新的脂肪因子SP3在脂肪分化中的作用及机制研究

As adipogenesis is a key step in the pathogenesis of obesity, identifying key factors that control adipocyte differentiation is vital to understanding adipose tissue biology and pathology. To identify novel genes that highly expressed in adipocytes, we compared expression levels of human expressed sequence tag (EST) sequences by cDNA microarray and identified a candidate EST, who coding for a novel protein that assolated with obesity. We refer to the novel gene as SP3 (secret protein 3). Here we provide the first report that white adipose tissue expresses high levels of SP3, and the level associated with the degree of obesity. Furthermore,Nutritional manipulation (such as fasting、refeeding、obesity and insulin resistance) could cause a change of its expression. In vitro, 3T3-L1 cell showed an increased SP3 expression in differentiated cells,but with biphasic expression during the process. Additionally, forced expression of SP3 in 3T3-L1 cells down-regulated the expression of adipogenic marker genes and inhibited the adipogenic program. In vivo, we constructed adipocity tissue specially SP3 transgenic mice, and the transgenic mice showed a decrease in percent body fat and adipocyte size. We conclude that SP3 is a novel adipose-derived signaling molecule that regulates adipogenesis, and further investigation is needed to uncover the mechanisms underlying the inhibitory effects. This study will push forward the function analysis of SP3 and provide novel molecular targets and new view for the development of treatment strategies for obesity and related diseases.

脂肪分化异常是肥胖发生的关键环节, 因而识别新的参与脂肪分化的调控因子对于我们了解脂肪组织的生理及病理学尤为重要。前期研究应用cDNA微阵方法从脂肪组织中筛选出一个与肥胖相关的新基因，我们命名为SP3。研究发现SP3为分泌蛋白；在脂肪组织高表达且与体脂含量正相关；其表达同时受营养信号（如饥饿、再进食、肥胖和胰岛素抵抗等）的影响。在3T3-L1细胞分化过程中，随脂肪细胞成熟SP3表达逐渐增多，但在整个过程呈双相表达。慢病毒稳转SP3抑制3T3-L1细胞的脂肪分化成熟，且抑制脂肪分化关键转录因子和成熟相关基因的表达；进一步构建SP3脂肪组织特异性转基因小鼠，与对照小鼠相比，转基因动物脂肪组织重量减少和脂肪细胞体积变小。综上，前期研究结果初步提示新的脂肪因子SP3调控脂肪细胞分化，其作用机制尚待进一步深入研究。本项目的开展将会拓展SP3的功能研究，为肥胖及相关疾病的防治提供新的靶点和思路。

脂肪组织是最大的内分泌器官，能够分泌大量的脂肪因子（激素和细胞因子）参与机体的能量代谢。本课题组在该项目的支持下，首次证实SP3为新的脂肪因子，其表达与机体营养状态相关。随后对该基因进行功能研究，发现SP3在3T3-L1脂肪细胞诱导分化过程中呈双相表达趋势，脂肪细胞系中过表达SP3能够抑制脂肪分化成熟,抑制脂肪分化关键转录因子PPAR-γ, C/EBP-α的表达；脂肪组织特异性转基因动物在高脂诱导下体重、体脂含量、脂肪细胞体积数目、胰岛素敏感性、脂肪分化相关脂肪因子和炎症因子的表达较野生对照动物均有差异。综上，体内外实验均证实SP3抑制脂肪细胞分化成熟。进一步机制研究提示SP3抑制脂肪分化作用与其参与转录因子PPAR-γ, C/EBP-α，脂肪成熟marker AP2及炎症因子IL-1-β、IL-6、TNF-α之间的crosstalk相关，目前该部分研究结果已撰写成文，准备投递。课题组在该项目的支持下，进一步研究发现SP3通过调控下丘脑炎症因子IL-1-β、IL-6的表达抑制食欲，该研究结果已发表。综上，本课题组研究结果具有原创性，拓展了目前人们对新的脂肪因子功能研究的认识，为肥胖及其相关代谢紊乱的防治提供新的思路。