Deletion of the Cardiomyocyte Glucocorticoid Receptor Leads to Sexually Dimorphic Changes in Cardiac Gene Expression and Progression to Heart Failure

Background The contribution of glucocorticoids to sexual dimorphism in the heart is essentially unknown. Therefore, we sought to determine the sexually dimorphic actions of glucocorticoid signaling in cardiac function and gene expression. To accomplish this goal, we conducted studies on mice lacking glucocorticoid receptors (GR) in cardiomyocytes (cardioGRKO mouse model). Methods and Results Deletion of cardiomyocyte GR leads to an increase in mortality because of the development of spontaneous cardiac pathology in both male and female mice; however, females are more resistant to GR signaling inactivation in the heart. Male cardioGRKO mice had a median survival age of 6 months. In contrast, females had a median survival age of 10 months. Transthoracic echocardiography data showed phenotypic differences between male and female cardioGRKO hearts. By 3 months of age, male cardioGRKO mice exhibited left ventricular systolic dysfunction. Conversely, no significant functional deficits were observed in female cardioGRKO mice at the same time point. Functional sensitivity of male hearts to the loss of cardiomyocyte GR was reversed following gonadectomy. RNA-Seq analysis showed that deleting GR in the male hearts leads to a more profound dysregulation in the expression of genes implicated in heart rate regulation (calcium handling). In agreement with these gene expression data, cardiomyocytes isolated from male cardioGRKO hearts displayed altered intracellular calcium responses. In contrast, female GR-deficient cardiomyocytes presented a response comparable with controls. Conclusions These data suggest that GR regulates calcium responses in a sex-biased manner, leading to sexually distinct responses to stress in male and female mice hearts, which may contribute to sex differences in heart disease, including the development of ventricular arrhythmias that contribute to heart failure and sudden death. Examination of transcriptome under two different conditions (Normal GR levels in cardiomyocytes vs. no GR expression in cardiomyocytes)背景 糖皮质激素对心脏性别二态性的调控贡献目前尚不完全明确。为此，本研究旨在阐明糖皮质激素信号通路在心脏功能与基因表达层面发挥的性别二态性调控作用。为达成该研究目标，我们针对心肌细胞特异性敲除糖皮质激素受体（glucocorticoid receptor, GR）的小鼠（cardioGRKO小鼠模型）开展了相关实验。 方法与结果 心肌细胞GR敲除会导致雌雄小鼠均出现自发性心脏病理改变，进而提升死亡率；但雌性小鼠对心脏GR信号通路失活的耐受性更强。雄性cardioGRKO小鼠的中位存活年龄为6个月，与之相比，雌性小鼠的中位存活年龄可达10个月。经胸超声心动图检测结果显示，雌雄cardioGRKO小鼠的心脏表型存在显著差异。至3月龄时，雄性cardioGRKO小鼠已出现左心室收缩功能障碍；而在相同时间点的雌性cardioGRKO小鼠中，未观察到显著的功能缺损。雄性小鼠心脏对心肌细胞GR缺失的功能敏感性可通过性腺切除术逆转。RNA测序（RNA-Seq）分析结果表明，雄性小鼠心脏中GR缺失会引发与心率调控（钙离子处理）相关基因的表达出现更为显著的失调。与该基因表达数据相符的是，从雄性cardioGRKO小鼠心脏分离得到的心肌细胞，其细胞内钙离子应答发生了改变；与之相反，雌性GR缺陷型心肌细胞的应答情况与对照组小鼠无显著差异。 结论 上述数据表明，GR以性别偏向性的方式调控钙离子应答，致使雌雄小鼠心脏对应激刺激产生截然不同的应答反应，这或许是心脏疾病存在性别差异的诱因之一，其中包括可引发心力衰竭与猝死的室性心律失常的发生发展。本研究同时对两种实验条件下的心肌细胞转录组进行了检测：心肌细胞正常GR表达水平组与心肌细胞GR完全缺失组。