The Molecular Mechanism Involved In Estrogen-induced In CSE Expression And Hydrogen Sulfide Production In Cardiomyocytes

It has been well-recognized that there are significant gender differences of the incidence of cardiovascular disease. Premenopausal women have a marked lower incidence of cardie disease than age-matched men. In post-menopausal women, this gender advantage is lost. Studies have shown that estrogen has cardiovascular protective active effects, but the exact mechanisms are not yet fully clarified. Hydrogen sulfide (H2S) is a newly characterized endogenous gasotransmitter. It is generated from L-cysteine predominantly by cystathionine y lyase (CSE) in heart tissuse. Endogenous H2S as an endogenous myocardial protective mechanism was widespread concerned in recent years. Our previous work has found that estrogen replacement plays a role against oxidative damage and increase CSE expression in OVX rats, However, whether endogenous H2S contributes to the protective effects of estrogen against oxidative stress has not been reported. Therefore, the main topic of our research focues on the role of endogenous CSE/H2S pathway in the protective effects of17β-estradiol against oxidative injury in cardiomyocytes. Furthermore, the molecular mechansm involved in estrogen-induced CSE expression and H2S production were also investigated.Research contents and resultsPart one:CSE contributes to the protective effects of E2against oxidative stress in cardiomyocytesTreatment of cardiomyocytes with E2(10nmol/L) alone could promote cell survival, reduce supernatant LDH concentration and cell cleaved caspase3expression, as well as increased phosphorylation of Akt in primary cultured neonatal cardiomyocytes exposed to H2O2(200umol/L). The cardioprotective effects of E2were significantly reduced by pharmacological inhibitor of CSE or knockdown of CSE in cultured cardiomyocytes.Part one:Effect of estrogen on CSE expression and endogenous H2S productionIn primary cultured neonatal cardiomyocytes, we found that estrogen (10-10-10-7mol/L) significantly increase CSE mRNA and protein expression in a dose-dependent manner in the cultured myocardial cells, and10nM estrogen led to a more than3-fold increase of CSE protein expression (p<0.05). In addition, lOnM estrogen significantly increased endogenous H2S production in cardiomyocytes.Part two:Estrogen receptor a mediates the effect of estrogen on CSE expressionIn primary cultured neonatal cardiomyocytes, we found that the estrogen-mediated upregulation of CSE expression was blocked by nonselective estrogen receptor (ER) antagonist ICI182780and ERa antagonist MPP, but not by ERβ selective antagonist THC. Using small interfering RNA (siRNA) targeting ERa, we found that ERa siRNA completly blocked the estrogen-mediated upregulation of CSE expression. These results suggest that estrogen may promote CSE expression mainly through ERa.Part four:Transcription factor SP1plays a critical role in E2-mediated up-regulation of CSE expressionIn primary cultured neonatal cardiomyocytes, we found that estrogen (10-10-10-7mol/L) can upregulate SP1mRNA and protein levels in a dose-dependent manner. SP1knockdown not only caused a decrease in basal CSE expression, but also abolished the induction of CSE expression by estrogen. Transfection with PGL3-CSE-promoter luciferase reporter gene (PGL3-CSE) containing SP1binding sites into rat cardiomyocytes derived cell line H9C2cells, we found that basal luciferase acitivity was significantly increased as compared with cells transfected with PGL3control plasmid, and estrogen significantly induced pGL3-CSE promoter transcriptional activity. In order to investigate whether the SP1binding sites involved in the regulation of CSE expression, we constructed SP1sites mutant of pGL3-CSE promoter reporter plasmid (pGL3-CSE mutant). We found that in H9C2cells transfected with pGL3-CSE mutant plasmid, luciferase activity was significantly lower than those cells transfected with wild-type CSE promoter reporter plasmid. In addition, there is no significant effect of estrogen on the transcriptional activativity of pGL3-CSE mutant. Taken together, these results suggest that SP1plays a critical role in estrogen-induced expression of CSE in rat cardiomyocytes.Part five:E2stimulates Spl expression through repressing miR-22Recently, miR-22has been found to mediate the transcriptional regulation of Spl. In primary cultured neonatal cardiomyocytes, we found that estrogen (10-10-10-7mol/L) inhibited miR-22expression in a dose-dependent manner. In addition, miR-22inhibitor significantly enhanced Spl mRNA and protein expression, whereas miR-22mimic not only decreased basal Spl mRNA and protein expression, but also reversed the E2-induced Spl expression. All these results suggest estrogen stimulates Spl expression through repressing miR-22in cultured cardiomyocytes.Part six:E2stimulates ERa expression through repressing miR-22It has been found that miR-22can regulate the expression of ERa. We found that estrogen treatment can up-regulate the expression of ERa. MiR-22mimic not only inhibited the basal expression of ERa, but also blocked the estrogen-induced upregulation of ERa expression. These results suggest that estrogen stimulates ERa expression through repressing miR-22in cultured cardiomyocytes.Part seven:Estrogen replacement significantly promotes CSE and SP1expression, whereas represses miR-22expression in heart tissues of ovariectomized (OVX) ratsFemale SD rats were randomly divided into three groups:the sham operated group as control (Sham), the ovariectomy group (Ovx) and the Ovx rats with estrogen replacement therapy group (Ovx+E2). Ovx+E2group was administered daily with30μg/kg17β-estradiol via hypodermic injection after ovariectomized. The other two groups were administered with vehicle. Twelve weeks later, left ventricular tissues were harvested, and then CSE, SP1and miR-22expression were observed. We found CSE, SP1expression were significantly down-regulated, however miR-22was up-regulated after OVX. Estrogen replacement can restore the levels of CSE, SP1and miR-22expression to the level of sham group.ConclusionThis study shows that estrogen can up-regulate the expression of CSE in myocardial cells, thereby promoting endogenous H2S generation. Endogenous CSE/H2S play an important role in the protective effect of estrogen against oxidative damage in cardiomyocytes. The mechanism of estrogen-induced CSE expression is related to inhibition of miR-22, which in turn results in the increased expression of SP1and ERa.