P690Macrophage Stat3 promotes progression of aortic dissection via M1 differentiation and smooth muscle dedifferentiation

Aortic dissection (AD) is a common and fatal aortic disease for which molecular pathogenesis is largely unknown. Mutations of genes that are specific for differentiated smooth muscle cells (SMCs), including myosin heavy chain and smooth muscle alpha-actin, are causally involved in familial AD, indicating that abnormal differentiation of SMCs may underlie the pathogenesis of AD. On the other hand, animal experiments indicate the critical role of inflammatory cytokines including IL-6 and MCP-1 in AD pathogenesis. It is unknown how SMC differentiation and inflammatory response are related to each other in the context of AD. To understand the linkage between inflammatory response and smooth muscle phenotype, we deleted Socs3 gene specifically in macrophages (mSocs3-KO) to augment the Stat3 activity in mice and compared them with wild type mice (WT). We used a mouse model of aortic stress that was induced by periaortic application of CaCl2 and continuous infusion of angiotensin II (Ca+AngII) as previously reported (Sci Rep 4:4051). After applying Ca+AngII, aorta initially showed no morphological changes (stress-intact), which was followed by the development of a minor injury (<0.2 mm in length) at the branching point of the celiac artery (stress-injury). Later, the minor injury progressed to the fully developed AD with hematoma that extended above the celiac artery. One week after the Ca+AngII treatment, WT aorta showed 59% of stress-intact, 36% of stress-injury and 5% of AD. At the same time point, mSocs3-KO aorta showed 54% of stress-intact, 41% of stress-injury and 5% of AD, showing no significant difference compared to WT. However, 6 weeks after the Ca+AngII treatment, mSocs3-KO aorta showed 25% of AD, whereas WT aorta showed only 11% of AD, indicating that Stat3 in macrophages promoted the progression of AD. Immunostaining and imaging cytometry demonstrated higher Stat3 activity in macrophages in mSocs3-KO compared to WT both at the stage of stress-intact and at the stage of stress-injury. Macrophages in mSocs3-KO aorta at the stage of stress-injury showed higher M1/M2 ratio compared to WT. Immunoblotting of SMemb revealed functional dedifferentiation of SMCs at the stage of stress-injury both in WT and mSocs3-KO. Interestingly, mSocs3-KO showed functional dedifferentiation of SMCs at the stage of stress-intact, whereas WT showed normal differentiation of SMCs at this stage. Accelerated dedifferentiation of SMCs in mSocs3-KO was associated with augmented TGF-beta signaling as indicated by the increase in phospho-Smad2 in aorta.