ANGIOTENSIN II, IGF-1 AND SKELETAL MUSCLE ATROPHY

描述（由申请人提供）：恶病质是慢性疾病（如心力衰竭、肾衰竭和癌症）的主要并发症。在这些条件下，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。 IGF-1信号传导，诱导线粒体功能障碍，消耗肌肉ATP，并抑制5 '-腺苷一磷酸活化蛋白激酶（AMPK）信号传导，阻止对能量消耗的正常反应。AMPK与5-氨基咪唑-4-甲酰胺核糖核苷（AICAR）的激活恢复能量平衡，防止血管紧张素II消耗，表明AMPK在血管紧张素II对骨骼肌的作用中起着关键作用。血管紧张素II还可能通过AT 1a受体（AT 1aR）介导的Notch信号抑制，通过耗尽肌肉干细胞（MuSC）室，降低骨骼肌损伤后的再生能力。IGF-1的肌肉特异性过表达激活AMPK，增加MuSC，并防止Ang II诱导的消耗，暗示AMPK和MuSC是肌肉中Ang II和IGF- 1的相反作用的关键点。该项目的长期目标是了解血管紧张素II如何改变骨骼肌生物学以及IGF-1如何发挥其对血管紧张素II诱导的消耗的保护作用;我们将通过三个具体目标实现这些目标：具体目标1。证明能量平衡和AMPK信号传导受损介导ANG II诱导的骨骼肌萎缩，并确定相关机制。我们将使用血管紧张素II输注骨骼肌特异性AT 1aR-/-小鼠、AMPK激酶死亡（AMPK-KD）小鼠、Akt-/-小鼠和过表达组成型活性AMPK或Akt的构建体，以检查血管紧张素II对能量平衡的负面影响是否由AMPK和/或Akt信号传导的改变介导，并确定AICAR介导的拯救机制。我们还将研究人类骨骼肌组织样本。具体目标二：证明Ang II诱导的胰岛素/IGF-1抵抗以及葡萄糖和蛋白质代谢的失调可通过IGF-1激活AMPK来预防。我们将利用AMPK-KD小鼠、MLC-IGF-1小鼠（肌肉特异性IGF-1转基因小鼠）、肌肉特异性IGF-1 R-/-小鼠来评估Ang II对胰岛素/IGF-1信号传导的影响，以检查IGF-1的拯救作用是否是AMPK依赖的，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，并通过这种机制改变肌肉再生。我们将使用人体组织样本，MLC-IGF-1小鼠，AT 1aR-/-小鼠，Myf 5LacZ/+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。我们的研究结果将为Ang II损害骨骼肌代谢、耗尽MuSC和抑制再生的机制提供关键见解;以及IGF-1对骨骼肌的新作用的见解。这些发现将允许开发创新疗法来治疗RAS被激活的慢性疾病中的恶病质。

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.