Targeting autophagy in ALS: a complex mission.

Several neurodegenerative diseases share a common neuropathology, primarily featuring the presence of abnormal protein inclusions in the brain containing specific misfolded proteins. Strategies to decrease the load of protein aggregates and oligomers are considered relevant targets for therapeutic intervention. Many studies indicate that macroautophagy is a selective and efficient mechanism for the degradation of misfolded mutant proteins related to neurodegeneration, without affecting the levels of the corresponding wild-type form. In fact, activation of autophagy by rapamycin treatment decreases the accumulation of protein aggregates and alleviates disease features in animal models of Huntington disease and other disorders affecting the nervous system. Recent evidence, however, indicates that the expression of several disease-related genes may actually impair autophagy activity at different levels, including omegasome formation, substrate recognition, lysosomal acidity and autophagosome membrane nucleation. A recent report from Zhang and co-workers indicates that treatment of an amyotrophic lateral sclerosis (ALS) mouse model with rapamycin actually exacerbates neuronal loss and disease progression, associated with enhanced apoptosis. This study reflects the need for a better understanding of the contribution of autophagy to ALS and other neurodegenerative diseases since this pathway may not only operate as a cleaning-up mechanism. Then, autophagy impairment may be part of the pathological mechanisms underlying the disease, whereas augmenting autophagy levels above a certain threshold could lead to detrimental effects in neuronal function and survival. Combinatorial strategies to repair the autophagy deficit and also enhance the activation of the pathway may result in a beneficial impact to decrease the content of protein aggregates and damaged organelles, improving neuronal function and survival.