The role of GHS-R in macrophage reprogramming during meta-inflammation

肥胖会促进脂肪组织和肝脏等外围组织的慢性炎症，从而导致广泛的代谢功能障碍，这一现象被称为“化炎症”。巨噬细胞是炎症反应的关键免疫调节剂，由促炎症的M1和抗炎的M2组成。重新编程巨噬细胞极化被认为在治疗肥胖引起的炎症和代谢功能障碍方面具有巨大的潜力。然而，巨噬细胞极化的调节机制还不是很清楚。生长激素促分泌素受体(GHS-R)是已知的与营养感受性肥胖胃肠激素Ghrelin结合的受体。我们对GHS-R全局缺失小鼠的研究表明，GHS-R是一种重要的代谢调节因子；它的信号激活表明全身代谢和炎症状态。我们报道，GHS-R消融可以预防饮食诱导的肥胖和衰老过程中的胰岛素抵抗。我们也有证据表明GHS-R在巨噬细胞中具有细胞自主性，并且GHS-R的敲除使巨噬细胞向M2谱转移。我们假设GHS-R是巨噬细胞极化的关键调节因子；在饮食诱导的肥胖下，GHS-R将巨噬细胞重新编程为促炎状态，导致脂肪组织和肝脏中的炎症和脂质堆积。我们将使用我们新产生的髓系特异性GHS-R基因敲除和重新表达的小鼠来揭示GHS-R在巨噬细胞极化中的作用和相关机制。将进行以下全面和互补的特异性目标：目的1.确定在饮食诱导的肥胖下，巨噬细胞GHS-R是否促进巨噬细胞的促炎极化，增加脂肪组织和肝脏中的炎症和脂肪沉积(体内研究)。目的2.研究GHS-R是否通过细胞自主作用控制巨噬细胞极化，并通过旁分泌作用促进脂肪细胞和肝细胞的炎症(体外研究)。目的3.探讨GHS-R调节巨噬细胞极化的分子机制。我们预计GHS-R在脂肪组织和肝脏的巨噬细胞极化和化炎症中起关键作用。具体地说，我们预测GHS-R通过胰岛素信号对脂肪酸氧化和糖酵解的信号通路进行重新编程，进而调节促炎细胞因子的表达。这一提议将阐明调节巨噬细胞表型开关的新范式，并可能揭示一种新的调节机制，将营养感知、炎症和新陈代谢联系起来。这项提议还将提供“概念验证”证据，证明在巨噬细胞中靶向GHS-R是否将是对抗肥胖和炎症的独特而有效的策略。

Obesity promotes chronic inflammation in peripheral tissues such as adipose tissue and liver, which leads to a wide range of metabolic dysfunctions, a phenomenon called “meta-inflammation”. Macrophages are key immune-modulators of meta-inflammation, comprised of pro-inflammatory M1 and anti-inflammatory M2. Reprograming macrophage polarization is thought to have great potential for treatment of obesity-induced inflammation and metabolic dysfunctions. However, the regulatory mechanisms of macrophage polarization are not well understood. Growth hormone secretagogue receptor (GHS-R), is known to bind to nutrient-sensing obesogenic gut hormone ghrelin. Our studies with GHS-R global deletion mice have shown that GHS-R is an essential metabolic regulator; its signaling activation is indicative of systemic metabolic and inflammatory state. We reported that GHS-R ablation protects against diet-induced obesity and insulin resistance in aging. We also have evidence that GHS-R has cell-autonomous effect in macrophages, and knockdown of GHS-R shifts macrophages toward M2 spectrum. We hypothesize that GHS-R is a key regulator of macrophage polarization; GHS-R reprograms macrophages toward pro-inflammatory state under diet-induced obesity, leading to inflammation and lipid accumulation in adipose tissue and liver. We will unravel the roles and pertinent mechanisms of GHS-R in macrophage polarization using our newly-generated myeloid-specific GHS-R knockout and re-expression mice. The following comprehensive and complementary Specific Aims will be conducted: Aim 1. Determine whether macrophage GHS-R promotes pro-inflammatory polarization of macrophages under diet-induced obesity, increasing inflammation and lipid deposition in adipose tissue and liver (In vivo studies). Aim 2. Examine whether GHS-R controls macrophage polarization via cell-autonomous action, and promotes inflammation in adipocytes and hepatocytes via paracrine action (Ex vivo studies). Aim 3. Investigate molecular mechanisms by which GHS-R regulates macrophage polarization. We anticipate that GHS-R has a crucial role in macrophage polarization and meta-inflammation in adipose tissues and liver. Specifically, we predict that GHS-R, via insulin signaling, reprograms signaling pathways of fatty acid oxidation and glycolysis, in turn regulating the expression of pro-inflammatory cytokines. This proposal will shed light on a new paradigm for regulating macrophage phenotypic switch, and likely uncover a novel regulatory mechanism linking nutrient sensing, inflammation and metabolism. This proposal will also provide “proof-of-concept” evidence whether targeting GHS-R in macrophages would be an unique and powerful strategy for combating obesity and inflammation.