Eicosapentaenoic acid activation of free fatty acid receptor 4 prevents fibrosis, microvascular rarefaction, and diastolic dysfunction; implications for heart failure preserved ejection fraction

所有心力衰竭（HF）诊断中超过一半是射血分数保留的HF（HFpEF），这是一种复杂的 定义为HF症状但左心室EF“正常”的综合征。HFpEF的特征是舒张压 功能障碍、充盈受损、肥大和利钠肽升高。目前还没有治疗方法 提高HFpEF患者的生存率。HFpEF的病理性重塑包括间质纤维化和 微血管稀疏，导致舒张期僵硬、心室充盈受损和运动 不容忍纤维化是由于成纤维细胞的活化导致细胞外基质产生增加， 成纤维细胞增殖和成纤维细胞向肌成纤维细胞转化。微血管稀疏与 炎症和内皮细胞死亡，导致氧输送受损，降低收缩压和 舒张期储备和加重运动不耐受。我们发现ω3-多不饱和脂肪酸（ω3- PUFA）抑制肌成纤维细胞转化，防止间质纤维化和舒张功能障碍， 部分类似于HFpEF（主动脉横缩窄，TAC）的小鼠模型。此外，我们发现， 二十碳五烯酸（EPA）的血液水平与间质纤维化的预防相关，但EPA不是 在体内被并入成纤维细胞膜，这是一种传统的作用机制。相反，我们发现， 脂肪酸受体4（FFAR 4），一种长链脂肪酸的G蛋白偶联受体，是足够的， 需要防止心肌成纤维细胞转化。其他研究小组报告说，ω3-PUFAs 诱导后肢缺血中血管生成，EPA激活FFAR 4以诱导VEGF-A表达。因此，在本发明中， EPA可能通过预防纤维化和微血管稀疏对HFpEF具有双重益处。在人类中，ω3- PUFA可减少冠心病猝死，但疗效问题仍然存在。然而，未能 达到足够的ω3-PUFA水平或治疗指数，可能解释了先前的阴性结果。因此我们 假设EPA（治疗水平）足够膳食摄取和FFAR 4的活化预防纤维化， HFpEF的微血管稀疏和舒张功能障碍。为了测试这一点，我们将：1）确定红细胞是否 EPA浓度（EPA指数）与预防纤维化、微血管稀疏和舒张功能相关。 TAC后功能障碍。我们还将用一种新的FFAR 4配体cpdA靶向FFAR 4，作为一种潜在的免疫调节剂。 治疗方法，以逆转TAC后的重塑。2)确定高血浆水平的EPA是否能预防 使用来自多项研究的数据， 动脉粥样硬化试验的种族研究（梅萨）。3)使用成纤维细胞特异性FFAR 4敲除小鼠来确定 FFAR 4是EPA介导的预防纤维化、微血管稀疏和舒张功能障碍所必需的 跟踪TAC。其影响将是：1）确定EPA的新的心脏保护功能，2）定义一个 EPA介导的心脏保护的治疗指数，3）为EPA/EPA的临床功效提供证据。 FFAR 4预防HFpEF，和4）描述EPA的新作用机制，FFAR 4的激活。

Over half of all heart failure (HF) diagnoses are HF with preserved ejection fraction (HFpEF), a complex syndrome defined by symptoms of HF but a `normal' left ventricular EF. HFpEF is characterized by diastolic dysfunction, impaired filling, hypertrophy, and elevated natriuretic peptides. Presently, there are no treatments that improve survival in patients with HFpEF. Pathologic remodeling in HFpEF includes interstitial fibrosis and microvascular rarefaction, which contribute to diastolic stiffness, impaired ventricular filling, and exercise intolerance. Fibrosis results from activation of fibroblasts leading to increased extracellular matrix production, fibroblast proliferation, and fibroblast-to-myofibroblast transformation. Microvascular rarefaction is associated with inflammation and endothelial cell death, leading to impaired oxygen delivery, reducing systolic and diastolic reserve, and exacerbating exercise intolerance. We found that ω3-polyunsaturated fatty acids (ω3- PUFA) inhibited myofibroblast transformation and prevented interstitial fibrosis and diastolic dysfunction in a mouse model that partially resembles HFpEF (transverse aortic constriction, TAC). Further, we found that blood levels of eicosapentaenoic acid (EPA) correlated with prevention of interstitial fibrosis, but EPA was not incorporated into fibroblast membranes in vivo, a traditional mechanism of action. Rather, we found that free fatty acid receptor 4 (FFAR4), a G-protein coupled receptor for long-chain fatty acids, was sufficient and required to prevent myofibroblast transformation in cardiac fibroblasts. Other groups reported that ω3-PUFAs induce angiogenesis in hind-limb ischemia, and EPA activates FFAR4 to induce VEGF-A expression. Thus, EPA might have a dual benefit in HFpEF by preventing fibrosis and microvascular rarefaction. In humans, ω3- PUFAs reduce sudden death in coronary heart disease, but questions of efficacy remain. However, failure to achieve adequate ω3-PUFA levels, or a therapeutic index, likely explains prior negative results. Thus, we hypothesize that sufficient dietary uptake of EPA (therapeutic level) and activation of FFAR4 prevents fibrosis, microvascular rarefaction, and diastolic dysfunction in HFpEF. To test this we will: 1) Determine if erythrocyte EPA concentration (EPA-index) correlates with prevention of fibrosis, microvascular rarefaction, and diastolic dysfunction following TAC. We will also target FFAR4 with cpdA, a novel FFAR4 ligand, as a potential therapeutic approach to reverse remodeling following TAC. 2) Determine if high plasma levels of EPA prevent progression of left ventricular hypertrophy and fibrosis as well as HFpEF in humans using data from the Multi- Ethnic Study of Atherosclerosis trial (MESA). 3) Use fibroblast-specific FFAR4 knockout mice to determine if FFAR4 is required for EPA mediated prevention of fibrosis, microvascular rarefaction, and diastolic dysfunction following TAC. The impact will be to: 1) Identify novel cardioprotective functions of EPA, 2) Define a therapeutic index for EPA-mediated cardioprotection, 3) Provide evidence for the clinical efficacy of EPA/ FFAR4 to prevent HFpEF, and 4) Delineate a novel mechanism of action for EPA, activation of FFAR4.