Differential Expression of Mcp-1 and Its Receptor CCR2 in Glucose Primed Human Mesangial Cells

Abstract

Background: Glomerular mononuclear cell infiltration is associated with the development of a diffuse glomerulosclerosis in patients with diabetic nephropathy. Monocyte chemoattractant protein-1 (MCP-1) plays an important role in the recruitment and accumulation of monocytes and lymphocytes within the glomerulus. In the present study, we examined whether the ambient glucose concentration alters the expression of MCP-1 and its receptor CCR2 in primary human mesangial cells (HMC). Methods: MCP-1 mRNA expression was assessed by Northern blot and CCR2 mRNA expression by RT-PCR analysis. MCP-1 protein production was determined by ELISA. Migration studies were performed to assess functional MCP-1 receptor expression. Results: Exposure of HMC to 30 m M D-glucose led to a 30% increase in MCP-1 mRNA expression as compared to 5 m M D-glucose and osmotic controls while there was no difference in MCP-1 protein production. Simultaneously, CCR2 mRNA expression was down-regulated in HMC exposed to 30 m M D-glucose. 5 m M D-glucose primed HMC showed a dose-dependent migration towards MCP-1 that was dose-dependently inhibited by pertussis toxin, the broad-spectrum chemokine antagonist vMIP-II as well as the CCR2 receptor antagonist (1–8del)MCP-1 – demonstrating functional activity of MCP-1 receptor expression in primary HMC. In accordance with the downregulatory effects of 30 m M D-glucose on CCR2 mRNA expression no migratory response towards MCP-1 was observed under these conditions. The additional proinflammatory stimulus TNFα increased MCP-1 protein production in 30 as compared to 5 m M D-glucose primed HMC (2,194 ± 568 vs. 1,422 ± 379 pg MCP-1/10⁴ cells × ml in 30 vs. 5 m M D-glucose primed HMC +24 h TNFα 500 U/ml, p = 0.002). However, this was not associated with an increased MCP-1 mRNA transcription. The 30 m M D-glucose induced downregulation of CCR2 mRNA expression was prevented in the presence of TNFα. Conclusion: High ambient glucose does not affect mesangial MCP-1 release and decreases its CCR2 receptor expression. However, in the presence of an inflammatory stimulus these effects of high glucose are reversed and an autocrine pathway of MCP-1 develops in mesangial cells.