ANGIOTENSIN II, IGF-1 AND SKELETAL MUSCLE ATROPHY

描述(申请人提供)：恶病质是慢性疾病的主要并发症，如心力衰竭、肾衰竭和癌症。在这些情况下，肾素-血管紧张素系统(RAS)经常被激活。我们已经证明血管紧张素II(Ang II)诱导骨骼肌萎缩，而胰岛素样生长因子1(IGF-1)阻止它。血管紧张素-2干扰胰岛素和 IGF-1信号转导导致线粒体功能障碍，耗尽肌肉ATP，抑制5‘-腺苷一磷酸活化蛋白激酶(AMPK)信号转导，阻止对能量耗竭的正常反应。用5-氨基咪唑-4-甲酰胺核糖核苷(AICAR)激活AMPK可恢复能量平衡，防止Ang II的浪费，提示AMPK在Ang II对骨骼肌的作用中起重要作用。血管紧张素转换酶II可能通过AT1a受体(AT1aR)介导的抑制Notch信号通路来耗尽肌肉干细胞(MUSC)，从而降低骨骼肌损伤后的再生能力。肌肉特异性过表达IGF-1可以激活AMPK，增加MUSC，并防止Ang II诱导的消瘦，这意味着AMPK和MUSC是Ang II和IGF-1在肌肉中相反作用的关键汇聚点。本项目的长期目标是了解Ang II如何改变骨骼肌生物学，以及IGF-1如何发挥其对Ang II诱导的骨骼肌萎缩的保护作用；我们将通过三个具体目标来实现这些目标：具体目标1.证明能量平衡和AMPK信号通路的受损介导Ang II诱导的骨骼肌萎缩并确定相关机制。我们将使用Ang II与骨骼肌特异性AT1aR-/-小鼠、AMPK-KD小鼠、Akt-/-小鼠以及过表达固有活性AMPK或Akt的小鼠一起输注，以检测Ang II对能量平衡的负面影响是否通过AMPK和/或Akt信号的改变来介导，并探讨AICAR介导的救援机制。我们还将研究人类骨骼肌组织样本。特异性目的2：证明AMPK的IGF-1活化可预防Ang II诱导的胰岛素/IGF-1抵抗和糖和蛋白质代谢紊乱。我们将利用AMPK-KD小鼠，MLC-IGF-1小鼠(肌肉特异性IGF-1转基因)，肌肉特异性IGF-1R-/-小鼠来评估Ang II对胰岛素/IGF-1信号转导的影响，以检验IGF-1的救援作用是否依赖于AMPK，并研究AICAR的作用。具体目标3：证明Ang II和IGF-1调节肌肉干细胞，并通过这一机制改变肌肉再生。我们将使用人类组织样本、MLC-IGF-1小鼠、AT1aR-/-小鼠、Myf5LacZ/+小鼠和心脏毒素损伤模型来研究Ang II抑制和IGF-1刺激肌肉再生的机制。我们的结果将对Ang II损害骨骼肌代谢、耗尽MUSC和抑制再生的机制提供关键的见解，以及对IGF-1对骨骼肌的新作用的见解。这些发现将允许开发创新的疗法来治疗RAS激活的慢性条件下的恶病质。

DESCRIPTION (provided by applicant): Cachexia is a major complication of chronic diseases such as heart failure, kidney failure and cancer. In these conditions the renin-angiotensin system (RAS) is often activated. We have shown that Angiotensin II (Ang II) induces skeletal muscle wasting, while Insulin-like growth factor 1 (IGF-1) prevents it. Ang II disrupts insulin and IGF-1 signaling, induces mitochondrial dysfunction, depletes muscle ATP, and inhibits 5'-Adenosine Monophosphate Activated Protein Kinase (AMPK) signaling, preventing the normal response to energy depletion. Activation of AMPK with 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR) restores energy balance and prevents Ang II wasting, indicating that AMPK plays a critical role in Ang II effects on skeletal muscle. Ang II also reduces the regenerative capacity of skeletal muscle following injury by depleting the muscle stem cell (MuSC) compartment, likely via AT1a receptor (AT1aR) mediated inhibition of Notch signaling. Muscle specific overexpression of IGF-1 activates AMPK, increases MuSC, and prevents Ang II-induced wasting, implicating AMPK and MuSC as key points of convergence for the opposing effects of Ang II and IGF- 1 in muscle. The long-term objectives of this project are to understand how Ang II alters skeletal muscle biology and how IGF-1 exerts its protective effects against Ang II-induced wasting; we will achieve these goals through three specific aims: Specific Aim 1. To demonstrate that impairment of energy balance and AMPK signaling mediate ANG II-induced skeletal muscle atrophy and to determine the mechanisms involved. We will use Ang II infusion with skeletal muscle specific AT1aR-/- mice, AMPK kinase dead (AMPK- KD) mice, Akt-/- mice, and constructs overexpressing constitutively active AMPK or Akt to examine whether the negative effects of Ang II on energy balance are mediated by alterations in AMPK and/or Akt signaling, and to ascertain the mechanisms of AICAR mediated rescue. We will also study human skeletal muscle tissue samples. Specific Aim 2: To demonstrate that Ang II induced insulin/IGF-1 resistance and dysregulation of glucose and protein metabolism are prevented by IGF-1 activation of AMPK. We will utilize AMPK-KD mice, MLC-IGF-1 mice (muscle specific IGF-1 transgenics), muscle specific IGF-1R-/- mice to assess effects of Ang II on insulin/IGF-1 signaling, to examine if rescue effects of IGF-1 are AMPK-dependent and study the effects of AICAR. Specific Aim 3: To demonstrate that Ang II and IGF-1 regulate muscle stem cells and, via this mechanism, alter muscle regeneration. We will use human tissue samples, MLC-IGF-1 mice, AT1aR-/- mice, Myf5LacZ/+ mice and the cardiotoxin-injury model to examine mechanisms whereby Ang II inhibits and IGF-1 stimulates muscle regeneration. Our results will provide key insights into mechanisms whereby Ang II impairs skeletal muscle metabolism, depletes MuSC and inhibits regeneration; as well as insights into novel effects of IGF-1 on skeletal muscle. These findings will allow development of innovative therapies to treat cachexia in chronic conditions in which the RAS is activated.