Cells are constantly suffering damage, the protein machinery harmed by reactive metabolic byproducts, other waste chemicals building up, and various subsystems failing. Efficient repair processes run continually, but at varying paces in response to circumstances. Degenerative aging is nothing more an accumulation of unrepaired damage in and between cells, and many of the ways to slow degenerative aging in laboratory animals are associated with a higher level of the cellular repair and housekeeping processes known as autophagy.
Here is a short open access review that providing an introduction to the processes of autophagy and their significance, with diagrams to clarify some of the descriptions:
Cellular damage occurs in response to genetic perturbations, nutrient deprivation, aging, and environmental toxins. The task of managing general and specific cellular damage is largely under the control of the highly regulated process called autophagy. The term autophagy is used to describe lysosomal-mediated degradation of intracellular contents, which can be divided into 3 basic mechanisms: (1) chaperone-mediated autophagy, (2) microautophagy, and (3) macroautophagy.
Macroautophagy is the most extensively studied autophagy process. One major function of macroautophagy is the control of accumulation of over-produced, long-lived or damaged proteins. Deficiencies of macroautophagy may contribute to accumulation of protein aggregates, which are apparent in a number of neurodegenerative diseases.
Chaperone-mediated autophagy, initiated by chaperone Hsc70, recognizes one protein at a time, and Hsc70 carries the protein to the lysosomes via binding to the lysosomal associated membrane protein (LAMP2A). Whether additional chaperones and lysosomal receptors participate in chaperone-mediated autophagy is unknown.
Microautophagy is achieved by invagination of lysosomal membranes. Lipid, protein or organelles can be degraded through this pathway. Whether lipid, organelles and other proteins are marked by specific modifications to be recognized by the lysosomes is highly likely but the majority of these have yet to be defined.
Autophagic removal of mitochondria is important for mitochondrial quality control. Poor quality mitochondria may enhance cellular oxidative stress, generate apoptosis signals, and induce cell death. Because healthy mitochondrial function is essential for cell survival, selective removal of a subset of dysfunctional mitochondria is a highly regulated process and requires coordinated functions of mitochondrial and cytosolic proteins. This is controlled by a complex array of proteins which are constantly being revised and enhanced.