TDP-43 Proteinopathies in ALS and FTLD: Mechanistic Insights and Therapeutic Approaches.

TAR DNA-binding protein 43 (TDP-43) is a vital RNA/DNA-binding protein involved in RNA metabolism, playing a key role in the pathogenesis of amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD). Approximately 97% of sporadic ALS (sALS), familial ALS (fALS) and FTLD cases are associated with pathological inclusions of hyperphosphorylated and ubiquitinated TDP-43 and genetic mutations in TAR DNA binding protein (TARDBP). Besides TARDBP, mutations in other genes such as C9ORF72, SOD1, FUS, and NEK1 are also linked to other fALS cases. Cytoplasmic mislocalization, aberrant post-translational modifications, and amyloid- like aggregation characterize TDP-43 pathology. These pathological changes impair essential cellular processes, including gene expression, mRNA stability, and RNA metabolism. Mechanisms of TDP-43-induced toxicity include disruption of endocytosis, mitochondrial dysfunction, and progressive cellular damage. Additionally, liquid-liquid phase separation (LLPS) and prion-like propagation are emerging as central features of its pathological spread. This review summarizes advances in understanding TDP-43's physiological functions and pathological mechanisms in ALS and FTLD. It highlights key processes underlying TDP-43 toxicity, such as aggregation, selective neuronal vulnerability, and regional susceptibility. Finally, this review summarizes evolving therapeutic strategies aimed at mitigating TDP-43-related toxicity through disaggregation, targeting mislocalization, and addressing upstream dysfunctions and challenges faced in the development of effective therapies for ALS and FTLD.