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. While 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 as well as in common animal models of CVD.

Estrogen signaling appears critical in the heart. However a mechanistic understanding of the role of estrogen in the cardiac myocyte is lacking. Moreover, there are multiple cell types in the heart and multiple estrogen receptor (ER) isoforms. Therefore, we studied expression, localization, transcriptional and signaling activity of ERs in isolated cardiac myocytes. We found only ERα RNA (but no ERβ RNA) in cardiac myocytes using two independent methods. The vast majority of full-length ERα protein (ERα66) localizes to cardiac myocyte nuclei where it is competent to activate transcription. Alternate isoforms of ERα encoded by the same genomic locus (ERα46 and ERα36) have differential transcriptional activity in cardiac myocytes but also primarily localize to nuclei. In contrast to other reports, no ERα isoform is competent to activate MAPK or PI3K signaling in cardiac myocytes. Together these data support a role for ERα at the level of transcription in cardiac myocytes.

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Background: Sex is an important modifier of the development of cardiovascular disease; women consistently display less hypertrophy, fewer changes in pathologic gene expression, and less cardiac dysfunction compared to men exposed to the same pathological stimuli. The signaling pathways responsible for these sexual dimorphisms, especially within the cardiomyocyte, are not well understood. Objective: To investigate sexual dimorphisms in activation of signaling pathways and expression of genes related to cardiomyocyte contractility in response to a pathological stimulus in isolated adult rat ventricular myocytes (ARVMs). Methods: ARVMs from both sexes were isolated using a Langendorff perfusion apparatus and treated with the β-adrenergic agonist isoproterenol (ISO) or vehicle (saline) for 24 hours. Activated signaling molecules were detected by performing a phospho-kinase antibody array (R&D Systems) in ARVMs isolated from two rats of each sex treated with ISO or vehicle. Total RNA was isolated from these cells, and real-time PCR was used to determine expression levels of calcium handling genes, including Cav1.2 and sodium calcium exchanger (NCX1). Results: A distinct profile of activated signaling molecules was observed between male and female ARVMs in response to ISO. Female ARVMs displayed activation of kinases such as Akt, ERK1/2, p38α, GSK3α/β and MSK1/2. Male ARVMs were characterized by an activation of signaling molecules such as PLCγ1, RSK1/2/3 and c-Jun. ARVMs of both sexes displayed activation of signaling molecules such as eNOS, STAT3 and mTOR. Because the activated signaling molecules identified with the array can modulate expression of calcium handling genes, expression of these genes was analyzed. In response to ISO treatment, female ARVMs displayed an increase in NCX1 expression normalized to vehicle (1.63 ± 0.079) as well as Cav1.2 expression (1.48 ± 0.072). However, these increases were not observed in male cells. Conclusions: Cardiomyocytes isolated from rats of different sexes display distinct responses to the pathological stimulus ISO. Understanding the mechanisms responsible for these sexual dimorphisms can lead to the development of more effective treatment options for both men and women with cardiovascular disease.