Abstract-Increased mineralocorticoid levels plus high salt promote vascular inflammation and cardiac tissue remodeling.Mineralocorticoid receptors are expressed in many cell types of the cardiovascular system, including monocytes/macrophages and other inflammatory cell types. Although mineralocorticoid receptors are expressed in monocytes/macrophages, their role in regulating macrophage function to date has not been investigated. We, thus, used the Cre/LoxP-recombination system to selectively delete mineralocorticoid receptors from monocytes/macrophages with the lysozyme M promoter used to drive Cre expression (MR flox/flox /LysM Cre/Ϫ mice). Male mice from each genotype (MR flox/flox or wild-type and MR flox/flox /LysM Cre/Ϫ mice) were uninephrectomized, given 0.9% NaCl solution to drink, and treated for 8 days or 8 weeks with either vehicle (nϭ10) or deoxycorticosterone (nϭ10). Equivalent tissue macrophage numbers were seen for deoxycorticosterone treatment of each genotype at 8 days; in contrast, plasminogen activator inhibitor type 1 and NAD(P)H oxidase subunit 2 levels were increased in wild-type but not in MR flox/flox / LysM Cre/Ϫ mice given deoxycorticosterone. Baseline expression of other inflammatory genes was reduced in MR flox/flox /LysM Cre/Ϫ mice compared with wild-type mice. At 8 weeks, deoxycorticosterone-induced macrophage recruitment and connective tissue growth factor and plasminogen activator inhibitor type 1 mRNA levels were similar for each genotype; in contrast, MR flox/flox /LysMCre/Ϫ mice showed no increase in cardiac fibrosis or blood pressure, as was seen in wild-type mice at 8 weeks. These data demonstrate the following points: (1) mineralocorticoid receptor signaling regulates basal monocyte/macrophage function; (2) macrophage recruitment is not altered by loss of mineralocorticoid receptor signaling in these cells; and (3) a novel and significant role is seen for macrophage signaling in the regulation of cardiac remodeling and systolic blood pressure in the deoxycorticosterone/salt model. T he clinical use of mineralocorticoid receptor (MR) antagonists added to the current standard of care reduces morbidity and mortality in patients with congestive heart failure 1,2 and reduces blood pressure and proteinuria as monotherapy in essential hypertension. 3 Although the precise mechanism for this protection remains to be determined, considerable insights have been obtained from experimental models of mineralocorticoid/salt-mediated cardiac fibrosis 4 -6 ; hypertension, cardiac hypertrophy, and fibrosis are key responses to the administration of aldosterone or deoxycorticosterone (DOC) concurrently with a high salt intake for 8 weeks. Importantly, the pathogenesis of cardiac fibrosis is independent of hypertension and cardiac hypertrophy in this model, suggesting a direct role for MR activation in driving the onset and progression of cardiovascular disease. 4 -6 We and others have previously identified vascular inflammation (ie, osteopontin and plasminogen activator inhibitor type 1 [PA...

Recent studies have identified novel pathological roles for mineralocorticoid receptors (MR) in specific cell types in cardiovascular disease. The mechanisms by which MR promotes inflammation and fibrosis involve multiple cell-specific events. To identify the role of MR in endothelial cells (EC-MR), the current study explored the vascular responses to aldosterone in wild-type (WT) and EC-null mice (EC-MRKO). Nitric oxide function was impaired in the thoracic aorta and mesenteric arteries of aldosterone-treated WT mice. Although endothelial nitric oxide function was equivalently impaired in the mesenteric arteries of aldosterone-treated EC-MRKO mice, endothelial function was unaffected in the aorta, suggesting a differential role for EC-MR depending on the vascular bed. Second, the contribution of EC-MR to cardiovascular inflammation, fibrosis, and hypertension was determined in WT and EC-MRKO treated with deoxycorticosterone/salt for 8 days or 8 weeks. At 8 days, loss of EC-MR prevented macrophage infiltration and the expression of proinflammatory genes in the myocardium. Increased cardiac fibrosis was not detected in either genotype at this time, mRNA levels of profibrotic genes were significantly lower in EC-MRKO mice versus WT. At 8 weeks, deoxycorticosterone/salt treatment increased macrophage recruitment and proinflammatory gene expression in WT but not in EC-MRKO. Collagen deposition and connective tissue growth factor expression were significantly reduced in EC-MRKO versus WT. Interestingly, systolic blood pressure was equivalently elevated in deoxycorticosterone/salt treated WT and EC-MRKO. Our data demonstrate that (1) EC-MR signaling contributes to vascular nitric oxide function in large conduit arteries but not in resistance vessels and (2) an independent role for EC-MR in the inflammatory and profibrotic response to deoxycorticosterone/salt.

Mineralocorticoid receptor (MR) activation promotes the development of cardiac fibrosis and heart failure. Clinical evidence demonstrates that MR antagonism is protective even when plasma aldosterone levels are not increased. We hypothesize that MR activation in macrophages drives the profibrotic phenotype in the heart even when aldosterone levels are not elevated. The aim of the present study was to establish the role of macrophage MR signaling in mediating cardiac tissue remodeling caused by nitric oxide (NO) deficiency, a mineralocorticoid-independent insult. Male wild-type (MRflox/flox) and macrophage MR-knockout (MRflox/flox/LysMCre/+; mac-MRKO) mice were uninephrectomized, maintained on 0.9% NaCl drinking solution, with either vehicle (control) or the nitric oxide synthase (NOS) inhibitor NG-nitro-l-arginine methyl ester (L-NAME; 150 mg/kg/d) for 8 wk. NO deficiency increased systolic blood pressure at 4 wk in wild-type L-NAME/salt-treated mice compared with all other groups. At 8 wk, systolic blood pressure was increased above control in both L-NAME/salt treated wild-type and mac-MRKO mice by approximately 28 mm Hg by L-NAME/salt. Recruitment of macrophages was increased 2- to 3-fold in both L-NAME/salt treated wild-type and mac-MRKO. Inducible NOS positive macrophage infiltration and TNFα mRNA expression was greater in wild-type L-NAME/salt-treated mice compared with mac-MRKO, demonstrating that loss of MR reduces M1 phenotype. mRNA levels for markers of vascular inflammation and oxidative stress (NADPH oxidase 2, p22phox, intercellular adhesion molecule-1, G protein-coupled chemokine receptor 5) were similar in treated wild-type and mac-MRKO mice compared with control groups. In contrast, L-NAME/salt treatment increased interstitial collagen deposition in wild-type by about 33% but not in mac-MRKO mice. mRNA levels for connective tissue growth factor and collagen III were also increased above control treatment in wild-type (1.931 ± 0.215 vs. 1 ± 0.073) but not mac-MRKO mice (1.403 ± 0.150 vs. 1.286 ± 0.255). These data demonstrate that macrophage MR are necessary for the translation of inflammation and oxidative stress into interstitial and perivascular fibrosis after NO deficiency, even when plasma aldosterone is not elevated.