The small giant actor in the pathogenesis of neurodegenerative diseases: Microtubules.

Neurodegenerative diseases are a clinically and pathologically diverse group of disorders characterized by progressive neuronal dysfunction, synaptic impairment, and neuronal loss. Although research has traditionally focused on disease-associated protein misfolding and aggregation, increasing evidence implicates abnormalities of cytoskeletal organization and intracellular transport in several neurodegenerative conditions. Microtubules contribute to neuronal polarity, axonal and dendritic transport, organelle distribution, and synaptic maintenance. These functions are regulated in part by tubulin isotypes, post-translational modifications collectively described as the tubulin code, microtubule-associated proteins, and molecular motors. This narrative review examines evidence linking alterations in these processes with Alzheimer's disease, Parkinson's disease, frontotemporal dementia, Huntington's disease, amyotrophic lateral sclerosis, and prion disease. We summarize proposed interactions among microtubule instability, impaired axonal transport, mitochondrial dysfunction, and disease-associated proteins, including tau, α-synuclein, mutant huntingtin, TDP-43, and prion protein. Evidence connecting tau pathology with microtubule dysfunction is comparatively well established in Alzheimer's disease and MAPT-related tauopathies, whereas findings in other disorders are more heterogeneous and are frequently derived from cellular or animal models. We also discuss emerging experimental approaches, candidate biomarkers, and investigational microtubule-directed treatments. However, no tubulin-specific biomarker or microtubule-targeted disease-modifying treatment discussed in this review has yet been clinically validated. Overall, microtubule dysfunction may represent one component of broader, disease-specific pathological networks rather than a universal primary cause of neurodegeneration. Further longitudinal and clinical studies are needed to determine whether microtubule-related alterations act as causes, consequences, or modifiers of disease progression.