Key Laboratory of Nutrition and Metabolism, Institute for Nutritional Sciences, Graduate School of the Chinese Academy of Sciences, Chinese Academy of Sciences, Shanghai, China.
PLoS One. 2011 May 11;6(5):e19559. doi: 10.1371/journal.pone.0019559.
Amylin is the most abundant component of islet amyloid implicated in the development of type 2 diabetes. Plasma amylin levels are elevated in individuals with obesity and insulin resistance. Monocyte chemoattractant protein-1 (MCP-1, CCL2) is involved in insulin resistance of obesity and type 2 diabetes. We investigated the effect of MCP-1 on amylin expression and the underlying mechanisms with murine pancreatic β-cell line MIN6 and pancreatic islets.
METHODOLOGY/PRINCIPAL FINDINGS: We found that MCP-1 induced amylin expression at transcriptional level and increased proamylin and intermediate forms of amylin at protein level in MIN6 cells and islets. However, MCP-1 had no effect on the expressions of proinsulin 1 and 2, as well as prohormone convertase (PC) 1/3 and PC2, suggesting that MCP-1 specifically induces amylin expression in β-cells. Mechanistic studies showed that although there is no detectable CCR2 mRNA in MIN6 cells and islets, pretreatment of MIN6 cells with pertussis toxin inhibited MCP-1 induced amylin expression, suggesting that alternative Gi-coupled receptor(s) mediates the inductive effect of MCP-1. MCP-1 rapidly induced ERK1/2 and JNK phosphorylation. Inhibitors for MEK1/2 (PD98059), JNK (SP600125) or AP1 (curcumin) significantly inhibited MCP-1-induced amylin mRNA expression. MCP-1 failed to induce amylin expression in pancreatic islets isolated from Fos knockout mice. EMSA showed that JNK and ERK1/2 were involved in MCP-1-induced AP1 activation. These results suggest that MCP-1 induces murine amylin expression through AP1 activation mediated by ERK1/2 or JNK. Further studies showed that treatment of MIN6 cells with NF-κB inhibitor or overexpression of IκBα dominant-negative construct in MIN6 cells significantly inhibited MCP-1-induced amylin expression, suggesting that NF-κB related signaling also participates in MCP-1-induced murine amylin expression.
CONCLUSIONS/SIGNIFICANCE: MCP-1 induces amylin expression through ERK1/2/JNK-AP1 and NF-κB related signaling pathways independent of CCR2. Amylin upregulation by MCP-1 may contribute to elevation of plasma amylin in obesity and insulin resistance.
胰岛淀粉样多肽是 2 型糖尿病发病过程中涉及的最丰富的成分。肥胖和胰岛素抵抗个体的血浆胰岛淀粉样多肽水平升高。单核细胞趋化蛋白-1（MCP-1，CCL2）参与肥胖和 2 型糖尿病的胰岛素抵抗。我们研究了 MCP-1 对胰岛β细胞系 MIN6 细胞和胰岛中胰岛淀粉样多肽表达的影响及其潜在机制。
方法/主要发现：我们发现 MCP-1 在 MIN6 细胞和胰岛中诱导转录水平的胰岛淀粉样多肽表达，并增加前胰岛淀粉样多肽和胰岛淀粉样多肽的中间形式。然而，MCP-1 对前胰岛素 1 和 2 以及前激素转化酶（PC）1/3 和 PC2 的表达没有影响，表明 MCP-1 特异性诱导β细胞中的胰岛淀粉样多肽表达。机制研究表明，尽管 MIN6 细胞和胰岛中没有检测到可检测的 CCR2 mRNA，但 MIN6 细胞的百日咳毒素预处理抑制了 MCP-1 诱导的胰岛淀粉样多肽表达，表明替代 Gi 偶联受体（s）介导 MCP-1 的诱导作用。MCP-1 可快速诱导 ERK1/2 和 JNK 磷酸化。MEK1/2（PD98059）、JNK（SP600125）或 AP1（姜黄素）抑制剂显著抑制 MCP-1 诱导的胰岛淀粉样多肽 mRNA 表达。从 Fos 敲除小鼠分离的胰岛中，MCP-1 未能诱导胰岛淀粉样多肽表达。EMSA 显示 JNK 和 ERK1/2 参与 MCP-1 诱导的 AP1 激活。这些结果表明，MCP-1 通过 ERK1/2 或 JNK 介导的 AP1 激活诱导鼠胰岛淀粉样多肽表达。进一步的研究表明，MIN6 细胞中 NF-κB 抑制剂的处理或 MIN6 细胞中 IκBα显性负性构建体的过表达显著抑制 MCP-1 诱导的胰岛淀粉样多肽表达，表明 NF-κB 相关信号也参与 MCP-1 诱导的鼠胰岛淀粉样多肽表达。
结论/意义：MCP-1 通过独立于 CCR2 的 ERK1/2/JNK-AP1 和 NF-κB 相关信号通路诱导胰岛淀粉样多肽表达。MCP-1 诱导的胰岛淀粉样多肽上调可能导致肥胖和胰岛素抵抗患者血浆胰岛淀粉样多肽水平升高。
