Abstract 2319: Estrogen Receptor Beta Mediates Increased Activation of PI3k/Akt, Decreased Expression of Caspase-3, -8, Up-Regulation of Bcl-2, and Improved Myocardial Function in Female Hearts following Ischemia
Introduction: Females have a lower incidence of heart failure and improved survival after myocardium ischemia/reperfusion (I/R) compared to males. Although estrogen-suppressed cardiomyocyte apoptosis may be mediated through the PI3K/Akt pathway, it is unclear whether this action is mediated via estrogen receptor beta (ERb). In addition, TNFR1 signaling resistance and upregulation of STAT3/SOCS3/VEGF have been noted in female hearts following I/R. However, the relationship between ERb and TNFR/STAT3/SOCS3/VEGF cascades has not been elucidated. We hypothesized that:
ERb mediates estrogen-induced cardioprotection through PI3K/Akt and anti-apoptotic signaling in females, but not males;
ERb may facilitate protection via TNFR/STAT3/SOCS3/VEGF-mediated cascades.
Methods: Isolated male and female mouse hearts from ERb knockout (ERbKO) and wild type (WT) (n = 5/group) were subjected to 20-minute ischemia followed by 60-minute reperfusion (Langendorff). Myocardial function (LVDP) was monitored. After I/R, hearts were analyzed for activation of Akt, PI3K and STAT3, expression of caspase-3, − 8, Bcl-2, SOCS3, TNFR1 and TNFR2 (Western blot), and VEGF production (ELISA). Student’s t-test, p < 0.05 = statistically significant.
Results: ERb deficiency significantly decreased post-ischemic recovery of LVDP (% equilibration) in females (43 ± 6.2% vs. WT 62.9 ± 2.9%), but not males. Reduced activation of Akt (% phosphor-/total-) (91 ± 12.5% vs. WT 162 ± 38.9%) and PI3K (14.6 ± 4.4% vs. WT 47.6 ± 6.7%) was noted in female KO hearts. In addition, ERb ablation increased caspase-3 (% GAPDH) by 197%, caspase-8 by 46%, and decreased Bcl-2 by 48% only in females compared to their WT. However, ERbKO did not markedly change myocardial STAT3, SOCS3, VEGF, TNFR1 and TNFR2 in both genders following I/R.
Conclusions: ERb mediates myocardial protection via upregulation of PI3K/Akt activation, decreased caspase-3, -8, and increased Bcl-2 in female hearts following I/R. This represents the first evidence of ERb-mediated PI3K/Akt and anti-apoptotic signaling in myocardium, and may lend insight into the mechanistic pathways behind the observed variation in clinical outcomes between males and females after MI.
This research has received full or partial funding support from the American Heart Association, AHA Midwest Affiliate (Illinois, Indiana, Iowa, Kansas, Michigan, Minnesota, Missouri, Nebraska, North Dakota, South Dakota & Wisconsin).