Center for Cardiovascular Research and Division of Cardiology, Department of Internal Medicine, Washington University School of Medicine, St. Louis, Missouri, United States of America.
John Cochran VA Medical Center, St. Louis, Missouri, United States of America.
PLoS Biol. 2019 May 14;17(5):e3000245. doi: 10.1371/journal.pbio.3000245. eCollection 2019 May.
Lysosomes are ubiquitous acidified organelles that degrade intracellular and extracellular material trafficked via multiple pathways. Lysosomes also sense cellular nutrient levels to regulate target of rapamycin (TOR) kinase, a signaling enzyme that drives growth and suppresses activity of the MiT/TFE family of transcription factors that control biogenesis of lysosomes. In this study, we subjected worms lacking basic helix-loop-helix transcription factor 30 (hlh-30), the Caenorhabditis elegans MiT/TFE ortholog, to starvation followed by refeeding to understand how this pathway regulates survival with variable nutrient supply. Loss of HLH-30 markedly impaired survival in starved larval worms and recovery upon refeeding bacteria. Remarkably, provision of simple nutrients in a completely defined medium (C. elegans maintenance medium [CeMM]), specifically glucose and linoleic acid, restored lysosomal acidification, TOR activation, and survival with refeeding despite the absence of HLH-30. Worms deficient in lysosomal lipase 2 (lipl-2), a lysosomal enzyme that is transcriptionally up-regulated in starvation in an HLH-30-dependent manner, also demonstrated increased mortality with starvation-refeeding that was partially rescued with glucose, suggesting a critical role for LIPL-2 in lipid metabolism under starvation. CeMM induced transcription of vacuolar proton pump subunits in hlh-30 mutant worms, and knockdown of vacuolar H+-ATPase 12 (vha-12) and its upstream regulator, nuclear hormone receptor 31 (nhr-31), abolished the rescue with CeMM. Loss of Ras-related GTP binding protein C homolog 1 RAGC-1, the ortholog for mammalian RagC/D GTPases, conferred starvation-refeeding lethality, and RAGC-1 overexpression was sufficient to rescue starved hlh-30 mutant worms, demonstrating a critical need for TOR activation with refeeding. These results show that HLH-30 activation is critical for sustaining survival during starvation-refeeding stress via regulating TOR. Glucose and linoleic acid bypass the requirement for HLH-30 in coupling lysosome nutrient sensing to survival.
溶酶体是普遍存在的酸化细胞器，可降解通过多种途径运输的细胞内和细胞外物质。溶酶体还能感知细胞的营养水平，以调节雷帕霉素靶蛋白（TOR）激酶的活性，TOR 激酶是一种信号酶，可促进生长并抑制控制溶酶体生物发生的 MiT/TFE 家族转录因子的活性。在这项研究中，我们使缺乏碱性螺旋-环-螺旋转录因子 30（hlh-30）的线虫（秀丽隐杆线虫 MiT/TFE 同源物）饥饿后再喂食，以了解该途径如何在可变营养供应下调节生存。hlh-30 的缺失显着损害了饥饿幼虫线虫的生存能力，并在再喂食细菌时恢复。值得注意的是，在完全定义的培养基（秀丽隐杆线虫维持培养基[CeMM]）中提供简单营养素，特别是葡萄糖和亚油酸，尽管没有 hlh-30，也能恢复溶酶体酸化、TOR 激活和再喂食时的生存能力。溶酶体脂肪酶 2（lipl-2）缺乏的线虫，一种在 hlh-30 依赖性饥饿中转录上调的溶酶体酶，也表现出随着饥饿-再喂食而死亡率增加，这部分通过葡萄糖得到挽救，表明 LIPL-2 在饥饿下的脂质代谢中起关键作用。CeMM 诱导 hlh-30 突变线虫中液泡质子泵亚基的转录，液泡 H+-ATPase 12（vha-12）及其上游调节剂核激素受体 31（nhr-31）的敲低消除了 CeMM 的挽救作用。Ras 相关 GTP 结合蛋白 C 同源物 1 RAGC-1 的缺失，哺乳动物 RagC/D GTPase 的同源物，赋予饥饿-再喂食致死性，RAGC-1 的过表达足以挽救饥饿的 hlh-30 突变线虫，表明再喂食时 TOR 的激活是至关重要的。这些结果表明，HLH-30 的激活对于通过调节 TOR 来维持饥饿-再喂食应激期间的生存是至关重要的。葡萄糖和亚油酸绕过 hlh-30 在将溶酶体营养感应与生存联系起来的需求。
