Pathogenesis of Osteoporosis

Circulating Extracellular Vesicles Express Receptor Activator of Nuclear Factor κB Ligand and Other Molecules Informative of the Bone Metabolic Status of Mouse Models of Experimentally Induced Osteoporosis

Extracellular vesicles (EVs) are potent means of cell-to-cell communication. They are released in biological fluids, including blood, urine, and saliva, and can be exploited to identify new biomarkers of diseases. We hypothesized that EVs contain molecular cargos involved in bone metabolism, possibly mirroring biological differences between postmenopausal and disuse osteoporosis. We tested this hypothesis in primary murine osteoblasts subjected to steroid depletion or to unloading, and in the serum of animal models of osteoporosis induced by ovariectomy or hindlimb tail suspension. EVs were isolated by ultracentrifugation and analysed by transmission electron microscopy, cytofluorimetry, immunoblotting and RT-PCR. Large-scale analyses were performed by Real-Time arrays and Proteome Profiler™ Antibody arrays. Finally, precise titration of analytes was carried out by ELISA assay. In vitro, we confirmed an increased release of EVs enriched in surface RANKL by primary mouse osteoblasts subjected to steroid depletion or simulated microgravity compared to controls. In vivo, circulating EVs isolated from the sera of control female mice expressed RANKL along with other genes associated with bone metabolism. Serum EVs from ovariectomized or hindlimb tail-suspended mice showed distinct molecular profiles. They expressed RANKL with different kinetics, while transcriptomic and proteomic profiles uncovered unique molecular signatures that discriminated the two conditions, unveiling exclusive molecules expressed in time- and osteoporosis type-dependent manner. These results suggest that circulating EVs could represent a new tool for monitoring the onset and the progression of diverse types of the disease in mice, paving the way for their exploitation to diagnose human osteoporosis in liquid biopsies.

The Positive Association between Muscle Mass and Bone Status Is Conserved in Men with Diabetes: A Retrospective Cross-Sectional and Longitudinal Study

Bone and muscle are known to be correlated and interact chemically each other. Diabetes affects the health status of these two types of organ. There has been lack of studies of men on this topic. This study aims to investigate the relationship between bone and muscle status in men with and without diabetes. This study enrolled 318 and 88 men with and without diabetes, respectively, between April 2007 and December 2017. The appendicular skeletal muscle index (ASMI) was correlated with femoral neck bone mineral density (BMD), total hip BMD, and the trabecular bone score (TBS) in both groups (p < 0.001−0.008). In analysis of the changes in muscle mass and bone-related parameters over the 3 years, the ASMI was correlated with total hip BMD only in diabetes group (p = 0.016) and the TBS in both groups (p < 0.001−0.046). This study showed that the positive correlation between muscle mass and bone status was largely conserved in diabetic group in men. Moreover, in a long-term perspective, muscle mass might be more correlated with the bone microarchitecture or bone quality than bone density, and the association between muscle mass and total hip BMD could be stronger in the diabetic group.

Drug discovery of sclerostin inhibitors

Sclerostin, a protein secreted from osteocytes, negatively regulates the WNT signaling pathway by binding to the LRP5/6 co-receptors and further inhibits bone formation and promotes bone resorption. Sclerostin contributes to musculoskeletal system-related diseases, making it a promising therapeutic target for the treatment of WNT-related bone diseases. Additionally, emerging evidence indicates that sclerostin contributes to the development of cancers, obesity, and diabetes, suggesting that it may be a promising therapeutic target for these diseases. Notably, cardiovascular diseases are related to the protective role of sclerostin. In this review, we summarize three distinct types of inhibitors targeting sclerostin, monoclonal antibodies, aptamers, and small-molecule inhibitors, from which monoclonal antibodies have been developed. As the first-in-class sclerostin inhibitor approved by the U.S. FDA, the monoclonal antibody romosozumab has demonstrated excellent effectiveness in the treatment of postmenopausal osteoporosis; however, it conferred high cardiovascular risk in clinical trials. Furthermore, romosozumab could only be administered by injection, which may cause compliance issues for patients who prefer oral therapy. Considering these above safety and compliance concerns, we therefore present relevant discussion and offer perspectives on the development of next-generation sclerostin inhibitors by following several ways, such as concomitant medication, artificial intelligence-based strategy, druggable modification, and bispecific inhibitors strategy.

Novel Biodegradable Composite of Calcium Phosphate Cement and the Collagen I Mimetic P-15 for Pedicle Screw Augmentation in Osteoporotic Bone

Osteoporotic vertebral fractures often necessitate fusion surgery, with high rates of implant failure. We present a novel bioactive composite of calcium phosphate cement (CPC) and the collagen I mimetic P-15 for pedicle screw augmentation in osteoporotic bone. Methods involved expression analysis of osteogenesis-related genes during osteoblastic differentiation by RT-PCR and immunostaining of osteopontin and Ca²⁺ deposits. Untreated and decalcified sheep vertebrae were utilized for linear pullout testing of pedicle screws. Bone mineral density (BMD) was measured using dual-energy X-ray absorptiometry (DEXA). Expression of ALPI II (p < 0.0001), osteopontin (p < 0.0001), RUNX2 (p < 0.0001), and osteocalcin (p < 0.0001) was upregulated after co-culture of MSC with CPC-P-15. BMD was decreased by 28.75% ± 2.6%. Pullout loads in untreated vertebrae were 1405 ± 6 N (p < 0.001) without augmentation, 2010 ± 168 N (p < 0.0001) after augmentation with CPC-P-15, and 2112 ± 98 N (p < 0.0001) with PMMA. In decalcified vertebrae, pullout loads were 828 ± 66 N (p < 0.0001) without augmentation, 1324 ± 712 N (p = 0.04) with PMMA, and 1252 ± 131 N (p < 0.0078) with CPC-P-15. CPC-P-15 induces osteoblastic differentiation of human MES and improves pullout resistance of pedicle screws in osteoporotic and non-osteoporotic bone.

U.S. Montmorency Tart Cherry Juice Decreases Bone Resorption in Women Aged 65-80 Years

Pre-clinical studies have demonstrated that tart cherries, rich in hydroxycinnamic acids and anthocyanins, protect against age-related and inflammation-induced bone loss. This study examined how daily consumption of Montmorency tart cherry juice (TC) alters biomarkers of bone metabolism in older women. Healthy women, aged 65–80 years (n = 27), were randomly assigned to consume ~240 mL (8 fl. oz.) of juice once (TC1X) or twice (TC2X) per day for 90 d. Dual-energy x-ray absorptiometry (DXA) scans were performed to determine bone density at baseline, and pre- and post-treatment serum biomarkers of bone formation and resorption, vitamin D, inflammation, and oxidative stress were assessed. Irrespective of osteoporosis risk, the bone resorption marker, tartrate resistant acid phosphatase type 5b, was significantly reduced with the TC2X dose compared to baseline, but not with the TC1X dose. In terms of indicators of bone formation and turnover, neither serum bone-specific alkaline phosphatase nor osteocalcin were altered. No changes in thiobarbituric acid reactive substances or high sensitivity C-reactive protein were observed in response to either TC1X or TC2X. We conclude that short-term supplementation with the higher dose of tart cherry juice decreased bone resorption from baseline without altering bone formation and turnover biomarkers in this cohort.

Immunoexpression pattern of autophagy mediators in alveolar bone osteoclasts following estrogen withdrawal in female rats

It is known that estrogen deficiency increases osteoclast formation and activity. Autophagy, a cell survival pathway, has been shown to be crucial for osteoclast function. However, little is known about the effects of estrogen depletion on osteoclast autophagy. Here, we evaluated the effects of estrogen deficiency in the immunoexpression of autophagy mediators in alveolar bone osteoclasts of ovariectomized rats. Twelve adult female rats were ovariectomized (OVX-group) or SHAM-operated (SHAM-group). After three weeks, the rats were euthanized and maxillary fragments containing alveolar bone of the first molars were processed for light microscopy or transmission electron microscopy (TEM). Paraffin-sections were subjected to the TRAP method (osteoclast marker) or to the immunohistochemical detections of beclin-1, LC3α, and p62 (autophagy mediators); araldite-sections were processed for TEM. The number of TRAP-positive osteoclasts and the number of immunolabeled-multinucleated cells (MNCs) along the alveolar bone surface of the first molar were computed. The number of TRAP-positive osteoclasts and the number of beclin-1-, LC3α- and p62-immunolabelled osteoclasts were significantly higher in OVX-group than the SHAM-group. MNCs were frequently located juxtaposed to Howship lacunae along the alveolar bone surface, indicating that these cells are osteoclasts. TEM revealed osteoclasts exhibiting autophagosomes. Our data indicate that autophagy plays an important role during estrogen deficiency-induced osteoclastogenesis. Thus, our results contribute to a better understanding on the role of autophagy on osteoclasts under estrogenic deficiency, and reinforce the idea that modulation of autophagy may be a useful tool to inhibit excessive oral bone resorption in post-menopausal women.

Effects of testosterone and 17β-estradiol on osteogenic and adipogenic differentiation capacity of human bone-derived mesenchymal stromal cells of postmenopausal women

Progressive bone loss is a predominant symptom of aging and osteoporosis. Therefore, the effects of sex steroids (i.e. testosterone and 17β-estradiol) on the differentiation capacity of human bone-derived mesenchymal stromal cells (hMSCs), as progenitors of osteoblasts and adipocytes, are of particular interest. The objectives of the present study were, thus, to elucidate whether bone-derived hMSCs of postmenopausal women produce aromatase (CYP19A1) and, whether they modulate their differentiation behaviour in response to testosterone and 17β-estradiol (E2), in relation to their steroid receptor expression. Supplementation of testosterone resulted in a considerable formation of E2 under osteogenic and adipogenic culture conditions, whereas E2 synthesis remained minimal in the cells cultured in basal medium. Concomitant with high aromatase expression and 17β-estradiol formation of the cells cultured in osteogenic medium supplemented with testosterone, a distinct promotion of late-stage osteogenesis was found, as shown by significant matrix mineralization and a notable increase in osteogenic markers. These effects were abrogated by the aromatase inhibitor anastrozole. Under adipogenic conditions, testosterone reduced the occurrence of lipid droplets and led to a decrease in PPARγ and AR expression, independent of anastrozole. Regardless of the culture conditions, ERα was detectable whilst ERβ was not. In conclusion, aromatase activity is limited to differentiated hMSCs and the resulting 17β-estradiol enhances late osteogenic differentiation stages via ERα. Adipogenic differentiation, on the other hand, is reduced by both sex steroids: testosterone via AR and 17β-estradiol.

Asymmetrical methyltransferase PRMT3 regulates human mesenchymal stem cell osteogenesis via miR-3648

Histone arginine methylation, which is catalyzed by protein arginine methyltransferases (PRMTs), plays a key regulatory role in various biological processes. Several PRMTs are involved in skeletal development; however, their role in the osteogenic differentiation of mesenchymal stem cells (MSCs) is not completely clear. In this study, we aimed to elucidate the function of PRMT3, a type-I PRMT that catalyzes the formation of ω-mono- or asymmetric dimethyl arginine, in MSCs osteogenesis. We found that PRMT3 promoted MSCs osteogenic commitment and bone remodeling. PRMT3 activated the expression of miR-3648 by enhancing histone H4 arginine 3 asymmetric dimethylation (H4R3me2a) levels at promoter region of the gene. Overexpression of miR-3648 rescued impaired osteogenesis in PRMT3-deficient cells. Moreover, administration of Prmt3 shRNA or a chemical inhibitor of PRMT3 (SGC707) caused an osteopenia phenotype in mice. These results indicate that PRMT3 is a potential therapeutic target for the treatment of bone regeneration and osteopenia disorders.

Maximizing your "nutrition minute": Bridging nutritional gaps across the life span

BACKGROUND AND PURPOSE

Poor diet quality has been associated with increased mortality and an increased risk of chronic disease. Given the shortfalls in the typical American diet and the prevalence of nutrition-related chronic disease among US adults, the need for nutrition education is paramount. Nurse practitioners (NPs) are well placed to provide basic nutrition counseling but often face challenges to making this a reality. In a typical office visit, the time available to discuss diet and nutrition can be as little as one minute or less.

METHODS

Nutritional issues of concern facing specific age and risk groups are reviewed. The "Nutrition Minute," a tool comprising 5 questions that enable NPs to identify patients at higher risk of nutritional shortfalls, has been developed.

CONCLUSIONS

Nutrition counseling includes discussion of not only fat, carbohydrate, and protein intake, but also micronutrient intake. Although a food-first approach to nutrition is preferred, nutritional shortfalls exist even in the best diets. Supplementation with a multivitamin is an effective approach to bridge many nutritional gaps and can be recommended for many patients with poor diet quality. In addition to shortfalls apparent from a patient's diet, nutritional needs change across the life span (e.g., women of childbearing age and older persons) and in those with certain medical conditions such as diabetes and obesity.

IMPLICATIONS FOR PRACTICE

Although NPs clearly have an important role to play in the nutrition management of many patients, they should work in collaboration with registered dietitians wherever possible, especially for medical nutrition therapy in those patients needing specialist counseling, such as those with diabetes, obesity, cardiovascular disease, and renal disease.

Osteoclasts-Key Players in Skeletal Health and Disease

The differentiation of osteoclasts (OCs) from early myeloid progenitors is a tightly regulated process that is modulated by a variety of mediators present in the bone microenvironment. Once generated, the function of mature OCs depends on cytoskeletal features controlled by an αvβ3-containing complex at the bone-apposed membrane and the secretion of protons and acid-protease cathepsin K. OCs also have important interactions with other cells in the bone microenvironment, including osteoblasts and immune cells. Dysregulation of OC differentiation and/or function can cause bone pathology. In fact, many components of OC differentiation and activation have been targeted therapeutically with great success. However, questions remain about the identity and plasticity of OC precursors and the interplay between essential networks that control OC fate. In this review, we summarize the key principles of OC biology and highlight recently uncovered mechanisms regulating OC development and function in homeostatic and disease states.

Osteoporosis in Men

The prevalence of osteoporosis is estimated to be 18% in men, but 30% of all fractures occur in men. With age, men experience a gradual decline in testosterone production and bone density. The rate of trabecular bone loss in the lumbar spine in men over age 50 can be double the rate of loss in men under age 50. Endogenous testosterone, estradiol, and their metabolites play a role in maintaining bone health, but their specific effects on bone turnover have been difficult to elucidate. Recently, large cohort studies have provided more detailed information confirming estrogen’s associations and further characterizing the effect of endogenous testosterone and its metabolites on bone mineral density and fractures. Very few clinical trials have assessed the impact of testosterone replacement therapy (TRT) on bone density and fractures in men. The few studies that have been conducted are generally small and not robust enough to show the true treatment effect of TRT and adequately determine its safety. In the absence of data on patient outcomes, it is important for pharmacists to understand the impact of drug therapy on biomarkers and surrogate markers of disease for optimal pharmacotherapy selection and monitoring.

The reproductive-cell cycle theory of aging: an update

The Reproductive-Cell Cycle Theory posits that the hormones that regulate reproduction act in an antagonistic pleiotrophic manner to control aging via cell cycle signaling; promoting growth and development early in life in order to achieve reproduction, but later in life, in a futile attempt to maintain reproduction, become dysregulated and drive senescence. Since reproduction is the most important function of an organism from the perspective of the survival of the species, if reproductive-cell cycle signaling factors determine the rate of growth, determine the rate of development, determine the rate of reproduction, and determine the rate of senescence, then by definition they determine the rate of aging and thus lifespan. The theory is able to explain: 1) the simultaneous regulation of the rate of aging and reproduction as evidenced by the fact that environmental conditions and experimental interventions known to extend longevity are associated with decreased reproductive-cell cycle signaling factors, thereby slowing aging and preserving fertility in a hostile reproductive environment; 2) two phenomena that are closely related to species lifespan-the rate of growth and development and the ultimate size of the animal; 3). the apparent paradox that size is directly proportional to lifespan and inversely proportional to fertility between species but vice versa within a species; 4). how differing rates of reproduction between species is associated with differences in their lifespan; 5). why we develop aging-related diseases; and 6). an evolutionarily credible reason for why and how aging occurs-these hormones act in an antagonistic pleiotrophic manner via cell cycle signaling; promoting growth and development early in life in order to achieve reproduction, but later in life, in a futile attempt to maintain reproduction, become dysregulated and drive senescence (dyosis). In essence, the Reproductive-Cell Cycle Theory can explain aging in all sexually reproductive life forms.