Failure to resolve inflammation contributes to juvenile onset cardiac damage in a mouse model of Duchenne Muscular Dystrophy

Absence of dystrophin protein causes cardiac dysfunction in patients with Duchenne muscular dystrophy (DMD). Unlike boys with DMD, the common mouse model of DMD (B10-mdx) does not manifest cardiac deficits until late adulthood. This has limited our understanding of the mechanism and therapeutic approaches to target the pediatric onset of cardiac pathology in DMD. Here we show that the mdx mouse model on the DBA/2J genetic background (D2-mdx) displays juvenile-onset cardiac degeneration. Molecular and histological analysis revealed that cardiac damage in this model is linked to increased leukocyte chemotactic signaling and an inability to resolve inflammation. These deficiencies result in chronic inflammation and fibrotic conversion of the extracellular matrix (ECM) in the juvenile D2-mdx heart. To address these pathologies, we tested the utility of pro-resolution therapy to clear chronic cardiac inflammation. Use of an N-formyl peptide receptor (FPR) agonist helped physiologically resolve inflammation and mitigate the downstream events that lead to fibrotic degeneration of cardiomyocytes, preventing juvenile onset cardiac muscle loss. These results establish the utility of D2-mdx model to study events associated with pediatric-onset cardiac damage and demonstrates pro-resolution therapy as an alternate to anti-inflammatory therapy for treating degenerative cardiac pathology that leads to cardiomyopathy in DMD. Overall design: To investigate the transcriptional landscape of the DMD disease condition in cardiac muscle, a bulk RNASeq analysis was performed using RNA extracted from 4 DMD (D2md-x) and 3 Wild type (B10-mdx) age matched 6 week old male mouse heart.

杜氏肌营养不良症（Duchenne muscular dystrophy, DMD）患者体内抗肌萎缩蛋白（dystrophin）的缺失会引发心功能异常。与DMD男性患儿不同，常用DMD小鼠模型B10-mdx直至成年晚期才会出现心脏功能缺陷，这一局限制约了我们对DMD儿童期心脏病变的发病机制与靶向治疗策略的认知。本研究发现，搭载DBA/2J遗传背景的mdx小鼠模型（D2-mdx）可表现出青少年起病的心脏退行性病变。分子与组织学分析显示，该模型的心脏损伤与白细胞趋化信号通路激活及炎症消退障碍密切相关，此类缺陷会导致幼年D2-mdx小鼠心脏出现慢性炎症与细胞外基质（extracellular matrix, ECM）纤维化重塑。为干预上述病理进程，我们评估了促消退疗法（pro-resolution therapy）清除慢性心脏炎症的应用潜力。实验结果表明，N-甲酰肽受体（N-formyl peptide receptor, FPR）激动剂可通过生理性途径消退炎症，缓解介导心肌细胞纤维化退行性变的下游事件，从而阻止青少年期心肌丢失。本研究证实，D2-mdx模型可用于研究儿童期心脏损伤相关的病理事件，并证明促消退疗法可作为抗炎疗法的替代方案，用于治疗DMD中引发心肌病的退行性心脏病变。整体实验设计：为探究DMD疾病状态下心肌的转录组特征，我们对4只DMD（D2-mdx）与3只同周龄6周龄雄性野生型（B10-mdx）小鼠的心脏提取总RNA，开展批量RNA测序（bulk RNASeq）分析。