STAT4 regulates CD8+Treg/Tfh cell axis and promotes atherogenesis in insulin-resistant Ldlr−/− mice

The metabolic syndrome support atherosclerosis, but the exact mechanisms for accelerated atherogenesis remain unclear. While the pro-inflammatory role of signal transducer and activator of transcription 4 (STAT4) in atherosclerosis and diet-induced insulin resistance (IR) was recently established, an impact of STAT4 on atherogenesis in conditions of IR is not known. To study the role of STAT4 in IR-accelerated atherosclerosis we generated Stat4 −/− Ldlr −/− mice that were fed a diabetogenic diet with added cholesterol (DDC). DDC fed Stat4 −/− Ldlr −/− mice demonstrated improved glucose tolerance, insulin sensitivity, and a 36% reduction in atherosclerosis compared with Ldlr −/− controls. Interestingly, we detected a reduction in T follicular helper (Tfh) and plasma B cells, but a sharp elevation in CD8 + Tregs in spleens and aortas of Stat4 −/− Ldlr −/− versus Ldlr −/− mice. Similarly, STAT4 deficiency supported CD8 + Treg differentiation in vitro . Additionally, Stat4-deficient CD8 + Tregs suppressed Tfh and germinal center B cell development upon immunization with KLH indicating an important role for STAT4 in CD8 + Treg functions in vivo . Effects of STAT4 deficiency were not only restricted to T cells, but had a significant impact on macrophage phenotype. Stat4 −/− Ldlr −/− macrophages displayed decreased IFNγ and MHC-II expression. Conditioned media from Stat4 −/− Ldlr −/− MFs supported CD8 + Treg but not Tfh cell differentiation in TGFβ-dependent manner, suggesting a role for MF-specific STAT4 in Th cell differentiation. These new findings suggest a novel mechanism by which STAT4 supports atherosclerosis in obese, IR Ldlr−/− mice via increases in MF activation, and modulation of the Tfh/ CD8 + Treg axis systemically and within the aorta.