Vitamin D receptor protein is associated with interleukin-6 in human skeletal muscle

Analysis of Potential Vitamin D Molecule Biomarkers: Association of Calcitriol and Its Hydroxylation Efficiency Ratio with Cardiovascular Disease Risk in Rheumatoid Arthritis Patients

Rheumatoid arthritis (RA) is a multifactorial autoimmune disease in which hypovitaminosis D by calcidiol quantification has been associated with disease severity. However, other vitamin D molecules could be implicated in RA pathophysiology and its comorbidities such as cardiovascular disease (CVD), which impacts the severity and mortality of RA patients. This study aimed to assess the relationship between calcidiol, calcitriol, its hydroxylation efficiency ratio, and the soluble vitamin D receptor (sVDR) and clinical and CVD risk variables to propose potential vitamin D molecule biomarkers for RA. A cross-sectional study of females was conducted on 154 RA patients and 201 healthy subjects (HS). Calcidiol, calcitriol, and the sVDR were measured in blood serum, and vitamin D hydroxylation efficiency was estimated using the calcitriol/calcidiol ratio score. CVD risk was calculated by the high-sensitivity C-reactive protein (hs-CRP) cutoff values. Disease activity was evaluated with the Disease Activity Score for 28 standard joints (DAS28-CRP). Results: The hydroxylation efficiency ratio and calcitriol serum levels were higher in RA patients with hypovitaminosis D (p < 0.001). Moreover, RA patients had a higher probability of a high hydroxylation efficiency ratio (OR = 2.02; p = 0.02), calcitriol serum levels (OR = 2.95; p < 0.001), and sVDR serum levels (OR = 5.57; p < 0.001) than HS. This same pattern was also observed in RA patients with high CVD risk using CRP serum levels; they showed a higher hydroxylation efficiency ratio (OR = 4.51; p = 0.04) and higher calcitriol levels (OR = 5.6; p < 0.01). Calcitriol correlates positively with the sVDR (r = 0.21, p = 0.03), CRP (r = 0.28, p < 0.001), and cardiometabolic indexes (p < 0.001) also showed discrimination capacity for CVD risk in RA patients with CRP ≥ 3 mg/L (AUC = 0.72, p < 0.01). In conclusion, hypovitaminosis D in RA patients was characterized by a pattern of a higher hydroxylation efficiency ratio and higher calcitriol and sVDR serum levels. Notably, higher calcitriol serum levels and a higher vitamin D hydroxylation efficiency ratio were associated with higher CVD risk in RA patients.

Synbiotics and Surgery: Can Prebiotics and Probiotics Affect Inflammatory Surgical Outcomes?

PURPOSE OF REVIEW

Prebiotics, probiotics, and synbiotics have received increasing attention over the years for their beneficial impact on the gut microbiome and for their systemic anti-inflammatory effects. They have also been shown to improve surgical outcomes. Here, we review the inflammatory effects of surgery as well as the data which suggests a benefit of prebiotics, probiotics, and synbiotics taken in the perioperative period.

RECENT FINDINGS

Synbiotics and fermented foods may have an even greater anti-inflammatory effect than probiotics or prebiotics alone. Recent data suggest that the anti-inflammatory effects and microbiome changes brought on by prebiotics, probiotics, and synbiotics have the potential to improve surgical outcomes. We highlight the potential to alter systemic inflammation, surgical and hospital-acquired infections, colorectal cancer formation, recurrence, and anastomotic leak. Synbiotics could also impact metabolic syndrome. Prebiotics, probiotics, and especially synbiotics may be extremely beneficial when taken in the perioperative period. Even short-term gut microbiome pre-habilitation could alter surgical outcomes significantly.

Vitamin D supplementation and immune-related markers: an update from nutrigenetic and nutrigenomic studies

Vitamin D is both a nutrient and a neurologic hormone that plays a critical role in modulating immune responses. While low levels of vitamin D are associated with increased susceptibility to infections and immune-related disorders, vitamin D supplementation has demonstrated immunomodulatory effects that can be protective against various diseases and infections. Vitamin D receptor is expressed in immune cells that have the ability to synthesise the active vitamin D metabolite. Thus, vitamin D acts in an autocrine manner in a local immunologic milieu in fighting against infections. Nutrigenetics and nutrigenomics are the new disciplines of nutritional science that explore the interaction between nutrients and genes using distinct approaches to decipher the mechanisms by which nutrients can influence disease development. Though molecular and observational studies have proved the immunomodulatory effects of vitamin D, only very few studies have documented the molecular insights of vitamin D supplementation. Until recently, researchers have investigated only a few selected genes involved in the vitamin D metabolic pathway that may influence the response to vitamin D supplementation and possibly disease risk. This review summarises the impact of vitamin D supplementation on immune markers from nutrigenetics and nutrigenomics perspective based on evidence collected through a structured search using PubMed, EMBASE, Science Direct and Web of Science. The research gaps and shortcomings from the existing data and future research direction of vitamin D supplementation on various immune-related disorders are discussed.

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.

Vitamin D, Its Role in Recovery after Muscular Damage Following Exercise

Aside from its role in bone metabolism, vitamin D is a key immunomodulatory micronutrient. The active form of vitamin D (1,25(OH)D) seems to modulate the innate immune system through different mechanisms. The vitamin is involved in the differentiation of monocytes into macrophages, increasing the phagocytic and chemotactic functions of these cells. At the same time, vitamin D enables efferocytosis and prevents immunopathology. In addition, vitamin D is involved in other processes related to immune function, such as inflammation. Regarding muscle tissue, vitamin D plays an active role in muscle inflammatory response, protein synthesis, and regulation of skeletal muscle function. Two mechanisms have been proposed: A direct role of 1,25(OH)D binding to vitamin D receptors (VDRs) in muscle cells and the modulation of calcium transport in the sarcoplasmic reticulum. This second mechanism needs additional investigation. In conclusion, vitamin D seems to be effective in cases of deficiency and/or if there is a great muscular commitment, such as in high intensity exercises.

High-dose vitamin D administration and resistance exercise training attenuate the progression of obesity and improve skeletal muscle function in obese p62-deficient mice

Vitamin D (VitD) possesses antiadipogenic and ergogenic properties that could be effective to counteract obesity-related adverse health consequences. Therefore, our overall hypothesis was that VitD could ameliorate obesity-induced insulin resistance, systemic inflammation, and loss of skeletal muscle mass and function in an obesity animal model, p62-deficient mice. Furthermore, it was hypothesized that resistance exercise training (RT) could enhance the benefits of VitD by upregulating protein expression of vitamin D receptor in skeletal muscle. Forty 24-week-old male p62-deficient mice were assigned to the following 4 groups (10/group) for a 10-week intervention: control (p62C, no treatment), VitD (VD, 1000 IU vitamin D₃/kg/d), RT (ladder climbing, 3 times per week), or combined treatment (VRT, VD + RT). Serum VitD levels increased in VD and VRT (P < .05). Total body mass increased in p62C, VD, and VRT, but fat mass increased only in p62C (P < .05). Loss of skeletal muscle function was reported only in p62C (P < .05). Improved blood glucose levels and lower spleen mass were reported in RT and VRT compared to p62C (P < .05). However, the hindlimb muscle wet weights; myofiber cross-sectional area; and expression levels of the regulatory proteins for insulin signaling, inflammation, and muscle growth were not changed by any intervention. In conclusion, VitD administration attenuated the progression of obesity and preserved skeletal muscle function in p62-deficient mice. However, the obese mice improved systemic insulin sensitivity and inflammation only when the intervention involved RT.

Pleiotropic actions of Vitamin D in composite musculoskeletal trauma

Composite tissue injuries are the result of high energy impacts caused by motor vehicle accidents, gunshot wounds or blasts. These are highly traumatic injuries characterized by wide-spread, penetrating wounds affecting the entire musculoskeletal system, and are generally defined by frank volumetric muscle loss with concomitant segmental bone defects. At the tissue level, the breadth of damage to multiple tissue systems, and potential for infection from penetration, have been shown to lead to an exaggerated, often chronic inflammatory response with subsequent dysregulation of normal musculoskeletal healing mechanisms. Aside from the direct effects of inflammation on myogenesis and osteogenesis, frank muscle loss has been shown to directly impair fracture union and ultimately contribute to failed wound regeneration. Care for these injuries requires extensive surgical intervention and acute care strategies. However, often these interventions do not adequately mitigate inflammation or promote proper musculoskeletal injury repair and force amputation of the limb. Therefore, identification of factors that can promote tissue regeneration and mitigate inflammation could be key to restoring wound healing after composite tissue injury. One such factor that may directly affect both inflammation and tissue regeneration in response to these multi-tissue injuries may be Vitamin D. Beyond traditional roles, the pleiotropic and localized actions of Vitamin D are increasingly being recognized in most aspects of wound healing in complex tissue injuries - e.g., regulation of inflammation, myogenesis, fracture callus mineralization and remodeling. Conversely, pre-existing Vitamin D deficiency leads to musculoskeletal dysfunction, increased fracture risk or fracture non-unions, decreased strength/function and reduced capacity to heal wounds through increased inflammation. This Vitamin D deficient state requires acute supplementation in order to quickly restore circulating levels to an optimal level, thereby facilitating a robust wound healing response. Herein, the purpose of this review is to address the roles and critical functions of Vitamin D throughout the wound healing process. Findings from this review suggest that careful monitoring and/or supplementation of Vitamin D may be critical for wound regeneration in composite tissue injuries.

A single bout of high-intensity exercise modulates the expression of vitamin D receptor and vitamin D-metabolising enzymes in horse skeletal muscle

BACKGROUND

The expressions of vitamin D receptor (VDR) and vitamin D-metabolising enzymes (CYP27B1 and CYP24A1) in skeletal muscle have been reported. However, the regulation of this vitamin D system in horse skeletal muscle after high-intensity exercise has not yet been elucidated.

OBJECTIVES

To investigate the effect of high-intensity exercise on the expression of vitamin D system-related proteins in horse skeletal muscle and its associations with skeletal muscle stem cell (SMSC) activity and serum 25(OH)D level.

STUDY DESIGN

Longitudinal study.

METHODS

Six healthy ponies (5 geldings, 1 mare; age 6.3 ± 2.2 years) were studied. Serum and muscle samples were taken from the jugular vein and gluteus medius respectively. Samples were collected at pre-exercise, post-exercise, 1 and 3 weeks after a single bout of high-intensity exercise. Protein expression levels of VDR, CYP27B1, CYP24A1, OxPhos and Pax7 (SMSC marker) were determined using immunohistochemical analysis. Oxidative capacity and intramuscular glycogen content were evaluated using histochemical analysis. Blood biochemistry was analysed for lactate concentration and creatine kinase (CK), and 25(OH)D activity.

RESULTS

High-intensity exercise significantly upregulated Pax7 and VDR protein expression, which correlated with significantly increased blood lactate and serum CK levels immediately post-exercise. Serum 25(OH)D₂ level correlated with CYP27B1 protein expression in skeletal muscle, and it reduced significantly immediately post-exercise and at 1 and 3 weeks post-exercise. However, CYP24A1 protein expression was unchanged throughout study periods.

MAIN LIMITATION

The healthy ponies could not represent a fit population of racehorses and eventers.

CONCLUSIONS

The rapid increase in Pax7 and VDR protein expression along with serum CK level after high-intensity exercise demonstrated an association between SMSC activity and activation of the vitamin D system in response to muscle injury in horses. Moreover, a decrease in CYP27B1 protein expression, correlated with a reduction in serum 25(OH)D₂ , may indicate a compromised vitamin D metabolism after high-intensity exercise.

Characterization of Skeletal Muscle Endocrine Control in an In Vitro Model of Myogenesis

Skeletal muscle has remarkable regenerative abilities regulated by a highly orchestrated process involving the activation of cellular and molecular responses, which are dependent on satellite cells. These cells maintain the stem cell population and provide numerous myogenic cells that proliferate, differentiate, fuse and lead to new myofiber formation for a functional contractile tissue. We have isolated and characterized satellite cells obtained from human biopsies and established an in vitro model of myogenesis, evaluating muscle regeneration, monitoring the dynamic increases of the specific myogenic regulatory factors and the final formation of multinucleated myofibers. As the skeletal muscle is an endocrine tissue able of producing many substances that can act on distant organs, and it can be physiologically modulated by a variety of hormones, we embarked in a project of characterization of muscle cell endocrinology machinery. The expression of a large array of hormone receptors was quantified during the process of myogenesis. The results obtained showed a significant and generalized increase of all the tested hormone receptors along the process of differentiation of human cultured cells from myoblasts to myocytes. Interestingly, also the production of the myokine irisin increased in a parallel manner. These findings point to the human cultured myoblasts as an ideal model to characterize the skeletal muscle endocrine machinery and its hormonal regulation.

Evidence-Based Role of Nutrients and Antioxidants for Chronic Pain Management in Musculoskeletal Frailty and Sarcopenia in Aging

Musculoskeletal disorders in aging and pain are closely connected because of multiple mechanisms leading to loss of mobility and autonomy. Pain is predictive of diability and worsening frailty and the strength of this relationship increases with the severity of pain. This study presents a systematic review of randomized controlled trials, cross sectional studies, and observational studies based on treatment of pain in adults with musculoskeletal disorders using nutritional non-pharmacological (nutrients and antioxidants) interventions. The review found the efficiency of the following topics: (a) accession of the patient to a dietary counselling (e.g., daily recommended amount of protein-equivalent to at least of 1 g of protein per kilogram of body weight); (b) intake of glutamic acid-rich such as soy, egg, and cod and tryptophan-rich foods such as milk and peanuts-or taking quick-acting, free-form supplements; (c) supplementation of vitamin D and magnesium, if lacking; (d) weekly consumption of fish or supplements of omega-3 fatty acids; and (e) availability of botanicals, in particular curcumin and gingerol. These non-pharmacological interventions can help the pain therapist to create a personalized medicine (precision medicine), acting with the maximum efficacy and safety, and also reducing the dosage of analgesic drugs needed.

Targeting Age-Dependent Functional and Metabolic Decline of Human Skeletal Muscle: The Geroprotective Role of Exercise, Myokine IL-6, and Vitamin D

In the elderly, whole-body health largely relies on healthy skeletal muscle, which controls body stability, locomotion, and metabolic homeostasis. Age-related skeletal muscle structural/functional deterioration is associated with a higher risk of severe comorbid conditions and poorer outcomes, demanding major socioeconomic costs. Thus, the need for efficient so-called geroprotective strategies to improve resilience and ensure a good quality of life in older subjects is urgent. Skeletal muscle senescence and metabolic dysregulation share common cellular/intracellular mechanisms, potentially representing targets for intervention to preserve muscle integrity. Many factors converge in aging, and multifaceted approaches have been proposed as interventions, although they have often been inconclusive. Physical exercise can counteract aging and metabolic deficits, not only in maintaining tissue mass, but also by preserving tissue secretory function. Indeed, skeletal muscle is currently considered a proper secretory organ controlling distant organ functions through immunoactive regulatory small peptides called myokines. This review provides a current perspective on the main biomolecular mechanisms underlying age-dependent and metabolic deterioration of skeletal muscle, herein discussed as a secretory organ, the functional integrity of which largely depends on exercise and myokine release. In particular, muscle-derived interleukin (IL)-6 is discussed as a nutrient-level biosensor. Overall, exercise and vitamin D are addressed as optimal geroprotective strategies in view of their multi-target effects.

Vitamin D and Skeletal Muscle: Emerging Roles in Development, Anabolism and Repair

This special issue article will focus on morphologic and functional roles of vitamin D in muscle, from strength to contraction to development and ageing and will characterise the controversy of VDR's expression in skeletal muscle, central to our understanding of vitamin D's effects on this tissue.

The relationship of serum vitamin D receptor levels with disease activity and clinical parameters in patients with ankylosing spondylitis

Objectives

The aim of this study was to investigate the relationship between serum vitamin D receptor (SVDR) levels and disease activity parameters in patients with ankylosing spondylitis (AS).

Patients and methods

Between July 2016 and January 2017, a total of 62 patients (51 males, 11 females; mean age 36.5±12.8 years; range, 23 to 49 years) with AS and 32 healthy volunteers (25 males, 7 females; mean age 41.57±13.6 years; range, 26 to 48 years) were included in the study. The SVDR levels were measured using the enzyme-linked immunosorbent assay. Erythrocyte sedimentation rate (ESR) and serum C-reactive protein (CRP) levels were recorded. The Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) scores were used to assess disease activity.

Results

Although there was no significant difference between the patient and control groups (p=0.66), SVDR levels were significantly elevated in patients with active AS (BASDAI score ≥4) (p=0.01). The SVDR levels significantly increased in AS patients with peripheral joint involvement and enthesitis (p=0.01, p=0.05, respectively). The SVDR levels significantly elevated in patients treated with non-steroidal anti- inflammatory drugs, compared to those treated with biological agents and control group (p=0.01, p=0.03, respectively). The SVDR levels were positively correlated with the BASDAI, CRP and ESR in the patient group (p=0.01, r=0.751; p=0.01, r=0.75; p=0.01, r=0.81, respectively).

Conclusion

Our study results suggest that serum SVDR levels are associated with the disease activity and clinical parameters in patients with AS. Based on these findings, SVDR level may be used as a marker of disease activity in AS.

Relationship Between Serum Vitamin D Level and Ectopic Pregnancy: A Case-Control Study

Objective: To compare the difference in Vitamin D level between women with ectopic pregnancy and control group. Materials and methods: In the present case-control study, 150 patients with ectopic pregnancy were included as case group and 150 women with normal pregnancy as a control group. Then, serum vitamin D levels were measured in both groups and they were then compared with each other. P less than 0.05 was considered statistically significant. Results: The mean age in ectopic pregnancy group was 28.12 ± 5.91 and 27.35 ± 6.21 years old in control group; the difference between two groups was not statistically significant (p = 0.43). The vitamin D level in control group was higher than that of ectopic pregnancy group (p = 0.002). Of all patients, 182 patients (60.66%) had vitamin D deficiency and 64 patients (21.33%) had vitamin D insufficiency. Conclusion: Serum vitamin D level among patients with ectopic pregnancy was statistically lower than women with normal pregnancy.

Does nutrition play a role in the prevention and management of sarcopenia?

There is a growing body of evidence that links nutrition to muscle mass, strength and function in older adults, suggesting that it has an important role to play both in the prevention and management of sarcopenia. This review summarises the discussions of a working group [ESCEO working group meeting 8th September 2016] that met to review current evidence and to consider its implications for preventive and treatment strategies. The review points to the importance of 'healthier' dietary patterns that are adequate in quality in older age, to ensure sufficient intakes of protein, vitamin D, antioxidant nutrients and long-chain polyunsaturated fatty acids. In particular, there is substantial evidence to support the roles of dietary protein and physical activity as key anabolic stimuli for muscle protein synthesis. However, much of the evidence is observational and from high-income countries. Further high-quality trials, particularly from more diverse populations, are needed to enable an understanding of dose and duration effects of individual nutrients on function, to elucidate mechanistic links, and to define optimal profiles and patterns of nutrient intake for older adults.

Adipose stem cells from obese patients show specific differences in the metabolic regulators vitamin D and Gas5

Adipose tissue is a significant source of mesenchymal stem cells for regenerative therapies; however, caution should be taken as their environmental niche can affect their functional properties. We have previously demonstrated the negative impact of obesity on the function of adipose-derived stem cells (ASCs). Here we have evaluated other possible properties and targets that are altered by obesity such as the recently described long non-coding molecule Gas5, which is involved in glucocorticoid resistance. Using ASCs isolated from obese (oASCs) and control subjects (cASCs), we have analyzed additional metabolic and inflammatory conditions that could be related with their impaired therapeutic potential and consequently their possible usefulness in the clinic.

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Altered genetic and metabolic targets by obesity in adipose stem cells population

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Gas5 involved in glucocorticoid resistance such as altered target

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Additional metabolic and inflammation conditions on obese adipose stem cells

Potential role for the VDR agonist elocalcitol in metabolic control: Evidences in human skeletal muscle cells

Vitamin D plays a pivotal role to maintain skeletal muscle integrity and health. Vitamin D deficiency characterizes inflammatory myopathy (IM) and diabetes, often overlapping diseases involving skeletal muscle damage. Vitamin D receptor (VDR) agonists likely exert beneficial effects in both IM and metabolic disturbances. We aim to evaluate in vitro the effect of elocalcitol, a non-hypercalcemic VDR agonist, on the biomolecular metabolic machinery of human skeletal muscle cells (Hfsmc), vs. insulin (I). We analyzed GLUT4, Flotillin-1, Caveolin-3 and Caveolin-1 cell expression/localization; mTOR, AKT, ERK and 4E-BP1 phosphorylation; IL-6 myokine release; VDR expression. We investigated in vivo vitamin D status in IM subjects, evaluating VDR muscular expression and serum vitamin D with metabolism-related parameters, as glycemia, triglycerides, cholesterol, resistin and adiponectin. In Hfsmc, elocalcitol exerted an I-like effect, promoting GLUT4 re-localization in Flotillin-1, Caveolin-3 and Caveolin-1 positive sites and mTOR, AKT, ERK, 4E-BP1 activation; it enhanced IL-6 myokine release. IM subjects, all normoglycemic, showed VDR/vitamin D deficiency that, together with high lipidemic and resistin profile, possibly increases the risk to develop metabolic diseases. VDR agonists as elocalcitol may be therapeutic tools for skeletal muscle integrity/function maintenance, an indispensable condition for health homeostasis.

Nutritional Considerations for Healthy Aging and Reduction in Age-Related Chronic Disease

A projected doubling in the global population of people aged ≥60 y by the year 2050 has major health and economic implications, especially in developing regions. Burdens of unhealthy aging associated with chronic noncommunicable and other age-related diseases may be largely preventable with lifestyle modification, including diet. However, as adults age they become at risk of "nutritional frailty," which can compromise their ability to meet nutritional requirements at a time when specific nutrient needs may be high. This review highlights the role of nutrition science in promoting healthy aging and in improving the prognosis in cases of age-related diseases. It serves to identify key knowledge gaps and implementation challenges to support adequate nutrition for healthy aging, including applicability of metrics used in body-composition and diet adequacy for older adults and mechanisms to reduce nutritional frailty and to promote diet resilience. This review also discusses management recommendations for several leading chronic conditions common in aging populations, including cognitive decline and dementia, sarcopenia, and compromised immunity to infectious disease. The role of health systems in incorporating nutrition care routinely for those aged ≥60 y and living independently and current actions to address nutritional status before hospitalization and the development of disease are discussed.

Vitamin D deficiency, behavioral atypicality, anxiety and depression in children with chromosome 22q11.2 deletion syndrome

Chromosome 22q11.2 deletion syndrome (22q11.2DS) is a complex developmental disorder with serious medical, cognitive and emotional symptoms across the lifespan. This genetic deletion also imparts a lifetime risk for developing schizophrenia that is 25-30 times that of the general population. The origin of this risk is multifactorial and may include dysregulation of the stress response and immunological systems in relation to brain development. Vitamin D is involved in brain development and neuroprotection, gene transcription, immunological regulation and influences neuronal signal transduction. Low levels of vitamin D are associated with schizophrenia, depression and anxiety in the general population. Yet, little is known about how vitamin D levels in children with 22q11.2DS could mediate risk of psychosis in adulthood. Blood plasma levels of vitamin D were measured in children aged 7-16 years with (n=11) and without (n=16) 22q11.2DS in relation to parent reports of children's anxiety and atypicality. Anxiety and atypicality in childhood are risk indicators for the development of schizophrenia in those with 22q11.2DS and the general population. Children with 22q11.2DS had lower vitamin D levels, as well as elevated anxiety and atypicality compared with typical peers. Higher levels of anxiety, depression and internalizing problems but not atypicality were associated with lower levels of vitamin D. Vitamin D insufficiency may relate to higher levels of anxiety and depression, in turn contributing to the elevated risk of psychosis in this population. Further study is required to determine casual linkages between anxiety, stress, mood and vitamin D in children with 22q11.2DS.

Effects of intramuscular administration of 1α,25(OH)2D3 during skeletal muscle regeneration on regenerative capacity, muscular fibrosis, and angiogenesis

The recent discovery of the vitamin D receptor (VDR) in regenerating muscle raises the question regarding the action of vitamin D3 on skeletal muscle regeneration. To investigate the action of vitamin D3 on this process, the tibialis anterior muscle of male C57BL/6 mice (10 wk of age) was injected with 1.2% BaCl2 to induce extensive muscle injury. The bioactive form of vitamin D3 [1α,25(OH)2D3] was administered daily via intramuscular injections during the regenerative phase (days 4-7 postinjury). Physiological and supraphysiological doses of 1α,25(OH)2D3 relative to 1 μg/kg muscle wet weight and mouse body weight were investigated. Muscle samples were collected on day 8 postinjury to examine proteins related to vitamin D3 metabolism (VDR, CYP24A1, and CYP27B1), satellite cell differentiation and regenerative muscle fiber formation [myogenin and embryonic myosin heavy chain (EbMHC)], protein synthesis signaling (Akt, p70 S6K1, 4E-BP1, and myostatin), fiber-type composition (fast and slow MHCs), fibrous formation (vimentin), and angiogenesis (CD31). Administration of 1α,25(OH)2D3 at physiological and supraphysiological doses enhanced VDR expression in regenerative muscle. Moreover, CYP24A1 and vimentin expression was increased, accompanying decreased myogenin and EbMHC expression at the supraphysiological dose. However, there was no change in CYP27B1, Akt, p70 S6K1, 4E-BP1, myostatin, fast and slow MHCs, or CD31 expression at any dose investigated. Taken together, administration of 1α,25(OH)2D3 at a supraphysiological dose decreased satellite cell differentiation, delayed regenerative muscle fiber formation, and increased muscular fibrosis. However, protein synthesis signaling, fiber-type composition, and angiogenesis were not affected by either 1α,25(OH)2D3 administration at a physiological or supraphysiological dose.