LPS促进ICA细胞释放儿茶酚胺的分子机制及其在脓毒症心肌损伤中的作用

Cardiac dysfunction is a leading cause of mortality in septic patients, but its mechanism has not been fully understood and no specific therapy exists. It has been demonstrated that cardiac catecholamine is involved in the pathogenesis of sepsis-induced myocardial injury, the intrinsic cardiac adrenergic (ICA) cells synthesize catecholamines, and the released catecholamines from ICA cells can regulate cardiac development and ischemia-induced myocardial injury. However, it is unclear whether catecholamines from ICA cells contribute to sepsis-induced myocardial injury. Our preliminary study observed that lipopolysaccharide (LPS) increased catecholamine synthesis and release in ICA cells, which promoted tumor necrosis factor-alpha (TNF-alpha) production in LPS-challenged cardiomyocytes, but the mechanisms responsible for the increased catecholamine release from ICA cells by LPS needs to be identified. Therefore, the aim of the present study is to investigate the molecular mechanisms for increased catecholamines release from ICA cells by LPS and to identify the role of catecholamines released from ICA cells in sepsis-induced neonatal and adult myocardial injury, via analysis of TLR4 and adrenoceptor-associated signal pathways, myocardial inflammation and energy metabolisms as well as cardiac development, by using cultured ICA cells, neonatal and adult rat cardiomyocytes as well as the neonatal and adult rat models of sepsis-induced myocardial injury. These investigations will further explain the molecular mechanisms for sepsis-triggered myocardial injury, especially for the effect of neonatal sepsis on cardiac development and myocardium, and help to find new therapeutic strategies for the treatment of sepsis cardiomyopathy.

心功能障碍是脓毒症患者死亡的重要原因，但其机制尚未明了，目前缺乏有效治疗措施。业已证明，心脏儿茶酚胺（CA）参与了脓毒症心肌损伤的发生机制；而且，心脏内源性肾上腺素能(ICA)细胞可以释放CA，这种CA调节心脏发育和缺血性心肌损伤。然而，ICA细胞来源的CA在脓毒症心肌损伤中有何作用？尚不清楚。我们发现脂多糖(LPS)能促进ICA细胞释放CA，这种CA可促进LPS刺激的心肌细胞释放TNF-α，但LPS促进ICA细胞释放CA的机制并不清楚。因此，本项目利用培养的ICA细胞、乳鼠和成年鼠心肌细胞以及乳鼠和成年鼠脓毒症心肌损伤模型，从TLR4与肾上腺素能受体信号通路、心肌炎症、能量代谢和心脏发育的角度，探讨LPS促进ICA细胞释放CA的机制及其在脓毒症心肌损伤中的作用，对进一步阐明脓毒症心肌损伤的机制，特别是新生儿脓毒症对心脏发育和心肌的作用机制，以及寻找新的脓毒症心肌病的治疗策略具有重要意义。

心功能障碍是脓毒症患者死亡的重要原因，目前缺乏有效的治疗措施。心脏内源性肾上腺素能(ICA)细胞可以释放儿茶酚胺(CA)。然而，ICA细胞来源的CA 在脓毒症心肌损伤中有何作用？尚不清楚。本项目利用培养的ICA细胞、乳鼠和成年鼠心肌细胞以及乳鼠和成年鼠脓毒症心肌损伤模型，从TLR4与肾上腺素能受体信号通路、心肌炎症、能量代谢和心脏发育的角度，探讨LPS促进ICA 细胞释放CA的机制及其在脓毒症心肌损伤中的作用。研究发现，ICA细胞上表达TLR4，LPS激活TLR4促进ICA细胞酪氨酸羟化酶(TH)与多巴胺-beta-羟化酶(DBH)的表达，增加ICA细胞合成去甲肾上腺素(NE)。LPS通过TLR4-MyD88/TRIF信号通路、激活TH启动子，增加TH基因转录。ICA细胞释放的NE通过持续激活心肌细胞β1-AR，活化CaMKII信号途经，调控心肌细胞TLR4下游信号通路，促进LPS诱导乳鼠心肌细胞产生TNF-α。然而，LPS刺激的ICA细胞并不产生TNF-α。进一步研究发现，LPS处理出生后第1天乳鼠引起心脏NE和炎症细胞因子增多，促进心肌脂质转运，抑制心肌脂肪酸代谢，促进线粒体损伤与分裂，抑制乳鼠心脏发育与成熟，导致成年期心脏心肌收缩与舒张功能障碍。在LPS攻击前给予DBH抑制剂Nepicastat处理可降低乳鼠心脏ICA细胞合成NE，抑制过度升高的NE对心脏炎症反应的促进作用，改善心肌代谢，降低LPS处理乳鼠的死亡率，减轻乳鼠心肌发育与成熟异常，改善LPS攻击的乳鼠成年后心脏收缩与舒张功能。在成体大鼠实验中，证实DBH抑制剂能显著抑制LPS诱导的心脏ICA细胞NE的产生，并减轻LPS诱导的离体大鼠心脏功能障碍。在体实验发现，脓毒症后12 h给予多巴胺-β-羟化酶抑制剂治疗，明显改善脓毒症大鼠生存、减轻脓毒症诱导的大鼠心功能障碍，其机制一方面可能与其降低NE水平、进而降低炎症细胞因子的产生，另一方面与其升高心脏多巴胺的水平，改善心肌细胞代谢，减轻心肌细胞炎症反应和凋亡有关。本研究取得的成果为脓毒症心肌病的治疗提供了新的策略。