanding pathological mechanisms in the motor cortex and spinal cord, there is growing evidence that extra-motor brain regions may also play a role in the pathogenesis or progression of ALS. We generated 165 sample-matched post-mortem brain transcriptomes from 22 sporadic ALS patients with pTDP-43 pathological staging and 11 non-neurological controls. For each individual, five brain regions underwent mRNA sequencing: motor cortex (pTDP-43 inclusions always present), prefrontal cortex and hippocampus (pTDP-43 inclusions sometimes present), and occipital cortex and cerebellum (pTDP-43 inclusions rarely present). We examined gene expression, cell-type composition, transcript usage (% contribution of a transcript to total gene expression) and alternative splicing, comparing ALS-specific changes between brain regions. We also considered whether post-mortem pTDP-43 pathological stage classification defined ALS subgroups with distinct gene expression profiles. Significant gene expression changes were observed in ALS cases for all five brain regions, with the cerebellum demonstrating the largest number of total (> 3,000) and unique (60%) differentially expressed genes. Pathway enrichment and predicted activity were largely concordant across brain regions, suggesting that ALS-linked mechanisms, including inflammation, mitochondrial dysfunction and oxidative stress, are also dysregulated in non-motor brain regions. Switches in transcript usage were identified for a small set of genes including increased usage of a POLDIP3 transcript, associated with TDP-43 loss-of-function, in the cerebellum and a XBP1 transcript, indicative of unfolded protein response activity, in the motor cortex. Extensive variation in RNA splicing was identified in the ALS brain, with 26-41% of alternatively spliced genes unique to a given brain region. This included detection of TDP-43-associated cryptic splicing events such as the STMN2 cryptic exon which was shown to have a pTDP-43 pathology-specific expression pattern. Finally, ALS patients with stage 4 pTDP-43 pathology demonstrated distinct gene and protein expression changes in the cerebellum. Together our findings highlighted widespread transcriptome alterations in ALS post-mortem brain and showed that, despite the absence of pTDP-43 pathology in the cerebellum, extensive and pTDP-43 pathological stage-specific RNA changes are evident in this brain region.

ID: 40501554
Title: Molecular subtyping based on hippocampal cryptic exon burden reveals proteome-wide changes associated with TDP-43 pathology across the spectrum of LATE and Alzheimer's Disease.
Abstract: TDP-43 pathology is a defining feature of Limbic-Predominant Age-Related TDP-43 Encephalopathy neuropathologic change (LATE-NC) and is frequently comorbid with Alzheimer's disease neuropathologic change (ADNC). However, the molecular consequences of co-occurring LATE-NC and ADNC pathology (TDP-43, β-amyloid, and tau protein pathologies) remain unclear. Here, we conducted a comparative biochemical, molecular, and proteomic analysis of hippocampal tissue from 90 individuals spanning control, LATE-NC, ADNC, and ADNC+LATE-NC groups to assess the impact of cryptic exon (CE) inclusion, phosphorylated TDP-43 pathology (pTDP-43), and AD-related pathologies (β-amyloid, and tau) on the proteome. ADNC+LATE-NC cases exhibited the highest burden of CE inclusion as quantified by measuring the levels of known TDP-43 regulated CEs within eight transcripts: STMN2, UNC13A, ELAVL3, KALRN, ARHGAP32, CAMK2B, PFKP, and SYT7. While CE levels correlated with pTDP-43 pathology, they were more strongly correlated with each other, suggesting that the molecular signature of CE inclusion may serve as a more sensitive measure of TDP-43 dysfunction than pTDP-43 pathology alone. Unbiased classification based on the relative abundance of these eight CEs stratified individual cases into low, intermediate, and high CE burden subtypes, largely independent of β-amyloid and tau pathology. Proteome-wide correlation analysis revealed a bias toward reduced protein levels from genes harboring TDP-43-regulated CEs in cases with high cumulative CE burden. Notably, proteins significantly decreased under high CE burden included canonical STMN2, ELAVL3, and KALRN, as well as kinesin proteins that are genetically associated with amyotrophic lateral sclerosis. Co-expression network analysis identified both shared and distinct biological processes across CE subtypes and pathways associated with pTDP-43, tau, β-amyloid pathologies, and CE accumulation in the hippocampus. Protein modules associated with TDP-43 loss of function were prioritized by integrating proteomic data from TDP-43-depleted human neurons with the hippocampal co-expression network. Specifically, we observed decreased endosomal vesicle, microtubule-binding, and synaptic modules, alongside an increase in RNA-binding modules. These results provide new insights into the proteomic impact of CE burden across the spectrum of LATE and AD pathological severity, highlighting the molecular consequences of TDP-43 dysfunction in neurodegenerative disease.

ID: 41256508
Title: Integrative multiomic analysis links TDP-43-driven splicing defects to cascading proteomic disruption of ALS/FTD pathways.
Abstract: Loss of nuclear TDP-43 is a hallmark of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Although TDP-43 is known to regulate RNA processing, including repression of cryptic exons, we currently lack a systems-level understanding of the consequences of TDP-43 loss. To address this, we generated multiomic datasets, including RNA-seq and proteomics, from human iPSC-derived neurons depleted of TDP-43. We found that differentially spliced genes, many expressing cryptic exons, had the greatest protein reductions. Surprisingly, nearly half of differentially expressed proteins were neither mis-spliced, nor differentially expressed genes; most of these also had no reported mis-splicing in seven additional post-mortem and iPSC-derived neuron datasets. Integrative network analysis identified a high-confidence disease-specific subnetwork of over 700 interacting proteins, enriched for mRNA processing, synaptic function, and autophagy. Comparison with post-mortem ALS and FTD samples revealed convergent protein and pathway disruptions. We experimentally validated network-predicted effects of cryptic splicing in ATG4B, STMN2, and DAPK1. Our analyses reveal new TDP-43-dependent molecular cascades and nominate central genes as potential ALS/FTD therapeutic targets.

ID: 41292965
Title: A human forebrain organoid model phenocopies dysregulated RNA and protein homeostasis in ALS/FTD-associated TDP-43 proteinopathies.
Abstract: TAR DNA-binding protein 43 (TDP-43) proteinopathy is a central hallmark of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD), yet current experimental models fail to reproduce the full pathological spectrum without external stress or TDP-43 overexpression. This study aims to establish a human induced pluripotent stem cells (iPSC)-derived system that spontaneously manifests TDP-43 pathology driven by an ALS-associated TDP-43 mutation. We generated forebrain 3-D organoid cultures from iPSC carrying the TDP-43 K181E patient mutation. Single-cell RNA sequencing was used to define transcriptional alterations across cell types, and enhanced crosslinking immunoprecipitation (eCLIP) was applied to examine the global RNA binding and splicing defects in mutant organoids. We further used immunostaining, RT-PCR and biochemical assays to confirm TDP-43 proteinopathy and validate findings from the multi-omics analyses. The TDP-43 K181E organoids recapitulated key disease features, including cytoplasmic p-TDP-43 accumulation, RNA dysregulation, and cryptic exon inclusion. Single-cell analysis revealed a population of immature neurons with enhanced neuroinflammation and altered translation capacity. Comparative transcriptomics showed that the ALS mutation-induced transcriptional changes strongly overlap with those in ALS patient-derived brains. eCLIP analysis showed that mutant TDP-43 exhibited altered RNA-binding specificity, resulting in widespread RNA mis-splicing and cryptic exon inclusion. RT-PCR confirmed PRDM2, a gene regulating cell senescence, is mis-spliced in mutant cells. These defects collectively disrupt neuronal homeostasis and cell-cell communications. Our iPSC-derived forebrain organoid model displays spontaneous TDP-43 proteinopathies and associated molecular dysfunctions without artificial manipulation. The model offers a robust platform for dissecting the mechanisms of TDP-43-mediated neurodegeneration and advancing therapeutic discovery in ALS and FTD.

ID: 41393069
Title: Proteomic Identification of ALDOA as a Pathogenic TDP-43 Interaction Partner in ALS.
Abstract: Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease affecting both upper and lower motor neurons, and its pathogenesis has not been fully elucidated. TAR DNA-binding protein 43 (TDP-43), as one of the key pathogenic genes in ALS, participates in the disease process through interactions with various proteins. This study aims to investigate the interaction mechanism between TDP-43 and aldolase A (ALDOA) in ALS. HEK293T cell models transfected with wild-type and mutant TDP-43 (TDP-43M337V) plasmids were constructed. The interaction between TDP-43 and ALDOA was analyzed through proteomic screening of specific peptides and co-immunoprecipitation, and the co-localization of the two in cells was detected by immunofluorescence. Changes in ALDOA expression levels after intervention with mutant TDP-43 were detected by Western blot and quantitative real-time PCR. Proteomic analysis identified ALDOA as a potential interacting protein of TDP-43. Protein-protein interaction (PPI) analysis, co-immunoprecipitation, and immunofluorescence experiments further confirmed that both wild-type and mutant TDP-43 interact with ALDOA. Western blot and quantitative real-time PCR results showed that, compared with the wild-type TDP-43 group, the ALDOA expression was significantly increased in the TDP-43M337V mutant group. TDP-43 interacts with ALDOA in ALS, and the TDP-43M337V mutation significantly promotes ALDOA expression, suggesting that ALDOA may be involved in the pathogenesis of TDP-43-mediated ALS. These findings provide new insights into the pathogenesis of ALS and highlight a potential therapeutic target.

ID: 41394670
Title: TDP-43 suppression of ATP8A2 cryptic splicing implicates phosphatidylserine-driven neuroinflammation in ALS/FTD.
Abstract: Inappropriate externalization of phosphatidylserine (PS) is a candidate mechanism of pathogenic neuroinflammation, a critical driver of neurodegenerative disease. ATP8A2, a flippase that maintains PS on the plasma membrane inner leaflet, is mutated in both Wabbler-lethal mice and patients with the ataxia syndrome CAMRQ4. Here, we identify ATP8A2 as a target of TDP-43 cryptic exon suppression, and demonstrate that ATP8A2 loss leads to immune-mediated neurodegeneration. ATP8A2 splicing is significantly dysregulated following TDP-43 depletion in human neurons and in brains of patients with Amyotrophic Lateral Sclerosis-Frontotemporal Dementia (ALS-FTD). In mice, Atp8a2 loss increases PS exposure and promotes neuroinflammation. Depletion of peripheral macrophages rescues motor axon degeneration and doubles Atp8a2 knockout mouse lifespan, while depletion of both peripheral macrophages and central microglia quadruples lifespan and improves coordination. Hence, ATP8A2 is a pathologically relevant TDP-43 target and inhibition of phagocytic immune cell attack against neurons is a potential treatment for patients with CAMRQ4 and ALS-FTD.

ID: 41542389
Title: TDP-43 dysfunction leads to the accumulation of cryptic transposable element-derived exons, crypTEs, in iPSC derived neurons and ALS/FTD patient tissues.
Abstract: TDP-43 is an RNA and DNA binding protein that plays major roles in regulating RNA processing. In particular, TDP-43 dysfunction leads to the accumulation of cryptic splice isoforms that result from improperly spliced mRNAs. In addition to its role in regulating splicing, TDP-43 is also known to regulate the expression of transposable elements (TEs). TEs are mobile genetic elements which comprise a significant proportion of the human genome, but are normally silenced in healthy somatic cells. TEs are interspersed throughout the genome, both in gene-depleted regions and within gene introns and gene regulatory sequences. We used optimized long-read RNA sequencing assays to generate catalogs of mis-spliced and mis-expressed genes and TEs in human neurons depleted for TDP-43. In addition to known TDP-43 driven cryptic isoforms, we identified hundreds of TDP-43 dependent spliced RNAs that form cryptic gene-TE fusion events as a result of mis-splicing of TE sequences into gene transcripts. Among these TDP-43 dependent cryptic gene-TE transcripts (crypTEs), we found: TEs that provide alternate gene promoters/5'UTRs, TEs that act as cassette exons inside host gene mRNAs, as well as TEs that provide alternate transcript 3' ends. These cryptic gene-TE fusions are predicted to induce aberrant expression of ALS relevant genes, nonsense mediated decay (NMD) products, as well as novel peptides from gene-TE fusions within the gene coding sequence. Using coupled long-read RNA (Iso-seq) and single-nucleus (snRNA-seq) profiles from postmortem ALS tissues, we further verified that many of these crypTE transcripts are enriched in frontal cortex samples from ALS donors with cognitive involvement (ALSci) and associated with altered expression of those genes in deep layer cortical excitatory neurons. In short, TDP-43 dependent crypTEs greatly expand the catalogs of TDP-43 dependent cryptic splice isoforms and represent a novel mechanism by which TE dysregulation impacts ALS.

ID: 41573891
Title: Dual-targeting snRNA gene therapy rescues STMN2 and UNC13A splicing in TDP-43 proteinopathies.
Abstract: Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder caused by the selective deterioration of motor neurons in the central nervous system (CNS). A key driver of this pathogenesis is nuclear loss of ALS-associated protein TDP-43, leading to mis-splicing of TDP-43 targets including important neuronal genes STMN2 and UNC13A . Here, we have developed a gene therapy strategy for ALS and related TDP-43 proteinopathies, to correct mis-splicing of both STMN2 and UNC13A cryptic exons using small nuclear RNAs (snRNAs) encoded from a single vector. We identified promoter sequence elements to increase therapeutic snRNA expression by 10-fold, then further optimized the expression cassette with combinatorial snRNA targeting to rescue multiple cryptic splicing targets. The engineered snRNAs restored normal pre-mRNA processing of both STMN2 and UNC13A transcripts despite TDP-43 loss of function, rescuing stathmin-2 protein levels in iPSC derived motor neurons, restoring their axonal regeneration capacity to wild-type levels. In addition, adeno-associated virus (AAV) delivery of the snRNAs to the murine central nervous system in the constitutive cryptic splicing model Stmn2 HumΔGU fully restored cortical Stmn2 pre-mRNA processing, highlighting the utility of snRNAs as a therapeutic modality in vivo . Together, this study demonstrates that snRNAs are a promising and versatile therapeutic strategy for the simultaneous correction of multiple aberrant transcripts affected by cryptic splicing in TDP-43 proteinopathies.

ID: 41612503
Title: Diagnostic potential of cryptic exon-derived peptides in serum extracellular vesicles for sporadic amyotrophic lateral sclerosis.
Abstract: Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterized by progressive degeneration and loss of upper and lower motor neurons, with approximately 90% of cases being sporadic (sporadic ALS, SALS). A reliable diagnostic biomarker remains an unmet clinical need in SALS, with misdiagnosis and diagnostic delay hindering early management. The mislocalization of the RNA-binding protein TDP-43 (encoded by TARDBP), a pathological hallmark of SALS, could lead to aberrant splicing that produces transcripts with cryptic exons and, consequently, cryptic peptides. This study proposes cryptic peptides in serum extracellular vesicles as a novel candidate diagnostic biomarker of SALS. We included 10 healthy controls and 20 patients with SALS and quantified cryptic peptides predicted from cryptic exon sequences using mass spectrometry-based proteomics. Cryptic peptides from four proteins (RANBP1, IGLON5, ACTN1, ALPK2) were detected in participants, with the IGLON5 cryptic peptide detected significantly more frequently in SALS than in HC (adjusted P = 0.044). The number of detected cryptic peptides classified SALS and healthy controls with acceptable performance (area under the curve = 0.82). In conclusion, cryptic peptides could have diagnostic performance for SALS, warranting further validation.

ID: 41720774
Title: A neurotoxic cryptic peptide arising from TDP-43-dependent cryptic splicing of PKN1.
Abstract: Dysfunction of transactive response DNA-binding protein 43 (TDP-43) drives neurodegeneration in amyotrophic lateral sclerosis (ALS) and Alzheimer's disease (AD), in part through inducing aberrant RNA splicing. However, whether such mis-splicing yields stable, pathogenic proteins remains unclear. Here, we identify a TDP-43-repressed cryptic exon in Protein kinase N1 (PKN1), designated PKN1-5a1, which is activated in ALS patient brains and introduces a premature termination codon. This aberrant transcript escapes nonsense-mediated decay and is translated into a truncated peptide, PKN1-N207 (PKN207), detectable in AD brains with TDP-43 pathology. In mice, PKN207 impairs cognition, memory, and synaptic plasticity. Our findings demonstrate that TDP-43 loss-induced cryptic splicing can generate stable neurotoxic polypeptides, revealing a peptide-mediated mechanism in TDP-43 proteinopathies.

ID: 41761273
Title: TDP-43-driven alternative splicing of UQCRC2 modulates mitochondrial bioenergetics.
Abstract: TAR DNA-binding protein 43 (TDP-43) is a nuclear RNA-binding protein. It has emerged as a key regulator of RNA processing, such as alternative splicing events, which are essential for cellular homeostasis. The mislocalization and aggregation of TDP-43 are closely associated with mitochondrial dysfunction. However, the mechanisms by which the formation TDP-43 contributes to mitochondrial impairment remain poorly understood. In this study, we confirmed that the TDP-43 loss leads to dramatic alterations in mitochondrial morphology and a significant reduction in respiratory capacity. Further analysis of oxidative phosphorylation (OXPHOS) complex assembly revealed a selective disruption of complex III activity. Notably, the core complex III subunit UQCRC2 was significantly decreased as long as TDP-43 was knocked down. The transcript analysis showed that the loss of TDP-43 results in aberrant alternative splicing of the nuclear-encoded UQCRC2 transcript. In parallel, this mis-splicing event was consistently observed in both dividing cells, including HEK293T, and in the neuroblastoma cell line SH-SY5Y, suggesting that TDP-43-mediated regulation of UQCRC2 splicing can be potentially conserved across a wide range of cell types. These findings indicate a novel role for TDP-43 in maintaining mitochondrial integrity via regulation of UQCRC2 expression and splicing, providing mechanistic insight into how dysregulated RNA processing contributes to mitochondrial bioenergetic deficits.

ID: 41860868
Title: Subtyping based on hippocampal cryptic exon burden reveals proteome-wide changes associated with TDP-43 and Alzheimer's disease pathology.
Abstract: TDP-43 pathology defines limbic-predominant age-related TDP-43 encephalopathy (LATE-NC) and frequently co-occurs with Alzheimer's disease neuropathologic change (ADNC), yet the molecular consequences of overlapping pathology remain unclear. We performed biochemical and proteomic analyses of postmortem hippocampal tissue from 90 individuals spanning control, LATE-NC, ADNC, and ADNC+LATE-NC groups. Cryptic exon (CE) inclusion was quantified across eight TDP-43-regulated transcripts and related to phosphorylated TDP-43 (pTDP-43), amyloid, and tau pathology. ADNC+LATE-NC cases showed the highest CE levels. Although CE inclusion correlated with pTDP-43, CE measures were more strongly intercorrelated and defined low, intermediate, and high CE subtypes largely independent of amyloid and tau. Proteome-wide analyses revealed reduced abundance of CE-target proteins and disruption of synaptic, endosomal, and RNA-binding pathways in high CE cases. These signatures overlapped with changes in TDP-43-depleted human i3Neurons, supporting biological relevance. Overall, CE burden provides a robust molecular classifier of TDP-43 dysfunction across LATE-NC and ADNC.

ID: 41952326
Title: Biochemical and Immunohistochemical Associations of TDP-43 and Cryptic RNA With Hippocampal and Amygdala Volumetrics in Alzheimer's Disease.
Abstract: Immunohistochemically (IHC) measured transactive response DNA-binding protein 43 (TDP-43) inclusions are observed in Alzheimer's disease (AD) and are associated with medial temporal lobe atrophy. Accumulation of cryptic exons occurs in AD in response to TDP-43 pathology. We aimed to assess relationships between IHC and biochemically measured insoluble TDP-43 and cryptic exons and assess associations with hippocampal and amygdala volume loss and atrophy rates on magnetic resonance imaging (MRI). Eighty-one neuropathologically diagnosed AD cases were analyzed. For biochemistry, insoluble TDP-43 was quantified using a Meso-scale discovery (MSD) immunoassay. IHC-TDP burden was quantified with digital histopathology. Cryptic RNAs were assessed via quantitative real-time polymerase chain reaction (qRT-PCR). Thirty-eight cases had serial brain MRI. Hippocampal and amygdala volumes were calculated using FreeSurfer. Regression models were used to investigate associations among IHC-TDP-43 status/burden, MSD-TDP status/levels, cryptic RNAs, and hippocampal and amygdala volumes and atrophy rates. IHC-TDP(+) cases exhibited elevated levels of MSD-TDP and cryptic RNAs (KCNQ2, STMN2, and UNC13A) and increased MSD-TDP levels were associated with increased cryptic RNA levels, in the hippocampus and amygdala. IHC-TDP(+) cases had smaller hippocampal and amygdala volumes compared to IHC-TDP(-) cases. MSD-TDP(+) cases had smaller hippocampal volumes and faster amygdala rates of atrophy compared with MSD-TDP(-) cases. Higher KCNQ2 and UNC13A levels were associated with smaller amygdala volumes. MSD-TDP level is a reliable surrogate for IHC-based TDP-43 status. Both TDP-43 and cryptic RNA levels are associated with reduced medial temporal volumes, suggesting cryptic exons may be playing a role in brain volume loss in AD. ANN NEUROL 2026;100:193-205.

ID: 41996987
Title: Decoding RNA splicing pathology: Alternative splicing in amyotrophic lateral sclerosis and its therapeutic potential.
Abstract: Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder marked by progressive motor neuron loss, leading to muscle weakness, paralysis, and respiratory failure. Dysregulation of RNA metabolism and splicing has emerged as a central mechanism in ALS pathogenesis. TARDBP (TAR DNA-binding protein), FET family proteins (FUS, EWSR1, TAF15), SOD1 (Superoxide Dismutase 1), and C9orf72 (Chromosome 9 Open Reading Frame 72) are key genes associated with ALS that regulate RNA processing, alternative splicing, and nuclear-cytoplasmic transport. Mutations or mislocalization of these proteins result in nuclear loss-of-function and cytoplasmic gain-of-function toxicity, promoting protein aggregation, sequestering spliceosomal components, and impairing spliceosome assembly. This leads to the aberrant inclusion of cryptic exons in essential neuronal genes, such as STMN2 (Stathmin 2) and UNC13A (Unc-13 Homolog A), resulting in the production of truncated proteins, defective axonal maintenance, and impaired synaptic function. TDP-43 pathology, a hallmark of ALS, disrupts splicing and RNA transport, while C9orf72 repeat expansions and FET protein mutations exacerbate cytoplasmic aggregation and stress granule dynamics. Mutant SOD1 contributes via mitochondrial dysfunction, endoplasmic reticulum stress, and disrupted axonal transport. Therapeutic strategies targeting these mechanisms are advancing rapidly. Gene replacement therapy, which restores STMN2 expression, and antisense oligonucleotides (ASOs) targeting mutant transcripts show promise in preclinical and early clinical studies. Complementary approaches, including the inhibition of stress kinases and the activation of autophagy, reduce cytoplasmic protein aggregation and support neuronal homeostasis. This review provides a comprehensive overview of RNA splicing regulation, spliceosomal dysfunction, and cryptic exon incorporation in ALS. Understanding the interplay among splicing defects, RNA-binding protein pathology, and neuronal degeneration is critical for developing next-generation multimodal therapies to restore RNA processing, reduce toxic protein accumulation, and promote motor neuron survival.

ID: 42178983
Title: Protein Disulfide Isomerase Disassembles TDP-43/G3BP1 Condensates and Antagonizes TDP-43 Pathological Aggregates.
Abstract: Cytoplasmic mislocalization and aggregation of transactive response DNA-binding protein-43 (TDP-43) is a common pathological feature of amyotrophic lateral sclerosis (ALS), frontotemporal lobar degeneration, and Alzheimer's disease with TDP-43 pathology (AD-TDP); the exact role of protein disulfide isomerase (PDI), an enzyme with chaperone activity, in modulating the pathological behavior of TDP-43 is unknown. In this study, we report that wild-type PDI, through its specific interaction with TDP-43, markedly attenuates phase separation of TDP-43, competitively displaces G3BP1 to disassemble TDP-43/G3BP1 condensates, and further counteracts the pathological mislocalization, abnormal phosphorylation, and pathological aggregation of TDP-43 through the b' domain of the enzyme. Ultimately, this alleviates mitochondrial damage and neuronal toxicity caused by TDP-43 aggregation and suppresses UNC13A cryptic splicing in stressed cells. In the presence of abnormal forms of PDI, however, PDI loses its activity, and stress granules containing TDP-43 are assembled into amyloid fibrils, resulting in mitochondrial impairment and neuronal cell death in ALS and AD-TDP patients. These findings not only provide new insights into the pathogenic mechanisms of TDP-43 in neurodegenerative diseases such as ALS and AD-TDP, but also propose PDI as a potential therapeutic target.

ID: 42311236
Title: Functional Analyses in Patient-Derived Neurons Establish Pathogenicity for STXBP1 Splice Variant c.429+5G>A.
Abstract: Pathogenic STXBP1 variants cause a broad spectrum of neurodevelopmental disorders. We investigated a patient with developmental delay but no seizures, carrying a heterozygous, predicted splice site variant, c.429+5G>A, initially classified as a variant of uncertain significance. Patient-derived neurons had normal morphology in vitro, but > 40% reduced MUNC18-1/STXBP1 protein and mRNA levels, comparable with two established loss-of-function variants (Asp262Val and Arg235*). Nonsense-mediated decay inhibition increased transcript levels, and RT-PCR/minigene analysis demonstrated Exon 6 skipping, resulting in a frameshift and premature stop codon. Relative to a large cohort of typically developing children, EEG biomarker analysis revealed elevated long-range temporal correlations in beta and gamma bands, increased delta power, and reduced excitation/inhibition ratio in the beta band. This multimodal assessment demonstrates that c.429+5G>A is a disease-causing variant, and the value of combining functional and clinical data for accurate variant interpretation. Based on this, the patient was included in the EU STXBP1 registry ESCO.

ID: 42320547
Title: Proteomic analysis reveals early pathological defects in corticospinal motor neurons of a spastin model of hereditary spastic paraplegia, which are improved by NU-9 treatment.
Abstract: Upper motor neuron (UMN) degeneration is a characteristic feature of hereditary spastic paraplegia (HSP), a genetically heterogeneous heritable neurodegenerative disorder resulting from mutations in over ninety genes. The mutations in the SPAST gene, which encodes the microtubule-severing protein spastin, are responsible for about 40% of all HSP cases. To date, the cellular and molecular mechanisms linking mutant spastin protein to UMN vulnerability in HSP patients remain unknown and there are no disease modifying therapies. To address this knowledge gap, we isolated pure populations of corticospinal motor neurons (CSMN; a.k.a. UMN in mice) from SPASTC448Y-UeGFP reporter mice at two pre-symptomatic time points and performed bottom-up proteomic analyses to reveal changes in their proteome that informs the underlying causes of their initial vulnerability. We find dynamic changes in their proteome and that limitations with cytoarchitectural integrity and stability of key organelles contribute to their neuronal vulnerability. Since the compound NU-9 was shown to improve similar cellular problems in CSMN that are diseased due to misfolded SOD1 toxicity and TDP-43 pathology, we further investigated its effect on the well-established pathological features of HSP that are recapitulated in the SPASTC448Y mice. We find that NU-9 treatment (100 mg/kg, for 100 days) significantly prevented degeneration of corticospinal axons, restored the integrity of mitochondria and endoplasmic reticulum, and reduced the presence of electron-dense accumulations in the CSMN of SPASTC448Y mice.

ID: 42427729
Title: Unveiling the Hidden Rules: Enhancing NMD Prediction for Protein-Truncating Variants.
Abstract: Nonsense-mediated decay (NMD) is a conserved RNA quality-control pathway that degrades transcripts containing premature termination codons. Because roughly a third of pathogenic variants in ClinVar can lead to truncated protein synthesis, predicting whether such transcripts undergo NMD is central to interpreting variant effects, yet the canonical 50-55 nucleotide rule explains only about half of observed outcome variability. Using paired whole-genome and RNA-sequencing from 10,306 individual samples in the Trans-Omics for Precision Medicine (TOPMed) program, we quantified NMD efficiency for 5,749 germline truncating variants via allele-specific expression and trained a gradient-boosting classifier, TrunCat, that distinguished NMD-sensitive from NMD-escape transcripts with ∼78% ROC-AUC (Receiver Operating Characteristic - Area Under the Curve). A reduced model using the ten features with the highest mean SHAP (SHapley Additive exPlanations) value as a measure of each feature's average contribution to predictions nearly matched this performance. Applied across large variant databases and a rare-disease cohort, the model produced NMD outcome predictions, with variants of uncertain significance showing higher predicted escape than pathogenic ones. This framework confirms the canonical rule, identifies non-canonical determinants, and offers a scalable resource for interpreting protein-truncating variants.

ID: 42434347
Title: A role for EHMT2 in a novel autosomal recessive neurodevelopmental syndrome? A case report.
Abstract: EHMT1 and EHMT2 encode histone methyltransferases that form an epigenetic complex mediating mono- and dimethylation of histone H3 at lysine 9 (H3K9me1/2). This complex modulates fundamental biological processes during embryonic and post-natal development. While EHMT1 has an established role in neurodevelopmental disease, with heterozygous pathogenic variants causing Kleefstra syndrome type 1 (KS1), the contribution of EHMT2 to neurodevelopmental disorders remains to be established. To date, seven probands harboring de novo heterozygous EHMT2 variants and one individual with a homozygous splice variant have been reported, all presenting with phenotypes and DNA methylation episignatures overlapping with KS1. A male proband was referred for Genetics evaluation due to global developmental delay, autism spectrum disorder, hypotonia, dysmorphisms, posterior fossa malformation, congenital heart disease, umbilical hernia, and genitourinary anomalies. Trio genome sequencing identified compound heterozygous variants in EHMT2 (NM_006709.5:c.2648_2649del; p.(Glu883Glyfs*48), paternally inherited; NM_006709.5:c.2344-19_2344-16del; r.spl, maternally inherited). DNA methylation episignature profiling and RNA-sequencing were performed to assess the molecular consequences of these EHMT2 variants. Proband phenotype strongly overlapped with that of KS1 and previously reported individuals with autosomal dominant and recessive EHMT2-related neurodevelopmental disorder. DNA methylation episignature was consistent with KS1. Transcripts bearing the paternally inherited EHMT2 frameshift variant were under-represented in the RNA-sequencing data, likely reflecting partial nonsense-mediated decay. The maternally inherited EHMT2 variant causes multiple aberrant splicing events in a subset of transcripts (∼25%), including retention of 291 nucleotides from intron 18, which generates a nonsense variant in the canonical EHMT2 transcript. Our findings support a role for EHMT2 in an autosomal recessive neurodevelopmental disorder and allowed anticipatory guidance for the patient's family.

ID: 42442601
Title: DIS3L2 and Nonsense-mediated Decay: United to Degrade.
Abstract: Nonsense-mediated decay (NMD) is a vital RNA surveillance mechanism in eukaryotic cells that ensures mRNA quality and regulates gene expression. NMD targets mRNAs with premature translation-termination codons to prevent the production of potentially harmful truncated proteins. But NMD is also involved in modulating the expression of physiological mRNAs to maintain cellular homeostasis. This NMD function is particularly relevant to calibrate the cellular transcriptome in response to environmental signals and stress. Its conservation across eukaryotes highlights its essential role. When active, NMD promotes mRNA degradation involving exoribonucleases such as XRN1 (5'-3') and the exosome (3'-5'). DIS3L2, an exosome-independent exonuclease that primarily targets substrates marked by the non-templated addition of uridine residues to the 3' end of RNA molecules by terminal uridylyl transferases, can also degrade some NMD substrates, especially those that underwent 3' end uridylation. This review explores DIS3L2's interaction with the NMD pathway (DIS3L2/NMD pathway) and the human disorders associated with a dysfunctional DIS3L2/NMD pathway. A better understanding of the interplay between NMD and DIS3L2 will certainly allow the development of novel treatments for disorders associated with an affected DIS3L2/NMD pathway.

ID: 42448936
Title: EIF4A3-dependent nonsense-mediated decay buffers AML1-ETO9a dosage and modulates outcome in t(8;21) acute myeloid leukemia.
Abstract: t(8;21) acute myeloid leukemia (AML) is driven by AML1-ETO, which undergoes alternative splicing to generate AML1-ETO9a (AE9a), a truncated isoform with enhanced leukemogenic activity. Although t(8;21) AML is considered favorable-risk, clinical outcomes are heterogeneous, and AE9a expression varies markedly among patients. How cells restrain this oncogenic isoform remains unclear. Here, we identify nonsense-mediated mRNA decay (NMD) as an isoform-specific buffer of AE9a dosage. Inclusion of the ETO9a cassette exon introduces premature termination codons and generates an NMD-sensitive transcript. In primary t(8;21) AML CD34⁺ hematopoietic stem and progenitor cells, AE9a inclusion inversely correlated with NMD-factor expression, and high EIF4A3 expression was associated with improved overall survival specifically in t(8;21) AML, but not in other AML subtypes. Pharmacological inhibition of SMG1 or EIF4A3 and genetic depletion of NMD factors increased AE9a abundance in t(8;21) AML cell lines and primary patient cells, with cytoplasmic transcript accumulation and increased AE9a protein. Conversely, EIF4A3 overexpression reduced AE9a RNA and protein, restrained t(8;21) AML cell growth, spared healthy CD34⁺ progenitor expansion, and enhanced idarubicin sensitivity. These findings define EIF4A3-dependent NMD as a checkpoint linking RNA surveillance to oncogenic fusion-isoform dosage, leukemic fitness, and chemosensitivity in t(8;21) AML, providing a mechanistic explanation for clinical heterogeneity in t(8;21) AML. EIF4A3-dependent NMD buffers AE9a dosage and modulates t(8;21) AML cell fitness and chemosensitivity: Schematic model summarizing the proposed AE9a-NMD axis in t(8;21) AML. Alternative splicing of AML1-ETO generates the ETO9a cassette exon, producing a PTC-containing AE9a transcript. After nuclear export, ribosome engagement with the PTC-containing AE9a mRNA recruits the NMD machinery, including UPF factors, SMG factors, DHX34, and the exon-junction complex component EIF4A3. Efficient NMD promotes AE9a mRNA decay and limits AE9a protein accumulation. High EIF4A3/NMD activity therefore lowers AE9a dosage, restrains t(8;21) AML cell proliferation, enhances chemosensitivity to idarubicin, and is associated with improved patient survival. Conversely, impaired NMD activity permits AE9a accumulation and may increase leukemic fitness. This model defines an isoform-specific, NMD-buffered oncogenic dosage checkpoint in t(8;21) AML.

ID: 42499671
Title: Global Changes in Unproductive Splicing and NMD Efficiency in Tumors.
Abstract: The nonsense-mediated mRNA decay (NMD) pathway is a mRNA quality control mechanism which not only degrades deleterious transcripts but also orchestrates a large number of post-transcriptional regulatory programs through unproductive splicing. We have developed a robust metric derived from splicing quantification in the RNA-seq data to measure NMD efficiency at a sample level. We demonstrate that NMD efficiency varies substantially both between and within tissues, with the magnitude of the variation comparable to that observed upon knockdown of the core NMD factor UPF1. By analyzing TCGA cancer cohorts, we further show that, in many tumors, unproductive splicing events undergo coordinated changes towards either collective suppression or collective activation of NMD isoforms, which is indicative of global deregulation of the activity of the NMD pathway. Consistently, we observed a striking divergence of NMD efficiency in cancers from the tissue-specific baseline level, suggesting that tumors partially erase the NMD signature of their tissue of origin. The application of the developed metric to RNA-binding protein knockdowns made it possible to identify several novel potential regulators of NMD efficiency. In sum, this study provides a solid framework for quantifying NMD efficiency, describes its biological and clinical relevance, and opens new avenues for dissecting mechanisms of post-transcriptional gene expression regulation by the NMD pathway.

ID: 42541567
Title: Targeting TDP-43 in sporadic amyotrophic lateral sclerosis.
Abstract: Amyotrophic lateral sclerosis (ALS) is a rapidly progressive neurodegenerative disorder characterized by motor neuron degeneration leading to early mortality. Despite advances in understanding genetic and molecular contributors, effective disease-modifying therapies for sporadic ALS are of limited utility. The identification of the accumulation of TAR DNA-binding protein 43 (TDP-43) in 97% of total ALS cases represents a critical pathogenic hallmark. This review examines key biological mechanisms underlying TDP-43 pathology, emerging therapeutic strategies, and evolving approaches to clinical trial design and biomarker development. TDP-43 loss of nuclear function, leading to widespread RNA missplicing, and inclusion of cryptic exons, represents an early and critical event in ALS pathogenesis causing downstream dysregulation of key neuronal genes such as STMN2 and UNC13A contributing to axonal degeneration and synaptic dysfunction. Therapeutic strategies targeting these pathways are currently under investigation. Additional approaches aim to ameliorate TDP-43 gain-of-function through cytoplasmic TDP-43 aggregation or modulating processes such as stress responses and RNA metabolism, although clinical translation has been challenging. Advances in biomarkers, including neurofilament light chain and cryptic exon-derived peptides, provide tools for developing efficient clinical trials. However, heterogeneity in disease progression and limitations of available clinical endpoints complicate trial design. Integration of biological insights with biomarker-driven patient stratification and optimized trial methodologies is essential to improve clinical trial outcomes. Emerging biomarkers may enable earlier diagnosis, monitoring of therapeutic response, and personalized treatment approaches. Continued alignment of biological discovery with innovative clinical trial design holds promise for advancing effective therapies and transforming the future of ALS.