Mechanisms of lymphatic valve and pump dysfunction in lymphedema

描述（由申请人提供）：淋巴运输逆着静水压力梯度发生，因此关键依赖于淋巴肌的内在收缩功能，即“淋巴泵”。该泵系统的故障与多种形式的淋巴水肿有关，在美国每年有超过 1000 万人受其困扰。关于淋巴水肿中淋巴管如何以及为何变得功能障碍，人们知之甚少。临床研究表明，淋巴管舒张压升高，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，并没有提供对因果关系的深入了解。 我们最近开创了对小鼠分离的单个淋巴管和淋巴管链的淋巴瓣和泵功能进行定量研究的方法；因此，当淋巴管在规定条件下承受增加的压力负载时，我们可以严格测试泵的功能，其中所有压力、直径和阀门位置都是已知或受控的。此外，我们可以在淋巴疾病的小鼠模型中做到这一点。我们的结果表明，即使在健康的血管中，也会出现两种类型的泵故障，以响应流入/流出压力的逐渐升高，模拟附属肢体中血管上的压力负载。 1）泵要么逐渐减弱，直至无法喷射，使输出阀关闭；或 2) 输出阀“锁定”打开，造成灾难性后果，因为通过它的压力在收缩期达到平衡。缺乏转录因子FOXC2（控制淋巴管发育和维持）的小鼠，瓣膜闭锁现象加剧；它的缺乏概括了人类疾病淋巴水肿双毛病。重要的是，这两种情况都可以纠正。我们将利用健康小鼠和 Foxc2 缺陷小鼠，测试在淋巴水肿发生过程中淋巴泵经历的静水压环境中导致收缩和瓣膜功能障碍的机制。将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到体内腹股沟淋巴网络的研究中。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：淋巴肌的机械特性、瓣膜的特性以及收缩波的协调；此外，我们提出泵功能障碍可以通过β-肾上腺素能激动剂逆转。目的： 1) 确定当健康的淋巴管被迫在升高的流出压力下泵送时，阀门锁定和泵故障的潜在机制； 2) 确定Foxc2/-和诱导型Foxc2-/-原发性淋巴水肿模型中淋巴阀和泵功能障碍的后果； 3) 确定在健康和 Foxc2 缺陷的血管中通过药理学挽救淋巴泵功能障碍的原则。这种治疗失败的淋巴泵的方法代表了一种潜在的新策略，用于治疗多种先天性和获得性淋巴水肿的常见潜在诱因。

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 ?- 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.