Mechanisms of lymphatic valve and pump dysfunction in lymphedema

描述（由申请人提供）：淋巴运输是在静水压力梯度下进行的，因此主要依赖于淋巴肌的固有收缩功能，即“淋巴泵”。这种泵系统的故障与多种形式的淋巴水肿有关，每年在美国有超过1000万人遭受这种疾病的折磨。淋巴水肿患者淋巴管功能失调的原因和机制尚不清楚。临床研究显示淋巴舒张压升高，血管直径增大，收缩幅度严重受损，瓣膜明显功能不全。然而，这些发现是事后的，并没有提供因果关系的洞察力。我们最近开创了定量研究小鼠孤立的单个淋巴管和淋巴管链的淋巴阀和泵功能的方法；因此，在已知或控制所有压力、直径和阀门位置的情况下，当淋巴管在规定的条件下承受增加的压力载荷时，我们可以严格测试泵的功能。此外，我们也可以在淋巴疾病的小鼠模型中做同样的实验。我们的研究结果表明，即使在健康的血管中，也会发生两种类型的泵故障，以响应流入/流出压力的逐渐上升，模拟依赖端对血管的压力负荷。1)泵逐渐减弱，直至不能弹出，输出阀关闭；或者2)输出阀被“锁”开，造成灾难性后果，因为整个输出阀的压力在收缩状态下达到平衡。在缺乏转录因子FOXC2的小鼠中，阀锁加剧，FOXC2控制淋巴阀的发育和维持；它的缺陷再现了人类疾病淋巴水肿。重要的是，这两种情况都可以得到纠正。我们将测试淋巴泵在淋巴水肿发展过程中所经历的静水环境中导致收缩和瓣膜功能障碍的机制，使用健康和foxc2缺陷小鼠，从小鼠腘窝和腹股沟淋巴网络中分离单个或多个淋巴管并进行体外研究；然后，我们将把这些概念应用于腹股沟淋巴网络的体内研究。我们的中心假设是，淋巴泵在施加负荷下的效率取决于三个关键变量的相互作用：淋巴肌肉的机械特性、瓣膜的特性和收缩波的协调；此外，我们提出α-肾上腺素能激动剂可以逆转泵功能障碍。目的：1)确定当健康的淋巴管在流出压力升高的情况下被迫泵送时，阀锁和泵失效的机制；2)确定原发性淋巴水肿Foxc2+/-和诱导型Foxc2-/-模型中淋巴阀和淋巴泵功能障碍的后果；3)确定在健康和foxc2缺陷血管中拯救淋巴泵功能障碍的药理学原理。这种治疗淋巴泵失败的方法代表了一种潜在的新策略，可以治疗多种形式的先天性和后天性淋巴水肿。

DESCRIPTION (provided by applicant): Lymph transport occurs against a hydrostatic pressure gradient and thus relies critically on the intrinsic contractile function of lymphatic muscle, the "lymphatic pump". Failure of this pump system is associated with many forms of lymphedema, afflicting over 10 million people annually in the USA. Little is known about how and why lymphatic vessels become dysfunctional in lymphedema. Clinical studies reveal that lymphatic diastolic pressure is elevated, vessel diameter enlarged, contraction amplitude severely impaired, and the valves apparently incompetent. Yet these findings are post-hoc and do not provide insight into cause or effect. We have recently pioneered methods for quantitative studies of lymphatic valve and pump function in isolated single lymphangions and chains of lymphangions in the mouse; thus we can rigorously test pump function when a lymphangion is subjected under defined conditions to increased pressure loads where all pressures, diameters and valve positions are known or controlled. Additionally, we can do this in mouse models of lymphatic disease. Our results reveal that two types of pump failure occur, even in healthy vessels, in response to a progressive rise in inflow / outflow pressure, simulating the pressure load on the vessel in a dependent extremity. 1) The pump either gradually weakens until it cannot eject, leaving the output valve closed; or 2) the output valve "locks" open, with catastrophic consequences, as pressure across it equilibrates in systole. Valve lock is exacerbated in mice deficient in the transcription factor FOXC2, which controls the development and maintenance of lymphatic valves; its deficiency recapitulates the human disease lymphedema distichiasis. Importantly, both conditions can be corrected. We will test the mechanisms leading to contractile and valve dysfunction in the hydrostatic environment experienced by the lymph pump during the development of lymphedema, utilizing both healthy and Foxc2-deficient mice Single or multiple lymphangions will be isolated from murine popliteal and inguinal lymphatic networks and studied in vitro; we will then apply the concepts to the study of inguinal lymphatic networks in vivo. Our central hypothesis is that the efficiency of the lymphatic pump under an imposed load depends on the interaction of three key variables: the mechanical properties of lymphatic muscle, the properties of the valves, and the coordination of the contraction wave; further, we propose that pump dysfunction can be reversed by α-adrenergic agonists. Aims: 1) Determine the mechanisms underlying valve lock and pump failure when healthy lymphangions are forced to pump against elevated outflow pressure; 2) Determine the consequences of lymphatic valve and pump dysfunction in Foxc2+/- and inducible Foxc2-/- models of primary lymphedema; 3) Determine the principles by which lymph pump dysfunction can be rescued pharmacologically in healthy and Foxc2-deficient vessels. This approach to treating a failed lymph pump represents a potential new strategy for treating a common underlying contributor to many forms of both congenital and acquired lymphedema.