Oxidative Stress Causes Mineralocorticoid Receptor Activation in Rat Cardiomyocytes

Abstract

Abstract-Overactivation of the mineralocorticoid receptor signaling is implicated in cardiovascular disease, including hypertensive heart disease. Oxidative stress is suggested to augment mineralocorticoid receptor signal transduction, but the precise mechanisms remain unclear. Mineralocorticoid receptor activity is regulated by multiple factors, in addition to plasma ligand levels. We previously identified Rac1 GTPase as a modulator of mineralocorticoid receptor activity.Here we show that oxidative stress induces mineralocorticoid receptor activation in a ligand-independent, Rac1-depenent manner in cardiomyocytes. Oxidant stress was induced in rat cultured cardiomyocytes (H9c2) by L-buthionine sulfoximine (BSO), an inhibitor of glutathione synthesis. BSO depleted intracellular glutathione and concomitantly increased reactive oxygen species (199%; PϽ0.01). BSO significantly enhanced the corticosterone-induced, mineralocorticoid receptor-dependent luciferase reporter activity (186%; PϽ0.01) and basal luciferase activity without ligand stimulation. These effects were inhibited by the antioxidant N-acetylcysteine. The ligand independency of BSO action was indicated using a mutant mineralocorticoid receptor that does not bind ligands. With this mutant mineralocorticoid receptor, BSO-evoked mineralocorticoid receptor activation remained intact, whereas ligand-induced mineralocorticoid receptor activation was abolished. We next examined the involvement of Rac1. BSO increased active Rac1 in a redox-dependent fashion, and Rac inhibition suppressed the enhancing effect of BSO. Constitutively active Rac1, indeed, potentiated mineralocorticoid receptor transactivation. Furthermore, mineralocorticoid receptor transactivation by BSO was accompanied by enhanced nuclear accumulation of mineralocorticoid receptor. We conclude that alteration of redox state modulates mineralocorticoid receptor-dependent transcriptional activity via Rac1 in the heart. This redox-sensitive, ligand-independent mineralocorticoid receptor activation may contribute to the processes by which oxidant stress promotes cardiac injury. (Hypertension. 2012;59[part 2]:500-506.)

Rho GTPases, oxidation, and cell redox control

“…They found that L-buthionine sulfoximine (BSO), which depletes intracellular glutathione, increased the active form of Rac1, and this effect was blocked by the antioxidant N-acetylcysteine (NAC). 119 Consistent with their findings with BSO, H 2 O 2 also activated Rac1. 119 Similarly, H 2 O 2 treatment led to a robust increase in GTP-bound Rac1 in neutrophils derived from C57/BL6 control mice.…”

“…119 Consistent with their findings with BSO, H 2 O 2 also activated Rac1. 119 Similarly, H 2 O 2 treatment led to a robust increase in GTP-bound Rac1 in neutrophils derived from C57/BL6 control mice. 120 Chronic exposure of normal mouse mammary gland epithelial (NMuMG) cells to H 2 O 2 not only elevated Rac1 activity but also greatly enhanced cell invasiveness.…”

Rac1-Mediated Activation of Mineralocorticoid Receptor in Pressure Overload–Induced Cardiac Injury

“…These findings are compatible with our previous observation in cultured cardiomyocytes that overexpression of active Rac1 induced MR activation in a ligand-independent manner in cells cultured with serum-depleted medium or when the cellular MR gene was replaced with a ligand-resistant mutant. 18 Given that the ligand binding of MR in cardiomyocytes is already saturated at steady state by the absence of 11β-HSD2, Rac1 serves as an enhancer of MR activation via increased nuclear MR translocation in the pressure-overloaded heart, in a similar manner to the essential role for Rac1 in the nuclear localization of β-catenin, a transcription factor involved in canonical Wnt signaling. 35 Aberrant Rac1-mediated MR activation in the myocardium was supported by changes in the expression of various target genes of MR in the myocardium.…”

NSC23766, a Widely Used Inhibitor of Rac1 Activation, Additionally Acts as a Competitive Antagonist at Muscarinic Acetylcholine Receptors

“…Cardiac myocyte-specific overexpression of an active form of Rac predisposes the heart to postischemic contractile dysfunction (Talukder et al, 2013). Through activation of NADPH oxidase, Rac1 activation contributes to oxidative stress, which promotes cardiac injury and dysfunction (Maack et al, 2003;Endou et al, 2004;Elnakish et al, 2012;Nagase et al, 2012;Zhang et al, 2012;Ma et al, 2013). Moreover, Rac1 is essential for the hypertrophic response in the heart (Sussman et al, 2000;Satoh et al, 2006;Vettel et al, 2012).…”