Sclerostin activity plays a key role in the negative effect of glucocorticoid signaling on osteoblast function in mice

Molecular mechanisms and treatment strategies for estrogen deficiency-related and glucocorticoid-induced osteoporosis: a comprehensive review

Osteoporosis, a debilitating condition characterized by reduced bone mass and increased fracture risk, is notably influenced by estrogen deficiency and glucocorticoid treatment. This comprehensive review elucidates the molecular mechanisms underpinning estrogen deficiency-related osteoporosis (EDOP) and glucocorticoid-induced osteoporosis (GIOP). The role of estrogen in bone metabolism is critically examined, highlighting its regulatory effects on bone turnover and formation through various signaling pathways. Conversely, this review explores how glucocorticoids disrupt bone homeostasis, focusing on their impact on osteoclast and osteoblast function and the subsequent alteration of bone remodeling processes. The pathogenesis of both conditions is intertwined, with estrogen receptor signaling pathways and the role of inflammatory cytokines being pivotal in driving bone loss. A detailed analysis of pathogenetic and risk factors associated with EDOP and GIOP is presented, including lifestyle and genetic factors contributing to disease progression. Modern therapeutic approaches emphasize pharmacologic, non-pharmacologic, and herbal treatments for managing EDOP and GIOP. In summary, current therapeutic strategies highlight the efficacy and the safety of various interventions. This review concludes with future directions for research, suggesting a need for novel treatment modalities and a deeper understanding of the underlying mechanisms of osteoporosis. By addressing the multifaceted nature of EDOP and GIOP, this work aims to provide insights into developing targeted therapeutic strategies and improving patient outcomes in osteoporosis management.

Impact of glucocorticoids on osteocytes and on the lacuno-canalicular system of maxillary and mandibular alveolar bone

In long bones, glucocorticoids are known to cause a decrease in bone formation and an increase in bone resorption, leading to a condition of osteoporosis also during growth. However, there are few studies on the effect of glucocorticoids on alveolar bone. The aim of the present study was to evaluate the impact of chronic administration of glucocorticoids on osteocytes and the lacuno-canalicular system of maxillary and mandibular alveolar bone in growing rats. Male Wistar rats were administered intramuscular dexamethasone (7 mg/kg b.w.) or saline solution once a week for 5 weeks. After euthanasia, mandibles and upper maxillae were resected and processed for micro-computed tomography, histological, and immunohistochemical evaluation. Glucocorticoids induced morphological changes in the lacuno-canalicular system and apoptosis of alveolar bone osteocytes and had no effect on SOST/sclerostin osteocyte expression. Our findings suggest that the deleterious effect of glucocorticoids on alveolar bone is associated with osteocyte apoptosis and lacuno-canalicular system changes, whereas Wnt/β catenin pathway regulation in osteocytes appears to play no significant role in the pathogenesis of glucocorticoid-induced bone loss.

Bone Effects of Anti-Cancer Treatments in 2024

Considerable progress has been made in the management of cancer patients in the last decade with the arrival of anti-cancer immunotherapies (immune checkpoint inhibitors) and targeted therapies. As a result, a broad spectrum of cancers, not just hormone-sensitive ones, have seen several patients achieve profound and prolonged remissions, or even cures. The management of medium- and long-term side-effects of treatment and quality of life of patients are essential considerations. This is especially true for bone, as bone fragility can lead to increased fractures and loss of autonomy, ultimately reducing the possibility of resuming physical activity. Physical activity is essential for lasting oncological remission and prevention of fatigue. While the issue of hormone therapies and their association with breast cancer has been recognized for some time, the situation is relatively new with regards to targeted therapies and immunotherapies. This is particularly challenging given the wide range of available targeted therapies and their application to numerous cancer types. This article provides a comprehensive review of the bone effects of the main anti-cancer therapies currently in use. The review goes beyond glucocorticoids and hormone therapies and discusses for each drug category what is known regarding cellular effects, BMD effects, and fracture incidence.

Enhanced therapeutic efficacy of Eupolyphaga sinensis Walker in females through sex-specific metabolomic-pharmacodynamic divergence

Eupolyphaga sinensis Walker (ESW), a medicinal insect used in traditional Chinese medicine, is renowned for its effects on blood circulation, stasis resolution, and bone and tendon healing. The underlying reasons for the clinical preference for female ESW remain unclear. Previous investigations were limited in scope, focusing narrowly on female specimens, large-molecule compounds, and single pharmacological effect. This study systematically compared female and male ESW in terms of composition and therapeutic efficacy. Metabolomics identified 31 compound types in both female and male ESW, including lipids, amino acids, and fatty acids. Female ESW exhibited significantly higher levels of 8 bioactive compounds, 15 small peptides, and 13 prostaglandins compared to male ESW, which contribute to immunity enhancement, antithrombotic effects, and improved bone metabolism. These differences may underlie the superior medicinal efficacy of female ESW. In the thrombosis model, ESW can cause vasodilation, reduce blood cell aggregation and thrombosis rate of mice tails. It also improved t-PA levels, prolonged APTT, and enhanced hepatic SOD activity, with female ESW showing stronger effects on MDA and D2D levels, indicating its stronger ability to protect cells from damage and fibrinolytic effect. In the osteoporosis model, ESW increased femur length, liver, and thymus indices while regulating serum BALP and Mg levels. Female ESW notably reduced TRACP-5b, OT/BGP, P, and Cu to normal levels, indicating its stronger ability to improved bone metabolism, corrected disturbances in calcium-phosphorus metabolism, and regulated serum inorganic elements. Overall, female ESW exhibited a greater abundance of bioactive components and demonstrated superior anti-thrombotic and anti-osteoporotic effects. These findings highlight the superior therapeutic effects of female ESW due to its enriched bioactive components, supporting its clinical preference while underscoring the potential of male ESW for uilization of resource.

Decreasing miR-433-3p Activity in the Osteoblast Lineage Blunts Glucocorticoid-mediated Bone Loss

Glucocorticoid excess causes bone loss due to decreased bone formation and increased bone resorption; miR-433-3p is a microRNA (miRNA) that negatively regulates bone formation in male mice by targeting Runx2 as well as RNAs involved in Wnt, protein kinase A, and endogenous glucocorticoid signaling. To examine the impact of miR-433-3p on glucocorticoid-mediated bone loss, transgenic mice expressing a miR-433-3p tough decoy inhibitor in the osteoblast lineage were administered prednisolone via slow-release pellets. Bone loss was greater in control mice treated with prednisolone compared with miR-433-3p tough decoy mice due to higher osteoclast activity in the controls. In whole femurs, Rankl was significantly higher in prednisolone-treated controls compared with miR-433-3p tough decoy mice. Surprisingly, negative regulators of Wnt signaling Sost and Dkk1 were higher in miR-433-3p tough decoy mice and were unaffected by prednisolone. Luciferase- 3'-untranslated region reporter assays demonstrated that Sost is a novel miR-433-3p target, whereas Dkk1 is a previously validated miR-433-3p target. miR-433-3p levels are lower in matrix-synthesizing osteoblasts than in more osteocytic cells; thus the impact of miR-433-3p on the osteoblast lineage may be dependent on cell context: it is a negative regulator in matrix-depositing osteoblasts by targeting RNAs important for differentiation and function but a positive regulator in osteocytes, due to its ability to target prominently expressed negative regulators of Wnt signaling, Sost and Dkk1. The mechanisms by which miR-433-3p indirectly regulates glucocorticoid-mediated osteoclastogenesis remain unknown. However, we speculate that this regulation may be mediated by miR-433-3p activity in osteocytes, which play an important role in controlling osteoclastogenesis.

Prenatal dexamethasone exposure reduces osteoprogenitor proliferation in mice via histone modifications at the Mkp-1 gene locus

Prenatal dexamethasone exposure (PDE) has long-term consequences in bone development, though the underlying mechanisms remain unclear. Our results show that PDE offspring exhibit reduced bone mass, fewer osteoblasts and diminished osteoprogenitors proliferation. Further analyses show that PDE increases MKP-1 expression, while decreasing H3 lysine 9 dimethylation (H3K9me2) and H3 lysine 27 trimethylation (H3K27me3) at the Mkp-1 gene locus. Mechanistically, dexamethasone suppresses osteoprogenitors proliferation by upregulating MKP-1 expression, notably through the inhibition of H3K9me2 and H3K27me3 modifications, which promote demethylation and transcriptional activation of the Mkp-1 gene. Importantly, restoring histone methylation balance with PFI-90 or GSK-J4 treatment blocks the inhibitory effects of PDE on MAPK signaling in osteoprogenitors, and mitigates the detrimental impact of PDE on osteoprogenitor proliferation and bone development in the offspring. This study provides new insights into the epigenetic mechanism by which PDE disrupts long-term programming of fetal osteoprogenitor proliferation, ultimately impairing long bone growth in offspring.

Treatment of glucocorticoid-induced osteoporosis with concurrent denosumab and romosozumab: a case report

Osteoporosis is a metabolic bone disorder for which treatment options include antiresorptive therapies (e.g., bisphosphonates, denosumab); anabolics (e.g., teriparatide, abaloparatide); and dual mechanisms (e.g., romosozumab). Management of osteoporosis with concurrent antiresorptive and anabolic agents may be superior to monotherapy, as demonstrated in the DATA trial with the combination of denosumab and teriparatide. However, there is limited experience with the combination of denosumab and romosozumab, which may be an alternative antiresorptive/anabolic regimen for individuals who are not candidates for PTH receptor agonists. In this case, we present a young man with glucocorticoid-induced osteoporosis who could not tolerate a daily injectable anabolic and who experienced improvement in bone mineral density with concurrent denosumab and off-label romosozumab administration.

The Relationship between Sclerostin and Kidney Transplantation Mineral Bone Disorders: A Molecule of Controversies

Kidney transplantation is the most effective treatment option for most patients with end-stage kidney disease due to reduced mortality, decreased cardiovascular events and increased quality of life compared to patients treated with dialysis. However, kidney transplantation is not devoid of both acute and chronic complications including mineral bone disorders (MBD) which are already present in patients with chronic kidney disease (CKD) before kidney transplantation. The natural history of MBD after kidney transplantation is variable and new markers are needed to define MBD after kidney transplantation. One of these promising molecules is sclerostin. The main action of sclerostin is to inhibit bone formation and mineralization by blocking osteoblast differentiation and function. In kidney transplant recipients (KTRs), various studies have shown that sclerostin is associated with graft function, bone parameters, vascular calcification, and arterial stiffness although non-uniformly. Furthermore, data for inhibition of sclerostin with monoclonal antibody romosozumab for treatment of osteoporosis is available for general population but not in KTRs which osteoporosis is highly prevalent. In this narrative review, we have summarized the studies investigating the change of sclerostin before and after kidney transplantation, the relationship between sclerostin and laboratory parameters, bone metabolism and vascular calcification in the context of kidney transplantation. We also pointed out the uncertainties, explained the causes of divergent findings and suggest further potential study topics regarding sclerostin in kidney transplantation.

Association of serum sclerostin levels with marrow adiposity in postmenopausal women with glucocorticoid-induced osteoporosis

BACKGROUND

Glucocorticoids and sclerostin act as inhibitors of the Wnt signaling pathway, thereby hindering bone formation. Given the pathway's intricate association with mesenchymal stem cells, the hypothesis suggests that heightened sclerostin levels may be intricately linked to an augmentation in marrow adiposity induced by glucocorticoids. This study endeavored to delve into the nuanced relationship between circulating sclerostin and bone marrow adipose tissue in postmenopausal women grappling with glucocorticoid-induced osteoporosis (GIO).

METHODS

In this cross-sectional study, 103 patients with autoimmune-associated diseases underwent glucocorticoid treatment, boasting an average age of 61.3 years (standard deviation 7.1 years). The investigation encompassed a thorough assessment, incorporating medical history, anthropometric data, biochemical analysis, and dual-energy X-ray absorptiometry measurements of lumbar and femoral bone mineral density (BMD). Osteoporosis criteria were established at a T-score of -2.5 or lower. Additionally, MR spectroscopy quantified the vertebral marrow fat fraction.

RESULTS

BMD at the femoral neck, total hip, and lumbar spine showcased an inverse correlation with marrow fat fraction (r = -0.511 to - 0.647, P < 0.001). Serum sclerostin levels exhibited a positive correlation with BMD at various skeletal sites (r = 0.476 to 0.589, P < 0.001). A noteworthy correlation emerged between circulating sclerostin and marrow fat fraction at the lumbar spine (r = -0.731, 95% CI, -0.810 to -0.627, P < 0.001). Multivariate analysis brought to light that vertebral marrow fat fraction significantly contributed to sclerostin serum concentrations (standardized regression coefficient ß = 0.462, P < 0.001). Even after adjusting for age, body mass index, physical activity, renal function, BMD, and the duration and doses of glucocorticoid treatment, serum sclerostin levels maintained a significant correlation with marrow fat fraction.

CONCLUSIONS

Circulating sclerostin levels exhibited a noteworthy association with marrow adiposity in postmenopausal women grappling with GIO.

Apocynin exerts cytoprotective effects on dexamethasone-induced osteoblasts by inhibiting oxidative stress through the Nrf2 signalling pathway

Steroid-induced femoral head necrosis (SIFHN) is a serious clinical complication that is caused by prolonged or excessive use of glucocorticoids (GCs). Osteoblast apoptosis and osteogenic differentiation dysfunction caused by GC-induced oxidative stress and mitochondrial impairment are strongly implicated in SIFHN. Apocynin (APO) is a kind of acetophenone extracted from an herb. In recent years, APO has received much attention for its antiapoptotic and antioxidant properties. This study aimed to investigate whether APO could protect against SIFHN and explore the mechanism. In our study, low-dose APO had no toxic effects on osteoblasts and restored dexamethasone (Dex)-treated osteoblasts by improving survival, inhibiting OS and restoring mitochondrial dysfunction. Mechanistically, APO alleviated Dex-induced osteoblast injury by activating the Nrf2 pathway, and the use of ML385 to block Nrf2 significantly eliminated the protective effect of APO. In addition, APO could reduce the formation of empty lacunae, restore bone mass and promote the expression of Nrf2 in SIFHN rats. In conclusion, APO protects osteoblasts from Dex-induced oxidative stress and mitochondrial dysfunction through activation of the Nrf2 pathway and may be a beneficial drug for the treatment of SIFHN.

Chronic Kidney Disease-Mineral Bone Disease biomarkers in kidney transplant patients

Background:

Chronic Kidney Disease associated with Mineral Bone Disease (CKD-MBD) is frequent in kidney transplant patients. Post-transplantation bone disease is complex, especially in patients with pre-existing metabolic bone disorders that are further affected by immunosuppressive medications and changes in renal allograft function. Main biochemical abnormalities of mineral metabolism in kidney transplantation (KTx) include hypophosphatemia, hyperparathyroidism (HPTH), insufficiency or deficiency of vitamin D, and hypercalcemia.

Objective:

This review aimed to summarize the pathophysiology and main biomarkers of CKD-MBD in KTx.

Methods:

A comprehensive and non-systematic search in PubMed was independently made with an emphasis on biomarkers in mineral bone disease in KTx.

Results:

CKD-MBD can be associated with numerous factors including secondary HPTH, metabolic dysregulations before KTx, and glucocorticoids therapy in post-transplant subjects. Fibroblast growth factor 23 (FGF23) reaches normal levels after KTx with good allograft function, while calcium, vitamin D and phosphorus, ultimately, result in hypercalcemia, persistent vitamin D insufficiency, and hypophosphatemia respectively. As for PTH levels, there is an initial tendency of a significant decrease, followed by a raise due to secondary or tertiary HPTH. In regard to sclerostin levels, there is no consensus in the literature.

Conclusion:

KTx patients should be continuously evaluated for mineral homeostasis and bone status, both cases with successful kidney transplantation and those with reduced functionality. Additional research on CKD-MBD pathophysiology, diagnosis, and management is essential to guarantee long-term graft function, better prognosis, good quality of life, and reduced mortality for KTx patients.

Benzofuran pyran hybrid prevents glucocorticoid induced osteoporosis in mice via modulation of canonical Wnt/β-catenin signaling

Glucocorticoid induced osteoporosis (GIOP) is the second most leading cause of osteoporosis. We have identified a compound, a benzofuran pyran hybrid compound 4e that has osteogenic potential and we wanted to assess its efficacy in GIOP in male mice. We assessed the effect of dexamethasone and compound 4e on primary osteoblasts using various cell based and immunofluorescence assays. For in vivo studies we administered methylprednisolone and compound 4e as a prophylactic measure in male Balb/c mice for 28 days and then evaluated the effect on bone microarchitecture by microCT, bone formation by histology along with clinically relevant bone markers. Compound 4e preserved osteoblast differentiation as evident by higher ALP positive cells and mineralization in compound treated groups. Compound 4e also increased the expression of osteogenic genes. This compound guarded β-catenin expression both in vitro and in vivo as confirmed by western blot and immunofluorescence assays. This led to the preservation of bone microarchitecture and cortical thickness at 2.5 mg kg⁻¹ and 5 mg kg⁻¹ doses. Further compound 4e enhanced bone formation rate and regulated osteocyte death. The osteogenic potential of compound 4e was reflected by an increased level of serum marker osteocalcin and decreased levels of SOST and CTX-I. Overall, Compound 4e is able to overcome the catabolic effect of dexamethasone on bone by targeting the canonical WNT/β-catenin signaling as evidenced by both in vitro and in vivo studies.

Trabecular bone score and sclerostin concentrations in patients with primary adrenal insufficiency

BACKGROUND

Patients with primary adrenal insufficiency need lifelong replacement therapy with glucocorticoids and mineralocorticoids, which may influence their bone quality.

AIM

The aim of the study was to evaluate densitometry parameters, trabecular bone score and sclerostin concentrations in patients with primary adrenal insufficiency in comparison to control group.

MATERIALS AND METHODS

We included 29 patients (62% females) with diagnose of autoimmune primary adrenal insufficiency (mean age 49.7 ± 11.7 years, mean duration of the disease 13.2± 13.6 years) and 33 healthy subjects (adjusted with age, sex and body mass index). Bone mineral density at the femoral neck, lumbar spine, total body and trabecular bone score were evaluated. Serum sclerostin concentrations were measured.

RESULTS

There were no significant differences in densitometry parameters (T-score, Z-score, bone mineral density in all locations) as well as in trabecular bone score in patients with adrenal insufficiency in comparison to control group. Mean serum sclerostin concentration was significantly higher in patients with adrenal insufficiency than in control group (44.7 ± 23.5 vs 30.7 ± 10.4 pmol/l, p=0.006). There was a negative correlation between trabecular bone score and the duration of adrenal insufficiency and age, also a negative correlation between femoral neck and total densitometry parameters and 24-hour urine cortisol as a marker of hydrocortisone daily dose in patients with adrenal insufficiency.

CONCLUSIONS

The bone status in patients with primary adrenal insufficiency was not impaired in comparison to control group, while sclerostin concentration was higher. The duration of the disease and higher hydrocortisone doses may affect negatively bone status.

Effect of adrenocorticotropic hormone infusion on circulating sclerostin levels

Glucocorticoid use is the most common cause of secondary osteoporosis. Poor skeletal health related to glucocorticoid use is thought to involve inhibition of the Wnt/β-catenin signaling pathway, a key pathway in osteoblastogenesis. Sclerostin, a peptide produced primarily by osteocytes, is an antagonist of the Wnt/β-catenin signaling pathway, raising the possibility that sclerostin is involved in glucocorticoids' adverse effects on bone. The aim of this study was to determine whether an acute infusion of cosyntropin (i.e. ACTH(1-24)), which increases endogenous cortisol, increases serum sclerostin levels as compared to a placebo infusion. This study was performed using blood samples obtained from a previously published, double-blind, placebo-controlled, randomized, cross-over study among healthy men and women who received infusions of placebo or cosyntropin after being supine and fasted overnight (ClinicalTrials.gov NCT02339506). A total of 17 participants were analyzed. There was a strong correlation (R2 = 0.65, P < 0.0001) between the two baseline sclerostin measurements measured at the start of each visit, and men had a significantly higher average baseline sclerostin compared to women. As anticipated, cosyntropin significantly increased serum cortisol levels, whereas cortisol levels fell during placebo infusion, consistent with the diurnal variation in cortisol. There was no significant effect of cosyntropin as compared to placebo infusions on serum sclerostin over 6-24 h (P = 0.10). In conclusion, this randomized, placebo-controlled study was unable to detect a significant effect of a cosyntropin infusion on serum sclerostin levels in healthy men and women.

Osteoblastic glucocorticoid signaling exacerbates high-fat-diet- induced bone loss and obesity

Chronic high-fat diet (HFD) consumption not only promotes obesity and insulin resistance, but also causes bone loss through mechanisms that are not well understood. Here, we fed wild-type CD-1 mice either chow or a HFD (43% of energy from fat) for 18 weeks; HFD-fed mice exhibited decreased trabecular volume (-28%) and cortical thickness (-14%) compared to chow-fed mice. In HFD-fed mice, bone loss was due to reduced bone formation and mineral apposition, without obvious effects on bone resorption. HFD feeding also increased skeletal expression of sclerostin and caused deterioration of the osteocyte lacunocanalicular network (LCN). In mice fed HFD, skeletal glucocorticoid signaling was activated relative to chow-fed mice, independent of serum corticosterone concentrations. We therefore examined whether skeletal glucocorticoid signaling was necessary for HFD-induced bone loss, using transgenic mice lacking glucocorticoid signaling in osteoblasts and osteocytes (HSD2^OB/OCY-tg mice). In HSD2^OB/OCY-tg mice, bone formation and mineral apposition rates were not suppressed by HFD, and bone loss was significantly attenuated. Interestingly, in HSD2^OB/OCY-tg mice fed HFD, both Wnt signaling (less sclerostin induction, increased β-catenin expression) and glucose uptake were significantly increased, relative to diet- and genotype-matched controls. The osteocyte LCN remained intact in HFD-fed HSD2^OB/OCY-tg mice. When fed a HFD, HSD2^OB/OCY-tg mice also increased their energy expenditure and were protected against obesity, insulin resistance, and dyslipidemia. Therefore, glucocorticoid signaling in osteoblasts and osteocytes contributes to the suppression of bone formation in HFD-fed mice. Skeletal glucocorticoid signaling is also an important determinant of glucose uptake in bone, which influences the whole-body metabolic response to HFD.

MicroRNA-29a in Osteoblasts Represses High-Fat Diet-Mediated Osteoporosis and Body Adiposis through Targeting Leptin

Skeletal tissue involves systemic adipose tissue metabolism and energy expenditure. MicroRNA signaling controls high-fat diet (HFD)-induced bone and fat homeostasis dysregulation remains uncertain. This study revealed that transgenic overexpression of miR-29a under control of osteocalcin promoter in osteoblasts (miR-29aTg) attenuated HFD-mediated body overweight, hyperglycemia, and hypercholesterolemia. HFD-fed miR-29aTg mice showed less bone mass loss, fatty marrow, and visceral fat mass together with increased subscapular brown fat mass than HFD-fed wild-type mice. HFD-induced O₂ underconsumption, respiratory quotient repression, and heat underproduction were attenuated in miR-29aTg mice. In vitro, miR-29a overexpression repressed transcriptomic landscapes of the adipocytokine signaling pathway, fatty acid metabolism, and lipid transport, etc., of bone marrow mesenchymal progenitor cells. Forced miR-29a expression promoted osteogenic differentiation but inhibited adipocyte formation. miR-29a signaling promoted brown/beige adipocyte markers Ucp-1, Pgc-1α, P2rx5, and Pat2 expression and inhibited white adipocyte markers Tcf21 and Hoxc9 expression. The microRNA also reduced peroxisome formation and leptin expression during adipocyte formation and downregulated HFD-induced leptin expression in bone tissue. Taken together, miR-29a controlled leptin signaling and brown/beige adipocyte formation of osteogenic progenitor cells to preserve bone anabolism, which reversed HFD-induced energy underutilization and visceral fat overproduction. This study sheds light on a new molecular mechanism by which bone integrity counteracts HFD-induced whole-body fat overproduction.

Dietary supplementary glutamine and L-carnitine enhanced the anti-cold stress of Arbor Acres broilers

Newborn poultry in cold regions often suffer from cold stress, causing a series of changes in their physiology and metabolism, leading to slow growth and decreased production performance. However, a single anti-stress substance cannot completely or maximally eliminate or alleviate the various effects of cold stress on animals. Therefore, the effects of the supplemented glutamine and L-carnitine on broilers under low temperature were evaluated in this study. Broilers were randomly allocated into 16 groups which were respectively fed with different levels of glutamine and L-carnitine according to the L16 (45) orthogonal experimental design for 3 weeks (the first week is the adaptive feeding period; the second and third weeks are the cold exposure period). Growth performance was recorded, and blood samples were collected during cold exposure. The results showed the supplementation had altered the plasma parameters, growth performance and cold-induced oxidative stress. The increase of corticosterone and suppression of thyroid hormone was ameliorated. Supplemented groups had lower daily feed intake and feed-to-gain ratio, higher daily weight gain and better relative weights of immune organs. Plasma glucose, total protein, blood urea nitrogen and alkaline phosphatase changed as well. Oxidative stress was mollified due to the improved activities of superoxide dismutase and glutathione peroxidase, heightened total antioxidant capacity and stable malondialdehyde. Dietary glutamine and L-carnitine improve the growth performance, nutritional status and cold stress response of broilers at low temperature, and their interaction occurred.

Cellular senescence mediates the detrimental effect of prenatal dexamethasone exposure on postnatal long bone growth in mouse offspring

Background

Prenatal dexamethasone exposure (PDE) induces low birth weight and retardation of fetal bone development which are associated with lower peak bone mass in adult offspring. Here we evaluated whether and how PDE affects postnatal long bone growth in mouse offspring.

Methods

Pregnant mice were injected subcutaneously with dexamethasone (1.2 mg/kg/day) every morning from gestational days (GD) 12–14. Femurs and tibias of 2-, 4-, 6-, and 12-week-old female offspring were harvested for histological, immunofluorescence, flow cytometric analysis, or microcomputed tomography (μCT) measurement.

Results

PDE leads to impaired bone remodeling as well as decreased bone mass in the long bone of female mouse offspring. During postnatal bone growth, significant decrease of CD45⁻CD29⁺CD105⁺Sca-1⁺ bone marrow mesenchymal stem cells (BMSCs) and CD45⁻Nestin⁺ cells, loss of type H vessels, and increment of cellular senescence were found in metaphysis of long bone in mouse offspring after PDE. We further show that eliminating the excessive senescent cells with dasatinib (5 mg/kg/day) and quercetin (50 mg/kg/day) during GD 12–14 rescues the above toxic effect of PDE on the postnatal long bone growth in female mouse offspring.

Conclusion

Cellular senescence mediates the toxic effect of PDE on postnatal long bone growth in mouse offspring, and inhibition of cellular senescence may be proposed for treating the retardation of bone growth caused by PDE.

The Role of Sclerostin in Bone and Ectopic Calcification

Sclerostin, a 22-kDa glycoprotein that is mainly secreted by the osteocytes, is a soluble inhibitor of canonical Wnt signaling. Therefore, when present at increased concentrations, it leads to an increased bone resorption and decreased bone formation. Serum sclerostin levels are known to be increased in the elderly and in patients with chronic kidney disease. In these patient populations, there is a high incidence of ectopic cardiovascular calcification. These calcifications are strongly associated with cardiovascular morbidity and mortality. Although data are still controversial, it is likely that there is a link between ectopic calcification and serum sclerostin levels. The main question, however, remains whether sclerostin exerts either a protective or deleterious role in the ectopic calcification process.

Blocking glucocorticoid signaling in osteoblasts and osteocytes prevents mechanical unloading-induced cortical bone loss

Bone loss has been supposed to be the greatest damage to the health of astronauts. It is generally believed that the mechanical unloading induced by microgravity is the main cause of bone loss. However, besides mechanical unloading, many evidences from animal models and spaceflight missions indicate that microgravity conditions can cause some stress reactions and elevated endogenous glucocorticoid (GC) levels. High levels of GCs can lead to bone loss. This study aimed to investigate whether elevated GC levels are involved in hindlimb unloading (HLU)-induced bone loss in mice. Col2.3-11β-hydroxysteroid dehydrogenase type 2 (Col2.3-11β-HSD2) transgenic mice which are characterized by specific blocking GC signaling in mature osteoblasts and osteocytes were used. Male 14-week-old Col2.3-11β-HSD2 transgenic mice and wild type littermates were tail-suspended or kept under ambulatory conditions. At the endpoint, the tibias were examined by micro-computed tomography and histomorphometry, and bone turnover was analyzed by serum biochemistry, histochemistry staining, immunohistochemistry, and real-time PCR. Mice exposed to unloading occurred a significant increase in serum GC concentrations. Compared with non-unloaded controls, HLU led to a severe damage in cortical bone microstructure and bone strength of the tibia in wild type mice but not transgenic littermates. Osteoblast activity and bone formation were inhibited, whereas osteoclast activity and bone resorption were promoted in the tibial cortical bone of wild type mice following HLU, features absented in transgenic mice. Furthermore, HLU resulted in a significant increase in the number of sclerostin-producing and receptor activator of nuclear factor-κ B ligand (RANKL)-positive osteocytes, and apoptotic osteoblasts and osteocytes in wild type mice of unloading but not in unloaded transgenic mice. In conclusion, cortical bone loss during HLU is mediated through enhancing GC signaling in osteoblasts and osteocytes and subsequently restraining bone formation and activating bone resorption. It suggests that elevated GC levels play an important role in cortical bone loss in response to mechanical unloading.

Unraveling the osteocyte in CKD-MBD post-renal transplantation

Changes in indices of mineral metabolism, bone protein expression, and bone turnover were assessed between pre- and post-renal transplant bone biopsies obtained 12 months apart. Circulating sclerostin and fibroblast growth factor 23 (FGF-23) levels decreased, and a low bone turnover state was highly prevalent on follow-up. In contrast, bone sclerostin expression increased, whereas FGF-23 bone expression was unchanged/decreased. These findings underscore the limitations of circulating biomarkers and the critical role of bone biopsy to understand osteocyte biology in chronic kidney disease-mineral bone disorder.

Anabolics in the management of glucocorticoid-induced osteoporosis: an evidence-based review of long-term safety, efficacy and place in therapy

Introduction

Glucocorticoid-induced osteoporosis is an underrecognized complication of chronic glucocorticoid therapy characterized by a decrease in new bone formation. Anabolic therapies, such as teriparatide, a recombinant human parathyroid hormone, combat the disease by promoting new bone growth.

Aims

This article outlines the pathophysiology of glucocorticoid-induced osteoporosis and details the evidence of efficacy, safety, and patterns of use of teriparatide and other future anabolic therapies.

Evidence review

In multiple clinical trials, teriparatide has been shown to significantly increase lumbar spine bone mineral density (BMD) in patients with glucocorticoid-induced osteoporosis when compared with placebo, alendronate, and risedronate. When compared with alendronate, significantly fewer vertebral fractures were noted in the teriparatide group. Adverse effects noted in clinical trials include nausea, insomnia, flushing, myalgias, and mild hypercalcemia/hyperuricemia. Early studies in rats noted an increased incidence of osteosarcoma; however, an increased rate beyond levels seen in general populations has not been noted in human studies or with long-term pharmacovigilance. Abaloparatide and romosozumab are newer anabolic therapies that have shown some benefit in postmenopausal osteoporosis but have not yet been studied in the chronic glucocorticoid population.

Place in therapy

Major specialty organizations continue to recommend bisphosphonates as first-line therapy in glucocorticoid-induced osteoporosis due to the proven benefit and relative affordability. However, the use of anabolics shows promise to improve outcomes by increasing BMD and reducing fracture-associated morbidity and mortality and has a role for selected populations at high fracture risk.

Regulation of sclerostin in glucocorticoid-induced osteoporosis (GIO) in mice and humans

Glucocorticoids (GC) are used for the treatment of inflammatory diseases, including various forms of arthritis. However, their use is limited, amongst others, by adverse effects on bone. The Wnt and bone formation inhibitor sclerostin was recently implicated in the pathogenesis of GC-induced osteoporosis. However, data are ambiguous. The aim of this study was to assess the regulation of sclerostin by GC using several mouse models with high GC levels and two independent cohorts of patients treated with GC. Male 24-week-old C57BL/6 and 18-week-old DBA/1 mice exposed to GC and 12-week-old mice with endogenous hypercortisolism displayed reduced bone formation as indicated by reduced levels of P1NP and increased serum sclerostin levels. The expression of sclerostin in femoral bone tissue and GC-treated bone marrow stromal cells, however, was not consistently altered. In contrast, GC dose- and time-dependently suppressed sclerostin at mRNA and protein levels in human mesenchymal stromal cells, and this effect was GC receptor dependent. In line with the human cell culture data, patients with rheumatoid arthritis (RA, n = 101) and polymyalgia rheumatica (PMR, n = 21) who were exposed to GC had lower serum levels of sclerostin than healthy age- and sex-matched controls (-40%, P < 0.01 and -26.5%, P < 0.001, respectively). In summary, sclerostin appears to be differentially regulated by GC in mice and humans as it is suppressed by GCs in humans but is not consistently altered in mice. Further studies are required to delineate the differences between GC regulation of sclerostin in mice and humans and assess whether sclerostin mediates GC-induced osteoporosis in humans.

Glucose dependent miR-451a expression contributes to parathyroid hormone mediated osteoblast differentiation

Parathyroid hormone (PTH; amino acid 1-34, known as teriparatide) has reported promoting differentiation and glucose uptake in osteoblasts. However, how PTH regulates glucose metabolism to facilitate osteoblast differentiation is not understood. Here, we report that PTH promotes glucose dependent miR-451a expression which stimulates osteoblast differentiation. In addition to glucose uptake, PTH suppresses AMPK phosphorylation via PI3K-mTOR-AKT axis thereby preventing phosphorylation and inactivation of octamer-binding transcription factor 1 (OCT-1) which has been reported to act on the promoter region of miR-451a. Modulation of AMPK activity controls miR-451a levels in differentiating osteoblasts. Moreover, pharmacological inhibition of PI3K-mTOR-AKT axis suppressed miR-451a via increased AMPK activity. We report that this glucose regulated miRNA is an anabolic target and transfection of miR-451a mimic induces osteoblast differentiation and mineralization in vitro. These actions were mediated through the suppression of Odd-skipped related 1 (Osr1) and activation of Runx2 transcription. When injected in vivo, the miR-451a mimic significantly increased osteoblastogenesis, mineralization, reversed ovariectomy induced bone loss and improved bone strength. Together, these findings suggest that enhanced osteoblast differentiation associated with bone formation in case of PTH therapy is also a consequence of elevated miR-451a levels via glucose regulation. Consequently, this miRNA has the potential to be a therapeutic target for conditions of bone loss.

Active cushing syndrome patients have increased ectopic fat deposition and bone marrow fat content compared to cured patients and healthy subjects: a pilot 1H-MRS study

OBJECTIVE

Glucocorticoid excess is one of the most important causes of bone disorders. Bone marrow fat (BMF) has been identified as a l new mediator of bone metabolism. Cushing syndrome (CS), is a main regulator of adipose tissue distribution but its impact on BMF is unknown. The objective of the study was to evaluate the effect of chronic hypercortisolism on BMF.

DESIGN

This was a cross-sectional study. Seventeen active and seventeen cured ACTH-dependent CS patients along with seventeen controls (matched with the active group for age and sex) were included.

METHODS

the BMF content of the femoral neck and L3 vertebrae were measured by 1H-MRS on a 3-Tesla wide-bore magnet. BMD was evaluated in patients using dual-energy X-ray absorptiometry.

RESULTS

Active CS patients had higher BMF content both in the femur (82.5±2.6%) and vertebrae (70.1±5.1%) compared to the controls (70.8±3.6%, p=0.013 and 49.0±3.7% p=0.005, respectively). In cured CS patients (average remission time of 43 months), BMF content was not different from controls at both sites (72.3±2.9% (femur) and 46.7%±5.3% (L3)). BMF content was positively correlated with age, fasting plasma glucose, HbA1c, triglycerides and visceral adipose tissue in the whole cohort and negatively correlated with BMD values in the CS patients .

CONCLUSIONS

Accumulation of BMF is induced by hypercortisolism. In remission patients BMF reached values of controls. Further studies are needed to determine whether this increase in marrow adiposity in CS is associated with bone loss.

Molecular mechanisms of glucocorticoids on skeleton and bone regeneration after fracture

Glucocorticoid hormones (GCs) have profound effects on bone metabolism. Via their nuclear hormone receptor - the GR - they act locally within bone cells and modulate their proliferation, differentiation, and cell death. Consequently, high glucocorticoid levels - as present during steroid therapy or stress - impair bone growth and integrity, leading to retarded growth and glucocorticoid-induced osteoporosis, respectively. Because of their profound impact on the immune system and bone cell differentiation, GCs also affect bone regeneration and fracture healing. The use of conditional-mutant mouse strains in recent research provided insights into the cell-type-specific actions of the GR. However, despite recent advances in system biology approaches addressing GR genomics in general, little is still known about the molecular mechanisms of GCs and GR in bone cells. Here, we review the most recent findings on the molecular mechanisms of the GR in general and the known cell-type-specific actions of the GR in mesenchymal cells and their derivatives as well as in osteoclasts during bone homeostasis, GC excess, bone regeneration and fracture healing.