Inhibition of GSK3 beta as potential therapy for DM1

描述（由申请人提供）：1型肌强直营养不良症（DM1）是一种复杂的神经肌肉疾病，其特征是骨骼肌萎缩、无力、肌强直和胰岛素抵抗。DM1是由扩大的RNA CUG重复序列引起的，这些重复序列通过RNA结合蛋白CUGBP1和MBNL1错误地调节RNA稳态。DM1降低突变CUG重复序列毒性的治疗方法正在积极发展；然而，目前仍没有治愈DM1的方法。在这里，我们提出检验糖原合成酶激酶3？（GSK3?）改善DM1小鼠模型骨骼肌病理。我们发现突变的CUG重复序列增加了酶活性和GSK3？DM1患者的骨骼肌活检和DM1小鼠模型的骨骼肌，HSALR小鼠。我们发现，锂（Li）是一种已知的GSK3？或与强效GSK3抑制剂？TDZD-8，减少内核纤维数量，增加握力，减轻肌强直。这种HSALR小鼠肌肉病理的改善伴随着GSK3？通过纠正其中一个GSK3？底物，细胞周期蛋白D3。抑制GSK3对细胞周期蛋白D3的修正导致CUGBP1的抑制性形式减少，导致骨骼肌萎缩和无力。因为这些GSK3抑制剂降低了GSK3？GSK3 ?，本提案的具体目标1将检查GSK3基因的基因减少是否存在？会导致DM1肌肉病理的减少。实现GSK3的基因还原？？肌肉特异性GSK3？击倒；击倒；将KO)小鼠与HSALR小鼠杂交，产生HSALR/S？KO小鼠。HSALR/S患者肌肉病理的改善？KO小鼠将为开发基于GSK3抑制剂的DM1患者治疗提供背景。既然Li被FDA批准用于治疗情绪疾病又因为GSK3的有效抑制剂？在其他疾病的临床前研究中，这些抑制剂的应用可能会加速使用GSK3抑制剂治疗DM1的发展。GSK3？表明GSK3？也可能在DM1中发生改变。DM1患者易患2型糖尿病（T2D）。众所周知，GSK3？在t2dm患者的骨骼肌中增高。GSK3？在T2D中引起糖原合成酶活性降低，导致糖原合成减少和葡萄糖代谢改变。我们假设GSK3？HSALR小鼠骨骼肌中葡萄糖和胰岛素不敏感，易患T2D。这一假设将在Aim 2中进行检验。综上所述，我们的研究将表明GSK3？可能改善DM1小鼠模型的肌肉病理，增强胰岛素和葡萄糖敏感性。在DM1小鼠模型中获得的知识将转化为DM1的临床治疗。

DESCRIPTION (provided by applicant): 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 3? (GSK3?) improves skeletal muscle pathology in the DM1 mouse model. We found that the mutant CUG repeats increase enzymatic activity and the levels of GSK3? 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 GSK3?, or with the potent inhibitor of GSK3?, 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 GSK3? activity and by correction of expression of one of the GSK3? substrates, cyclin D3. The correction of cyclin D3 by the inhibition of GSK3??leads to the reduction of the suppressive form of CUGBP1, which causes skeletal muscle atrophy and weakness. Since these GSK3 inhibitors reduce both GSK3? and GSK3?, Specific Aim 1 of this proposal will examine if a genetic reduction of GSK3? in HSALR mice will lead to the reduction of DM1 muscle pathology. To achieve the genetic reduction of GSK3??? muscle specific GSK3? knock out (S?KO) mice are crossed with HSALR mice, producing HSALR/S?KO mice. Improvement of muscle pathology in HSALR/S?KO 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 GSK3? are used in the pre-clinical studies for other diseases, the application of these inhibitors might accelerate the development of DM1 therapy using GSK3??inhibitors. The increase of GSK3? in DM1 muscle suggests that other substrates of GSK3? might be also altered in DM1. Patients with DM1 have a predisposition to Type 2 Diabetes (T2D). It is known, that GSK3? is increased in skeletal muscle of patients with T2D. The increase of GSK3? 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 GSK3? 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 GSK3? 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.