Kharroubi I, Lee C-H, Hekerman P, Darville M I, Evans R M, Eizirik D L, Cnop M
Laboratory of Experimental Medicine, Université Libre de Bruxelles, CP-618, 808 Route de Lennik, Brussels, 1070, Belgium.
Diabetologia. 2006 Oct;49(10):2350-8. doi: 10.1007/s00125-006-0366-5. Epub 2006 Aug 5.
AIMS/HYPOTHESIS: Inflammatory mediators contribute to pancreatic beta cell death in type 1 diabetes. Beta cells respond to cytokine exposure by activating gene networks that alter cellular metabolism, induce chemokine release (thereby increasing insulitis), and cause apoptosis. We have previously shown by microarray analysis that exposure of INS-1E cells to IL-1beta + IFN-gamma induces the transcription factor peroxisome proliferator-activated receptor (Ppar)-delta and several of its target genes. PPAR-delta controls cellular lipid metabolism and is a major regulator of inflammatory responses. We therefore examined the role of PPAR-delta in cytokine-treated beta cells.
Primary beta cells that had been purified by fluorescence-activated cell sorting and INS-1E cells were cultured in the presence of the cytokines TNF-alpha, IL-1beta, or IL-1beta + IFN-gamma, or the synthetic PPAR-delta agonist GW501516. Gene expression was analysed by real-time PCR. PPAR-delta, monocyte chemoattractant protein (MCP-1, now known as CCL2) promoter and NF-kappaB activity were determined by luciferase reporter assays.
Exposure of primary beta cells or INS-1E cells to cytokines induced Ppar-delta mRNA expression and PPAR-delta-dependent CD36, lipoprotein lipase, acyl CoA synthetase and adipophilin mRNAs. Cytokines and the PPAR-delta agonist GW501516 also activated a PPAR-delta response element reporter in beta cells. Unlike immune cells, neither INS-1E nor beta cells expressed the transcriptional repressor B-cell lymphoma-6 (BCL-6). As a consequence, PPAR-delta activation by GW501516 did not decrease cytokine-induced Mcp-1 promoter activation or mRNA expression, as reported for macrophages. Transient transfection with a BCL-6 expression vector markedly reduced Mcp-1 promoter and NF-kappaB activities in beta cells.
CONCLUSIONS/INTERPRETATION: Cytokines activate the PPAR-delta gene network in beta cells. This network does not, however, regulate the pro-inflammatory response to cytokines because beta cells lack constitutive BCL-6 expression. This may render beta cells particularly susceptible to propagating inflammation in type 1 diabetes.
目的/假设：炎症介质在1型糖尿病中导致胰腺β细胞死亡。β细胞通过激活改变细胞代谢、诱导趋化因子释放（从而加剧胰岛炎）并导致细胞凋亡的基因网络来响应细胞因子暴露。我们之前通过微阵列分析表明，将INS-1E细胞暴露于白细胞介素-1β + 干扰素-γ会诱导转录因子过氧化物酶体增殖物激活受体（Ppar）-δ及其几个靶基因。PPAR-δ控制细胞脂质代谢，是炎症反应的主要调节因子。因此，我们研究了PPAR-δ在细胞因子处理的β细胞中的作用。
通过荧光激活细胞分选纯化的原代β细胞和INS-1E细胞在细胞因子肿瘤坏死因子-α、白细胞介素-1β或白细胞介素-1β + 干扰素-γ，或合成的PPAR-δ激动剂GW501516存在的情况下培养。通过实时PCR分析基因表达。通过荧光素酶报告基因测定法测定PPAR-δ、单核细胞趋化蛋白（MCP-1，现称为CCL2）启动子和核因子-κB活性。
将原代β细胞或INS-1E细胞暴露于细胞因子会诱导Ppar-δ mRNA表达以及PPAR-δ依赖性的CD36、脂蛋白脂肪酶、酰基辅酶A合成酶和脂肪亲和素mRNA。细胞因子和PPAR-δ激动剂GW501516也激活了β细胞中的PPAR-δ反应元件报告基因。与免疫细胞不同，INS-1E细胞和β细胞均不表达转录抑制因子B细胞淋巴瘤-6（BCL-6）。因此，GW501516激活PPAR-δ不会像巨噬细胞那样降低细胞因子诱导的Mcp-1启动子激活或mRNA表达。用BCL-6表达载体进行瞬时转染可显著降低β细胞中Mcp-1启动子和核因子-κB活性。
结论/解读：细胞因子激活β细胞中的PPAR-δ基因网络。然而，该网络并不调节对细胞因子的促炎反应，因为β细胞缺乏组成型BCL-6表达。这可能使β细胞在1型糖尿病中特别容易引发炎症。
