The Role of Leptin in Susceptibility to Amebiasis

描述(申请人提供)：溶组织内阿米巴是引起肠道阿米巴病和阿米巴肝脓肿的致病原虫。据估计，每年有5000万人感染和100,000人死亡，营养不良会增加感染的敏感性。细胞因子样激素瘦素在能量营养不良时减少。最近有证据表明，瘦素是阿米巴病易感性的关键介质，包括：1)在临床研究中发现瘦素受体胞外域的一个多态性(Q223R)显著增加了小鼠的易感性；2)证明Q223R多态也增加了小鼠的易感性；3)发现组织特异性缺失的瘦素受体在肠道上皮而不是在下丘脑，增加了小鼠的易感性；以及4)证明在单细胞中表达瘦素受体使它们在体外对阿米巴杀伤具有抵抗力。综上所述，这些数据表明瘦素信号直接保护肠上皮细胞免受溶组织埃希菌的细胞毒作用，但其保护机制尚不清楚。该项目的中心假设是，Q223R基因多态解除了瘦素受体信号的调控，并创造了一种允许组织溶解埃希菌感染的肠道上皮细胞。下面的目的是阐述Q223R多态的功能和瘦素信号在细胞对溶组织埃希氏菌易感性中的作用。具体目标1将通过测试Q223R多态是否改变瘦素结合和/或瘦素受体的表面表达来评估Q223R多态的功能后果。我们还将测试Q223R多态是否通过瘦素受体改变JAK2、SHP-2、STAT5和STAT3通路的激活。具体目标2将确定SHP-2、STAT5和STAT3信号通过瘦素受体在细胞对溶组性埃希菌易感性中的作用。已确定的信号通路将得到验证，瘦素受体介导的保护的下游效应器将通过微阵列分析进行探索。通过评估瘦素受体单一多态性的特定分子后果，我们将开始描绘一种新的粘膜免疫防御机制。这项工作可能会对其他肠道病原体、肠易激疾病和肠癌的发病机制产生影响。此外，更好地了解将营养不良和免疫反应联系起来的信号事件将对世界各地儿童的健康产生积极影响。 公共卫生相关性：这项研究将评估瘦素受体单一多态性与儿童阿米巴病易感性密切相关的特定分子后果。对阿米巴病的营养和免疫反应信号事件有更深入的了解，将对全世界儿童的健康产生积极影响。

DESCRIPTION (provided by applicant): Entamoeba histolytica is the pathogenic protozoan responsible for intestinal amebiasis and amebic liver abscess. E. histolytica is estimated to cause 50 million infections and 100,000 deaths annually and malnutrition is known to increase susceptibility to infection. The cytokine-like hormone leptin is reduced in the energy malnourished. Recent evidence that leptin is a pivotal mediator of susceptibility to amebiasis includes: 1) the identification of a polymorphism (Q223R) in the extracellular domain of the leptin receptor that significantly increases susceptibility in clinical studies; 2) demonstration that the Q223R polymorphism also increases susceptibility in mice; 3) the finding that tissue-specific deletion of the leptin receptor at the intestinal epithelium, but not in the hypothalamus, increases susceptibility in mice; and 4) demonstration that expression of the leptin receptor in single cells renders them resistant to amebic killing in vitro. Together these data indicate that leptin signaling directly protects intestinal epithelial cells from E. histolytica cytotoxicity, however the mechanism of protection is not understood. The central hypothesis of this project is that the Q223R polymorphism deregulates leptin receptor signaling and creates an intestinal epithelium that is permissive to E. histolytica infection. The following aims address the function of the Q223R polymorphism and the role of leptin signaling in cellular susceptibility to E. histolytica. Specific aim 1 will evaluate the functional consequences of the Q223R polymorphism by testing if leptin binding and/or surface expression of the leptin receptor is altered by the Q223R polymorphism. We will also test if the Q223R polymorphism alters activation of JAK2, SHP-2, STAT5 and STAT3 pathways through the leptin receptor. Specific aim 2 will determine the role of SHP-2, STAT5 and STAT3 signaling through the leptin receptor in cellular susceptibility to E. histolytica. The signaling pathway identified will be validated and downstream effectors of leptin receptor-mediated protection will be explored by microarray analysis. By evaluating the specific molecular consequences of a single polymorphism in the leptin receptor, we will begin to delineate a novel mechanism of mucosal immune defense. This work may have implications for the pathogenesis of other enteric pathogens, irritable bowel disease and intestinal cancer. Additionally, a greater understanding of the signaling events that connect malnutrition and the immune response will positively impact the health of children worldwide. PUBLIC HEALTH RELEVANCE: This research will evaluate the specific molecular consequences of a single polymorphism in the leptin receptor that is strongly associated with susceptibility to amebiasis in children. A greater understanding of the signaling events that connect nutrition and the immune response to amebiasis will positively impact the health of children worldwide.