Mycophenolic Acid Displays IMPDH-Dependent and IMPDH-Independent Effects on Renal Fibroblast Proliferation and Function

Abstract

The aim of this study was to elucidate the role of mycophenolic acid (MPA) in cellular pathways of renal fibrosis. Different assays were applied in a renal fibroblast model using COS-7 cells: assays for cell proliferation, scratch wound closure and collagen matrix contraction, gene quantification, and Western blotting. The results indicate that MPA treatment leads to inosine monophosphate dehydrogenase (IMPDH)-dependent inhibition of fibroblast proliferation and wound closure as well as an unexpected IMPDH-independent inhibition of collagen matrix contraction. Interestingly, the IMPDH-independent expression of CTGF after 6 hours incubation with MPA was significantly decreased; however, it became significantly increased and IMPDH-dependent after 24 hours of incubation and longer. Increased mRNA level of COL1A1, TGFbeta1, and TNFalpha was observed after MPA treatment. An unanticipated finding was the divergent and late MPA effect leading to a significant increase of TGFbeta1 and CTGF gene expression. The results suggest that long-term incubation with MPA alters signals located upstream of transforming growth factor-beta. Furthermore, the protein expression of the apoptotic marker ANXA5 was analyzed in the cell line to exclude apoptosis-related effects using 0.1 to 100 micromol/L MPA. Moreover, in COL4A3-deficient mice treated with different doses of mycophenolate mofetil, we found no significant differences in the gene expression of the same genes supporting the idea of a TGFbeta-independent pathway of tubulointerstitial fibrosis in this model for progressive renal disease. In conclusion, the current study indicates that MPA displays IMPDH-dependent and IMPDH-independent effects on renal fibroblast proliferation and function as well as complex signal transduction in COS-7-cells. Alternative inhibitory pathways may contribute to antifibrotic effect of MPA.