Axonal pathology and impaired axo-glial crosstalk as early drivers of neurodegeneration.

Axonal dysfunction is a critical event in neurodegenerative diseases, which can precede neuronal loss. For instance, in multiple sclerosis, chronic demyelination leads to axonal transection and downstream neurological deficits, yet in other neurodegenerative conditions, the causal relationship between axonal pathology and disease progression remains elusive. While defects in axonal transport, cytoskeletal integrity, and organelle trafficking are observed in Alzheimer's disease and the frontotemporal dementia-amyotrophic lateral sclerosis spectrum, a question remains: Are axonal defects merely downstream consequences of somatic neurodegeneration, or do they actively drive pathogenesis? Emerging evidence suggests that early axonal dysfunction may accelerate disease progression through disrupted connectivity, retrograde degeneration, and neuroinflammation. Here, we highlight current evidence on axonal pathophysiology across Alzheimer's disease and frontotemporal dementia-amyotrophic lateral sclerosis. We first outline the makeup of the mature axonal compartment, as well as the processes related to axonal maintenance, which include myelination, glial support, and microtubule-dependent transport mechanisms. We further compare axonal perturbations in Alzheimer's disease and frontotemporal dementia-amyotrophic lateral sclerosis, exploring commonalities as potential convergent mechanisms. Therapeutic strategies to stabilize axons by maintaining microtubule dynamics, restoring energetics, or modulating glial support could therefore theoretically offer neuroprotection if performed selectively on vulnerable neuronal subsets and early in the disease course. Ultimately, by reframing axonal pathology as a primary driver rather than an epiphenomenon, this review underscores the importance of targeting axonal health in neurodegenerative diseases.