Exposure to Stress Alters Cardiac Gene Expression and Exacerbates Myocardial Ischemic Injury in the Female Murine Heart

Mental stress is a risk factor for myocardial infarction in women. The central hypothesis of this study is that restraint stress induces sex-specific changes in gene expression in the heart, which leads to an intensified response to ischemia/reperfusion injury due to the development of a pro-oxidative environment in female hearts. We challenged male and female C57BL/6 mice in a restraint stress model to mimic the effects of mental stress. Exposure to restraint stress led to sex differences in the expression of genes involved in cardiac hypertrophy, inflammation, and iron-dependent cell death (ferroptosis). Among those genes, we identified tumor protein p53 and cyclin-dependent kinase inhibitor 1A (p21), which have established controversial roles in ferroptosis. The exacerbated response to I/R injury in restraint-stressed females correlated with downregulation of p53 and nuclear factor erythroid 2-related factor 2 (Nrf2, a master regulator of the antioxidant response system-ARE). S-female hearts also showed increased superoxide levels, lipid peroxidation, and prostaglandin-endoperoxide synthase 2 (Ptgs2) expression (a hallmark of ferroptosis) compared with those of their male counterparts. Our study is the first to test the sex-specific impact of restraint stress on the heart in the setting of I/R and its outcome.

Glucocorticoid Inhibition of Estrogen Regulation of the Serotonin Receptor 2B in Cardiomyocytes Exacerbates Cell Death in Hypoxia/Reoxygenation Injury

Background Stress has emerged as an important risk factor for heart disease in women. Stress levels have been shown to correlate with delayed recovery and increased mortality after a myocardial infarction. Therefore, we sought to investigate if the observed sex-specific effects of stress in myocardial infarction may be partly attributed to genomic interactions between the female sex hormones, estrogen (E2), and the primary stress hormones glucocorticoids. Methods and Results Genomewide studies show that glucocorticoids inhibit estrogen-mediated regulation of genes with established roles in cardiomyocyte homeostasis. These include 5-HT2BR (cardiac serotonin receptor 2B), the expression of which is critical to prevent cardiomyocyte death in the adult heart. Using siRNA, gene expression, and chromatin immunoprecipitation assays, we found that 5-HT2BR is a primary target of the glucocorticoid receptor and the estrogen receptor α at the level of transcription. The glucocorticoid receptor blocks the recruitment of estrogen receptor α to the promoter of the 5-HT2BR gene, which may contribute to the adverse effects of stress in the heart of premenopausal women. Using immunoblotting, TUNEL (terminal deoxynucleotidal transferase-mediated biotin-deoxyuridine triphosphate nick-end labeling), and flow cytometry, we demonstrate that estrogen decreases cardiomyocyte death by a mechanism relying on 5-HT2BR expression. In vitro and in vivo experiments show that glucocorticoids inhibit estrogen cardioprotection in response to hypoxia/reoxygenation injury and exacerbate the size of the infarct areas in myocardial infarction. Conclusions These results established a novel mechanism underlying the deleterious effects of stress on female cardiac health in the setting of ischemia/reperfusion.

SUN-586 CXCR2 Repression by Glucocorticoids in Adipose Tissue

Obesity-induced type 2 diabetes (T2D) is a significant risk factor of cardiovascular disease (CVD), which affects 28.1 million adults in the United States. Adipose tissue chronic inflammation is one of the main factors that drive obesity-induced insulin resistance (IR) and T2D. Despite several studies that have shown a link between obesity, adipose tissue inflammation, and IR/T2D, the mechanisms underlying this association are not well understood. Synthetic glucocorticoids are widely used for their potent anti-inflammatory actions; however, their use is hampered due to off-target side effects. Glucocorticoids exert profound effects on adipose tissue, including the regulation of adipocyte metabolism and immune functions. However, whether their effects on adipose tissue are positive or negative it is still a controversial topic. Genome-wide microarray data obtained from adipocyte-specific glucocorticoid receptor (GR) knockout (AdipoGRKO) mice showed that lack of GR leads to a significant increase in the expression of pro-inflammatory genes in white adipose tissue (WAT). Moreover, WAT isolated from adipoGRKO mice demonstrated significant increase in immune cell infiltration, which correlates with our gene expression data. Among the most up-regulated genes, we found the C-X-C Motif Chemokine Receptor 2 (CXCR2), which is a critical mediator of chemotaxis to the sites of inflammation. Although studies have shown the presence of CXCR2 in adipocytes and suggested the contribution of CXCR2 signaling in adipocyte development, its role in obesity-driven adipose tissue inflammation is unknown. This led us to hypothesize that adipocyte specific administration of glucocorticoids can reduce obesity-induced adipocyte inflammation by inhibiting CXCR2 gene transcription and signaling. Our in vitro studies using 3T3-L1 cells derived adipocytes showed that treatment with the synthetic glucocorticoid, Dexamethasone (Dex) led to a significant repression of CXCR2 mRNA and protein levels. Correlating with these results, Dex treatment significantly inhibited macrophage migration to adipocytes in a mechanism dependent on GR activation and repression of CXCR2. Furthermore, these results were recapitulated in vivo. Together our findings suggest that local delivery of glucocorticoids to adipose tissue could ameliorate inflammation and reduce the risk of developing IR and T2D.

Deletion of the Cardiomyocyte Glucocorticoid Receptor Leads to Sexually Dimorphic Changes in Cardiac Gene Expression and Progression to Heart Failure

Background

The contribution of glucocorticoids to sexual dimorphism in the heart is essentially unknown. Therefore, we sought to determine the sexually dimorphic actions of glucocorticoid signaling in cardiac function and gene expression. To accomplish this goal, we conducted studies on mice lacking glucocorticoid receptors (GR) in cardiomyocytes (cardioGRKO mouse model).

Methods and Results

Deletion of cardiomyocyte GR leads to an increase in mortality because of the development of spontaneous cardiac pathology in both male and female mice; however, females are more resistant to GR signaling inactivation in the heart. Male cardioGRKO mice had a median survival age of 6 months. In contrast, females had a median survival age of 10 months. Transthoracic echocardiography data showed phenotypic differences between male and female cardioGRKO hearts. By 3 months of age, male cardioGRKO mice exhibited left ventricular systolic dysfunction. Conversely, no significant functional deficits were observed in female cardioGRKO mice at the same time point. Functional sensitivity of male hearts to the loss of cardiomyocyte GR was reversed following gonadectomy. RNA‐Seq analysis showed that deleting GR in the male hearts leads to a more profound dysregulation in the expression of genes implicated in heart rate regulation (calcium handling). In agreement with these gene expression data, cardiomyocytes isolated from male cardioGRKO hearts displayed altered intracellular calcium responses. In contrast, female GR‐deficient cardiomyocytes presented a response comparable with controls.

Conclusions

These data suggest that GR regulates calcium responses in a sex‐biased manner, leading to sexually distinct responses to stress in male and female mice hearts, which may contribute to sex differences in heart disease, including the development of ventricular arrhythmias that contribute to heart failure and sudden death.

Do bronchial biopsies represent mast cell density in airways? A stereological study

Endobronchial biopsy specimens may not adequately represent inflammatory cell counts throughout the airway wall. The present study aimed to compare mast cell density in biopsies and airway sections using both stereological and nonstereological methods. Post mortem biopsies and adjacent transverse sections were obtained from a mean of five proximal airways per case in 10 subjects who had died of nonrespiratory causes. Tryptase-positive mast cells were measured stereologically in 30-mum sections and nonstereologically in 5-microm sections using an optical disector (cells x mm(-3)) and cell profiles (cells x mm(-2)), respectively. Reference areas included the inner and total airway wall and to 100 microm below the basement membrane. Case means, based on four or more biopsy sites, significantly correlated with those on transverse sections for counts over the inner airway wall only, using both stereological and nonstereological methods. Cells x mm(-3) and cells x mm(-2) were significantly correlated within all reference areas. When endobronchial biopsies are obtained from at least four proximal airways per case, inter-subject comparisons of mean mast cell density in the inner airway wall are as well represented by counts on biopsies as they are on transverse sections. This is the case using either three-dimensional, stereological or two-dimensional, nonstereological methods.

Increased mast cells and neutrophils in submucosal mucous glands and mucus plugging in patients with asthma

BACKGROUND

Mucus plugging of the airways is invariably seen in cases of fatal asthma, mucus production is associated with asthma attacks, and the area of submucosal glands is increased in asthma. Mediators secreted from mast cells and neutrophils can stimulate mucous gland secretion. A study was undertaken to count the mast cells and neutrophils in submucosal glands and to relate cell numbers to the presence of mucus in the airway lumen.

METHODS

Cartilaginous airways obtained at necropsy from cases of fatal asthma (n=8), non-fatal asthma (n=8), and control cases (n=8) were examined. Contiguous transverse sections were stained for mast cell tryptase and neutrophil elastase, and with Periodic Acid Schiff solution to identify mucus. Mucous gland area, lumen area, and the percentage of the relaxed lumen area occupied by mucus (mucus occupying ratio, MOR) were measured. Mast cells (intact and degranulated) and neutrophils per area of submucosal gland were calculated.

RESULTS

Compared with controls, the cases of fatal asthma had increased mucous gland area, MOR, percentage of degranulated mast cells, and numbers of neutrophils in the submucosal glands (p<0.05). In cases of non-fatal asthma the MOR and the numbers of mast cells and neutrophils in the submucosal glands were increased (p<0.05). When all cases were pooled together, the MOR correlated with the total number of mast cells (r=0.55, p=0.005) and with the number of degranulated mast cells in the submucosal glands (r=0.51, p=0.013), but not with the number of neutrophils (r=0.21, p=0.121).

CONCLUSION

These results show that mucous gland area, MOR, and mucous gland inflammation are increased in asthma and that degranulation of mast cells may contribute to secretion of mucus into the lumen in cases of fatal asthma.

Distribution and degranulation of airway mast cells in normal and asthmatic subjects

It was hypothesized that the distribution and activation of mast cells across the airway wall may reflect their function in asthma. The density of mast cells (intact and degranulated) within airway compartments in cartilaginous and membranous airways, obtained from autopsies on patients with fatal asthma, nonfatal asthma, and nonasthmatic control cases have been examined. In cartilaginous airways, the mean+/-SE density of mast cells in control cases was 27+/-9 cells x mm(-2). It was similar in nonfatal asthma (24+/-2 cells x mm(-2)) but reduced (p<0.05) in fatal asthma cases (16+/-2 cells x mm(-2)). In membranous airways, the density of mast cells in control cases was 155+/-21 cells x mm(-2) and was higher (p<0.05) in cases of nonfatal (270+/-51 cells x mm(-2)) and fatal asthma (219+/-26 cells x mm(-2)). Mast-cell density was greatest on the smooth muscle and mucous glands in cartilaginous airways and on the smooth muscle and outer airway wall in membranous airways. The percentage of degranulated mast cells was higher (p<0.05) in cases of asthma, related to disease severity, and was higher in cartilaginous than membranous airways. Degranulation was greatest on the smooth muscle in fatal asthma cases. Mast-cell distribution and degranulation varies between cartilaginous and membranous airways and across the airway wall. Degranulation of mast cells is related to asthma severity. The increased degranulation in proximal airways may reflect stimulation via the inhaled route.

The airway longitudinal elastic fiber network and mucosal folding in patients with asthma

A submucosal network of elastic fibers in a collagen and myofibroblast matrix form discrete longitudinal bundles (LB) in the bronchial tree. The LB may affect airway function by altering the mechanical properties of the airway wall or by changing the folding behavior of the airway mucosa. The area and number of LB were quantified from 12 cases each of fatal asthma (FA), nonfatal asthma (NF), and nonasthmatic (NA) control cases on elastic-trichrome stained airways. The effects of group, sex, age, and smoking were examined using multiple linear regression. The area fraction of LB increased (p < 0.05) approximately twofold in cases of FA compared with NA control cases in both large and small airways. The areas of LB were increased in smokers, older subjects, and men (p < 0.05). The number of mucosal folds was related to the number of longitudinal bundles in asthmatics and nonasthmatics and was not different between groups. Collagen and myofibroblasts were increased (p < 0.05) in LB of FA and NF cases compared with NA control cases. The increased size and altered composition of LB in asthma may influence airway function; however, excessive airway narrowing in asthma is not due to altered numbers of mucosal folds.

Bronchial blood vessel dimensions in asthma

The extent to which the bronchial vasculature contributes to airway wall thickening in large and small airways in patients with asthma is unknown. The aim of this study was to quantify the number and the area occupied by blood vessels in the airway submucosa of patients with and without asthma. We used the monoclonal antibody Factor VIII to measure the blood vessels between the airway basement membrane and the outer border of the smooth muscle. In large cartilaginous airways in patients with fatal asthma, the number and area of large blood vessels were increased and the number and area of small blood vessels were decreased, compared with that in patients with nonfatal asthma and control subjects. However, the total number of blood vessels and the total area occupied by blood vessels per square millimeter in the airway submucosa were similar in patients with fatal asthma or nonfatal asthma and in control subjects in all airway size groups. Blood vessels were distended to a mean value of 80% of their estimated maximal area. The increased number of larger vessels in patients with fatal asthma raises the possibility that vascular congestion associated with an acute severe asthma attack may distend blood vessels. The finding of similar numbers of blood vessels per square millimeter of submucosa in control subjects and in patients with asthma suggests that blood vessels increase in number in patients with asthma only in proportion to increased airway wall area. It is unlikely that submucosal vessels could act as capacitance vessels and significantly alter inner airway wall thickness.

Is salmeterol ergogenic?

OBJECTIVE

To assess the effects of 50 micrograms of inhaled salmeterol on pulmonary function, selected physical capacities, and fine motor control in 16 nonasthmatic male cyclists and triathletes, mean age of 23.2 (SD = 3.5) years.

DESIGN

Randomized double-blind placebo-controlled crossover trial.

SETTING

Human Physical Performance Laboratory, the University of Western Australia.

SUBJECTS

Sixteen healthy male high-performance nonasthmatic athletes with a mean age of 23.2 years participated in the study.

INTERVENTION

Subjects attended three experimental testing sessions at which salmeterol (50 micrograms), a placebo, or "no treatment" was administered in random order in a double-blind fashion, on separate occasions, prior to exercise.

MAIN OUTCOME MEASURES

During each testing, session lung function was measured before and 10 min after the treatment. Tests of reaction time and hand steadiness and then two anaerobic cycle tests followed. The first, a 10-s all-out sprint was followed, after a 3-min rest, by a 30-s all-out sprint performed on a front access bicycle ergometer. After 10 min recovery, leg flexion-extension peak torque was measured on a Biodex isokinetic dynamometer at speeds of 120 and 180 degrees s-1.

MAIN RESULTS

Lung function variables, reaction time, movement time, alactic anaerobic power, lactacid anaerobic power, and leg-flexion and leg-extension muscular strength were similar among the three treatment groups.

CONCLUSIONS

The preexercise administration of 50 micrograms of inhaled salmeterol has no performance-enhancing effects in nonasthmatic athletes. We believe that athletes with asthma should be permitted to use salmeterol before competition.