Abstract P252: Smooth Muscle At1a Receptor Mediates Perivascular Fibrosis In Angiotensin Ii-infused Mice

Angiotensin II (Ang II) signaling via AT1 receptor has been shown to play a critical role in the pathogenesis of hypertension, cardiovascular hypertrophy and fibrosis. We have demonstrated that ADAM17 expressed in vascular smooth muscle cells (VSMC) mediates EGF receptor activation and promotes cardiac hypertrophy and perivascular fibrosis induced by Ang II. It is conceivable that Ang II signaling in VSMCs specifically initiates cardiovascular remodeling, such as hypertrophy and fibrosis. In a recent study, deficiency of smooth muscle AT1a receptors results in diminished hypertension and protection from cardiac hypertrophy induced by Ang II. However, we have limited understanding whether smooth muscle AT1a receptors affects hypertensive fibrosis in vasculature. Thus, this study was designed to elucidate the roles of the AT1a receptor in VSMCs in cardiovascular remodeling including fibrosis during Ang II stimulation using VSMC AT1a receptor deficient mice. To delete the AT1a receptor from VSMCs, we crossed C57BL/6 transgenic mouse lines expressing Cre recombinase under the control of the sm22α promoter (KIsm22α-Cre). Male AT1a flox/flox KIsm22α-Cre+/- (SMKO) and Controls (AT1a flox/flox KIsm22α-Cre-/-) mice were infused with Ang II (1 μg/kg/min) for 2 weeks via osmotic mini-pump. In Control mice, Ang II infusion for 2 weeks induced cardiac hypertrophy indicated by heart-to-body weight ratio and echocardiogram. After 2 weeks of Ang II infusion, heart-to-body weight ratios were significantly increased in Control mice compared with AT1a SMKO mice (6.04 versus 4.89, respectively, p=0.032). Cardiac wall hypertrophy was seen in Controls after 2 weeks of Ang II infusion, which was attenuated in AT1a SMKOs. Control mice (n=5) showed vascular medial hypertrophy and perivascular fibrosis, whereas these phenotypic changes were attenuated in SMKO mice (n=4). In conclusion, AT1a receptors from VSMC could mediate Ang II-induced cardiovascular hypertrophy and perivascular fibrosis. Whether the data can be fully explained by the prevention of hypertension remains to be determined, the data contrast to the past manuscript showing a protective effect in AT1a flox/flox S100A4-Cre+/- mice (fibroblast silencing) with Ang II infusion.

Abstract 3551: Cyclophilin a Promotes Angiotensin II-Induced Inflammation and Cardiovascular Hypertrophy in Mice

Background - Cyclophilin A (CyPA) is a chaperone protein secreted from vascular smooth muscle cells (VSMC) in response to reactive oxygen species (ROS). We have recently demonstrated that extracellular CyPA stimulates at least 3 signaling pathways (ERK1/2, Akt and JAK) and mediates numerous cellular effects of ROS. Angiotensin II (Ang II) induces ROS through NADPH oxidases and activates matrix metalloproteinase (MMP) in VSMC. ROS and MMPs have been demonstrated to mediate cardiac hypertrophy and remodeling. We hypothesized that VSMC-derived CyPA contributes to AngII-induced cardiovascular hypertrophy in vivo due to its proinflammatory properties. Methods and Results - ApoE −/− and ApoE −/− CyPA −/− mice were treated with AngII (1000 ng/min/kg for 4 weeks) to induce cardiac hypertrophy. Long-term infusion of AngII significantly increased heart/body weight ratio in ApoE −/− mice, which was significantly less in ApoE −/− CyPA −/− mice (6.6±1.0 vs. 4.8±0.7, P <0.01). Echocar-diography confirmed a significantly greater increase in LV mass in ApoE −/− mice compared to ApoE −/− CyPA −/− mice (112% vs. 47%). Perivascular accumulation of inflammatory cells and cardiac myofibroblasts in ApoE −/− mice was significantly greater than in ApoE −/− CyPA −/− mice. Consequently, coronary artery ROS production (DHE fluorescence) and MMP activation (in situ zymography) were markedly increased by AngII in ApoE −/− mice compared to ApoE −/− CyPA −/− mice. To determine the source of CyPA, bone marrow cells (BMCs) transplantation was performed. The heart/body weight ratio was still higher in ApoE −/− mice compared with ApoE −/− CyPA −/− mice after reconstitution with GFP + CyPA +/+ BMCs (6.7±0.6 vs. 5.6±0.9, P <0.01). Recruitment of GFP + BMCs to the heart in chimeric ApoE −/− mice was significantly greater than the chimeric ApoE −/− CyPA −/− mice (count/area; 218±63 vs. 109±43, P <0.01). To prove a vascular source of CyPA was essential, VSMC-specific CyPA overexpressing mice were generated. In these mice there was a significant increase in cardiac MMP activity after AngII infusion (VSMC-Tg > WT > CyPA −/− ). Conclusion - CyPA is a novel mediator of AngII-induced cardiac hypertrophy by stimulating vascular ROS production, MMP activation, and inflammatory cell recruitment. This research has received full or partial funding support from the American Heart Association, AHA Founders Affiliate (Connecticut, Maine, Massachusetts, New Hampshire, New Jersey, New York, Rhode Island, Vermont).