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1-2百万人， 美国，这是一个重大的财政负担。IBD会增加其他疾病的风险因素 结肠直肠癌和动脉粥样硬化等疾病。肠上皮细胞（IEC）形成物理屏障 保护身体免受肠道环境的伤害，而肠道上皮的损伤会导致 有害分子和生物体的进入，激活粘膜免疫。溶血磷脂酸 (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，介导多种 可以调节各种细胞类型的存活和增殖的作用。在六种已知的LPA受体中，LPA 5 R是 在胃肠道（GI）中高度表达。最近的一项早期全基因组关联研究（GWAS）- 一组IBD鉴定了GPCR GPR 35内的单核苷酸多态性。随后的一项研究表明， LPA是GPR 35的内源性配体，将异常的LPA介导的信号传导与 IBD。LPA 5 R在胃肠道中的显著表达和异常LPA介导的信号传导的暗示 提示我们产生一种新的小鼠模型，其中LPA 5 R可以诱导性或组成性缺失。 初步研究表明，LPA 5 R的可诱导缺失导致隐窝IEC凋亡、严重结肠炎， 发病率增加，对绒毛IEC无明显影响。相反，LPA 5 R组成性缺失的小鼠， 看起来很正常，这意味着补偿性保护。令人惊讶的是，我们发现， LPA 5 R的组成性缺失对电离辐射或尼古丁诱导的细胞凋亡更具抗性，这表明 过度补偿的细胞存活然而，组成型和诱导型缺失均导致上皮细胞凋亡增加。 在绒毛上皮中，LPA 5 R的通透性和上皮连接蛋白表达降低，表明LPA 5 R 调节上皮屏障功能。我们假设LPA 5 R维持肠上皮的完整性， 通过调节隐窝上皮细胞的存活和刷状缘的上皮屏障功能。我们将 研究LPA 5 R缺失后IEC死亡的根本原因以及LPA 5 R在IEC再生中的作用 (aim 1）。我们将确定IEC存活代偿性增加的潜在机制， 组成性缺失和测试的假设，过度补偿的隐窝细胞存活促进生存 异常细胞对压力的反应（目的2）。此外，我们将研究上皮屏障功能障碍， LPA 5 R的缺乏增加了肠道炎症，同时增加了IEC存活， 对结肠肿瘤的易感性（目的3）。这些研究将揭示LPA 5 R的新功能 维持肠上皮细胞。我们预计，成功完成这项研究将确定 LPA 5 R作为上皮修复和结肠肿瘤形成的关键调节因子， 研究将具有重大的转化潜力，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.