Estrogen exerts concentration-dependent pro-and anti-hypertrophic effects on adult cultured ventricular myocytes. Role of NHE-1 in estrogen-induced hypertrophy

Abstract 

Estrogen has been shown to protect the heart and attenuate myocardial hypertrophy and left ventricular remodelling through as yet to be defined mechanisms. In the present study we examined concentration-dependent effects of estrogen on hypertrophy of adult rat cardiomyocytes, potential underlying mechanisms related to intracellular pH (pH_i) and possible sex-dependent responses. Cardiomyocytes were isolated from adult male and female Sprague–Dawley rats and used immediately for pH_i determinations or cultured and subsequently treated for 24 h with 17β-estradiol to assess hypertrophic responses. Fluorometric measurements with the pH_i-sensitive dye BCECF demonstrated that at 1 pM 17β-estradiol increased pH_i (+0.05 pH units in females and +0.12 pH units in males, P<0.05) by a rapid non-genomic mechanism that was blocked by the sodium-hydrogen exchange isoform 1 (NHE-1) specific inhibitor AVE-4890 (AVE, 5 μM). Treatment with 1 pM 17β-estradiol for 24 h increased cell size (females: 20%, P<0.05; males: 29%, P<0.05) and ANP expression (females: 414%, P<0.05; males: 497%, P<0.05) in a NHE-1-, and ERK1/2 MAPK-dependent manner. At 1 nM, 17β-estradiol decreased pH_i (females: −0.24 pH units, P<0.05; males: −0.07 pH units, P<0.05) which was also prevented by AVE, although at this concentration the hormone had no direct hypertrophic effect but instead prevented hypertrophy induced by phenylephrine. Our results show that low levels of estrogen produce cardiomyocyte hypertrophy through ERK/NHE-1 activation and intracellular alkalinization whereas an antihypertrophic effect is seen at high concentrations. These effects may further our understanding of the role of estrogen in heart disease particularly associated with hypertrophy.

Abbreviations: ANP, atrial natriuretic peptide, AVE, AVE-4890, BCECF, 2′,7′-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein, βE2, 17β-estradiol, ICI, ICI182,780, NHE-1, Na⁺-H⁺ exchanger 1, pH_i, intracellular pH, PD, PD98059, PE, phenylephrine, RT-PCR, Real-time-polymerase chain reaction

Keywords: Estrogen, Sodium-hydrogen exchanger 1, Hypertrophy, Cardiomyocytes, Mitogen-activated protein kinase