Dual-specificity phosphatase action in muscle disease

摘要 骨骼肌纤维化与一系列破坏性的骨骼肌萎缩疾病有关 被称为肌营养不良症。尽管纤维化本身并不是肌肉营养不良的原因，但它是一种 导致骨骼肌顺应性受损的疾病的重大混杂方面， 收缩能力和患者发病率。在营养不良的骨骼肌中，结构蛋白的突变使 肌肉结构不稳定，导致易受损伤、出现坏死、炎症和 修复；其慢性化最终导致纤维化。我们发现有丝分裂原激活蛋白 激酶(MAPK)磷酸酶-5(MKP5)是一种双特异性蛋白酪氨酸磷酸酶 失活p38MAPK和c-jun氨基末端激酶1和2(JNK1/2)，是骨骼的中枢调节因子 肌肉纤维化。MKP5在发生纤维化的小鼠模型中过表达，包括来自 杜兴氏肌营养不良症小鼠及其基因缺失抑制了这种疾病。从机制上讲，MKP5是 对于转化生长因子-β(转化生长因子-β)级联的激活是必不可少的，转化生长因子-转化生长因子是一种主要的促纤维化因子 路径。P38MAPK和JNK的激活参与了肝纤维化的发生。然而，我们的发现 提示在MKP5介导的MAPK去磷酸化和转化生长因子-β之间存在更复杂的相互作用 成纤维细胞和肌肉中的受体激活。MKP5在调节转化生长因子-β信号转导中的作用 因此，这些细胞类型中的纤维化既不是在体内探索的，也不是用药物来评估的。 治疗潜力的有效性。最重要的假设是MKP5作为一个关键分子 纤维性骨骼肌病检查站。在目标1中，我们将定义MKP5的单元格操作类型 通过产生组织特异性的MKP5基因敲除导致骨骼肌纤维化。我们将测试MKP5是否在 在骨骼肌纤维化模型中，肌纤维和/或成纤维细胞有助于疾病的进展。在……里面 目的2，我们将确定MKP5在纤维化中的作用的分子基础，通过定义它是如何参与 介导转化生长因子-β途径的促纤维化作用。在目标3中，我们将确定 使用一种新的一流变构MKP5抑制剂作为抗纤维化治疗的MKP5抑制。总而言之， 这些研究将确定MKP5如何确立其作为调节因子的作用的病理生理学基础 骨骼肌纤维化。这一项目的成功完成将为 认为MKP5是治疗营养不良肌肉疾病纤维化的靶点。

ABSTRACT Fibrosis in skeletal muscle is associated with a collection of devastating skeletal muscle wasting disorders known as the muscular dystrophies. Although fibrosis, per se, is not causal to the muscular dystrophies it is a significant confounding facet of the disease that contributes to impaired skeletal muscle compliance, contractility and patient morbidity. In dystrophic skeletal muscle, mutations in structural proteins render the muscle architecturally unstable resulting in susceptibility to damage, onset of necrosis, inflammation and repair; the chronicity of which culminates in fibrosis. We have discovered that the mitogen-activated protein kinase (MAPK) phosphatase-5 (MKP5), which is a dual-specificity protein tyrosine phosphatase that directly inactivates p38 MAPK and c-Jun NH2 terminal kinases 1 and 2 (JNK1/2), is a central mediator of skeletal muscle fibrosis. MKP5 is overexpressed in mouse models that develop fibrosis, including skeletal muscle from Duchenne's muscular dystrophy mice and its genetic loss curtails the disease. Mechanistically, MKP5 is essential for the activation of the transforming growth factor-β (TGF-β) cascade which is a major pro-fibrogenic pathway. Activation of p38 MAPK and JNK have been implicated in driving fibrosis. However, our findings suggest a more complex interplay exists between MKP5-mediated MAPK dephosphorylation and TGF-β receptor activation in both fibroblasts and muscle. The contribution of MKP5 to regulate TGF-β signaling and thus fibrosis in these cell types has yet to be explored neither in vivo nor exploited pharmacologically to assess validity of therapeutic potential. The overarching hypothesis is that MKP5 acts as a critical molecular checkpoint for fibrotic skeletal muscle disease. In Aim 1, we will define the cell type of action for MKP5 in skeletal muscle fibrosis by generating tissue-specific knockouts of MKP5. We will test whether MKP5 in either the myofiber and/or fibroblast contributes to disease progression in models of fibrosis for skeletal muscle. In Aim 2, we will identify the molecular basis for the actions of MKP5 in fibrosis by defining how it is involved in mediating the pro-fibrogenic actions of the TGF-β pathway. In Aim 3, we will determine the effectiveness of MKP5 inhibition as an anti-fibrotic therapy using a novel first-in-class allosteric MKP5 inhibitor. Collectively, these studies will define the pathophysiological basis for how MKP5 establishes its role as a regulator of skeletal muscle fibrosis. The successful completion of this project will provide proof-of-principle towards the notion that MKP5 represents a target for the treatment of fibrosis in dystrophic muscle diseases.