Inhibition of miR-497 Attenuates Oral Submucous Fibrosis by Inhibiting Myofibroblast Transdifferentiation in Buccal Mucosal Fibroblasts

PURPOSE

Oral submucous fibrosis (OSF) is a common chronic condition with poor prognosis, and existing therapies for OSF are limited in effectiveness. This study was designed to explore the role of miR-497 in arecoline (AR)-induced OSF.

MATERIALS AND METHODS

After miR-497 was silenced or overexpressed in buccal mucosa fibroblasts (BMFs), different concentrations of AR (5-200 μg/ml) were applied to incubate BMFs, and 50 μg/ml of AR was chosen for subsequent experiments. Thereafter, collagen gel contraction assay was used to detect the contractile capacity of BMFs. Transwell assay and wound healing assay were applied to detect migration and invasiveness of the cells. In addition, immunofluorescence staining, qRT-PCR and western blot were conducted to measure the expression of miR-497, collagen I and α-SMA, as well as the phosphorylation of Smad2 and Smad3.

RESULTS

After successful inhibition or overexpression of miR-497 in AR-induced BMFs, the results showed that miR- 497 inhibition suppressed the contractility, migration and invasiveness of AR-induced BMFs, whereas overexpression of miR-497 produced the opposite. In addition, miR-497 inhibition down-regulated the expression level of collagen I and α-SMA in AR-exposed BMFs. Furthermore, TGF-β1 expression, Smad2 and Smad3 phosphorylation were also repressed in AR-induced BMFs after miR-497 inhibition. Correspondingly, overexpression of miR-497 reversed the expression of the aforementioned proteins.

CONCLUSION

miR-497 inhibition may attenuate OSF by inhibiting myofibroblast transdifferentiation in BMFs via the TGF-β1/Smads signaling pathway, indicating that miR-497 might represent an underlying target for treating OSF.

Arecoline-induced myofibroblast transdifferentiation from human buccal mucosal fibroblasts is mediated by ZEB1

Oral submucous fibrosis (OSF) is considered as a pre-cancerous condition of the oral mucosa and is highly associated with habitual areca quid chewing. Arecoline is the major alkaloid in areca quid and is thought to be involved in the pathogenesis of OSF. Our previous studies have demonstrated that arecoline could induce epithelial–mesenchymal transition (EMT)-related factors in primary human buccal mucosal fibroblasts (BMFs). Therefore, we investigated the expression of zinc finger E-box binding homeobox 1 (ZEB1), which is a well-known transcriptional factor in EMT, in OSF tissues and its role in arecoline-induced myofibroblast transdifferentiation from BMFs. The expression of ZEB1, as well as the myofibroblast marker α-smooth muscle actin (α-SMA), was significantly increased in OSF tissues, respectively. With immunofluorescence analysis, arecoline induced the formation of α-SMA-positive stress fibres in BMFs expressing nuclear ZEB1. Arecoline also induced collagen contraction of BMFs in vitro. By chromatin immunoprecipitation, the binding of ZEB1 to the α-SMA promoter in BMFs was increased by arecoline. The promoter activity of α-SMA in BMFs was also induced by arecoline, while knockdown of ZEB1 abolished arecoline-induced α-SMA promoter activity and collagen contraction of BMFs. Long-term exposure of BMFs to arecoline induced the expression of fibrogenic genes and ZEB1. Silencing of ZEB1 in fibrotic BMFs from an OSF patient also suppressed the expression of α-SMA and myofibroblast activity. Inhibition of insulin-like growth factor receptor-1 could suppress arecoline-induced ZEB1 activation in BMFs. Our data suggest that ZEB1 may participate in the pathogenesis of areca quid–associated OSF by activating the α-SMA promoter and inducing myofibroblast transdifferentiation from BMFs.

Regulation of protease-activated receptor-1 expression in human buccal fibroblasts stimulated with arecoline

BACKGROUND

The purpose of this study was to compare the major thrombin receptor protease-activated receptor-1 (PAR-1) expression in normal human buccal mucosa and oral submucous fibrosis (OSF) specimens and further explore the potential mechanisms that may lead to induce PAR-1 expression.

METHODS

Thirty OSF and 10 normal buccal mucosa specimens were examined by immunohistochemistry. Buccal mucosal fibroblasts (BMFs) were challenged with arecoline by using Western blot analysis. N-acetyl-L-cysteine (NAC), LY294002, herbimycin A, NS-398, and PD98059 were added to find the possible regulatory mechanisms.

RESULTS

PAR-1 expression was significantly higher in OSF specimens (p < .05). Arecoline was found to elevate PAR-1 expression in a dose-dependent and time-dependent manner (p < .05). The addition of NAC, LY294002, herbimycin A, NS398, and PD98059 markedly inhibited the arecoline-induced PAR-1 expression (p < .05).

CONCLUSION

PAR-1 expression is significantly upregulated in areca quid chewing-associated OSF. Arecoline-induced PAR-1 expression was downregulated by NAC, LY294002, herbimycin A, NS398, and PD98059.