The essential CMA components have been detected only in birds and mammals hence, the paucity of appropriate model systems such as yeast and flies may explain the delayed elucidation of CMA. It has been recognized that there is crosstalk between macroautophagy and CMA, and they can at least partly compensate for their functional loss each other, indicating that CMA activity may has a crucial role in the pathogenesis of aging-associated pulmonary disorders with insufficient macroautophagy. Insufficient macroautophagy, including mitochondria-selective mitophagy enhances mitochondrial reactive oxygen species (ROS) production, which regulates cellular senescence in epithelial cells and myofibroblast differentiation in fibroblasts in terms of COPD and IPF pathogenesis. Both IPF and COPD are aging-associated pulmonary disorders and the lysosomal function declines with aging. We have reported pathogenic involvement of macroautophagy in idiopathic pulmonary fibrosis (IPF), a form of progressive fibrosing interstitial pneumonia and in chronic obstructive pulmonary disease (COPD), which is characterized by progressive airflow limitation mainly caused by cigarette smoke (CS) exposure. Because macroautophagy is the best-characterized form of autophagy, recent studies of the molecular mechanisms and pathophysiological effects of autophagy have mainly focused on macroautophagy. The fusion of a lysosome with the autophagosome to form the autolysosome is a crucial process for degradation. During the process of macroautophagy, substrate proteins and organelles are sequestered by the autophagosome. Microautophagy requires small components of the cytoplasm to be engulfed by direct invagination into lysosomes. CMA is a type of selective autophagy for the lysosomal degradation of proteins with the KFERQ peptide motif. Three forms of distinct autophagy have been identified: chaperon-mediated autophagy (CMA), microautophagy, and macroautophagy (Fig. Further understanding of CMA machinery may shed light on the molecular mechanisms of refractory disorders and lead to novel treatment modalities through CMA modulation.Īutophagy is a highly conserved mechanism of delivering cytoplasmic components for lysosomal degradation to maintain the homeostatic balance between the synthesis, degradation, and recycling of cellular proteins and organelles. With respect to pulmonary disorders, the involvement of CMA has been demonstrated in lung cancer and chronic obstructive pulmonary disease (COPD) pathogenesis through regulating apoptosis. Recent advances have uncovered not only physiological but also pathological role of CMA in multiple organs, including neurodegenerative disorders, kidney diseases, liver diseases, heart diseases, and cancers through the accumulation of unwanted proteins or increased degradation of target proteins with concomitant metabolic alterations resulting from CMA malfunction. Lysosome-associated membrane protein type 2A (LAMP2A) is responsible for substrate binding and internalization to lysosomes, and thus, the lysosomal expression level of LAMP2A is a rate-limiting factor for CMA. Among the three major autophagic pathways, chaperone-mediated autophagy (CMA) is primarily characterized by its selective nature of protein degradation, which is mediated by heat shock cognate 71 kDa protein (HSC70: also known as HSPA8) recognition of the KFERQ peptide motif in target proteins. Autophagy is a highly conserved mechanism of delivering cytoplasmic components for lysosomal degradation.
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