We have demonstrated that long-term 17β-estradiol attenuated
fibrosis after
myocardial infarction, but recent evidence suggests that
estrogen mediates more rapid cellular effects. RhoA has been shown to play a role in the control of myocardial
fibrosis by regulating the actin-regulatory
protein cofilin. We sought to elucidate whether RhoA activity regulates
estradiol-induced
fibrosis after
infarction in ovariectomized female rats. Twenty-four hours after coronary
ligation, female Wistar rats were randomized into control or
estradiol treatment for 4 weeks starting from 2 weeks after
bilateral ovariectomy. There were similar
infarct sizes among the infarcted groups. Myocardial
fibrosis was significantly reduced, as measured by
hydroxyproline content, Sirius Red staining and actin polymerization after administering
estradiol.
Estradiol treatment was associated with RhoA/
Rho kinase inhibition evidenced by increased phosphorylation of RhoA and decreased phosphorylation of downstream factors including
cofilin. Administration of PPT, a specific ERα agonist, or a membrane impermeable
estrogen-
albumin construct also inhibited
cofilin phosphorylation, suggesting that
cofilin phosphorylation is achieved through the recruitment of a membrane ERα. The ERβ-selective agonist,
DPN, did not alter
cofilin phosphorylation levels, but the ER antagonist,
ICI 182,780 increased
cofilin phosphorylation levels. G-15 (an inhibitor of
G-protein coupled
estrogen receptor) did not affect the phosphorylation as compared with
estradiol alone. The inhibitor of
Rho kinase,
Y-27632, attenuated
cofilin phosphorylation levels, similar to the effect produced by
estradiol. These results indicate that chronic use of
estradiol after
infarction attenuates cardiac
fibrosis by inhibiting RhoA/ROCK/
cofilin pathway, which is exerted through membrane ERα-mediated receptor mechanism.
KEY MESSAGE: Postinfarction was associated with increased cardiac
fibrosis. Myocardial
fibrosis was significantly reduced after administering
estradiol (E2). Administration of the membrane ERα agonist PPT or
E2-BSA inhibited
cofilin phosphorylation. Combination of E2 and
Y-27632 did not enhance the attenuation of
cofilin phosphorylation. Chronic use of E2 attenuated cardiac
fibrosis by inhibiting the RhoA/ROCK/
cofilin pathway via ERα.