Autophagy: Many paths to the same end.

Different mechanisms lead to the degradation of intracellular proteins in the lysosomal compartment. Activation of one autophagic pathway or another, under specific cellular conditions, plays an important role in the ability of the cell to adapt to environmental changes. Each form of autophagy has its own individual characteristics, but it also shares common steps and components with the others. This interdependence of the autophagic pathways confers to the lysosomal system, both specificity and flexibility on substrate degradation. We describe in this review some of the recent findings on the molecular basis and regulation for each of the different autophagic pathways. We also discuss the cellular consequences of their interdependent function. Malfunctioning of the autophagic systems has dramatic consequences, especially in non-dividing differentiated cells. Using the heart as an example of such cells, we analyze the relevance of autophagy in aging and cell death, as well as in different pathological conditions. (Mol Cell Biochem 263: 55-72, 2004).