Sex Differences Across the Lifespan: A Focus on Cardiometabolism

Overview

It is well established that many adult diseases originate in utero or neonatally upon exposure to various insults. ^{2 –5} Indirect effects transmitted through the maternal circulation or effects mediated through the placenta or direct effects on the fetus itself have been proposed and various experimental animal models and clinical studies involving human subjects have been undertaken. ^{6 –8} Some of these early insults on the fetus can be nutritional (e.g., maternal obesity and some forms of diabetes), physiological (e.g., maternal hypertension), and chemical exposure (e.g., environmental toxicant or excess steroid exposure or intake of psychosomatic drugs). The transgenerational effects can be regulated at the genetic level or epigenetically regulated and transmitted. ^{9 –15} Epidemiology studies also provide great insights into the fetal origins of adult disease. ¹⁰ The following presentations were made based on the above general theme.

Jacquetta Trasler, PhD, McGill University, presented interesting findings on how folic acid protects against artificial reproductive technology (ART)-derived mouse embryo abnormalities; however, very high doses of folic acid (5 mg/day) were associated with reduced embryo size, psychomotor impairment, and autism. This is particularly significant because, ART is known to result in an increase in sex-specific hypomethylation in placenta and embryos. ^{16 –18} Through her studies, she also demonstrated differences in threshold levels of folic acid in male versus female embryos and how these could influence transgenerational phenotypes.

Yoel Sadovsky, MD, PhD, Magee-Women's Research Institute, spoke about how placental-specific and paternally expressed imprinted miRNA clusters confer resistance to viral invasion in a process mediated by exosomes. ^{19 –22} He provided strong evidence and deep molecular insight into the entire mechanism of exosome trafficking and uptake. He also generated humanized mouse models harboring the miRNA cluster and its expression in placenta. Thus, this is a new area of research that focuses on how placenta safeguards fetal growth and development.

Thomas Jansson, MD, PhD, University of Colorado School of Medicine, discussed health consequences of birth to an obese mother and the possible mechanisms responsible for these effects and how to intervene to address this major and alarming problem of transgenerational obesity transmission. ^{23 –25} He discussed both maternal and fetal consequences of maternal obesity, some of which are sex specific: on the maternal side, hyperinsulinemia, increase in leptin levels, and decrease in adiponectin are hallmarks, whereas on the fetal side, overgrowth, increased adiposity, and increased insulin resistance at birth are representative factors. He implicated adiponectin as a key regulator of placental function ²⁵ and based on studies in rodents, this protein could potentially be used in intervention studies designed to alleviate the complications.

Paul Rozance, MD, University of Colorado School of Medicine, discussed how intrauterine growth restriction (IUGR) impacts early programming of fetal pancreatic function and adaptation. His presentation was primarily focused on how placental insufficiency causes decreased nutrient transport leading to IUGR. ^{26 –28} Normal pancreatic beta cells require oxygen, amino acid, and glucose supply for insulin secretion to support somatic growth. In IUGR, fetal beta cell mass is reduced, and circulating insulin concentrations are lower. His work using a placental insufficiency-induced IUGR model in the pregnant sheep model illustrated how key aspects of the fetal pancreas are affected. ^29,30 His studies have further demonstrated that fetal leucine infusion in IUGR can correct many of the pancreatic functional defects, including impaired glucose-stimulated insulin secretion. ^31,32

Janet Catov, PhD, Magee-Women's Research Institute, presented epidemiological data on the relationship between preterm birth (PTB) and the incidence of later life cardiovascular disease (CVD) in the mother. Preeclampsia (PE), pregnancy-induced hypertension, and gestational diabetes are known risk factors for CVD. ^{33 –35} Her data indicated that women who deliver preterm are also at risk for CVD. Compared with Europe (∼6%), US PTB rates are high (∼12%) and show ethnic differences in incidence such that African Americans have a significantly higher prevalence than Caucasians (16% African American vs. 10% white). She also provided strong correlations of PTB to maternal metabolic syndrome, high blood pressure, and impaired placental vascular development, and other defects leading to different vasculopathies. ^{33 –35}

Gaps identified

Overview

It is well known that acute exercise differentially affects whole-body glucose and fatty acid metabolism. ³⁶ The effects of chronic exercise training are mostly limited to skeletal muscle adaptations or physiologically relevant signaling pathways in the heart. ^{37 –39} How chronic exercise training helps general metabolism under cardiac disease conditions is not well explored. Moreover, sex differences in exercise benefits on cardiometabolic phenotypes and other organ systems are not well understood in the normal physiological state or in the setting of diabetes. In addition, how parental exercise affects maternal offspring's general metabolic health is also poorly understood. Keeping these issues as a thematic background, the following presentations were made.

Laurie Goodyear, PhD, Joslin Diabetes Center, Harvard University focused on the chronic effects of maternal and paternal exercise on the metabolic health of offspring. She systematically presented experimental paradigms using rat models and showing how exercise (maternal, paternal, or both) contributes to offspring health outcomes. Of particular note were her data demonstrating that maternal exercise before and during pregnancy significantly improves glucose tolerance and decrease in insulin levels in offspring. ^{40 –42} She demonstrated the exercise-mediated effects through liver/hepatocytes and noted that these may play a role in metabolic health of offspring. She also considered other factors that include epigenetic, hormonal, and placental factors. In particular, her current work focuses on modulating AMP kinase-mediated epigenetic enzymes, Tet1, Tet2, and Tet3 in liver and how mother's serum preparations can influence liver and placental proteins, and whose effects may be transgenerationally transmitted.

Paul MacLean, PhD, University of Colorado School of Medicine, focused on the concept that exercise may be beneficial for weight loss maintenance. ⁴³ He posed the question as to whether exercise counters the biological drive to gain weight. His work suggests there is a large variability in response to all obesity and weight loss maintenance treatments, including exercise and the sex differences that may exist, need to be better defined. He discussed the Accumulating Data to Optimally Predict Obesity Treatment (ADOPT) Core measures project as the first step toward personalized treatments for obesity. ^44,45

Jane Reusch, MD, University of Colorado School of Medicine, emphasized the sex differences in type 2 diabetes (T2D) across the life span. Her studies focused on mitochondrial dysfunction in T2D and how reduced oxygenation during exercise in diabetes can affect blood flow, blood flow distribution, and muscle perfusion leading to inefficient oxygen delivery in these patients. ^{46 –48} She asked the question of whether there is an “exercise pill” but noted that exercise is the best approach to a healthy lifestyle.

Lisa Chow, MD, University of Minnesota, discussed results from the Coronary Artery Risk Development in Young Adults (CARDIA) study that focused on the effects of health behaviors on the sex-specific development of coronary artery risk in patients with diabetes. ^{49 –52} This study included nearly 5000 African American and non-Hispanic white male and female subjects. In-person follow-up occurred at various year intervals and nearly 3500 people were seen at year 30. In addition, at nearly 5-year intervals, follow-ups and prediabetes/diabetes status were assessed in these participants. The advantages of this large cohort study include presence of a long-term prospective cohort, objective documentation of covariates, and objective documentation of outcomes such as metabolic syndrome, prediabetes, and diabetes. Her studies identify implications of diet, particularly that consumption of dairy and the Mediterranean diet reduces the risk of metabolic syndrome and poor physical fitness. ^{49 –52} She concluded that the Mediterranean diet in young adulthood protects against development of prediabetes/diabetes at midlife. She also concluded that fitness in young adults is protective.

Amy Huebschmann, MD, University of Colorado School of Medicine, covered the topic of Bench to Bedside: A dissemination and implementation approach to exercise surveying a vast body of literature. ^{53 –55} In particular she discussed the Be Active trial for which she highlighted several limitations. She noted that Be Active trial, which was focused on surveying the current practices of implementation of approaches to exercise was not fully powered. This study only addressed a limited set of implementation outcomes and these may be more robustly addressed in a fully powered trial. Another limitation was with regard to reimbursement. Medicare chronic disease management codes cannot be billed by practices participating in Medicare Accountable Care Organizations. Dr. Huebschmann concluded that review articles that seek to identify interventions for real-world applications should assess pragmatism for real-world delivery and effectiveness. Her pilot trial of a reimbursable, pragmatic, and evidence-based physical activity intervention shows promise for improving physical activity and function for T2D patients.

Gaps identified

Overview

Causes of sex differences in risk factors for heart disease are not well known. Some studies have implicated estrogen as a contributing factor to these differences. ^{56 –59} Women cancer survivors develop cardiac complications much frequently. ⁵⁶ Sex differences in heart failure (HF), coronary heart disease, and heart failure with preserved ejection fraction are some of the emerging areas to which more attention needs to be paid. The role of other diseases and/or treatments (such as chemotherapy) in leading to cardiac comorbidity is also an understudied issue. The following speakers highlighted their work in these areas with a focus on understanding sex differences in risk factors for heart disease, improvements in diagnosis, and treatment.

Esther Kim, MD, Vanderbilt University, focused on spontaneous coronary artery dissection (SCAD), a tear that forms in an artery in the heart, and that mostly occurs in women at 45–53 years of age. ^{60 –62} This is different than atherosclerosis and no cardiac risk factors have been identified for this condition. Although SCAD is medically manageable, the tear can recur in a different artery/vessel and impaired quality of life is an issue. Beta-blockers are in use as a treatment option but treatments remain only partially effective. ^{60 –62} Both fibromuscular dysplasia and pregnancy have been associated with developing SCAD. At the molecular level, expression of TGF beta ligands 1 and 2 is affected and Dr. Kim noted that there is some evidence that COL3A1 mutation can result in SCAD. ^{60 –62}

David Kao, MD, University of Colorado School of Medicine, presented insights into complex phenotyping in patients with HF with preserved ejection fraction (HF_PEF). He discussed the etiology and how to personalize the HF_PEF management. ^{63 –65} At present, there are no proven effective therapies for HF_PEF, which is associated with significant morbidity and mortality. HF_PEF affects particularly postmenopausal women. Women, in general have fewer other medical conditions, survive longer, but feel worse than men. ⁶⁵ He concluded that complex phenotyping can produce a unified description of patient populations with biologic underpinnings. Complex phenotyping takes into account algorithmic identification of trait combinations for better treatments and patient outcomes. ⁶⁶ It also involves cluster-based phenotyping and includes age, sex, cardiac disease, arterial fibrillation, vascular disease, and alcohol use.

JoAnn Lindenfeld, MD, Vanderbilt University, surveyed and summarized shared risk factors for heart disease and cancer. She noted that cancer survivors often develop or have worsening CV risk factors. On the contrary, breast cancer patients have no known history of increased heart attack incidence. ^67,68 However, if they were treated with chemotherapy, heart disease occurrence increases. In some patients, fatigue is a factor because of decreased cardiorespiratory fitness. ^67,68 She also pointed out that cancer immunotherapy may be less effective in women.

Puja Mehta, MD, Emory University, focused on the role of inflammation in nonobstructive ischemic heart disease in women. She identified knowledge gaps as to the links between inflammation, microvascular dysfunction, and myocardial ischemia. These may be influenced by several psychological risk factors such as depression and anxiety and other triggers. Ischemia and nonobstructive CAD are major clinical problems that differentially impact women. ^69,70 At least 50% of these patients have coronary microvascular dysfunction (CMD) resulting in abnormal myocardial blood flow. ^69,70 She also provided evidence that CMD is not benign and is associated with major cardiovascular events. Inflammation is a risk factor for CMD and IL1beta is identified as one of the targets. An anti-inflammatory human monoclonal antibody called canakinumab has been tried in patients but studies indicated that it had some side effects. ^71,72 More studies are warranted to test its efficacy.

Linda Peterson, MD, Washington University, highlighted sex differences in HF. Common risk factors for HF are obesity and diabetes and affect mostly women compared with men. ⁷³ Heart failure with reduced ejection fraction (HFrEF) is caused by pulmonary edema, fluid/pleural perfusion, and blood flow in the wrong direction into lungs. It is more common in women than men. ^{73 –75} Sex differences in drug effects are also noticed in terms of absorption, distribution, metabolism, and elimination. Takotsubo cardiomyopathy, sudden weakness of heart muscle occurs between 58 and 75 years of age in 90% of postmenopausal women. ^76,77 Dr. Peterson presented positron emission tomography (PET) metabolic imaging studies of myocardial metabolism in men and women using ¹¹ C-tracer compounds (acetate, palmitate, lactate, and glucose). ^73,78,79

Gaps identified

Overview

Circadian rhythms play fundamental roles in physiology and metabolic homeostasis. ^{80 –83} Dysregulation of the circadian system is associated with various diseases. Several discoveries have unraveled the molecular mechanisms of circadian rhythms, which ultimately led to the 2017 Nobel Prize in Physiology or Medicine awarded to three circadian biologists. ^84,85 These initial discoveries were made possible by large-scale mutagenesis screens that identified several molecular components of the circadian clock machinery and a number of central “master regulators” and tissue-specific genes identified in mice. ^86,87 Systematic mutations in these genes resulted in novel genetic tools, which can be used to examine sex differences in cardiometabolic health phenotypes because of circadian disruption in these mice. ^88,89 In clinical studies, some of these phenotypes can be recapitulated in humans by manipulating sleep duration and/or circadian rhythms. Both insufficient sleep and circadian disruption result in impaired cardiometabolic outcomes. ^88,89 Some of the pioneers in the sleep and circadian fields presented the following seminars under this theme.

Fred Turek, PhD, Northwestern University, who coined the term “circadian medicine” summarized his work on circadian dysregulation and its impact on obesity, diabetes, and CVD. ⁹⁰ Dr. Turek's work has implicated genetic and environmental factors as contributing to circadian dysregulation. He was one of the earliest investigators who performed large-scale N-ethyl-N-nitrosourea (ENU) mutagenic screens in mice and discovered a series of mutants in Clock, Bmal, Cry, and Period genes. ⁸⁷ His group also determined that CLOCK affects multiple metabolic pathways and further identified sex differences in body weight in Clock mutants. ⁹¹ Environmental factors such as the timing of feeding and sleep duration are linked to insulin resistance and obesity in mice. ^90,91

Kathryn Reid, PhD, Northwestern University, classified differences in sleep times and patterns and how these are associated with gestational diabetes mellitus (GDM). ⁹² Objective short sleep duration and late sleep midpoint are associated with GDM but not gestational hypertension (GHTN)/PE. ⁹³ Subjective short sleep duration was not associated with either GDM or GHTN/PE. Subjective late sleep midpoint is associated with GDM but not GHTN/PE. She concluded that sleep duration and circadian misalignment are novel risk factors for adverse pregnancy outcomes. She also introduced the nulliparous pregnancy outcomes study called nu MOM 2B that monitors mothers-to-be for predicting the adverse events over the course of pregnancy.

Monika Haack, PhD, Harvard University, discussed recovery sleep, which can partially restore cardiometabolic homeostasis following partial sleep deprivation. ^{94 –96} She highlighted the sleep-immune relationship in women. ^94,95 She further highlighted sex differences between the pro- and counter-inflammatory responses to sleep restriction and recovery, and sex differences in prevalence of sleep disorders. ^94,95 For instance, insomnia is 1.5 times more common in women than men. Sleep disorders associated with inflammation and infectious diseases are also more common in women. In many of these women, IL-6, a proinflammatory cytokine remains elevated compared with men. Normally, glucocorticoid and IL-10 elicit counter-inflammatory responses. She concluded that sex differences in the balance between pro- and counter-inflammatory responses to sleep deficiency likely result in differential susceptibility of women and men to various diseases.

Satchidananda Panda, PhD, Salk Institute for Biological Studies, pioneered the concept of time-restricted eating for the prevention and management of chronic diseases. ^{97 –99} He suggested sleep, metabolism, and physical activity constitute the Circadian Code, and disruption or mistiming of any factor is associated with elevated disease risk. ^{97 –99} His work has led to biological and clinical insights regarding timing of behaviors and he coined the phrase “training the clock, clocking the drugs and drugging the clock.” ^100,101 His work on melanopsin, a blue light sensing protein and how it is regulated has led to exciting treatments for postpartum depression and created a “lightning revolution.” ^102,103 His concluding question was: can good (physical) behavior override the effect of a bad gene?

Gaps identified

Overview

Prominent sex differences exist in the incidence of diabetes and cardiometabolic defects. Across the complex integrated physiology of diabetes, there are many unexplored sex and gender differences. ^104,105 This session spanned new data in islet function, cardiovascular pathology, and access and utilization of diabetes clinical support. One emerging field is how the sex steroids—androgens and estrogens—directly act at the level of the pancreatic beta cells and contribute to beta cell physiology and diabetes in men versus women. ^106,107 Sex-specific metabolomic assessment of coronary artery calcification is one classic example of a sex difference identified in women compared with men. ^{108 –110} Coronary artery calcification is normally more prevalent in postmenopausal women. Sex-based differences in cardiac metabolism and metabolic flexibility examined using novel methods reveal differences in metabolic flexibility. ^111,112 A clinician focusing on community-based diabetes care exemplifies a feasible program of bringing diabetes awareness to the public, and more so to middle and high school students. ^113,114 These new approaches were discussed in this theme.

Franck Mauvais-Jarvis, MD, PhD, Tulane University, presented provocative findings on androgen regulation of sex differences in glucose homeostasis and diabetes. ^115,116 He presented data that indicated testosterone in men augments the function of pancreatic beta cells and improves insulin action in skeletal muscle. In contrast, in women, he reported that estrogen decreases glucose-mediated insulin secretion in pancreatic beta cells. Of interest, androgen deprivation therapy increases the risk of diabetes and CV risk by 28%. To directly study testosterone action in beta cells, his laboratory developed a beta-cell-specific androgen receptor gene deletion mouse model. ^{117 –119} These mice develop insulin deficiency and diabetes. In further studies, islet cells cultured in dihydro testosterone (DHT) secrete insulin and DHT action could not be blocked by the androgen receptor antagonist flutamide. ^{117 –119} These studies led to the identification of nonclassical extranuclear androgen receptor in beta cells and a new testis–islet cell axis. ^{117 –119} Moreover, clinically, men with severe low T have high diabetes risk and women with high androgen levels (such as polycystic ovarian syndrome) have beta cell dysfunction and have increased insulin secretion and hyperinsulinemia. ¹¹⁸

Virginia Miller, PhD, Mayo Clinic, focused on metabolism and coronary artery calcification in menopausal women. ¹¹¹ She discussed various factors that contribute to vascular vulnerabilities and leading to PE. ¹²⁰ These factors play critical roles in causing PE at younger age and predict premature CVD. Genetic factors, autonomic dysregulation, metabolic factors (obesity and diabetes), and blood-borne factors that cause hypercoagulability and innate immunity are all key factors. PE-mediated vascular vulnerabilities lead to future risk of coronary calcification. Her laboratory has developed a screen to identify metabolomic profiles of postmenopausal women. Early data suggest that PE and other factors as associated with metabolic “signatures” that indicate higher risk for calcification. Because coronary artery calcification is a continuous process, she suggested it is desirable to make multiple measurements of metabolites at different time points to clarify predictive and possible causal metabolic mediators.

Anne Peters, MD, Keck School of Medicine of USC, presentation focused on community-based diabetes care with the primary goal to reduce diabetes, obesity, and related health conditions in East and South Los Angeles. ¹¹⁴ Her approach and experience with the community has taught multiple lessons. Community-based diabetes care involves physicians interfacing with the communities in which they work. Women, as the major curators of family food and dynamics, need to be able to access the resources needed for good nutrition and optimal interface with the medical community. Solutions to issues need to come from the communities themselves. If a sustainable partnership is created, meaningful change can occur. Dr. Peters was able to establish a healthy new farmers market in a neighborhood that had previously no farmer's market. In addition, working with parents and school teachers, she was able to replace the content of typical vending machines containing unhealthy items and replacing them with healthy foods/snacks in schools. Her community-based work also led to the establishment of a Center for Population Health and Health Disparities, which is affiliated to the University of California, Los Angeles.

Gaps identified

Overview

Age-related changes occur in the musculoskeletal system that include some well-described sex differences, such as the accelerated midlife bone and muscle loss in women but not men. ¹²¹ However, in addition to changes in mass, skeletal muscle metabolic dysfunction can indirectly affect the overall body nutrient homeostasis. ¹²² Whether sex differences impact these changes is an interesting yet understudied area of research. A similar scenario is also true in the case of bone metabolism, which is influenced by various factors and disease conditions. One common phenomenon that integrates these two interrelated organs is calcium homeostasis. Circadian clock regulation is another emerging pathway that could influence muscle metabolism.

Connie Weaver, PhD, Purdue University, discussed subgroup differences in mineral metabolism and bone health. Fracture rates are more prevalent in boys than girls across ethnicity groups. ¹²³ The metabolic response to diet also varies between boys and girls across lifespan. Of particular note, calcium absorption varies by life stage (young vs. old and boys vs. girls). Dr. Weaver presented clinical trial studies involving boys and girls and using stable Ca++ isotope absorption and excretion rates using urine, blood, and stool samples. These studies have direct implications to bone health differences in boys and girls. Her studies indicated that boys have higher bone accretion than girls and boys use and retain Ca++ more efficiently than girls, which accounts for better bone formation in boys than girls. Her presentation also highlighted large racial differences in sodium retention and excretion in response to sodium intake between black and white adolescent girls.

Wendy Kohrt, PhD, University of Colorado School of Medicine, focused on exercise and bone metabolism. In particular, she focused on exercise-related bone loss, disruption of Ca++ homeostasis and coronary artery calcification. ¹²⁴ She presented evidence on how acute effects of exercise may lead to bone loss by the robust activation of bone resorption that persists for several hours after the cessation of exercise. ^125,126 Sweat produced during exercise may contribute to dermal Ca++ loss during exercise. However, this does not explain the large decrease in serum Ca++ levels during exercise, which provokes increases in PTH and bone resorption as a way to mobilize Ca++ from bone and attenuate the decline in serum Ca++. Intriguingly, the magnitude of the disruption in calcium homeostasis during exercise appears to be directly related to both the intensity and volume of exercise performed, and these two factors have also been linked to the development of coronary artery calcification in endurance athletes.

Beata Lecka Czernik, PhD, University of Toledo, described skeletal integration of energy homeostasis with a particular focus on fractures in T1D and T2D. ^127,128 Fracture rates are higher in both types of diabetic disease regardless of bone mineral density (BMD), which is lower in T1D and higher in T2D, as compared with nondiabetic individuals of the same age and sex. ^127,128 In general, diabetic patients have low bone quality and low bone turnover, which predispose bone to fractures. ^127,128 Although both diabetic men and women have similar rate of fractures, the after-fracture mortality is higher in men than in women. She also provided data on increased fractures incidence in older women, but not in men, who were treated with antidiabetic thiazolidinediones (TZD) class of drugs. Finally, she demonstrated that a new experimental drug, which targets the same as TZDs mechanisms controlling insulin sensitivity, possesses desired antidiabetic efficacy while increases bone formation by negatively regulating sclerostin. Of interest, this drug exerts sex-specific effects in male and female mice suggesting that it may have different effects in men and women. ^129,130 Dr. Czernik concluded that it is possible to develop a drug that will be beneficial for both diabetes and osteoporosis.

Karyn Esser, PhD, University of Florida, introduced the concept of circadian rhythms and the timing mechanism that underlies daily rhythms. Circadian rhythms are the daily 24-hour cycles in physiology and behavior such as sleep/wake cycles and daily changes in blood pressure. ¹³¹ The molecular mechanism controlling circadian rhythms is called the molecular clock and the core components include the following: BMAL1, CLOCK, PER 1 and 2, and CRY 1, 2. The molecular clock mechanism exists in virtually all cells throughout the body and in addition to keeping time, these factors modulate a large program of gene expression. ^132,133 Her presentation focused on muscle-specific and temporal inactivation of Bmal1 gene in mice. ^134,135 Using this as a genetic tool, she demonstrated in these mice the forelimb grip strength and maximum isometric force parameters are reduced, insulin is elevated, there is higher glucose tolerance, and mice are less fat. The muscles also exhibit increased fibrosis, changes in walking gait, and changes in bone and cartilage. Thus, her studies provided direct evidence that molecular clocks function in skeletal muscle tissues. This work now paves the way to identifying if sex differences exist in this particular tissue.

Gaps identified