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

背景：已鉴定的15个C1q/肿瘤坏死因子相关蛋白(CTRPs)家族成员代表一组脂联素类似物。CTRP-3是一种主要在脂肪组织中表达的分泌性蛋白，影响免疫学和代谢过程，是内源性脂多糖拮抗剂，具有抗炎作用，也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在单核细胞和脂肪细胞中的抗炎作用已经得到了很好的描述，在体外也在脂多糖诱导的炎症中得到了很好的描述。这项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基因敲除的小鼠模型(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在肥胖和减肥导致的脂肪组织减少过程中的调节作用。为了解决这些问题，将分析接受减肥手术(分别接受胃旁路手术或胃袖手术)或参与基于饮食的减肥计划的肥胖个体的局部脂肪组织和全身性CTRP-3表达。方法：除了关注脂肪组织发育、形态和代谢的新转基因小鼠模型的表型特征外，还将分析脂肪细胞CTRP-3表达异常对脂多糖诱导的炎症以及标准或特殊饮食(定义为高脂和高糖饮食)小鼠代谢状态和过程的影响。实验环境将包括不同脂肪组织仓库的组织学、生化和分子分析，以及脂肪组织中常驻免疫系统细胞的特征。糖耐量测试和脂肪分析将用于阐明脂肪细胞来源的CTRP-3在全身新陈代谢中的作用。在人类肥胖队列中，CTRP-3水平将根据全身浓度以及在皮下和内脏脂肪组织中的局部表达进行分析。展望：脂肪细胞特异性CTRP-3基因敲除的分子特征以及在肥胖条件下CTRP-3调控的研究和针对减肥的不同方法将极大地提高我们对这种蛋白在代谢和脂肪组织炎症中的作用的理解，并将有助于开发未来治疗肥胖症和代谢综合征的潜在药物靶点。

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.