Abstract 473: Fluid Shear Stress Specifically Exacerbates Chlamydia pneumoniae-mediated Pro-inflammatory Responses in Monocytes

Abstract

Background and Significance The precise role of Chlamydia pneumoniae infection in various stages of the atherosclerosis is not well understood. During the transit from lung to the atherosclerotic sites, C. pneumoniae-infected monocytes travel through circulation and are subjected to shear stress due to blood flow. Elucidating the effects of these mechanical stimuli on infected monocytes is critical in our understanding of the link between C. pneumoniae infection and atherosclerosis. Objectives We hypothesized that fluid shear stress alters the inflammatory response of C. pneumoniae-infected monocytes. Using an in vitro model of blood flow, we determined the effect of physiological levels of shear stress on monocyte responses pertinent to atherosclerosis including cytokine secretion, adhesion molecule expression, intracellular signaling, and endothelial adhesion. Methods Primary human monocytes and THP-1 cells were infected with C. pneumoniae at an MOI-2 for 2 h at 35 °C with intermittent rocking, and cultured for 36 h. The infected cells were then subjected to a shear stress of 7.5 dyn/cm2 for 1 h, and the supernatants were analyzed for a panel of 17 cytokines, and the cells were analyzed for signaling proteins, surface receptors, and endothelial adhesion. Uninfected cells and static conditions were used as controls, and a P<0.05 (Student’s t-test) was considered significant. Results We observed that shear stress on infected cells resulted in a caspase-independent upregulation of pro-inflammatory IL-1β (3-fold), a modest increase in MIP-1α and MIP-1β, a decrease in anti-inflammatory IL-10, and no change in other cytokines including TNFα and IL-12. These changes were manifested as an increase in the adhesion of monocytes to endothelium activated with the infected supernatants. We also observed differences in the chemotaxis of monocytes exposed to sheared vs. static supernatants. Conclusions We observe that physiological shear stress drives Chlamydia infected monocytes towards a pro-inflammatory state in circulation suggesting a critical synergy between mechanical and chemical factors in atherogenesis.