Biology subjects

Parameswaran, J.

Publications and source records attributed to Parameswaran, J..

5 recordsLinked to original sources

bioRxiv2026

Temporal RNA splicing dysregulation in a human multicellular model of C9orf72 ALS

Amyotrophic lateral sclerosis (ALS) is a complex and heterogenous disease, comprising of familial and sporadic forms, numerous genetic mutations, and a wide range of affected cell types and proposed dysregulated processes. While the usage of in vitro cell cultures, mouse models, and postmortem patient tissue have advanced our understanding of ALS disease mechanisms, the temporal progression of the disease and how early molecular changes evolve remain poorly understood. Here, we establish human spinal cord organoids (hSpO) derived from C9orf72 patient induced pluripotent stem cells (C9-ALS hiPSCs) as a platform to model longitudinal changes across the disease trajectory. We show that C9-ALS hSpO recapitulate hallmark C9orf72-related pathologies, increased cell death, and progressive neuronal dysfunction. We further identify RNA splicing dysregulation as an early and persistent feature of C9-ALS, with splicing signatures in hSpO closely mirroring those observed in postmortem patient tissue. Finally, prediction of RNA binding proteins (RBPs) that induce early splicing changes in C9-ALS reveals signatures consistent with a broad RBP network dysfunction. Together, this work establishes hSpO as an in vitro system for investigating early disease mechanisms of ALS in a human multicellular context and highlights dysregulated events that precede cell death.

neuroscience↗

bioRxiv2026

TMEM106B C-terminal fragments drive nucleocytoplasmic transport failure and TDP-43 mislocalization in the aging human brain

TMEM106B is a lysosomal membrane protein and major genetic modifier of multiple neurodegenerative diseases, including frontotemporal lobar degeneration, Alzheimers disease, and amyotrophic lateral sclerosis. Proteolytically generated C-terminal fragments of TMEM106B assemble into amyloid fibrils that accumulate in the brains of individuals with neurodegenerative disease and in cognitively normal aged adults, yet how these fibrils produce neuronal dysfunction has remained unclear. Here, we show that cytosolic and lysosome-directed TMEM106B C-terminal fragments (CTF and gCTF) form detergent-insoluble amyloid aggregates, drive redistribution of endogenous TDP-43 from the nucleus to the cytoplasm, and accelerate neuronal death. Unbiased proximity proteomics identified the inner nuclear membrane LAP1-TorsinA axis as a fragment-specific interactome, and co-immunoprecipitation confirmed a direct physical interaction between gCTF and LAP1 that was not observed with full-length TMEM106B. Fragment expression disrupted Lamin B1 organization, mislocalized the nuclear import machinery KPNB1 and RanGAP1, and impaired importin-dependent nuclear transport in primary cortical neurons. Critically, neurons harboring endogenous TMEM106B fibrillar pathology in aged human frontal cortex exhibited the same phenotypes, namely disrupted Lamin B1 and LAP1 localization and cytoplasmic redistribution of TDP-43, whereas fibril-negative neurons from the same cases and younger control tissue retained intact nuclear envelope organization. These findings define TMEM106B proteinopathy as an upstream driver of nuclear envelope disruption and nucleocytoplasmic transport failure, linking a widespread feature of brain aging to a central mechanism of neurodegeneration.

neuroscience↗

bioRxiv2025

Lack of motor defects and ALS-like neuropathology in heterozygous Sptlc1 Exon 2 deletion mice

Mutations in the human SPTLC1 gene have recently been linked to early onset amyotrophic lateral sclerosis (ALS), characterized by global atrophy, motor impairments, and symptoms such as tongue fasciculations. All known ALS-linked SPTLC1 mutations cluster within exon 2 and a specific variant, c.58G>T, results in exon 2 skipping. However, it is unclear how the exon 2 deletion affects SPTLC1 function in vivo and contributes to ALS pathogenesis. Leveraging the high genomic sequence similarity between mouse and human SPTLC1, we created a novel mouse model with a CRISPR/Cas9-mediated deletion of exon 2 in the endogenous murine Sptlc1 locus. While heterozygous mice did not develop motor defects or ALS-like neuropathology, homozygous mutants died prematurely. These findings indicate that Sptlc1 {Delta}Exon2 heterozygous mice do not replicate the disease phenotype but provide valuable insights into SPTLC1 biology and serve as a useful resource for future mechanistic studies.

neuroscience↗

bioRxiv2022

Antisense, but not sense, repeat expanded RNAs activate PKR/eIF2α-dependent integrated stress response in C9orf72 FTD/ALS

GGGGCC (G4C2) hexanucleotide repeat expansion in the C9orf72 gene is the most common genetic cause of frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS). The repeat is bidirectionally transcribed and confers gain of toxicity. However, the underlying toxic species is debated, and it is not clear whether antisense CCCCGG (C4G2) repeat expanded RNAs contribute to disease pathogenesis. Our study shows that C9orf72 (C4G2) antisense repeat expanded RNAs trigger the activation of the PKR/eIF2-dependent integrated stress response independent of dipeptide repeat proteins that are produced through repeat-associated non-AUG initiated translation, leading to global translation inhibition and stress granule formation. Increased phosphorylation of PKR/eIF2 is also observed in the frontal cortex of C9orf72 FTD/ALS patients. Finally, only antisense (C4G2), but not sense (G4C2), repeat expanded RNAs can activate the PKR/eIF2 pathway. These results provide a mechanism by which antisense repeat expanded RNAs elicit neuronal toxicity in FTD/ALS caused by C9orf72 repeat expansions.

neuroscience↗

bioRxiv2022

ALS-linked KIF5A ΔExon27 mutant causes neuronal toxicity through gain of function

Mutations in the human kinesin family member 5A (KIF5A) gene were recently identified as a genetic cause of amyotrophic lateral sclerosis (ALS). Several KIF5A ALS variants cause exon 27 skipping and produce motor proteins with an altered C-terminal tail (referred to as {Delta}Exon27). However, the underlying pathogenic mechanism is still unknown. In this study, we performed a comprehensive analysis of {Delta}Exon27 at the single-molecule, cellular, and organism levels. Our results show that {Delta}Exon27 is prone to form cytoplasmic aggregates and is neurotoxic. The mutation relieves motor autoinhibition and increases motor self-association, leading to drastically enhanced processivity on microtubules. Finally, ectopic expression of {Delta}Exon27 in Drosophila melanogaster causes wing defects, motor impairment, paralysis and premature death. Our results suggest gain of function as an underlying disease mechanism in KIF5A-associated ALS.

neuroscience↗