Autophagy in aging and in neurodegenerative disorders.

Autophagy (ATG) is the process of bulk degradation and recycling of long-lived proteins, macromolecular aggregates, and damaged intracellular organelles. Cellular homeostasis requires continuous removal of worn-out components and replacement with newly synthesized ones. Studies in yeast and other mammalian systems have increased our knowledge of the molecular mechanism of autophagy and the role of autophagy in various pathological conditions. Discovery of the genes involved in the process of autophagy has provided insight into the involvement of various molecular pathways. Growing evidence has indicated that diminished autophagic activity may play a pivotal role in the aging process. Cellular aging is characterized by a progressive accumulation of nonfunctional cellular components owing to oxidative damage and a decline in turnover rate and housekeeping mechanisms. Lysosomes are key organelles in the aging process due to their involvement in both macroautophagy and other housekeeping mechanisms. Autophagosomes themselves have limited degrading capacity and rely on fusion with lysosomes. Accumulation of defective mitochondria also appears to be critical in the progression of aging. Inefficient removal of nonfunctional mitochondria by lysosomes constitutes a major issue in the aging process. Autophagy has been associated with a growing number of pathological conditions, including cancer, myopathies, and neurodegenerative disorders. In this review, we discuss the cellular and molecular mechanisms involved in autophagy, the mechanisms of aging, and the possible role of autophagy in this process. Understanding the mechanisms by which autophagy impacts aging may provide useful molecular targets for pharmaceuticals designed to delay aging or correct conditions of premature aging.