ROLE OF LEPTIN IN WOUND ANGIOGENESIS

描述(由申请人提供)： 伤口的愈合是一个复杂的、精心安排的过程，需要通过新生血管快速有效地恢复被切断的微循环。因此，各种血管生成因子及其细胞受体被主动上调，以响应通常在伤口环境中发展的条件，最明显的是缺氧。在这些血管生成因子中，P.I.已经确定多效性细胞因子瘦素是这一谱系中的重要成员，并随后证实瘦素基因的表达是由缺氧引起的。虽然瘦素在体重调节中发挥核心作用，但它也是一种强大的血管生成因子，作用于靶向内皮细胞，靶细胞表达全功能的、具有信号活性的瘦素受体。鉴于新生血管在正常伤口愈合过程中的关键作用，这里假设瘦素的血管生成活性对伤口愈合很重要。与这一观点一致的是，众所周知，瘦素和瘦素受体缺失的小鼠模型显示出严重的伤口愈合障碍。P.I.实验室进行的研究表明，瘦素在伤口中上调，用瘦素治疗伤口可以促进正常小鼠的愈合，恢复瘦素缺失小鼠的愈合，但不能恢复瘦素受体缺失小鼠的愈合。此外，瘦素治疗加速了伤口内小口径血管的形成，更早地达到了简单伤口愈合的典型血管密度终点。此外，本研究的初步结果表明，瘦素能迅速增加各种低氧诱导基因的表达，包括低氧诱导因子-1(HIF-1)。在这些研究的基础上，假设瘦素促进血管生成的机制反映了缺氧驱动的与HIF-1的协同作用，从而导致一组血管生成基因的协调反应。因此，瘦素促进血管生成的发现，再加上最近对瘦素在伤口愈合中的作用以及低氧条件下瘦素合成的调节的观察，表明缺氧和瘦素诱导的伤口新生血管是参与正常组织修复过程的两个相互关联的重要事件。因此，本研究的两个中心假设是：1)瘦素的血管生成功能是其促进伤口愈合活性的关键要求；2)低氧和瘦素诱导的伤口新生血管是正常组织修复过程所必需的两个关键的、相互关联的事件。这些假说在研究计划中的具体目的如下：1)表征和比较正常、瘦素缺失和瘦素受体缺失小鼠的伤口血管生成反应；2)确定从正常、瘦素缺失和瘦素受体缺失小鼠分离的真皮微血管内皮细胞体外形成血管结构的能力；以及3)确定瘦素和缺氧诱导因子-1协同诱导伤口早期缺氧敏感基因表达的机制(S)。这项研究将有助于解释瘦素促进伤口新生血管的生理机制，并有助于理解正常和受损伤口愈合的机制。

DESCRIPTION (provided by applicant): The healing of a wound is a complex, orchestrated process that requires rapid and effective restoration of the severed nicrocirculation through neovascularization. Accordingly, a variety of angiogenic factors and their cellular receptors are actively upregulated in response to conditions that typically develop in the wound environment, most notably hypoxia. Among these angiogenic factors, the P.I. has identified the pleiotropic cytokine leptin as an important member of this repertoire and subsequently established that expression of the leptin gene is acutely induced by hypoxia. Although leptin plays a central role in body weight regulation, it is also a potent angiogenic factor that acts upon target endothelial cells, which express fully functional, signaling-competent leptin receptors. Given the crucial role of neovascularization for normal wound healing progression, it is hypothesized here that the angiogenic activity of leptin is important for wound resolution. Consistent with this idea, it is well known that leptin- and leptin receptor-null mouse models exhibit severe impairment of wound healing. Studies conducted in the P.I. laboratory indicate that leptin is upregulated in wounds, and that treatment of wounds with leptin enhances healing in normal mice and restores healing in leptin-null mice, but not in leptin receptor-null mice. Furthermore, leptin treatment accelerates formation of small caliber vessels within the wound, achieving earlier the vascular density endpoint typical of uncomplicated wound healing. In addition, preliminary results shown in this proposal indicate that leptin rapidly increases expression of various hypoxia-inducible genes, including hypoxia inducible factor-1 (HIF-1). Based on these studies, it is hypothesized that the mechanism of angiogenesis promoted by leptin reflects a hypoxia-driven, cooperative interaction with HIF-1, whereby a coordinated response of a group of angiogenic genes ensues. Thus, the discovery that leptin promotes angiogenesis, coupled with more recent observations documenting the role of leptin in wound healing and the regulation of leptin synthesis under hypoxic conditions, suggest that hypoxia and leptin-induced neovascularization in the wound are two crucial, mutually linked events that participate in the normal tissue repair process. Therefore, two ensuing central hypotheses in this proposal are: 1) The angiogenic function of leptin is a key requirement for its wound healing-promoting activity; and 2) Hypoxia- and leptin-induced neovascularization in the wound are two crucial, linked events that are necessary for the normal tissue repair process. These hypotheses are explored in the research plan by the following specific aims: 1) to characterize and compare the wound angiogenic response in normal, leptin-null, and leptin receptor-null mice; 2) to determine the ability of dermal microvascular endothelial cells isolated from normal, leptin-null, and leptin receptor-null mice to form vascular structures in response to leptin in vitro; and 3) to identify the mechanism(s) by which leptin and HIF-1 coordinately induce expression of early hypoxia-sensitive genes in wounds.. The proposed research will help explain the physiological mechanisms by which leptin promotes wound neovascularization and will contribute to the understanding of the mechanisms of normal and impaired wound healing.