Angiotensin II induces IL-6 expression and the Jak-STAT3 pathway in aortic adventitia of LDL receptor-deficient mice

Abstract

Angiotensin II (A-II), the major effector peptide of the renin angiotensin system potently accelerates progression of atherosclerosis. To investigate its effects on vascular inflammatory mechanisms, we elucidated vascular cytokine expression during early lesion development in A-II-infused atherosclerosis-prone LDLR −/− mice. Male LDLR −/− mice were placed on a "Western" high-fat diet for 4 weeks, followed by sham or A-II infusion for 7 weeks. Equal blood pressures and elevations in serum lipids were seen in both groups. Mice were sacrificed when significant AII-induced plaque development was first detectable, aortae were explanted and culture media assayed for secreted cytokines. Nine cytokines were significantly induced with interleukin-6 (IL-6) being the most highly secreted. Local IL-6 production was confirmed by in situ mRNA hybridization and immunostaining, where the most abundant IL-6 was found in the aortic adventitia, with lesser production by the medial and intimal layers. Immunofluorescence colocalization showed IL-6 expression by fibroblasts and activated macrophages. Activation of downstream IL-6 signaling mediated by the Jak-STAT3 pathway was demonstrated by inducible phospho-Tyr 705 -STAT3 formation in the adventitia and endothelium (of IL-6 +/+ mice only). These findings define cytokine profiles in the A-II infusion model and demonstrate that IL-6, produced by activated macrophages and fibroblasts in the adventitia, induces the Jak-STAT3 pathway during early A-II-induced atherosclerosis.

An adventitial IL-6/MCP1 amplification loop accelerates macrophage-mediated vascular inflammation leading to aortic dissection in mice

“…The results were similar, with enhanced IL-6 secretion observed in the older animals ( Figure 1C). Importantly, cytokine secretion was apparently independent of the presence of vascular hemorrhage; in fact, we previously have shown that cytokines are produced and secreted locally using in situ hybridization and time series analysis of aortic explants (29,39,40). Similarly, Ang II induced a significant, 2-fold increase in MCP-1 secretion in young animals and an enhanced, 4.7-fold increase in the older animals ( Figure 1C).…”

“…To establish the vascular cytokine response to Ang II infusion, aortic explants from young (<2 months old) and older (7-10 months of age) mice after 10 days infusion were prepared and cytokine secretion analyzed (29). Analysis of IL-6 secreted by the total aorta revealed a 3.7-fold increase in production in the young mice and a greater, 6.3-fold increase in the older mice (P < 0.001, 2-way ANOVA; Figure 1C).…”

“…Besides leukocyte infiltration and cytokine production, the adventitia is highly reactive to the process of aneurysm formation, where marked proliferation, fibrosis, and myofibroblast transformation are seen (28). It is increasingly being accepted that adventitial inflammation may play a key role in the genesis and maintenance of vascular inflammation in aortic aneurysms (26,29) and atherosclerotic vascular disease (30)(31)(32)(33). Consequently, understanding the processes controlling cellular recruitment and leukocytic activation in the adventitia may provide fundamental insights into the pathogenesis of a diverse spectrum of cardiovascular diseases.…”

Multifaceted Role of Angiotensin II in Vascular Inflammation and Aortic Aneurysmal Disease

“…Conversely, in wild type mice, Ang II infusion potently induces IL-6 expression in the aorta, making IL-6 the most abundantly secreted cytokine that has yet been detected. IL-6 is predominantly expressed by fibroblasts and activated macrophages in the adventitia, with lesser amounts in the media and intimal layers (Recinos, et al, 2007). IL-6 signaling pathway was locally activated in Ang II-induced aortic aneurysms (Tieu, et al, 2009),where its action promotes monocytic activation and adventitial macrophage accumulation via a chemokine MCP-1-CCR2-based mechanism (Ishibashi, et al, 2004;Tieu, et al, 2009).…”

CARMA3: A novel scaffold protein in regulation of NF-κB activation and diseases

“…IL-6 leads to the recruitment of circulating leukocytes and macrophages into the vascular wall, thereby leading to oxidation of lipoprotein, and atherogenesis [21] . It has been shown that Ang Ⅱ infusion induces IL-6 production, which results in atherogenesis and vascular diseases [102] . IL-6 is an NF-κB targeted gene.…”