Lymphatic pacemaking and pumping in lymphedema: function, dysfunction, and rescue

淋巴水肿中的淋巴起搏和泵送：功能、功能障碍和救援

• 批准号: 8882898
• 负责人: Michael John Davis
• 金额: $ 38.38万
• 依托单位: UNIVERSITY OF MISSOURI-COLUMBIA
• 依托单位国家: 美国
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-04-01 至 2019-03-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/8882898
• 关键词: Action Potentials; Address; Adrenergic Agents; Affect; Agonist; Automobile Driving; Calcium; Caliber; Chronic; Clinical Research; Data; Defect; Development; Diastolic blood pressure; Edema; Event; Exhibits; Failure; Frequencies; Functional disorder; Heart; Human; Hydrostatic Pressure; Image; Intervention; Intrinsic drive; Ion Channel; Ions; Knockout Mice; Knowledge; Laboratories; Limb structure; Lymph; Lymphatic; Lymphatic System; Lymphatic vessel; Lymphedema; Maintenance; Measurable; Measures; Mediating; Membrane Potentials; Methods; Mus; Muscle; Norepinephrine; Output; Pacemakers; Peripheral; Phase; Positioning Attribute; Potassium Channel; Predisposition; Property; Proteins; Pump; Role; Smooth Muscle; Smooth Muscle Myocytes; System; Testing; Transgenic Mice; adrenergic; base; efficacy testing; experience; flexibility; human disease; insight; lymphatic pump; mouse model; novel; palliative; patch clamp; pressure; primary lymphedema; public health relevance; response; transcription factor; voltage; voltage clamp

 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 types of lymphedema. Little is known about why lymphatic vessels become dysfunctional, but clinical studies reveal an elevated lymphatic diastolic pressure, enlarged diameter, impaired or absent contractions, and what appear to be incompetent valves. Collectively these findings point to underlying problems with the lymphatic pacemaker, pump and valves. In this proposal we will test the mechanisms leading to contraction and valve dysfunction at pressures experienced by the lymph pump during the development of lymphedema. Recently we developed methods to measure the membrane potential of lymphatic smooth muscle (LSM) in isolated, pressurized mouse lymphatics and patch clamp methods to study selected ion currents in LSM cells. We will apply those methods to transgenic mouse models to study the ionic basis of the electrical pacemaker that drives spontaneous and pressure-regulated contractions. Our preliminary results challenge the existing dogma about the pacemaking mechanism in LSM and suggest it is controlled by interactions between voltage- gated Ca2+ channels and KCNQ K+ channels. Our new data show the same channels operate in human LSM. We have developed methods to test valve and pump function in isolated single lymphangions from the mouse when the vessel is subjected to increasing output pressure, simulating the load on a vessel in a dependent extremity. Our results provide new insights into how the lymph pump fails when pressure is elevated. The pump either gradually weakens until it cannot eject, or the output valve "locks" open catastrophically. Importantly, we find that both types of pump failure can be corrected by the administration of norepinephrine (NE) to activate the pacemaker while preserving contractile strength and tone for normal valve gating. Although pump failure occurs in some normal vessels subjected to elevated pressure, susceptibility to failure is increased of mice deficient in the transcription factor FOXC2, which controls the development and maintenance of lymphatic valves. Foxc2+/- mice recapitulate the human disease lymphedema distichiasis. Our central hypothesis is that lymphatic pacemaking, pump strength, and valve function are closely interrelated such that failure of any one disables the lymph pump and leads to lymphedema. We propose that pump dysfunction can be rescued by pharmacological intervention in normal, Foxc2+/- and inducible Foxc2-/- mice. This hypothesis will be tested by 3 aims: 1) Determine the ionic basis of the lymphatic action potential and pacemaking. 2) Determine the ionic mechanisms by which pressure modulates the lymphatic pacemaker. 3) Determine the mechanisms by which NE modulates the lymphatic pacemaker and can rescue a lymphatic vessel that is made dysfunctional by an elevated pressure load or valve defect. This approach to treating a failed lymph pump represents a potential new strategy for treating a key underlying cause of lymphedema.

 描述(申请人提供)：淋巴运输发生在流体静压梯度的情况下，因此严重依赖淋巴肌肉的内在收缩功能，即“淋巴泵”。这种泵系统的故障与多种类型的淋巴水肿有关。淋巴管功能障碍的原因知之甚少，但临床研究显示淋巴管舒张压升高、管径增大、收缩受损或无收缩，以及似乎功能不全的瓣膜。总而言之，这些发现指出了淋巴起搏器、泵和瓣膜的潜在问题。在这项建议中，我们将测试在淋巴泵在淋巴水肿发展过程中所经历的压力下导致收缩和瓣膜功能障碍的机制。最近，我们发展了在分离、加压的小鼠淋巴管中测量淋巴管平滑肌(LSM)膜电位的方法，并发展了膜片钳方法来研究LSM细胞中的选择性离子电流。我们将把这些方法应用于转基因小鼠模型，以研究驱动自发和压力调节收缩的电子起搏器的离子基础。我们的初步结果挑战了现有关于LSM起搏机制的教条，表明LSM的起搏机制受电压门控钙通道和KCNQ K+通道之间的相互作用控制。我们的新数据显示，在人类LSM中，同样的通道也在运行。我们已经开发了一种方法，当血管受到增加的输出压力时，在小鼠的单个淋巴管中测试瓣膜和泵的功能，模拟依赖四肢的血管上的负荷。我们的结果为淋巴泵在压力升高时如何失效提供了新的见解。泵要么逐渐变弱，直到无法排出，要么输出阀灾难性地“锁定”打开。重要的是，我们发现两种类型的泵故障都可以通过给予去甲肾上腺素(NE)来激活起搏器来纠正，同时保持正常瓣膜门控的收缩强度和音调。尽管在压力升高的情况下，一些正常血管会发生泵故障，但缺乏转录因子FOXC2的小鼠发生故障的可能性增加。转录因子FOXC2控制淋巴瓣的发育和维护。FOXC2+/-小鼠重述了人类疾病淋巴水肿病。我们的中心假设是淋巴起搏、泵的强度和瓣膜功能是密切相关的，因此任何一个的失败都会使淋巴泵失效并导致淋巴水肿。我们认为，在正常、FOXC2+/-和可诱导的FOXC2-/-小鼠中，通过药物干预可以挽救泵功能障碍。这一假说将通过三个目的得到验证：1)确定淋巴动作电位和起搏的离子基础。2)确定压力调节淋巴起搏器的离子机制。3)确定NE调节淋巴起搏器和挽救因压力负荷升高或瓣膜缺陷而功能障碍的淋巴管的机制。这种治疗失败的淋巴泵的方法代表了一种潜在的新策略，用于治疗淋巴水肿的关键潜在原因。