Inhibition of GSK3 beta as potential therapy for DM1

强直性肌营养不良症1型(DM1)是一种以骨骼肌为特征的复杂神经肌肉疾病 消瘦、虚弱、肌强直和胰岛素抵抗。DM1是由扩展的RNA CUG重复引起的 通过RNA结合蛋白CUGBP1和MBNL1错误调节RNA动态平衡。治疗方法 对于DM1降低毒性的突变CUG重复序列正在积极开发；然而，仍然没有治愈 DM1。在这里，我们建议检验一种假设，即糖原合成酶的遗传抑制 激酶3b(GSK3b)改善DM1小鼠模型的骨骼肌病理。我们发现， 突变的CUG重复序列增加了骨骼肌活检组织中的酶活性和GSK3b的水平 患者的DM1和骨骼肌中的DM1小鼠模型、HSALR小鼠。我们展示了 用已知的GSK3b抑制剂锂(Li)或有效的GSK3b抑制剂治疗HSALR小鼠， TDZD-8，减少内核纤维数量，增加握力，减少肌强直。是这样的 HSALR小鼠肌肉病理的改善伴随着GSK3b活性的正常化 并通过校正GSK3b底物之一细胞周期蛋白D3的表达。细胞周期蛋白D3的校正 抑制GSK3b导致CUGBP1抑制形式减少，从而导致骨骼肌 萎缩和虚弱。由于这些GSK3抑制剂同时降低了GSK3b和GSK3a，因此本研究的特定目标1 一项提案将研究HSALR小鼠GSK3b基因的减少是否会导致DM1的减少 肌肉病理学。为了实现GSK3b的遗传减少，肌肉特异性GSK3b基因敲除(SbKO) 小鼠与HSALR小鼠杂交，产生HSALR/SbKO小鼠。大鼠肌肉组织病理学的改善 HSALR/SbKO小鼠将为开发治疗DM1患者的方法提供背景，该方法将是 基于GSK3的抑制剂。由于LI被FDA批准用于治疗情绪疾病，因为 GSK3b的抑制剂被用于其他疾病的临床前研究，这些抑制剂的应用 可能会加速使用GSK3b抑制剂的DM1治疗的发展。DM1中GSK3b的增加 肌肉提示，GSK3b的其他底物在DM1中也可能发生改变。患有DM1的患者有 2型糖尿病的易感性(T2D)。已知，患者骨骼肌中GSK3b含量增加 使用T2D。T2D中GSK3b的增加导致糖原合成酶活性降低，从而导致 糖原合成减少，糖代谢改变。我们假设 HSALR小鼠骨骼肌中GSK3b的增加导致葡萄糖和胰岛素不敏感 T2D的易感性。这一假设将在目标2中得到检验。总而言之，我们的研究将表明， GSK3b基因抑制可能改善小鼠肌肉病理，增强胰岛素和葡萄糖敏感性 DM1小鼠模型。在DM1小鼠模型中获得的知识将转化为临床治疗 是DM1的。

Myotonic Dystrophy type 1 (DM1) is a complex neuromuscular disease characterized by skeletal muscle wasting, weakness, myotonia and insulin resistance. DM1 is caused by the expanded RNA CUG repeats that misregulate RNA homeostasis through RNA-binding proteins, CUGBP1 and MBNL1. Therapeutic approaches for DM1 reducing toxicity of the mutant CUG repeats are actively developing; however, there is still no cure for DM1. Here we propose to examine the hypothesis that the genetic inhibition of Glycogen Synthase kinase 3b (GSK3b) improves skeletal muscle pathology in the DM1 mouse model. We found that the mutant CUG repeats increase enzymatic activity and the levels of GSK3b in skeletal muscle biopsies from patients with DM1 and in skeletal muscle of the DM1 mouse model, HSALR mice. We showed that the treatments of HSALR mice with lithium (Li), a known inhibitor of GSK3b, or with the potent inhibitor of GSK3b, TDZD-8, reduce the number of fibers with internal nuclei, increase grip strength and reduce myotonia. Such improvement of muscle pathology in the HSALR mice was accompanied by the normalization of GSK3b activity and by correction of expression of one of the GSK3b substrates, cyclin D3. The correction of cyclin D3 by the inhibition of GSK3b leads to the reduction of the suppressive form of CUGBP1, which causes skeletal muscle atrophy and weakness. Since these GSK3 inhibitors reduce both GSK3b and GSK3a, Specific Aim 1 of this proposal will examine if a genetic reduction of GSK3b in HSALR mice will lead to the reduction of DM1 muscle pathology. To achieve the genetic reduction of GSK3b, muscle specific GSK3b knock out (SbKO) mice are crossed with HSALR mice, producing HSALR/SbKO mice. Improvement of muscle pathology in HSALR/SbKO mice will provide a background for the development of therapy for DM1 patients which will be based on the inhibitors of GSK3. Since Li is approved by FDA to treat mood diseases and because potent inhibitors of GSK3b are used in the pre-clinical studies for other diseases, the application of these inhibitors might accelerate the development of DM1 therapy using GSK3b inhibitors. The increase of GSK3b in DM1 muscle suggests that other substrates of GSK3b might be also altered in DM1. Patients with DM1 have a predisposition to Type 2 Diabetes (T2D). It is known, that GSK3b is increased in skeletal muscle of patients with T2D. The increase of GSK3b in T2D causes a reduction of the activity of glycogen synthase that leads to the reduction of the glycogen synthesis and alteration of glucose metabolism. We hypothesize that the increase of GSK3b in skeletal muscle of HSALR mice causes glucose and insulin insensitivity and predisposition to T2D. This hypothesis will be tested in the Aim 2. In summary, our study will show if the genetic inhibition of GSK3b might improve muscle pathology and enhance insulin and glucose sensitivity in the DM1 mouse model. The knowledge, obtained in mouse model of DM1, will be translated to the clinical therapy of DM1.