Gender differences in GRK2 in cardiovascular diseases and its interactions with estrogen

G protein-coupled receptor kinase 2 (GRK2) is a multifunctional protein involved in regulating G protein-coupled receptor (GPCR) and non-GPCR signaling in the body. In the cardiovascular system, increased expression of GRK2 has been implicated in the occurrence and development of several cardiovascular diseases (CVDs). Recent studies have found gender differences in GRK2 in the cardiovascular system under physiological and pathological conditions, where GRK2's expression and activity are increased in males than in females. The incidence of CVDs in premenopausal women is lower than in men of the same age, which is related to estrogen levels. Given the shared location of GRK2 and estrogen receptors, estrogen may interact with GRK2 by modulating vital molecules such as calmodulin (CaM), caveolin, RhoA, nitrate oxide (NO), and mouse double minute 2 homolog (Mdm2), via signaling pathways mediated by estrogen's genomic (ERα and ERβ), and non-genomic (GPER) receptors, conferring cardiovascular protection in females. Highlighting the gender differences in GRK2 and understanding its interaction with estrogen in the cardiovascular system is pertinent in treating gender-related CVDs. As a result, this article explores the gender differences of GRK2 in the cardiovascular system and its relationship with estrogen during disease conditions. Estrogen's protective and therapeutic effects and its mechanism on GRK2-related cardiovascular diseases have also been discussed.

Cardiac proteomics reveals sex chromosome-dependent differences between males and females that arise prior to gonad formation

Sex disparities in cardiac homeostasis and heart disease are well documented, with differences attributed to actions of sex hormones. However, studies have indicated sex chromosomes act outside of the gonads to function without mediation by gonadal hormones. Here, we performed transcriptional and proteomics profiling to define differences between male and female mouse hearts. We demonstrate, contrary to current dogma, cardiac sex disparities are controlled not only by sex hormones but also through a sex-chromosome mechanism. Using Turner syndrome (XO) and Klinefelter (XXY) models, we find the sex-chromosome pathway is established by X-linked gene dosage. We demonstrate cardiac sex disparities occur at the earliest stages of heart formation, a period before gonad formation. Using these datasets, we identify and define a role for alpha-1B-glycoprotein (A1BG), showing loss of A1BG leads to cardiac defects in females, but not males. These studies provide resources for studying sex-biased cardiac disease states.

Cardiac Fibroblasts Mediate a Sexually Dimorphic Fibrotic Response to β-Adrenergic Stimulation

Background

Biological sex is an important modifier of cardiovascular disease and women generally have better outcomes compared with men. However, the contribution of cardiac fibroblasts (CFs) to this sexual dimorphism is relatively unexplored.

Methods and Results

Isoproterenol (ISO) was administered to rats as a model for chronic β‐adrenergic receptor (β‐AR)‐mediated cardiovascular disease. ISO‐treated males had higher mortality than females and also developed fibrosis whereas females did not. Gonadectomy did not abrogate this sex difference. To determine the cellular contribution to this phenotype, CFs were studied. CFs from both sexes had increased proliferation in vivo in response to ISO, but CFs from female hearts proliferated more than male cells. In addition, male CFs were significantly more activated to myofibroblasts by ISO. To investigate potential regulatory mechanisms for the sexually dimorphic fibrotic response, β‐AR mRNA and PKA (protein kinase A) activity were measured. In response to ISO treatment, male CFs increased expression of β1‐ and β2‐ARs, whereas expression of both receptors decreased in female CFs. Moreover, ISO‐treated male CFs had higher PKA activity relative to vehicle controls, whereas ISO did not activate PKA in female CFs.

Conclusions

Chronic in vivo β‐AR stimulation causes fibrosis in male but not female rat hearts. Male CFs are more activated than female CFs, consistent with elevated fibrosis in male rat hearts and may be caused by higher β‐AR expression and PKA activation in male CFs. Taken together, our data suggest that CFs play a substantial role in mediating sex differences observed after cardiac injury.

No impact of sex and age on beta-adrenoceptor-mediated inotropy in human right atrial trabeculae

AIM

There is an increasing awareness of the impact of age and sex on cardiovascular diseases (CVDs). Differences in physiology are suspected. Beta-adrenoceptors (beta-ARs) are an important drug target in CVD and potential differences might have significant impact on the treatment of many patients. To investigate whether age and sex affects beta-AR function, we analysed a large data set on beta-AR-induced inotropy in human atrial trabeculae.

METHODS

We performed multivariable analysis of individual atrial contractility data from trabeculae obtained during heart surgery of patients in sinus rhythm (535 trabeculae from 165 patients). Noradrenaline or adrenaline were used in the presence of the beta₂ -selective antagonist (ICI 118 551, 50 nmol/L) or the beta₁ -selective antagonist (CGP 20712A, 300 nmol/L) to stimulate beta₁ -AR or beta₂ -AR respectively. Agonist concentration required to achieve half-maximum inotropic effects (EC₅₀ ) was taken as a measure of beta-AR sensitivity.

RESULTS

Impact of clinical variables was modelled using multivariable mixed model regression. As previously reported, chronic treatment with beta-blockers sensitized beta-AR. However, there was no significant interaction between basal force, maximum force and beta-AR sensitivity when age and sex were modelled continuously. In addition, there was no statistically significant effect of body mass index or diabetes on atrial contractility.

CONCLUSION

Our large, multivariable analysis shows that neither age nor sex affects beta-AR-mediated inotropy or catecholamine sensitivity in human atrial trabeculae. These findings may have important clinical implications because beta-ARs, as a common drug target in CVD and heart failure, do not behave differently in women and men across age decades.

Gender Differences in Cardiac Hypertrophy

Cardiac hypertrophy is an adaptive response to abnormal physiological and pathological stimuli, which can be classified into concentric and eccentric hypertrophy, induced by pressure overload or volume overload, respectively. In both physiological and pathological scenarios, females generally show a more favorable form of hypertrophy compared with their male counterparts. However once established, cardiac hypertrophy is a stronger risk factor for heart failure in females. Pre-menopausal women are better protected against cardiac hypertrophy compared with men, but this protection is abolished following menopause and is partially restored after estrogen replacement therapy. Estrogen exerts its protection by counteracting pro-hypertrophy signaling pathways, whereas androgen mostly plays an opposite role in cardiac hypertrophy. We here summarize the progress in the understanding of sexual dimorphisms in cardiac hypertrophy and highlight recent breakthroughs in the regulatory role of sex hormones and their intricate molecular networks, in order to shed light on gender-oriented therapeutic efficacy for pathological hypertrophy.

Female rats with severe left ventricle volume overload exhibit more cardiac hypertrophy but fewer myocardial transcriptional changes than males

Aortic valve regurgitation (AR) imposes a volume overload (VO) to the left ventricle (LV). Male rats with a pathological heart overload usually progress more quickly towards heart failure than females. We examined whether a sexual dimorphism exists in the myocardial transcriptional adaptations to AR. Adult Wistar male and female rats either underwent a sham operation or were induced with AR and then followed for 26 weeks. Female AR rats gained relatively more LV mass than males (75 vs. 42%). They had a similar increase in LV chamber dimensions compared to males but more wall thickening. On the other hand, fatty acid oxidation (FAO)-related LV enzyme activity was only decreased in AR males. The expression of genes encoding FAO-related enzymes was only reduced in AR males and not in females. A similar situation was observed for the expression of genes involved in mitochondrial biogenesis or function as well as for genes encoding for transcription factors implicated in the control of bioenergetics and mitochondrial function (Errα, Errγ or Pgc1α). Although females develop more LV hypertrophy from severe VO, their myocardial gene expression remains closer to normal. This could provide survival benefits for females with severe VO.

The Importance of Biological Sex and Estrogen in Rodent Models of Cardiovascular Health and Disease

Nearly one-third of deaths in the United States are caused by cardiovascular disease (CVD) each year. In the past, CVD was thought to mainly affect men, leading to the exclusion of women and female animals from clinical studies and preclinical research. In light of sexual dimorphisms in CVD, a need exists to examine baseline cardiac differences in humans and the animals used to model CVD. In humans, sex differences are apparent at every level of cardiovascular physiology from action potential duration and mitochondrial energetics to cardiac myocyte and whole-heart contractile function. Biological sex is an important modifier of the development of CVD with younger women generally being protected, but this cardioprotection is lost later in life, suggesting a role for estrogen. Although endogenous estrogen is most likely a mediator of the observed functional differences in both health and disease, the signaling mechanisms involved are complex and are not yet fully understood. To investigate how sex modulates CVD development, animal models are essential tools and should be useful in the development of therapeutics. This review will focus on describing the cardiovascular sexual dimorphisms that exist both physiologically and in common animal models of CVD.

Sex differences in SR Ca(2+) release in murine ventricular myocytes are regulated by the cAMP/PKA pathway

Previous studies have shown that ventricular myocytes from female rats have smaller contractions and Ca(2+) transients than males. As cardiac contraction is regulated by the cyclic adenosine monophosphate (cAMP)/protein kinase A (PKA) pathway, we hypothesized that sex differences in cAMP contribute to differences in Ca(2+) handling. Ca(2+) transients (fura-2) and ionic currents were measured simultaneously (37°C, 2Hz) in ventricular myocytes from adult male and female C57BL/6 mice. Under basal conditions, diastolic Ca(2+), sarcoplasmic reticulum (SR) Ca(2+) stores, and L-type Ca(2+) current did not differ between the sexes. However, female myocytes had smaller Ca(2+) transients (26% smaller), Ca(2+) sparks (6% smaller), and excitation-contraction coupling gain in comparison to males (23% smaller). Interestingly, basal levels of intracellular cAMP were lower in female myocytes (0.7±0.1 vs. 1.7±0.2fmol/μg protein; p<0.001). Importantly, PKA inhibition (2μM H-89) eliminated male-female differences in Ca(2+) transients and gain, as well as Ca(2+) spark amplitude. Western blots showed that PKA inhibition also reduced the ratio of phospho:total RyR2 in male hearts, but not in female hearts. Stimulation of cAMP production with 10μM forskolin abolished sex differences in cAMP levels, as well as differences in Ca(2+) transients, sparks, and gain. To determine if the breakdown of cAMP differed between the sexes, phosphodiesterase (PDE) mRNA levels were measured. PDE3 expression was similar in males and females, but PDE4B expression was higher in female ventricles. The inhibition of cAMP breakdown by PDE4 (10μM rolipram) abolished differences in Ca(2+) transients and gain. These findings suggest that female myocytes have lower levels of basal cAMP due, in part, to higher expression of PDE4B. Lower cAMP levels in females may attenuate PKA phosphorylation of Ca(2+) handling proteins in females, and may limit positive inotropic responses to stimulation of the cAMP/PKA pathway in female hearts.

Sex and sex hormones in cardiac stress--mechanistic insights

Important sex differences in the onset and characteristics of cardiovascular disease are evident, yet the mechanistic details remain unresolved. Men are more susceptible to cardiovascular disease earlier in life, though younger women who have a cardiovascular event are more likely to experience adverse outcomes. Emerging evidence is prompting a re-examination of the conventional view that estrogen is protective and testosterone a liability. The heart expresses both androgen and estrogen receptors and is functionally responsive to circulating sex steroids. New evidence of cardiac aromatase expression indicates local estrogen production may also exert autocrine/paracrine actions in the heart. Cardiomyocyte contractility studies suggest testosterone and estrogen have contrasting inotropic actions, and modulate Ca(2+) handling and transient characteristics. Experimentally, sex differences are also evident in cardiac stress responses. Female hearts are generally less susceptible to acute ischemic damage and associated arrhythmias, and generally are more resistant to stress-induced hypertrophy and heart failure, attributed to the cardioprotective actions of estrogen. However, more recent data show that testosterone can also improve acute post-ischemic outcomes and facilitate myocardial function and survival in chronic post-infarction. The myocardial actions of sex steroids are complex and context dependent. A greater mechanistic understanding of the specific actions of systemic/local sex steroids in different cardiovascular disease states has potential to lead to the development of cardiac therapies targeted specifically for men and women.

Enhanced striatal β1-adrenergic receptor expression following hormone loss in adulthood is programmed by both early sexual differentiation and puberty: a study of humans and rats

After reproductive senescence or gonadectomy, changes occur in neural gene expression, ultimately altering brain function. The endocrine mechanisms underlying these changes in gene expression beyond immediate hormone loss are poorly understood. To investigate this, we measured changes in gene expression the dorsal striatum, where 17β-estradiol modulates catecholamine signaling. In human caudate, quantitative PCR determined a significant elevation in β1-adrenergic receptor (β1AR) expression in menopausal females when compared with similarly aged males. No differences were detected in β2-adrenergic and D1- and D2-dopamine receptor expression. Consistent with humans, adult ovariectomized female rats exhibited a similar increase in β1AR expression when compared with gonadectomized males. No sex difference in β1AR expression was detected between intact adults, prepubertal juveniles, or adults gonadectomized before puberty, indicating the necessity of pubertal development and adult ovariectomy. Additionally, increased β1AR expression in adult ovariectomized females was not observed if animals were masculinized/defeminized with testosterone injections as neonates. To generate a model system for assessing functional impact, increased β1AR expression was induced in female-derived cultured striatal neurons via exposure to and then removal of hormone-containing serum. Increased β1AR action on cAMP formation, cAMP response element-binding protein phosphorylation and gene expression was observed. This up-regulation of β1AR action was eliminated with 17β-estradiol addition to the media, directly implicating this hormone as a regulator of β1AR expression. Beyond having implications for the known sex differences in striatal function and pathologies, these data collectively demonstrate that critical periods early in life and at puberty program adult gene responsiveness to hormone loss after gonadectomy and potentially reproductive senescence.

Sex differences in animal models for cardiovascular diseases and the role of estrogen

Clinical findings show sex differences in the manifestation of a number of cardiovascular diseases (CVD). However, the underlying molecular mechanisms are incompletely understood. Multiple animal models suggest sex differences in the manifestation of CVD, and provide strong experimental evidence that different major pathways are regulated in a sex-specific manner. In most animal studies females display a lower mortality, less severe hypertrophy, and better preserved cardiac function compared with male counterparts. The data support the hypothesis that female sex and/or the sex hormone estrogen (17β-estradiol; E2) may contribute to the sexual dimorphism in the heart and to a better outcome of cardiac diseases in females. To improve our understanding of the sex-based molecular and cellular mechanisms of CVD and to develop new therapeutic strategies, the use of appropriate animal models is essential. This review highlights recent findings from animal models relevant for studying the mechanisms of sexual dimorphisms in the healthy and diseased heart, focusing on physiological hypertrophy (exercise), pathological hypertrophy (volume and pressure overload induced hypertrophy), and heart failure (myocardial infarction). Furthermore, the potential effects of E2 in these models will be discussed.

Specific interactions between Epac1, β-arrestin2 and PDE4D5 regulate β-adrenergic receptor subtype differential effects on cardiac hypertrophic signaling

β1 and β2 adrenergic receptors (βARs) are highly homologous but fulfill distinct physiological and pathophysiological roles. Here we show that both βAR subtypes activate the cAMP-binding protein Epac1, but they differentially affect its signaling. The distinct effects of βARs on Epac1 downstream effectors, the small G proteins Rap1 and H-Ras, involve different modes of interaction of Epac1 with the scaffolding protein β-arrestin2 and the cAMP-specific phosphodiesterase (PDE) variant PDE4D5. We found that β-arrestin2 acts as a scaffold for Epac1 and is necessary for Epac1 coupling to H-Ras. Accordingly, knockdown of β-arrestin2 prevented Epac1-induced histone deacetylase 4 (HDAC4) nuclear export and cardiac myocyte hypertrophy upon β1AR activation. Moreover, Epac1 competed with PDE4D5 for interaction with β-arrestin2 following β2AR activation. Dissociation of the PDE4D5-β-arrestin2 complex allowed the recruitment of Epac1 to β2AR and induced a switch from β2AR non-hypertrophic signaling to a β1AR-like pro-hypertrophic signaling cascade. These findings have implications for understanding the molecular basis of cardiac myocyte remodeling and other cellular processes in which βAR subtypes exert opposing effects.

Gender related alterations of β-adrenoceptor mechanisms in heart failure due to arteriovenous fistula

This study was undertaken to determine gender related changes in different components of β-adrenoceptor (β-AR) system in response to arteriovenous fistula (AV-shunt), which is known to produce heart failure due to volume overload. AV-shunt was induced in male and female rats for 16 weeks by the needle technique; ovariectomized (OVX) rats treated with or without estrogen were also used. Although AV-shunt for 16 weeks produced cardiac hypertrophy in both sexes, male animals showed cardiac dysfunction whereas cardiac performance was maintained in females. Both β(1) -AR and β(2) -AR protein content and mRNA levels were decreased in male and increased in female hearts post-AV-shunt. The basal adenylyl cyclase (AC) activity was lower in the female heart; however, AC protein content and the increase in epinephrine (EPi)-stimulated AC activity were greater in the female AV-shunt group as compared to males. While AC V/VI and β-arrestin 2 mRNA levels were decreased in males, mRNA level for GRK2 was increased in females post-AV-shunt. In contrast to intact females, AV-shunt OVX animals showed depressed cardiac function, decreased β(1) -AR, β(2) -AR, and AC protein content, as well as reduced EPi-stimulated AC activity. Treatment of OVX rats with 17-β estradiol attenuated the AV-shunt induced changes in β-AR and AC protein content as well as cardiac dysfunction. These results reveal that β-AR signal transduction system in response to AV-shunt is downregulated in males and upregulated in females. Furthermore, estrogen appears to play an important role in the upregulation of β-AR mechanisms and the maintenance of cardiac function in AV-shunt females.

Sex differences and the effects of ovariectomy on the β-adrenergic contractile response

The presence of sex differences in myocardial β-adrenergic responsiveness is controversial, and limited studies have addressed the mechanism underlying these differences. Studies were performed using isolated perfused hearts from male, intact female and ovariectomized female mice to investigate sex differences and the effects of ovarian hormone withdrawal on β-adrenergic receptor function. Female hearts exhibited blunted contractile responses to the β-adrenergic receptor agonist isoproterenol (ISO) compared with males but not ovariectomized females. There were no sex differences in β(1)-adrenergic receptor gene or protein expression. To investigate the role of adenylyl cyclase, phosphodiesterase, and the cAMP-signaling cascade in generating sex differences in the β-adrenergic contractile response, dose-response studies were performed in isolated perfused male and female hearts using forskolin, 3-isobutyl-1-methylxanthine (IBMX), and 8-(4-chlorophenylthio)adenosine 3',5'-cyclic monophosphate (CPT-cAMP). Males showed a modestly enhanced contractile response to forskolin at 300 nM and 5 μM compared with females, but there were no sex differences in the response to IBMX or CPT-cAMP. The role of the A(1) adenosine receptor (A(1)AR) in antagonizing the β-adrenergic contractile response was investigated using both the A(1)AR agonist 2-chloro-N(6)-cyclopentyl-adenosine and A(1)AR knockout (KO) mice. Intact females showed an enhanced A(1)AR anti-adrenergic effect compared with males and ovariectomized females. The β-adrenergic contractile response was potentiated in both male and female A(1)ARKO hearts, with sex differences no longer present above 1 nM ISO. The β-adrenergic contractile response is greater in male hearts than females, and minor differences in the action of adenylyl cyclase or the A(1)AR may contribute to these sex differences.