Dual-specificity phosphatase action in muscle disease

摘要 骨骼肌纤维化与一系列破坏性骨骼肌消耗性疾病有关 被称为肌肉萎缩症。虽然纤维化本身不是肌营养不良症的原因，但它是一种慢性病。 导致骨骼肌顺应性受损的疾病的显著混杂方面， 收缩性和患者发病率。在营养不良的骨骼肌中，结构蛋白的突变使骨骼肌中的蛋白质发生突变。 肌肉结构不稳定，导致对损伤、坏死、炎症和 修复;慢性化最终导致纤维化。我们发现丝裂原活化蛋白 激酶（MAPK）磷酸酶-5（MKP 5），其是一种双特异性蛋白酪氨酸磷酸酶，直接 失活p38 MAPK和c-Jun NH 2末端激酶1和2（JNK 1/2），是骨骼肌细胞凋亡的中心介质， 肌肉纤维化MKP 5在发生纤维化的小鼠模型中过表达，包括骨骼肌， 杜氏肌营养不良症小鼠及其基因缺失可以减少这种疾病。从机械上讲，MKP 5是 对于转化生长因子-β（TGF-β）级联的活化是必需的，所述级联是主要的促纤维化因子， 通路p38 MAPK和JNK的激活与驱动纤维化有关。然而，我们的发现 提示MKP 5介导MAPK去磷酸化和TGF-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活化。MKP 5在调节TGF-β信号转导中的作用及 因此，这些细胞类型中的纤维化尚未在体内探索，也未在体外开发以评估 治疗潜力的有效性。总体假设是MKP 5作为一种关键分子， 纤维化骨骼肌疾病的检查点。在目标1中，我们将定义MKP 5作用的细胞类型， 通过产生MKP 5的组织特异性敲除来治疗骨骼肌纤维化。我们将测试MKP 5是否在 肌纤维和/或成纤维细胞有助于骨骼肌纤维化模型中的疾病进展。在 目的2，我们将通过定义MKP 5如何参与纤维化， 介导TGF-β途径的促纤维化作用。在目标3中，我们将确定 MKP 5抑制作为一种抗纤维化疗法，使用新型的一流变构MKP 5抑制剂。总的来说， 这些研究将确定MKP 5如何确立其作为调节剂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 MKP 5代表用于治疗营养不良性肌肉疾病中的纤维化的靶点的观点。

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.