TDP43 A315T

TDP-43 (TAR DNA-binding protein 43) normally resides in the cell nucleus where it regulates RNA processing, but in most ALS and FTD cases it mislocalizes to the cytoplasm and forms toxic aggregates. The M337V mutation, located in the C-terminal region of the protein (amino acid position 337), is classified as pathogenic by expert panels and has never been observed in healthy populations, strongly supporting its role in disease causation. The AlphaFold2 structural prediction of M337V achieved a moderate average confidence score of 64.9 pLDDT, indicating substantial uncertainty in the predicted structure. This moderate confidence likely reflects the inherently disordered nature of TDP-43's C-terminal region where M337V resides. While this prediction provides hypotheses about structural changes, the low confidence means direct structural comparisons should be interpreted cautiously and require experimental validation. Experimental studies demonstrate that M337V causes cellular dysfunction through multiple mechanisms that begin before obvious protein aggregates appear. In motor neurons derived from both mouse and patient stem cells, even low levels of M337V expression impair cell survival, reduce neurite outgrowth, slow axonal transport of essential cargo, and disrupt energy metabolism by reducing glycolysis [3]. Patient-derived neurons carrying M337V show increased levels of both soluble and detergent-resistant TDP-43, have a 2.76-fold higher death risk, and display heightened vulnerability to inhibition of survival signaling pathways [3]. These findings indicate the mutation creates a toxic gain of function rather than simply reducing normal TDP-43 activity. The M337V mutation alters TDP-43's biophysical properties in ways that promote aggregation and disrupt normal cellular organization. The mutation increases the protein's tendency to form irreversible aggregates and alters its behavior in stress granules (temporary RNA-protein clusters that form during cellular stress). M337V also abnormally increases binding to another RNA-binding protein called FUS, which disrupts normal regulatory mechanisms. Studies in C. elegans worms show that cytoplasmic TDP-43 causes behavioral problems and cellular dysfunction before any neurons actually die, suggesting that early functional impairments drive disease progression [1][4]. Recent research has identified that TDP-43 toxicity involves DNA damage and changes in multiple cellular pathways. Neurons from both sporadic ALS patients and those with familial mutations show increased DNA damage, decreased levels of the protective protein SIRT1, and increased levels of acetylated p53 (a stress response protein) [3]. When researchers restored SIRT1 levels, it rescued neurodegeneration in patient neurons, suggesting potential therapeutic strategies. Additionally, inhibiting the enzyme GSK3 (glycogen synthase kinase 3) reduces TDP-43 toxicity through a mechanism involving caspases (cellular executioner proteins), providing another potential treatment avenue [2].