ROLE OF CALPAIN ON THE DIFFERENTIATION AND FUNCTION OF ADIPOCYTES

Calpain是一种钙激活的非溶酶体中性硫醇蛋白酶（EC 3.4.22.17），存在于多种真核细胞中。钙蛋白酶通常以非活性形式存在，并被钙离子和磷脂激活。在3T3-L1前脂肪细胞分化的有丝分裂克隆扩增阶段，钙蛋白酶的活性是必需的。我们研究了阻断钙蛋白酶活性可以增强成人原始间充质ST-13前脂肪细胞的脂肪形成，而使用标准激素分化ST-13前脂肪细胞不需要有丝分裂克隆扩增。我们还研究了钙蛋白酶阻断是否会诱导成熟ST-13脂肪细胞的胰岛素抵抗。将ST-13前脂肪细胞暴露于calpain抑制剂N-benzyloxycarbonyl-L-leucyl-L-leucinal或calpastatin（一种特定的内源性calpain抑制剂）的过表达，刺激了脂肪细胞表型的获得。calpastatin在ST-13脂肪细胞中的过表达可刺激脂肪细胞特异性CCAAT/增强子结合蛋白a （C/EBP α）、过氧化物酶体增殖物激活受体γ (PPARγ)、甾醇调节元件结合蛋白1 （SREBP-1）和胰岛素信号分子、胰岛素受体α、胰岛素受体底物和GLUT4的表达。然而，胰岛素刺激的葡萄糖摄取减少了约52%。这些结果表明，与胚胎3T3-L1前脂肪细胞相比，钙蛋白酶可负调控成人原始间充质ST-13前脂肪细胞的脂肪形成，并且钙蛋白酶是成熟ST-13脂肪细胞中胰岛素刺激的葡萄糖摄取所必需的。

Calpain is a calcium-activated non-lysosomal neutral thiol protease (EC 3.4.22.17) present in a wide variety of eukaryotic cells. Calpain is usually present as an inactive form and is activated by calcium ions and phospholipids. The activity of calpain is required during the mitotic clonal expansion phase of 3T3-L1 preadipocyte differentiation. We addressed that blocking calpain activity enhances the adipogenesis of adult primitive mesenchymal ST-13 preadipocytes, the differentiation of which using standard hormones does not require mitotic clonal expansion. We also examined whether a calpain blockade induces insulin resistance in mature ST-13 adipocytes. Exposing ST-13 preadipocytes to the calpain inhibitor, N-benzyloxycarbonyl-L-leucyl-L-leucinal or to the overexpression of calpastatin, a specific endogenous inhibitor of calpain, stimulated acquisition of the adipocyte phenotype. Overexpression of calpastatin in ST-13 adipocytes stimulated the expression of the adipocyte-specific CCAAT/enhancer-binding protein a (C/EBP α), peroxisome proliferator-activated receptor γ (PPARγ), sterol regulatory element-binding protein 1 (SREBP-1) and the insulin signaling molecules, insulin receptor α, insulin-receptor substrates and GLUT4. However, insulin-stimulated glucose uptake was reduced by approximately 52%. These results suggest that calpain negatively regulates adipogenesis in adult primitive mesenchymal ST-13 preadipocytes in contrast to that of embryonic 3T3-L1 preadipocytes and is required for the insulin-stimulated glucose uptake in mature ST-13 adipocytes.