Inhibition of IkB Degradation Reduces Collagen Production via Downregulation of Androgen Receptor Expression in Dihydropyridine-Induced Gingival Overgrowth Cells

The dihydropyridine-induced gingival overgrowth (DIGO) is one of the side effects in hypertension patients during the treatment. DIGO is aggravated by inflammation and collagen accumulation. Nifedipine, one of the dihydropyridines, causes the gingival overgrowth through androgen receptor (AR) and transforming growth factor (TGF)-beta1 signaling in patients. Until now, there is no medication for the drug-induced gingival overgrowth, it is needed to research for DIGO treatment. This project aims to verify the mechanism of DIGO and to develop drugs for the disease. We first assure that proteasome inhibitors attenuate IL-β- and nifidipine-induced collagen overproduction in cultured gingival fibroblasts, and the further study will assess the therapeutic efficiency of the inhibitors in DIGO rat. In the 1st year, based on the preliminary results, we observed that the nuclear factor (NF)-κB was associated with DNA probe derived from the AR promoter, and the further study will confirm that NF-κB indeed binds to AR gene promoter in gingival fibroblast. By site directed mutagenesis, we will determine the role of NF-κB binding on AR promoter activity. In addition, we also evaluate whether PI3K and AKT are involved in NF-κB-mediated AR expression In the 2nd year, based on proteasome inhibitors suppress inflammatory reaction by preventing IκB degradation, we will examine whether proteasome inhibitors (MG132, epigallocatechin gallate (EGCG) and bortezomib) decrease the AR expression through attenuating NF-κB binding to AR promoter. The effect of proteasome inhibitors on AR-mediated collagen production will be studied. For specificity, the transfection of shRNA targeting proteasome subunits will also be used to confirm the importance of NF-κB in AR promoter activity. In the 3rd year, based on the in vitro study in the past two years, we find that proteasome inhibitors decrease IL-β and/or nifedipine-induced collagen production in gingival fibroblast, the treatment should be applied in animal models of DIGO. The nifedipine-induced DIGO rat model will be established, and then we will evaluate the efficacy and safety of bortezomib and/or EGCG in DIGO rats, the possible undesirable side effects are also be noted. We expect proteasome inhibitors act as a potent therapeutic drug for the treatment of DIGO by the suppression of NF-κB-induced AR promoter activity, and then subsequently reducing collagen production.