Targeting mitochondria to restore failed adaptation to exercise in diabetes

Glucagon-like peptide-1 receptor agonists rescued diabetic vascular endothelial damage through suppression of aberrant STING signaling

Glucagon-like peptide-1 receptor agonists (GLP-1 RAs) protect against diabetic cardiovascular diseases and nephropathy. However, their activity in diabetic retinopathy (DR) remains unclear. Our retrospective cohort study involving 1626 T2DM patients revealed superior efficacy of GLP-1 RAs in controlling DR compared to other glucose-lowering medications, suggesting their advantage in DR treatment. By single-cell RNA-sequencing analysis and immunostaining, we observed a high expression of GLP-1R in retinal endothelial cells, which was down-regulated under diabetic conditions. Treatment of GLP-1 RAs significantly restored the receptor expression, resulting in an improvement in retinal degeneration, vascular tortuosity, avascular vessels, and vascular integrity in diabetic mice. GO and GSEA analyses further implicated enhanced mitochondrial gene translation and mitochondrial functions by GLP-1 RAs. Additionally, the treatment attenuated STING signaling activation in retinal endothelial cells, which is typically activated by leaked mitochondrial DNA. Expression of STING mRNA was positively correlated to the levels of angiogenic and inflammatory factors in the endothelial cells of human fibrovascular membranes. Further investigation revealed that the cAMP-responsive element binding protein played a role in the GLP-1R signaling pathway on suppression of STING signaling. This study demonstrates a novel role of GLP-1 RAs in the protection of diabetic retinal vasculature by inhibiting STING-elicited inflammatory signals.

Low Response to Aerobic Training in Metabolic Disease: Role of Skeletal Muscle

Aerobic exercise is established to increase cardiorespiratory fitness (CRF), which is linked to reduced morbidity and mortality. However, people with metabolic diseases such as type 1 and type 2 diabetes may be more likely to display blunted improvements in CRF with training. Here, we present evidence supporting the hypothesis that altered skeletal muscle signaling and remodeling may contribute to low CRF with metabolic disease.

Mitochondrial contributions to vascular endothelial dysfunction, arterial stiffness, and cardiovascular diseases

Cardiovascular disease (CVD) affects one in three adults and remains the leading cause of death in America. Advancing age is a major risk factor for CVD. Recent plateaus in CVD-related mortality rates in high-income countries after decades of decline highlight a critical need to identify novel therapeutic targets and strategies to mitigate and manage the risk of CVD development and progression. Vascular dysfunction, characterized by endothelial dysfunction and large elastic artery stiffening, is independently associated with an increased CVD risk and incidence and is therefore an attractive target for CVD prevention and management. Vascular mitochondria have emerged as an important player in maintaining vascular homeostasis. As such, age- and disease-related impairments in mitochondrial function contribute to vascular dysfunction and consequent increases in CVD risk. This review outlines the role of mitochondria in vascular function and discusses the ramifications of mitochondrial dysfunction on vascular health in the setting of age and disease. The adverse vascular consequences of increased mitochondrial-derived reactive oxygen species, impaired mitochondrial quality control, and defective mitochondrial calcium cycling are emphasized, in particular. Current evidence for both lifestyle and pharmaceutical mitochondrial-targeted strategies to improve vascular function is also presented.

Inorganic Nitrite Supplementation Improves Endothelial Function With Aging: Translational Evidence for Suppression of Mitochondria-Derived Oxidative Stress

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Targeting mitochondrial fitness as a strategy for healthy vascular aging

Cardiovascular diseases (CVD) are the leading cause of death worldwide and aging is the primary risk factor for CVD. The development of vascular dysfunction, including endothelial dysfunction and stiffening of the large elastic arteries (i.e., the aorta and carotid arteries), contribute importantly to the age-related increase in CVD risk. Vascular aging is driven in large part by oxidative stress, which reduces bioavailability of nitric oxide and promotes alterations in the extracellular matrix. A key upstream driver of vascular oxidative stress is age-associated mitochondrial dysfunction. This review will focus on vascular mitochondria, mitochondrial dysregulation and mitochondrial reactive oxygen species (ROS) production and discuss current evidence for prevention and treatment of vascular aging via lifestyle and pharmacological strategies that improve mitochondrial health. We will also identify promising areas and important considerations ('research gaps') for future investigation.

Sex Differences Across the Lifespan: A Focus on Cardiometabolism

Women's health and sex differences research remain understudied. In 2016, to address the topic of sex differences, the Center for Women' s Health Research (CWHR) at the University of Colorado (cwhr@ucdenver.edu) held its inaugural National Conference, "Sex Differences Across the Lifespan: A Focus on Metabolism" and published a report summarizing the presentations. Two years later, in 2018, CWHR organized the 2nd National Conference. The research presentations and discussions from the 2018 conference also addressed sex differences across the lifespan with a focus on cardiometabolism and expanded the focus by including circadian physiology and effects of sleep on cardiometabolic health. Over 100 participants, including basic scientists, clinicians, policymakers, advocacy group leaders, and federal agency leadership participated. The meeting proceedings reveal that although exciting advances in the area of sex differences have taken place, significant questions and gaps remain about women's health and sex differences in critical areas of health. Identifying these gaps and the subsequent research that will result may lead to important breakthroughs.

Supplemental Oxygen Improves In Vivo Mitochondrial Oxidative Phosphorylation Flux in Sedentary Obese Adults With Type 2 Diabetes

Type 2 diabetes is associated with impaired exercise capacity. Alterations in both muscle perfusion and mitochondrial function can contribute to exercise impairment. We hypothesized that impaired muscle mitochondrial function in type 2 diabetes is mediated, in part, by decreased tissue oxygen delivery and would improve with oxygen supplementation. Ex vivo muscle mitochondrial content and respiration assessed from biopsy samples demonstrated expected differences in obese individuals with (n = 18) and without (n = 17) diabetes. Similarly, in vivo mitochondrial oxidative phosphorylation capacity measured in the gastrocnemius muscle via ³¹P-MRS indicated an impairment in the rate of ADP depletion with rest (27 ± 6 s [diabetes], 21 ± 7 s [control subjects]; P = 0.008) and oxidative phosphorylation (P = 0.046) in type 2 diabetes after isometric calf exercise compared with control subjects. Importantly, the in vivo impairment in oxidative capacity resolved with oxygen supplementation in adults with diabetes (ADP depletion rate 5.0 s faster, P = 0.012; oxidative phosphorylation 0.046 ± 0.079 mmol/L/s faster, P = 0.027). Multiple in vivo mitochondrial measures related to HbA_1c These data suggest that oxygen availability is rate limiting for in vivo mitochondrial oxidative exercise recovery measured with ³¹P-MRS in individuals with uncomplicated diabetes. Targeting muscle oxygenation could improve exercise function in type 2 diabetes.

Metabolic Effects of Exercise Training Among Fitness-Nonresponsive Patients With Type 2 Diabetes: The HART-D Study

OBJECTIVE

To evaluate the impact of exercise training (ET) on metabolic parameters among participants with type 2 diabetes mellitus (T2DM) who do not improve their cardiorespiratory fitness (CRF) with training.

RESEARCH DESIGN AND METHODS

We studied participants with T2DM participating in the Health Benefits of Aerobic and Resistance Training in Individuals With Type 2 Diabetes (HART-D) trial who were randomized to a control group or one of three supervised ET groups for 9 months. Fitness response to ET was defined as a change in measured peak absolute oxygen uptake (ΔVO(2peak), in liters per minute) from baseline to follow-up. ET participants were classified based on ΔVO(2peak) into fitness responders (ΔVO(2peak) ≥5%) and nonresponders (ΔVO(2peak) <5%), and changes in metabolic profiles were compared across control, fitness responder, and fitness nonresponder groups.

RESULTS

A total of 202 participants (mean age 57.1 ± 7.9 years, 63% women) were included. Among the exercise groups (n = 161), there was substantial heterogeneity in ΔVO(2peak); 57% had some improvement in CRF (ΔVO(2peak) >0), with only 36.6% having a ≥5% increase in VO(2peak). Both fitness responders and nonresponders (respectively) had significant improvements in hemoglobin A1c and measures of adiposity (ΔHbA(1c): -0.26% [95% CI -0.5 to -0.01] and -0.26% [-0.45 to -0.08]; Δwaist circumference: -2.6 cm [-3.7 to -1.5] and -1.8 cm [-2.6 to -1.0]; Δbody fat: -1.07% [-1.5 to -0.62] and -0.75% [-1.09 to -0.41]). No significant differences were observed in the degree of change of these metabolic parameters between fitness responders and nonresponders. Control group participants had no significant changes in any of these metabolic parameters.

CONCLUSIONS

ET is associated with significant improvements in metabolic parameters irrespective of improvement in cardiorespiratory fitness.

Nitric oxide in follicle development and oocyte competence

Apart from its well-known role in regulating endothelial function, in mammals, nitric oxide (NO) is an important signaling molecule involved in many processes, regulating different biological functions. It has been demonstrated that NO plays a role in the physiology of the reproductive system, where it acts in controlling the activity of reproductive organs in both sexes. In the female of several animal species, experimental data suggest the presence of an intraovarian NO-generating system, which could be involved in the control of follicular development. The role of NO in regulating follicular atresia by apoptosis is still controversial, as a dual action depending mostly on its concentration has been documented. NO also displays positive effects on follicle development and selection related to angiogenic events and it could also play a modulatory role in steroidogenesis in ovarian cells. Both in monovulatory and poliovulatory species, the increase in PGE2production induced by NO via a stimulatory effect on COX-2 activity appears to be a common ovulatory mechanism. Considerable evidence also exists to support an involvement of the NO/NO synthase system in the control of meiotic maturation of cumulus–oocyte complexes.

SIRT3 protects endothelial cells from high glucose-induced cytotoxicity

Diabetes is a frequent and increasing public health problem with a large economic burden in modern society. Endothelial cells dysfunction was involved in the development of diabetes-associated diseases. Sirtuins are a conserved family of NAD-dependent deacetylases. However, the role of sirtuins in diabetes-associated endothelial cell dysfunction was relatively unknown. In this study, we focus on the intrinsic link between SIRT3, a mitochondrial sirtuin, and high glucose-induced endothelial cells dysfunction. We showed that loss of SIRT3 expression was associated with decreased viability in endothelial cells from diabetes patients. Knockdown of SIRT3 decreased viability of endothelia cells exposed to high glucose condition. Further, mechanistic study showed that SIRT3 repression results in SOD2 acetylation, leading to SOD2 inactivation, which enhanced high glucose-induced oxidative stress in endothelial cells. Our data suggested that SIRT3 protects endothelial cells from high glucose-induced cytotoxicity. Our findings are considered a significant step toward a better understanding of diabetes-associated vascular diseases.