Sarcopenia in cirrhosis is mediated by a hyperammonemic stress response

肝硬化中的肌肉减少症是由高氨血症应激反应介导的

• 批准号: 9751852
• 负责人: Srinivasan Dasarathy
• 金额: $ 57.59万
• 依托单位: CLEVELAND CLINIC LERNER COM-CWRU
• 依托单位国家: 美国
• 财政年份: 2018
• 资助国家: 美国
• 起止时间: 2018-08-01 至 2022-04-30
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/9751852
• 关键词: ATF6 gene; Abbreviations; Acids; Amino Acid Transporter; Amino Acids; Amino Acyl-tRNA Synthetases; Ammonia; Autophagocytosis; Binding Proteins; Biochemical; Branched-Chain Amino Acids; CCL21 gene; Caliber; Catabolism; Cell model; Cellular Stress; Cellular Stress Response; Characteristics; Cirrhosis; Clinical; Complex; Complication; DNA Damage; Data; Diamines; Edetic Acid; Embryo; Endoplasmic Reticulum; Endoplasmic Reticulum Degradation Pathway; Enzymes; Equilibrium; Ethylenes; Eukaryotic Initiation Factor-2; Event; Experimental Models; Exposure to; FRAP1 gene; Feedback; Fibroblasts; Foundations; Genetic Transcription; Glutamate-Ammonia Ligase; Glutamine; Green Fluorescent Proteins; Growth; Homologous Gene; Human; Hyperammonemia; Impairment; Inositol; Intervention; Leucine; Limb structure; Link; Liver diseases; MAPK8 gene; Magnetic Resonance Imaging; Mass Fragmentography; Mediating; Mediator of activation protein; Molecular; Mus; Muscle; Muscle Fibers; Muscular Atrophy; Outcome; Pathway interactions; Patients; Phase; Phenylalanine; Phosphorylation; Phosphotransferases; Physiological; Plasma; Polymerase Chain Reaction; Prevalence; Protein Biosynthesis; Protein Kinase; Protein Synthesis Inhibition; Protein phosphatase; Proteins; Proteolysis; Publishing; RNA; RNA Splicing; Recovery; Rodent Model; Signal Pathway; Signal Transduction; Skeletal Muscle; Supplementation; Surgical Portacaval Shunt; Surgical Portosystemic Shunt; Testing; Thapsigargin; Therapeutic; Therapeutic Intervention; Time; Tissues; Transfer RNA; Translation Initiation; Tunicamycin; Variant; activating transcription factor; activating transcription factor 4; adaptive intervention; ammonium acetate; biological adaptation to stress; clinical translation; effective therapy; endoplasmic reticulum stress; experimental study; extracellular; gain of function; hepatic ureagenesis; in vivo; inhibitor/antagonist; mRNA Transcript Degradation; mouse model; muscle form; new therapeutic target; novel; prevent; proteostasis; purine metabolism; response; sarcopenia; sensor; skeletal muscle wasting; small molecule inhibitor; solute; stressor; targeted treatment; therapeutic target; transcription factor CHOP; uptake

ABSTRACT In cirrhosis, hyperammonemia is a consistent abnormality due to impaired hepatic ureagenesis and portosystemic shunting. Sarcopenia or loss of skeletal muscle mass is a major complication of hyperammonemia in cirrhosis and portosystemic shunting. Despite nearly universal recognition of the prevalence and adverse clinical consequences of sarcopenia, there are no effective therapies because the mechanisms of muscle loss in cirrhosis are not well understood. Loss of muscle mass occurs due to dysregulated protein homeostasis or proteostasis with impaired protein synthesis and increased proteolysis by autophagy. Protein homeostasis during cellular stress is achieved by activating an integrated stress response (ISR) in response to eIF2α phosphorylation via the activating transcription factor 4. Ammonia is a cellular stressor that is generated during amino acid catabolism, purine metabolism and synthesis in the gut. We identified a unique cellular stress response in the skeletal muscle that we have termed the hyperammonemic stress response (HASR). During HASR, we observed an increased phosphorylation and activation of the eIF2α kinase and amino acid deficiency sensor, general control nonderepressed 2 (GCN2) that is reversed by L- leucine supplementation. These perturbations resemble an amino acid deficiency response despite increased cellular L-leucine concentrations during hyperammonemia. Interestingly, we also observed that only one of the 3 components of the unfolded protein response (UPR), IRE1α, is activated during HASR. Interestingly, the other 2 limbs of the UPR: PERK, the classical mediator of Endoplasmic Reticulum (ER) stress and ATF6 were not activated during HASR. Unlike the cellular stress responses with eIF2α phosphorylation, the integrated stress response with induction of ATF4 and its targets that support translational recovery were also not observed during HASR. These observations show that HASR shares some characteristics of amino acid deficiency response (without deficiency) and some features of the UPR. Our preliminary and published data suggest a concentration and time dependent initial adaptive that progresses to a maladaptive phase in the skeletal muscle results in sarcopenia. We hypothesized that HASR is activated in response to hyperammonemia and involves a GCN2/mTORC1 axis that represses protein synthesis and induces an adaptive response of increased amino acid uptake and proteostasis control via the amino acid transporter SLC7A5. We also hypothesize that during HASR, only the IRE1α/XBP1s is activated with increased autophagy and mRNA degradation via RIDD (Regulated IRE1α dependent decay). The mechanisms of HASR and interventions that can increase protective adaptations to hyperammonemia in myotubes will be studied in a comprehensive array of cellular and rodent models of hyperammonemia and in the skeletal muscle of human cirrhotics in 3 specific aims. In each aim, a specific molecular therapeutic intervention will be tested with the potential for rapid clinical translation to reverse and potentially prevent sarcopenia in liver disease.

摘要 在肝硬化中，高氨血症是由于肝脏尿素生成受损而导致的持续异常， 门体分流术肌肉减少症或骨骼肌质量损失是一种主要的并发症， 肝硬化门体分流症高氨血症尽管几乎普遍承认 肌肉减少症的患病率和不良临床后果，没有有效的治疗方法，因为 肝硬化中肌肉损失的机制还不清楚。肌肉质量的损失是由于 蛋白质稳态失调或蛋白质稳态受损，蛋白质合成和蛋白质水解增加， 自噬细胞应激过程中蛋白质的稳态是通过激活整合的应激反应来实现的 (ISR)通过激活转录因子4应答eIF 2 α磷酸化。氨是一种细胞 在肠道中氨基酸代谢、嘌呤代谢和合成过程中产生的应激因子。我们 在骨骼肌中发现了一种独特的细胞应激反应，我们称之为高氨血症 应激反应（HASR）。在HASR期间，我们观察到eIF 2 α的磷酸化和活化增加， 激酶和氨基酸缺乏传感器，一般控制非去阻遏2（GCN 2），由L- 亮氨酸补充剂。这些扰动类似于氨基酸缺乏反应，尽管增加 高氨血症时细胞L-亮氨酸浓度。有趣的是，我们还观察到， 未折叠蛋白反应（UPR）的3个组分IRE 1 α在HASR期间被激活。有趣的是 UPR的另外两个分支：PERK，内质网（ER）应激的经典介质和ATF 6， 在HASR期间未激活。与eIF 2 α磷酸化的细胞应激反应不同，整合的 诱导ATF 4及其支持翻译恢复的靶点的应激反应也不 在HASR期间观察到。这些观察结果表明，HASR具有氨基酸的某些特征 缺陷答复（无缺陷）和普遍定期审议的一些特点。我们的初步和公布的数据 表明了一种浓度和时间依赖性的初始适应性， 骨骼肌导致肌肉减少症。我们假设HASR是响应于 高氨血症，并涉及GCN 2/mTORC 1轴，该轴抑制蛋白质合成并诱导高氨血症。 通过氨基酸转运蛋白增加氨基酸摄取和蛋白质稳态控制的适应性反应 SLC7A5。我们还假设，在HASR过程中，只有IRE 1 α/XBP 1 s被激活，自噬增加 RIDD（Regulated IRE1α dependent decay）。HASR的机制和 可以增加肌管对高氨血症的保护性适应的干预措施将在一个 高氨血症的细胞和啮齿动物模型以及人骨骼肌中的综合阵列 三个具体目标的理论。在每一个目标中，将用以下方法测试特定的分子治疗干预： 快速临床转化的潜力，以逆转和潜在地预防肝病中的肌肉减少症。