The function of lysophosphatidic acid receptor LPA5R in intestinal inflammation and epithelial damage

炎症性肠病(IBD)，包括克罗恩病和溃疡性结肠炎，影响着100-200万人 对美国来说，这是一个重大的财政负担。IBD增加了其他疾病的风险因素 结直肠癌和动脉粥样硬化等疾病。肠上皮细胞(IECS)构成物理屏障 这会保护身体免受肠道恶劣环境的影响，对肠道上皮的破坏会导致 有毒分子和有机体的进入，激活粘膜免疫。溶血磷脂酸 脂联素(LPA)是一种天然存在的生物活性脂质，作用于G蛋白偶联受体家族，介导 可以调节各种细胞类型的存活和增殖的效果。在已知的六种LPA受体中，LPA5R是 在胃肠道(GI)高表达。最近的一项全基因组关联研究(GWAS)早期- 一组IBD患者在GPCRGPR35内发现了单核苷酸多态。随后的一项研究表明 认为LPA是GPR35的内源性配体，将LPA介导的异常信号与糖尿病的发病机制联系起来 IBD。LPA5R在胃肠道的显著表达及LPA介导的信号转导异常 提示我们建立了一种新的小鼠模型，在该模型中，LPA5R可以被诱导或结构性地删除。 初步研究表明，LPA5R的可诱导缺失导致隐窝IEC凋亡、严重结肠炎和 发病率增加，对绒毛IECS无明显影响。相比之下，LPA5R结构性缺失的小鼠 看起来正常，建议进行补偿性保护。令人惊讶的是，我们发现隐窝上皮细胞 LPA5R的结构性缺失对电离辐射或细胞因子诱导的细胞凋亡更具抵抗力，提示 过度补偿细胞存活。然而，结构性和诱导性缺失都会导致上皮细胞数量增加 绒毛上皮通透性和上皮结合蛋白表达降低，提示LPA5R 调节上皮屏障功能。我们假设LPA5R维持肠道上皮细胞的完整性 通过调节隐窝上皮细胞的存活和刷状缘处的上皮屏障功能。我们会 探讨LPA5R缺失导致IEC死亡的潜在原因及LPA5R在IEC再生中的作用 (目标1)。我们将确定IEC存活率补偿性增加的潜在机制 结构性缺失并检验过度补偿的隐窝细胞存活促进小鼠存活的假说 应激反应的异常细胞(目标2)。此外，我们将研究上皮屏障功能障碍在 LPA5R的缺失会加剧肠道炎症，并伴随IEC存活率的增加而增加 结肠肿瘤的易感性(目标3)。拟议的研究将揭示LPA5R的新功能 维持肠道上皮细胞的功能。我们预计，这项研究的成功完成将确定 LPA5R作为上皮修复和结肠肿瘤的关键调节因子，以及由此产生的发现 研究将具有巨大的翻译潜力，最终可能扩展到人类疾病 未来。

Inflammatory bowel disease (IBD), including Crohn’s disease and ulcerative colitis, affects 1-2 million people in the United States, and is a significant financial burden for the country. IBD increases the risk factor for other diseases such as colorectal cancer and atherosclerosis. Intestinal epithelial cells (IECs) form the physical barrier that protects the body from the hostile environment of the gut, and damage to the intestinal epithelium leads to the entry of noxious molecules and organisms, which activates the mucosal immunity. Lysophosphatidic acid (LPA), a naturally occurring bioactive lipid, acts on a family of G protein-coupled receptors to mediate multiple effects that can regulate survival and proliferation of various cell types. Of six known LPA receptors, LPA5R is highly expressed in the gastrointestinal (GI) tract. A recent genome-wide association study (GWAS) for early on- set of IBD identified a single nucleotide polymorphism within the GPCR GPR35. A subsequent study has shown that LPA is an endogenous ligand of GPR35, linking aberrant LPA-mediated signaling to the pathogenesis of IBD. Significant expression of LPA5R in the GI tract and the suggestion of aberrant LPA-mediated signaling prompted us to generate a novel mouse model in which LPA5R can be deleted inducibly or constitutively. Preliminary studies show that inducible deletion of LPA5R resulted in crypt IEC apoptosis, severe colitis, and increased morbidity, without visible effects on villus IECs. In contrast, mice with constitutive deletion of LPA5R appear normal, suggesting compensatory protection. Surprisingly, we found that crypt epithelial cells with constitutive deletion of LPA5R are more resistant to ionizing radiation- or cytokine-induced apoptosis, suggesting overcompensated cell survival. However, both constitutive and inducible deletion resulted in increased epithelial permeability and decreased epithelial junctional protein expression in villus epithelium, suggesting that LPA5R regulates epithelial barrier function. We hypothesize that LPA5R maintains the integrity of intestinal epithelium by regulating survival of crypt epithelial cells and the epithelial barrier functions at the brush border. We will investigate the underlying cause of IEC death upon LPA5R deletion and the role of LPA5R in IEC regeneration (aim 1). We will determine the underlying mechanism for the compensatory increase in IEC survival in constitutive deletion and test the hypothesis that overcompensated crypt cell survival promotes survival of abnormal cells in response to stress (aim 2). Additionally, we will investigate that epithelial barrier dysfunction in the absence of LPA5R that elevates intestinal inflammation and, together with increased IEC survival, increases the susceptibility to colon neoplasia (aim 3). The proposed studies should reveal the novel functions of LPA5R in the maintenance of intestinal epithelium. We anticipate that successful completion of this study will identify LPA5R as a key regulator of epithelial repair and colonic neoplasia, and the findings generated from these studies will have significant translational potential that may eventually be extended to human disease in the future.