Pathogenic Proteins Driving ALS Pathogenesis: Molecular Mechanisms and Translational Therapeutic Perspectives

Amyotrophic Lateral Sclerosis (ALS) is a fatal neurodegenerative disease characterized by the progressive degeneration of motor neurons, with protein aggregation as a central pathological hallmark. Key pathogenic proteins, including TDP-43, SOD1, FUS, and dipeptide repeat proteins (DPRs) from C9orf72 expansions, drive disease progression through diverse but converging mechanisms. TDP-43 proteinopathy, present in nearly all ALS cases, involves cytoplasmic mislocalization, misfolding, and aggregation, disrupting RNA processing, protein transport, and DNA repair. Similarly, SOD1 and FUS mutations promote toxic protein aggregation, impairing cellular homeostasis and contributing to neuronal dysfunction. C9orf72-derived DPRs exert toxicity by interfering with nucleocytoplasmic transport. The propagation of these pathogenic proteins between neurons and glia, often via prion-like mechanisms, underlies the characteristic spread of ALS pathology throughout the nervous system. Cellular protective responses, such as molecular chaperones and the ubiquitin-proteasome system, attempt to mitigate aggregation but are often overwhelmed in disease states. Mitochondrial dysfunction, oxidative stress, and disturbances in calcium homeostasis are also implicated, with evidence showing that SOD1 mutations can alter redox balance and mitochondrial function in both neurons and non-neuronal cells. Impaired DNA repair mechanisms, involving proteins such as TDP-43, FUS, NEK1, and VCP, have emerged as important contributors to ALS pathogenesis, linking protein aggregation to genomic instability. Recent therapeutic strategies focus on directly targeting misfolded proteins using small molecules, peptides, or antisense oligonucleotides to inhibit aggregation or enhance clearance, offering hope for disease modification. Understanding the interplay between protein aggregation, impaired RNA metabolism, and cellular stress responses is crucial for developing effective translational therapies for ALS.