Bacterial DNA promotes proliferation of rat pancreatic stellate cells thorough toll-like receptor 9: potential mechanisms for bacterially induced fibrosis

We hoped to clarify the possible role of CpG DNA as a trigger factor for overt pancreatic inflammation of pancreatic stellate cells (PSCs). Pancreatic stellate cells were isolated from the male Lewis rat. The expression of Toll-like receptor 9 (TLR9) messenger RNA and protein were evaluated by reverse transcription-polymerase chain reaction and immunofluorescent cytochemistry. Internalization of CpG DNA was analyzed by confocal laser scanning microscopy. Pancreatic stellate cells were incubated with CpG DNA, and then cell proliferation and migration were assessed. Constitutive expression of TLR9 occurs at the messenger RNA and protein levels. After several minutes of CpG DNA administration, CpG DNA was observed on the cell membrane surface and in the cytoplasm and found to be translocating into the perinucleus of PSCs. Pancreatic stellate cells migrated and proliferated in dose- and time-dependent manners in response to simulation by CpG DNA. Proliferation of PSCs was observed 3 hours after administration (earlier than platelet-derived growth factor-induced proliferation), suggesting that PSCs respond readily to provide innate immunity. Endosomal acidification inhibitors attenuated CpG DNA-induced signaling, leading to suppression of DNA synthesis by PSCs. Our findings demonstrate that bacterial DNA promotes migration and proliferation of PSCs and suggest that bacterial DNA can initiate and sustain pancreatic inflammation and fibrosis by means of TLR9.