Mechanisms of vitamin D action in skeletal muscle

Vitamin D deficiency induces erectile dysfunction: Role of superoxide and Slpi

BACKGROUND AND PURPOSE

Epidemiological studies suggest a relationship between vitamin D deficiency and erectile dysfunction (ED). We hypothesized that vitamin D deficiency or vitamin D receptor (VDR) knockout causes ED and analysed the underlying molecular mechanisms.

EXPERIMENTAL APPROACH

Erectile function was assessed in vivo in anaesthetized male mice or rats by evaluating intracavernosal pressure (ICP) and in vitro in male Vdr-/- mice, and rat or human isolated corpora cavernosa (CCs) mounted in a myograph. Bulk RNA-sequencing (RNA-seq) transcriptomic analysis was performed in rat CCs. Vitamin D deficiency was induced in rats fed a vitamin D-free diet for 5 months.

KEY RESULTS

CCs from human donors with low plasma vitamin D exhibited reduced nitric oxide (NO)-dependent erectile function. This ED was also reproduced in vitamin D-deficient rats and VDR knockout mice, in vivo and ex vivo, and is associated with penile fibrosis and reduced response to the phosphodiesterase 5 inhibitor (PDE5i) sildenafil. CCs from deficient rats show increased superoxide levels, and their impaired erectile function was restored by superoxide scavengers. Transcriptomic analysis, real-time polymerase chain reaction (RT-PCR) and Western blot showed down-regulated secretory leukocyte protease inhibitor (Slpi). Moreover, recombinant SLPI prevented superoxide-induced ED, while Slpi gene silencing led to reduced erectile function in a superoxide-dependent manner.

CONCLUSION AND IMPLICATIONS

Vitamin D deficiency or VDR knockout reduces erectile function. We suggest that this effect is mediated by increased superoxide levels and down-regulation of SLPI. Vitamin D deficiency might be an aetiological factor for vascular ED and for the therapeutic failure of PDE5i.

Nutritional Approach to Diabetic Sarcopenia: A Comprehensive Review

PURPOSE OF THE REVIEW

The aim of this review is to discuss and evaluate diabetic sarcopenia (DS) and its relationship with nutrition by discussing the mechanisms of diabetic sarcopenia in detail and comprehensively reviewing the literature.

RECENT FINDINGS

Type 2 diabetes (T2DM) affects approximately 25% of people aged 50 years and over and indicates a significant the cost of health for the elderly. Nutrition is an important part of these treatment approaches, and in this review, the literature was comprehensively reviewed, focusing on understanding the mechanisms of DS and discussing its relationship with nutrition. A comprehensive search was conducted on Web of Science, Google Scholar, Scopus, Science Direct, and PubMed from inception up to July 2024. The aim of nutritional treatment for DS is to improve muscle mass, muscle strength and physical performance while improving diabetes-related metabolic risk and glucose levels. In this context, it is important to determine energy intake in individuals with DS according to calorie intake exceeding 30 kcal/kg. For these individuals, a protein intake of at least 1-1.2 g/kg/day is recommended, with an emphasis on the number and timing of meals and a nutritional pattern rich in branched chain amino acids (BCAA). In addition, it is important to adopt a diet rich in antioxidants and to choose diet patterns that contain sufficient levels of macro and micronutrients. The Mediterranean diet model can be a good diet option for individuals with DS. Comprehensive studies in this field are needed so that clinicians can make specific dietary recommendations for DS.

Vitamin D and its receptor in skeletal muscle are associated with muscle disease manifestation, lipid metabolism and physical fitness of patients with myositis

BACKGROUND

Low levels of vitamin D have been associated with several autoimmune diseases. A growing body of evidence supports the association of vitamin D with skeletal muscle damage, regeneration, and energy and lipid metabolism. The aim was to analyse vitamin D and its receptor (VDR) in the muscle tissue of patients with idiopathic inflammatory myopathies (IIM) and to relate them to clinical parameters and muscle lipid and energy metabolism.

METHODS

Forty-six patients with IIM and 67 healthy controls (HC) were included in the study. 27 IIM patients participated in a 24-week exercise intervention. Muscle biopsies were obtained from 7 IIM patients before/after training, 13 non-exercising IIM controls, and 21 HC. Circulating concentrations of 25(OH)D and 1,25(OH)D were measured. Gene expression of VDR and CYP27B1, the enzyme converting 25(OH)D to hormonally active 1,25(OH)D, was determined by qPCR in muscle tissue and primary muscle cells. Lipid oxidative metabolism was assessed in muscle tissue (mRNA, qPCR) and primary muscle cells (radioactive assays).

RESULTS

Lower levels of active 1,25(OH)D were observed in IIM patients compared with HC (mean ± SD: 125.0 ± 45.4 vs. 164.7 ± 49.2 pmol/L; p < 0.0001). 25(OH)D was associated with CRP (r = -0.316, p = 0.037), MITAX (r = -0.311, p = 0.040) and HAQ (r = -0.390, p = 0.009) in IIM. After 24 weeks of training, active 1,25(OH)D was associated with MMT8 (r = 0.866, p < 0.0001), FI-2 (r = 0.608, p = 0.013) and HAQ (r = -0.537, p = 0.032). Gene expression of both VDR and CYP27B1 in primary muscle cells decreased after training (p = 0.031 and p = 0.078, respectively). Associations of VDR mRNA in muscle tissue with MMT-8 (IIM: r = -0.559, p = 0.013), serum CK (HC: r = 0.484, p = 0.031), myoglobin (IIM: r = 0.510, p = 0.026) and myostatin (IIM: r = -0.519, p = 0.023) were observed. The expression of VDR in differentiated muscle cells correlated negatively with the complete oxidation of palmitic acid (r = -0.532, p = 0.028). Muscle mRNA of carnitine palmitoyl transferase 1 (CPT1) (downregulated in IIM, p = 0.001) correlated positively with serum 1,25(OH) vitamin D (r = 0.410, p = 0.042).

CONCLUSION

Reduced biologically active vitamin D in circulation suggests its impaired metabolism in IIM. Serum vitamin D levels and gene expression of its receptor and activating enzyme in muscle tissue were modified by regular exercise and associated with disease manifestations, physical fitness, and muscle lipid metabolism of IIM patients.

Effects of High-Dose Vitamin D3 Supplementation on Pig Performance, Vitamin D Content in Meat, and Muscle Transcriptome in Pigs

Vitamin D is known for its role in calcium homeostasis, bone health, and immune function. Recent research has explored its effects on muscle functionality and meat quality in pigs. This study examined high-dose vitamin D3 supplementation in pigs, focusing on growth, blood and tissue vitamin D3 levels, and muscle transcriptome changes. Thirty pigs were divided into three groups, given different amounts of oral supplementation: control, 5000 IU/kg and 10,000 IU/kg vitamin D3. Biochemical and haematological blood parameters, vitamin D content in blood and muscle, and kidney calcium content were evaluated. RNA-seq and qPCR analysed muscle transcriptome changes, while gene set enrichment analysis (GSEA) identified gene expression enrichments. Results showed that 5000 IU/kg vitamin D3 supplementation altered blood parameters like platelet anisocytosis and glucose levels but did not affect body weight, weight gain, or feed intake. Kidney calcium content increased with supplementation. The muscle (longissimus dorsi) vitamin D content increased, suggesting the potential for biofortified pork, although still not optimal as a dietary vitamin D source. Transcriptome analysis revealed minimal gene expression changes, with only the interferon-gamma receptor 2 (IFNGR2) gene differentially expressed at the highest dose. GSEA indicated enrichment in ATP metabolic processes and electron transport chain genes in the 5000 IU/kg group, and immune system, cholesterol, steroid, and fatty acid metabolism genes in the 10,000 IU/kg group. Despite literature suggesting a role for vitamin D in muscle gene expression and growth improvement, this study found its effects limited.

Causal relationship between vitamin D and stress urinary incontinence: Two-sample Mendelian randomization study

Observational studies have found an association between vitamin D and stress urinary incontinence (SUI); however, this conclusion remains controversial, and the causal relationship is unclear. This study aimed to investigate the causal relationship between vitamin D and SUI using a Mendelian randomization (MR) approach. We conducted an MR analysis utilizing publicly available summary data from genome-wide association studies on European ancestry for SUI, vitamin D levels, vitamin D supplementation, and vitamin D deficiency. Regression models such as the inverse variance-weighted (IVW) method, MR-Egger, weighted median, and weighted mode were used for analysis, along with heterogeneity tests, sensitivity analyses, and pleiotropy assessments.MR analysis indicated that vitamin D levels, vitamin D deficiency, and vitamin D supplementation were not causally associated with SUI (IVW OR: 0.999, 95% CI: 0.992-1.006, P = .786); (IVW OR: 1.000, 95% CI: 1.000-1.000, P = .646); (IVW OR: 1.000, 95% CI: 1.000-1.001, P = .064). No evidence of horizontal pleiotropy or heterogeneity was found (P > .05). Our findings do not support a causal relationship between vitamin D and SUI. The incidental effect of SUI and vitamin D may be mediated by other factors, warranting further observational studies and clinical trials.

Low Serum Vitamin D Levels Are Associated with Reduced Muscle Strength in Women with Breast Cancer

Vitamin D insufficiency has been frequent in women with breast cancer (BC), as well as impaired muscle strength (MS), and a possible relationship between these conditions has been investigated in different populations, except in women with BC. This study aimed to analyze the association between serum vitamin D levels and MS in women with BC. Observational cross-sectional study carried out with adult women with BC, without metastasis/recurrence, with up to 12 months of diagnosis. Serum 25(OH)D concentration was categorized as insufficient (<30 ng/mL) or sufficient (≥30 ng/mL). MS was assessed by the Handgrip Strength test and divided into strength tertiles of the population itself: 1st tertile (6-21 kg), 2nd tertile (22-26 kg), and 3rd tertile (27-39 kg). Adjusted multinomial logistic regression models verified the association of serum vitamin D levels in MS tertiles, with a significance of 5%. A total of 151 women were evaluated. Most women had insufficient levels of vitamin D (70%). Insufficient serum vitamin D levels were associated with the 1st and 2nd tertile of MS (odds ratio [OR]: 5.74, 95% confidence interval [CI]: 1.77-18.64, P = 0.004; OR: 4.48, 95% CI: 1.34-14.97, P = 0.015, respectively). Serum vitamin D insufficiency incresed the probability to present lower tertiles of MS in women with BC.

Unravelling the transcriptomic symphony of muscle ageing: key pathways and hub genes altered by ageing and caloric restriction in rat muscle revealed by RNA sequencing

Age-related muscle wasting, sarcopenia is an extensive loss of muscle mass and strength with age and a major cause of disability and accidents in the elderly. Mechanisms purported to be involved in muscle ageing and sarcopenia are numerous but poorly understood, necessitating deeper study. Hence, we employed high-throughput RNA sequencing to survey the global changes in protein-coding gene expression occurring in skeletal muscle with age. Caloric restriction (CR) is a known prophylactic intervention against sarcopenia. Therefore, total RNA was isolated from the muscle tissue of both rats fed ad libitum and CR rats. RNA-seq data were subjected to Gene Ontology, pathway, co-expression, and interaction network analyses. This revealed the functional pathways most activated by both ageing and CR, as well as the key "hub" proteins involved in their activation.RNA-seq revealed 442 protein-coding genes to be upregulated and 377 to be downregulated in aged muscle, compared to young muscle. Upregulated genes were commonly involved in protein folding and immune responses; meanwhile, downregulated genes were often related to developmental biology. CR was found to suppress 69.7% and rescue 57.8% of the genes found to be upregulated and downregulated in aged muscle, respectively. In addition, CR uniquely upregulated 291 and downregulated 304 protein-coding genes. Hub genes implicated in both ageing and CR included Gc, Plg, Irf7, Ifit3, Usp18, Rsad2, Blm and RT1-A2, whilst those exclusively implicated in CR responses included Alb, Apoa1, Ambp, F2, Apoh, Orm1, Mx1, Oasl2 and Rtp4. Hub genes involved in ageing but unaffected by CR included Fgg, Fga, Fgb and Serpinc1. In conclusion, this comprehensive RNA sequencing study highlights gene expression patterns, hub genes and signalling pathways most affected by ageing in skeletal muscle. This data may provide the initial evidence for several targets for potential future therapeutic interventions against sarcopenia.

Vitamin D status and its determinants in German elite athletes

PURPOSE

This study investigated elite German athletes to (1) assess their serum 25(OH)D levels and the prevalence of insufficiency, (2) identify key factors influencing serum 25(OH)D levels, and (3) analyze the association between serum 25(OH)D levels and handgrip strength.

METHODS

In this cross-sectional study, a total of 474 athletes (231 female), aged 13-39 years (mean 19.3 years), from ten Olympic disciplines were included. Serum 25(OH)D levels were analyzed via liquid chromatography-mass spectrometry, and 17 single nucleotide polymorphisms (SNPs) related to vitamin D metabolism were determined using leukocyte DNA. Grip strength was measured unimanually using a hand-held dynamometer. Multiple linear regressions were used to analyze the influence of SNPs, age, sex, season (summer vs. winter), and discipline (indoor vs. outdoor) on 25(OH)D status. Linear regression analyzed the relationship between handgrip strength and serum 25(OH)D levels.

RESULTS

In total, 55.5% (n = 263) of athletes demonstrated insufficient serum 25(OH)D levels (< 30 ng/mL, < 75 nmol/L), with 16% (n = 76) showing levels below 20 ng/mL (50 nmol/L). After correction for multiple testing, significant influences on 25(OH)D levels were observed for the C allele of VDBP rs7041 (AC Genotype: β ^  = 7.46, p < .001; CC Genotype: β ^  = 6.23, p = .001). Age (all p < .01) and discipline (indoor vs. outdoor; all p < .05) also influenced serum 25(OH)D levels. Furthermore, serum 25(OH)D was positively associated with handgrip strength ( β ^ = 0.01, p < .001).

CONCLUSION

A high prevalence of insufficient 25(OH)D levels (< 30 ng/mL, < 75 nmol/L) was observed. We identified certain genetic variants as well as age and discipline as predictors of serum 25(OH)D levels. This knowledge may guide individualized diagnostic, nutritional, and supplementation strategies.

The Effect of Vitamin D3 on Serum Creatine Phosphokinase Level in Patients with Multiple Trauma: A Pilot Randomized Clinical Trial

Background

Multiple trauma can cause an increase in creatine phosphokinase (CPK) and subsequently rhabdomyolysis and acute kidney injury (AKI). This study was designed to evaluate the effect of vitamin D3 on the serum CPK level and the incidence of rhabdomyolysis-induced AKI in patients with multiple trauma.

Methods

Patients with serum CPK levels <1000 IU/L were followed as the control 1 group. Subjects with serum CPK levels ≥1000 IU/L were randomly allocated to the control 2 or intervention group at Imam Hossein Medical Center, Tehran, Iran in 2020. Patients in the intervention group received a single dose of vitamin D3 (300,000 units) on the recruitment day. The serum level of CPK was recorded every 3 days for 14 days. Parametric and non-parametric tests were used to compare the CPK values between groups.

Results

Forty-six patients, consisting of 16, 15, and 15 in control 1, control 2, and intervention arms of the study were recruited, respectively. Unlike control groups, the significant steadily decreasing trend was seen only in the intervention group (P<0.001). This significant decrease in the intervention arm was observed on days 5 to 7 (P=0.001) and on days 8 to 10 (P<0.001) compared to the baseline. Patients in the intervention group had a lower number of AKI or need for dialysis (P=0.869 and P=0.670 for AKI and dialysis, respectively) than control group 2, although the differences were not significant.

Conclusion

The current study revealed that vitamin D3, could prevent the increasing trend of CPK during the first days and accelerate the normalization of CPK in patients with elevated CPK due to multiple trauma.Trial Registration Number: IRCT20120703010178N23.

The relationships of serum vitamin D concentration with linear speed and change of direction performance in soccer players

The aim of the study was to establish whether the level of 25 hydroxyvitamin D (25(OH)D) in serum has an influence on speed (m/s) and change of direction (COD, s) performance. Twenty male soccer players from the top league participated in the study. All subjects were evaluated for the serum concentration of 25(OH)D at the beginning of the preseason. The linear sprint test was performed at 5 m and 30 m, and COD (time and deficit) at the beginning (BPP) and after (APP) 6 weeks of the preparatory period. The results revealed that 20% of soccer players had a significant deficiency of 25(OH)D (<20 ng/mL) and 30% had insufficient 25(OH)D levels (between 20 and 30 ng/mL). Positive correlations were found between the training effect for the ∆COD (BPP-APP) (p = 0.003) and ∆deficit (BPP-APP) (p = 0.039). Significant differences were noticed for the ∆COD (m = 0.60 [s]) and ∆deficit (m = 0.56[s]) in the soccer players whose 25(OH)D concentration was <=30 ng/mL, and for the ∆COD (p = 0.002) and ∆deficit (p = 0.017) in the soccer players whose 25(OH)D concentration was >30 ng/mL. The training effect was significantly higher for the soccer players whose 25(OH)D concentration was above 30 ng/mL. Soccer players with higher 25(OH)D levels achieved superior results in the COD test and demonstrated better deficit outcomes, affirming the positive influence of 25(OH)D on muscle metabolism.

The Effect of Multi-Ingredient Protein versus Collagen Supplementation on Satellite Cell Properties in Males and Females

INTRODUCTION

Skeletal muscle satellite cells (SC) contribute to the adaptive process of resistance exercise training (RET) and may be influenced by nutritional supplementation. However, little research exists on the impact of multi-ingredient supplementation on the SC response to RET.

PURPOSE

We tested the effect of a multi-ingredient supplement (MIS) including whey protein, creatine, leucine, calcium citrate, and vitamin D on SC content and activity as well as myonuclear accretion, SC and myonuclear domain compared with a collagen control (COL) throughout a 10-wk RET program.

METHODS

Twenty-six participants underwent a 10-wk linear RET program while consuming either the MIS or COL supplement twice daily. Muscle biopsies were taken from the vastus lateralis at baseline and 48 h after a bout of damaging exercise, before and after RET. Muscle tissue was analyzed for SC and myonuclear content, domain, acute SC activation, and fiber cross-sectional area (fCSA).

RESULTS

MIS resulted in a greater increase in type II fCSA following 10 wk of RET (effect size (ES) = 0.89) but not myonuclear accretion or SC content. Change in myonuclei per fiber was positively correlated with type I and II and total fiber hypertrophy in the COL group only, indicating a robust independent effect of MIS on fCSA. Myonuclear domain increased similarly in both groups, whereas SC domain remained unchanged following RET. SC activation was similar between groups for all fiber types in the untrained state but showed a trend toward greater increases with MIS after RET (ES = 0.70).

CONCLUSIONS

SC responses to acute damaging exercise and long-term RET are predominantly similar in MIS and COL groups. However, MIS can induce greater increases in type II fCSA with RET and potentially SC activation following damage in the trained state.

Association between dietary vitamin D intake and low muscle mass in US adults: results from NHANES 2011-2018

Purpose

To investigate the association between dietary vitamin D intake and low muscle mass (LMM) in a representative adult population, accounting for total energy intake and other potential confounders.

Materials and methods

This cross-sectional study utilized data from the National Health and Nutrition Examination Survey (NHANES) involving 8,443 participants. Dietary vitamin D intake was assessed using 24-h dietary recalls, and LMM was defined based on appendicular lean mass (ALM) adjusted for body mass index (BMI). Multivariable logistic regression models were used to examine the association between quartiles of dietary vitamin D intake and the odds of LMM, adjusting for age, gender, race/ethnicity, BMI, total energy intake, and additional covariates.

Results

In Model 1, after adjusting for age, gender, race/ethnicity, BMI, and poverty-to-income ratio, participants in the highest quartile of vitamin D intake had an odds ratio (OR) of 0.54 (95% CI: 0.37-0.79) compared to the lowest quartile, with a p for trend <0.001. In Model 2, after further adjustment for total energy intake and several covariates, the association was attenuated but remained borderline significant (p for trend = 0.051). In Model 3, after adjusting for additional health-related factors, the OR for the highest quartile was 0.70 (95% CI: 0.47-1.05), with a significant p for trend of 0.029.

Conclusion

This study suggests that higher dietary vitamin D intake may be associated with a reduced risk of LMM. Further longitudinal research is needed to confirm these findings and explore potential interactions between vitamin D and other dietary factors in muscle mass preservation.

Effect of serum 25-hydroxyvitamin D level on quadriceps strength: a systematic review and meta-analysis

BACKGROUND

Vitamin D deficiency has been linked to poor muscle function, cartilage degeneration, and the development of knee osteoarthritis. However, the impact of serum 25-hydroxyvitamin D [25(OH)D] level on quadriceps muscle strength remains inconclusive, largely due to variations in study designs, differences in study populations, and the influence of confounding factors such as co-supplementation with other vitamins. The existing literature presents mixed findings, highlighting the need for a comprehensive evaluation of the available evidence.

PURPOSE

This systematic review and meta-analysis aim to summarise.

STUDY DESIGN

Systematic review; Level of evidence, 4.

METHODS

Searches were conducted using Medline (Ovid), Embase (Ovid), CINAHL (EBSCOhost), and SPORTDiscus (EBSCOhost), which aimed to summarise recent (published after 2000 and before March 1st, 2024) studies reporting the effects of serum 25(OH)D levels on quadriceps strength. Appraisal tool for Cross-Sectional Studies (AXIS) for cross-sectional studies and Quality in Prognosis Studies (QUIPS) for longitudinal studies. Results from the AXIS and QUIPS tools were used for GRADE quality assessment. The review was carried out using PRIMSA guidelines and registered in PROSPERO (ID: CRD42022313240).

RESULTS

Four hundred studies were screened and 28 studies with 5752 participants were included. 28 published studies (24 cross-sectional and 4 longitudinal) were identified. Key results supported the significant positive correlation between serum 25(OH)D levels and isokinetic quadriceps strength at 180°/s in elderly and athletic populations with a correlation coefficient of 0.245 (95%CI: 0.078-0.398, p = 0.004). However, no significant correlation was found with isometric quadriceps strength or isokinetic strength at 60°/s (r = 0.190, p = 0.085). There was only a weak negative correlation with MVC.

CONCLUSION

This review found a statistically significant positive correlation between serum 25(OH)D levels and isokinetic quadriceps strength. This has important clinical implications, especially in the elderly cohort, with higher 25(OH)D levels being associated with a reduced incidence of falls and fragility fractures.

Effects of vitamin D supplementation on muscle strength in middle-aged and elderly individuals: a retrospective, propensity score-matched study

Introduction

The aim of this study is to investigate the impact of vitamin D supplementation on the muscle strength of the elderly.

Methods

This retrospective, propensity score-matched study included 160 middle-aged and elderly individuals from a community in Beijing, China. The control group (n=110) received health education and lifestyle guidance, while the intervention group (n=50) was given oral vitamin D supplementation in addition to health education and lifestyle guidance. All participants underwent laboratory tests, muscle function, and physical function at baseline and follow-up.

Results

In the propensity score-matched cohort of 41 patients per group, the levels of serum calcium and 25-hydroxyvitamin D in both groups were improved significantly by the end of the study (p<0.05), with the intervention group showing a more significant improvement. The muscle strength of the left lower limb in the intervention group significantly increased after the intervention (p<0.05). The results also showed that the grip strength and pinch strength of the patients in both groups increased after the intervention, and the difference between the two groups was statistically significant (p<0.05).

Discussion

The findings of this study suggest that vitamin D supplementation, in conjunction with lifestyle guidance and health education, is beneficial for enhancing the upper and lower limb strength of patients.

Vitamin D Supplementation Improves Physical Performance in Athletes and Healthy Aging in Physically Active Adults

Vitamin D deficiency is a significant global public health issue, even in regions with all year sun exposure. Currently, the scientific community has not yet reached a unanimous agreement regarding the optimum levels of vitamin D and the precise threshold values. Additional efforts are required to standardize the evaluation of vitamin D insufficiency and deficiency and to provide uniform treatment guidelines. Epidemiological studies have identified a broad spectrum of estimated prevalences in athletes. Their performance when participating in sports. depend on their muscles, heart and lung function. It seems that athletes have significantly lower levels of vitamin D compared to the general population. However, there is a lack of comprehensive studies and systematic reviews on this subject, making it challenging to reach conclusions due to variations in laboratory techniques and cut-off values. While there is an abundant of research on the supplementation of vitamin D and its benefits, it is challenging to provide general recommendations for athletes due to the limitations of extrapolation. However, there is a rather high occurrence of Vitamin D deficiency among individuals who engage in regular physical activity. Supplementing with Vitamin D helps prevents osteoporosis, bone fractures, enhances muscle strength, avoids lung infections, heart failure, and arrhythmias. It is generally safe when used in appropriate quantities, given its wide therapeutic range. Athletes can decrease the occurrence of training dropouts caused by infection, arrhythmias, muscular weakness and potentially prevent the inability to participate in competitions through correct nutrition and vitamin D supplementation. Keywords: vitamin D; sports; muscle; heart, athletes rehabilitation, vitamin D, ventricular premature contractions, physical activity

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.

Combined Nutrition with Exercise: Fueling the Fight Against Sarcopenia Through a Bibliometric Analysis and Review

Objective

This bibliometric analysis and review aimed to examine the current research status and trends in the combination of nutrition and exercise training for sarcopenia. Additionally, it sought to provide researchers with future research directions in this field.

Methods

Relevant publications were obtained from the Web of Science Core Collection (WoSCC) database, covering the period from January 1995 to October 2023. The collected publications were analyzed using CiteSpace, VOSviewer, Bibliometrix, and Review Manager.

Results

Out of the 2528 retrieved publications, the United States emerged as the leading contributor in terms of publication volume. The University of Texas System was identified as the most productive institution. Luc J C van Loon emerged as the most published author in this field. Analysis of keywords revealed recent hot topics and emerging areas of interest, such as "gut microbiota" and "mechanisms". Upon further evaluation, resistance training (RT) and protein supplementation were identified as the most commonly employed and effective methods.

Conclusion

RT and protein supplementation are widely recognized as effective strategies. Future research should focus on investigating the molecular aspects of sarcopenia. Moreover, the potential therapeutic role of gut microbiota in sarcopenia requires further comprehensive investigation in human subjects to establish its correlation.

A narrative review of the effects of vitamin D3 on orthodontic tooth movement: Focus on molecular and cellular mechanisms

Orthodontic tooth movement (OTM) is a critical process in dental alignment, driven by the application of calibrated orthodontic forces. This study delves into the intricate molecular and cellular mechanisms by which vitamin D3 influences OTM. Vitamin D3 is identified as a critical regulator in bone metabolism, enhancing osteoblast activity and bone formation while also modulating osteoclast quantity and RANKL expression, essential for the remodeling of the alveolar bone. The precise mechanisms through which vitamin D3 facilitates these processes are explored, highlighting its potential in accelerating bone remodeling and, consequently, tooth alignment. This comprehensive review underscores vitamin D3's anabolic impact on bone metabolism and its pivotal role in the synthesis and mineralization processes governed by osteoblasts. The findings illuminate vitamin D3's promise in augmenting orthodontic therapy, suggesting its utility in improving treatment efficiency and reducing duration. However, the need for further research into the optimal application of vitamin D3 in orthodontics is emphasized, particularly concerning dosage, timing, and delivery methods.

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.

Dairy Matrix Effects: Physicochemical Properties Underlying a Multifaceted Paradigm

When food products are often considered only as a source of individual nutrients or a collection of nutrients, this overlooks the importance of interactions between nutrients, but also interactions between nutrients and other constituents of food, i.e., the product matrix. This product matrix, which can be defined as 'The components of the product, their interactions, their structural organization within the product and the resultant physicochemical properties of the product', plays a critical role in determining important product properties, such as product stability, sensory properties and nutritional and health outcomes. Such matrix effects can be defined as 'the functional outcome of specific component(s) as part of a specific product matrix'. In this article, dairy matrix effects are reviewed, with particular emphasis on the nutrition and health impact of dairy products. Such matrix effects are critical in explaining many effects of milk and dairy products on human nutrition and health that cannot be explained solely based on nutrient composition. Examples hereof include the low glycemic responses of milk and dairy products, the positive impact on dental health, the controlled amino acid absorption and the absence of CVD risk despite the presence of saturated fatty acids. Particularly, the changes occurring in the stomach, including, e.g., coagulation of casein micelles and creaming of aggregated fat globules, play a critical role in determining the kinetics of nutrient release and absorption.

Identification of Active Components for Sports Supplements: Machine Learning-Driven Classification and Cell-Based Validation

The identification of active components is critical for the development of sports supplements. However, high-throughput screening of active components remains a challenge. This study sought to construct prediction models to screen active components from herbal medicines via machine learning and validate the screening by using cell-based assays. The six constructed models had an accuracy of >0.88. Twelve randomly selected active components from the screening were tested for their active potency on C2C12 cells, and 11 components induced a significant increase in myotube diameters and protein synthesis. The effect and mechanism of luteolin among the 11 active components as potential sports supplements were then investigated by using immunofluorescence staining and high-content imaging analysis. It showed that luteolin increased the skeletal muscle performance via the activation of PGC-1α and MAPK signaling pathways. Thus, high-throughput prediction models can be effectively used to screen active components as sports supplements.

High-fat diet effects on contractile performance of isolated mouse soleus and extensor digitorum longus when supplemented with high dose vitamin D

Evidence suggests vitamin D3 (VD) supplementation can reduce accumulation of adipose tissue and inflammation and promote myogenesis in obese individuals, and thus could mitigate obesity-induced reductions in skeletal muscle (SkM) contractility. However, this is yet to be directly investigated. This study, using the work-loop technique, examined effects of VD (cholecalciferol) supplementation on isolated SkM contractility. Female mice (n = 37) consumed standard low-fat diet (SLD) or high-fat diet (HFD), with or without VD (20,000 IU/kg-1 ) for 12 weeks. Soleus and EDL (n = 8-10 per muscle per group) were isolated and absolute and normalized (to muscle size and body mass) isometric force and power output (PO) were measured, and fatigue resistance determined. Absolute and normalized isometric force and PO of soleus were unaffected by diet (P > 0.087). However, PO normalized to body mass was reduced in HFD groups (P < 0.001). Isometric force of extensor digitorum longus (EDL) was unaffected by diet (P > 0.588). HFD reduced EDL isometric stress (P = 0.048) and absolute and normalized PO (P < 0.031), but there was no effect of VD (P > 0.493). Cumulative work during fatiguing contractions was lower in HFD groups (P < 0.043), but rate of fatigue was unaffected (P > 0.060). This study uniquely demonstrated that high-dose VD had limited effects on SkM contractility and did not offset demonstrated adverse effects of HFD. However, small and moderate effect sizes suggest improvement in EDL muscle performance and animal morphology in HFD VD groups. Given effect sizes observed, coupled with proposed inverted U-shaped dose-effect curve, future investigations are needed to determine dose/duration specific responses to VD, which may culminate in improved function of HFD SkM.

Pathophysiological-Based Nutritional Interventions in Cirrhotic Patients with Sarcopenic Obesity: A State-of-the-Art Narrative Review

In recent decades, following the spread of obesity, metabolic dysfunction has come to represent the leading cause of liver disease. The classical clinical presentation of the cirrhotic patient has, therefore, greatly changed, with a dramatic increase in subjects who appear overweight or obese. Due to an obesogenic lifestyle (lack of physical activity and overall malnutrition, with an excess of caloric intake together with a deficit of proteins and micronutrients), these patients frequently develop a complex clinical condition defined as sarcopenic obesity (SO). The interplay between cirrhosis and SO lies in the sharing of multiple pathogenetic mechanisms, including malnutrition/malabsorption, chronic inflammation, hyperammonemia and insulin resistance. The presence of SO worsens the outcome of cirrhotic patients, affecting overall morbidity and mortality. International nutrition and liver diseases societies strongly agree on recommending the use of food as an integral part of the healing process in the comprehensive management of these patients, including a reduction in caloric intake, protein and micronutrient supplementation and sodium restriction. Based on the pathophysiological paths shared by cirrhosis and SO, this narrative review aims to highlight the nutritional interventions currently advocated by international guidelines, as well as to provide hints on the possible role of micronutrients and nutraceuticals in the treatment of this multifaceted clinical condition.

Active vitamin D increases myogenic differentiation in C2C12 cells via a vitamin D response element on the myogenin promoter

Background: Skeletal muscle development during embryogenesis depends on proliferation of myoblasts followed by differentiation into myotubes/multinucleated myofibers. Vitamin D (VD) has been shown to affect these processes, but there is conflicting evidence within the current literature on the exact nature of these effects due to a lack of time course data. With 20%-40% of pregnant women worldwide being VD deficient, it is crucial that a clearer understanding of the impact of VD on myogenesis is gained. Methods: A detailed 8-day differentiation time course was used where C2C12 cells were differentiated in control media (2% horse serum) or with different concentrations of active VD, 1,25 (OH)2D3 (10-13 M, 10-11 M, 10-9 M or 10-7 M), and measurements were taken at 6 time points. DNA, creatine kinase and protein assays were carried out as well as quantitative PCR to determine expression of Myf5, MyoD, myogenin, MHC I, and MHC neonatal, MHC embryonic, MHC IIa, MHC IIx, and MHC IIb mRNAs. Transfections were carried out using one vector containing the myogenin promoter and another containing the same promoter with a 3 base mutation within a putative vitamin D response element (VDRE) to determine effects of 1,25 (OH)2D3 on myogenin transcription. Finally, a ChIP assay was performed to determine whether the VD receptor (VDR) binds to the putative VDRE. Results: 1,25(OH)2D3 caused an inhibition of proliferation and an increase in differentiation in C2C12 cells. Myf5, myogenin, MHC I, and MHC neonatal, MHC embryonic, MHC IIa, MHC IIx, and MHC IIb expression were all increased by 1,25(OH)2D3. Myotube size was also increased by VD. When the putative VDRE on the myogenin promoter was mutated, the increase in expression by VD was lost. ChIP analysis revealed that the VDR does bind to the putative VDRE on the myogenin promoter. Conclusion: Active VD directly increases myogenin transcription via a functional VDRE on the myogenin promoter, resulting in increased myogenic differentiation, increased expression of both the early and late MHC isoforms, and also increased myotube size. These results highlight the importance of VD status during pregnancy for normal myogenesis to occur, but further in vivo work is needed.

Effect of vitamin D3 supplementation in winter on physical performance of university students: a one-month randomized controlled trial

BACKGROUND

There is epidemiological evidence which suggests an association between 25-hydroxyvitamin D [25(OH)D] levels and bone and muscle function; however, it is unclear whether vitamin D supplementation has an added benefit beyond bone health. Here, we investigated the effects of vitamin D3 supplementation (1 month) on physical performance in Chinese university students in winter.

METHODS

One hundred and seventeen eligible subjects with 25(OH)D (19.2 ± 7.8 ng/mL) were randomly assigned to either vitamin D3 supplement (N = 56; 1000 IU/day) or the control (N = 61) group for 1 month. Pre- and post-measurements included: 1) serum levels of 25(OH)D; 2) musculoskeletal and pulmonary function [vertical jump height (VJH) and right handgrip strength (RHS), forced vital capacity (FVC), and forced expiratory volume at 1s (FEV1)]; 3) bone turnover markers [parathyroid hormone (PTH), n-terminal osteocalcin (N-MID), and calcium]; 4) hemoglobin-related parameters [hemoglobin (Hb), hematocrit (HCT), red blood cells (RBC), and red cell distribution width (RDW)]; 5) lipid parameters [total triglycerides (TG), total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), and low-density lipoprotein cholesterol (LDL-C)]; 6) Fatigue-related indicators [serum creatine kinase (CK), lactate dehydrogenase (LDH), and total testosterone (T)]. In addition, aerobic capacity was assessed by measuring maximal oxygen uptake (VO2max) at baseline.

RESULTS

During wintertime, supplementation with 1000 IU/d of vitamin D3 significantly increased serum 25(OH)D levels (from 18.85 ± 7.04 to 26.98 ± 5.88 ng/mL, p < 0.05), accompanied by a decrease of PTH (p < 0.05). However, vitamin D3 supplementation did not significantly impact the physical performance, serum lipid parameters, and bone turnover markers of students. Furthermore, 25(OH)D was found to be positively correlated with VJH and negatively correlated with PTH and TC at the beginning and end of the study (p < 0.05). In addition, the multiple linear regression analysis showed that 25(OH)D combined with athletic, gender, height, weight, Hb, and FVC could account for 84.0% of the VO2max value.

CONCLUSIONS

The study demonstrated that one-month of 1000 IU/d of vitamin D3 supplementation during the winter had beneficial effects on 25(OH)D status and PTH. However, vitamin D3 intervention was not sufficient to improve physical performance. Furthermore, 25(OH)D levels combined with athletic, Hb and FVC could be a predictor of VO2max.

Current Research on Vitamin D Supplementation against Sarcopenia: A Review of Clinical Trials

Vitamin D plays an important role in skeletal muscle function and metabolism. The aim of this review was A) to discuss the clinical evidence of vitamin D supplementation either alone or combined with other strategies in the prevention of sarcopenia in non-sarcopenic individuals and B) to critically discuss the clinical evidence on the effect of vitamin D combined with other strategies on muscle strength, mass and function in sarcopenic individuals without vitamin D deficiency. Sparse clinical data on non-sarcopenic individuals indicate that vitamin D alone has a subtle beneficial effect on knee extensor strength at doses 880-1600 IU/day without improving handgrip strength or muscle mass. When co-administered with other supplements such as protein, mixed effects appear to prevent the decline of muscle mass, possibly delaying the onset of sarcopenia in non-sarcopenic individuals, at doses of 800-1,000 IU/day over 6-12 weeks. In sarcopenic individuals, vitamin D 100-1,000 IU/day co-supplementation with protein results in increased handgrip strength between 9.8-40.5%. However, there is no strong clinical evidence that vitamin D dosage correlates with changes in muscle strength or mass. Potential sources of discrepancy among studies are discussed. Future studies with appropriate experimental design are essential to dissect the net effect of vitamin D on sarcopenia.

Association of serum 25-hydroxyvitamin D with urinary incontinence in elderly men: evidence based on NHANES 2007-2014

Background

The correlation between serum 25-hydroxyvitamin D (25(OH)D) and different sub-types of urinary incontinence in elderly men continues to be uncertain. Hence, we performed this research to evaluate whether serum 25(OH)D levels are correlated with urinary incontinence among elderly men.

Methods

The present study incorporated the male population aged 50 years and above from four cycles of the NHANES database spanning from 2007 to 2014, for the purpose of analysis. The assessment of urinary incontinence was carried out through a correlation questionnaire, while standardized liquid chromatography-tandem mass spectrometry (LC-MS/MS) was adopted to quantify serum 25(OH)D. A weighted multi-factorial logistic regression analysis was carried out to ascertain and investigate any potential correlation that may exist between serum 25(OH)D and urinary incontinence in senior males.

Results

Ultimately, a sum of 4663 elderly men were involved in our analysis. The outcomes of the univariable analysis illustrated that the group with vitamin D deficiency exhibited augmented odds of all three urinary incontinence types in comparison to the vitamin D-sufficient group. After accounting for age, race, and BMI, no appreciable variations in the outcomes were noticed. However, after accounting for all covariates, only SUI (OR = 1.677; 95% confidence interval (CI) = 1.074-2.618) and MUI (OR = 1.815; 95% confidence interval (CI) = 1.010-3.260) demonstrated statistical significance.

Conclusion

Decreased serum 25(OH)D levels were connected with stress urinary incontinence and mixed urinary incontinence in elderly men.

Advances in the beneficial effects of nutrition on stroke-related Sarcopenia: A narrative review

Stroke is one of the most common causes of disability in adults. Sarcopenia is a syndrome characterized by progressive systemic muscle loss and functional decline. The decrease in skeletal muscle mass and muscle function throughout the body after stroke cannot be explained by neurological motor disorders due to brain injury alone, it is considered to be a secondary sarcopenia known as stroke-related sarcopenia. Mounting evidences showed that stroke-related sarcopenia might promote the occurrence and development of sarcopenia through various pathogenesis such as muscle atrophy, dysphagia, inflammation, and malnutrition, etc. At present, the main indicators used to assess malnutrition in patients with stroke-related sarcopenia include temporalis muscle thickness, calf circumference, phase angle, geriatric nutritional risk index and mini-nutritional assessment short-form, etc. Currently, there is no particularly effective method to curb its progression, but supplementation with essential amino acids, whey protein combined with vitamin D, high energy diet, avoiding Polypharmacy, as well as increasing physical activity level and reducing sedentary lifestyle may improve the malnutrition status of stroke patients, and increase the muscle mass and skeletal muscle index, further delay or even prevent the development of stroke-related sarcopenia. This article reviews the latest research progress on the characteristics, epidemiology, pathogenesis and the role of nutrition in stroke-related sarcopenia, so as to provide reference for the clinical treatment and rehabilitation of stroke-related sarcopenia.

A parathyroid hormone/salt-inducible kinase signaling axis controls renal vitamin D activation and organismal calcium homeostasis

The renal actions of parathyroid hormone (PTH) promote 1,25-vitamin D generation; however, the signaling mechanisms that control PTH-dependent vitamin D activation remain unknown. Here, we demonstrated that salt-inducible kinases (SIKs) orchestrated renal 1,25-vitamin D production downstream of PTH signaling. PTH inhibited SIK cellular activity by cAMP-dependent PKA phosphorylation. Whole-tissue and single-cell transcriptomics demonstrated that both PTH and pharmacologic SIK inhibitors regulated a vitamin D gene module in the proximal tubule. SIK inhibitors increased 1,25-vitamin D production and renal Cyp27b1 mRNA expression in mice and in human embryonic stem cell-derived kidney organoids. Global- and kidney-specific Sik2/Sik3 mutant mice showed Cyp27b1 upregulation, elevated serum 1,25-vitamin D, and PTH-independent hypercalcemia. The SIK substrate CRTC2 showed PTH and SIK inhibitor-inducible binding to key Cyp27b1 regulatory enhancers in the kidney, which were also required for SIK inhibitors to increase Cyp27b1 in vivo. Finally, in a podocyte injury model of chronic kidney disease-mineral bone disorder (CKD-MBD), SIK inhibitor treatment stimulated renal Cyp27b1 expression and 1,25-vitamin D production. Together, these results demonstrated a PTH/SIK/CRTC signaling axis in the kidney that controls Cyp27b1 expression and 1,25-vitamin D synthesis. These findings indicate that SIK inhibitors might be helpful for stimulation of 1,25-vitamin D production in CKD-MBD.

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.

Sarcopenia-a geriatric pandemic : A narrative review

With growing life expectancy, the prevalence of frailty and sarcopenia will continuously increase during the next decades. Geographical differences have been described, and depending on the population studied, sarcopenia is evident in 10% of community-dwelling people, increasing up to 40 to 50% among those living in nursing homes. Sarcopenia is a complex age-related process of multifactorial pathogenesis, influenced by lifestyle, nutrition, biological processes during aging, and also immunological and endocrine mechanisms. For diagnostic criteria, physical parameters (muscle mass measurement) and functional aspects (muscle strength, gait speed, physical performance) are required. In routine clinical care, screening patients using the SARC‑F questionnaire is recommended by recent guidelines of the European Workgroup for Sarcopenia.

Vitamin D Inadequacy Affects Skeletal Muscle Index and Physical Performance in Lumbar Disc Degeneration

Lumbar disc degeneration (LDD) is one of the fundamental causes of low back pain. The aims of this study were to determine serum 25-hydroxyvitamin D (25(OH)D) levels and physical performance and to investigate the relationship between serum vitamin D levels, muscle strength and physical activity in elderly patients with LDD. The participants were 200 LDD patients, including 155 females and 45 males aged 60 years and over. Data on body mass index and body composition were collected. Serum 25(OH)D and parathyroid hormone levels were measured. Serum 25(OH)D was classified into the insufficiency group: <30 ng/mL and the sufficiency group: ≥30 ng/mL. Muscle strength was assessed by grip strength, and physical performance (short physical performance battery) was evaluated by the balance test, chair stand test, gait speed, and Timed Up and Go (TUG) test. Serum 25(OH)D levels in LDD patients with vitamin D insufficiency were significantly lower than in those with vitamin D sufficiency (p < 0.0001). LDD patients with vitamin D insufficiency had a prolonged time in physical performance on gait speed (p = 0.008), chair stand test (p = 0.013), and TUG test (p = 0.014) compared to those with vitamin D sufficiency. Additionally, we found that serum 25(OH)D levels were significantly correlated with gait speed (r = -0.153, p = 0.03) and TUG test (r = -0.168, p = 0.017) in LDD patients. No significant associations with serum 25(OH)D status were observed for grip strength and balance tests among patients. These findings demonstrate that higher serum 25(OH)D levels are associated with better physical performance in LDD patients.

Severe deficiency of vitamin D has no negative effect on physical performance during military training

BACKGROUND

Decreased physical fitness and inferior physical performance are potentially life-threatening risk factors in a combat situation. To examine the effect of vitamin D on physical performance, a prospective study of young men conscripts in the Estonian Army was designed. The hypothesis of the study was that severe deficiency of vitamin D has a negative effect on physical performance.

METHODS

All conscripts (N.=410) entering 10-month military service in July 2015 at the Kuperjanov Battalion were asked to participate. Initially, a total of 98 conscripts volunteered to participate. A prospective longitudinal study with a 10-month follow-up period was performed. The Army Physical Fitness Test (APFT) was performed three times, and hand grip strength, and blood serum values of 25(OH)D, parathyroid hormone (PTH) and calcium (Ca) were measured four times.

RESULTS

A significant decrease in the levels of 25(OH)D compared with baseline values were found, with a lowest mean value of 31.9 nmol/L in March 2016 (P<0.001). No significant differences were found in serum Ca levels. In March 2016, PTH was significantly higher in the severe deficiency group (<25 nmol/L of 25(OH)D) (P=0.02). No significant differences were found in terms of the APFT or hand grip strength between conscripts with severe deficiency of 25(OH)D or values >25 nmol/L. The main finding of the present study was that severe 25(OH)D deficiency was common among male conscripts during the winter season but had no negative effect on physical performance in terms of the APFT test and hand grip strength test.

CONCLUSIONS

Severe vitamin D deficiency during the winter season is common but has no negative effect on physical performance in young, physically active men in military service.

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.

Distinguishing between ante factum and post factum properties of animal cell lines and demonstrating their use in grouping ray-finned fish cell lines into invitromes

In this review, animal cell lines are considered to have two classes of attributes: "before-the-fact" (ante factum) and "after-the-fact" (post factum) properties. Fish cell lines from Actinopterygii (ray-finned fishes) are used to illustrate this distinction and to demonstrate how these properties can be used in various ways to categorize cell lines into groups or invitromes. Before-the-fact properties are set at initiation and are properties of the sample and species from which the cell line arose and of the scientist(s) who developed the cell line. On the basis of the Actinopterygii sample, invitromes exist for embryos, larvae, juveniles, adults, and spawning fish, and for most solid organs but rarely for biological fluids. For species, invitromes exist for only a small fraction of the Actinopterygii total. As to their development, scientists from around the world have contributed to invitromes. By contrast, after-the-fact properties are limitless and become apparent during development, characterization, use, and storage of the cell line. For ray-finned invitromes, cell lines appear to acquire immortality during development, are characterized poorly for differentiation potential, have numerous uses, and are stored formally only sporadically. As an example of applying these principles to a specific organ, the skeletal muscle invitrome is used. For ante factum properties, the cell lines are mainly from trunk muscle of economically important fish from 11 orders, 15 families, 19 genera, and 21 species of ray-finned fishes. For post factum properties, fibroblast-like and myogenic cell lines have been described but epithelial-like FHM is most widely used and curated. Considering cell lines by their before- and after-the-fact properties should facilitate integration of new cell lines into the literature and help incorporate the discipline of cell biology into other research areas, particularly the natural history of fishes.

Risk Factors Affecting Muscle Mass Decline in Maintenance Hemodialysis Patients

Objective

There is a high prevalence of sarcopenia in maintenance hemodialysis (MHD) patients, which is known to be associated with increased mortality. This study is aimed at analyzing the risk factors affecting muscle mass decline in MHD patients.

Methods

This retrospective study included MHD patients who underwent two body composition assessments in October 2013 and November 2017. Depending on whether there was muscle loss or not, the patients were divided into a normal muscle mass (NMM) group and a muscle mass decline (MMD) group. According to the muscle mass decline rate, patients in the MMD group were further classified into a low-rate group and a high-rate group. Biochemical variables, serum vitamin concentrations, anthropometric data, SGA, muscle mass, handgrip, and daily steps were assessed. Risk factors for muscle mass decline were screened by multivariate logistic analysis and linear regression analysis.

Results

Of the 72 MHD patients included in this study, 33 were male and 39 were female with a mean age of 56.80 ± 10.86 years and a mean dialysis duration of 7.50 ± 5.20 years. Age (P = .014) and serum 25(OH)D (P = .040) were found to be associated with a higher risk of muscle mass decline after adjusting for gender, dialysis vintage, albumin, and hs-CRP (P = .040). Further analysis found that dialysis vintage (β = 0.285, P = .030), 25(OH)D (β = -0.351, P = .007), and log NT-proBNP (β = 0.312, P = .020) were risk factors associated with the muscle mass decline rate in MHD patients.

Conclusion

Age and serum 25(OH)D were associated with a higher risk of muscle mass decline, while 25(OH)D, dialysis vintage, and NT-proBNP were associated with the muscle mass decline rate in MHD patients.

Calcitriol increases MBNL1 expression and alleviates myotonic dystrophy phenotypes in HSALR mouse models

BACKGROUND

Myotonic dystrophy type 1 (DM1), one of the most common forms of adult-onset muscular dystrophy, is caused by abnormally expanded CTG repeats in the 3' untranslated region of the DMPK gene. The CUG repeats transcribed from the expanded CTG repeats sequestrate a splicing factor, MBNL1, causing the clinical symptoms in DM1. Nowadays, only symptomatic treatments are available for DM1, and no rational therapy is available. Recently, upregulation of MBNL1 expression has been found to be one of the promising therapies for DM1.

METHODS

All experiments were conducted in the C2C12 myoblasts and HSA^LR mice, a DM1 mouse model. Real-time PCR and western blot were used to detect the mRNA and protein level, respectively. The rotarod exercise, grip strength and hanging time were used to evaluate the muscle strength of mice.

RESULTS

In this study, we demonstrated that calcitriol, an active form of vitamin D3, increased MBNL1 in C2C12 mouse myoblasts as well as in HSA^LR mice model for DM1. In HSA^LR mice model, calcitriol improved muscle strength, and corrected aberrant splicing in skeletal muscle. Besides, calcitriol reduced the number of central nuclei, and improved muscle histopathology in HSA^LR mice. In addition, we identified that calcitriol upregulated MBNL1 expression via activating the promoter of Mbnl1 in C2C12 myogenic cells.

CONCLUSION

Our study suggests that calcitriol is a potential pharmacological strategy for DM1 that enhances MBNL1 expression.

The role of vitamin D on redox regulation and cellular senescence

Vitamin D is considered an essential micronutrient for human health that is metabolized into a multifunctional secosteroid hormone. We can synthesize it in the skin through ultraviolet B (UVB) rays or acquire it from the diet. Its deficiency is a major global health problem that affects all ages and ethnic groups. Furthermore, dysregulation of vitamin D homeostasis has been associated with premature aging, driven by various cellular processes, including oxidative stress and cellular senescence. Various studies have shown that vitamin D can attenuate oxidative stress and delay cellular senescence, mainly by inducing the expression of nuclear factor erythroid 2-related factor 2 (Nrf2) and Klotho and improving mitochondrial homeostasis, proposing this vitamin as an excellent candidate for delaying aging. However, the mechanisms around these processes are not yet fully explored. Therefore, in this review, the effects of vitamin D on redox regulation and cellular senescence are discussed to propose new lines of research and clinical applications of vitamin D in the context of age-related diseases.

Vitamin D levels in post-acute hip fractured patients and their association with rehabilitation outcomes

PURPOSE

To report on serum 25-hydroxyvitamin D (25(OH)D) levels in post-acute hip fractured patients, revealed the associations between serum 25(OH)D levels and hip fractured patients' baseline characteristics and rehabilitation outcomes.

MATERIALS AND METHODS

A retrospective study (9/2017-9/2020) of 493 hip fractured patients. 25(OH)D levels were recorded following the patient's baseline characteristics and outcome measures, including the functional independence measure and motor functional independence measure effectiveness. The sample was divided into three groups: deficient (<30 nmol/l), insufficient (30-75 nmol/l) and sufficient (>75 nmol/l) 25(OH)D levels. ANOVA and chi-square test tests compared the groups. Multiple linear analysis assessed the associations between the 25(OH)D and discharge functional independence measure score.

RESULTS

25(OH)D deficiency was found in 20.3% of the patients. The only baseline characteristic significantly associated with serum 25(OH)D levels was dementia. The group with deficient levels of 25(OH)D exhibited a significantly higher rate of low education, low admission albumin levels and a reduced handgrip strength compared to the insufficient/sufficient groups. All functional measure scores were significantly lower in the deficient (25(OH)D) group compared with the insufficient/sufficient patient groups. 25(OH)D levels were found to be significantly associated with the discharge functional independence measure score.

CONCLUSIONS

Routine screening for 25(OH)D levels is mandatory in post-acute hip fracture patients as it may affect rehabilitation outcomes.Implications for Rehabilitation25-hydroxyvitamin D 25(OH)D levels are associated with rehabilitation outcomes in post-acute hip fractured patients.A routine screening for 25(OH)D levels and standardized supplementation protocol during the acute and post-acute rehabilitation setting is recommended as it may improve the quality of care.

Exploration of mitochondrial defects in sarcopenic hip fracture patients

Severe cases of age-related loss of muscle function and mass are clinically unique to sarcopenia. Mitochondrial dysfunction has been associated with aging and sarcopenia, but the causal connection in this context is not well eluded. Here we investigated different aspects of mitochondrial respiration in sarcopenia. Open muscle biopsies were taken from a total of 31 hip fracture patients, older than 70 years. Patients were assigned a sarcopenia Z-score based on EWGSOP2 criteria. Primary myoblast cultures were generated from the muscle tissue samples and used for real time metabolic measurement. Muscle and serum samples showed correlation of high Z-scores with reduced mitochondrial complex I activity, increased tricarboxylic acid cycle (TCA) metabolites, reduced vitamin D₃ levels, and signs of an altered iron metabolism. Primary myoblast cultures gained from the same muscle biopsies did not show significant mitochondrial defects. We hypothesize that a sum of external consequences, including vitamin D₃ deficiency and iron deficiency caused by disturbances in the iron metabolism, result in complex I deficiency, which in turn affects the TCA and contributes to muscle weakness and loss.

In vitro chemotherapy-associated muscle toxicity is attenuated with nutritional support, while treatment efficacy is retained

Purpose: Muscle-wasting and treatment-related toxicities negatively impact prognosis of colorectal cancer (CRC) patients. Specific nutritional composition might support skeletal muscle and enhance treatment support. In this in vitro study we assess the effect of nutrients EPA, DHA, L-leucine and vitamin D3, as single nutrients or in combination on chemotherapy-treated C2C12-myotubes, and specific CRC-tumor cells.

Materials and Methods: Using C2C12-myotubes, the effects of chemotherapy (oxaliplatin, 5-fluorouracil, oxaliplatin+5-fluorouracil and irinotecan) on protein synthesis, cell-viability, caspase-3/7-activity and LDH-activity were assessed. Addition of EPA, DHA, L-leucine and vitamin D3 and their combination (SNCi) were studied in presence of above chemotherapies. Tumor cell-viability was assessed in oxaliplatin-treated C26 and MC38 CRC cells, and in murine and patient-derived CRC-organoids.

Results: While chemotherapy treatment of C2C12-myotubes decreased protein synthesis, cell-viability and increased caspase-3/7 and LDH-activity, SNCi showed improved protein synthesis and cell viability and lowered LDH activity. The nutrient combination SNCi showed a better overall performance compared to the single nutrients. Treatment response of tumor models was not significantly affected by addition of nutrients.

Conclusions: This in vitro study shows protective effect with specific nutrition composition of C2C12-myotubes against chemotherapy toxicity, which is superior to the single nutrients, while treatment response of tumor cells remained.

The Efficacy of Vitamin D Supplementation in the Treatment of Fibromyalgia Syndrome and Chronic Musculoskeletal Pain

Fibromyalgia syndrome (FMS) and chronic widespread musculoskeletal pain (CMP) are diffuse suffering syndromes that interfere with normal activities. Controversy exists over the role of vitamin D in the treatment of these diseases. We carried out a systematic literature review of randomized controlled trials (RCT) to establish whether vitamin D (25OHD) deficiency is more prevalent in CMP patients and to assess the effects of vitamin D supplementation in pain management in these individuals. We searched PubMed, Physiotherapy Evidence Database (PEDro), and the Cochrane Central Register of Controlled Trials (CENTRAL) for RCTs published in English from 1 January 1990 to 10 July 2022. A total of 434 studies were accessed, of which 14 satisfied the eligibility criteria. In our review three studies, of which two had the best-quality evidence, a correlation between diffuse muscle pain and 25OHD deficiency was confirmed. Six studies, of which four had the best-quality evidence, demonstrated that appropriate supplementation may have beneficial effects in patients with established blood 25OHD deficiency. Eight studies, of which six had the best-quality evidence, demonstrated that 25OHD supplementation results in pain reduction. Our results suggest a possible role of vitamin D supplementation in alleviating the pain associated with FMS and CMP, especially in vitamin D-deficient individuals.

Vitamin D, liver-related biomarkers, and distribution of fat and lean mass in young patients with Fontan circulation

INTRODUCTION/AIM

Young patients with Fontan circulation may have low serum 25-hydroxyvitamin D levels, an affected liver, and unhealthy body compositions. This study aimed to explore the association between vitamin D intake/levels, liver biomarkers, and body composition in young Fontan patients.

METHOD

We collected prospective data in 2017 to 2018, obtained with food-frequency questionnaires, biochemical analyses of liver biomarkers, and dual-energy X-ray absorptiometry scans in 44 children with Fontan circulation. Body compositions were compared to matched controls (n = 38). Linear regression analyses were used to investigate associations of biomarkers, leg pain, and lean mass on serum levels of 25-hydroxyvitamin D. Biomarkers were converted to z scores and differences were evaluated within the Fontan patients.

RESULTS

Our Fontan patients had a daily mean vitamin D intake of 9.9 µg and a mean serum 25-hydroxyvitamin D of 56 nmol/L. These factors were not associated with fat or lean mass, leg pain, or biomarkers of liver status. The Fontan patients had significantly less lean mass, but higher fat mass than controls. Male adolescents with Fontan circulation had a greater mean abdominal fat mass than male controls and higher cholesterol levels than females with Fontan circulation.

CONCLUSION

Vitamin D intake and serum levels were not associated with body composition or liver biomarkers in the Fontan group, but the Fontan group had lower lean mass and higher fat mass than controls. The more pronounced abdominal fat mass in male adolescents with Fontan circulation might increase metabolic risks later in life.

Vitamin-D Deficiency and Supplementation Altered the Network of the Coronary Arteries in a Rodent Model—In Situ Video Microscopic Technique

The aim of our study was to identify whether vitamin-D deficiency (VDD) can alter the geometry of the coronary-resistance-artery system. Male Wistar rats were divided into vitamin-D-deficient (VD−, n = 10) and vitamin-D-supplemented (VD+, n = 8) groups. After eight weeks, branches and segments of the left-anterior-descending-coronary-artery (LAD) network were analyzed by a video-microscopy technique. Segments were divided into 50 μm-long cylindrical ring units. VDD did not increase the number of morphological abnormalities. The number of segments did not differ between the groups (VD−: 210 and VD+: 224; pooled data of 8 networks). A larger lumen area of branches was found in VD+ group, while 1–4-order branches were lengthier in the VD− group. VD− rats had less rich coronary-resistance-artery networks in terms of 50 µm-long units. (VD−: 6365 vs. VD+: 6602; pooled data of 8 networks). VD+ animals were richer in the 100–350 µm outer diameter range, and VD− animals were richer in the 400–550 µm-diameter units. In VD− rats, 150–200 and 300 µm units were almost missing at higher flow distances from the orifice. Serum vitamin-D alterations caused by dietary changes can affect the geometry of the coronary-artery network, which may contribute to vitamin-D-dependent changes in cardiovascular mortality.

Frequency of Vitamin D Deficiency and Associated Factors in Long-term Bariatric Surgery Patients: a Cross-sectional Study

BACKGROUND

Vitamin D deficiency is a common consequence of bariatric surgery (BS). However, few studies have evaluated influential factors and to date there are no studies investigating individual ultraviolet B (UVB) radiation levels in BS patients. This study aimed to evaluate vitamin D deficiency and its associated factors, including UVB radiation, in Roux-Y gastric bypass (RYGB) patients.

METHODS

This study included 104 adults (90.4% female) at least 5 years after RYGB. Patients underwent surgery in private hospitals (Private; n = 47) or in two public hospitals, one with ongoing outpatient care (Active; n = 17), and the other with discontinued service for BS (Discontinued; n = 40). 25-hydroxyvitamin D (25(OH)D) concentrations were analyzed by chemiluminescence, individual UVB radiation levels by dosimeter badges. Vitamin D intake, anthropometric, skin phototype, sociodemographic and lifestyle patterns were also assessed.

RESULTS

Mean age was 49.6 ± 9.1 years and post-operative period 8.7 ± 2.2 years. The prevalence of 25(OH)D deficiency and insufficiency was 25.0% and 51.9% respectively. 25(OH)D concentration differed among the hospitals (private = 26.2 ± 8.5; active = 28.7 ± 11.4; discontinued = 23.5 ± 6.5 ng/mL; p = 0.038). A total of 26.2% of the variance observed in 25(OH)D concentrations was explained by daily UVB radiation levels (β = 0.224; p = 0.032) and vitamin D intake (β = 0.431; p < 0.001), controlling for age and BMI.

CONCLUSION

A quarter of the evaluated patients presented vitamin D deficiency, which was associated with the discontinuation of the health care, higher BMI, lower vitamin D intake, and lower individual UVB radiation levels.

Medium and long-chain structured triacylglycerol enhances vitamin D bioavailability in an emulsion-based delivery system: combination of in vitro and in vivo studies

Vitamin D (VitD) is an essential fat-soluble micronutrient required for maintaining and regulating calcium homeostasis. Although sunlight can provide VitD, epidemiological studies indicate that the occurrence of VitD deficiency and insufficiency is widespread. Lipids are required at all stages of VitD digestion and absorption. In this research two different medium and long-chain triacylglycerol structures, possessing identical fatty acid composition lipids, namely structured triacylglycerol (STG), and physical mixtures of medium/long-chain triacylglycerol (MCT/LCT), were selected. Our results demonstrated that STG had a significant VitD bioavailability compared to MCT/LCT. In terms of the lipid digestion and absorption, the extent of the higher free fatty acid released (69.42%, p < 0.05), extent of lipolysis (89.28%, p < 0.05), lipolysis rate (0.06 s^-1, p < 0.05), and the ratio of the long-chain fatty acid to medium-chain fatty acid of STG (4.8, p < 0.05), result in a higher capacity for accommodating VitD when forming mixed micelles (61.31%, p < 0.05). An in vivo animal study also demonstrated that STG significantly increases the delivery ability of VitD (18.75 ng mL^-1, p < 0.05). The findings of this work may have unique applications for designing novel interesterified lipids with an effective delivery capacity for fat-soluble nutrients.

A Narrative Review of the Evidence for Variations in Serum 25-Hydroxyvitamin D Concentration Thresholds for Optimal Health

Vitamin D3 has many important health benefits. Unfortunately, these benefits are not widely known among health care personnel and the general public. As a result, most of the world's population has serum 25-hydroxyvitamin D (25(OH)D) concentrations far below optimal values. This narrative review examines the evidence for the major causes of death including cardiovascular disease, hypertension, cancer, type 2 diabetes mellitus, and COVID-19 with regard to sub-optimal 25(OH)D concentrations. Evidence for the beneficial effects comes from a variety of approaches including ecological and observational studies, studies of mechanisms, and Mendelian randomization studies. Although randomized controlled trials (RCTs) are generally considered the strongest form of evidence for pharmaceutical drugs, the study designs and the conduct of RCTs performed for vitamin D have mostly been flawed for the following reasons: they have been based on vitamin D dose rather than on baseline and achieved 25(OH)D concentrations; they have involved participants with 25(OH)D concentrations above the population mean; they have given low vitamin D doses; and they have permitted other sources of vitamin D. Thus, the strongest evidence generally comes from the other types of studies. The general finding is that optimal 25(OH)D concentrations to support health and wellbeing are above 30 ng/mL (75 nmol/L) for cardiovascular disease and all-cause mortality rate, whereas the thresholds for several other outcomes appear to range up to 40 or 50 ng/mL. The most efficient way to achieve these concentrations is through vitamin D supplementation. Although additional studies are warranted, raising serum 25(OH)D concentrations to optimal concentrations will result in a significant reduction in preventable illness and death.

Systemic ablation of vitamin D receptor leads to skeletal muscle glycogen storage disorder in mice

BACKGROUND

Vitamin D deficiency leads to pathologies of multiple organ systems including skeletal muscle. Patients with severe vitamin D deficiency exhibit muscle weakness and are susceptible to frequent falls. Mice lacking a functional vitamin D receptor (VDR) develop severe skeletal muscle atrophy immediately after weaning. But the root cause of myopathies when vitamin D signalling is impaired is unknown. Because vitamin D deficiency leads to metabolic changes as well, we hypothesized that the skeletal muscle atrophy in mice lacking VDR may have a metabolic origin.

METHODS

We analysed wild-type (WT) mice as well as vitamin D receptor null (vdr-/-) mice for skeletal muscle proteostasis, energy metabolism, systemic glucose homeostasis, and muscle glycogen levels. Dysregulation of signalling pathways as well as the glycogen synthesis and utilization machinery were also analysed using western blots. qRT-PCR assays were performed to understand changes in mRNA levels.

RESULTS

Skeletal muscles of vdr-/- exhibited higher expression levels of muscle-specific E3 ubiquitin ligases and showed increased protein ubiquitination, suggesting up-regulation of protein degradation. Foxo1 transcription factor was activated in vdr-/- while Foxo3 factor was unaffected. Fasting protein synthesis as well as mTORC1 pathways were severely down-regulated in vdr-/- mice. Skeletal muscle ATP levels were low in vdr-/- (0.58 ± 0.18 μmol/mL vs. 1.6 ± 0.0.14 μmol/mL, P = 0.006), leading to increased AMPK activity. Muscle energy deprivation was not caused by decreased mitochondrial activity as we found the respiratory complex II activity in vdr-/- muscles to be higher compared with WT (0.29 ± 0.007 mU/μL vs. 0.16 ± 0.005 mU/μL). vdr-/- mice had lower fasting blood glucose levels (95 ± 14.5 mg/dL vs. 148.6 ± 6.1 mg/dL, P = 0.0017) while they exhibited hyperlactataemia (7.42 ± 0.31 nmol/μL vs. 4.95 ± 0.44 nmol/μL, P = 0.0032), suggesting systemic energy deficiency in these mice. Insulin levels in these mice were significantly lower in response to intraperitoneal glucose injection (0.69 ± 0.08 pg/mL vs. 1.11 ± 0.09 pg/mL, P = 0.024). Skeletal muscles of these mice exhibit glycogen storage disorder characterized by increased glycogen accumulation. The glycogen storage disorder in vdr-/- muscles is driven by increased glycogen synthase activity and decreased glycogen phosphorylase activity. Increased glycogenin expression supports higher levels of glycogen synthesis in these muscles.

CONCLUSIONS

The results presented show that lack of vitamin D signalling leads to a glycogen storage defect in the skeletal muscles, which leads to muscle energy deprivation. The inability of vdr-/- skeletal muscles to use glycogen leads to systemic defects in glucose homeostasis, which in turn leads to proteostasis defects in skeletal muscles and atrophy.

TNF Signaling Acts Downstream of MiR-322/-503 in Regulating DM1 Myogenesis

Myotonic dystrophy type 1 (DM1) is caused by the expanded CUG repeats and usually displays defective myogenesis. Although we previously reported that ectopic miR-322/-503 expression improved myogenesis in DM1 by targeting the toxic RNA, the underlying pathways regulating myogenesis that were aberrantly altered in DM1 and rescued by miR-322/-503 were still unknown. Here, we constructed DM1 and miR-322/-503 overexpressing DM1 myoblast models, which were subjected to in vitro myoblast differentiation along with their corresponding controls. Agreeing with previous findings, DM1 myoblast showed remarkable myogenesis defects, while miR-322/-503 overexpression successfully rescued the defects. By RNA sequencing, we noticed that Tumor necrosis factor (TNF) signaling was the only pathway that was significantly and oppositely altered in these two experimental sets, with it upregulated in DM1 and inhibited by miR-322/-503 overexpression. Consistently, hyperactivity of TNF signaling was detected in two DM1 mouse models. Blocking TNF signaling significantly rescued the myogenesis defects in DM1. On the contrary, TNF-α treatment abolished the rescue effect of miR-322/-503 on DM1 myogenesis. Taking together, these results implied that TNF signaling mediated the myogenesis defects in DM1 and might act downstream of miR-322/-503 in regulating the myogenesis in DM1. Moreover, the inhibition of TNF signaling benefiting myogenesis in DM1 provided us with a novel therapeutic strategy for DM1.

Vitamin D/Vitamin D Receptor Signaling Attenuates Skeletal Muscle Atrophy by Suppressing Renin-Angiotensin System

The nutritional level of vitamin D may affect musculoskeletal health. We have reported that vitamin D is a pivotal protector against tissue injuries by suppressing local renin-angiotensin system (RAS). This study aimed to explore the role of the vitamin D receptor (VDR) in the protection against muscle atrophy and the underlying mechanism. A cross-sectional study on participants (n = 1034) in Shanghai (China) was performed to analyze the association between vitamin D level and the risk of low muscle strength as well as to detect the circulating level of angiotensin II (Ang II). In animal studies, dexamethasone (Dex) was applied to induce muscle atrophy in wild-type (WT) and VDR-null mice, and the mice with the induction of muscle atrophy were treated with calcitriol for 10 days. The skeletal muscle cell line C2C12 and the muscle satellite cells were applied in in vitro studies. The increased risk of low muscle strength was correlated to a lower level of vitamin D (adjusted odds ratio [OR] 0.58) accompanied by an elevation in serum Ang II level. Ang II impaired the myogenic differentiation of C2C12 myoblasts as illustrated by the decrease in the area of myotubes and the downregulation of myogenic factors (myosin heavy chain [MHC] and myogenic differentiation factor D [MyoD]). The phenotype of muscle atrophy induced by Dex and Ang II was aggravated by VDR ablation in mice and in muscle satellite cells, respectively, and mediated by RAS and its downstream phosphatidylinositol 3-kinase/protein kinase B/forkhead box O1 (PI3K/Akt/FOXO1) signaling. Calcitriol treatment exhibited beneficial effects on muscle function as demonstrated by the increased weight-loaded swimming time, grip strength, and fiber area, and improved fiber type composition via regulating ubiquitin ligases and their substrates MHC and MyoD through suppressing renin/Ang II axis. Taken together, VDR protects against skeletal muscle atrophy by suppressing RAS. Vitamin D could be a potential agent for the prevention and treatment of skeletal muscle atrophy. © 2021 American Society for Bone and Mineral Research (ASBMR).