Impact of Chronic Angiotensin Treatment on the Responses of Isolated Cardiac Fibroblasts to Acute Pro‐Fibrotic Stimuli

Abstract

Pathological cardiac remodeling involving fibrosis can lead to heart failure in people with hypertension. We have recently demonstrated that angiotensin II (AngII)‐induced increases in left ventricular collagen content and macrophage infiltration are attenuated by concomitant bradykinin‐B1 receptor (B1R) antagonism in Sprague‐Dawley (SD) rats. Given that AngII has been shown to upregulate B1R, the goal of the present study was to determine the impact of B1R stimulation on fibroblast physiology following chronic (in vivo) or acute (in vitro) treatment with AngII. Adult male SD rats were implanted with osmotic mini‐pumps that delivered AngII (200 ng/kg/min) or saline for 4 weeks. Cardiac fibroblasts were isolated from the left ventricle of saline and AngII‐treated rats and passaged to P1. Cells were treated in vitro with AngII (1uM), a selective B1R agonist (Lys‐ [Des‐Arg9], 100 nM), AngII+B1R agonist or vehicle for 48 hr. Transforming growth factor beta 1 (TGF‐β1) and monocyte chemoattractant protein 1 (MCP‐1) were assessed in culture media. Expression of the matricellular protein periostin and the pro‐oxidant NADPH oxidase 2 (Nox2) were determined in cell lysate by western blot. Fibroblasts isolated from rats chronically treated with AngII secreted elevated levels of MCP‐1 in vitro (p<0.05), when compared to control fibroblasts. Although MCP‐1 secretion was not further modified by acute AngII treatment, stimulation with the B1R agonist tended to reduce MCP‐1 levels. TGF‐β1 release was not different from cells isolated from saline or AngII infused rats. However, in vitro incubation with AngII significantly increased secretion of TGF‐β1 to a similar degree in fibroblasts isolated from saline or AngII treated rats. B1R stimulation had no impact on TGF‐β1 levels. Periostin expression tended to be increased in fibroblasts isolated from AngII infused rats, while Nox2 expression was not different. Acutely, AngII tended to increase Nox2 expression in vitro to a greater degree in fibroblasts that were isolated from saline‐infused rats. Selective B1R stimulation in vitro resulted in a significant 1.77‐fold upregulation of Nox2 only in fibroblasts isolated from saline treated rats (p<0.05). Combined AngII+B1R stimulation did not further increase Nox2 expression. Taken together, these data demonstrate that upregulation of MCP‐1 production and periostin induced by chronic AngII persist at least to P1 in isolated cardiac fibroblasts. Moreover, chronic AngII resulted in an attenuated increase in Nox2 in response to acute AngII stimulation. Notably, we demonstrate for the first time that selective B1R activation results in a marked increase in Nox2 expression in cardiac fibroblasts. Although B1R antagonism has been shown to offset fibrotic and inflammatory effects of AngII in vivo, acute effects of AngII stimulation are not enhanced in the presence of B1R stimulation. Future studies will determine the extent to which in vivo or in vitro B1R antagonism prevents AngII‐induced fibroblast activation. Investigation of oxidative stress and the nature of Nox2 regulation by B1R activation may provide greater insight into the impact of bradykinin on fibroblast physiology.Support or Funding InformationSpringboard, UA COM‐PThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.