Cantley James, Burchfield James G, Pearson Gemma L, Schmitz-Peiffer Carsten, Leitges Michael, Biden Trevor J
Diabetes and Obesity Research Program, Garvan Institute of Medical Research, Darlinghurst, New South Wales, Australia.
Diabetes. 2009 Aug;58(8):1826-34. doi: 10.2337/db09-0132. Epub 2009 Apr 28.
Insufficient insulin secretion is a hallmark of type 2 diabetes, and exposure of beta-cells to elevated lipid levels (lipotoxicity) contributes to secretory dysfunction. Functional ablation of protein kinase C epsilon (PKCepsilon) has been shown to improve glucose homeostasis in models of type 2 diabetes and, in particular, to enhance glucose-stimulated insulin secretion (GSIS) after lipid exposure. Therefore, we investigated the lipid-dependent mechanisms responsible for the enhanced GSIS after inactivation of PKCepsilon.
We cultured islets isolated from PKCepsilon knockout (PKCepsilonKO) mice in palmitate prior to measuring GSIS, Ca(2+) responses, palmitate esterification products, lipolysis, lipase activity, and gene expression.
The enhanced GSIS could not be explained by increased expression of another PKC isoform or by alterations in glucose-stimulated Ca(2+) influx. Instead, an upregulation of the amplifying pathways of GSIS in lipid-cultured PKCepsilonKO beta-cells was revealed under conditions in which functional ATP-sensitive K(+) channels were bypassed. Furthermore, we showed increased esterification of palmitate into triglyceride pools and an enhanced rate of lipolysis and triglyceride lipase activity in PKCepsilonKO islets. Acute treatment with the lipase inhibitor orlistat blocked the enhancement of GSIS in lipid-cultured PKCepsilonKO islets, suggesting that a lipolytic product mediates the enhancement of glucose-amplified insulin secretion after PKCepsilon deletion.
Our findings demonstrate a mechanistic link between lipolysis and the amplifying pathways of GSIS in murine beta-cells, and they suggest an interaction between PKCepsilon and lipolysis. These results further highlight the therapeutic potential of PKCepsilon inhibition to enhance GSIS from the beta-cell under conditions of lipid excess.
胰岛素分泌不足是2型糖尿病的一个标志，β细胞暴露于升高的脂质水平（脂毒性）会导致分泌功能障碍。已表明蛋白激酶Cε（PKCε）的功能缺失可改善2型糖尿病模型中的葡萄糖稳态，特别是在脂质暴露后增强葡萄糖刺激的胰岛素分泌（GSIS）。因此，我们研究了PKCε失活后导致GSIS增强的脂质依赖性机制。
在测量GSIS、Ca(2+)反应、棕榈酸酯化产物、脂肪分解、脂肪酶活性和基因表达之前，我们将从PKCε基因敲除（PKCεKO）小鼠分离的胰岛在棕榈酸中培养。
GSIS增强不能用另一种PKC同工型表达增加或葡萄糖刺激的Ca(2+)内流改变来解释。相反，在功能性ATP敏感性钾（K(+)）通道被绕过的条件下，发现脂质培养的PKCεKOβ细胞中GSIS的放大途径上调。此外，我们显示PKCεKO胰岛中棕榈酸酯化为甘油三酯池的酯化增加，脂肪分解速率和甘油三酯脂肪酶活性增强。用脂肪酶抑制剂奥利司他进行急性处理可阻断脂质培养的PKCεKO胰岛中GSIS的增强，这表明一种脂解产物介导了PKCε缺失后葡萄糖放大的胰岛素分泌的增强。
我们的研究结果证明了小鼠β细胞中脂肪分解与GSIS放大途径之间的机制联系，并提示PKCε与脂肪分解之间存在相互作用。这些结果进一步突出了在脂质过量条件下抑制PKCε以增强β细胞GSIS的治疗潜力。
