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（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类型的淋巴水肿有关。人们对淋巴管功能失调的原因知之甚少，但临床研究显示淋巴管舒张压升高、直径增大、收缩受损或缺失，以及瓣膜功能不全。总的来说，这些发现表明淋巴起搏器、泵和瓣膜存在潜在问题。在本提案中，我们将测试在淋巴水肿发生过程中淋巴泵所经历的压力下导致收缩和瓣膜功能障碍的机制。 最近，我们开发了测量分离的加压小鼠淋巴管中淋巴平滑肌 (LSM) 膜电位的方法，以及研究 LSM 细胞中选定离子电流的膜片钳方法。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起搏器的离子基础。我们的初步结果挑战了关于 LSM 起搏机制的现有教条，并表明它是由电压门控 Ca2+ 通道和 KCNQ K+ 通道之间的相互作用控制的。我们的新数据显示，人类 LSM 中也存在相同的通道。 我们开发了方法，当血管受到增加的输出压力时，测试小鼠分离的单个淋巴管中的阀门和泵功能，模拟依赖肢血管上的负载。我们的研究结果为了解压力升高时淋巴泵如何失效提供了新的见解。泵要么逐渐减弱直至无法喷射，要么输出阀灾难性地“锁定”打开。重要的是，我们发现这两种类型的泵衰竭都可以通过服用去甲肾上腺素（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。虽然一些承受高压的正常血管会发生泵衰竭，但缺乏转录因子 FOXC2 的小鼠对泵衰竭的敏感性会增加，FOXC2 控制淋巴瓣的发育和维护。 Foxc2+/- 小鼠重现了人类疾病双丝淋巴水肿。 我们的中心假设是，淋巴起搏、泵力和瓣膜功能密切相关，任何一项的故障都会使淋巴泵失效并导致淋巴水肿。我们认为，正常、Foxc2+/- 和诱导型 Foxc2-/- 小鼠中的泵功能障碍可以通过药物干预来挽救。该假设将通过 3 个目标进行检验：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 调节淋巴起搏器并挽救因压力负荷升高或瓣膜缺陷而功能失调的淋巴管的机制。这种治疗失败的淋巴泵的方法代表了治疗淋巴水肿关键根本原因的潜在新策略。