Social Isolation Stress Provokes Atherosclerosis Through HPA-axis Over-Activation, Toll- Like Receptors, and Macrophage Polarization

Abstract Background: It has been well documented that social isolation stress (SIS) can accelerate the formation of atherosclerotic plaque through inflammation. In this regard, this study aimed to elucidate the relation between HPA-axis, toll-like receptors (TLRs), as well as M1/M2 macrophage ratio and atherosclerosis in socially isolated (SI) animals.Methods: We used small interfering RNA (siRNA) against the glucocorticoid receptor (GR) to evaluate the relation between HPA-axis and TLRs. RT-PCR, ELISA, flow cytometry, and immunohistochemistry were used to assess any relation between atherosclerosis and TLRs, M1/M2 ratio, pro-inflammatory cytokines, and cell adhesion molecules in aortic tissue. Finally, we used TAK-242 (0.3 mg/kg, intraperitoneally), a selective antagonist of TLR4, as a possible prophylactic agent in formation of atherosclerotic plaque in-vivo.Results: We observed that SI animals had higher serum concentration of corticosterone and higher body weight in comparison to normal animals. In SI animals, results of in-vitro study showed that knocking-down of the GR in bone marrow–derived monocytes significantly decreased the expression of TLR4. In-vivo study suggested higher expression of TLR4 on circulating monocytes and higher M1/M2 ratio in aortic samples. Pathological study showed a mild formation of pre-atherosclerotic changes in SI animals. Finally, we observed that treating animals with TAK-242 could significantly inhibit the formation of pre-atherosclerotic changes.Conclusion: SIS can possibly increase the risk of atherosclerosis through over-activating HPA-axis and subsequently led to TLR4 up-regulation, tissue inflammation, high M1/M2 ratio in endothelium. Thus, TLR4 inhibitors might be a novel treatment to reduce the risk of atherosclerosis-induced by chronic stress.