A pathological hallmark of ALS is the presence of cytoplasmic inclusions or protein
aggregates in affected motor neurons [2], suggesting that impairment of protein degradation
plays a role in the disease process. Unlike mitotic cells, which are able to clear aggregates of
intracellular proteins through their dilution or asymmetric distribution during cell division [3],
postmitotic neurons rely on two major pathways of protein degradation for aggregate removal:
the ubiquitin-proteasome system (UPS) and autophagy-associated lysosomal degradation.
Whereas the UPS mostly mediates the degradation of short-lived proteins conjugated with
ubiquitin, the autophagy-based system preferentially targets long-lived proteins and damaged
organelles [4]. Dysfunction of these two pathways has been implicated in the pathogenesis of
various neurodegenerative diseases including ALS [4].
Although the precise role of autophagy in the pathogenesis of ALS is still under
controversy, emerging evidence supports the notion that defects in autophagic flux may
contribute to the demise of motor neurons and disease progression in ALS [5]. Various stages
of the autophagy-dependent lysosomal degradation of protein aggregates may be impaired in
individuals with this disease. In this review, we summarize the case for a potential role of
autophagic dysfunction in the pathogenesis of ALS.