Molecular Mechanism of type 2 diabetes mellitus-mediated heart failure with preserved ejection fraction

Type 2 diabetes mellitus (T2DM) is a metabolic disease associated with several comorbidities, including cardiac dysfunction leading to heart failure with preserved ejection fraction (HFpEF), in turn resulting in T2DM-induced cardiomyopathy (T2DM-CM). However, the molecular mechanisms underlying the development of T2DM-CM are poorly understood. It is hypothesized that molecular alterations in myopathic genes induced by diabetes promote the development of HFpEF, whereas cardiac myosin inhibitors can rescue the resultant T2DM-induced cardiomyopathy. To test this hypothesis, a Leptin receptor-deficient db/db homozygous (Lepr db/db) mouse model was used to define the pathogenesis of T2DM-CM. Echocardiographic studies at 4 and 6 months revealed that Lepr db/db hearts started developing cardiac dysfunction by four months, and left ventricular hypertrophy with diastolic dysfunction was evident at 6 months. Strikingly, the level of cardiac myosin binding protein-C phosphorylation was significantly increased in Lepr db/db mouse hearts. RNA-seq data analysis, followed by functional enrichment, revealed the differential regulation of genes related to cardiac dysfunction in Lepr db/db heart tissues. Finally, using isolated skinned papillary muscles and freshly isolated cardiomyocytes, CAMZYOS (mavacamten, which is a prescription heart medicine used for symptomatic obstructive hypertrophic cardiomyopathy treatment (herein after denotes as MYK-461), was tested for its ability to rescue T2DM-CM. Compared with controls, MYK-461 significantly reduced force generation in papillary muscle fibers and cardiomyocyte contractility in the db/db group. This line of evidence shows that 1) T2DM-CM is associated with hyperphosphorylation of cardiac myosin binding protein-C and 2) MYK-461 significantly lessened disease progression, suggesting its promise as a therapeutic treatment for HFpEF. To investigate the molecular mechanism underlying the development of T2DM CM, 6 months old leptin receptor deficient db/db homozygous mouse models were employed to understand the development of diabetic cardiomyopathy using in vivo echocardiographic features, phosphorylation status of Mybpc3 and high throughput RNA sequencing of cardiac tissues.2型糖尿病（Type 2 diabetes mellitus, T2DM）是一种伴随多种合并症的代谢性疾病，其中包括可引发射血分数保留型心力衰竭（heart failure with preserved ejection fraction, HFpEF）的心脏功能障碍，进而导致2型糖尿病相关心肌病（T2DM-induced cardiomyopathy, T2DM-CM）。然而，T2DM-CM发生发展的分子机制仍尚不明确。现有假说认为，糖尿病诱导的肌病相关基因分子改变可促进HFpEF的发生，而心肌肌球蛋白抑制剂可逆转由此引发的2型糖尿病相关心肌病。为验证该假说，本研究采用瘦素受体缺陷纯合db/db（Lepr db/db）小鼠模型以阐明T2DM-CM的发病机制。分别于造模后4个月和6个月开展超声心动图检测，结果显示Lepr db/db小鼠心脏于4个月时即出现心脏功能障碍，6个月时可观察到明确的左心室肥厚伴舒张功能障碍。值得注意的是，Lepr db/db小鼠心脏组织中心肌肌球蛋白结合蛋白-C的磷酸化水平显著升高。通过RNA测序（RNA-seq）数据分析结合功能富集分析，发现Lepr db/db小鼠心脏组织中与心脏功能障碍相关的基因存在差异表达调控。最后，本研究通过通透化离体乳头肌与新鲜分离的心肌细胞两种模型，测试了CAMZYOS（mavacamten，一种用于治疗症状性梗阻性肥厚型心肌病的处方心脏药物，下文简称MYK-461）逆转T2DM-CM的效果。与对照组相比，MYK-461可显著降低db/db小鼠乳头肌纤维的肌力产生能力与心肌细胞的收缩功能。本研究的证据表明：1）T2DM-CM与心肌肌球蛋白结合蛋白-C的过度磷酸化密切相关；2）MYK-461可显著延缓疾病进展，提示其有望成为HFpEF的治疗药物。为进一步探究T2DM-CM发生发展的分子机制，本研究选用6月龄瘦素受体缺陷纯合db/db小鼠模型，通过在体超声心动图特征、Mybpc3磷酸化状态检测以及心脏组织高通量RNA测序，解析糖尿病心肌病的发生发展过程。