Tartare-Deckert S, Chavey C, Monthouel M N, Gautier N, Van Obberghen E
Institut National de la Santé et de la Recherche Médicale U145, IFR 50, Avenue de Valombrose, 06107 Nice Cédex 2, France.
J Biol Chem. 2001 Jun 22;276(25):22231-7. doi: 10.1074/jbc.M010634200. Epub 2001 Apr 9.
Alterations in the expression level of genes may contribute to the development and pathophysiology of obesity. To find genes differentially expressed in adipose tissue during obesity, we performed suppression subtractive hybridization on epididymal fat mRNA from goldthioglucose (GTG) obese mice and from their lean littermates. We identified the secreted protein acidic and rich in cysteine (SPARC), a protein that mediates cell-matrix interactions and plays a role in modulation of cell adhesion, differentiation, and angiogenesis. SPARC mRNA expression in adipose tissue was markedly increased (between 3- and 6-fold) in three different models of obesity, i.e. GTG mice, ob/ob mice, and AKR mice, after 6 weeks of a high fat diet. Immunoblotting of adipocyte extracts revealed a similar increase in protein level. Using a SPARC-specific ELISA, we demonstrated that SPARC is secreted by isolated adipocytes. We found that insulin administration to mice increased SPARC mRNA in the adipose tissue. Food deprivation had no effect on SPARC expression, but after high fat refeeding SPARC mRNA levels were significantly increased. Our results reveal both hormonal and nutritional regulation of SPARC expression in the adipocyte, and importantly, its alteration in obesity. Finally, we show that purified SPARC increased mRNA levels of plasminogen activator inhibitor 1 (PAI-1) in cultured rat adipose tissue suggesting that elevated adipocyte expression of SPARC might contribute to the abnormal expression of PAI-1 observed in obesity. We propose that SPARC is a newly identified autocrine/paracrine factor that could affect key functions in adipose tissue physiology and pathology.
基因表达水平的改变可能有助于肥胖症的发生发展及其病理生理学过程。为了找到肥胖期间在脂肪组织中差异表达的基因，我们对来自金硫葡萄糖（GTG）肥胖小鼠及其瘦的同窝小鼠的附睾脂肪mRNA进行了抑制性消减杂交。我们鉴定出了富含半胱氨酸的酸性分泌蛋白（SPARC），该蛋白介导细胞与基质的相互作用，并在调节细胞黏附、分化和血管生成中发挥作用。在高脂饮食6周后，三种不同的肥胖模型，即GTG小鼠、ob/ob小鼠和AKR小鼠的脂肪组织中，SPARC mRNA表达显著增加（3至6倍）。脂肪细胞提取物的免疫印迹显示蛋白水平有类似的增加。使用SPARC特异性酶联免疫吸附测定，我们证明SPARC由分离的脂肪细胞分泌。我们发现给小鼠注射胰岛素会增加脂肪组织中的SPARC mRNA。禁食对SPARC表达没有影响，但高脂再喂养后SPARC mRNA水平显著增加。我们的结果揭示了脂肪细胞中SPARC表达的激素和营养调节，重要的是，其在肥胖中的改变。最后，我们表明纯化的SPARC会增加培养的大鼠脂肪组织中纤溶酶原激活物抑制剂1（PAI-1）的mRNA水平，这表明脂肪细胞中SPARC表达的升高可能导致肥胖中观察到的PAI-1异常表达。我们提出SPARC是一种新鉴定的自分泌/旁分泌因子，可能影响脂肪组织生理和病理中的关键功能。
