SREBP-Mediated Regulation of Intestinal Epithelial Homeostasis

肥胖正在迅速上升，并与代谢失调、心血管疾病发病率和胃肠道恶性肿瘤发病率增加有关。此外，肥胖是由高脂肪、高胆固醇饮食驱动的，而这些饮食本身就是胃肠道癌症的严重风险因素。肠上皮细胞是人体内分裂最快的细胞，它依赖于肠干细胞（ISCs）等祖细胞来维持其增殖。虽然膳食脂质可以调节ISCs，但脂质影响肠道增殖的机制尚不清楚。脂质生物合成受固醇调节元件结合蛋白（SREBPs）调节。我最近的研究表明，SREBP在维持肠上皮细胞的生长方面也起着关键作用。令人惊讶的是，我发现SREBP-2的缺乏会阻止胆固醇的合成，导致肠道过度生长和肠道祖细胞数量的增加。我推测，这种肠道增殖能力的增加是由SREBP-2敲除后SREBP-1的代偿性刺激引起的。接下来，我发现SREBP-1在肠道中的过表达再现了这种肠道过度生长，证实了控制脂肪酸合成的SREBP-1是肠道上皮生长的关键调节因子。本研究的目的是确定SREBPs控制肠上皮细胞增殖的分子机制。中心假设是SREBP通过产生维持肠祖细胞增殖的脂质代谢物来维持肠上皮细胞的稳态。因此，将追求以下具体目标：（1）确定SREBP-1如何驱动肠上皮细胞的生长。(2)确定SREBP介导其对肠道生长影响的细胞区室。(3)使用无偏转录组和脂质组分析，以确定脂质代谢产物及其生物合成酶，这些酶是SREBP对上皮细胞影响的基础。这些目标将通过使用Cre-loxP工具的新型小鼠模型来实现，以调节体内肠道中的基因和标志物表达，RNA-seq和脂质组学测量，以及用于体外机制实验的肠道类器官。这项提议的预期结果是确定SREBPs调节肠道生长的机制。这一结果将具有积极的翻译影响，因为新鉴定的脂质调节剂将代表可以被操纵的新的治疗靶点是可行的。生长刺激物可在肠癌的情况下被抑制以产生抗癌作用，或在短肠的情况下被刺激。最后，更好地了解肠道脂质代谢将有助于开发新的治疗肥胖并发症的方法，如NAFLD，这在美国很流行。

Obesity is rapidly on the rise and is associated with dysregulated metabolism, cardiovascular morbidity and increased rates of gastrointestinal malignancies. Moreover, obesity is driven by high-fat, high-cholesterol diets that are themselves serious risk factors for gastrointestinal cancers. The most rapidly-dividing cells in the body reside in the intestinal epithelium, which relies on progenitor cells like intestinal stem cells (ISCs) to sustain it. While dietary lipids are known to regulate ISCs, the mechanisms by which lipids affect intestinal proliferation are not well understood. Lipid biosynthesis is regulated by sterol regulatory element-binding proteins (SREBPs). My recent studies have demonstrated that SREBPs also have a critical role in sustaining growth of the intestinal epithelia. I found, surprisingly, that a deficiency of SREBP-2, which blocks cholesterol synthesis, results in marked intestinal overgrowth and increased numbers of intestinal progenitor cells. I hypothesized that this increase in proliferatory capacity of the intestine was caused by a compensatory stimulation of SREBP-1 in the SREBP-2 knockouts. Next, I found that overexpression of SREBP-1 in intestine reproduced this intestinal overgrowth, confirming that SREBP-1, which controls fatty acid synthesis, is a key regulator of intestinal epithelial growth. The goal of this proposal is to determine the molecular mechanisms by which SREBPs controls intestinal epithelial proliferation. The central hypothesis is that SREBPs maintain homeostasis of intestinal epithelia by producing lipid metabolites that sustain proliferation of intestinal progenitors. Thus, the following specific aims will be pursued: (1) To determine how SREBP-1 drives the growth of intestinal epithelia. (2) To identify the cellular compartment(s) where SREBPs mediate their effects on intestinal growth. (3) Using unbiased transcriptome and lipidome profiling, to identify the lipid metabolites and their biosynthetic enzymes that underlie the effects of SREBPs on the epithelium. These aims will be achieved with novel mouse models using Cre-loxP tools to modulate gene and marker expression in intestine in vivo, RNA-seq and lipidomics measurements, and intestinal organoids for in vitro mechanistic experiments. The expected outcome of this proposal is the identification of mechanisms by which SREBPs regulates intestinal growth. This outcome will have positive translational impact because it is feasible that the newly-identified lipid regulators will represent novel therapeutic targets that could be manipulated pharmacologically. Growth stimuli could be inhibited in the setting of intestinal cancers for anti-cancer effect or stimulated in the setting of short bowel. Lastly, a better understanding of intestinal lipid metabolism in the intestine will facilitate the development of new treatments for complications of obesity like NAFLD, which is epidemic in the U.S.