TL;DR
It is suggested that mutant Htt does not reduce CMA activity and that enhancing CMA activity to clear mutant Htt may be a novel strategy for the management of HD.
Mutant C9orf72 has been extensively studied as a major genetic cause of amyotrophic lateral sclerosis and frontotemporal dementia, and is also known to generate Huntington's disease (HD)-like phenocopies. However, despite this strong disease association, the role of wild-type C9orf72 (wt-C9orf72) in neurodegeneration remains largely unexplored. HD is a neurodegenerative disease, and characterized by the accumulation of misfolded mutant Huntingtin (mHTT) and impaired proteostasis, yet the upstream mechanisms driving ubiquitin-proteasome system (UPS) dysfunction are not fully understood. Here, we identify a previously unrecognized modulatory role of wt-C9orf72 in regulating mHTT aggregation in experimental HD models. Analysis of public transcriptomic datasets reveal context-dependent C9ORF72 expression changes across HD-related human datasets, while C9orf72 levels are increased in R6/2 mouse brain lysates. Functional analyses reveal that overexpression of wt-C9orf72 increases mHTT aggregation and is accompanied by increased apoptotic signaling and reduced cell viability. Unbiased proteomic profiling identifies Stat1 as a key downstream effector. Mechanistically, wt-C9orf72 promotes Stat1 activation and nuclear translocation, leading to transcriptional upregulation of Isg15, a ubiquitin-like modifier. Elevated Isg15 disrupts UPS function, resulting in accumulation of polyubiquitinated proteins and impaired proteasomal degradation. Importantly, genetic suppression of Stat1 or Isg15 significantly attenuates C9orf72-associated mHTT aggregation, supporting a functional C9orf72-Stat1-Isg15 axis. Consistent with these cell-based findings, Stat1, phosphorylated Stat1 and Isg15 levels are elevated in the cortex and striatum of R6/2 HD mouse brains. Collectively, our findings identify a novel wt-C9orf72-Stat1-Isg15 axis that promotes proteasomal dysfunction and mHTT aggregation, providing new insights into wt-C9orf72-associated protein homeostasis.
Protein degradation systems have profound effects on signaling pathways and molecular networks that regulate organogenesis. Chaperone Mediated Autophagy (CMA) has been linked to neurodegenerative and neurodevelopmental diseases, however, its role in mammalian brain development remains poorly understood. Here, we identify a regulatory role of CMA pathway in neural stem cell (NSC) differentiation. We show that CMA is active in NSCs, while expression of LAMP2A, the principal limiting component of CMA, is associated with the induction of neurogenesis. Most importantly, overexpression and loss-of-function experiments of LAMP2A in NSCs suggest an inductive role of CMA in neuronal differentiation. Moreover, we demonstrate that LAMP2A is involved in NSC fate decisions by interfering with NOTCH1 signaling pathway. Our data support a model in which LAMP2A-dependent CMA contributes to neuronal fate acquisition through suppression of NOTCH1 signaling, and provide a mechanistic framework that may help explain the reported genetic involvement of LAMP2 gene and CMA in neurodevelopmental disorders.
These findings support the value of preclinical models for translational studies, and autophagy enhancement as a potential therapeutic strategy for HSPB8-related myopathy, and evaluated trehalose, a natural disaccharide that induces HSPB8 and enhances autophagy.
Proteostasis failure drives multiple neurodegenerative disorders (NDs), and ATP-independent chaperone pathways that support neuronal proteostasis remain poorly defined. Here, we identify the N6-methyladenosine (m6A)-binding protein YTHDC1 as an ATP-independent molecular chaperone, whose activity is mediated by a highly acidic polyaspartate/glutamate (polyD/E) segment. YTHDC1 prevents protein misfolding and aggregation, unfolds kinetically trapped substrates, and resolubilizes pre-formed aggregates. Deletion of the polyD/E segment abolishes these activities, whereas aromatic-cage mutants retain chaperone activity, demonstrating independence from m6A recognition. We identify the amyotrophic lateral sclerosis (ALS)-associated RNA-binding protein hnRNPA1 as a YTHDC1 client. YTHDC1 maintains liquid-like hnRNPA1 condensates, delays fibrillization of disease-associated mutants, and limits stress-granule sequestration, while mitigating mutant hnRNPA1-induced neurite growth defects in primary neurons. These findings define a proteostatic function of YTHDC1 and highlight its chaperone activity as a potential target for mitigating protein aggregation in ALS-related NDs. Researchers identify the RNA-binding protein YTHDC1 as an ATP-independent molecular chaperone that prevents harmful protein aggregation, revealing a link between RNA regulation and protein quality control in neurodegeneration.
