Université de Pau et des Pays de l'Adour, E2S UPPA, INRAE, UMR1419 Nutrition Métabolisme et Aquaculture, F-64310 Saint-Pée-sur-Nivelle, France.
INRAE, UR1037 Laboratory of Fish Physiology and Genomics, Campus de Beaulieu, Rennes, France.
Mol Biol Evol. 2020 Oct 1;37(10):2887-2899. doi: 10.1093/molbev/msaa127.
Chaperone-mediated autophagy (CMA) is a major pathway of lysosomal proteolysis recognized as a key player of the control of numerous cellular functions, and whose defects have been associated with several human pathologies. To date, this cellular function is presumed to be restricted to mammals and birds, due to the absence of an identifiable lysosome-associated membrane protein 2A (LAMP2A), a limiting and essential protein for CMA, in nontetrapod species. However, the recent identification of expressed sequences displaying high homology with mammalian LAMP2A in several fish species challenges that view and suggests that CMA likely appeared earlier during evolution than initially thought. In the present study, we provide a comprehensive picture of the evolutionary history of the LAMP2 gene in vertebrates and demonstrate that LAMP2 indeed appeared at the root of the vertebrate lineage. Using a fibroblast cell line from medaka fish (Oryzias latipes), we further show that the splice variant lamp2a controls, upon long-term starvation, the lysosomal accumulation of a fluorescent reporter commonly used to track CMA in mammalian cells. Finally, to address the physiological role of Lamp2a in fish, we generated knockout medaka for that specific splice variant, and found that these deficient fish exhibit severe alterations in carbohydrate and fat metabolisms, in consistency with existing data in mice deficient for CMA in liver. Altogether, our data provide the first evidence for a CMA-like pathway in fish and bring new perspectives on the use of complementary genetic models, such as zebrafish or medaka, for studying CMA in an evolutionary perspective.
伴侣蛋白介导的自噬（CMA）是溶酶体蛋白水解的主要途径，被认为是控制许多细胞功能的关键因素，其缺陷与多种人类疾病有关。迄今为止，由于在非四足动物物种中缺乏可识别的溶酶体相关膜蛋白 2A（LAMP2A），这种细胞功能被认为仅限于哺乳动物和鸟类，因为 LAMP2A 是 CMA 的限制和必需蛋白。然而，最近在几种鱼类中鉴定出与哺乳动物 LAMP2A 具有高度同源性的表达序列，这一观点受到了挑战，并表明 CMA 可能在进化过程中出现的时间比最初想象的要早。在本研究中，我们全面描绘了脊椎动物 LAMP2 基因的进化历史，并证明了 LAMP2 确实出现在脊椎动物谱系的根部。使用来自斑马鱼（Oryzias latipes）的成纤维细胞系，我们进一步表明，剪接变体 lamp2a 在长期饥饿时控制着荧光报告分子在溶酶体中的积累，该报告分子常用于跟踪哺乳动物细胞中的 CMA。最后，为了解决 Lamp2a 在鱼类中的生理作用，我们生成了该特定剪接变体的敲除斑马鱼，发现这些缺陷型鱼类在碳水化合物和脂肪代谢方面表现出严重改变，与肝脏中缺乏 CMA 的小鼠的现有数据一致。总之，我们的数据为鱼类中存在 CMA 样途径提供了第一个证据，并为利用互补的遗传模型（如斑马鱼或斑马鱼）从进化角度研究 CMA 提供了新的视角。
