Chuang Chia Chi, Yang Rong Sen, Tsai Keh Sung, Ho Feng Ming, Liu Shing Hwa
Institute of Toxicology, College of Medicine, National Taiwan University, No. 1, Section 1, Jen-Ai Road, Taipei 10043, Taiwan.
Endocrinology. 2007 Sep;148(9):4267-75. doi: 10.1210/en.2007-0179. Epub 2007 May 31.
The molecular events of hyperglycemia-triggered increase in adipogenic induction of lipid accumulation remain unclear. We examined the effects of hyperglycemia on adipogenic induction of lipid accumulation and its involved signaling molecules, such as phosphoinositide 3-kinase (PI3K), ERKs, and peroxisome proliferator-activated receptor gamma (PPAR gamma). Bone marrow-derived mesenchymal stem cells (MSCs) isolated from FVB/N mice were capable of differentiating into adipocytes in adipogenic medium. The effects of high glucose (HG) (25.5 mm) were assessed in vitro by RT-PCR, ELISA, flow cytometry, immunostaining, and immunoblotting. The in vivo effect of hyperglycemia was further studied in streptozotocin (STZ)-induced diabetic FVB/N mice. Exposure of MSCs to HG enhanced adipogenic induction of lipid accumulation as compared with 5.5 mm glucose. HG increased PPAR gamma expression and PI3K activity and its downstream effector Akt phosphorylation during adipogenesis. Inhibition of PI3K/Akt activity with PI3K inhibitor LY294002 or by expressing the dominant negative p85 or Akt prevented the HG-enhanced PPAR gamma-dependent adipogenic induction of lipid accumulation. Moreover, HG increased the phosphorylation of ERK1/2 during adipogenesis. MAPK/ERK inhibitor PD98059 inhibited the PI3K activity, Akt phosphorylation, and lipid accumulation triggered by HG. PI3K inhibitor LY294002 did not affect the HG-increased ERK1/2 phosphorylation during adipogenesis. We next observed that adipogenic induction of lipid accumulation of MSCs isolated from STZ-induced diabetic mice is enhanced. Moreover, triglyceride, PPAR gamma expression, phosphorylated Akt and ERK1/2, and marrow fat in bones of STZ-diabetic mice were also increased. These results suggest that hyperglycemia enhances the adipogenic induction of lipid accumulation through an ERK1/2-activated PI3K/Akt-regulated PPAR gamma pathway.
高血糖引发脂质积累的脂肪生成诱导增加的分子事件仍不清楚。我们研究了高血糖对脂质积累的脂肪生成诱导及其相关信号分子的影响，如磷酸肌醇3激酶（PI3K）、细胞外调节蛋白激酶（ERK）和过氧化物酶体增殖物激活受体γ（PPARγ）。从FVB/N小鼠分离的骨髓间充质干细胞（MSC）能够在脂肪生成培养基中分化为脂肪细胞。通过逆转录聚合酶链反应（RT-PCR）、酶联免疫吸附测定（ELISA）、流式细胞术、免疫染色和免疫印迹法在体外评估高糖（HG）（25.5 mM）的作用。在链脲佐菌素（STZ）诱导的糖尿病FVB/N小鼠中进一步研究高血糖的体内作用。与5.5 mM葡萄糖相比，将MSC暴露于HG可增强脂质积累的脂肪生成诱导。在脂肪生成过程中，HG增加PPARγ表达、PI3K活性及其下游效应物Akt磷酸化。用PI3K抑制剂LY294002或通过表达显性负性p85或Akt抑制PI3K/Akt活性可阻止HG增强的PPARγ依赖性脂质积累的脂肪生成诱导。此外，在脂肪生成过程中HG增加ERK1/2的磷酸化。丝裂原活化蛋白激酶/ERK抑制剂PD98059抑制HG触发的PI3K活性、Akt磷酸化和脂质积累。PI3K抑制剂LY294002不影响脂肪生成过程中HG增加的ERK1/2磷酸化。接下来我们观察到，从STZ诱导的糖尿病小鼠分离的MSC的脂质积累的脂肪生成诱导增强。此外，STZ糖尿病小鼠的甘油三酯、PPARγ表达、磷酸化的Akt和ERK1/2以及骨髓脂肪也增加。这些结果表明，高血糖通过ERK1/2激活的PI3K/Akt调节的PPARγ途径增强脂质积累的脂肪生成诱导。
