Muscling in on mitochondrial sexual dimorphism; role of mitochondrial dimorphism in skeletal muscle health and disease

Alcohol Impairs Bioenergetics and Differentiation Capacity of Myoblasts from Simian Immunodeficiency Virus-Infected Female Macaques

Alcohol misuse and HIV independently induce myopathy. We previously showed that chronic binge alcohol (CBA) administration, with or without simian immunodeficiency virus (SIV), decreases differentiation capacity of male rhesus macaque myoblasts. We hypothesized that short-term alcohol and CBA/SIV would synergistically decrease differentiation capacity and impair bioenergetic parameters in female macaque myoblasts. Myoblasts from naïve (CBA-/SIV-), vehicle [VEH]/SIV, and CBA/SIV (N = 4-6/group) groups were proliferated (3 days) and differentiated (5 days) with 0 or 50 mM ethanol (short-term). CBA/SIV decreased differentiation and increased non-mitochondrial oxygen consumption rate (OCR) versus naïve and/or VEH/SIV. Short-term alcohol decreased differentiation; increased maximal and non-mitochondrial OCR, mitochondrial reactive oxygen species (ROS) production, and aldolase activity; and decreased glycolytic measures, ATP production, mitochondrial membrane potential (ΔΨm), and pyruvate kinase activity. Mitochondrial ROS production was closely associated with mitochondrial network volume, and differentiation indices were closely associated with key bioenergetic health and function parameters. Results indicate that short-term alcohol and CBA non-synergistically decrease myoblast differentiation capacity. Short-term alcohol impaired myoblast glycolytic function, driving the bioenergetic deficit. Results suggest potentially differing mechanisms underlying decreased differentiation capacity with short-term alcohol and CBA, highlighting the need to elucidate the impact of different alcohol use patterns on myopathy.

Mitochondrial Content, but Not Function, Is Altered With a Multimodal Resistance Training Protocol and Adequate Protein Intake in Leucine-Supplemented Pre/Frail Women

Background: Frailty is a clinical condition associated with loss of muscle mass and strength (sarcopenia). Mitochondria are centrally implicated in frailty and sarcopenia. Leucine (Leu) can alter mitochondrial content in myocytes, while resistance training (RT) is the strongest stimulus to counteract sarcopenia and may enhance mitochondrial biogenesis. Objective: We determined the effects of Leu supplementation and RT on mitochondrial content and function in pre/frail elderly women in a randomized double-blinded placebo-controlled study. Methods: Nineteen pre/frail elderly women (77.5 ± 1.3 y, BMI: 25.1 ± 0.9 kg/m²), based on the Frailty Phenotype, underwent 3-months of RT 3×/week with protein-optimized diet and were randomized to 7.5 g/d of Leu supplementation or placebo alanine (Ala). Pre/post-intervention mitochondrial respiration, reactive oxygen species (ROS) production, calcium retention capacity (CRC), time to permeability transition pore (mPTP) opening, mitochondrial voltage-dependent anion channel (VDAC) protein content, leg press 1-repetition maximum (1RM), and 6-min walk test (6MWT) were measured. Results: No time, supplementation, or interaction effects were observed for respiration, ROS, time to mPTP opening, and CRC. VDAC levels significantly increased in the Leu group post-intervention (p = 0.012). Both groups significantly increased leg press 1RM and 6MWT, with no effect of supplementation. Discussion: Leu supplementation with 3 months of RT increased mitochondrial content. Future studies should investigate if there is an increase in mitochondrial turnover or a shift in quality control (mitophagy) in leucine supplemented pre/frail elderly women who undergo 12 weeks of RT. Clinical Trial Registration: ClinicalTrials.gov, identifier: NCT01922167.

Sexual dimorphism in cardiometabolic health: the role of adipose tissue, muscle and liver

Obesity is associated with many adverse health effects, such as an increased cardiometabolic risk. Despite higher adiposity for a given BMI, premenopausal women are at lower risk of cardiometabolic disease than men of the same age. This cardiometabolic advantage in women seems to disappear after the menopause or when type 2 diabetes mellitus develops. Sexual dimorphism in substrate supply and utilization, deposition of excess lipids and mobilization of stored lipids in various key metabolic organs (such as adipose tissue, skeletal muscle and the liver) are associated with differences in tissue-specific insulin sensitivity and cardiometabolic risk profiles between men and women. Moreover, lifestyle-related factors and epigenetic and genetic mechanisms seem to affect metabolic complications and disease risk in a sex-specific manner. This Review provides insight into sexual dimorphism in adipose tissue distribution, adipose tissue, skeletal muscle and liver substrate metabolism and tissue-specific insulin sensitivity in humans, as well as the underlying mechanisms, and addresses the effect of these sex differences on cardiometabolic health. Additionally, this Review highlights the implications of sexual dimorphism in the pathophysiology of obesity-related cardiometabolic risk for the development of sex-specific prevention and treatment strategies.

Reduced Mitochondrial Content, Elevated Reactive Oxygen Species, and Modulation by Denervation in Skeletal Muscle of Prefrail or Frail Elderly Women

Denervation and mitochondrial impairment are implicated in age-related skeletal muscle atrophy and may play a role in physical frailty. We recently showed that denervation modulates muscle mitochondrial function in octogenarian men, but this has not been examined in elderly women. On this basis, we tested the hypothesis that denervation plays a modulating role in mitochondrial impairment in skeletal muscle from prefrail or frail elderly (FE) women. Mitochondrial respiratory capacity and reactive oxygen species emission were examined in permeabilized myofibers obtained from vastus lateralis muscle biopsies from FE and young inactive women. Muscle respiratory capacity was reduced in proportion to a reduction in a mitochondrial marker protein in FE, and mitochondrial reactive oxygen species emission was elevated in FE versus young inactive group. Consistent with a significant accumulation of neural cell adhesion molecule-positive muscle fibers in FE (indicative of denervation), a 50% reduction in reactive oxygen species production after pharmacologically inhibiting the denervation-mediated reactive oxygen species response in FE women suggests a significant modulation of mitochondrial function by denervation. In conclusion, our data support the hypothesis that denervation plays a modulating role in skeletal muscle mitochondrial function in FE women, suggesting therapeutic strategies in advanced age should focus on the causes and treatment of denervation.

Estrogens, Estrogen Receptors Effects on Cardiac and Skeletal Muscle Mitochondria

Mitochondria are unique organelles present in almost all cell types. They are involved not only in the supply of energy to the host cell, but also in multiple biochemical and biological processes like calcium homeostasis, production, and regulation of reactive oxygen species (ROS), pH control, or cell death. The importance of mitochondria in cell biology and pathology is increasingly recognized. Being maternally inherited, mitochondria exhibit a tissue-specificity, because most of the mitochondrial proteins are encoded by the nuclear genome. This renders them exquisitely well-adapted to the physiology of the host cell. It is thus not surprising that mitochondria show a sexual dimorphism and that they are also prone to the influence of sex chromosomes and sex hormones. Estrogens affect mitochondria through multiple processes involving membrane and nuclear estrogen receptors (ERs) as well as more direct effects. Moreover, estrogen receptors have been identified within mitochondria. The effects of estrogens on mitochondria comprise protein content and specific activity of mitochondrial proteins, phospholipid content of membranes, oxidant and anti-oxidant capacities, oxidative phosphorylation, and calcium retention capacities. Herein we will briefly review the life cycle and functions of mitochondria, the importance of estrogen receptors and the effects of estrogens on heart and skeletal muscle mitochondria.

Understanding sex differences in the regulation of cancer-induced muscle wasting

PURPOSE OF REVIEW

We highlight evidence for sexual dimorphism in preclinical and clinical studies investigating the cause and treatment of cancer cachexia.

RECENT FINDINGS

Cancer cachexia is unintended bodyweight loss occurring with cancer, and skeletal muscle wasting is a critical predictor of negative outcomes in the cancer patient. Skeletal muscle exhibits sexual dimorphism in fiber type, function, and regeneration capacity. Sex differences have been implicated in skeletal muscle metabolism, mitochondrial function, immune response to injury, and myogenic stem cell regulation. All of these processes have the potential to be involved in cancer-induced muscle wasting. Unfortunately, the vast majority of published studies examining cancer cachexia in preclinical models or cancer patients either have not accounted for sex in their design or have exclusively studied males. Preclinical studies have established that ovarian function and estradiol can affect skeletal muscle function, metabolism and mass; ovarian function has also been implicated in the sensitivity of circulating inflammatory cytokines and the progression of cachexia.

SUMMARY

Females and males have unique characteristics that effect skeletal muscle's microenvironment and intrinsic signaling. These differences provide a strong rationale for distinct causes for cancer cachexia development and treatment in males and females.