Does autophagy worsen or improve the survival of dopaminergic neurons?

In eukaryotic cells intracellular components are mainly degraded by autophagy and the ubiquitin-proteasome system. Autophagy is more flexible compared with the ubiquitin-proteasome system and it is involved in the degradation of long-lived proteins and organelles, such as mitochondria, which cannot be degraded by the ubiquitin-proteasome. Although autophagy is able to compensate for ubiquitin-proteasome dysfunction, the opposite does not occur. Autophagy is frequently involved in neurodegeneration; however, there is no consensus on its role in cell survival, as it can be either neuroprotective or neurotoxic. With respect to dopaminergic neurons, there is evidence that autophagy occurs during damage to substantia nigra neurons such as in Parkinson's disease. Moreover, a variety of inherited forms of Parkinson's disease are characterized by mutated proteins that belong to the autophagy pathway. Inhibition of autophagy precipitates dopaminergic cell death, whereas autophagy activation rescues the death of nigral dopaminergic neurons induced by proteasome inhibitors. Taken together, this evidence suggests that autophagy improves the survival of dopaminergic cells. (C) 2009 Elsevier Ltd. All rights reserved.