Skeletal muscle wasting: the estrogen side of sexual dimorphism

Sex differences in muscle health in simulated micro- and partial-gravity environments in rats

Skeletal muscle size and strength are important for overall health for astronauts. However, how male and female muscle may respond differently to micro- and partial-gravity environments is not fully understood. The purpose of this study was to determine how biological sex and sex steroid hormones influence the progression of muscle atrophy after long term exposure to micro and partial gravity environments in male and female rats. Male and female Fisher rats (n ​= ​120) underwent either castration/ovariectomy or sham surgeries. After two weeks recovery, animals were divided into microgravity (0g), partial-gravity (40% of weight bearing, 0.4g), or full weight bearing (1g) interventions for 28 days. Measurements of muscle size and strength were evaluated prior to and after interventions. At 0g, females lost more dorsiflexion strength, plantar flexion strength, and other metrics of muscle size compared to males; castration/ovariectomy did not influence these differences. Additionally, at 0.4g, females lost more dorsiflexion strength, plantar flexion strength, and other metrics of muscle strength compared to males; castration/ovariectomy did not influence these differences. Females have greater musculoskeletal aberrations during exposure to both microgravity and partial-gravity environments; these differences are not dependent on the presence of sex steroid hormones. Correspondingly, additional interventions may be necessary to mitigate musculoskeletal loss in female astronauts to protect occupational and overall health.

Influence of sexual dimorphism on satellite cell regulation and inflammatory response during skeletal muscle regeneration

After injury, skeletal muscle regenerates thanks to the key role of satellite cells (SC). The regeneration process is supported and coordinated by other cell types among which immune cells. Among the mechanisms involved in skeletal muscle regeneration, a sexual dimorphism, involving sex hormones and more particularly estrogens, has been suggested. However, the role of sexual dimorphism on skeletal muscle regeneration is not fully understood, likely to the use of various experimental settings in both animals and human. This review aims at addressing how sex and estrogens regulate both the SC and the inflammatory response during skeletal muscle regeneration by considering the different experimental designs used in both animal models (i.e., ovarian hormone deficiency, estrogen replacement or supplementation, treatments with estrogen receptors agonists/antagonists and models knockout for estrogen receptors) and human (hormone therapy replacement, pre vs. postmenopausal, menstrual cycle variation…).

IGF-1 Therapy Improves Muscle Size and Function in Experimental Peripheral Arterial Disease

Lower-extremity peripheral arterial disease (PAD) has increased in prevalence, yet therapeutic development has remained stagnant. Skeletal muscle health and function has been strongly linked to quality of life and medical outcomes in patients with PAD. Using a rodent model of PAD, this study demonstrates that treatment of the ischemic limb with insulin-like growth factor (IGF)-1 significantly increases muscle size and strength without improving limb hemodynamics. Interestingly, the effect size of IGF1 therapy was larger in female mice than in male mice, highlighting the need to carefully examine sex-dependent effects in experimental PAD therapies.

Influence of gonadectomy on muscle health in micro- and partial-gravity environments in rats

Gonadal hormones, such as testosterone and estradiol, modulate muscle size and strength in males and females. However, the influence of sex hormones on muscle strength in micro- and partial-gravity environments (e.g., the Moon or Mars) is not fully understood. The purpose of this study was to determine the influence of gonadectomy (castration/ovariectomy) on progression of muscle atrophy in both micro- and partial-gravity environments in male and female rats. Male and female Fischer rats (n = 120) underwent castration/ovariectomy (CAST/OVX) or sham surgery (SHAM) at 11 wk of age. After 2 wk of recovery, rats were exposed to hindlimb unloading (0 g), partial weight bearing at 40% of normal loading (0.4 g, Martian gravity), or normal loading (1.0 g) for 28 days. In males, CAST did not exacerbate body weight loss or other metrics of musculoskeletal health. In females, OVX animals tended to have greater body weight loss and greater gastrocnemius loss. Within 7 days of exposure to either microgravity or partial gravity, females had detectable changes to estrous cycle, with greater time spent in low-estradiol phases diestrus and metestrus (∼47% in 1 g vs. 58% in 0 g and 72% in 0.4 g animals, P = 0.005). We conclude that in males testosterone deficiency at the initiation of unloading has little effect on the trajectory of muscle loss. In females, initial low estradiol status may result in greater musculoskeletal losses.NEW & NOTEWORTHY We find that removal of gonadal hormones does not exacerbate muscle loss in males or females during exposure to either simulated microgravity or partial-gravity environments. However, simulated micro- and partial gravity did affect females' estrous cycles, with more time spent in low-estrogen phases. Our findings provide important data on the influence of gonadal hormones on the trajectory of muscle loss during unloading and will help inform NASA for future crewed missions to space and other planets.

Anorexia nervosa and muscle health: A systematic review of our current understanding and future recommendations for study

OBJECTIVE

Conduct a systematic review on muscle size and strength in individuals with anorexia nervosa (AN).

METHOD

In accordance with PRISMA guidelines, we searched Pubmed for articles published between 1995 and 2022 using a combination of search terms related to AN and muscle size, strength, or metabolism. After two authors screened articles and extracted data, 30 articles met inclusion criteria. Data were coded, and a risk bias was conducted for each study.

RESULTS

The majority of studies focused on muscle size/lean mass (60%, n = 18) and energy expenditure (33%, n = 9), with few studies (17%, n = 5) investigating muscle function or possible mechanisms underlying muscle size (20%, n = 6). Studies supported that individuals with AN have smaller muscle size and reduced energy expenditure relative to controls. In some studies (33%, n = 10) recovery from AN was not sufficient to restore muscle mass or function. Mechanisms underlying short and long-term musculoskeletal alterations have not been thoroughly explored.

DISCUSSION

Muscle mass and strength loss may be an unexplored component of physiological deterioration during and after AN. More research is necessary to understand intramuscular alterations during AN and interventions to facilitate muscle mass and functional gain following weight restoration in AN.

PUBLIC SIGNIFICANCE

Muscle health is important for optimal health and is reduced in individuals with AN. However, we do not understand how muscle is altered at the cellular level throughout the course of AN. Here we review what is currently known regarding muscle health during AN and with weight restoration.

Sex Differences in Inflammation and Muscle Wasting in Aging and Disease

Only in recent years, thanks to a precision medicine-based approach, have treatments tailored to the sex of each patient emerged in clinical trials. In this regard, both striated muscle tissues present significant differences between the two sexes, which may have important consequences for diagnosis and therapy in aging and chronic illness. In fact, preservation of muscle mass in disease conditions correlates with survival; however, sex should be considered when protocols for the maintenance of muscle mass are designed. One obvious difference is that men have more muscle than women. Moreover, the two sexes differ in inflammation parameters, particularly in response to infection and disease. Therefore, unsurprisingly, men and women respond differently to therapies. In this review, we present an up-to-date overview on what is known about sex differences in skeletal muscle physiology and disfunction, such as disuse atrophy, age-related sarcopenia, and cachexia. In addition, we summarize sex differences in inflammation which may underly the aforementioned conditions because pro-inflammatory cytokines deeply affect muscle homeostasis. The comparison of these three conditions and their sex-related bases is interesting because different forms of muscle atrophy share common mechanisms; for instance, those responsible for protein dismantling are similar although differing in terms of kinetics, severity, and regulatory mechanisms. In pre-clinical research, exploring sexual dimorphism in disease conditions could highlight new efficacious treatments or recommend implementation of an existing one. Any protective factors discovered in one sex could be exploited to achieve lower morbidity, reduce the severity of the disease, or avoid mortality in the opposite sex. Thus, the understanding of sex-dependent responses to different forms of muscle atrophy and inflammation is of pivotal importance to design innovative, tailored, and efficient interventions.

Does initial skeletal muscle size or sex affect the magnitude of muscle loss in response to 14 days immobilization?

We aimed to determine whether there was a relationship between pre-immobilization skeletal muscle size and the magnitude of muscle atrophy following 14 days of unilateral lower limb immobilization. Our findings (n = 30) show that pre-immobilization leg fat-free mass and quadriceps cross-sectional area (CSA) were unrelated to the magnitude of muscle atrophy. However, sex-based differences may be present, but confirmatory work is required. In women, pre-immobilization leg fat-free mass and CSA were associated with changes in quadriceps CSA after immobilization (n = 9, r² = 0.54-0.68; P < 0.05). The extent of muscle atrophy is not affected by initial muscle mass, but there is potential for sex-based differences.

Sex differences in musculoskeletal injury and disease risks across the lifespan: Are there unique subsets of females at higher risk than males for these conditions at distinct stages of the life cycle?

Sex differences have been reported for diseases of the musculoskeletal system (MSK) as well as the risk for injuries to tissues of the MSK system. For females, some of these occur prior to the onset of puberty, following the onset of puberty, and following the onset of menopause. Therefore, they can occur across the lifespan. While some conditions are related to immune dysfunction, others are associated with specific tissues of the MSK more directly. Based on this life spectrum of sex differences in both risk for injury and onset of diseases, a role for sex hormones in the initiation and progression of this risk is somewhat variable. Sex hormone receptor expression and functioning can also vary with life events such as the menstrual cycle in females, with different tissues being affected. Furthermore, some sex hormone receptors can affect gene expression independent of sex hormones and some transitional events such as puberty are accompanied by epigenetic alterations that can further lead to sex differences in MSK gene regulation. Some of the sex differences in injury risk and the post-menopausal disease risk may be "imprinted" in the genomes of females and males during development and sex hormones and their consequences only modulators of such risks later in life as the sex hormone milieu changes. The purpose of this review is to discuss some of the relevant conditions associated with sex differences in risks for loss of MSK tissue integrity across the lifespan, and further discuss several of the implications of their variable relationship with sex hormones, their receptors and life events.

Effects of the menstrual cycle phase on anterior cruciate ligament neuromuscular and biomechanical injury risk surrogates in eumenorrheic and naturally menstruating women: A systematic review

BACKGROUND

Eumenorrheic women experience cyclic variations in sex hormones attributed to the menstrual cycle (MC) which can impact anterior cruciate ligament (ACL) properties, knee laxity, and neuromuscular function. This systematic review aimed to examine the effects of the MC on ACL neuromuscular and biomechanical injury risk surrogates during dynamic tasks, to establish whether a particular MC phase predisposes women to greater ACL injury risk.

METHODS

PubMed, Medline, SPORTDiscus, and Web of Science were searched (May-July 2021) for studies that investigated the effects of the MC on ACL neuromuscular and biomechanical injury risk surrogates. Inclusion criteria were: 1) injury-free women (18-40 years); 2) verified MC phases via biochemical analysis and/or ovulation kits; 3) examined neuromuscular and/or biomechanical injury risk surrogates during dynamic tasks; 4) compared ≥1 outcome measure across ≥2 defined MC phases.

RESULTS

Seven of 418 articles were included. Four studies reported no significant differences in ACL injury risk surrogates between MC phases. Two studies showed evidence the mid-luteal phase may predispose women to greater risk of non-contact ACL injury. Three studies reported knee laxity fluctuated across the MC; two of which demonstrated MC attributed changes in knee laxity were associated with changes in knee joint loading (KJL). Study quality (Modified Downs and Black Checklist score: 7-9) and quality of evidence were low to very low (Grading of Recommendations Assessment Development and Evaluation: very low).

CONCLUSION

It is inconclusive whether a particular MC phase predisposes women to greater non-contact ACL injury risk based on neuromuscular and biomechanical surrogates. Practitioners should be cautious manipulating their physical preparation, injury mitigation, and screening practises based on current evidence. Although variable (i.e., magnitude and direction), MC attributed changes in knee laxity were associated with changes in potentially hazardous KJLs. Monitoring knee laxity could therefore be a viable strategy to infer possible ACL injury risk.

Neuropathic-like Pain Symptoms and Their Association with Muscle Strength in Patients with Chronic Musculoskeletal Pain

The relationship between sarcopenia and pain remains unclear; thus, this study evaluated whether muscle strength is independently associated with neuropathic-like pain symptoms in patients with chronic musculoskeletal pain. A cut-off score of painDETECT ≥13 was used to indicate a possible neuropathic component. Handgrip strength was measured, and muscle mass was estimated. A total of 2599 patients, including 439 patients who reported neuropathic-like pain symptoms (16.9%), were included for analysis. Handgrip strength was significantly lower in patients experiencing neuropathic-like pain symptoms (23.23 ± 10.57 vs. 24.82 ± 10.43 kg, p < 0.001), and this result was chiefly found in female patients. However, there was no difference in estimated muscle mass. Shorter duration of pain, opioid usage, pain in lower limbs, sleep disturbance, and lower handgrip strength were significantly associated with neuropathic-like pain symptoms. In patients with handgrip strength below the reference values by sex, experiencing radiating pain and at least moderate sensory symptoms by light touch and thermal stimulation were more frequently reported. In conclusion, lower handgrip strength appeared to be an independent factor associated with symptoms suggestive of neuropathic pain in this population. Interventional studies are required to determine whether improvement in muscle strength can reduce the neuropathic pain component in chronic musculoskeletal pain.

The importance of biological sex in cardiac cachexia

Cardiac cachexia is a catabolic muscle wasting syndrome observed in approximately 1 in 10 heart failure patients. Increased skeletal muscle atrophy leads to frailty and limits mobility which impacts quality of life, exacerbates clinical care, and is associated with higher rates of mortality. Heart failure is known to exhibit a wide range of prevalence and severity when examined across individuals of different ages and with co-morbidities related to diabetes, renal failure and pulmonary dysfunction. It is also recognized that men and women exhibit striking differences in the pathophysiology of heart failure as well as skeletal muscle homeostasis. Given that both skeletal muscle and heart failure physiology are in-part sex dependent, the diagnosis and treatment of cachexia in heart failure patients may depend on a comprehensive examination of how these organs interact. In this review we explore the potential for sex-specific differences in cardiac cachexia. We summarize advantages and disadvantages of clinical methods used to measure muscle mass and function and provide alternative measurements that should be considered in preclinical studies. Additionally, we summarize sex-dependent effects on muscle wasting in preclinical models of heart failure, disuse, and cancer. Lastly, we discuss the endocrine function of the heart and outline unanswered questions that could directly impact patient care.

Estradiol and Estrogen-like Alternative Therapies in Use: The Importance of the Selective and Non-Classical Actions

Estrogen is one of the most important female sex hormones, and is indispensable for reproduction. However, its role is much wider. Among others, due to its neuroprotective effects, estrogen protects the brain against dementia and complications of traumatic injury. Previously, it was used mainly as a therapeutic option for influencing the menstrual cycle and treating menopausal symptoms. Unfortunately, hormone replacement therapy might be associated with detrimental side effects, such as increased risk of stroke and breast cancer, raising concerns about its safety. Thus, tissue-selective and non-classical estrogen analogues have become the focus of interest. Here, we review the current knowledge about estrogen effects in a broader sense, and the possibility of using selective estrogen-receptor modulators (SERMs), selective estrogen-receptor downregulators (SERDs), phytoestrogens, and activators of non-genomic estrogen-like signaling (ANGELS) molecules as treatment.

Interconnection between Cardiac Cachexia and Heart Failure—Protective Role of Cardiac Obesity

Cachexia may be caused by congestive heart failure, and it is then called cardiac cachexia, which leads to increased morbidity and mortality. Cardiac cachexia also worsens skeletal muscle degradation. Cardiac cachexia is the loss of edema-free muscle mass with or without affecting fat tissue. It is mainly caused by a loss of balance between protein synthesis and degradation, or it may result from intestinal malabsorption. The loss of balance in protein synthesis and degradation may be the consequence of altered endocrine mediators such as insulin, insulin-like growth factor 1, leptin, ghrelin, melanocortin, growth hormone and neuropeptide Y. In contrast to many other health problems, fat accumulation in the heart is protective in this condition. Fat in the heart can be divided into epicardial, myocardial and cardiac steatosis. In this review, we describe and discuss these topics, pointing out the interconnection between heart failure and cardiac cachexia and the protective role of cardiac obesity. We also set the basis for possible screening methods that may allow for a timely diagnosis of cardiac cachexia, since there is still no cure for this condition. Several therapeutic procedures are discussed including exercise, nutritional proposals, myostatin antibodies, ghrelin, anabolic steroids, anti-inflammatory substances, beta-adrenergic agonists, medroxyprogesterone acetate, megestrol acetate, cannabinoids, statins, thalidomide, proteasome inhibitors and pentoxifylline. However, to this date, there is no cure for cachexia.