Physiology - Research Publications

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    Macrophage Mineralocorticoid Receptor Signaling Plays a Key Role in Aldosterone-Independent Cardiac Fibrosis
    Bienvenu, LA ; Morgan, J ; Rickard, AJ ; Tesch, GH ; Cranston, GA ; Fletcher, EK ; Delbridge, LMD ; Young, MJ (ENDOCRINE SOC, 2012-07-01)
    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.
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    Cardiomyocyte Mineralocorticoid Receptors Are Essential for Deoxycorticosterone/Salt-Mediated Inflammation and Cardiac Fibrosis
    Rickard, AJ ; Morgan, J ; Bienvenu, LA ; Fletcher, EK ; Cranston, GA ; Shen, JZ ; Reichelt, ME ; Delbridge, LM ; Young, MJ (LIPPINCOTT WILLIAMS & WILKINS, 2012-12-01)
    Because the role of mineralocorticoid receptors in specific cell types in cardiac remodeling remains unknown, we have compared cardiac responses with deoxycorticosterone/salt in cardiomyocyte mineralocorticoid receptor-null (MyoMRKO) and wild-type (WT) mice at 8 days and 8 weeks. No differences in cardiac function between untreated WT and MyoMRKO mice were found, whereas profibrotic markers were reduced in MyoMRKO hearts at baseline. At 8 days, MyoMRKO showed monocyte/macrophage recruitment equivalent to WT mice in response to deoxycorticosterone/salt but a suppression of markers of fibrosis compared with WT. At 8 weeks, MyoMRKO mice showed no deoxycorticosterone/salt-induced increase in inflammatory cell infiltration and collagen deposition or in proinflammatory gene expression. Although some profibrotic markers were equivalently increased in both genotypes, MyoMRKO mice also showed increased baseline levels of mRNA and protein for the transforming growth factor-β/connective tissue growth factor inhibitor decorin compared with WT that was accompanied by higher levels of matrix metalloproteinase 2/matrix metalloproteinase 9 activity. These data point to a direct role for cardiomyocyte mineralocorticoid receptor in both deoxycorticosterone/salt-induced tissue inflammation and remodeling and suggest potential mechanisms for the cardioprotective effects of selective mineralocorticoid receptor blockade in cardiomyocytes that may involve regulation of matrix metalloproteinase 2/matrix metalloproteinase 9 activity and the transforming growth factor-β-connective tissue growth factor profibrotic pathway.