Chlamydia pneumoniae invades into vascular smooth muscle cells through the CXCR4-β-arrestin 2 pathway via TLR2/CXCR4 crosstalk

Abstract

Vascular smooth muscle cell (VSMC) dysfunction plays an important role in the pathogenesis of atherosclerosis. Chlamydia pneumoniae (C. pneumoniae) has been shown to infect and grow in VSMCs, and causes VSMC dysfunction, thereby promoting atherosclerosis development. However, it is an enigma how C. pneumoniae invades into VSMCs. In this study, we explored the specific mechanism of C. pneumoniae invading into VSMCs, and found that TLR2 expression and CXCR4 phosphorylation level were elevated after C. pneumoniae infection, and the translocation of TLR2 and CXCR4 to the membrane were increased at 15 min postinfection and reached the peak at 60 min, and then decreased at 180 min. The interaction between TLR2 and CXCR4 was enhanced in this process by co-immunoprecipitation and proximity ligation assays (PLA). The results from immunofluorescence staining demonstrated that C. pneumoniae invasion rate was dramatically decreased after knockdown of both TLR2 and CXCR4 compared with silencing of either TLR2 or CXCR4. Moreover, during C. pneumoniae invasion into VSMCs, the interaction between CXCR4 and β-arrestin2 was enhanced, and mutation of CXCR4 Ser339 resulted in the lack of β-arrestin2 recruitment. After TLR2 knockdown by siRNA, CXCR4 phosphorylation was decreased, and the translocation of CXCR4 to the membrane was abrogated, and CXCR4 was unable to recruit β-arrestin2 during C. pneumoniae invasion into VSMCs. In conclusion, C. pneumoniae invades into VSMCs through the CXCR4-β-arrestin2 pathway via TLR2/CXCR4 crosstalk, providing the first evidence for TLR2/CXCR4 interaction as well as receptor-mediated intracellular signaling that is exploited for C. pneumoniae invasion.