Stat3β mitigates development of atherosclerosis in apolipoprotein E-deficient mice

The transcription factor Stat3 is an activator of systemic inflammatory genes. Two isoforms of Stat3 are generated by alternative splicing, Stat3α and Stat3β. The β isoform lacks the transactivation domain but retains other functions, including dimerization and DNA binding. Stat3β-deficient mice exhibit elevated expression of systemic inflammatory genes and are hyperresponsive to lipopolysaccharide, suggesting that Stat3β functions predominantly as a suppressor of systemic inflammation. To test whether Stat3β deficiency would provoke pathologic effects associated with chronic inflammation, we asked whether selective removal of Stat3β would exacerbate the development of atherosclerosis in apolipoprotein E-deficient mice. In apoE^-/-Stat3β^-/- mice atherosclerotic plaque formation was significantly enhanced relative to apoE ^-/-Stat3β^+/+ controls. The ability of Stat3β deficiency to promote atherosclerosis was more pronounced in female mice, but could be unmasked in males by feeding a high fat diet. Infiltrating macrophages were not increased in aortas of apoE^-/-Stat3β^-/- mice. In contrast, the proportion of pro-inflammatory T_H17 cells was significantly elevated in aortic infiltrates from apoE ^-/-Stat3β^-/- mice, relative to paired apoE ^-/-Stat3β^+/+ littermates. These observations indicate that Stat3β can suppress pathologic sequelae associated with chronic inflammation. Our findings further suggest that in Stat3β-deficient mice the unopposed action of Stat3α may enhance atherogenesis in part by promoting differentiation of T_H17 cells.