ملاتونین به عنوان یک تنظیم کننده درونی بیماری ها: نقش خودخواری Melatonin as an endogenous regulator of diseases: The role of autophagy

Introduction: Autophagy is a lysosomal degradation process in eukaryote cells that removes misfolded proteins and damaged organelles in order to maintain cellular homeostasis in response to starvation and other stresses [1]. During autophagy, damaged components are engulfed in double-membrane vesicles, or autophagosomes. Then, autophagosomes fuse with lysosomes and create autophagolysosomes. The contents of autophagolysosomes are degraded by lysosomal hydrolytic enzymes [2]. There are particular forms of autophagy in which specific proteins or components are delivered to the autophagolysosomes for degradation. These selective types of autophagy include degradation of endoplasmic reticulum (ER-phagy), peroxisomes (pexophagy), and mitochondria (mitophagy) [3]. Activation of a molecular complex containing the serine/threonine kinase ULK1 is the first step in the initiation of autophagy which is inhibited following activation of the mammalian target of rapamycin (mTOR) [4]. Nucleation of the autophagosomal membrane is controlled by the Bcl-2-interacting protein (beclin)-1 which increases phosphatidylinositol 3-phosphate production. Two distinct ubiquitin-like conjugation systems participate in the elongation step of autophagy. The ubiquitin-like autophagy-related (Atg)7 activation promotes Atg12 conjugation to Atg5 forming a complex with Atg16L1. In the second conjugation system, the microtubule-associated protein 1 light chain (LC)3-I is converted to a membrane-bound LC3-II form. Then, LC3 binds to the adaptator protein p62 sequestrosome 1 (p62/SQSTM1) which facilitates the degradation of damaged components in the lysosomes [2]. Thus, the LC3-II/LC3-I ratio is considered an index of autophagy.