Overexpression of the vitamin D receptor (VDR) induces skeletal muscle hypertrophy

Anti-sarcopenic effects of active vitamin D through modulation of anabolic and catabolic signaling pathways in human skeletal muscle: A randomized controlled trial

BACKGROUND

The muscle-building and strengthening effects of the active form of vitamin D in humans remain unclear.

METHODS

In this ancillary study of the Diabetes Prevention with active Vitamin D trial, we examined clinical and experimental aspects to investigate the effects and mechanisms of eldecalcitol, an active form of vitamin D, in preventing sarcopenia. We examined changes in molecules involved in muscle synthesis and degradation pathways in muscle samples from 32 participants before and after 1 year of eldecalcitol or placebo treatment. The protein levels of molecules involved in muscle synthesis and degradation pathways were examined using western blotting. Additionally, the skeletal muscle and body fat volumes were measured using bioelectrical impedance analysis with a body composition analyzer.

RESULTS

We found that eldecalcitol treatment for 1 year resulted in higher phosphorylation levels of mTOR and FOXO1 signaling pathways, which are associated with increased muscle mass and strength than those with placebo treatment. Body composition measurements at 1 year showed that the eldecalcitol group had significantly higher skeletal muscle mass (1.9 % vs. -3.4 %, p = 3.26E-9) and muscle strength (4.1 % vs. -0.7 %, p = 2.57E-17), and lower fat mass (-3.2 % vs. 1.8 %, p = 1.73E-12) than those in the placebo group.

CONCLUSION

This study suggested that the active form of vitamin D regulates the protein synthesis and degradation pathways in human skeletal muscle and may help prevent sarcopenia. This study was registered at UMIN clinical trials registry, UMIN 000005394.

Sarcopenia Seems to Be Common in Older Patients With Restless Legs Syndrome

BACKGROUND

Restless legs syndrome (RLS) is a disorder characterized by nocturnally exacerbating pain that leads to significant sleep disturbances. The hormonal and metabolic changes caused by sleep disruption may increase the incidence of muscle-related diseases like sarcopenia in older adults, which is defined by a progressive loss of muscle strength and mass. This study aimed to investigate the relationship between RLS and sarcopenia, which may affect each other through common pathophysiological pathways in older adults.

METHODS

This was a cross-sectional study including 109 patients with RLS and 220 without RLS who applied to the geriatric clinic. RLS was assessed using the Turkish version of the International Restless Legs Syndrome Study Group (IRLSSG). Sarcopenia was diagnosed according to the European Working Group on Sarcopenia in Older People-2 criteria. All the demographics, comorbid conditions, medications and findings of comprehensive geriatric assessments were recorded. The association between RLS and sarcopenia was examined by logistic regression.

RESULTS

The mean age was 75 ± 7.4 and 73.8 ± 7 years for the RLS and the control groups, respectively (p > 0.05) and the ratio of females was higher in the RLS group (69.7% vs. 57.9%) (p = 0.035). The frequencies of coronary artery disease (CAD), hypertension (HT) and peripheral artery disease (PAD) were significantly higher in RLS patients (p = 0.020, p = 0.047, p = 0.010, respectively), while the prevalence of anaemia was 41% and 25-OH Vitamin D levels (25[OH]D) were higher than in the control group (p < 0.001). The frequency of probable sarcopenia and sarcopenia was higher in patients with RLS than in controls (20% vs. 11%, p = 0.037 and 8% vs. 2.3%, p = 0.047, respectively). A significant association between RLS and an increased likelihood of probable sarcopenia, sarcopenia and slow gait speed (odds ratio [OR]: 2.621, 95% confidence interval [CI] [1.265, 5.431]; OR: 4.542, 95% CI [1.284, 16.071]; OR: 2.663, 95% CI [1.432, 4.951], respectively) was found after adjusting for factors such as gender, HT, CAD, PAD, serum 25(OH)D levels, anaemia, chronic kidney disease (CKD) and nutritional status. However, the significance of low muscle mass disappeared (p > 0.05).

CONCLUSION

This study demonstrated that sarcopenia is prevalent among older patients with RLS, which seems to be associated with low muscle strength and slow gait speed. Given the negative health outcomes related to sarcopenia, interventions aimed at preventing its development could be significantly beneficial for patients with RLS in older adults as well.

The Effects of Vitamin D on Muscle Strength Are Influenced by Testosterone Levels

BACKGROUND

Although the role of vitamin D receptor (VDR) in muscle mass and strength is well established, the effects of vitamin D (VD) on muscle remain controversial due to various factors. Herein, the influence of sex on the effects of VD on muscle function and the underlying reasons was explored.

METHODS

Male and female Sod1 gene knockout (SKO) mice, serving as a model for skeletal muscle atrophy, were treated with the VD active analogue calcipotriol, and RNA sequencing was employed to investigate this potential signalling pathway. The National Health and Nutrition Examination Survey (NHANES) database was utilized to explore whether testosterone affects the correlation between VD and grip strength in human participants. Experiments involving C2C12 cells and castrated male mice subjected to immobilization were conducted to demonstrate the enhancing effects of testosterone on VD function.

RESULTS

In male SKO mice, Vdr expression in the gastrocnemius muscle was positively correlated with grip strength (R2 = 0.4689, p < 0.001), whereas no such correlation was identified in female mice. At 28 weeks of age, both male and female SKO mice exhibited significantly reduced grip strength compared to Sod1 wild-type (SWT) mice, and calcipotriol restored grip strength in male SKO mice (SWT-veh: 0.0716 ± 0.0006, SWT-cal: 0.0686 ± 0.0010, SKO-veh: 0.0601 ± 0.0010, SKO-cal: 0.0703 ± 0.0007; p < 0.05). Calcipotriol increased muscle protein synthesis and mitochondrial biogenesis while decreasing inflammation and atrogenes in gastrocnemius muscle of male SKO mice. However, the effect of calcipotriol on muscle was not significant in female SKO mice. Compared to wild-type mice, both male and female SKO mice exhibited reduced levels of 1,25(OH)2D3 due to ROS-induced hepatic CYP3A4 overexpression, thereby excluding the influence of baseline VD levels. The serum 25(OH)D3 and testosterone interactively affect grip strength in adults (p < 0.05). Using C2C12 cells differentiated into myotubes, testosterone significantly enhanced the inducing effects of VD on VDR, androgen receptor (AR), P-AKT, PGC1α, Beclin1 and LC3B. Calcipotriol improved grip strength in sham-operated mice but had a negligible effect on grip strength in castrated mice. However, a significant improvement in grip strength was observed in castrated mice following testosterone restoration (p < 0.05).

CONCLUSIONS

This study demonstrates the existence of sex heterogeneity in the effects of VD on muscle and that testosterone enhances the strength and molecular responses to VD. These findings underscore the importance of considering testosterone levels when utilizing VD to enhance muscle strength.

Age-dependent effect of vitamin D supplementation on musculoskeletal health in chronic spinal cord injury patients: A pilot study

OBJECTIVE

To determine the effect of vitamin D supplementation on changes in body composition associated with musculoskeletal health status in patients with chronic SCI and vitamin D deficiency as a response to age.

DESIGN

Prospective drug-intervention study.

SETTING

Department of rehabilitation medicine, Veterans Health Service Medical Center.

PARTICIPANTS

Seventeen patients with vitamin D insufficiency/deficiency (<30 ng/mL) and chronic SCI were divided into two groups: groups A <65 years (n = 8) and B ≥65 years of age (n = 9).

INTERVENTIONS

Both groups received 800 IU/day cholecalciferol for 12 weeks.

OUTCOME MEASURES

We used blood samples to evaluate metabolites related to vitamin D, testosterone (T), lipid profiles, and sex hormone-binding globulin (SHBG). Bioelectrical impedance analysis (BIA) was used to evaluate body composition.

RESULTS

Group A had significantly better baseline clinical characteristics for all BIA measurements. SHGB was significantly higher in Group B (P = 0.003) and albumin was significantly higher in Group A (P = 0.000). When comparing pre- to post-treatment, Group A showed a significant improvement in T (P = 0.042), total cholesterol (P = 0.035), and triglyceride (P = 0.025) levels, whereas Group B significantly increased vitamin D (P = 0.038) and protein mass (PM) (P = 0.034) levels.

CONCLUSION

This study suggested that addressing vitamin D deficiency in patients with SCI had different effects in young and older adults, with both groups showing positive changes in body composition. Particularly, the increase in PM on BIA measurements in elderly patients at high risk of sarcopenia was encouraging.

Lower risk of the deterioration of muscle mass and function in oral active vitamin D users among Incident peritoneal dialysis patients: a 12-month follow-up cohort study

Data in terms of how active vitamin D supplementation affects muscle mass and function in end-stage renal disease (ESRD) patients has led to inconclusive results. The main goal of this research was to examine the association of active vitamin D supplementation and risk of the deterioration of muscle mass and function among ESRD patients on peritoneal dialysis (PD). Eligible ESRD patients on PD were prospectively included, and followed up at 3-month intervals in the tertiary care center. Based on the medications during the 12-month follow-up period, the patients were divided into two groups (vitamin D users and non-users). The deterioration of muscle mass and function was identified utilizing the criteria set by the Asian Working Group on Sarcopenia in 2019 (AWGS 2019). Primary outcome was defined as the deterioration of muscle mass and function at the end of the 12-month follow-up. The absolute diffecence and 95% confidence interval (CI) of the incidence of deterioration between vitamin D users and non-users was estimated. The association of vitamin D supplementation with risk of the deterioration of muscle mass and function during the 12-month follow-up period, was examined by employing multivariate logistic regression models. A total of 229 incident PD patients (6 of whom were lost in follow-up) were included. During the entire study period, 54.7% (122/223) of the remaining patients were considered users of oral active vitamin D. The incidence of deterioration in muscle mass and function was 30.5% (68/223) throughout the entire follow-up. In this regard, the rate was 23.0% (28/122) that received oral active vitamin D, while it was 39.6% (40/101) in the group that did not receive it, with an absolute diffecence of -16.6% (95% CI - 4.5, - 28.7) and an estimated relative risk (RR) of 0.784 (95% CI 0.651-0.943). After adjustment for potential confounding factors in logistic regression model, vitamin D users group was still associated with decreased risk of the deterioration of muscle mass and function (OR 0.330, 95% CI 0.159-0.683, P = 0.003). In secondary analysis, the relationship between oral active vitamin D and the deterioration of muscle mass and function remained consistent (≤ 0.25 µg per day vs. non-users; OR 0.300, 95% CI 0.131-0.688, P = 0.004); however, no significant relationship was identified in patients receiving a mean daily dose of > 0.25 µg compared with non-users (OR 0.389, 95% CI 0.146-1.034, P = 0.058). These results indicate that active vitamin D supplementation was significantly associated with a decreased risk of the deterioration of muscle mass and function in incident PD patients with ESRD. However, the amount and type of vitamin D used and the duration of the intervention warrant further randomized controlled trials to confirm the possibility that such medication improves sarcopenia in ESRD patients.

Association of VDR Polymorphisms with Muscle Mass Development in Elite Young Soccer Players: A Pilot Study

The vitamin D receptor (VDR) is an important candidate gene in musculoskeletal phenotypes. Polymorphisms in the VDR have been previously associated with several pathologies and muscular strength in athletes and elderly people; however, the literature reported contradictory results. The object of this research was to verify the association between the most studied VDR variants (rs2228570, rs7975232, and rs1544410) and the increase in muscle mass in elite young soccer players. A sample of 55 soccer players (15-18 years old) from a professional team were selected for this study. DNA was extracted by the salting-out method, and polymorphisms were genotyped by PCR-RFLP, followed by 2% agarose gel electrophoresis. To test the effect of the three SNPs (single nucleotide polymorphisms), a logistic regression analysis was applied. The body composition determination was carried out through the skinfold thickness method, and the muscular area of the arm and lower limb were calculated using the Frisancho formula. All three polymorphisms met the Hardy-Weinberg equilibrium (p > 0.05) and their frequencies fell within the worldwide variability. A significant correlation between rs1544410 and the increase in calf muscle mass was observed. Individuals carrying the A allele showed higher calf muscular mass than those carrying the G allele (p = 0.034). Moreover, a haplotype analysis applied to the two SNPs in linkage disequilibrium (rs7975232 and rs1544410) showed that the AG haplotype appeared negatively correlated to the calf muscle area. In conclusion, we confirm an association between VDR polymorphisms and muscular mass that could encourage the genetic screening of the VDR gene to identify a potential risk of injury and for individual nutritional interventions.

Vitamin D and Sarcopenia in the Senior People: A Review of Mechanisms and Comprehensive Prevention and Treatment Strategies

This article reviews the mechanisms and prevention strategies associated with vitamin D and sarcopenia in older adults. As a geriatric syndrome, sarcopenia is defined by a notable decline in skeletal muscle mass and strength, which increases the risk of adverse health outcomes such as falls and fractures. Vitamin D, an essential fat-soluble vitamin, is pivotal in skeletal muscle health. It affects muscle function through various mechanisms, including regulating calcium and phosphorus metabolism, promoting muscle protein synthesis, and modulation of muscle cell proliferation and differentiation. A deficiency in vitamin D has been identified as a significant risk factor for the development of sarcopenia in older adults. Many studies have demonstrated that low serum vitamin D levels are significantly associated with an increased risk of sarcopenia. While there is inconsistency in the findings, most studies support the importance of vitamin D in maintaining skeletal muscle health. Vitamin D influences the onset and progression of sarcopenia through various pathways, including the promotion of muscle protein synthesis, the regulation of mitochondrial function, and the modulation of immune and inflammatory responses. Regarding the prevention and treatment of sarcopenia, a combination of nutritional, exercise, and pharmacological interventions is recommended. Further research should be conducted to elucidate the molecular mechanism of vitamin D in sarcopenia, to study genes related to sarcopenia, to perform large-scale clinical trials, to investigate special populations, and to examine the combined application of vitamin D with other nutrients or drugs. A comprehensive investigation of the interconnection between vitamin D and sarcopenia will furnish a novel scientific foundation and productive strategies for preventing and treating sarcopenia. This, in turn, will enhance the senior people's quality of life and health.

Antidepressant-like effects of tomatidine and tomatine, steroidal alkaloids from unripe tomatoes, via activation of mTORC1 in the medial prefrontal cortex in lipopolysaccharide-induced depression model mice

ABSTRACTKetamine, an N-methyl-D-aspartate receptor antagonist, produces rapid antidepressant effects in patients with treatment-resistant depression. However, owing to the undesirable adverse effects of ketamine, there is an urgent need for developing safer and more effective prophylactic and therapeutic interventions for depression. Preclinical studies have demonstrated that activation of the mechanistic target of rapamycin complex 1 (mTORC1) in the medial prefrontal cortex (mPFC) mediates the rapid antidepressant effects of ketamine. The steroidal alkaloid tomatidine and its glycoside α-tomatine (tomatine) can activate mTORC1 signaling in peripheral tissues/cells. We examined whether tomatidine and tomatine exerted prophylactic and therapeutic antidepressant-like actions via mPFC mTORC1 activation using a mouse model of lipopolysaccharide (LPS)-induced depression. Male mice were intraperitoneally (i.p.) administered tomatidine/tomatine before and after the LPS challenge to test their prophylactic and therapeutic effects, respectively. LPS-induced depression-like behaviors in the tail suspension test (TST) and forced swim test (FST) were significantly reversed by prophylactic and therapeutic tomatidine/tomatine administration. LPS-induced anhedonia in the female urine sniffing test was reversed by prophylactic, but not therapeutic, injection of tomatidine, and by prophylactic and therapeutic administration of tomatine. Intra-mPFC infusion of rapamycin, an mTORC1 inhibitor, blocked the prophylactic and therapeutic antidepressant-like effects of tomatidine/tomatine in TST and FST. Moreover, both tomatidine and tomatine produced antidepressant-like effects in ovariectomized female mice, a model of menopause-associated depression. These results indicate that tomatidine and tomatine exert prophylactic and therapeutic antidepressant-like effects via mTORC1 activation in the mPFC and suggest these compounds as promising candidates for novel prophylactic and therapeutic agents for depression.

Skeletal Muscle Injury in Chronic Kidney Disease-From Histologic Changes to Molecular Mechanisms and to Novel Therapies

Chronic kidney disease (CKD) is associated with significant reductions in lean body mass and in the mass of various tissues, including skeletal muscle, which causes fatigue and contributes to high mortality rates. In CKD, the cellular protein turnover is imbalanced, with protein degradation outweighing protein synthesis, leading to a loss of protein and cell mass, which impairs tissue function. As CKD itself, skeletal muscle wasting, or sarcopenia, can have various origins and causes, and both CKD and sarcopenia share common risk factors, such as diabetes, obesity, and age. While these pathologies together with reduced physical performance and malnutrition contribute to muscle loss, they cannot explain all features of CKD-associated sarcopenia. Metabolic acidosis, systemic inflammation, insulin resistance and the accumulation of uremic toxins have been identified as additional factors that occur in CKD and that can contribute to sarcopenia. Here, we discuss the elevation of systemic phosphate levels, also called hyperphosphatemia, and the imbalance in the endocrine regulators of phosphate metabolism as another CKD-associated pathology that can directly and indirectly harm skeletal muscle tissue. To identify causes, affected cell types, and the mechanisms of sarcopenia and thereby novel targets for therapeutic interventions, it is important to first characterize the precise pathologic changes on molecular, cellular, and histologic levels, and to do so in CKD patients as well as in animal models of CKD, which we describe here in detail. We also discuss the currently known pathomechanisms and therapeutic approaches of CKD-associated sarcopenia, as well as the effects of hyperphosphatemia and the novel drug targets it could provide to protect skeletal muscle in CKD.

Novel dietary strategies to manage sarcopenia

PURPOSE OF REVIEW

Sarcopenia is a wasting disease, mostly age-related in which muscle strength and mass decline, such as physical performance. With aging, both lower dietary protein intake and anabolic resistance lead to sarcopenia. Moreover, aging and sarcopenia display low-grade inflammation, which also worsen muscle condition. In this review, we focused on these two main targets to study dietary strategies.

RECENT FINDINGS

The better understanding in mechanisms involved in sarcopenia helps building combined dietary approaches including physical activity that would slow the disease progression. New approaches include better understanding in the choice of quality proteins, their amount and schedule and the association with antioxidative nutrients.

SUMMARY

First, anabolic resistance can be countered by increasing significantly protein intake. If increasing amount remains insufficient, the evenly delivery protein schedule provides interesting results on muscle strength. Quality of protein is also to consider for decreasing risk for sarcopenia, because varying sources of proteins appears relevant with increasing plant-based proteins ratio. Although new techniques have been developed, as plant-based proteins display a lower availability, we need to ensure an adapted overall amount of proteins. Finally, specific enrichment with leucine from whey protein remains the dietary combined approach most studied and studies on citrulline provide interesting results. As cofactor at the edge between anabolic and antioxidative properties, vitamin D supplementation is to recommend. Antioxidative dietary strategies include both fibers, vitamins, micronutrients and polyphenols from various sources for positive effects on physical performance. The ω 3 -polyunsaturated fatty acids also display positive modifications on body composition. Gut microbiota modifiers, such as prebiotics, are promising pathways to improve muscle mass and function and body composition in sarcopenic patients. Nutritional interventions could be enhanced by combination with physical activity on sarcopenia. In healthy older adults, promoting change in lifestyle to get near a Mediterranean diet could be one of the best options. In sarcopenia adults in which lifestyle changes appears unprobable, specific enrichement potentialized with physical activity will help in the struggle against sarcopenia. Longitudinal data are lacking, which makes it hard to draw strong conclusions. However, the effects of a physical activity combined with a set of nutrition interventions on sarcopenia seems promising.

Nutritional Strategies for Muscle Atrophy: Current Evidence and Underlying Mechanisms

Skeletal muscle can undergo detrimental changes in various diseases, leading to muscle dysfunction and atrophy, thus severely affecting people's lives. Along with exercise, there is a growing interest in the potential of nutritional support against muscle atrophy. This review provides a brief overview of the molecular mechanisms driving skeletal muscle atrophy and summarizes recent advances in nutritional interventions for preventing and treating muscle atrophy. The nutritional supplements include amino acids and their derivatives (such as leucine, β-hydroxy, β-methylbutyrate, and creatine), various antioxidant supplements (like Coenzyme Q10 and mitoquinone, resveratrol, curcumin, quercetin, Omega 3 fatty acids), minerals (such as magnesium and selenium), and vitamins (such as vitamin B, vitamin C, vitamin D, and vitamin E), as well as probiotics and prebiotics (like Lactobacillus, Bifidobacterium, and 1-kestose). Furthermore, the study discusses the impact of a combined approach involving nutritional support and physical therapy to prevent muscle atrophy, suggests appropriate multi-nutritional and multi-modal interventions based on individual conditions to optimize treatment outcomes, and enhances the recovery of muscle function for patients. By understanding the molecular mechanisms behind skeletal muscle atrophy and implementing appropriate interventions, it is possible to enhance the recovery of muscle function and improve patients' quality of life.

Molecular effects of Vitamin-D and PUFAs metabolism in skeletal muscle combating Type-II diabetes mellitus

Multiple post-receptor intracellular alterations such as impaired glucose transfer, glucose phosphorylation, decreased glucose oxidation, and glycogen production contribute to insulin resistance (IR) in skeletal muscle, manifested by diminished insulin-stimulated glucose uptake. Type-2 diabetes mellites (T2DM) has caused by IR, which is also seen in obese patients and those with metabolic syndrome. The Vitamin-D receptor (VDR) and poly unsaturated fatty acids (PUFAs) roles in skeletal muscle growth, shapes, and function for combating type-2 diabetes have been clarified throughout this research. VDR and PUFAs appears to show a variety of effects on skeletal muscle, in addition it shows a promising role on bone and mineral homeostasis. Individuals having T2DM are reported to suffer from severe muscular weakness and alterations in shape of the muscle. Several studies have investigated the effect on VDR on muscular strength and mass, which leads to Vitamin-D deficiency (VDD) in individuals, in which most commonly seen in elderly. VDR has been shown to affect skeletal cellular proliferation, intracellular calcium handling, as well as genomic activity in a variety of different ways such as muscle metabolism, insulin sensitivity, which is the major characteristic pathogenesis for IR in combating T2DM. The identified VDR gene polymorphisms are ApaI, TaqI, FokI, and BsmI that are associated with T2DM. This review collates informations on the mechanisms by which VDR activation takes place in skeletal muscles. Despite the significant breakthroughs made in recent decades, various studies show that IR affects VDR and PUFAs metabolism in skeletal muscle. Therefore, this review collates the data to show the role of VDR and PUFAs in the skeletal muscles to combat T2DM.

Effect of resistance training plus enriched probiotic supplement on sestrin2, oxidative stress, and mitophagy markers in elderly male Wistar rats

This study aimed to determine the effects of resistance training combined with a probiotic supplement enriched with vitamin D and leucine on sestrin2, oxidative stress, antioxidant defense, and mitophagy markers in aged Wistar rats. Thirty-five male rats were randomly assigned to two age groups (old with 18-24 months of age and young with 8-12 weeks of age) and then divided into five groups, including (1) old control (OC: n = 5 + 2 for reserve in all groups), (2) young control (YC: n = 5), (3) old resistance training (OR: n = 5), (4) old resistance training plus supplement (ORS: n = 5), and old supplement group (OS: n = 5). Training groups performed ladder climbing resistance training 3 times per week for 8 weeks. Training intensity was inserted progressively, with values equal to 65, 75, and 85, determining rats' maximal carrying load capacity. Each animal made 5 to 8 climbs in each training session, and the time of each climb was between 12 and 15 s, although the time was not the subject of the evaluation, and the climbing pattern was different in the animals. Old resistance plus supplement and old supplement groups received 1 ml of supplement 5 times per week by oral gavage in addition to standard feeding, 1 to 2 h post training sessions. Forty-eight hours after the end of the training program, 3 ml of blood samples were taken, and all rats were then sacrificed to achieve muscle samples. After 8 weeks of training, total antioxidant capacity and superoxide dismutase activity levels increased in both interventions. A synergistic effect of supplement with resistance training was observed for total antioxidant capacity, superoxide dismutase, and PTEN-induced kinase 1. Sestrin 2 decreased in intervention groups. These results suggest that resistance training plus supplement can boost antioxidant defense and mitophagy while potentially decreasing muscle strength loss.

Evolution of Vitamin D Status and Vitamin D Receptor Gene Expression Among Professional Handball Athletes During a Competitive Period. Relationship with Body Composition, Calcium, Magnesium and Phosphorous

INTRODUCTION

A generalized risk of vitamin D deficiency exists worldwide affecting also professional and elite athletes. This study assesses the evolution of vitamin D status and vitamin D receptor (VDR) gene expression and their relationship with body composition, calcium (Ca), magnesium (Mg) and phosphorous (P) among professional handball athletes during a competitive period.

METHODS

A total of 26 male subjects were recruited: 13 professional handball athletes and 13 non-athlete controls. An observational follow-up study was conducted in 2 time points over a 16-week period. Nutritional intake, body composition, and routinary biochemical parameters were measured via 24-hours recall, bioimpedance and enzyme immunoassay, respectively. Ca and Mg were measured by flame atomic absorption spectrophotometry and P was determined with the colorimetric method of Fiske-Subbarow. 25-hydroxyvitamin-D (25(OH)D) levels and its forms (i.e., 25(OH)D3 and 25(OH)D2) were measured by liquid chromatography-tandem mass spectrometry (LC-MS/MS), whereas VDR gene expression was measured by quantitative real time-polymerase chain reaction (qRT-PCR).

RESULTS

A total of 54% of the athletes showed deficient vitamin D status. Moreover, a prevalence of insufficient vitamin D status in handball players affected 46% at baseline, reaching 61% after 16 weeks. Vitamin D showed no evolution during the competitive period and no differences between groups were observed (all p ≥ 0.05). Handball players increased the VDR expression, enhanced body composition, Ca and Mg levels at 16-weeks follow-up (all p < 0.05). VDR gene expression was positively related with body mass and body mass index at follow-up in athletes (all p ≤ 0.038; r ≥ 0.579) and with Ca at baseline in controls (p = 0.026; r = 0.648). Finally, 25(OH)D2 form was directly associated with P in athletes at 16 weeks of study (p = 0.034; r = 0.588).

CONCLUSION

Players of indoor team sports such as handball would be a population at risk of vitamin D deficiency. The 16-weeks competition improved VDR gene expression, body composition, Ca and Mg levels. The associations observed between VDR gene expression and the variables of the study evidenced the importance of this receptor as a marker involved in health status in handball athletes despite vitamin D - although in a deficient status -, Ca, Mg and P showed no remarkable changes during the competition period.

Vitamin D status associates with skeletal muscle loss after anterior cruciate ligament reconstruction

BACKGROUNDAlthough 25-hydroxyvitamin D [25(OH)D] concentrations of 30 ng/mL or higher are known to reduce injury risk and boost strength, the influence on anterior cruciate ligament reconstruction (ACLR) outcomes remains unexamined. This study aimed to define the vitamin D signaling response to ACLR, assess the relationship between vitamin D status and muscle fiber cross-sectional area (CSA) and bone density outcomes, and discover vitamin D receptor (VDR) targets after ACLR.METHODSTwenty-one young, healthy, physically active participants with recent ACL tears were enrolled (17.8 ± 3.2 years, BMI 26.0 ± 3.5 kg/m2). Data were collected through blood samples, vastus lateralis biopsies, dual energy x-ray bone density measurements, and isokinetic dynamometer measures at baseline, 1 week, 4 months, and 6 months after ACLR. The biopsies facilitated CSA, Western blotting, RNA-seq, and VDR ChIP-seq analyses.RESULTSACLR surgery led to decreased circulating bioactive vitamin D and increased VDR and activating enzyme expression in skeletal muscle 1 week after ACLR. Participants with less than 30 ng/mL 25(OH)D levels (n = 13) displayed more significant quadriceps fiber CSA loss 1 week and 4 months after ACLR than those with 30 ng/mL or higher (n = 8; P < 0.01 for post hoc comparisons; P = 0.041 for time × vitamin D status interaction). RNA-seq and ChIP-seq data integration revealed genes associated with energy metabolism and skeletal muscle recovery, potentially mediating the impact of vitamin D status on ACLR recovery. No difference in bone mineral density losses between groups was observed.CONCLUSIONCorrecting vitamin D status prior to ACLR may aid in preserving skeletal muscle during recovery.FUNDINGNIH grants R01AR072061, R01AR071398-04S1, and K99AR081367.

Vitamin D3 Exerts Beneficial Effects on C2C12 Myotubes through Activation of the Vitamin D Receptor (VDR)/Sirtuins (SIRT)1/3 Axis

The onset of sarcopenia is associated with a decline in vitamin D receptor (VDR) expression, wherein reduced VDR levels contribute to muscle atrophy, while heightened expression promotes muscle hypertrophy. Like VDR, the age-related decline in protein deacetylase sirtuin (SIRT) expression is linked to the development of sarcopenia and age-related muscle dysfunction. This study aimed to investigate whether the VDR agonist 1,25-dihydroxyvitamin D3 (1,25VD3) exerts beneficial effects on muscles through interactions with sirtuins and, if so, the underlying molecular mechanisms. Treatment of 1,25VD3 in differentiating C2C12 myotubes substantially elevated VDR, SIRT1, and SIRT3 expression, enhancing their differentiation. Furthermore, 1,25VD3 significantly enhanced the expression of key myogenic markers, including myosin heavy chain (MyHC) proteins, MyoD, and MyoG, and increased the phosphorylation of AMPK and AKT. Conversely, VDR knockdown resulted in myotube atrophy and reduced SIRT1 and SIRT3 levels. In a muscle-wasting model triggered by IFN-γ/TNF-α in C2C12 myotubes, diminished VDR, SIRT1, and SIRT3 levels led to skeletal muscle atrophy and apoptosis. 1,25VD3 downregulated the increased expression of muscle atrophy-associated proteins, including FoxO3a, MAFbx, and MuRF1 in an IFN-γ/TNF-α induced atrophy model. Importantly, IFN-γ/TNF-α significantly reduced the mtDNA copy number in the C2C12 myotube, whereas the presence of 1,25VD3 effectively prevented this decrease. These results support that 1,25VD3 could serve as a potential preventive or therapeutic agent against age-related muscle atrophy by enhancing the VDR/SIRT1/SIRT3 axis.

Seasonal changes of vitamin D3 and ovarian steroidogenesis in the wild ground squirrels (Citellus dauricus Brandt)

There is mounting evidence that vitamin D3 regulates female reproductive function critically, while little is known about the function of seasonally variable vitamin D3 in regulating ovarian steroidogenesis. This study examined the seasonal expressions of vitamin D receptor (VDR), vitamin D metabolic molecules (CYP2R1, CYP27B1, and CYP24A1), and steroidogenic enzymes (P450scc, 3β-HSD, P450c17, and P450arom) in the ovaries of the wild ground squirrels (Citellus dauricus Brandt) during the different breeding seasons. VDR, CYP2R1, CYP27B1, and CYP24A1 were shown to be localized in different types of ovarian cells in the wild ground squirrels during the breeding and non-breeding seasons. Meanwhile, the mRNA levels of VDR, CYP2R1, CYP27B1, CYP11A1, HSD3B1, CYP17A1, and CYP19A1 in the ovaries were remarkably higher in the breeding season. Furthermore, RNA-seq data of ovaries revealed that 6036 genes were differentially expressed genes (DEGs); further analysis revealed that several DEGs known to be involved in ovarian steroidogenesis pathway and cellular response to vitamin D pathway were identified. In addition, during the breeding season, the concentrations of luteinizing hormone (LH), follicle-stimulating hormone (FSH), progesterone, and 17β-estradiol were greater in the serum of the wild female ground squirrels. This observation was positively correlated with seasonal changes in the concentration of 25(OH)D3, supporting the fact that the 25(OH)D3 content in the ovaries was significantly higher in the breeding season. These findings suggested that seasonal changes in vitamin D3 might regulate the ovarian steroidogenesis of the wild female ground squirrels.

Genome-wide epigenetic dynamics during postnatal skeletal muscle growth in Hu sheep

Hypertrophy and fiber transformation are two prominent features of postnatal skeletal muscle development. However, the role of epigenetic modifications is less understood. ATAC-seq, whole genome bisulfite sequencing, and RNA-seq were applied to investigate the epigenetic dynamics of muscle in Hu sheep at 3 days, 3 months, 6 months, and 12 months after birth. All 6865 differentially expressed genes were assigned into three distinct tendencies, highlighting the balanced protein synthesis, accumulated immune activities, and restrained cell division in postnatal development. We identified 3742 differentially accessible regions and 11799 differentially methylated regions that were associated with muscle-development-related pathways in certain stages, like D3-M6. Transcription factor network analysis, based on genomic loci with high chromatin accessibility and low methylation, showed that ARID5B, MYOG, and ENO1 were associated with muscle hypertrophy, while NR1D1, FADS1, ZFP36L2, and SLC25A1 were associated with muscle fiber transformation. Taken together, these results suggest that DNA methylation and chromatin accessibility contributed toward regulating the growth and fiber transformation of postnatal skeletal muscle in Hu sheep.

The Role of Vitamin D in Skeletal Muscle Repair and Regeneration in Animal Models and Humans: A Systematic Review

Vitamin D deficiency, prevalent worldwide, is linked to muscle weakness, sarcopenia, and falls. Muscle regeneration is a vital process that allows for skeletal muscle tissue maintenance and repair after injury. PubMed and Web of Science were used to search for studies published prior to May 2023. We assessed eligible studies that discussed the relationship between vitamin D, muscle regeneration in this review. Overall, the literature reports strong associations between vitamin D and skeletal myocyte size, and muscle regeneration. In vitro studies in skeletal muscle cells derived from mice and humans showed vitamin D played a role in regulating myoblast growth, size, and gene expression. Animal studies, primarily in mice, demonstrate vitamin D's positive effects on skeletal muscle function, such as improved grip strength and endurance. These studies encompass vitamin D diet research, genetically modified models, and disease-related mouse models. Relatively few studies looked at muscle function after injury, but these also support a role for vitamin D in muscle recovery. The human studies have also reported that vitamin D deficiency decreases muscle grip strength and gait speed, especially in the elderly population. Finally, human studies reported the benefits of vitamin D supplementation and achieving optimal serum vitamin D levels in muscle recovery after eccentric exercise and surgery. However, there were no benefits in rotator cuff injury studies, suggesting that repair mechanisms for muscle/ligament tears may be less reliant on vitamin D. In summary, vitamin D plays a crucial role in skeletal muscle function, structural integrity, and regeneration, potentially offering therapeutic benefits to patients with musculoskeletal diseases and in post-operative recovery.

Sarcopenia in liver cirrhosis: perspectives from epigenetics and microbiota

Sarcopenia is characterized by the loss of muscle mass and function. It is well known that sarcopenia is often associated with aging, while in recent years, sarcopenia comorbid with chronic diseases such as cirrhosis has attracted widespread attention, whose underlying molecular mechanisms remain unclear. Since cirrhosis and sarcopenia are assumed to be closely interrelated in terms of pathogenesis, this review innovatively discussed the role of epigenetic modifications and microecological dysregulation in sarcopenia in the context of liver cirrhosis. Here we illustrated the relationship between sarcopenia and cirrhosis in the aspect of epigenetics, dysbiosis, and the crosstalk between gene modifications and intestinal microecology. Furthermore, the alterations in cirrhosis patients with sarcopenia, such as inflammatory response and oxidative stress, are found to present synergistic effects in the pathways of epigenetics and dysbiosis leading to sarcopenia. This review proposes that microbiome-based therapies are promising to break the vicious cycle between epigenetic modification and dysbiosis, providing strong support for the use of intestinal microecological interventions to prevent sarcopenia in cirrhotic patients.

Evaluation and management of body composition changes in cancer patients

Wasting in cancer patients has long been recognized as a condition that adversely affects cancer patients' quality of life, treatment tolerance, and oncological outcomes. Historically, this condition was mainly evaluated by changes in body weight. However, this approach is not quite accurate because body weight is the overall change of all body compartments. Conditions such as edema and ascites can mask the severity of muscle and adipose tissue depletion. Changes in body composition assessment in cancer patients have historically been underappreciated because of the limited availability of measurement tools. As more evidence highlighting the importance of body composition has emerged, it is imperative to apply a more precise evaluation of nutritional status and a more targeted approach to provide nutritional support for cancer patients. In this review, we will discuss the modalities for evaluating body composition and how to manage body composition changes in cancer patients.

Implementation and Core Components of a Multimodal Program including Exercise and Nutrition in Prevention and Treatment of Frailty in Community-Dwelling Older Adults: A Narrative Review

Increasing disability-free life expectancy is a crucial issue to optimize active ageing and to reduce the burden of evitable medical costs. One of the main challenges is to develop pragmatic and personalized prevention strategies in order to prevent frailty, counteract adverse outcomes such as falls and mobility disability, and to improve quality of life. Strong evidence reports the effectiveness of exercise interventions to improve various physical parameters and muscle function that are cornerstones of frailty. Other findings also suggest that the interactions between nutrition and physical exercise with or without health behavior promotion prevent the development of frailty. Multimodal programs, including structured exercise, adequate dietary intervention and health behavior promotion, appear increasingly consensual. However, in order for implementation in real-life settings, some pitfalls need to be addressed. In this perspective, structuring and tailoring feasible, acceptable and sustainable interventions to optimize exercise training responses are essential conditions to warrant short, medium and long-term individual benefits. The different components of exercise programs appear to be fairly consensual and effective. However, specific composition of the programs proposed (frequency, intensity, type, time, volume and progressiveness) have to be tailored to individual characteristics and objectives in order to improve exercise responses. The intervention approaches, behavioral strategies and indications for these programs also need to be refined and framed. The main objective of this work is to guide the actions of healthcare professionals and enable them to widely and effectively implement multimodal programs including exercise, nutrition and behavioral strategies in real-life settings.

TGF-β1 stimulation and VDR-dependent activation modulate calcitriol action on skeletal muscle fibroblasts and Smad signalling-associated fibrogenesis

Fibroblasts play a pivotal role in fibrogenesis after skeletal muscle injury. Excess fibrous formation can disrupt contractile functions and delay functional recovery. Although vitamin D receptor (VDR) is expressed explicitly in regenerating muscle compared with uninjured muscle, how calcitriol [1α,25(OH)2D3] directly regulates skeletal muscle primary fibroblast proliferation, the transition to myofibroblasts, and Smad signalling-associated fibrogenesis is currently unknown. Herein, the effects of calcitriol on cultured skeletal muscle primary fibroblasts of male C57BL/6 mice (aged 1 month old) were investigated. The percentage of BrdU+ nuclei in primary fibroblasts was significantly decreased after calcitriol treatment; however, the antiproliferative effect of calcitriol was diminished after TGF-β1 stimulation to induce fibroblast to myofibroblast transition. This suppressive effect was associated with significantly decreased VDR expression in TGF-β1-treated cells. In addition, Vdr siRNA transfection abolished the effects of calcitriol on the suppression of α-SMA expression and Smad2/3 signalling in myofibroblasts, supporting that its antifibrogenic effect requires VDR activation. Compared with calcitriol, the antifibrotic agent suramin could inhibit fibroblast/myofibroblast proliferation and suppress the expression of TCF-4, which regulates fibrogenic determination. Collectively, these findings suggest that profibrotic stimulation and VDR-dependent activation could modulate the effects of calcitriol on skeletal muscle fibroblast proliferation and fibrogenesis processes. Therefore, TGF-β1 and VDR expression levels are crucial determinants for the antifibrogenic effect of calcitriol on skeletal muscle after injury.

Sarcopenia, osteoporosis and frailty

Muscles and bones are intricately connected tissues displaying marked co-variation during development, growth, aging, and in many diseases. While the diagnosis and treatment of osteoporosis are well established in clinical practice, sarcopenia has only been classified internationally as a disease in 2016. Both conditions are associated with an increased risk of adverse health outcomes such as fractures, dysmobility and mortality. Rather than focusing on one dimension of bone or muscle mass or weakness, the concept of musculoskeletal frailty captures the overall loss of physiological reserves in the locomotor system with age. The term osteosarcopenia in particular refers to the double jeopardy of osteoporosis and sarcopenia. Muscle-bone interactions at the biomechanical, cellular, paracrine, endocrine, neuronal or nutritional level may contribute to the pathophysiology of osteosarcopenia. The paradigm wherein muscle force controls bone strength is increasingly facing competition from a model centering on the exchange of myokines, osteokines and adipokines. The most promising results have been obtained in preclinical models where common drug targets have been identified to treat these conditions simultaneously. In this narrative review, we critically summarize the current understanding of the definitions, epidemiology, pathophysiology, and treatment of osteosarcopenia as part of an integrative approach to musculoskeletal frailty.

Can Vitamin D Levels Alter the Effectiveness of Short-Term Facelift Interventions?

Facelifting is increasingly popular among the population. It exceeded the limits of post-traumatic facia-reconstruction. Both the demand and the methods available are getting increasingly diverse. The minimally invasive technique revolutionized the facelift, although it took some time to completely comprehend the mechanics. The roles of vitamin D in numerous physiological processes in which it is involved have mostly been elucidated in the last decade. Our hypothesis is based on one of these roles, that is, vitamin D intervenes in changing the type of collagen by changing its location; therefore, collagen will have a supporting role for the subcutaneous tissue. A group of 156 patients with different facelifting methods was followed: 93 minimally invasive (NC), 49 classical surgery (C) and 14 with the combined technique (NC + C). The change in the subcutaneous tissue was monitored by an elastograph. The level of vitamin D was monitored in order to assess the immediate and long-term effects of vitamin D on the progression of subcutaneous fibrosis. It was proven that an optimal level of vitamin D has a beneficial effect in maintaining the volume of subcutaneous tissue in patients from the NC and NC + C groups, the best results being in the NC + C group. An increase in the subcutaneous volume was recorded, which leads to a decrease in elasticity (statistical significance p < 0.05) and the lowering of the subcutaneous tissue, and an increased amount of lowering corresponds to a lowering of vitamin D levels.

Effects of Probiotics and Vitamin D3 Supplementation on Sports Performance Markers in Male Mixed Martial Arts Athletes: A Randomized Trial

BACKGROUND

Strategies targeted at the intestine microbiome seem to be beneficial for professional athletes. The gut-muscle axis is associated with the inflammatory state, glucose metabolism, mitochondrial function, and central nervous system health. All these mechanisms may affect maximal oxygen uptake, muscle strength, and training adaptation. Moreover, the positive effect of certain bacterial strains may be enhanced by vitamin D. Thus, this study aimed to assess and compare the level of selected markers of sports performance of mixed martial arts (MMA) athletes supplemented with vitamin D₃ or probiotics combined with vitamin D₃.

METHODS

A 4-week randomized double-blind placebo-controlled clinical trial was conducted with 23 MMA male athletes assigned to the vitamin D₃ group (Vit D; n = 12) or probiotics + vitamin D₃ group (PRO + VitD; n = 11). Repeated measures of the creatine kinase level, lactate utilization ratio, and anaerobic performance were conducted.

RESULTS

After 4 weeks of supplementation, we found lower lactate concentrations 60 min after the acute sprint interval in the PRO + VitD group when compared to the Vit D group (4.73 ± 1.62 and 5.88 ± 1.55 mmol/L; p < 0.05). In addition, the intervention improved the total work (232.00 ± 14.06 and 240.72 ± 13.38 J kg^-1; p < 0.05), and mean power following the anaerobic exercise protocol (7.73 ± 0.47 and 8.02 ± 0.45 W kg^-1; p < 0.05) only in the PRO + VitD group. Moreover, there was an improvement in the lactate utilization ratio in the PRO + VitD group compared with the Vit D group as shown by the percentage of T60/T3 ratio (73.6 ± 6.9 and 65.1 ± 9.9%, respectively; p < 0.05). We also observed elevated serum 25(OH)D₃ concentrations after acute sprint interval exercise in both groups, however, there were no significant differences between the groups.

CONCLUSION

Four weeks of combined probiotic and vitamin D₃ supplementation enhanced lactate utilization and beneficially affected anaerobic performance in MMA athletes.

An Integrated Approach to Skeletal Muscle Health in Aging

A decline in muscle mass and function represents one of the most problematic changes associated with aging, and has dramatic effects on autonomy and quality of life. Several factors contribute to the inexorable process of sarcopenia, such as mitochondrial and autophagy dysfunction, and the lack of regeneration capacity of satellite cells. The physiologic decline in muscle mass and in motoneuron functionality associated with aging is exacerbated by the sedentary lifestyle that accompanies elderly people. Regular physical activity is beneficial to most people, but the elderly need well-designed and carefully administered training programs that improve muscle mass and, consequently, both functional ability and quality of life. Aging also causes alteration in the gut microbiota composition associated with sarcopenia, and some advances in research have elucidated that interventions via the gut microbiota-muscle axis have the potential to ameliorate the sarcopenic phenotype. Several mechanisms are involved in vitamin D muscle atrophy protection, as demonstrated by the decreased muscular function related to vitamin D deficiency. Malnutrition, chronic inflammation, vitamin deficiencies, and an imbalance in the muscle-gut axis are just a few of the factors that can lead to sarcopenia. Supplementing the diet with antioxidants, polyunsaturated fatty acids, vitamins, probiotics, prebiotics, proteins, kefir, and short-chain fatty acids could be potential nutritional therapies against sarcopenia. Finally, a personalized integrated strategy to counteract sarcopenia and maintain the health of skeletal muscles is suggested in this review.

Effect of different doses of cholecalciferol and calcidiol on meat quality parameters and skeletal muscle transcriptome profiles in swine

Skeletal muscle tissue is one of the potential targets for vitamin D actions. There are indications that vitamin D supplementation to swine has a positive effect on meat quality. However, these issues need further study, especially in terms of response to the use of different forms of vitamin D. We carried out a multi-purpose study to compare the effects of cholecalciferol and calcidiol on meat quality and muscle tissue transcriptome. Meat quality assessment and gene expression analysis were performed on longissimus dorsi samples collected from swine fed grower/finisher diets containing 2000 IU cholecalciferol/1500 IU cholecalciferol per kg (n = 8), 3000 IU cholecalciferol/2500 IU cholecalciferol per kg (n = 10), 2000 IU cholecalciferol +1000 IU calcidiol/1500 IU cholecaliferol +1000 IU calcidiol per kg (n = 8), and 2000 IU calcidiol/1500 IU calcidiol per kg (n = 8). The results suggest that increasing the dose of cholecalciferol and using calcidiol in the diet of finishers may improve meat texture parameters (shear force P = 0,014, toughness P = 0,048, cohesiveness P = 0,017, resilience P = 0,002). Shear force (68.46 N-51.42 N) and toughness (145.85 N-114.52 N) decreased the most under the effect of increasing cholecalciferol dosage. In turn, cohesiveness (0.60 N-0.65 N) and resilience (0.23 N-0.28 N) increased most strongly under the use of cholecalciferol+calcidiol. Moreover, the results indicate no significant effect of increasing cholecalciferol dose and use calcidiol in the swine diet on muscle tissue transcriptome.

Muscle plasticity is influenced by renal function and caloric intake through the FGF23-vitamin D axis

Skeletal muscle, the main metabolic engine in the body of vertebrates, is endowed with great plasticity. The association between skeletal muscle plasticity and two highly prevalent health problems: renal dysfunction and obesity, which share etiologic links as well as many comorbidities, is a subject of great relevance. It is important to know how these alterations impact on the structure and function of skeletal muscle because the changes in muscle phenotype have a major influence on the quality of life of the patients. This literature review aims to discuss the influence of a nontraditional axis involving kidney, bone, and muscle on skeletal muscle plasticity. In this axis, the kidneys play a role as the main site for vitamin D activation. Renal disease leads to a direct decrease in 1,25(OH)₂-vitamin D, secondary to reduction in renal functional mass, and has an indirect effect, through phosphate retention, that contributes to stimulate fibroblast growth factor 23 (FGF23) secretion by bone cells. FGF23 downregulates the renal synthesis of 1,25(OH)₂-vitamin D and upregulates its metabolism. Skeletal production of FGF23 is also regulated by caloric intake: it is increased in obesity and decreased by caloric restriction, and these changes impact on 1,25(OH)₂-vitamin D concentrations, which are decreased in obesity and increased after caloric restriction. Thus, both phosphate retention, that develops secondary to renal failure, and caloric intake influence 1,25(OH)₂-vitamin D that in turn plays a key role in muscle anabolism.

Differential effects of vitamin D on upper and lower body fat-free mass: potential mechanisms

Vitamin D insufficiency is a global health concern and low vitamin D status is regularly associated with reduced muscle mass and sarcopenia in observational research. Recent research using Mendelian randomization (MR) has highlighted the potentially causal positive effect of serum vitamin D (25(OH)D) on total, trunk and upper body appendicular fat-free mass (FFM). However, no such effect was found in lower body FFM, a result that mirrors the outcomes of some vitamin D intervention studies. Here we review the current literature on vitamin D, muscle mass and strength and discuss some potential mechanisms for the differing effects of vitamin D on upper and lower body FFM. In particular, differences in distribution of the vitamin D receptor as well as androgen receptors, in the upper and lower body musculature, will be discussed.

Effect of vitamin D3 vs. calcifediol on VDR concentration and fiber size in skeletal muscle

INTRODUCTION

This study sought to examine the effect of vitamin D₃ (VD₃) 3200 IU/d, calcifediol (HyD) 20mcg/d, or placebo on intramyonuclear vitamin D receptor (VDR) concentration, muscle fiber cross-sectional area (FCSA), and muscle satellite cell activation.

MATERIALS AND METHODS

It was conducted on a subset of the VD₃ (n = 12), HyD (n = 11), and placebo (n = 13) groups who participated in the 6-month randomized controlled HyD Osteopenia Study in postmenopausal women. Baseline and 6-month vastus lateralis muscle cross sections were probed for VDR, fiber type I and II, and PAX7 (satellite cell marker) using immunofluorescence.

RESULTS

Baseline mean ± SD age was 61 ± 4 years and serum 25-hydroxyvitamin D (25OHD) level was 55.1 ± 22.8 nmol/L. Baseline characteristics did not differ significantly by group. Six-month mean ± SD 25OHD levels were 138.7 ± 22.2 nmol/L (VD₃), 206.8 ± 68.8 nmol/L (HyD), and 82.7 ± 36.1 nmol/L (placebo), ANOVA P < 0.001. There were no significant group differences in 6-month change in VDR concentration (ANOVA P = 0.227). Mean ± SD percent 6-month changes in type I FCSA were 20.5 ± 32.7% (VD₃), - 6.6 ± 20.4% (HyD), and - 0.3 ± 14.0% (placebo, ANOVA P = 0.022). Type II FCSA or PAX7 concentration did not change significantly by group (all P > 0.358).

CONCLUSION

This study demonstrated no significant change in intramyonuclear VDR in response to either form of vitamin D vs. placebo. Type I FCSA significantly increased with VD₃, but not with HyD at 6 months. As type I fibers are more fatigue resistant than type II, enlargement in type I suggests potential for improved muscle endurance. Although HyD resulted in the highest 25OHD levels, no skeletal muscle benefits were noted at these high levels.

CLINICAL TRIAL

NCT02527668.

Seven-month wintertime supplementation of 1200 IU vitamin D has no effect on hand grip strength in young, physically active males: A randomized, controlled study

Background

Study Design

Methods

Results

Conclusion

Lack of significant seasonal association between serum 25(OH)D concentration, muscle mass and strength in postmenopausal women from the D-FINES longitudinal study

The aim of the present study was to assess the seasonal relationship between serum 25(OH)D concentration, lean mass and muscle strength. This was a secondary data analysis of a subgroup of 102 postmenopausal women participating in the 2006-2007 D-FINES (Vitamin D, Food Intake, Nutrition and Exposure to Sunlight in Southern England) study. The cohort was assessed as two age subgroups: <65 years (n=80) and ≥65 years (n=22). Outcome measures included lean mass (DXA), muscle strength (handgrip dynamometry) and serum 25(OH)D concentration (enzymeimmunoassay). Derived outcomes included appendicular skeletal muscle mass (ASM) and relative appendicular skeletal muscle index (RASM). Sarcopenia status was assessed using the European Working Group on Sarcopenia in Older People 2018 criteria. Non-parametric partial correlation using BMI as a covariate was used to evaluate the study aims. There were no statistically significant associations between total lean mass, ASM or RASM and 25(OH)D in any group at any season. There was a trend for handgrip strength to be positively associated with serum 25(OH)D concentration. There was a trend showing a higher prevalence of sarcopenia in women ≥65 years. Sarcopenia status appeared transient for five women. In conclusion, the present study found no significant association between vitamin D status and functional indicators of musculoskeletal health, which were additionally not affected by season.

Cattle breed type and anabolic implants impact calpastatin expression and abundance of mRNA associated with protein turnover in the longissimus thoracis of feedlot steers

Two methods that the beef cattle industry can use to improve efficiency, sustainability, and economic viability are growth promotants and crossbreeding cattle of different breed types. In the United States, over 90% of cattle receive an anabolic implant at some point during production resulting in an overall increase in skeletal muscle growth. Recent research suggests that the two main cattle breed types, Bos indicus and Bos taurus, respond differently to anabolic implants. The objective of this study was to characterize changes that occur in skeletal muscle following implanting in Bos indicus influenced steers or Bos taurus steers. Twenty steers were stratified by initial weight in a 2 × 2 factorial design examining two different breeds: Angus (AN; n = 10) or Santa Gertrudis influenced (SG; n = 10), and two implant strategies: no implant (CON; n = 10) or a combined implant containing 120 mg TBA and 24 mg E2 (IMP; n = 10; Revalor-S, Merck Animal Health). Skeletal muscle biopsies were taken from the longissimus thoracis (LT) 2 and 10 d post-implantation. The mRNA abundance of 24 genes associated with skeletal muscle growth were examined, as well as the protein expression of µ-calpain and calpastatin. Succinate dehydrogenase mRNA abundance was impacted (P = 0.05) by a breed × treatment interaction 2 d post-implanting, with SG-CON having a greater increased abundance than all other steers. A tendency for a breed × treatment interaction was observed for calpain-6 mRNA (P = 0.07), with SG-CON having greater abundance than AN-CON and SG-IMP. Additionally, calpastatin protein expression was altered (P = 0.01) by a breed × treatment interaction, with SG-CON and SG-IMP steers having increased expression (P = 0.01) compared with AN-CON steers. At 2 d post-implanting, a breed × treatment interaction was observed with SG-CON steers having greater (P = 0.05) mRNA abundance of mitogen-activated protein kinase compared with AN-CON steers. Furthermore, breed affected (P = 0.05) calpastatin abundance with AN steers having increased (P = 0.05) abundance 2 d post-implanting compared with SG steers. Meanwhile, implants tended to affect (P = 0.09) muscle RING finger protein-1 mRNA abundance, with CON steers having increased (P = 0.09) abundance compared with that of IMP steers. These findings suggest that cattle breed type and anabolic implants impact calpastatin expression and mRNA abundance associated with protein turnover in the LT of feedlot steers 2 and 10 d post-implantation.

Maternal vitamin D deficiency affects the morphology and function of glycolytic muscle in adult offspring rats

BACKGROUND

Fetal stage is a critical developmental window for the skeletal muscle, but little information is available about the impact of maternal vitamin D (Vit. D) deficiency (VDD) on offspring lean mass development in the adult life of male and female animals.

METHODS

Female rats (Wistar Hannover) were fed either a control (1000 IU Vit. D3/kg) or a VDD diet (0 IU Vit. D3/kg) for 6 weeks and during gestation and lactation. At weaning, male and female offspring were randomly separated and received a standard diet up to 180 days old.

RESULTS

Vitamin D deficiency induced muscle atrophy in the male (M-VDD) offspring at the end of weaning, an effect that was reverted along the time. Following 180 days, fast-twitch skeletal muscles [extensor digitorum longus (EDL)] from the M-VDD showed a decrease (20%; P < 0.05) in the number of total fibres but an increase in the cross-sectional area of IIB (17%; P < 0.05), IIA (19%; P < 0.05) and IIAX (21%; P < 0.05) fibres. The fibre hypertrophy was associated with the higher protein levels of MyoD (73%; P < 0.05) and myogenin (55% %; P < 0.05) and in the number of satellite cells (128.8 ± 14 vs. 91 ± 7.6 nuclei Pax7 + in the M-CTRL; P < 0.05). M-VDD increased time to fatigue during ex vivo contractions of EDL muscles and showed an increase in the phosphorylation levels of IGF-1/insulin receptor and their downstream targets related to anabolic processes and myogenic activation, including Ser ⁴⁷³ Akt and Ser ^21/9 GSK-3β. In such muscles, maternal VDD induced a compensatory increase in the content of calcitriol (two-fold; P < 0.05) and CYP27B1 (58%; P < 0.05), a metabolizing enzyme that converts calcidiol to calcitriol. Interestingly, most morphological and biochemical changes found in EDL were not observed in slow-twitch skeletal muscles (soleus) from the M-VDD group as well as in both EDL and soleus muscles from the female offspring.

CONCLUSIONS

These data show that maternal VDD selectively affects the development of type-II muscle fibres in male offspring rats but not in female offspring rats and suggest that the enhancement of their size and fatigue resistance in fast-twitch skeletal muscle (EDL) is probably due to a compensatory increase in the muscle content of Vit. D in the adult age.

Muscle strength after resistance training correlates to mediators of muscle mass and mitochondrial respiration in middle-aged adults

Skeletal muscle aging is a multi-dimensional pathology of atrophy, reduced strength, and oxidative damage. While some molecular targets may mediate both hypertrophic and oxidative adaptations in muscle, their responsiveness in humans and relationship with functional outcomes like strength remain unclear. Promising therapeutic targets to combat muscle aging like apelin, vitamin D receptor (VDR), and spermine oxidase (SMOX) have been investigated in preclinical models but the adaptive response in humans is not well defined. In an exploratory investigation, we examined how strength gains with resistance training relate to regulators of both muscle mass and oxidative function in middle-aged adults. Forty-one middle-aged adults (18M, 23F; 50±7y; 27.8±3.7kg/m²; mean±SD) participated in a 10-week resistance training intervention. Muscle biopsies and plasma were sampled at baseline and post-intervention. High-resolution fluo-respirometry was performed on a subset of muscle tissue. Apelin signaling (plasma apelin, P=0.002; Apln mRNA, P<0.001; apelin receptor mRNA Aplnr, P=0.001) increased with resistance training. Muscle Vdr mRNA (P=0.007) and Smox mRNA (P=0.027) were also upregulated after the intervention. Mitochondrial respiratory capacity increased (V_max, oxidative phosphorylation, and uncoupled electron transport system, P<0.050), yet there were no changes in ADP sensitivity (K_m P=0.579), hydrogen peroxide emission (P=0.469), nor transcriptional signals for mitochondrial biogenesis (nuclear respiratory factor 2, Gapba P=0.766) and mitofusion (mitochondrial dynamin like GTPase, Opa1 P=0.072). Muscular strength with resistance training positively correlated to Apln, Aplnr, Vdr, and Smox transcriptional adaptations, as well as mitochondrial respiratory capacity (unadjusted P<0.050, r=0.400-0.781). Further research is required to understand the interrelationships of these targets with aged muscle phenotype.

The Effect of Leucine Supplementation on Sarcopenia-Related Measures in Older Adults: A Systematic Review and Meta-Analysis of 17 Randomized Controlled Trials

BACKGROUND

The role of leucine in sarcopenia prevention remains unclear. We aimed to summarize the published data from randomized controlled trials (RCTs) to estimate the effect of leucine supplementation on sarcopenia-related measures in older adults.

METHODS

A systematic literature search was performed using the electronic databases PubMed, Embase, and Web of Science with restriction to randomized controlled trials design from January 1, 2009 to March 19, 2022. Sarcopenia-related measures included handgrip strength, total lean mass, gait speed, leg press, 6-min walk test, short-physical performance battery, timed up-and-go test and 30-s chair-stand test. Fixed- and random-effects meta-analysis models were used to generate pooled weighted mean differences (WMDs) and 95% CIs. Heterogeneity was examined in subgroup and sensitivity analyses. Publication bias assessments were performed.

RESULTS

A total of 17 RCTs enrolling 1418 subjects were identified. Leucine-isolated supplementation showed no effect on total lean mass (WMD = 0.03 kg, 95% CI: -0.51, 0.57, P = 0.917), handgrip strength (WMD = 1.23 kg, 95% CI: -0.58, 3.03, P = 0.183) and leg press (WMD = -1.35 kg, 95% CI: -7.46, 4.77, P = 0.666). However, leucine-combined supplementation including vitamin D showed a significant improvement in handgrip strength (WMD = 2.17 kg, 95% CI: 0.24, 4.10, P = 0.027) and gait speed (WMD = 0.03 m/s, 95% CI: 0.01, 0.05, P = 0.008).

CONCLUSION

Leucine-isolated supplementation did not improve muscle mass and strength in elderly. However, leucine-combined supplementation including vitamin D exhibited a significant benefit for muscle strength and performance including handgrip strength and gait speed in older adults. A combination of nutritional supplements would be a viable option for improving sarcopenia.

Exercise: A Possibly Effective Way to Improve Vitamin D Nutritional Status

Vitamin D deficiency has become a widespread public health problem owing to its potential adverse health effects. Generally, the nutritional status of vitamin D depends on sunlight exposure and dietary or supplementary intake. However, recent studies have found that exercise can influence circulating 25(OH)D levels; although, the results have been inconclusive. In this review, we focused on the effect of exercise on circulating vitamin D metabolites and their possible mechanisms. We found that endurance exercise can significantly increase serum 25(OH)D levels in vitamin D-deficient people but has no significant effect on vitamin D-sufficient people. This benefit has not been observed with resistance training. Only chronic endurance exercise training can significantly increase serum 1,25(OH)₂D, and the effect may be sex-dependent. Exercise may influence 25(OH)D levels in the circulation by regulating either the vitamin D metabolites stored in tissues or the utilization by target tissues. The effects of exercise on 25(OH)D levels in the circulation may be dependent on many factors, such as the vitamin D nutritional status, exercise type and intensity, and sex. Therefore, further research on the effects and mechanisms of exercise on vitamin D metabolites is required.

Effect of vitamin D monotherapy on indices of sarcopenia in community-dwelling older adults: a systematic review and meta-analysis

BACKGROUND

Vitamin D supplementation is proposed as a potentially effective nutritional intervention to mitigate the risk of sarcopenia. The aim of this systematic review and meta-analysis was to investigate the impact of vitamin D supplementation monotherapy on indices of sarcopenia in community-dwelling older adults.

METHODS

A comprehensive search of the literature was conducted in PubMed, Web of Science, Scopus, and Cochrane Library. Eligible randomized controlled trials (RCTs) compared the effect of vitamin D supplementation (as monotherapy) with placebo on indices of sarcopenia in older (>50 years) adults. Using the random effects inverse-variance model, we calculated the mean difference (MD) in handgrip strength (HGS), short physical performance battery (SPPB), timed up and go (TUG), and appendicular lean mass (ALM) between groups. We also calculated the standardized mean difference (SMD) in general muscle strength and general physical performance (composite plot of all muscle strength and physical performance outcomes, respectively) between groups.

RESULTS

Ten RCTs were included in the meta-analysis. A significant decrease in SPPB scores was observed with vitamin D supplementation compared with placebo (MD: -0.23; 95% CI -0.40 to -0.06; I²  = 0%; P = 0.007). Vitamin D supplementation conferred no effect on HGS (MD: -0.07 kg; 95% CI -0.70 to 0.55; I²  = 51%, P = 0.82), TUG (MD: 0.07 s; 95% CI -0.08 to 0.22; I²  = 0%, P = 0.35), ALM (MD: 0.06 kg/m² ; 95% CI: -0.32 to 0.44; I²  = 73%, P = 0.77), general muscle strength (SMD: -0.01; 95% CI -0.17 to 0.15; I²  = 42%, P = 0.90), or general physical performance (SMD: -0.02; 95% CI -0.23 to 0.18; I²  = 71%, P = 0.83).

CONCLUSIONS

Vitamin D supplementation did not improve any sarcopenia indices in community-dwelling older adults and may compromise some aspects of physical performance. Future studies are warranted to investigate the impact of vitamin D supplementation on individual indices of SPPB, including mobility and balance, in older adults.

12 Weeks of Physical Exercise Attenuates Oxidative Stress, Improves Functional Tests Performance, and Reduces Fall Risk in Elderly Women Independently on Serum 25(OH)D Concentration

The study aimed to evaluate if the 25(OH)D concentration is related to physical training responses. Moreover, to determine the association between serum 25(OH)D concentration and older women's physical performance, oxidative stress markers, inflammation, and bone metabolism. 37 older women (age 72.9 ± 5.2 years) were assigned into two groups: supplemented (SG) and non-supplemented (NSG). Then, the participants from SG and NSG were randomly assigned into exercised and non-exercised groups: exercise sufficient vitamin D group (ESD; n = 10), exercise insufficient vitamin D group (EID; n = 9), control sufficient vitamin D group (CSD; n = 9), and control insufficient vitamin D group (CID; n = 9). To assess the study aims time up and go test (TUG), 6 min walk test (6MWT), fall risk test (FRT), blood osteocalcin (OC), parathormone (PTH), calcium (Ca²⁺), sulfhydryl groups (SH), malondialdehyde (MDA), and interleukin-6 (IL-6) were performed. The results showed that a higher 25(OH)D concentration was in line with better physical performance and bone metabolism as well as lower inflammation. After 12 weeks of training we noted an improvement in 6MWT (from 374.0 ± 17.3 to 415.0 ± 18.8; p = 0.001 and from 364.8 ± 32.8 to 419.4 ± 32.3; p = 0.001 for EID and ESD, respectively), TUG (from 7.9 ± 0.5 to 6.8 ± 0.8; p = 0.001 and from 7.3 ± 1.5 to 6.4 ± 0.9; p = 0.002, for EID and ESD, respectively), reduction of fall risk (from 2.8 ± 0.8 to 1.9 ± 0.4; p = 0.003 and from 2.1 ± 1.1 to 1.6 ± 0.5; p = 0.047, for EID and ESD, respectively) and increase in SH groups (from 0.53 ± 0.06 to 0.58 ± 0.08; p = 0.012 and from 0.54 ± 0.03 to 0.59 ± 0.04; p = 0.005, for EID and ESD, respectively), regardless of the baseline 25(OH)D concentration. A decrease in PTH and OC concentration was observed only in EID group (from 57.7 ± 15.7 to 49.4 ± 12.6; p = 0.013 for PTH and from 27.9 ± 17.2 to 18.0 ± 6.2; p = 0.004 for OC). To conclude, vitamin D concentration among older women is associated with physical performance, fall risk, inflammation, and bone metabolism markers. Moreover, 12 weeks of training improved physical performance and antioxidant protection, regardless of baseline vitamin D concentration.

CORP: Gene delivery into murine skeletal muscle using in vivo electroporation

The strategy of gene delivery into skeletal muscles has provided exciting avenues in identifying new potential therapeutics towards muscular disorders and addressing basic research questions in muscle physiology through overexpression and knockdown studies. In vivo electroporation methodology offers a simple, rapidly effective technique for the delivery of plasmid DNA into post-mitotic skeletal muscle fibers and the ability to easily explore the molecular mechanisms of skeletal muscle plasticity. The purpose of this review is to describe how to robustly electroporate plasmid DNA into different hindlimb muscles of rodent models. Further, key parameters (e.g., voltage, hyaluronidase, plasmid concentration) which contribute to the successful introduction of plasmid DNA into skeletal muscle fibers will be discussed. In addition, details on processing tissue for immunohistochemistry and fiber cross-sectional area (CSA) analysis will be outlined. The overall goal of this review is to provide the basic and necessary information needed for successful implementation of in vivo electroporation of plasmid DNA and thus open new avenues of discovery research in skeletal muscle physiology.

Vitamin D in Osteosarcopenic Obesity

Osteosarcopenic obesity is a unique clinical condition where low bone and muscle mass coexist in individuals with obesity. Alterations in adipose tissue, skeletal muscle and bone are strictly interconnected, and vitamin D plays key roles in several metabolic pathways that are involved in maintaining musculoskeletal health and glucose homeostasis. We reviewed the available literature on mechanisms underlying osteosarcopenic obesity, with a focus on the role of vitamin D in the pathogenesis and treatment of the condition. We found that, although evidence from large observational studies and pre-clinical experiments strongly supports a role of vitamin D deficiency in the pathogenesis of osteosarcopenic obesity, the common belief that vitamin D improves musculoskeletal health lacks solid clinical evidence, as trials specifically aimed at assessing the effects of vitamin D supplementation in patients with osteosarcopenic obesity are not available, and trials that investigated the role of vitamin D on muscle and bone health in other patient populations either showed no or even detrimental effects. We conclude that large observational and interventional studies including individuals with osteosarcopenic obesity representative of different sex, age and race are needed to better define the role of vitamin D in the pathogenesis and treatment of this condition.

The relationship between dynapenia and vitamin D level in geriatric women with type 2 diabetes mellitus

Objective

In this study, we examined the possible relationship between dynapenia and vitamin D (VD) levels in geriatric women with type 2 diabetes mellitus (T2DM).

Methods

One hundred and twenty-two geriatric female patients aged 65-80 years with a diagnosis of T2DM were included in this prospective study. Physical examinations of the patients were performed, and biochemical tests were analyzed. The muscle strength of the patients was measured with a hand dynamometer. Dynapenia was defined as low grip strength with normal skeletal muscle mass index. In muscle strength measurements, for female patients, over 20 kg was accepted as normal and below 20 kg as decreased muscle strength. Patients were separated into three groups as <10 ng/ml, 10-30 ng/ml, and >30 ng/ml according to VD levels; according to the status of dynapenia, they were divided into two groups as dynapenic and non-dynapenic. By comparing all these parameters between these groups, the relationship between VD level and dynapenia was evaluated. In statistical analysis, significance was accepted as p<0.05.

Results

While 54 of the patients (44.3%) met the dynapenia criterion, 68 patients (55.7%) were non-dynapenic. Patients were first compared according to their dynapenia status. VD level was significantly lower in the dynapenic group (p<0.05). In the correlation analysis, a moderate positive correlation was found between muscle strength and VD (p=0.033, r: 0.23). The patients were then compared according to the VD groups. In the VD insufficient group, muscle strength (p=0.015), body mass index (p=0.025), systolic blood pressure (p<0.01), and glucose (p<0.01) were statistically significantly higher.

Conclusion

In the present study, we found a considerable relationship between VD levels and dynapenia in geriatric women with T2DM.

Serum 25-hydroxy vitamin D and the risk of low muscle mass in young and middle-aged Korean adults

OBJECTIVE

Despite the known benefit of vitamin D in reducing sarcopenia risk in older adults, its effect against muscle loss in the young population is unknown. We aimed to examine the association of serum 25-hydroxy vitamin D [25(OH)D] level and its changes over time with the risk of incident low muscle mass (LMM) in young and middle-aged adults.

DESIGN

This study is a cohort study.

METHODS

The study included Korean adults (median age: 36.9 years) without LMM at baseline followed up for a median of 3.9 years (maximum: 7.3 years). LMM was defined as the appendicular skeletal muscle (ASM) mass by body weight (ASM/weight) of 1 s.d. below the sex-specific mean for the young reference group. Cox proportional hazard models were used to estimate hazard ratios (HRs) with 95% CIs.

RESULTS

Of the 192,908 individuals without LMM at baseline, 19,526 developed LMM. After adjusting for potential confounders, the multivariable-adjusted HRs (95% CIs) for incident LMM comparing 25(OH)D levels of 25-<50, 50-<75, and ≥75 nmol/L to 25(OH)D <25 nmol/L were 0.93 (0.90-0.97), 0.85 (0.81-0.89), and 0.77 (0.71-0.83), respectively. The inverse association of 25(OH)D with incident LMM was consistently observed in young (aged <40 years) and older individuals (aged ≥40 years). Individuals with increased 25(OH)D levels (<50-≥50 nmol/L) or persistently adequate 25(OH)D levels (≥50 nmol/L) between baseline and follow-up visit had a lower risk of incident LMM than those with persistently low 25(OH)D levels.

CONCLUSIONS

Maintaining sufficient serum 25(OH)D could prevent unfavourable changes in muscle mass in both young and middle-aged Korean adults.

Dairy as a Source of Iodine and Protein in the UK: Implications for Human Health Across the Life Course, and Future Policy and Research

This narrative review summarizes key concepts in dairy nutrition for supporting human health throughout the life course. Milk and dairy products have been a staple component of our diet for thousands of years and provide a wide range of important nutrients that are otherwise difficult to obtain from dairy-free diets. In this review, we provide a broad perspective on the nutritional roles of iodine and dairy protein in supporting human health during pregnancy and early life, childhood and adolescence, mid- and later-life. New methodologies to identify biomarkers of dairy intake via high-throughput mass spectrometry are discussed, and new concepts such as the role of the food matrix in dairy nutrition are introduced. Finally, future policy and research related to the consumption of dairy and non-dairy alternatives for health are discussed with a view to improving nutritional status across the lifespan.

Single bout of exercise triggers the increase of vitamin D blood concentration in adolescent trained boys: a pilot study

Vitamin D is necessary for musculoskeletal health, however, the supplementation of vitamin D above the sufficiency level does not bring additional bone mass density (BMD), unlike physical exercise which enhances the bone formatting process. Regular physical activity has been shown to upregulate VDR expression in muscles and to increase circulating vitamin D. Here we investigate whether a single bout of exercise might change 25(OH)D₃ blood concentration and how it affects metabolic response to exercise. Twenty-six boys, 13.8 years old (SD ± 0.7) soccer players, participated in the study. The participants performed one of two types of exercise: the first group performed the VO₂max test until exhaustion, and the second performed three times the repeated 30 s Wingate Anaerobic Test (WAnT). Blood was collected before, 15 min and one hour after the exercise. The concentration of 25(OH)D₃, parathyroid hormone (PTH), interleukin-6 (IL-6), lactate, non-esterified fatty acids (NEFA) and glycerol were determined. 25(OH)D₃ concentration significantly increased after the exercise in all boys. The most prominent changes in 25(OH)D₃, observed after WAnT, were associated with the rise of PTH. The dimensions of response to the exercises observed through the changes in the concentration of 25(OH)D₃, PTH, NEFA and glycerol were associated with the significant increases of IL-6 level. A single bout of exercise may increase the serum’s 25(OH)D₃ concentration in young trained boys. The intensive interval exercise brings a more potent stimulus to vitamin D fluctuations in young organisms. Our results support the hypothesis that muscles may both store and release 25(OH)D₃.

VDR regulates simulated microgravity-induced atrophy in C2C12 myotubes

Muscle wasting is a major problem leading to reduced quality of life and higher risks of mortality and various diseases. Muscle atrophy is caused by multiple conditions in which protein degradation exceeds its synthesis, including disuse, malnutrition, and microgravity. While Vitamin D receptor (VDR) is well known to regulate calcium and phosphate metabolism to maintain bone, recent studies have shown that VDR also plays roles in skeletal muscle development and homeostasis. Moreover, its expression is upregulated in muscle undergoing atrophy as well as after muscle injury. Here we show that VDR regulates simulated microgravity-induced atrophy in C2C12 myotubes in vitro. After 8 h of microgravity simulated using 3D-clinorotation, the VDR-binding motif was associated with chromatin regions closed by the simulated microgravity and enhancer regions inactivated by it, which suggests VDR mediates repression of enhancers. In addition, VDR was induced and translocated into the nuclei in response to simulated microgravity. VDR-deficient C2C12 myotubes showed resistance to simulated microgravity-induced atrophy and reduced induction of FBXO32, an atrophy-associated ubiquitin ligase. These results demonstrate that VDR contributes to the regulation of simulated microgravity-induced atrophy at least in part by controlling expression of atrophy-related genes.

Genetically Determined Serum 25-Hydroxyvitamin D Is Associated with Total, Trunk, and Arm Fat-Free Mass: A Mendelian Randomization Study

PURPOSE

Low serum vitamin D status has been associated with reduced muscle mass in observational studies although the relationship is controversial and a causal association cannot be determined from such observations. Two-sample Mendelian randomization (MR) was applied to assess the association between serum vitamin D (25(OH)D) and total, trunk, arm and leg fat-free mass (FFM).

METHODS

MR was implemented using summary-level data from the largest genome-wide association studies (GWAS) on vitamin D (n=73,699) and total, trunk, arm and leg FFM. Inverse variance weighted method (IVW) was used to estimate the causal estimates. Weighted median (WM)-based method, and MR-Egger, leave-one-out were applied as sensitivity analysis.

RESULTS

Genetically higher serum 25(OH)D levels had a positive effect on total (IVW = Beta: 0.042, p = 0.038), trunk (IVW = Beta: 0.045, p = 0.023) and arm (right arm IVW = Beta: 0.044, p = 0.002; left arm IVW = Beta: 0.05, p = 0.005) FFM. However, the association with leg FFM was not significant (right leg IVW = Beta: 0.03, p = 0.238; left leg IVW = Beta: 0.039, p = 0.100). The likelihood of heterogeneity and pleiotropy was determined to be low (statistically non-significant), and the observed associations were not driven by single SNPs. Furthermore, MR pleiotropy residual sum and outlier test did not highlight any outliers.

CONCLUSIONS

Our results illustrate the potentially causal, positive effect of serum 25(OH)D concentration on total, trunk and upper body appendicular fat-free mass.

Vitamin D and Skeletal Muscle: Current Concepts From Preclinical Studies

Muscle weakness has been recognized as a hallmark feature of vitamin D deficiency for many years. Until recently, the direct biomolecular effects of vitamin D on skeletal muscle have been unclear. Although in the past, some reservations have been raised regarding the expression of the vitamin D receptor in muscle tissue, this special issue review article outlines the clear evidence from preclinical studies for not only the expression of the receptor in muscle but also the roles of vitamin D activity in muscle development, mass, and strength. Additionally, muscle may also serve as a dynamic storage site for vitamin D, and play a central role in the maintenance of circulating 25-hydroxy vitamin D levels during periods of low sun exposure. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Current Thoughts of Notch's Role in Myoblast Regulation and Muscle-Associated Disease

The evolutionarily conserved signaling pathway Notch is unequivocally essential for embryogenesis. Notch’s contribution to the muscle repair process in adult tissue is complex and obscure but necessary. Notch integrates with other signals in a functional antagonist manner to direct myoblast activity and ultimately complete muscle repair. There is profound recent evidence describing plausible mechanisms of Notch in muscle repair. However, the story is not definitive as evidence is slowly emerging that negates Notch’s importance in myoblast proliferation. The purpose of this review article is to examine the prominent evidence and associated mechanisms of Notch’s contribution to the myogenic repair phases. In addition, we discuss the emerging roles of Notch in diseases associated with muscle atrophy. Understanding the mechanisms of Notch’s orchestration is useful for developing therapeutic targets for disease.