Sex differences in cardiomyocyte connexin43 expression

Sex in cardiovascular disease: Why this biological variable should be considered in in vitro models

Cardiovascular disease (CVD), the world's leading cause of death, exhibits notable epidemiological, clinical, and pathophysiological differences between sexes. Many such differences can be linked back to cardiovascular sexual dimorphism, yet sex-specific in vitro models are still not the norm. A lack of sex reporting and apparent male bias raises the question of whether in vitro CVD models faithfully recapitulate the biology of intended treatment recipients. To ensure equitable treatment for the overlooked female patient population, sex as a biological variable (SABV) inclusion must become commonplace in CVD preclinical research. Here, we discuss the role of sex in CVD and underlying cardiovascular (patho)physiology. We review shortcomings in current SABV practices, describe the relevance of sex, and highlight emerging strategies for SABV inclusion in three major in vitro model types: primary cell, stem cell, and three-dimensional models. Last, we identify key barriers to inclusive design and suggest techniques for overcoming them.

LBBB and heart failure-Relationships among QRS amplitude, duration, height, LV mass, and sex

BACKGROUND

Height, left ventricular (LV) size, and sex were proposed as additional criteria for patient selection for cardiac resynchronization therapy (CRT) but their connections with the QRS complex in left bundle branch block (LBBB) are little investigated. We evaluated these.

METHODS

Among patients with "true" LBBB, QRS duration (QRSd) and amplitude, and LV hypertrophy indices, were correlated with patient's height and LV mass, and compared between sexes.

RESULTS

In this study cohort (n = 220; 60 ± 12 years; left ventricular ejection fraction [LVEF] 21 ± 7%; mostly New York Heart Association II-III, QRSd 165 ± 19 ms; 57% female; 70% responders [LVEF increased ≥5%]), LV mass was increased in all patients. QRS amplitude did not correlate with LV mass or height in any individual lead or with Sokolow-Lyon or Cornell-Lyon indices. QRSd did not correlate with height. In contrast, QRSd correlated strongly with LV mass (r = .51). CRT response rate was greater in women versus men (84% vs. 58%, p < .001) despite shorter QRSd [7% shorter (p < .0001)]. QRSd normalized for height resulted in a 2.7% and for LV mass 24% greater index in women.

CONCLUSION

True LBBB criteria do not exclude HF patients with increased LV mass. QRS amplitudes do not correlate with height or LV mass. Height does not affect QRSd. However, QRSd correlates with LV size. QRSd normalized for LV mass results in 24% greater value in women in the direction of sex-specific responses. LV mass may be a significant nonelectrical modifier of QRSd for CRT.

Female cardiovascular biology and resilience in the setting of physiological and pathological stress

For years, females were thought of as smaller men with complex hormonal cycles; as a result, females have been largely excluded from preclinical and clinical research. However, in the last ten years, with the increased focus on sex as a biological variable, it has become clear that this is not the case, and in fact, male and female cardiovascular biology and cardiac stress responses differ substantially. Premenopausal women are protected from cardiovascular diseases, such as myocardial infarction and resultant heart failure, having preserved cardiac function, reduced adverse remodeling, and increased survival. Many underlying biological processes that contribute to ventricular remodeling differ between the sexes, such as cellular metabolism; immune cell responses; cardiac fibrosis and extracellular matrix remodeling; cardiomyocyte dysfunction; and endothelial biology; however, it is unclear how these changes afford protection to the female heart. Although many of these changes are dependent on protection provided by female sex hormones, several of these changes occur independent of sex hormones, suggesting that the nature of these changes is more complex than initially thought. This may be why studies focused on the cardiovascular benefits of hormone replacement therapy in post-menopausal women have provided mixed results. Some of the complexity likely stems from the fact that the cellular composition of the heart is sexually dimorphic and that in the setting of MI, different subpopulations of these cell types are apparent. Despite the documented sex-differences in cardiovascular (patho)physiology, the underlying mechanisms that contribute are largely unknown due to inconsistent findings amongst investigators and, in some cases, lack of rigor in reporting and consideration of sex-dependent variables. Therefore, this review aims to describe current understanding of the sex-dependent differences in the myocardium in response to physiological and pathological stressors, with a focus on the sex-dependent differences that contribute to post-infarction remodeling and resultant functional decline.

Hypertension Induces Pro-arrhythmic Cardiac Connexome Disorders: Protective Effects of Treatment

Prolonged population aging and unhealthy lifestyles contribute to the progressive prevalence of arterial hypertension. This is accompanied by low-grade inflammation and over time results in heart dysfunction and failure. Hypertension-induced myocardial structural and ion channel remodeling facilitates the development of both atrial and ventricular fibrillation, and these increase the risk of stroke and sudden death. Herein, we elucidate hypertension-induced impairment of "connexome" cardiomyocyte junctions. This complex ensures cell-to-cell adhesion and coupling for electrical and molecular signal propagation. Connexome dysfunction can be a key factor in promoting the occurrence of both cardiac arrhythmias and heart failure. However, the available literature indicates that arterial hypertension treatment can hamper myocardial structural remodeling, hypertrophy and/or fibrosis, and preserve connexome function. This suggests the pleiotropic effects of antihypertensive agents, including anti-inflammatory. Therefore, further research is required to identify specific molecular targets and pathways that will protect connexomes, and it is also necessary to develop new approaches to maintain heart function in patients suffering from primary or pulmonary arterial hypertension.

The effect of sex and age on ex vivo cardiac electrophysiology: insight from a guinea pig model

Highlighting the importance of sex as a biological variable, we recently reported sex differences in guinea pig in vivo electrocardiogram (ECG) measurements. However, substantial inconsistencies exist in this animal model, with conflicting reports of sex-specific differences in cardiac electrophysiology observed in vivo and in vitro. Herein, we evaluated whether sexual dimorphism persists in ex vivo preparations, using an isolated intact heart preparation. Pseudo-ECG recordings were collected in conjunction with dual optical mapping of transmembrane voltage and intracellular calcium from Langendorff-perfused hearts. In contrast to our in vivo results, we did not observe sex-specific differences in ECG parameters collected from isolated hearts. Furthermore, we observed significant age-specific differences in action potential duration (APD) and Ca2+ transient duration (CaD) during both normal sinus rhythm (NSR) and in response to dynamic pacing but only a modest sex-specific difference in CaD30. Similarly, the alternans fluctuation coefficient, conduction velocity during sinus rhythm or in response to pacing, and electrophysiology parameters (atrioventricular nodal effective refractory period, Wenckebach cycle length) were comparable between males and females. Results of our study suggest that the observed sex-specific differences in in vivo ECG parameters from guinea pigs are diminished in ex vivo isolated heart preparations, although age-specific patterns are prevalent. To assess sex as a biological variable in cardiac electrophysiology, a comprehensive approach may be necessary using both in vitro measurements from cardiomyocyte or intact heart preparations with secondary follow-up in vivo studies.NEW & NOTEWORTHY We evaluated whether the guinea pig heart has intrinsic sex-specific differences in cardiac electrophysiology. Although we observed sex-specific differences in in vivo ECGs, these differences did not persist ex vivo. Using a whole heart model, we observed similar APD, CaD, conduction velocity, and alternans susceptibility in males and females. We conclude that sex-specific differences in guinea pig cardiac electrophysiology are likely influenced by the in vivo environment and less dependent on the intrinsic electrical properties of the heart.

Neurotoxic Astrocytes Directly Converted from Sporadic and Familial ALS Patient Fibroblasts Reveal Signature Diversities and miR-146a Theragnostic Potential in Specific Subtypes

A lack of stratification methods in patients with amyotrophic lateral sclerosis (ALS) is likely implicated in therapeutic failures. Regional diversities and pathophysiological abnormalities in astrocytes from mice with SOD1 mutations (mSOD1-ALS) can now be explored in human patients using somatic cell reprogramming. Here, fibroblasts from four sporadic (sALS) and three mSOD1-ALS patients were transdifferentiated into induced astrocytes (iAstrocytes). ALS iAstrocytes were neurotoxic toward HB9-GFP mouse motor neurons (MNs) and exhibited subtype stratification through GFAP, CX43, Ki-67, miR-155 and miR-146a expression levels. Up- (two cases) and down-regulated (three cases) miR-146a values in iAstrocytes were recapitulated in their secretome, either free or as cargo in small extracellular vesicles (sEVs). We previously showed that the neuroprotective phenotype of depleted miR-146 mSOD1 cortical astrocytes was reverted by its mimic. Thus, we tested such modulation in the most miR-146a-depleted patient-iAstrocytes (one sALS and one mSOD1-ALS). The miR-146a mimic in ALS iAstrocytes counteracted their reactive/inflammatory profile and restored miR-146a levels in sEVs. A reduction in lysosomal activity and enhanced synaptic/axonal transport-related genes in NSC-34 MNs occurred after co-culture with miR-146a-modulated iAstrocytes. In summary, the regulation of miR-146a in depleted ALS astrocytes may be key in reestablishing their normal function and in restoring MN lysosomal/synaptic dynamic plasticity in disease sub-groups.

Chronic Stress and Gonadectomy Affect the Expression of Cx37, Cx40 and Cx43 in the Spinal Cord

The study aimed to determine whether the exposure to chronic stress and/or performance of gonadectomy might lead to disturbance in the expression of connexin (Cx) 37, 40 and 43 in the spinal cord (SC), as a potential explanation for sex differences in stress-related chronic pain conditions. After the rats were sham-operated or gonadectomized, three 10-day sessions of sham or chronic stress were applied. Immunohistochemistry and transmission electron microscopy (TEM) were used to examine Cx localization and expression in the SC. The gonadectomy resulted in an increase of Cx37 expression in the dorsal horn (DH) of the female rats, but chronic stress suppressed the effects of castration. In male rats, only the combined effects of castration and chronic stress increased Cx37 expression. The influence of chronic stress on the DH Cx40 expression was inversely evident after the castration: increased in the ovariectomized female rats, while decreased in the orchidectomized male rats. We did not find any effect of chronic stress and castration, alone or together, on Cx43 expression in the DH, but the percentage of Cx43 overlapping the astrocyte marker glial fibrillary acidic protein (gfap) increased in the male stressed group after the castration. In conclusion, the association of the chronic stress with sex hormone depletion results in disturbances of the SC Cx expression and might be a possible mechanism of disturbed pain perception after chronic stress exposure.

Omacor Protects Normotensive and Hypertensive Rats Exposed to Continuous Light from Increased Risk to Malignant Cardiac Arrhythmias

Light pollution disturbs circadian rhythm, and this can also be deleterious to the heart by increased susceptibility to arrhythmias. Herein, we investigated if rats exposed to continuous light had altered myocardial gene transcripts and/or protein expression which affects arrhythmogenesis. We then assessed if Omacor^® supplementation benefitted affected rats. Male and female spontaneously hypertensive (SHR) and normotensive Wistar rats (WR) were housed under standard 12 h/12 h light/dark cycles or exposed to 6-weeks continuous 300 lux light for 24 h. Half the rats were then treated with 200 mg/100 g b.w. Omacor^®. Continuous light resulted in higher male rat vulnerability to malignant ventricular fibrillation (VF). This was linked with myocardial connexin-43 (Cx43) down-regulation and deteriorated intercellular electrical coupling, due in part to increased pro-inflammatory NF-κB and iNOS transcripts and decreased sarcoplasmic reticulum Ca²⁺ATPase transcripts. Omacor^® treatment increased the electrical threshold to induce the VF linked with amelioration of myocardial Cx43 mRNA and Cx43 protein levels and the suppression of NF-κB and iNOS. This indicates that rat exposure to continuous light results in deleterious cardiac alterations jeopardizing intercellular Cx43 channel-mediated electrical communication, thereby increasing the risk of malignant arrhythmias. The adverse effects were attenuated by treatment with Omacor^®, thus supporting its potential benefit and the relevance of monitoring omega-3 index in human populations at risk.

Matters of the heart: Cellular sex differences

Nearly all cardiovascular diseases show sexual dimorphisms in prevalence, presentation, and outcomes. Until recently, most clinical trials were carried out in males, and many animal studies either failed to identify the sex of the animals or combined data obtained from males and females. Cellular sex in the heart is relatively understudied and many studies fail to report the sex of the cells used for in vitro experiments. Moreover, in the small number of studies in which sex is reported, most of those studies use male cells. The observation that cells from males and females are inherently different is becoming increasingly clear - either due to acquired differences from hormones and other factors or due to intrinsic differences in genotype (XX or XY). Because of the likely contribution of cellular sex differences in cardiac health and disease, here, we explore differences in mammalian male and female cells in the heart, including the less-studied non-myocyte cell populations. We discuss how the heart's microenvironment impacts male and female cellular phenotypes and vice versa, including how secretory profiles are dependent on cellular sex, and how hormones contribute to sexually dimorphic phenotypes and cellular functions. Intracellular mechanisms that contribute to sex differences, including gene expression and epigenetic remodeling, are also described. Recent single-cell sequencing studies have revealed unexpected sex differences in the composition of cell types in the heart which we discuss. Finally, future recommendations for considering cellular sex differences in the design of bioengineered in vitro disease models of the heart are provided.

Role of Connexin 43 in an Inflammatory Model for TMJ Hyperalgesia

Temporomandibular joint disorders (TMD) consist of a heterogeneous group of conditions that present with pain in the temporomandibular joint (TMJ) region and muscles of mastication. This project assessed the role of connexin 43 (Cx43), a gap junction protein, in the trigeminal ganglion (TG) in an animal model for persistent inflammatory TMJ hyperalgesia. Experiments were performed in male and female rats to determine if sex differences influence the expression and/or function of Cx43 in persistent TMJ hyperalgesia. Intra-TMJ injection of Complete Freund's Adjuvant (CFA) caused a significant increase in Cx43 expression in the TG at 4 days and 10 days post-injection in ovariectomized (OvX) female rats and OvX females treated with estradiol (OvXE), while TG samples in males revealed only marginal increases. Intra-TG injection of interference RNA for Cx43 (siRNA Cx43) 3 days prior to recording, markedly reduced TMJ-evoked masseter muscle electromyographic (MMemg) activity in all CFA-inflamed rats, while activity in sham animals was not affected. Western blot analysis revealed that at 3 days after intra-TG injection of siRNA Cx43 protein levels for Cx43 were significantly reduced in TG samples of all CFA-inflamed rats. Intra-TG injection of the mimetic peptide GAP19, which inhibits Cx43 hemichannel formation, greatly reduced TMJ-evoked MMemg activity in all CFA-inflamed groups, while activity in sham groups was not affected. These results revealed that TMJ inflammation caused a persistent increase in Cx43 protein in the TG in a sex-dependent manner. However, intra-TG blockade of Cx43 by siRNA or by GAP19 significantly reduced TMJ-evoked MMemg activity in both males and females following TMJ inflammation. These results indicated that Cx43 was necessary for enhanced jaw muscle activity after TMJ inflammation in males and females, a result that could not be predicted on the basis of TG expression of Cx43 alone.

Connexin 43 and Connexin 26 Involvement in the Ponatinib-Induced Cardiomyopathy: Sex-Related Differences in a Murine Model

Cardiac connexins (Cxs) are proteins responsible for proper heart function. They form gap junctions that mediate electrical and chemical signalling throughout the cardiac system, and thus enable a synchronized contraction. Connexins can also individually participate in many signal transduction pathways, interacting with intracellular proteins at various cellular compartments. Altered connexin expression and localization have been described in diseased myocardium and the aim of this study is to assess the involvement of Cx43, Cx26, and some related molecules in ponatinib-induced cardiac toxicity. Ponatinib is a new multi-tyrosine kinase inhibitor that has been successfully used against human malignancies, but its cardiotoxicity remains worrisome. Therefore, understanding its signaling mechanism is important to adopt potential anti cardiac damage strategies. Our experiments were performed on hearts from male and female mice treated with ponatinib and with ponatinib plus siRNA-Notch1 by using immunofluorescence, Western blotting, and proteomic analyses. The altered cardiac function and the change in Cxs expression observed in mice after ponatinib treatment, were results dependent on the Notch1 pathway and sex. Females showed a lower susceptibility to ponatinib than males. The downmodulation of cardiac Cx43, Cx26 and miR-122, high pS368-Cx43 phosphorylation, cell viability and survival activation could represent some of the female adaptative/compensatory reactions to ponatinib cardiotoxicity.

Restoration of Adiponectin-Connexin43 Signaling Mitigates Myocardial Inflammation and Dysfunction in Diabetic Female Rats

ur preclinical findings replicated women's hypersensitivity to type-2 diabetes mellitus (T2DM)-evoked cardiac dysfunction along with demonstrating estrogen (E2)-dependent disruption of the cardiac adiponectin (APN)-connexin43 (Cx43) signaling. Whether the latter molecular anomaly underlies this women's cardiovascular health problem remains unknown. We hypothesized that restoration of the disrupted APN-Cx43 signaling alleviates this sex/E2-dependent cardiac dysfunction in diabetic female rats. To test this hypothesis, we administered the adiponectin receptor 1 (AdipoR1) agonist AdipoRon (30 mg/kg/d for 10 days) to female sham operated (SO) and ovariectomized (OVX) rats, which exhibited and lacked the T2DM left ventricular (LV) dysfunction, respectively, when fed high-fat diet and received low dose streptozotocin regimen; nondiabetic control SO and OVX rats received control diet and vehicle for streptozotocin. In T2DM SO rats, LV dysfunction, AdipoRon mitigated: (1) LV hypertrophy, (2) reductions in fractional shortening, LV developed pressure, dP/dtmax, dP/dtmin, and Tau. In LV tissues of the same rats, AdipoRon reversed reduction in Cx43 and elevations in TNFα, heme-oxygenase 1 (HO-1), and circulating cardiovascular risk factor asymmetric dimethylarginine. The findings also revealed ovarian hormones independent effects of AdipoRon, which included dampening of the pro-oxidant enzyme HO-1. These novel findings yield new insight into a causal role for compromised APN-Cx43 signaling in the E2-dependent hypersensitivity to T2DM-evoked cardiac inflammation and dysfunction. Equally important, the findings identify restoration of Cx43 signaling as a viable therapeutic modality for alleviating this women's cardiovascular health-related problem.

Non-coding RNAs and Cardiac Arrhythmias

Cardiac arrhythmias represent wide and heterogenic group of disturbances in the cardiac rhythm. Pathophysiology of individual arrhythmias is highly complex and dysfunction in ion channels/currents involved in generation or spreading of action potential is usually documented. Non-coding RNAs (ncRNAs) represent highly variable group of molecules regulating the heart expression program, including regulation of the expression of individual ion channels and intercellular connection proteins, e.g. connexins.Within this chapter, we will describe basic electrophysiological properties of the myocardium. We will focus on action potential generation and spreading in pacemaker and non-pacemaker cells, including description of individual ion channels (natrium, potassium and calcium) and their ncRNA-mediated regulation. Most of the studies have so far focused on microRNAs, thus, their regulatory function will be described into greater detail. Clinical consequences of altered ncRNA regulatory function will also be described together with potential future directions of the research in the field.

Lymphatic Function and Dysfunction in the Context of Sex Differences

Endothelial cells are the building blocks of the blood vascular system and exhibit well-characterized sexually dimorphic phenotypes with regard to chromosomal and hormonal sex, imparting innate genetic and physiological differences between male and female vascular systems and cardiovascular disease. However, even though females are predominantly affected by disorders of lymphatic vascular function, we lack a comprehensive understanding of the effects of sex and sex hormones on lymphatic growth, function, and dysfunction. Here, we attempt to comprehensively evaluate the current understanding of sex as a biological variable influencing lymphatic biology. We first focus on elucidating innate and fundamental differences between the sexes in lymphatic function and development. Next, we delve into lymphatic disease and explore the potential underpinnings toward bias prevalence in the female population. Lastly, we incorporate more broadly the role of the lymphatic system in sex-biased diseases such as cancer, cardiovascular disease, reproductive disorders, and autoimmune diseases to explore whether and how sex differences may influence lymphatic function in the context of these pathologies.

Modeling cardiac complexity: Advancements in myocardial models and analytical techniques for physiological investigation and therapeutic development in vitro

Cardiomyopathies, heart failure, and arrhythmias or conduction blockages impact millions of patients worldwide and are associated with marked increases in sudden cardiac death, decline in the quality of life, and the induction of secondary pathologies. These pathologies stem from dysfunction in the contractile or conductive properties of the cardiomyocyte, which as a result is a focus of fundamental investigation, drug discovery and therapeutic development, and tissue engineering. All of these foci require in vitro myocardial models and experimental techniques to probe the physiological functions of the cardiomyocyte. In this review, we provide a detailed exploration of different cell models, disease modeling strategies, and tissue constructs used from basic to translational research. Furthermore, we highlight recent advancements in imaging, electrophysiology, metabolic measurements, and mechanical and contractile characterization modalities that are advancing our understanding of cardiomyocyte physiology. With this review, we aim to both provide a biological framework for engineers contributing to the field and demonstrate the technical basis and limitations underlying physiological measurement modalities for biologists attempting to take advantage of these state-of-the-art techniques.

Mechanical activation of noncoding-RNA-mediated regulation of disease-associated phenotypes in human cardiomyocytes

How common polymorphisms in noncoding genome regions can regulate cellular function remains largely unknown. Here we show that cardiac fibrosis, mimicked using a hydrogel with controllable stiffness, affects the regulation of the phenotypes of human cardiomyocytes by a portion of the long noncoding RNA ANRIL, the gene of which is located in the disease-associated 9p21 locus. In a physiological environment, cultured cardiomyocytes derived from induced pluripotent stem cells obtained from patients who are homozygous for cardiovascular-risk alleles (R/R cardiomyocytes) or from healthy individuals who are homozygous for nonrisk alleles contracted synchronously, independently of genotype. After hydrogel stiffening to mimic fibrosis, only the R/R cardiomyocytes exhibited asynchronous contractions. These effects were associated with increased expression of the short ANRIL isoform in R/R cardiomyocytes, which induced a c-Jun N-terminal kinase (JNK) phosphorylation-based mechanism that impaired gap junctions (particularly, loss of connexin-43 expression) following stiffening. Deletion of the risk locus or treatment with a JNK antagonist was sufficient to maintain gap junctions and prevent asynchronous contraction of cardiomyocytes. Our findings suggest that mechanical changes in the microenvironment of cardiomyocytes can activate the regulation of their function by noncoding loci.

Estrogen-Dependent Disruption of Adiponectin-Connexin43 Signaling Underlies Exacerbated Myocardial Dysfunction in Diabetic Female Rats

The reasons for the higher severity of type 2 diabetes (T2DM)-associated cardiomyopathy in women, despite their inherent estrogen (E2)-dependent cardioprotection, remain unknown. We hypothesized that the reliance of the healthy females' hearts on augmented adiponectin (APN)-connexin 43 (Cx43) signaling becomes paradoxically detrimental when disrupted by T2DM in an E2-dependent manner. We tested this hypothesis in high-fat, low- dose streptozotocin diabetic rats and their controls with the following designations: 1) sham-operated (SO), 2) ovariectomized (OVX), 3) ovariectomized with E2 supplementation (OVX + E2), and 4) male. E2-replete (SO or OVX + E2) diabetic rats exhibited higher mortality and greater increases in left ventricular (LV) mass and reduced LV developed pressure, LV contractility, and fractional shortening but preserved ejection fraction. Further, compared with respective nondiabetic counterparts, the hearts of these E2-replete diabetic rats exhibited greater upregulation of cardiac estrogen receptor α and reductions in Cx43 expression and in the phosphorylation levels of the survival molecules extracellular regulating kinases 1/2 and phosphorylated AKT (pAKT). Whereas serum APN was reduced, independent of sex and ovarian hormone status in all DM rats, cardiac APN was most drastically reduced in DM SO rats. The present translational findings are the first to implicate ovarian hormones/E2 in the exacerbated myocardial dysfunction in female diabetic subjects and to suggest a pivotal role for malfunctioning cardiac APN-Cx43 signaling in this sex/E2-specific clinical problem.

Sexual difference of small RNA expression in Tetralogy of Fallot

Small RNAs, especially the microRNAs, have been revealed to play great roles in heart development and congenital heart defects. Several studies have shown dysregulated miRNAs in ventricular tissues of Tetralogy of Fallot (TOF) patients. In the present study, we conducted high throughput sequencing to obtain the global profiling of small RNA transcriptome in heart right ventricular samples from 10 age -matched TOF patients. These samples showed dominant composition of miRNA and mitochondrial associated RNAs. By sRNA cluster identification and differential gene expression analysis, significant sexual difference was discovered for sRNA expression in TOF patients. miR-1/miR-133, which have been identified as essential for cardiac development, account for the most variance of sRNA expression between sexes in TOF hearts.

Connexin 43 Plays a Role in Pulmonary Vascular Reactivity in Mice

Pulmonary arterial hypertension (PAH) is a chronic condition characterized by vascular remodeling and increased vaso-reactivity. PAH is more common in females than in males (~3:1). Connexin (Cx)43 has been shown to be involved in cellular communication within the pulmonary vasculature. Therefore, we investigated the role of Cx43 in pulmonary vascular reactivity using Cx43 heterozygous (Cx43+/−) mice and 37,43Gap27, which is a pharmacological inhibitor of Cx37 and Cx43. Contraction and relaxation responses were studied in intra-lobar pulmonary arteries (IPAs) derived from normoxic mice and hypoxic mice using wire myography. IPAs from male Cx43+/− mice displayed a small but significant increase in the contractile response to endothelin-1 (but not 5-hydroxytryptamine) under both normoxic and hypoxic conditions. There was no difference in the contractile response to endothelin-1 (ET-1) or 5-hydroxytryptamine (5-HT) in IPAs derived from female Cx43+/−mice compared to wildtype mice. Relaxation responses to methacholine (MCh) were attenuated in IPAs from male and female Cx43+/− mice or by pre-incubation of IPAs with 37,43Gap27. Nω-Nitro-L-arginine methyl ester (l-NAME) fully inhibited MCh-induced relaxation. In conclusion, Cx43 is involved in nitric oxide (NO)-induced pulmonary vascular relaxation and plays a gender-specific and agonist-specific role in pulmonary vascular contractility. Therefore, reduced Cx43 signaling may contribute to pulmonary vascular dysfunction.

Hyperandrogenemia reduces endothelium-derived hyperpolarizing factor-mediated relaxation in mesenteric artery of female rats

Women with polycystic ovary syndrome (PCOS) are often presented with hyperandrogenemia along with vascular dysfunction and elevated blood pressure. In animal models of PCOS, anti-androgen treatment decreased blood pressure, indicating a key role for androgens in the development of hypertension. However, the underlying androgen-mediated mechanism that contributes to increased blood pressure is not known. This study determined whether elevated androgens affect endothelium-derived hyperpolarizing factor (EDHF)-mediated vascular relaxation responses through alteration in function of gap junctional proteins. Female rats were implanted with placebo or dihydrotestosterone (DHT) pellets (7.5 mg, 90-day release). After 12 weeks of DHT exposure, blood pressure was assessed through carotid arterial catheter and endothelium-dependent mesenteric arterial EDHF relaxation using wire myograph. Connexin expression in mesenteric arteries was also examined. Elevated DHT significantly increased mean arterial pressure and decreased endothelium-dependent EDHF-mediated acetylcholine relaxation. Inhibition of Cx40 did not have any effect, while inhibition of Cx37 decreased EDHF relaxation to a similar magnitude in both controls and DHT females. On the other hand, inhibition of Cx43 significantly attenuated EDHF relaxation in mesenteric arteries of controls but not DHT females. Elevated DHT did not alter Cx37 or Cx40, but decreased Cx43 mRNA and protein levels in mesenteric arteries. In vitro exposure of DHT to cultured mesenteric artery smooth muscle cells dose-dependently downregulated Cx43 expression. In conclusion, increased blood pressure in hyperandrogenic females is due, at least in part, to decreased EDHF-mediated vascular relaxation responses. Decreased Cx43 expression and activity may play a role in contributing to androgen-induced decrease in EDHF function.

Amylin and diabetic cardiomyopathy - amylin-induced sarcolemmal Ca2+ leak is independent of diabetic remodeling of myocardium

Amylin is a pancreatic β-cell hormone co-secreted with insulin, plays a role in normal glucose homeostasis, and forms amyloid in the pancreatic islets of individuals with type-2 diabetes. Aggregated amylin is also found in blood and extra-pancreatic tissues, including myocardium. Myocardial amylin accumulation is associated with myocyte Ca²⁺ dysregulation in diabetic rats expressing human amylin. Whether deposition of amylin in the heart is a consequence of or a contributor to diabetic cardiomyopathy remains unknown. We used amylin knockout (AKO) mice intravenously infused with either human amylin (i.e, the aggregated form) or non-amyloidogenic (i.e., monomeric) rodent amylin to test the hypothesis that aggregated amylin accumulates in the heart in the absence of diabetes. AKO mice infused with human amylin, but not rodent amylin, showed amylin deposits in the myocardium. Cardiac amylin level was larger in males compared to females. Sarcolemmal Ca²⁺ leak and Ca²⁺ transients were increased in myocytes isolated from males infused with human amylin while no significant changes occurred in either females injected with human amylin or in rat amylin-infused mice. In isolated cardiac myocytes, the amylin receptor antagonist AC-187 did not effectively block the interaction of amylin with the sarcolemma. In conclusion, circulating aggregated amylin accumulates preferentially in male vs. female hearts and its effects on myocyte Ca²⁺ cycling do not require diabetic remodeling of the myocardium. This article is part of a Special issue entitled Cardiac adaptations to obesity, diabetes and insulin resistance, edited by Professors Jan F.C. Glatz, Jason R.B. Dyck and Christine Des Rosiers.

Connexins in Cardiovascular and Neurovascular Health and Disease: Pharmacological Implications

Connexins are ubiquitous channel forming proteins that assemble as plasma membrane hemichannels and as intercellular gap junction channels that directly connect cells. In the heart, gap junction channels electrically connect myocytes and specialized conductive tissues to coordinate the atrial and ventricular contraction/relaxation cycles and pump function. In blood vessels, these channels facilitate long-distance endothelial cell communication, synchronize smooth muscle cell contraction, and support endothelial-smooth muscle cell communication. In the central nervous system they form cellular syncytia and coordinate neural function. Gap junction channels are normally open and hemichannels are normally closed, but pathologic conditions may restrict gap junction communication and promote hemichannel opening, thereby disturbing a delicate cellular communication balance. Until recently, most connexin-targeting agents exhibited little specificity and several off-target effects. Recent work with peptide-based approaches has demonstrated improved specificity and opened avenues for a more rational approach toward independently modulating the function of gap junctions and hemichannels. We here review the role of connexins and their channels in cardiovascular and neurovascular health and disease, focusing on crucial regulatory aspects and identification of potential targets to modify their function. We conclude that peptide-based investigations have raised several new opportunities for interfering with connexins and their channels that may soon allow preservation of gap junction communication, inhibition of hemichannel opening, and mitigation of inflammatory signaling.

Sex differences in response to miRNA-34a therapy in mouse models of cardiac disease: identification of sex-, disease- and treatment-regulated miRNAs

KEY POINTS

MicroRNA (miRNA)-based therapies are in development for numerous diseases, including heart disease. Currently, very limited basic information is available on the regulation of specific miRNAs in male and female hearts in settings of disease. The identification of sex-specific miRNA signatures has implications for translation into the clinic and suggests the need for customised therapy. In the present study, we found that a miRNA-based treatment inhibiting miRNA-34a (miR-34a) was more effective in females in a setting of moderate dilated cardiomyopathy than in males. Furthermore, the treatment showed little benefit for either sex in a setting of more severe dilated cardiomyopathy associated with atrial fibrillation. The results highlight the importance of understanding the effect of miRNA-based therapies in cardiac disease settings in males and females.

ABSTRACT

MicroRNA (miRNA)-34a (miR-34a) is elevated in the diseased heart in mice and humans. Previous studies have shown that inhibiting miR-34a in male mice in settings of pathological cardiac hypertrophy or ischaemia protects the heart against progression to heart failure. Whether inhibition of miR-34a protects the female heart is unknown. Furthermore, the therapeutic potential of silencing miR-34a in settings of dilated cardiomyopathy (DCM) and atrial fibrillation (AF) has not been assessed previously. In the present study, we examined the effect of silencing miR-34a in males and females in (1) a model of moderate DCM and (2) a model of severe DCM with AF. The cardiac disease models were administered with a locked nucleic acid-modified oligonucleotide (LNA-antimiR-34a) at 6-7 weeks of age when the models display cardiac dysfunction and conduction abnormalities. Cardiac function and morphology were measured 6 weeks after treatment. In the present study, we show that inhibition of miR-34a provides more protection in the DCM model in females than males. Disease prevention in LNA-antimiR-34a treated DCM female mice was characterized by attenuated heart enlargement and lung congestion, lower expression of cardiac stress genes (B-type natriuretic peptide, collagen gene expression), less cardiac fibrosis and better cardiac function. There was no evidence of significant protection in the severe DCM and AF model in either sex. Sex- and treatment-dependent regulation of miRNAs was also identified in the diseased heart, and may explain the differential response of males and females. These studies highlight the importance of examining the impact of miRNA-based drugs in both sexes and under different disease conditions.

Regulation of connexin signaling by the epigenetic machinery

Connexins and their channels are involved in the control of all aspects of the cellular life cycle, ranging from cell growth to cell death, by mediating extracellular, intercellular and intracellular communication. These multifaceted aspects of connexin-related cellular signaling obviously require strict regulation. While connexin channel activity is mainly directed by posttranslational modifications, connexin expression as such is managed by classical cis/trans mechanisms. Over the past few years, it has become clear that connexin production is equally dictated by epigenetic actions. This paper provides an overview of the role of major determinants of the epigenome, including DNA methylation, histone acetylation and microRNA species, in connexin expression.

Connexin 43 is an emerging therapeutic target in ischemia/reperfusion injury, cardioprotection and neuroprotection

Connexins are widely distributed proteins in the body that are crucially important for heart and brain functions. Six connexin subunits form a connexon or hemichannel in the plasma membrane. Interactions between two hemichannels in a head-to-head arrangement result in the formation of a gap junction channel. Gap junctions are necessary to coordinate cell function by passing electrical current flow between heart and nerve cells or by allowing exchange of chemical signals and energy substrates. Apart from its localization at the sarcolemma of cardiomyocytes and brain cells, connexins are also found in the mitochondria where they are involved in the regulation of mitochondrial matrix ion fluxes and respiration. Connexin expression is affected by age and gender as well as several pathophysiological alterations such as hypertension, hypertrophy, diabetes, hypercholesterolemia, ischemia, post-myocardial infarction remodeling or heart failure, and post-translationally connexins are modified by phosphorylation/de-phosphorylation and nitros(yl)ation which can modulate channel activity. Using knockout/knockin technology as well as pharmacological approaches, one of the connexins, namely connexin 43, has been identified to be important for cardiac and brain ischemia/reperfusion injuries as well as protection from it. Therefore, the current review will focus on the importance of connexin 43 for irreversible injury of heart and brain tissues following ischemia/reperfusion and will highlight the importance of connexin 43 as an emerging therapeutic target in cardio- and neuroprotection.

Transgenic over-expression of YY1 induces pathologic cardiac hypertrophy in a sex-specific manner

YY1 can activate or repress transcription of various genes. In cardiac myocytes in culture YY1 has been shown to regulate expression of several genes involved in myocyte pathology. YY1 can also acutely protect the heart against detrimental changes in gene expression. In this study we show that cardiac over-expression of YY1 induces pathologic cardiac hypertrophy in male mice, measured by changes in gene expression and lower ejection fraction/fractional shortening. In contrast, female animals are protected against pathologic gene expression changes and cardiac dysfunction. Furthermore, we show that YY1 regulates, in a sex-specific manner, the expression of mammalian enable (Mena), a factor that regulates cytoskeletal actin dynamics and whose expression is increased in several models of cardiac pathology, and that Mena expression in humans with heart failure is sex-dependent. Finally, we show that sex differences in YY1 expression are also observed in human heart failure. In summary, this is the first work to show that YY1 has a sex-specific effect in the regulation of cardiac pathology.

Cardiac myocyte alternans in intact heart: Influence of cell-cell coupling and β-adrenergic stimulation

BACKGROUND

Cardiac alternans are proarrhythmic and mechanistically link cardiac mechanical dysfunction and sudden cardiac death. Beat-to-beat alternans occur when beats with large Ca(2+) transients and long action potential duration (APD) alternate with the converse. APD alternans are typically driven by Ca(2+) alternans and sarcoplasmic reticulum (SR) Ca(2+) release alternans. But the effect of intercellular communication via gap junctions (GJ) on alternans in the intact heart remains unknown.

OBJECTIVE

We assessed the effects of cell-to-cell coupling on local alternans in intact Langendorff-perfused mouse hearts, measuring single myocyte [Ca(2+)] alternans synchronization among neighboring cells, and effects of β-adrenergic receptor (β-AR) activation and reduced GJ coupling.

METHODS AND RESULTS

Mouse hearts (C57BL/6) were retrogradely perfused and loaded with Fluo8-AM to record cardiac myocyte [Ca(2+)] in situ with confocal microscopy. Single cell resolution allowed analysis of alternans within the intact organ during alternans induction. Carbenoxolone (25 μM), a GJ inhibitor, significantly increased the occurrence and amplitude of alternans in single cells within the intact heart. Alternans were concordant between neighboring cells throughout the field of view, except transiently during onset. β-AR stimulation only reduced Ca(2+) alternans in tissue that had reduced GJ coupling, matching effects seen in isolated myocytes.

CONCLUSIONS

Ca(2+) alternans among neighboring myocytes is predominantly concordant, likely because of electrical coupling between cells. Consistent with this, partial GJ uncoupling increased propensity and amplitude of Ca(2+) alternans, and made them more sensitive to reversal by β-AR activation, as in isolated myocytes. Electrical coupling between myocytes may thus limit the alternans initiation, but also allow alternans to be more stable once established.

Expression of circulating microRNA-1 and microRNA-133 in pediatric patients with tachycardia

Paroxysmal or persistent tachycardia in pediatric patients is a common disease. Certain circulating microRNAs (miRNAs) have been associated with arrhythmia. The present study investigated miRNAs in the plasma of pediatric patients with tachycardia. Forty pediatric subjects were included retrospectively: 24 with recurrent sustained tachycardia [seven cases of ventricular tachycardia (VT) and 17 cases of supraventricular tachycardia (SVT)] and 16 healthy controls. Circulating miR-1 and miR-133 in the plasma were detected by fluorescent quantitative polymerase chain reaction. miR-1 levels were significantly decreased in the arrhythmia group compared with those in the controls (P=0.004) whilst miR-133 expression levels were not significantly different between the two groups (P=0.456). Both miR-1 and miR-133 levels showed significant differences between the SVT and VT groups (P=0.004 and P=0.046, respectively), and a significant decrease in miR-1 levels was observed in the SVT group as compared with the controls (P<0.001). No significant difference was observed in the expression levels of miR-133. By contrast, miR-133 levels were significantly increased in the VT group compared with those in the controls (P=0.024), whereas no statistically significant difference was observed in the expression levels of miR-1. Receiver operating characteristic curves showed that 1/miR-1 was significant for the evaluation of tachycardia. Additionally, miR-1 produced enhanced sensitivity and specificity for the evaluation of SVT compared with miR-133, whereas miR-133 was a better marker to assess VT. This study demonstrated that miRNAs may be appropriate markers for pediatric tachycardia; miR-1 levels were decreased in the arrhythmia group compared with those in the healthy controls. Furthermore, patients with SVT had lower miR-1 expression levels while those with VT had higher miR-133 expression levels.

Role of multiple microRNAs in the sexually dimorphic expression of Cyp2b9 in mouse liver

Mouse cytochrome P450 2b9 (Cyp2b9) is a testosterone 16α-hydroxylase enzyme showing female-specific expression in many inbred mouse strains, including C57BL/6J. Previous studies have recognized that some sex-dependently secreted endogenous modulating factors were involved in the sexually dimorphic expression of Cyp2b9 through transcriptional regulation. In this study, we found evidence that some microRNAs contributed to the sexually biased expression of Cyp2b9 via post-transcriptional regulation. Cyp2b9 was upregulated in livers of hepatocyte-specific Dicer1 knockout mice at 3 weeks. The age-dependent downregulation of Cyp2b9 in the livers of male mice was diminished when Dicer1 was specifically knocked out in hepatocytes. When these data were combined with bioinformatics analysis and microRNA profiles of male and female mice, we found that 18 microRNAs were associated with the sexually dimorphic expression of Cyp2b9, which showed higher expression levels in male C57BL/6J mice when compared with females. Luciferase assays revealed that approximate half of these microRNAs repressed luciferase activity in a reporter system containing the 3'-untranslated region (3'-UTR) of Cyp2b9, and also inhibited Cyp2b9 protein expression. MicroRNA seed region mutation or mutations in putative binding sites of the microRNAs in Cyp2b9 3'-UTR led to the loss of the suppression of luciferase activity. There was also a negative correlation between the levels of these microRNAs and Cyp2b9. Our results suggested that multiple microRNAs participated in the regulation of Cyp2b9 expression, and that the lower expression levels of these microRNAs potentially contributed to the female-specific expression of Cyp2b9 in the livers of C57BL/6J mice.

miRNA regulated pathways in late stage murine lung development

Background

MicroRNAs play important roles in regulating biological processes, including organ morphogenesis and maturation. However, little is known about specific pathways regulated by miRNA during lung development. Between the canalicular and saccular stages of the developing lung several important cellular events occur, including the onset of surfactant synthesis, microvascular remodeling and structural preparation for subsequent alveolarization. The miRNAs that are actively regulated, and the identity of their targets during this important developmental interval in the lung remain elusive.

Results

Using TLDA low density real-time PCR arrays, the expression of 376 miRNAs in male and female fetal mouse lungs of gestational days E15 – E18 were profiled. Statistical analyses identified 25 and 37 miRNAs that changed significantly between sexes and with gestation, respectively. In silico analysis using Ingenuity Pathway Analysis (IPA) identified specific pathways and networks known to be targets of these miRNAs which are important to lung development. Pathways that are targeted by sex regulated miRNAs include retinoin, IGFR1, Tp53 and Akt. Pathways targeted by gestation-regulated miRNAs include VEGFA and mediators of glucose metabolism.

Conclusion

MiRNAs are differentially regulated across time and between sexes during the canalicular and saccular stages of lung development. Sex-associated differential miRNA expression may regulate the differences in structural and functional male and female lung development, as shown by networks generated using in silico analysis. These data provide a valuable resource to further enhance the understanding of miRNA control of lung development and maturation.

An emerging role for microRNAs in sexually dimorphic neurobiological systems

Over the past 20 years, our understanding of the basic mechanisms of gene regulation has vastly expanded due to the unexpected roles of small regulatory RNAs, in particular microRNAs (miRNAs). miRNAs add another layer of complexity to the regulation of effector molecules for nearly every physiological process, making them excellent candidate molecules as therapeutic targets, biomarkers, and disease predictors. Hormonal contributions to mature miRNA expression, biosynthetic processing, and downstream functions have only just begun to be investigated. Elucidating the physiological consequences of miRNA sexual dimorphism, and their associated regulatory processes, may be key toward understanding both normal and pathological processes in the brain. This short review provides a basic overview of miRNA biosynthesis, their role in normal brain development, and potential links to neurological diseases. We conclude with a brief discussion of the current knowledge of sex-specific miRNA processes in both the brain and the heart to conceptually integrate the relevance of miRNAs with the overarching theme ("sex differences in health and disease: brain and heart connections") of this special topics issue.