Influence of dietary vitamin D deficiency on bone strength, body composition, and muscle in ovariectomized rats fed a high-fat diet

The recent development, application, and future prospects of muscle atrophy animal models

Muscle atrophy, characterized by the loss of muscle mass and function, is a hallmark of sarcopenia and cachexia, frequently associated with aging, malignant tumors, chronic heart failure, and malnutrition. Moreover, it poses significant challenges to human health, leading to increased frailty, reduced quality of life, and heightened mortality risks. Despite extensive research on sarcopenia and cachexia, consensus in their assessment remains elusive, with inconsistent conclusions regarding their molecular mechanisms. Muscle atrophy models are crucial tools for advancing research in this field. Currently, animal models of muscle atrophy used for clinical and basic scientific studies are induced through various methods, including aging, genetic editing, nutritional modification, exercise, chronic wasting diseases, and drug administration. Muscle atrophy models also include in vitro and small organism models. Despite their value, each of these models has certain limitations. This review focuses on the limitations and diverse applications of muscle atrophy models to understand sarcopenia and cachexia, and encourage their rational use in future research, therefore deepening the understanding of underlying pathophysiological mechanisms, and ultimately advancing the exploration of therapeutic strategies for sarcopenia and cachexia.

A low-intensity lifelong exercise routine changes miRNA expression in aging and prevents osteosarcopenic obesity by modulating inflammation

Osteosarcopenic obesity (OSO) has been associated with increase immobility, falls, fractures, and other dysfunctions, which could increase mortality risk during aging. However, its etiology remains unknown. Recent studies revealed that sedentarism, fat gain, and epigenetic regulators are critical in its development. One effective intervention to prevent and treat OSO is exercise. Therefore, in the present study, by keeping rats in conditions of sedentarism and others under a low-intensity exercise routine, we established an experimental model of OSO. We determined the degree of sarcopenia, obesity, and osteopenia at different ages and analyzed the miRNA expression during the lifespan using miRNA microarrays from gastrocnemius muscle. Interestingly microarrays results showed that there is a set of miRNAs that changed their expression with exercise. The pathway enrichment analysis showed that these miRNAs are strongly associated with immune regulation. Further inflammatory profiles with IL-6/IL-10 and TNF-α/IL-10 ratios showed that exercised rats presented a lower pro-inflammatory profile than sedentary rats. Also, the body fat gain in the sedentary group increased the inflammatory profile, ultimately leading to muscle dysfunction. Exercise prevented strength loss over time and maintained skeletal muscle functionality over time. Differential expression of miRNAs suggests that they might participate in this process by regulating the inflammatory response associated with aging, thus preventing the development of OSO.

Effects of Vitamin D on Satellite Cells: A Systematic Review of In Vivo Studies

The non-classical role of vitamin D has been investigated in recent decades. One of which is related to its role in skeletal muscle. Satellite cells are skeletal muscle stem cells that play a pivotal role in skeletal muscle growth and regeneration. This systematic review aims to investigate the effect of vitamin D on satellite cells. A systematic search was performed in Scopus, MEDLINE, and Google Scholar. In vivo studies assessing the effect of vitamin D on satellite cells, published in English in the last ten years were included. Thirteen in vivo studies were analyzed in this review. Vitamin D increases the proliferation of satellite cells in the early life period. In acute muscle injury, vitamin D deficiency reduces satellite cells differentiation. However, administering high doses of vitamin D impairs skeletal muscle regeneration. Vitamin D may maintain satellite cell quiescence and prevent spontaneous differentiation in aging. Supplementation of vitamin D ameliorates decreased satellite cells' function in chronic disease. Overall, evidence suggests that vitamin D affects satellite cells' function in maintaining skeletal muscle homeostasis. Further research is needed to determine the most appropriate dose of vitamin D supplementation in a specific condition for the optimum satellite cells' function.

The pathophysiology of osteoporosis in obesity and type 2 diabetes in aging women and men: The mechanisms and roles of increased bone marrow adiposity

Osteoporosis is defined as a systemic skeletal disease characterized by decreased bone mass and micro-architectural deterioration leading to increased fracture risk. Osteoporosis incidence increases with age in both post-menopausal women and aging men. Among other important contributing factors to bone fragility observed in osteoporosis, that also affect the elderly population, are metabolic disturbances observed in obesity and Type 2 Diabetes (T2D). These metabolic complications are associated with impaired bone homeostasis and a higher fracture risk. Expansion of the Bone Marrow Adipose Tissue (BMAT), at the expense of decreased bone formation, is thought to be one of the key pathogenic mechanisms underlying osteoporosis and bone fragility in obesity and T2D. Our review provides a summary of mechanisms behind increased Bone Marrow Adiposity (BMA) during aging and highlights the pre-clinical and clinical studies connecting obesity and T2D, to BMA and bone fragility in aging osteoporotic women and men.

Nuclear Factor [Erythroid-derived 2]-like 2 and Mitochondrial Transcription Factor A Contribute to Moderate-intensity Swimming Effectiveness against Memory Impairment in Young Mice Induced by Concomitant Exposure to a High-calorie Diet during the Early Life Period

Increased energy food consumption during early-life has been associated with memory impairment. Swimming training has been reported to improve memory processes in rodent models. This study aimed to evaluate whether moderate-intensity swimming training counteracts learning and memory impairment in young mice fed a high-calorie diet during the early-life period. The contribution of hippocampal oxidative stress, as well as nuclear factor [erythroid-derived 2]-like 2/Kelch-like ECH-associated protein (NRF2/Keap-1/HO-1) and peroxisome proliferator-activated receptor gamma co-activator 1-alpha/mitochondrial transcription factor A (PCG-1α/mtTFA) signaling, in memory effects was also investigated. Three-week-old male Swiss mice received a high-calorie diet (20% fat; 20% carbohydrate enriched) or a standard diet from 21 to 49 postnatal days. Mice performed a moderate-intensity swimming protocol (5 days/week) and behavioral tests predictive of memory function. Mice fed a high-calorie diet and subjected to the swimming protocol performed better on short- and long-term spatial and object recognition memory tests than those fed a high-calorie diet. The swimming protocol modulated the hippocampal NRF2/Keap-1/HO-1 and mtTFA pathways in mice fed a high-calorie diet. Swimming training positively affected location and long-term memory, fat mass content, as well as NRF2/Keap-1/HO-1 and mtTFA proteins of control-diet-fed mice. In conclusion, a moderate-intensity swimming training evoked an adaptive response in mice fed a high-calorie diet by restoring different types of memory-impaired and hippocampal oxidative stress as well as upregulated the NRF2/Keap-1/HO-1 and mtTFA pathways.

Factors inducing transdifferentiation of myoblasts into adipocytes

Fat infiltration in skeletal muscle is observed in several myopathies, is associated with muscular dysfunction, and is strongly correlated with insulin resistance, diabetes, obesity, and aging. In animal production, skeletal muscle fat (also known as intermuscular and intramuscular fat) is positively related to meat quality including tenderness, flavor, and juiciness. Thus, understanding the cell origin and regulation mechanism of skeletal muscle fat infiltration is important for developing therapies against human myopathies as well as for improving meat quality. Notably, age, sarcopenia, oxidative stress, injury, and regeneration can activate adipogenic differentiation potential in myoblasts and affect fat accumulation in skeletal muscle. In addition, several transcriptional and nutritional factors can directly induce transdifferentiation of myoblasts into adipocytes. In this review, we focused on the recent progress in understanding the muscle-to-adipocyte differentiation and summarized and discussed the genetic, nutritional, and physiological factors that can induce transdifferentiation of myoblasts into adipocytes. Moreover, the regulatory roles and mechanisms of these factors during the transdifferentiation process were also discussed.

Vitamin A regulates fibroblast growth factor 23 (FGF23)

OBJECTIVES

Renal phosphate and vitamin D metabolism are regulated by proteohormone fibroblast growth factor 23 (FGF23), which is secreted by bone cells. FGF23 inhibits phosphate reabsorption and the production of calcitriol, active vitamin D (1,25(OH)₂D₃). FGF23 generated by other cells exerts further paracrine effects in the liver, heart, and immune system. The FGF23 plasma concentration is positively associated with the onset and progression of kidney and cardiovascular diseases, disclosing FGF23 as a potential disease biomarker. The effects of vitamin A on the expression of FGF23 are controversial. Vitamin A components, retinoids, are mainly effective through nuclear retinoic acid receptors (RAR) and exert different effects on bone. The aim of this study was to clarify whether vitamin A modulates the production of FGF23.

METHODS

We studied the relevance of vitamin A for FGF23 production. Fgf23 transcripts were determined by real-time quantitative polymerase chain reaction in UMR106 osteoblast-like cells and IDG-SW3 osteocytes. FGF23 protein in the cell culture supernatant was measured by enzyme-linked immunosorbent assay.

RESULTS

All-trans-retinoic acid, retinyl acetate, RAR agonist TTNPB (4-[(E)-2-(5,6,7,8-Tetrahydro-5,5,8,8-tetramethyl-2-naphthalenyl)-1-propenyl]benzoic acid), and 13-cis-retinoic acid downregulated the expression of the Fgf23 gene in a dose-dependent manner. This effect was significantly attenuated by RAR antagonist AGN193109 (4-[2-[5,6-Dihydro-5,5-dimethyl-8-(4-methylphenyl)-2-naphthalenyl]ethynyl]benzoic acid).

CONCLUSION

The present study demonstrated that vitamin A is a potent suppressor of FGF23 production through RAR.

Network and pathway-based analyses of genes associated with osteoporosis

Osteoporosis (OP) is a disease characterized by bone mass loss, bone microstructure damage, increased bone fragility, and easy fracture. The molecular mechanism underlying OP remains unclear.In this study, we identified 217 genes associated with OP, and formed a gene set [OP-related genes gene set (OPgset)].The highly enriched GOs and pathways showed OPgset genes were significantly involved in multiple biological processes (skeletal system development, ossification, and osteoblast differentiation), and several OP-related pathways (Wnt signaling pathway, osteoclast differentiation, steroid hormone biosynthesis, and adipocytokine signaling pathway). Besides, pathway crosstalk analysis indicated three major modules, with first module consisted of pathways mainly involved in bone development-related signaling pathways, second module in Wnt-related signaling pathway and third module in metabolic pathways. Further, we calculated degree centrality of a node and selected ten key genes/proteins, including TGFB1, IL6, WNT3A, TNF, PTH, TP53, WNT1, IGF1, IL10, and SERPINE1. We analyze the K-core and construct three k-core sub-networks of OPgset genes.In summary, we for the first time explored the molecular mechanism underlying OP via network- and pathway-based methods, results from our study will improve our understanding of the pathogenesis of OP. In addition, these methods performed in this study can be used to explore pathogenesis and genes related to a specific disease.