Investigation of CTRP-3 (C1q/TNF-related protein-3) functions in adipose tissue via characterization of a murine adipocyte-specific knockout model

背景：C1q/ tnf相关蛋白（CTRPs）家族的15个成员代表了一组脂联素类似物。CTRP-3是一种主要表达于脂肪组织的分泌蛋白，影响免疫和代谢过程，被认为是具有抗炎特性的内源性脂多糖（LPS）拮抗剂，是脂肪细胞生物学和代谢的重要调节因子。研究目的：脂肪因子CTRP-3的抗炎特性已经在体外单核细胞和脂肪细胞中得到了很好的描述，最近也在lps诱导的体内炎症中得到了很好的描述。介绍的研究将包括最近建立的基于Cre/ loxp的脂肪细胞特异性CTRP-3敲除小鼠模型（遗传背景：C57BL/6NTac）的特征，以研究CTRP-3的全身和局部组织功能。本研究的另一个目的是研究CTRP-3在肥胖和体重减轻引起的脂肪组织减少过程中的调节作用。为了解决这些问题，我们将分析接受减肥手术（分别接受胃旁路或胃套管）或参加饮食减肥计划的肥胖个体的局部脂肪组织和全身CTRP-3表达。方法：除了以脂肪组织发育、形态和代谢为重点的新型转基因小鼠模型的表型特征外，还将分析脂肪细胞CTRP-3表达功能失调对lps诱导的炎症以及标准或特殊饮食（定义为高脂肪和高糖饮食）小鼠代谢状态和过程的影响。实验设置将包括不同脂肪组织库的组织学、生化和分子分析，以及脂肪组织中常驻免疫系统细胞的表征。糖耐量试验和脂质分析将用于阐明脂肪细胞衍生的CTRP-3在全身代谢中的作用。在人类肥胖队列中，CTRP-3水平将根据全身浓度和皮下和内脏脂肪组织的局部表达进行分析。观点：脂肪细胞特异性CTRP-3基因敲除的分子特征，肥胖症条件下CTRP-3调控的研究，以及针对减肥的多种方法，将大大提高我们对该蛋白在代谢和脂肪组织炎症中的作用的理解，并有助于开发肥胖症和代谢综合征的潜在未来药物靶点。

Background: The 15 identified members of the family of C1q/TNF-related proteins (CTRPs) represent a group of adiponectin paralogs. CTRP-3, a secretory protein mainly expressed in adipose tissue, affects processes in both immunology and metabolism and has been characterized as an endogenous antagonist of lipopolysaccharide (LPS) with anti-inflammatory properties and as an important regulatory factor in adipocyte biology and metabolism.Aims of the study: The anti-inflammatory properties of the adipokine CTRP-3 have been well described in monocytes and in adipocytes in vitro and also recently in LPS-induced inflammation in vivo. The introduced study will comprise the characterization of a recently established Cre/loxP-based mouse model (genetic background: C57BL/6NTac) of an adipocyte-specific CTRP-3 knockout in order to investigate systemic and local tissue functions of CTRP-3. A further aim of the present study is to investigate CTRP-3 regulation in obesity and during adipose tissue reduction due to weight loss. To address these issues, both local adipose tissue and systemic CTRP-3 expression will be analyzed in obese individuals either undergoing bariatric surgery (receiving a gastric bypass or a gastric sleeve, respectively) or participating in a diet-based weight-loss program.Methods: In addition to a phenotypical characterization of the new transgenic mouse model focusing on adipose tissue development, morphology, and metabolism, the impact of dysfunctional adipocyte CTRP-3 expression on LPS-induced inflammation as well as on metabolic status and processes in mice on standard or special diets (defined high-fat and high-sugar diets) will be analyzed. Experimental settings will comprise histological, biochemical, and molecular analysis of different adipose tissue depots and characterization of resident immune system cells in adipose tissue. Glucose tolerance tests as well as lipid analysis will be applied to clarify the role of adipocyte-derived CTRP-3 in whole body metabolism. In the human obesity cohort, CTRP-3 levels will be analyzed with regard to systemic concentrations and to local expression in subcutaneous and in visceral adipose tissue.Perspectives: Molecular characterization of an adipocyte-specific CTRP-3 knockout as well as investigation of CTRP 3 regulation under the conditions of obesity and of diverse approaches aiming on weight-loss will substantially improve our understanding of the role of this protein in metabolism and in adipose tissue inflammation and will help to develop a potential future drug target in obesity and in the Metabolic Syndrome.