Mechanisms of lymphatic valve and pump dysfunction in lymphedema

描述（由申请人提供）：淋巴转运逆着流体静压梯度发生，因此关键依赖于淋巴肌的内在收缩功能，即“淋巴泵”。这种泵系统的故障与多种形式的水肿有关，在美国每年有超过1000万人受到影响。关于淋巴管如何以及为什么在水肿中变得功能障碍，我们知之甚少。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，瓣膜功能明显不全。然而，这些发现是事后的，并没有提供深入的原因或影响。 我们最近开创了在小鼠中孤立的单个淋巴管和淋巴管链中定量研究淋巴阀和泵功能的方法;因此，当淋巴管在规定条件下承受增加的压力负荷时，我们可以严格测试泵功能，其中所有压力，直径和阀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。我们的研究结果表明，两种类型的泵故障发生，即使在健康的血管中，在流入/流出压力的逐步上升，模拟在依赖端的血管上的压力负荷。1)泵逐渐减弱，直到无法弹出，使输出阀关闭;或者2）输出阀“锁定”打开，带来灾难性的后果，因为输出阀上的压力在收缩期达到平衡。在转录因子FOXC 2缺陷的小鼠中，阀锁加剧，FOXC 2控制淋巴阀的发育和维持;其缺陷重现了人类疾病双列体水肿。重要的是，这两种情况都可以纠正。我们将利用健康和Foxc 2缺陷小鼠，在水肿发展过程中，在淋巴泵经历的静水环境中测试导致收缩和瓣膜功能障碍的机制。将从小鼠腘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：淋巴肌的机械特性、瓣膜的特性和收缩波的协调;此外，我们提出泵功能障碍可以通过α-肾上腺素能受体激动剂逆转。目的：1）确定当健康淋巴管被迫泵送以抵抗升高的流出压力时，阀锁定和泵故障的潜在机制; 2）确定原发性水肿的Foxc 2 +/-和诱导型Foxc 2-/-模型中淋巴阀和泵功能障碍的后果; 3）确定在健康和Foxc 2缺陷血管中淋巴泵功能障碍可以被挽救的原则。这种治疗淋巴泵衰竭的方法代表了一种潜在的新策略，用于治疗多种形式的先天性和获得性水肿的共同潜在贡献者。

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.