Myocardial and Cardiomyocyte Stress Resilience Is Enhanced in Aromatase-Deficient Female Mouse Hearts Through CaMKIIδ Activation

Abstract

The role of sex steroids in cardioprotection is contentious, with large clinical trials investigating hormone supplementation failing to deliver outcomes expected from observational studies. Mechanistic understanding of androgen/estrogen myocardial actions is lacking. Using a genetic model of aromatase tissue deficiency (ArKO) in female mice, the goal of this investigation was to evaluate the capacity of a shift in cardiac endogenous steroid conversion to influence ischemia-reperfusion resilience by optimizing cardiomyocyte Ca2+ handling responses. In isolated normoxic cardiomyocytes, basal Ca2+ transient amplitude and extent of shortening were greater in ArKO myocytes, with preservation of diastolic Ca2+ levels. Isolated ArKO cardiomyocytes exposed to a high Ca2+ load exhibited greater Ca2+ transient and contractile amplitudes, associated with a greater postrest spontaneous sarcoplasmic reticulum Ca2+ load-release. Microarray differential gene expression analysis of normoxic ventricular tissues from ArKO vs wild-type identified a significant influence of aromatase on genes involved in cardiac Ca2+ handling and signaling [including calmodulin dependent kinase II (CaMKII)-δ], myofilament structure and function, glucose uptake and signaling, and enzymes controlling phosphorylation-specific posttranslational modification status. CaMKII expression was not changed in ventricular tissues, although CaMKIIδ activation and phosphorylation of downstream targets was enhanced in ArKO hearts subjected to ischemia-reperfusion. Overall, this investigation shows that relative withdrawal of estrogen in favor of testosterone through genetically induced tissue aromatase deficiency in females modifies the gene expression profile to effect inotropic support via optimized Ca2+ handling in response to stress, with a modest impact on basal function. Consideration of aromatase inhibition, acutely or chronically, may have a role in cardioprotection, of particular relevance to women.

Genome-Wide Temporal Profiling of Transcriptome and Open Chromatin of Early Cardiomyocyte Differentiation Derived From hiPSCs and hESCs

“…Enriched GO terms (BP) included “cell cycle” and “mitosis” of undifferentiated cells (day 0); embryonic development-related GO terms (such as “anterior/posterior pattern formation” and “pattern specification process”) for the mesoderm (day 2) to cardiac mesoderm transition (day 4); and cardiac development- and cardiomyocyte function-related terms from cardiac mesoderm to cardiomyocytes (day 30) ( e.g ., “heart development”, “heart morphogenesis” and “regulation of heart contraction”). The representative genes assigned to these GO terms included NANOG and SOX2 (known TFs in undifferentiated stem cells); 16 T , eomesodermin ( EOMES ), Wnt family member 3A ( WNT3A ), bone morphogenetic protein 2 ( BMP2 ), MESP1 and mix paired-like homeobox 1 ( MIXL1 ) (which are known key TFs and factors for mesoderm development); 11, 17-21 NKX2-5 , GATA binding protein 4 ( GATA4 ), T-box transcription factor 5 ( TBX5 ), heart and neural crest derivatives expressed 2 ( HAND2 ) and ISL1 (which are known TFs regulating cardiac development); 6, 12, 22 and TNNT2 , troponin I, cardiac muscle ( TNNI3 ), myosin light chain 3 ( MYL3 ) and calcium/calmodulin-dependent protein kinase II delta ( CAMK2D ) for cardiac structure and heart contraction 23-26 (Figure 2C). The similar dynamic changes in enriched GO terms are correlated with the concordant transcriptome profiles of the four cell lines, and also reflect features of the cardiac differentiation that were observed in previous studies in other model systems.…”

The protective role of estrogen and estrogen receptors in cardiovascular disease and the controversial use of estrogen therapy

“…Bell et al investigated the role of aromatase deficiency in I/R injury using aromatase knockout (ArKO) female mice and found that the recovery of left ventricular developed pressure as well calcium handling was substantially improved in ArKO versus wild-type (WT) mouse hearts [ 103 ]. Later on, the same group demonstrated that isolated cardiomyocytes from ArKO female mice exhibited greater basal calcium transient amplitude and shortening than in WT [ 104 ]. Isolated cardiomyocytes from ArKO female mice exposed to a high-calcium load also showed increased calcium transient and contractile amplitudes.…”

“…Isolated cardiomyocytes from ArKO female mice exposed to a high-calcium load also showed increased calcium transient and contractile amplitudes. The study concluded that the relative withdrawal of E2 in favor of testosterone may be positive inotropic via optimized calcium handling in response to stress and aromatase inhibition which could lead to cardioprotection [ 104 ]. Bell et al also studied whether upregulation of tissue aromatase expression could improve ischemic resilience in male hearts by subjecting male mice in which aromatase was transgenically upregulated (AROM+) to I/R injury [ 105 ].…”

Aromatase Blockade Is Associated With Increased Mortality in Acute Illness in Male Mice

“…Because increased estrogen stimulation of the intima results in vasodilation, increased intimal aromatase expression may benefit the response to acute illness by increasing blood flow to the heart and other tissues. However, the array of myocardial estrogen actions during acute illness may be complex with studies in aromatase knockout mice or aromatase-overexpressing mice, indicating that cardiac aromatase activity in a mouse model of ischemia is inversely related to myocardial recovery [ 19 , 23 , 34 ].…”