Autophagy or autophagocytosis (``self-eating'') refers to a process of degradation of cytoplasmic components within lysosomes, a unique process mediated by autophagosomes. Autophagy consists of several sequential steps: sequestration, transport to lysosomes, degradation and eventual re-utilization of degradation products. Autophagosomes engulf a portion of cytoplasm, thus autophagy is generally thought to be a nonselective degradation system regulated by many different cellular signaling pathways. Autophagy functions as a stress response upregulated by nutrient and energy starvation, oxidative stress, or other harmful conditions (such as damage to organelles, protein aggregation and infection by pathogens). Dysfunction of autophagy is associa