Endothelial dependent mechanisms of lymphatic dysfunction in metabolic syndrome and type-2 diabetes associated with obesity

项目摘要/摘要 肥胖和2型糖尿病都被认为是导致多发性硬化的主要危险因素 全球的心血管疾病。仅在美国，就有大约36%的成年人口肥胖，年龄超过25岁 数以百万计的人患有糖尿病。重要的是，2型糖尿病的流行已经被证明是戏剧性的 随着肥胖的增加而增加。令人惊讶的是，虽然肥胖症和淋巴功能障碍的迹象已经报道 糖尿病，淋巴功能障碍的机制尚不清楚。高效的淋巴运输依赖于 对淋巴肌肉细胞(LMC)固有的自发收缩的批判。这些宫缩是 由起搏部位产生的动作电位引发，然后在强烈的 耦合的LMC。与小动脉不同，淋巴管内皮细胞(LECs)和LMCs之间的电偶联 通过MEJ(肌内皮细胞连接)似乎相当有限；虽然这可能是焦点 产生起搏信号，防止去极化电流泄漏进入内皮，这个想法还没有 被调查过了。因此，淋巴管中是否有传导信号是完全未知的 可以调节LMC收缩的内皮细胞以及LECs和LECs之间的异质细胞串扰到什么程度 LMCs在淋巴功能中起一定作用。为这一提议获得的初步数据表明：1)信号 可以作为钙波在淋巴管内皮细胞中传导，这些波可以调节收缩 2)肥胖小鼠离体淋巴管的自发收缩功能受损(即 降低射血分数)；3)调节血管形成的丝氨酸蛋白酶抑制剂PAI-1 MEJs是代谢综合征、糖尿病和肥胖症的重要生物标志物，在淋巴管中表达上调 肥胖小鼠的血管与健康对照小鼠的血管比较；4)PAI-1的基因过表达 (tgPAI-1)在非肥胖小鼠中导致淋巴管收缩功能受损，而年龄-血管- 匹配的PAI-1 KO小鼠(PAI-1-/-)表现出改善的淋巴功能。这些结果表明新的内皮细胞- 调节淋巴管收缩的相关机制，将肥胖与淋巴管联系起来 收缩功能障碍，指出了PAI-1在调节淋巴功能中的一个新的关键作用，并提示其 作为治疗靶点的潜在用途，以改善与肥胖相关的淋巴功能障碍。因此， 要检验的假设是：a)淋巴管内皮细胞中的传导信号可以调节LMC的收缩能力 通过MEJ的直接LEC-LMC偶联和/或释放的因子的扩散；b)增加PAI- 1导致异常的细胞相互作用，上调MEJ的形成；c)PAI-1上调相关 肥胖通过内皮依赖机制导致淋巴功能受损；以及，d)PAI-1 抑制可以改善肥胖者的淋巴功能。这里提出的研究和结果将会扩大 我们对代谢淋巴功能障碍病理生理机制的认识 与肥胖相关的综合症和糖尿病。

PROJECT SUMMARY/ABSTRACT Obesity and type-2 diabetes are both considered major risk factors for the development of multiple cardiovascular diseases worldwide. In the US alone, about 36% of the adult population are obese and over 25 million suffer from diabetes. Importantly, the prevalence of type-2 diabetes has been shown to dramatically increase with obesity. Surprisingly, while signs of lymphatic dysfunction have been reported in obesity and diabetes, the mechanisms underlying lymphatic dysfunction are unknown. Efficient lymph transport relies critically on the intrinsic spontaneous contractions of lymphatic muscle cells (LMCs). These contractions are initiated by action potentials that originate at a pacemaking site and then rapidly propagate between the strongly- coupled LMCs. In contrast to arterioles, electrical coupling between lymphatic endothelial cells (LECs) and LMCs through MEJs (myoendothelial junctions) appears to be quite limited; while this may be essential for the focal generation of pacemaking signals, preventing leak of depolarizing current into the endothelium, the idea has not been investigated. Thus, it is completely unknown whether there are any conducted signals in the lymphatic endothelium that can regulate LMC contractility and to what extent heterocellular cross-talk between LECs and LMCs plays a role in lymphatic function. The preliminary data obtained for this proposal show that: 1) signals can be conducted as Ca2+ waves in the lymphatic endothelium, and these waves can regulate the contractile function of LMCs; 2) in obese mice, the spontaneous contractions of isolated lymphatic vessels are impaired (i.e. decreased ejection fraction); 3) the serine protease inhibitor PAI-1, which regulates the formation of vascular MEJs, is an important biomarker for metabolic syndrome, diabetes, and obesity and is upregulated in lymphatic vessels from obese mice compared to those from control healthy mice; and 4) genetic overexpression of PAI-1 (tgPAI-1) in non-obese mice results in lymphatic vessels with impaired contractility, while vessels from age- matched PAI-1 KO mice (PAI-1-/-) show improved lymphatic function. These results suggest novel endothelium- dependent mechanisms through which lymphatic contractions can be regulated, associate obesity with lymphatic contractile dysfunction, point to a novel, critical role for PAI-1 in regulating lymphatic function, and suggest its potential use as therapeutic target to ameliorate lymphatic dysfunction associated with obesity. Therefore, the hypotheses to be tested are: a) Conducted signals in the lymphatic endothelium can regulate LMC contractility through either direct LEC-LMC coupling via MEJs and/or diffusion of released factors; b) increased levels of PAI- 1 result in abnormal cellular interactions, upregulating the formation of MEJs; c) PAI-1 upregulation associated with obesity results in impaired lymphatic function through endothelium-dependent mechanisms; and, d) PAI-1 inhibition can ameliorate lymphatic function in obesity. The studies here proposed and their outcome will expand our understanding on the pathophysiological mechanisms leading to lymphatic dysfunction in metabolic syndrome and diabetes associated with obesity.