AIBP介导的胆固醇代谢在淋巴水肿和淋巴管生成中的作用及机制研究

Lymphatic vessels collect and transport interstitial fluid to venous circulation throughout the body. Lyphangiogenesis generates lymphatic vessels that are essential for maintenance of tissue fluid homeostasis and for immune surveillance as well as for lipid transport. Insufficient lymphangiogenesis, resulting from congenital disorders or arising in the setting of acquired damage to the lymphatic system, may result in lymphatic dysfuction, which impairs fluid drainage from the interstitium. Clinically, this manifests as lymphedema, a disease presenting as an accumulation of protein-rich fluid in the interstitial space, followed by tissue changes, including accumulation of hypercellular adipose and fibrotic tissue. More than 100 million people are affected by lymphedema worldwide. Unfortunately, effective therapeutic strategies to treat lymphedema are still lacking. Our recent evidence suggests that apoA1 binding protein (AIBP) may be part of the mechanistic link between lipid metabolism and lymphagiogenesis. By studying human lymphedematous tissues, we found that AIBP expression is increased in the affected tissues of lymphedema patients, indicating a role of AIBP in lymphangiogenesis. We then generated AIBP knockout mice, which are viable and fertile, and found loss of AIBP in mice impeded lymphangiogenesis. In human lymphatic endothelia cells (HLEC), AIBP and apoA1 combination promote in vitro lymphangiogenesis, while cav1 prohibits lymphatic tube formation. We also found VEGFR3 binds cav1 and is located in caveolae of HLEC. Moreover, MβCD, which disrupts caveolae by sequestering cholesterol, reduces plasma membrane cav-1 levels and facilitates in vitro lymphangiogenesis. Because AIBP-targeted cholesterol efflux disrupts caveolae, we therefore hypothesize that AIBP enhances cholesterol removal to disrupt caveolae, which abolishes cav-1 inhibition of VEGFR3 and results in augmented VEGFR3 signaling and lymphangiogenesis. Herein, my specific aims are: (1) To further determine the role of AIBP in lymphangiogenesis and lymphatic development; (2) To determine the molecular mechanisms about AIBP enhances VEGFR3 signaling by increasing cholesterol efflux and reducing the inhibition of cav-1 within caveolae. (3) To determine the effect of AIBP administration on lymphatic regeneration in murine model. Our studies on AIBP-regulated lymphangiogenesis will help guide the design of novel therapy.

淋巴管收集并转运组织间液体到静脉循环和全身各处，对组织稳态、免疫监视及脂类转运至关重要。淋巴管生成不足会造成淋巴回流受阻，即淋巴水肿，目前还没有有效治疗措施。我们发现调控胆固醇代谢的一个新蛋白——载脂蛋白A1结合蛋白（AIBP）在淋巴水肿病人皮肤组织中表达量明显变化，Aibp-/-小鼠中表明AIBP促进真皮组织中淋巴管生成，体外实验提示AIBP可能通过质膜微囊中cav-1调控淋巴管生成。因此，本课题提出AIBP通过增强胆固醇流出影响质膜微囊，从而减少质膜微囊中cav-1对VEGFR3信号通路的抑制作用来促进淋巴管生成。首先，将进一步研究AIBP对淋巴管生成的作用；其次，研究AIBP调控淋巴管生成的确切机制；最后，研究AIBP作为分泌蛋白，在病理性淋巴管生成中的作用及治疗价值。本课题将率先把胆固醇代谢和淋巴管生成联系起来，帮助理解淋巴管生成的调控机制，同时为淋巴水肿提供新的治疗方案。

淋巴管收集并转运组织间液体到静脉循环和全身各处，对组织稳态、免疫监视及脂类转运至关重要。淋巴管生成不足会造成淋巴回流受阻，即淋巴水肿，目前还没有有效治疗措施。我们发现调控胆固醇代谢的一个新蛋白——载脂蛋白A1结合蛋白（AIBP）在淋巴水肿病人皮肤组织中表达量明显变化，推测AIBP可能在淋巴水肿中发挥作用。于是，我们利用Aibp基因敲除小鼠和尾巴淋巴水肿模型，研究了AIBP在真皮组织淋巴管生成中的作用和作用机制，以及在淋巴水肿中的可能治疗价值。我们首先利用建立的Aibp基因敲除小鼠，分离真皮组织，研究了出生后第3、5、6天Aibp基因敲除小鼠真皮组织中淋巴管生成的情况，发现与对照同胞仔相比，Aibp基因敲除小鼠真皮组织中淋巴管面积、密度、出芽点和环状复合物均减少。这表明AIBP促进淋巴管生成，提示AIBP可以作为淋巴水肿的治疗靶点。机制上，AIBP与apoA1共同促进胆固醇从淋巴管内皮细胞流出，破坏质膜微囊的结构，从而解除了caveolin-1对VEGFR3的抑制作用，使VEGFR3信号通路活化和淋巴管生成增强。为了进一步支持AIBP作为淋巴水肿治疗靶点的潜力，我们在Aibp基因敲除小鼠中进行尾巴淋巴水肿造模，结果显示Aibp基因敲除小鼠尾巴水肿更加明显，支持AIBP促进淋巴管生成。进而，我们利用AIBP重组蛋白初步探讨了AIBP对淋巴水肿的可能治疗价值，重组蛋白治疗组小鼠尾部淋巴水肿有改善的趋势。因此，我们的结果支持AIBP作为淋巴水肿治疗靶点的可能性。本课题利用Aibp基因敲除小鼠模型和尾巴淋巴水肿模型，揭示了胆固醇代谢中的一个分泌蛋白AIBP，通过调节VEGFR3信号通路促进淋巴管生成，并揭示了AIBP在淋巴水肿的作用及作为治疗靶点的可能性，不仅可以帮助理解淋巴管生成的调控机制，而且可为淋巴水肿提供新的潜在治疗方案。