Myofiber androgen receptor increases muscle strength mediated by a skeletal muscle splicing variant of Mylk4

Dissecting loci that underpin the genetic correlations between production, fertility, and urea traits in Australian Holstein cattle

Unfavorable genetic correlations between milk production, fertility, and urea traits have been reported. However, knowledge of the genomic regions associated with these unfavorable correlations is limited. Here, we used the correlation scan method to identify and investigate the regions driving or antagonizing the genetic correlations between production vs. fertility, urea vs. fertility, and urea vs. production traits. Driving regions produce an estimate of correlation that is in the same direction as the global correlation. Antagonizing regions produce an estimate in the opposite direction of the global estimates. Our dataset comprised 6567, 4700, and 12,658 Holstein cattle with records of production traits (milk yield, fat yield, and protein yield), fertility (calving interval) and urea traits (milk urea nitrogen and blood urea nitrogen predicted using milk-mid-infrared spectroscopy), respectively. Several regions across the genome drive the correlations between production, fertility, and urea traits. Antagonizing regions were confined to certain parts of the genome and the genes within these regions were mostly involved in preventing metabolic dysregulation, liver reprogramming, metabolism remodeling, and lipid homeostasis. The driving regions were enriched for QTL related to puberty, milk, and health-related traits. Antagonizing regions were mostly related to muscle development, metabolic body weight, and milk traits. In conclusion, we have identified genomic regions of potential importance for dairy cattle breeding. Future studies could investigate the antagonizing regions as potential genomic regions to break the unfavorable correlations and improve milk production as well as fertility and urea traits.

Cell-specific functions of androgen receptor in skeletal muscles

Androgens play a vital role not only in promoting the development of male sexual characteristics but also in exerting diverse physiological effects, including the regulation of skeletal muscle growth and function. Given that the effects of androgens are mediated through androgen receptor (AR) binding, an understanding of AR functionality is crucial for comprehending the mechanisms of androgen action on skeletal muscles. Drawing from insights gained using conditional knockout mouse models facilitated by Cre/loxP technology, we review the cell-specific functions of AR in skeletal muscles. We focus on three specific cell populations expressing AR within skeletal muscles: skeletal muscle cells, responsible for muscle contraction; satellite cells, which are essential stem cells contributing to the growth and regeneration of skeletal muscles; and mesenchymal progenitors, situated in interstitial areas and playing a crucial role in muscle homeostasis. Furthermore, the indirect effects of androgens on skeletal muscle through extra-muscle tissue are essential, especially for the regulation of skeletal muscle mass. The regulation of genes by AR varies across different cell types and contexts, including homeostasis, regeneration and hypertrophy of skeletal muscles. The varied mechanisms orchestrated by AR collectively influence the physiology of skeletal muscles.

Multimodal cell atlas of the ageing human skeletal muscle

Muscle atrophy and functional decline (sarcopenia) are common manifestations of frailty and are critical contributors to morbidity and mortality in older people1. Deciphering the molecular mechanisms underlying sarcopenia has major implications for understanding human ageing2. Yet, progress has been slow, partly due to the difficulties of characterizing skeletal muscle niche heterogeneity (whereby myofibres are the most abundant) and obtaining well-characterized human samples3,4. Here we generate a single-cell/single-nucleus transcriptomic and chromatin accessibility map of human limb skeletal muscles encompassing over 387,000 cells/nuclei from individuals aged 15 to 99 years with distinct fitness and frailty levels. We describe how cell populations change during ageing, including the emergence of new populations in older people, and the cell-specific and multicellular network features (at the transcriptomic and epigenetic levels) associated with these changes. On the basis of cross-comparison with genetic data, we also identify key elements of chromatin architecture that mark susceptibility to sarcopenia. Our study provides a basis for identifying targets in the skeletal muscle that are amenable to medical, pharmacological and lifestyle interventions in late life.

Sex differences on constitutive long non-coding RNA expression: Modulatory effect of estradiol and testosterone in muscle cells

INTRODUCTION

Despite the growing awareness of sexual dimorphism between males and females under pathological and physiological conditions, sex bias in biomedical research in animal models and patients is still present nowadays. The main objective of this work was to investigate sex differences in constitutive long non-coding RNA expression in spinal cord and skeletal muscle from wild-type mice.

MATERIALS AND METHODS

To assess the influence of gender on long non-coding RNAs, we extracted RNA from tissues of male and female mice and analyzed the expression on nine long non-coding RNAs, selected for being among the most commonly studied or exerting an important role in muscle, at 50, 60, and 120 days of age.

RESULTS AND DISCUSSION

We observed age- and tissue-dependent significant sex differences, being more prominent in skeletal muscle. We also studied the effect of sex steroid hormones on long non-coding RNA expression in vitro, noticing a modulation of long non-coding RNA levels upon estradiol and dihydrotestosterone treatment in muscle.

CONCLUSIONS

Taken together, results obtained evidenced sex differences on constitutive long non-coding RNA expression and suggested an influence of steroid hormones complementary to other possible factors. These findings emphasize the importance of including both sexes in experimental design to minimize any potential sex bias.

Development of sexual dimorphism of skeletal muscles through the adrenal cortex, caused by androgen-induced global gene suppression

The zona fasciculata (zF) in the adrenal cortex contributes to multiple physiological actions through glucocorticoid synthesis. The size, proliferation, and glucocorticoid synthesis characteristics are all female biased, and sexual dimorphism is established by androgen. In this study, transcriptomes were obtained to unveil the sex differentiation mechanism. Interestingly, both the amount of mRNA and the expressions of nearly all genes were higher in females. The expression of Nr5a1, which is essential for steroidogenic cell differentiation, was also female biased. Whole-genome studies demonstrated that NR5A1 regulates nearly all gene expression directly or indirectly. This suggests that androgen-induced global gene suppression is potentially mediated by NR5A1. Using Nr5a1 heterozygous mice, whose adrenal cortex is smaller than the wild type, we demonstrated that the size of skeletal muscles is possibly regulated by glucocorticoid synthesized by zF. Taken together, considering the ubiquitous presence of glucocorticoid receptors, our findings provide a pathway for sex differentiation through glucocorticoid synthesis.

Nuclear-localized androgen receptor content following resistance exercise training is associated with hypertrophy in males but not females

Androgen receptor (AR) content has been implicated in the differential response between high and low responders following resistance exercise training (RET). However, the influence of AR expression on acute skeletal muscle damage and whether it may influence the adaptive response to RET in females is poorly understood. Thus, the purpose of this exploratory examination was to 1) investigate changes in AR content during skeletal muscle repair and 2) characterize AR-mediated sex-based differences following RET. A skeletal muscle biopsy from the vastus lateralis was obtained from 26 healthy young men (n = 13) and women (n = 13) at baseline and following 300 eccentric kicks. Subsequently, participants performed 10 weeks of full-body RET and a final muscle biopsy was collected. In the untrained state, AR mRNA expression was associated with paired box protein-7 (PAX7) mRNA in males. For the first time in human skeletal muscle, we quantified AR content in the myofiber and localized to the nucleus where AR has been shown to trigger cellular outcomes related to growth. Upon eccentric damage, nuclear-associated AR (nAR) content increased (p < .05) in males and not females. Males with the greatest increase in cross-sectional area (CSA) post-RET had more (p < .05) nAR content than females with the greatest gain CSA. Collectively, skeletal muscle damage and RET increased AR protein, and both gene and hypertrophy measures revealed sex differences in relation to AR. These findings suggest that AR content but more importantly, nuclear localization, is a factor that differentiates RET-induced hypertrophy between males and females.

Lifespan Effects of Muscle-Specific Androgen Receptor Overexpression on Body Composition of Male and Female Rats

Androgenic actions of gonadal testosterone are thought to be a major mechanism promoting sex differences in body composition across the lifespan. However, this inference is based on studies of androgen receptor (AR) function in late adolescent or emerging adult rodents. Here we assess body composition and AR expression in skeletal muscle of rats at defined ages, comparing wild-type (WT) to transgenic human skeletal actin-driven AR overexpression (HSAAR) rats which overexpress AR in skeletal muscle. Male and female HSAAR and WT Sprague Dawley rats (N = 288) underwent dual-energy x-ray absorptiometry (DXA) scanning and tissue collection at postnatal day (PND) 1, 10, 21, 42, 70, 183, 243, and 365. Expected sex differences in body composition and muscle mass largely onset with puberty (PND-21), with no associated changes to skeletal muscle AR protein. In adulthood, HSAAR increased tibialis anterior (TA) and extensor digitorum longus mass in males, and reduced the expected gain in gonadal fat mass in both sexes. In WT rats, AR protein was reduced in soleus, but not TA, throughout life. Nonetheless, soleus AR protein expression was greater in male rats than female rats at all ages of sexual development, yet only at PND-70 in TA. Overall, despite muscle AR overexpression effects, results are inconsistent with major sex differences in body composition during sexual development being driven by changes in muscle AR, rather suggesting that changes in ligand promote sexual differentiation of body composition during pubertal timing. Nonetheless, increased skeletal muscle AR in adulthood can be sufficient to increase muscle mass in males, and reduce adipose in both sexes.

Interactions among insulin resistance, epigenetics, and donor sex in gene expression regulation of iPSC-derived myoblasts

About 25% of people in the general population are insulin resistant, increasing the risk for type 2 diabetes (T2D) and metabolic disease. Transcriptomic analysis of induced pluripotent stem cells differentiated into myoblasts (iMyos) from insulin-resistant (I-Res) versus insulin-sensitive (I-Sen) nondiabetic individuals revealed that 306 genes increased and 271 genes decreased in expression in iMyos from I-Res donors with differences of 2-fold or more. Over 30 of the genes changed in I-Res iMyos were associated with T2D by SNPs and were functionally linked to insulin action and control of metabolism. Interestingly, we also identified more than 1,500 differences in gene expression that were dependent on the sex of the cell donor, some of which modified the insulin resistance effects. Many of these sex differences were associated with increased DNA methylation in cells from female donors and were reversed by 5-azacytidine. By contrast, the insulin sensitivity differences were not reversed and thus appear to reflect genetic or methylation-independent epigenetic effects.

Chicken muscle antibody array reveals the regulations of LDHA on myoblast differentiation through energy metabolism

Myoblast proliferation and differentiation are highly dynamic and regulated processes in skeletal muscle development. Given that proteins serve as the executors for the majority of biological processes, exploring key regulatory factors and mechanisms at the protein level offers substantial opportunities for understanding the skeletal muscle development. In this study, a total of 607 differentially expressed proteins between proliferation and differentiation in myoblasts were screened out using our chicken muscle antibody array. Biological function analysis revealed the importance of energy production processes and compound metabolic processes in myogenesis. Our antibody array specifically identified an upregulation of LDHA during differentiation, which was associated with the energy metabolism. Subsequent investigation demonstrated that LDHA promoted the glycolysis and TCA cycle, thereby enhancing myoblasts differentiation. Mechanistically, LDHA promotes the glycolysis and TCA cycle but inhibits the ETC oxidative phosphorylation through enhancing the NADH cycle, providing the intermediate metabolites that improve the myoblasts differentiation. Additionally, increased glycolytic ATP by LDHA induces Akt phosphorylation and activate the PI3K-Akt pathway, which might also contribute to the promotion of myoblasts differentiation. Our studies not only present a powerful tool for exploring myogenic regulatory factors in chicken muscle, but also identify a novel role for LDHA in modulating myoblast differentiation through its regulation of cellular NAD+ levels and subsequent downstream effects on mitochondrial function.

SIRT1 induction in the skeletal muscle of male mice partially attenuates changes to whole-body metabolism in response to androgen deprivation

In males, androgens regulate whole body metabolism. The components in androgen target organs contributing to whole-body metabolic function remain ill defined. Sirtuin1 (SIRT1) protein levels are lower in the limb muscle of male mice subjected to androgen deprivation. Because SIRT1 can influence whole-body metabolism, the purpose was to assess whether muscle specific SIRT1 induction attenuated changes to whole-body metabolism in response to androgen deprivation. Physically mature male mice containing an inducible muscle specific SIRT1 transgene (SIRT1) were subjected to a sham or castration surgery and compared to sham and castrated male mice where the SIRT1 transgene was not induced (WT). The respiratory exchange ratio (RER), energy expenditure, and carbohydrate and fat oxidation rates were determined using metabolic cages. Castration lowered RER in WT mice and the lower RER coincided with lower energy expenditure, lower carbohydrate oxidation rates, and higher fat oxidation rates. SIRT1 induction attenuated the castration-induced changes to RER and fat oxidation rates. Changes to energy expenditure and glucose oxidation rates were not affected by SIRT1. Decreases in muscle SIRT1 protein in males may partially contribute to the dysregulation of whole-body metabolism in response to androgen deprivation.

An overview on androgen-mediated actions in skeletal muscle and adipose tissue

Androgens are a class of steroid hormones primarily associated with male sexual development and physiology, but exert pleiotropic effects in either sex. They have a crucial role in various physiological processes, including the regulation of skeletal muscle and adipose tissue homeostasis. The effects of androgens are mainly mediated through the androgen receptor (AR), a ligand-activated nuclear receptor expressed in both tissues. In skeletal muscle, androgens via AR exert a multitude of effects, ranging from increased muscle mass and strength, to the regulation of muscle fiber type composition, contraction and metabolic functions. In adipose tissue, androgens influence several processes including proliferation, fat distribution, and metabolism but they display depot-specific and organism-specific effects which differ in certain context. This review further explores the potential mechanisms underlying androgen-AR signaling in skeletal muscle and adipose tissue. Understanding the roles of androgens and their receptor in skeletal muscle and adipose tissue is essential for elucidating their contributions to physiological processes, disease conditions, and potential therapeutic interventions.

SIRT1 induction in the skeletal muscle of male mice partially preserves limb muscle mass but not contractile force in response to androgen deprivation

In males, the factors that decrease limb muscle mass and strength in response to androgen deprivation are largely unknown. Sirtuin1 (SIRT1) protein levels are lower in the limb muscle of male mice subjected to androgen deprivation. The present study aimed to assess whether SIRT1 induction preserved limb muscle mass and force production in response to androgen deprivation. Physically mature male mice containing an inducible muscle-specific SIRT1 transgene were subjected to a sham or castration surgery and compared to sham and castrated male mice where the SIRT1 transgene was not induced. SIRT1 induction partially preserved whole-body lean mass, tibialis anterior (TA) mass and triceps surae muscle mass in response to castration. Further analysis of the TA muscle showed that muscle-specific SIRT1 induction partially preserved limb muscle soluble protein content and fibre cross-sectional area. Unilateral AAV9-mediated SIRT1 induction in the TA muscle showed that SIRT1 partially preserved mass by acting directly in the muscle. Despite those positive outcomes to limb muscle morphology, muscle-specific SIRT1 induction did not preserve the force generating capacity of the TA or triceps surae muscles. Interestingly, SIRT1 induction in females did not alter limb muscle mass or limb muscle strength even though females have naturally low androgen levels. SIRT1 also did not alter the androgen-mediated increase in limb muscle mass or strength in females. In all, these data suggest that decreases in SIRT1 protein in the limb muscle of males may partially contribute to the loss of limb muscle mass in response to androgen deprivation. KEY POINTS: SIRT1 induction in skeletal muscle of male mice subjected to androgen deprivation partially preserved limb muscle mass and fibre cross-sectional area. SIRT1 induction in skeletal muscle of male mice subjected to androgen deprivation did not prevent preserve limb muscle force generating capacity. SIRT1 induction in skeletal muscle of females did not alter baseline limb muscle mass, nor did it affect the androgen-mediated increase in limb muscle mass.

Cancer Cell-Extrinsic Roles for the Androgen Receptor in Prostate Cancer

Given the central role of the androgen receptor (AR) in prostate cancer cell biology, AR-targeted therapies have been the backbone of prostate cancer treatment for over 50 years. New data indicate that AR is expressed in additional cell types within the tumor microenvironment. Moreover, targeting AR for the treatment of prostate cancer has established side effects such as bone complications and an increased risk of developing cardiometabolic disease, indicating broader roles for AR. With the advent of novel technologies, such as single-cell approaches and advances in preclinical modeling, AR has been identified to have clinically significant functions in other cell types. In this mini-review, we describe new cancer cell-extrinsic roles for AR within the tumor microenvironment as well as systemic effects that collectively impact prostate cancer progression and patient outcomes.

Understanding the Effects of Trenbolone Acetate, Polyamine Precursors, and Polyamines on Proliferation, Protein Synthesis Rates, and the Abundance of Genes Involved in Myoblast Growth, Polyamine Biosynthesis, and Protein Synthesis in Murine Myoblasts

Research suggests that androgens increase skeletal muscle growth by modulating polyamine biosynthesis. As such, the objective of this study was to investigate effects of anabolic hormones, polyamine precursors, and polyamines relative to proliferation, protein synthesis, and the abundance of mRNA involved in polyamine biosynthesis, proliferation, and protein synthesis in C2C12 and Sol8 cells. Cultures were treated with anabolic hormones (trenbolone acetate and/or estradiol), polyamine precursors (methionine or ornithine), or polyamines (putrescine, spermidine, or spermine). Messenger RNA was isolated 0.5 or 1, 12, or 24 h post-treatment. The cell type had no effect (p > 0.10) on proliferation, protein synthesis, or mRNA abundance at any time point. Each treatment increased (p < 0.01) proliferation, and anabolic hormones increased (p = 0.04) protein synthesis. Polyamines increased (p < 0.05) the abundance of mRNA involved in polyamine biosynthesis, proliferation, and protein synthesis. Treatment with polyamine precursors decreased (p < 0.05) the abundance of mRNA involved in proliferation and protein synthesis. Overall, C2C12 and Sol8 myoblasts do not differ (p > 0.10) in proliferation, protein synthesis, or mRNA abundance at the time points assessed. Furthermore, anabolic hormones, polyamines, and polyamine precursors increase proliferation and protein synthesis, and polyamines and their precursors alter the abundance of mRNA involved in growth.

Worsening effect of testosterone deficiency on males with heart failure with preserved ejection fraction

BACKGROUND

Heart failure with preserved ejection fraction (HFpEF)is challenging. Patients usually have normal LV size and ejection fraction. This clinical syndrome develops from a complex interaction of several risk factors that cause organ dysfunction and clinical symptoms. There's evidence that testosterone deficiency is associated with a worse cardiometabolic profile and increased inflammatory markers. We thought that these changes might have an impact on heart failure pathogenesis. We aimed to study the relationship between testosterone level and symptoms in HFpEF.

METHODS

We studied 120 male patients with HFpEF. According to New York Heart Association (NYHA), patients were classified into I, II and III classes; class IV patients were excluded. All patients were subjected to clinical and echocardiographic examinations. In addition, we measured serum testosterone, cardio-metabolic profile, intracellular adhesive molecule-1(ICAM-1), P-selectin and nitric oxide (NO) levels.

RESULTS

Patients with testosterone deficiency had worse NYHA class and higher BNP P = (0.001). Additionally, they had a significantly worse metabolic profile; higher total cholesterol, triglycerides, LDL cholesterol, fasting insulin and HOMA-IR P = (0.005, 0.001, 0.001, 0.001), respectively. Also, they had higher inflammatory markers and worse endothelial functional parameters; (ICAM-1, NO and P- selectin) P = (0.001). Age, BNP and testosterone deficiency can be used as independent predictors of NYHA class III symptoms with a Testosterone cutoff value of 2.7 ng/ml.

CONCLUSION

Testosterone deficiency could be used as an independent predictor of symptom severity in HFpEF, and it aggravates systemic inflammation and endothelial dysfunction in these patients.

Deletion of Tfam in Prx1-Cre expressing limb mesenchyme results in spontaneous bone fractures

INTRODUCTION

Osteoblasts require substantial amounts of energy to synthesize the bone matrix and coordinate skeleton mineralization. This study analyzed the effects of mitochondrial dysfunction on bone formation, nano-organization of collagen and apatite, and the resultant mechanical function in mouse limbs.

MATERIALS AND METHODS

Limb mesenchyme-specific Tfam knockout (Tfam^f/f;Prx1-Cre: Tfam-cKO) mice were analyzed morphologically and histologically, and gene expressions in the limb bones were assessed by in situ hybridization, qPCR, and RNA sequencing (RNA-seq). Moreover, we analyzed the mitochondrial function of osteoblasts in Tfam-cKO mice using mitochondrial membrane potential assay and transmission electron microscopy (TEM). We investigated the pathogenesis of spontaneous bone fractures using immunohistochemical analysis, TEM, birefringence analyzer, microbeam X-ray diffractometer and nanoindentation.

RESULTS

Forelimbs in Tfam-cKO mice were significantly shortened from birth, and spontaneous fractures occurred after birth, resulting in severe limb deformities. Histological and RNA-seq analyses showed that bone hypoplasia with a decrease in matrix mineralization was apparent, and the expression of type I collagen and osteocalcin was decreased in osteoblasts of Tfam-cKO mice, although Runx2 expression was unchanged. Decreased type I collagen deposition and mineralization in the matrix of limb bones in Tfam-cKO mice were associated with marked mitochondrial dysfunction. Tfam-cKO mice bone showed a significantly lower Young's modulus and hardness due to poor apatite orientation which is resulted from decreased osteocalcin expression.

CONCLUSION

Mice with limb mesenchyme-specific Tfam deletions exhibited spontaneous limb bone fractures, resulting in severe limb deformities. Bone fragility was caused by poor apatite orientation owing to impaired osteoblast differentiation and maturation.

Specialized androgen synthesis in skeletal muscles that actuate elaborate social displays

Androgens mediate the expression of many reproductive behaviors, including the elaborate displays used to navigate courtship and territorial interactions. In some vertebrates, males can produce androgen-dependent sexual behavior even when levels of testosterone (T) is low in the bloodstream. One idea is that select tissues make their own androgens from scratch to support behavioral performance. We first study this phenomenon in the skeletal muscles that actuate elaborate sociosexual displays in downy woodpeckers and two songbirds. We show that the woodpecker display muscle maintains elevated T when the testes are regressed in the non-breeding season. Both the display muscles of woodpeckers, as well as the display muscles in the avian vocal organ (syrinx or SYR) of songbirds, express all transporters and enzymes necessary to convert cholesterol into bioactive androgens locally. In a final analysis, we broaden our study by looking for these same transporters and enzymes in mammalian muscles that operate at different speeds. Using RNA-seq data, we find that the capacity for de novo synthesis is only present in "superfast" extraocular muscle. Together, our results suggest that skeletal muscle specialized to generate extraordinary twitch-times and/or extremely rapid contractile speeds may depend on androgenic hormones produced locally within the muscle itself. Our study therefore uncovers an important new dimension of androgenic regulation of behavior.

Analysis of Gene Expression Microarray Data Reveals Androgen-Responsive Genes of Muscles in Polycystic Ovarian Syndrome Patients

Polycystic ovarian syndrome (PCOS) is an endocrine disorder that is characterized by hyperandrogenism. Therefore, information about androgen-induced molecular changes can be obtained using the tissues of patients with PCOS. We analyzed two microarray datasets of normal and PCOS muscle samples (GSE8157 and GSE6798) to identify androgen-responsive genes (ARGs). Differentially expressed genes were determined using the t-test and a meta-analysis of the datasets. The overlap between significant results of the meta-analysis and ARGs predicted from an external database was determined, and differential coexpression analysis was then applied between these genes and the other genes. We found 313 significant genes in the meta-analysis using the Benjamini–Hochberg multiple testing correction. Of these genes, 61 were in the list of predicted ARGs. When the differential coexpression between these 61 genes and 13,545 genes filtered by variance was analyzed, 540 significant gene pairs were obtained using the Benjamini–Hochberg correction. While no significant results were obtained regarding the functional enrichment of the differentially expressed genes, top-level gene ontology terms were significantly enriched in the list of differentially coexpressed genes, which indicates that a broad range of cellular processes is affected by androgen administration. Our findings provide valuable information for the identification of ARGs.

[Involvement of muscle stem cell in skeletal muscle hypertrophy induced by mechanical loading and drugs]

Skeletal muscle is the largest organ in our body, consisting of bundles of multinuclear cells called myofibers. Skeletal muscle is responsible for locomotion, metabolism, and life activities such as swallowing and respiration, and is also attracting attention as an endocrine organ. Skeletal muscle has two abilities, regeneration and adaptation, and the understanding of these mechanisms is expected to contribute to the development of therapies for muscle diseases such as muscular dystrophies and muscle atrophy. Skeletal muscle-specific stem cells, muscle satellite cells (MuSCs), are involved in these abilities. As well as other tissue stem cells, MuSCs are also maintained in a dormant state under steady-state conditions. However, when myofibers are damaged, they start to proliferate and eventually rebuilt new myofibers. While, muscle hypertrophy is one of the "adaptation", and MuSCs contribute to muscle hypertrophy by supplying new nuclei to myofibers. In contrast to studies of MuSCs during regeneration, the dynamics of MuSCs during hypertrophy had not been well studied. One reason is that the specific regulatory mechanisms of MuSC in hypertrophic muscle had not been elucidated. In addition to physical stimuli, drugs such as dopings, hormones, and myostatin inhibition are known to induce muscle hypertrophy. The necessity of MuSCs and new myonuclei in various model of muscle hypertrophy has been highly debated. In this review, we introduce the mechanism of MuSC proliferation specific to hypertrophic muscle, and outline the mechanism of muscle hypertrophy induced by exercise and drugs and the involvement of MuSCs.

Sexual dimorphism through androgen signaling; from external genitalia to muscles

Sexual dimorphisms can be seen in many organisms with some exhibiting subtle differences while some can be very evident. The difference between male and female can be seen on the morphological level such as discrepancies in body mass, presence of body hair in distinct places, or through the presence of specific reproductive structures. It is known that the development of the reproductive structures is governed by hormone signaling, most commonly explained through the actions of androgen signaling. The developmental program of the male and female external genitalia involves a common anlage, the genital tubercle or GT, that later on develop into a penis and clitoris, respectively. Androgen signaling involvement can be seen in the different tissues in the GT that express Androgen receptor and the different genes that are regulated by androgen in the mesenchyme and endoderm component of the GT. Muscles are also known to be responsive to androgen signaling with male and female muscles exhibiting different capabilities. However, the occurrence of sexual dimorphism in muscle development is unclear. In this minireview, a summary on the role of androgen in the sexually dimorphic development of the genital tubercle was provided. This was used as a framework on analyzing the different mechanism employed by androgen signaling to regulate the sexual dimorphism in muscle development.

Sex differences in metabolic pathways are regulated by Pfkfb3 and Pdk4 expression in rodent muscle

Skeletal muscles display sexually dimorphic features. Biochemically, glycolysis and fatty acid β-oxidation occur preferentially in the muscles of males and females, respectively. However, the mechanisms of the selective utilization of these fuels remains elusive. Here, we obtain transcriptomes from quadriceps type IIB fibers of untreated, gonadectomized, and sex steroid-treated mice of both sexes. Analyses of the transcriptomes unveil two genes, Pfkfb3 (phosphofructokinase-2) and Pdk4 (pyruvate dehydrogenase kinase 4), that may function as switches between the two sexually dimorphic metabolic pathways. Interestingly, Pfkfb3 and Pdk4 show male-enriched and estradiol-enhanced expression, respectively. Moreover, the contribution of these genes to sexually dimorphic metabolism is demonstrated by knockdown studies with cultured type IIB muscle fibers. Considering that skeletal muscles as a whole are the largest energy-consuming organs, our results provide insights into energy metabolism in the two sexes, during the estrus cycle in women, and under pathological conditions involving skeletal muscles.

Baba et al. analyzed the transcriptomes from quadriceps type IIB fibers of untreated, gonadectomized, and sex steroid-treated mice of both sexes and identified Pfkfb3 and Pdk4 as differentially regulated genes between males and diestrus females. The authors found that Pfkfb3 and Pdk4 may act as metabolic switches, showed male-enriched and estradiol-enhanced expression, respectively and contributed to sexually dimorphic metabolism.

Systemic delivery of a mitochondria targeted antioxidant partially preserves limb muscle mass and grip strength in response to androgen deprivation

Muscle mass is important for health. Decreased testicular androgen production (hypogonadism) contributes to the loss of muscle mass, with loss of limb muscle being particularly debilitating. Androgen replacement is the only pharmacological treatment, which may not be feasible for everyone. Prior work showed that markers of reactive oxygen species and markers of mitochondrial degradation pathways were higher in the limb muscle following castration. Therefore, we tested whether an antioxidant preserved limb muscle mass in male mice subjected to a castration surgery. Subsets of castrated mice were treated with resveratrol (a general antioxidant) or MitoQ (a mitochondria targeted antioxidant). Relative to the non-castrated control mice, lean mass, limb muscle mass, and grip strength were partially preserved only in castrated mice treated with MitoQ. Independent of treatment, markers of mitochondrial degradation pathways remained elevated in all castrated mice. Therefore, a mitochondrial targeted antioxidant may partially preserve limb muscle mass in response to hypogonadism.