Objective: To explore the effect of C-reactive protein (CRP) on the expression of Fcγ receptors in human renal tubular epithelial cells and determine the role of Fcγ receptors in CRP-induced expression of transforming growth factor β1 (TGFβ1).
Methods: Human renal tubular epithelial cells (HK-2) were cultured and stimulated with recombinant human CRP. The mRNA expression of Fcγ receptors, including FcγRI (CD64), FcγRIIa (CD32a) and FcγRIII (CD16), was detected by real-time polymerase chain reaction (PCR). On the basis of real-time PCR results, CD32a was selected for further analysis: the CD32a expression in HK-2 cells incubated with 10 mg/L CRP for 24 h was determined by flow cytometry and Western blotting. HK-2 cells were preincubated with or without anti-CD32a IgG, followed by the addition of recombinant human CRP. Subsequently the biological effects of CRP were tested. TGFβ1, type I collagen (ColI) and type IV collagen (ColIV) released into media were detected by enzyme-linked immunosorbent assay. And TGFβ1 mRNA expression was measured by real-time PCR.
Results: On real-time PCR, CRP was found to significantly up-regulate the CD32a mRNA expression in HK-2 cells in a dose-dependent manner (P < 0.01). The peak up-regulation was observed at a dose of 10 mg/L. In contrast, mRNAs of CD16 and CD64 were not detected in HK-2 cells. Flow cytometry showed that CD32a expressed on HK-2 cells incubated with 10 mg/L recombinant human CRP for 24 h accounted for 23.35% ± 7.43%, significantly higher than that on non-CRP-treated cells (1.66% ± 0.28%, P < 0.01). Western blotting showed that CRP up-regulated CD32a expression in a dose-dependent manner. And 10 mg/L CRP induced the peak effect. Antibodies to CD32a inhibited the stimulatory effect of CRP on the generation of TGFβ1, ColI and ColIV (all P < 0.05) and down-regulated the expression of TGFβ1 mRNA (P < 0.01).
Conclusion: The stimulation of CRP can significantly increase CD32a expression in renal tubular epithelial cells and up-regulate the expression of transforming growth factor TGFβ1 through CD32a receptor.