Chaperone mediated autophagy is deficient in spinal motoneurons of ALS patients with TDP-43 proteinopathy

Abstract

Amyotrophic Lateral Sclerosis (ALS) is a progressive neurodegenerative disease characterized by the selective loss of motor neurons (MNs), ultimately resulting in paralysis and respiratory failure within 3 to 5 years of onset. Fewer than 10% of ALS cases are familial (fALS), while the vast majority are sporadic (sALS) with an unknown etiology. A pathological hallmark of ALS is the accumulation of misfolded TDP-43 protein aggregates within MNs. Although TDP-43 is known to be degraded via chaperone-mediated autophagy (CMA), the status of CMA activity in sALS has not been previously explored. To investigate this, we analyzed CMA in human spinal cord tissue by assessing the expression of LAMP2A, a key lysosomal receptor and marker of CMA activity. In control samples, spinal cord MNs exhibited robust LAMP2A expression. In contrast, MNs from sALS patients showed a marked reduction in LAMP2A levels, coinciding with the presence of TDP-43 pathology. Notably, analysis of LC3, a marker of macroautophagy, revealed no significant differences in expression between control and sALS MNs. Interestingly, MNs within the Onuf’s nucleus, a population known to be resistant to degeneration in ALS, retained normal LAMP2A expression and did not exhibit TDP-43 aggregation in sALS cases. These findings demonstrated that CMA is essential for the clearance of TDP-43 in spinal cord MNs and that its dysfunction may contribute to the pathogenesis of sALS. Furthermore, the high dependence of spinal cord MNs on CMA activity may underlie their selective vulnerability to degeneration when CMA is impaired, and highlight CMA enhancement as a promising therapeutic strategy to restore proteostasis and prevent MN degeneration in ALS.