TUDCA promotes intracellular clearance of Burkholderia pseudomallei by inhibiting endoplasmic reticulum stress-induced apoptosis in RAW264.7 cells

Abstract

Objective To explore the action mechanism of tauroursodeoxycholic acid (TUDCA) promoting intracellular clearance of Burkholderia pseudomallei (B. pseudomallei) in RAW264.7 macrophages. Methods After TUDCA of different concentrations were used to treat RAW264.7 cells pre-infected with B. pseudomallei for 8 h or not, flow cytometry was applied to detect the apoptosis of the infected and control cells. In addition, another endoplasmic reticulum stress (ERS) inhibitor 4-PBA was used to detect the apoptosis and proliferation of host cells after B. pseudomallei infection with Annexin-V/PI double staining and MTT cell proliferation assay. Furthermore, after transfected with CHOP siRNA, Western blotting and flow cytometry were employed to detect the effect of TUDCA on the expression levels of Caspase-3 and Caspase-12 and the changes in apoptotic rate after B. pseudomallei infection, respectively. Finally, the effect of TUDCA on intracellular multiplication of infected RAW264.7 cells were observed to estimate the CFU value in the presence and absence of CHOP siRNA. Results Under different concentrations of TUDCA, 100 or 200 μmol/L TUDCA significantly reduced B. pseudomallei-induced apoptosis in RAW264.7 cells (P < 0.05). Meanwhile, both TUDCA and 4-PBA treatment could decrease the apoptosis induced by B. pseudomallei infection by ERS (P < 0.05). Further, the expression levels of Caspase-3 and Caspase-12 were obviously increased after B. pseudomallei infection compared with uninfected groups, but their expression levels in the siCHOP group was significantly lower than that in the siC group. Besides, flow cytometry also showed that TUDCA could reduce apoptosis induced by B. pseudomallei infection (P < 0.05), but no significant effect of TUDCA on apoptosis was observed under CHOP knockdown. Finally, intracellular CFU assay indicated that TUDCA treatment promoted the host cell clearance of B. pseudomallei (P < 0.05), but no such effect was observed in siCHOP group. Conclusion In B. pseudomallei infected RAW264.7 cells, TUDCA promotes the intracellular clearance of the bacteria by inhibiting ERS-induced apoptosis.

Keywords

• burkholderia pseudomallei
• tauroursodeoxycholic acid
• endoplasmic reticulum stress
• apoptosis