细胞自噬的形态学特征和功能意义

目的 自噬是细胞受到刺激后吞噬自身的细胞质或细胞器,最终将吞噬物在溶酶体内降解的过程.按吞噬物进入溶酶体的途径,自噬可分为巨自噬、微自噬和分子伴侣介导的自噬3类.在巨自噬,自噬前体包裹细胞质或细胞器后形成自噬体,继而自噬体与溶酶体结合形成自噬溶酶体,自噬体内容物被降解.在微自噬,溶酶体膜凹陷,直接吞噬细胞质、细胞器或细胞核,形成自噬体,然后被溶酶体酶降解.分子伴侣介导的自噬是通过溶酶体膜的受体将细胞质内的蛋白质转运入溶酶体.自噬从酵母至哺乳动物细胞均很保守,对于耐受饥饿和缺血,清除衰老细胞器,清除细菌和异物,维持细胞活性和延长寿命等起着重要作用.自噬活动受自噬基因的调控,自噬基因缺失或功能障碍时可导致某些疾病的发生.深入认识自噬过程以及由此产生的自噬体等结构及其功能有助于探讨自噬对于人体生理和病理作用的机制.本文综述了自噬的形态学特征及其功能意义.

Morphological features and functional implications of autophagy

Objective Autophagy is a process by which cells phogocytize intracellular cytoplasm or organelles when cells are stimulated and cargoes are eventually degraded in lysosomes. According to the ways in which cargoes are transported into lysosomes, types of autophagy are divided into macroautophagy, microautophagy and chaperone-mediated autophagy. In macroautophagy, the autophagosome precursor wraps cytoplasm or organelles to form an autophagosome. Then the autophagosome fuses with the lysosome forming the autophagolysosome. The cargoes are degraded in lysosome. In microautophagy, the lysosome engulfs cytoplasm, organelles or nucleus directly through invagination of the lysosomal membrane and formation of the autophagosome. Finally, the contents of the autophagosome are digested by lysosomal enzymes. In chaperone mediated autophagy, cytosolic proteins are translocated into the lysosome by lysosomal membrane receptor. Autophgy is evolutionarily conserved from yeasts to mammalian cells and plays important roles in tolerating starvation and ischemia, cleaning the senescent organelles, eliminating bacteria and foreign matters, maintaining cellular activities and extending longevity. Autophagic activities are regulated by autophagic genes. Deletion or dysfunction of autophagic genes may result in some diseases. Elucidating the processes of autophagy, autophagic structures and their functions is helpful for exploring mechanisms of roles of autophagy in physiological and pathological processes. This review focuses on morphological characteristics of the autophagic structures and functional implications of these structures.