Sex Differences in Cardiac Mitochondria in the New Zealand Obese Mouse

Three-dimensional mitochondria reconstructions of murine cardiac muscle changes in size across aging

With sparse treatment options, cardiac disease remains a significant cause of death among humans. As a person ages, mitochondria breakdown and the heart becomes less efficient. Heart failure is linked to many mitochondria-associated processes, including endoplasmic reticulum stress, mitochondrial bioenergetics, insulin signaling, autophagy, and oxidative stress. The roles of key mitochondrial complexes that dictate the ultrastructure, such as the mitochondrial contact site and cristae organizing system (MICOS), in aging cardiac muscle are poorly understood. To better understand the cause of age-related alteration in mitochondrial structure in cardiac muscle, we used transmission electron microscopy (TEM) and serial block facing-scanning electron microscopy (SBF-SEM) to quantitatively analyze the three-dimensional (3-D) networks in cardiac muscle samples of male mice at aging intervals of 3 mo, 1 yr, and 2 yr. Here, we present the loss of cristae morphology, the inner folds of the mitochondria, across age. In conjunction with this, the three-dimensional (3-D) volume of mitochondria decreased. These findings mimicked observed phenotypes in murine cardiac fibroblasts with CRISPR/Cas9 knockout of Mitofilin, Chchd3, Chchd6 (some members of the MICOS complex), and Opa1, which showed poorer oxidative consumption rate and mitochondria with decreased mitochondrial length and volume. In combination, these data show the need to explore if loss of the MICOS complex in the heart may be involved in age-associated mitochondrial and cristae structural changes.NEW & NOTEWORTHY This article shows how mitochondria in murine cardiac changes, importantly elucidating age-related changes. It also is the first to show that the MICOS complex may play a role in outer membrane mitochondrial structure.

Sex differences and estrogen effects in cardiac mitochondria in human aortic stenosis and in the mouse heart

Introduction

Sex differences in the adaptation to pressure overload have been described in humans, as well as animal models, and have been related to sex-specific expression of mitochondrial genes. We therefore tested whether sex differences in cardiac mitochondrial respiration exist in humans with aortic stenosis (AS). We also examined whether these potential differences may be at least partially due to sex hormones by testing if mitochondrial respiration is affected by estrogen (17ß-estradiol (E2)).

Methods

Consecutive patients undergoing transapical aortic valve implantation (TAVI) (women, n = 7; men, n = 10) were included. Cardiac biopsies were obtained during TAVI and used directly for mitochondrial function measurements. Male and female C57BL/6J mice (n = 8/group) underwent sham surgery or gonadectomy (GDX) at the age of 2 months. After 14 days, mice were treated once with intraperitoneally injected vehicle (placebo), 17ß-estradiol (E2), estrogen receptor alpha (ERα) agonist [propyl pyrazole triol (PPT)], or ER beta (ERβ) agonist (BAY-1214257). Thereafter, mitochondrial measurements were performed directly in cardiac skinned fibers from isolated left ventricles and musculus solei.

Results

Mitochondrial State-3 respiration was higher in female than that in male human heart biopsies (15.0 ± 2.30 vs. 10.3 ± 2.05 nmol/mL/min/mg, p< 0.05). In the mouse model, mitochondrial State-3 respiration decreased significantly after GDX in female (27.6 ± 1.55 vs. 21.4 ± 1.71 nmol/mL/min/mg; p< 0.05) and male hearts (30.7 ± 1,48 vs. 23.7 ± 2,23 nmol/mL/min/mg; p< 0.05). In ovariectomized female mice, E2 and ERβ-agonist treatment restored the State-3 respiration to intact placebo level, whereas ERα-agonist treatment did not modulate State-3 respiration. The treatment with E2, ERα-, or ERβ-agonist did not modulate the State-3 respiration in GDX male mice.

Conclusion

We identified sex differences in mitochondrial respiration in the diseased human heart. This is in alignment with known sex differences in the gene expression and proteome level at the functional level. E2 and ERβ affect cardiac mitochondrial function in the mouse model, suggesting that they may also contribute to the sex differences in the human heart. Their roles should be further investigated.

Impacts of a high-fat diet on the metabolic profile and the phenotype of atrial myocardium in mice

AIMS

Obesity, diabetes, and metabolic syndromes are risk factors of atrial fibrillation (AF). We tested the hypothesis that metabolic disorders have a direct impact on the atria favouring the formation of the substrate of AF.

METHODS AND RESULTS

Untargeted metabolomic and lipidomic analysis was used to investigate the consequences of a prolonged high-fat diet (HFD) on mouse atria. Atrial properties were characterized by measuring mitochondria respiration in saponin-permeabilized trabeculae, by recording action potential (AP) with glass microelectrodes in trabeculae and ionic currents in myocytes using the perforated configuration of patch clamp technique and by several immuno-histological and biochemical approaches. After 16 weeks of HFD, obesogenic mice showed a vulnerability to AF. The atrial myocardium acquired an adipogenic and inflammatory phenotypes. Metabolomic and lipidomic analysis revealed a profound transformation of atrial energy metabolism with a predominance of long-chain lipid accumulation and beta-oxidation activation in the obese mice. Mitochondria respiration showed an increased use of palmitoyl-CoA as energy substrate. APs were short duration and sensitive to the K-ATP-dependent channel inhibitor, whereas K-ATP current was enhanced in isolated atrial myocytes of obese mouse.

CONCLUSION

HFD transforms energy metabolism, causes fat accumulation, and induces electrical remodelling of the atrial myocardium of mice that become vulnerable to AF.

Leptin-mediated neural targets in obesity hypoventilation syndrome

Obesity hypoventilation syndrome (OHS) is defined as daytime hypercapnia in obese individuals in the absence of other underlying causes. In the United States, OHS is present in 10%-20% of obese patients with obstructive sleep apnea and is linked to hypoventilation during sleep. OHS leads to high cardiorespiratory morbidity and mortality, and there is no effective pharmacotherapy. The depressed hypercapnic ventilatory response plays a key role in OHS. The pathogenesis of OHS has been linked to resistance to an adipocyte-produced hormone, leptin, a major regulator of metabolism and control of breathing. Mechanisms by which leptin modulates the control of breathing are potential targets for novel therapeutic strategies in OHS. Recent advances shed light on the molecular pathways related to the central chemoreceptor function in health and disease. Leptin signaling in the nucleus of the solitary tract, retrotrapezoid nucleus, hypoglossal nucleus, and dorsomedial hypothalamus, and anatomical projections from these nuclei to the respiratory control centers, may contribute to OHS. In this review, we describe current views on leptin-mediated mechanisms that regulate breathing and CO2 homeostasis with a focus on potential therapeutics for the treatment of OHS.

Sex differences in heart mitochondria regulate diastolic dysfunction

Heart failure with preserved ejection fraction (HFpEF) exhibits a sex bias, being more common in women than men, and we hypothesize that mitochondrial sex differences might underlie this bias. As part of genetic studies of heart failure in mice, we observe that heart mitochondrial DNA levels and function tend to be reduced in females as compared to males. We also observe that expression of genes encoding mitochondrial proteins are higher in males than females in human cohorts. We test our hypothesis in a panel of genetically diverse inbred strains of mice, termed the Hybrid Mouse Diversity Panel (HMDP). Indeed, we find that mitochondrial gene expression is highly correlated with diastolic function, a key trait in HFpEF. Consistent with this, studies of a "two-hit" mouse model of HFpEF confirm that mitochondrial function differs between sexes and is strongly associated with a number of HFpEF traits. By integrating data from human heart failure and the mouse HMDP cohort, we identify the mitochondrial gene Acsl6 as a genetic determinant of diastolic function. We validate its role in HFpEF using adenoviral over-expression in the heart. We conclude that sex differences in mitochondrial function underlie, in part, the sex bias in diastolic function.

Current landscape of preclinical models of diabetic cardiomyopathy

Patients with diabetes have an increased risk of developing heart failure, preceded by (often asymptomatic) cardiac abnormalities, collectively called diabetic cardiomyopathy (DC). Diabetic heart failure lacks effective treatment, remaining an urgent, unmet clinical need. Although structural and functional characteristics of the diabetic human heart are well defined, clinical studies lack the ability to pinpoint the specific mechanisms responsible for DC. Preclinical animal models represent a vital component for understanding disease aetiology, which is essential for the discovery of new targeted treatments for diabetes-induced heart failure. In this review, we describe the current landscape of preclinical DC models (genetic, pharmacologically induced, and diet-induced models), highlighting their strengths and weaknesses and alignment to features of the human disease. Finally, we provide tools, resources, and recommendations to assist future preclinical translation addressing this knowledge gap.

Spontaneous Degenerative Aortic Valve Disease in New Zealand Obese Mice

Background Degenerative aortic valve (AoV) disease and resulting aortic stenosis are major clinical health problems. Murine models of valve disease are rare, resulting in a translational knowledge gap on underlying mechanisms, functional consequences, and potential therapies. Naïve New Zealand obese (NZO) mice were recently found to have a dramatic decline of left ventricular (LV) function at early age. Therefore, we aimed to identify the underlying cause of reduced LV function in NZO mice. Methods and Results Cardiac function and pulmonary hemodynamics of NZO and age-matched C57BL/6J mice were monitored by serial echocardiographic examinations. AoVs in NZO mice demonstrated extensive thickening, asymmetric aortic leaflet formation, and cartilaginous transformation of the valvular stroma. Doppler echocardiography of the aorta revealed increased peak velocity profiles, holodiastolic flow reversal, and dilatation of the ascending aorta, consistent with aortic stenosis and regurgitation. Compensated LV hypertrophy deteriorated to decompensated LV failure and remodeling, as indicated by increased LV mass, interstitial fibrosis, and inflammatory cell infiltration. Elevated LV pressures in NZO mice were associated with lung congestion and cor pulmonale, evident as right ventricular dilatation, decreased right ventricular function, and increased mean right ventricular systolic pressure, indicative for the development of pulmonary hypertension and ultimately right ventricular failure. Conclusions NZO mice demonstrate as a novel murine model to spontaneously develop degenerative AoV disease, aortic stenosis, and the associated end organ damages of both ventricles and the lung. Closely mimicking the clinical scenario of degenerative AoV disease, the model may facilitate a better mechanistic understanding and testing of novel treatment strategies in degenerative AoV disease.

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.

Sex-dependent vulnerability of fetal nonhuman primate cardiac mitochondria to moderate maternal nutrient reduction

Poor maternal nutrition in pregnancy affects fetal development, predisposing offspring to cardiometabolic diseases. The role of mitochondria during fetal development on later-life cardiac dysfunction caused by maternal nutrient reduction (MNR) remains unexplored. We hypothesized that MNR during gestation causes fetal cardiac bioenergetic deficits, compromising cardiac mitochondrial metabolism and reserve capacity. To enable human translation, we developed a primate baboon model (Papio spp.) of moderate MNR in which mothers receive 70% of control nutrition during pregnancy, resulting in intrauterine growth restriction (IUGR) offspring and later exhibiting myocardial remodeling and heart failure at human equivalent ∼25 years. Term control and MNR baboon offspring were necropsied following cesarean-section, and left ventricle (LV) samples were collected. MNR adversely impacted fetal cardiac LV mitochondria in a sex-dependent fashion. Increased maternal plasma aspartate aminotransferase, creatine phosphokinase (CPK), and elevated cortisol levels in MNR concomitant with decreased blood insulin in male fetal MNR were measured. MNR resulted in a two-fold increase in fetal LV mitochondrial DNA (mtDNA). MNR resulted in increased transcripts for several respiratory chain (NDUFB8, UQCRC1, and cytochrome c) and adenosine triphosphate (ATP) synthase proteins. However, MNR fetal LV mitochondrial complex I and complex II/III activities were significantly decreased, possibly contributing to the 73% decreased ATP content and increased lipid peroxidation. MNR fetal LV showed mitochondria with sparse and disarranged cristae dysmorphology. Conclusion: MNR disruption of fetal cardiac mitochondrial fitness likely contributes to the documented developmental programming of adult cardiac dysfunction, indicating a programmed mitochondrial inability to deliver sufficient energy to cardiac tissues as a chronic mechanism for later-life heart failure.

Neonatal Milk Fat Globule Membrane Supplementation During Breastfeeding Ameliorates the Deleterious Effects of Maternal High-Fat Diet on Metabolism and Modulates Gut Microbiota in Adult Mice Offspring in a Sex-Specific Way

Exposure to adverse events in early life increases the risk of chronic metabolic disease in adulthood. The objective of this study was to determine the significance of milk fat globule membrane (MFGM)-mediated alterations in the gut microbiome to the metabolic health of offspring in the long-term. Female C57BL/6 mice were fed either a high-fat diet (HFD) or a control diet for 3 weeks before pregnancy and throughout pregnancy and lactation. During lactation, pups from the HFD group were breast-fed with or without 1,000 mg/kg BW/day MFGM supplementation (HFD and HFD-MS group, respectively). After weaning, the offspring in each group were divided into male and female subgroups. The weaned mice were then shifted to a control diet for 8 weeks. At the eleventh week, stool samples were collected for 16S rRNA gene sequencing. Serum biochemical parameters were analyzed, and intraperitoneal glucose and insulin tolerance tests were performed. Neonatal supplementation with MFGM ameliorated metabolic disorder and improved glucose tolerance in offspring exposed to maternal HFD in a sex-specific manner. Furthermore, maternal HFD induced gut microbiota perturbation in offspring in adulthood. Neonatal MFGM supplementation significantly enriched g-Parabacteroides, g-Bifidobacterium, g-Faecalibaculum, and g-Lactobacillus in male offspring exposed to maternal HFD, while significantly enriched g-Parabacteroides and g-Alistipes in female offspring exposed to maternal HFD. These bacteria may be associated with the favorable changes in metabolism that occur in adulthood. Sex differences in the changes of metagenomic pathways related to oxidative phosphorylation, citrate cycle, electron transfer carries, and ubiquinone biosynthesis were also observed in the offspring. Maternal HFD has an adverse effect on the metabolism of offspring in later life. Neonatal MFGM supplementation could modulate the structure of gut microbiota communities and may have long-term protective effects on lipid and glucose metabolism, but these effects are sex dimorphic.

Amylin deposition activates HIF1α and 6-phosphofructo-2-kinase/fructose-2, 6-biphosphatase 3 (PFKFB3) signaling in failing hearts of non-human primates

Hyperamylinemia induces amylin aggregation and toxicity in the pancreas and contributes to the development of type-2 diabetes (T2D). Cardiac amylin deposition in patients with obesity and T2D was found to accelerate heart dysfunction. Non-human primates (NHPs) have similar genetic, metabolic, and cardiovascular processes as humans. However, the underlying mechanisms of cardiac amylin in NHPs, particularly related to the hypoxia inducible factor (HIF)1α and 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 3 (PFKFB3) signaling pathways, are unknown. Here, we demonstrate that in NHPs, amylin deposition in heart failure (HF) contributes to cardiac dysfunction via activation of HIF1α and PFKFB3 signaling. This was confirmed in two in vitro cardiomyocyte models. Furthermore, alterations of intracellular Ca2+, reactive oxygen species, mitochondrial function, and lactate levels were observed in amylin-treated cells. Our study demonstrates a pathological role for amylin in the activation of HIF1α and PFKFB3 signaling in NHPs with HF, establishing amylin as a promising target for heart disease patients.

Age and sex as confounding factors in the relationship between cardiac mitochondrial function and type 2 diabetes in the Nile Grass rat

Our study revisits the role of cardiac mitochondrial adjustments during the progression of type 2 diabetes mellitus (T2DM), while considering age and sex as potential confounding factors. We used the Nile Grass rats (NRs) as the animal model. After weaning, animals were fed either a Standard Rodent Chow Diet (SRCD group) or a Mazuri Chinchilla Diet (MCD group) consisting of high-fiber and low-fat content. Both males and females in the SRCD group, exhibited increased body mass, body mass index, and plasma insulin compared to the MCD group animals. However, the females were able to preserve their fasting blood glucose throughout the age range on both diets, while the males showed significant hyperglycemia starting at 6 months in the SRCD group. In the males, a higher citrate synthase activity-a marker of mitochondrial content-was measured at 2 months in the SRCD compared to the MCD group, and this was followed by a decline with age in the SRCD group only. In contrast, females preserved their mitochondrial content throughout the age range. In the males exclusively, the complex IV capacity expressed independently of mitochondrial content varied with age in a diet-specific pattern; the capacity was elevated at 2 months in the SRCD group, and at 6 months in the MCD group. In addition, females, but not males, were able to adjust their capacity to oxidize long-chain fatty acid in accordance with the fat content of the diet. Our results show clear sexual dimorphism in the variation of mitochondrial content and oxidative phosphorylation capacity with diet and age. The SRCD not only leads to T2DM but also exacerbates age-related cardiac mitochondrial defects. These observations, specific to male NRs, might reflect deleterious dietary-induced changes on their metabolism making them more prone to the cardiovascular consequences of aging and T2DM.

Rodent models of obesity

Obese or overweight people exceed one-third of the global population and obesity along with diabetes mellitus consist basic components of metabolic syndrome, both of which are known cardio-cerebrovascular risk factors with detrimental consequences. These data signify the pandemic character of obesity and the necessity for effective treatments. Substantial advances have been accomplished in preclinical research of obesity by using animal models, which mimic the human disease. In particular, rodent models have been widely used for many decades with success for the elucidation of the pathophysiology of obesity, since they share physiological and genetic components with humans and appear advantageous in their husbandry. The most representative rodents include the laboratory mouse and rat. Within this review, we attempted to consolidate the most widely used mice and rat models of obesity and highlight their strengths as well as weaknesses in a critical way. Our aim was to bridge the gap between laboratory facilities and patient's bed and help the researcher find the appropriate animal model for his/her obesity research. This tactful selection of the appropriate model of obesity may offer more translational derived results. In this regard, we included, the main diet induced models, the chemical/mechanical ones, as well as a selection of monogenic or polygenic models.

Sugar-Lowering Drugs for Type 2 Diabetes Mellitus and Metabolic Syndrome-Strategies for In Vivo Administration: Part-II

Diabetes is a complex disease characterized by hyperglycemia, together with polyuria, polydipsia, and polyphagia. While Type 1 diabetes mellitus (T1DM) results from genetic, environmental, or immune dysfunction factors leading to pancreatic β-cell destruction depriving the organism from endogenous insulin, Type 2 diabetes mellitus (T2DM) is characterized by peripheral insulin resistance. Depending on the type of diabetes mellitus and drug mechanism to study, the animal model should be carefully selected among the wide variety of the currently available ones. This review discusses the most common animal models currently employed to study T1DM and T2DM. Moreover, an overview on the administration routes that could be used is also discussed.

Diabetic Pregnancy and Maternal High-Fat Diet Impair Mitochondrial Dynamism in the Developing Fetal Rat Heart by Sex-Specific Mechanisms

Infants born to diabetic or obese mothers are at greater risk of heart disease at birth and throughout life, but prevention is hindered because underlying mechanisms remain poorly understood. Using a rat model, we showed that prenatal exposure to maternal diabetes and a high-fat diet caused diastolic and systolic dysfunction, myocardial lipid accumulation, decreased respiratory capacity, and oxidative stress in newborn offspring hearts. This study aimed to determine whether mitochondrial dynamism played a role. Using confocal live-cell imaging, we examined mitochondrial dynamics in neonatal rat cardiomyocytes (NRCM) from four prenatally exposed groups: controls, diabetes, high-fat diet, and combination exposed. Cardiac expression of dynamism-related genes and proteins were compared, and gender-specific differences were evaluated. Findings show that normal NRCM have highly dynamic mitochondria with a well-balanced number of fusion and fission events. Prenatal exposure to diabetes or a high-fat diet impaired dynamism resulting in shorter, wider mitochondria. Mechanisms of impaired dynamism were gender-specific and protein regulated. Females had higher expression of fusion proteins which may confer a cardioprotective effect. Prenatally exposed male hearts had post-translational modifications known to impair dynamism and influence mitophagy-mediated cell death. This study identifies mitochondrial fusion and fission proteins as targetable, pathogenic regulators of heart health in offspring exposed to excess circulating maternal fuels.