No bones about it: insulin modulates skeletal remodeling.

Advancing the hypothesis that bone remodeling is intimately linked to metabolic homeostasis, Fulzele et al. (2010) and Ferron et al. (2010) present evidence that insulin signaling promotes the activation of bone-forming osteoblasts and enhances production of osteocalcin, a secreted mediator of insulin sensitivity, through modulation of bone resorption.

Exploring mechanisms of increased cardiovascular disease risk with antipsychotic medications: Risperidone alters the cardiac proteomic signature in mice.

Atypical antipsychotic (AA) medications including risperidone (RIS) and olanzapine (OLAN) are FDA approved for the treatment of psychiatric disorders including schizophrenia, bipolar disorder and depression. Clinical side effects of AA medications include obesity, insulin resistance, dyslipidemia, hypertension and increased cardiovascular disease risk. Despite the known pharmacology of these AA medications, the mechanisms contributing to adverse metabolic side-effects are not well understood. To evaluate drug-associated effects on the heart, we assessed changes in the cardiac proteomic signature in mice administered for 4 weeks with clinically relevant exposure of RIS or OLAN. Using proteomic and gene enrichment analysis, we identified differentially expressed (DE) proteins in both RIS- and OLAN-treated mouse hearts (p < 0.05), including proteins comprising mitochondrial respiratory complex I and pathways involved in mitochondrial function and oxidative phosphorylation. A subset of DE proteins identified were further validated by both western blotting and quantitative real-time PCR. Histological evaluation of hearts indicated that AA-associated aberrant cardiac gene expression occurs prior to the onset of gross pathomorphological changes. Additionally, RIS treatment altered cardiac mitochondrial oxygen consumption and whole body energy expenditure. Our study provides insight into the mechanisms underlying increased patient risk for adverse cardiac outcomes with chronic treatment of AA medications.

A novel mouse model overexpressing Nocturnin results in decreased fat mass in male mice.

Nocturnin (NOCT) belongs to the Mg2+ dependent Exonucleases, Endonucleases, Phosphatase (EEP) family of enzymes that exhibit various functions in vitro and in vivo. NOCT is known to function as a deadenylase, cleaving poly-A tails from mRNA (messenger RNA) transcripts. Previously, we reported a role for NOCT in regulating bone marrow stromal cell differentiation through its interactions with PPARγ. In this study, we characterized the skeletal and adipose tissue phenotype when we globally overexpressed Noct in vivo. After 12 weeks of Noct overexpression, transgenic male mice had lower fat mass compared to controls, with no significant differences in the skeleton. Based on the presence of a mitochondrial target sequence in NOCT, we determined that mouse NOCT protein localizes to the mitochondria; subsequently, we found that NOCT overexpression led to a significant increase in the preadipocytes ability to utilize oxidative phosphorylation for ATP (adenosine triphosphate) generation. In summary, the effects of NOCT on adipocytes are likely through its novel role as a mediator of mitochondrial function.

High fat diet attenuates hyperglycemia, body composition changes, and bone loss in male streptozotocin-induced type 1 diabetic mice.

There is a growing and alarming prevalence of obesity and the metabolic syndrome in type I diabetic patients (T1DM), particularly in adolescence. In general, low bone mass, higher fracture risk, and increased marrow adipose tissue (MAT) are features of diabetic osteopathy in insulin-deficient subjects. On the other hand, type 2 diabetes (T2DM) is associated with normal or high bone mass, a greater risk of peripheral fractures, and no change in MAT. Therefore, we sought to determine the effect of weight gain on bone turnover in insulin-deficient mice. We evaluated the impact of a 6-week high-fat (HFD) rich in medium chain fatty acids or low-fat diet (LFD) on bone mass and MAT in a streptozotocin (STZ)-induced model using male C57BL/6J mice at 8 weeks of age. Dietary intervention was initiated after diabetes confirmation. At the endpoint, lower non-fasting glucose levels were observed in diabetic mice fed with high fat diet compared to diabetic mice fed the low fat diet (STZ-LFD). Compared to euglycemic controls, the STZ-LFD had marked polydipsia and polyphagia, as well as reduced lean mass, fat mass, and bone parameters. Interestingly, STZ-HFD mice had higher bone mass, namely less cortical bone loss and more trabecular bone than STZ-LFD. Thus, we found that a HFD, rich in medium chain fatty acids, protects against bone loss in a T1DM mouse model. Whether this may also translate to T1DM patients who are overweight or obese in respect to maintenance of bone mass remains to be determined through longitudinal studies.

Energy Metabolism of Bone.

Biological processes utilize energy and therefore must be prioritized based on fuel availability. Bone is no exception to this, and the benefit of remodeling when necessary outweighs the energy costs. Bone remodeling is important for maintaining blood calcium homeostasis, repairing micro cracks and fractures, and modifying bone structure so that it is better suited to withstand loading demands. Osteoclasts, osteoblasts, and osteocytes are the primary cells responsible for bone remodeling, although bone marrow adipocytes and other cells may also play an indirect role. There is a renewed interest in bone cell energetics because of the potential for these processes to be targeted for osteoporosis therapies. In contrast, due to the intimate link between bone and energy homeostasis, pharmaceuticals that treat metabolic disease or have metabolic side effects often have deleterious bone consequences. In this brief review, we will introduce osteoporosis, discuss how bone cells utilize energy to function, evidence for bone regulating whole body energy homeostasis, and some of the unanswered questions and opportunities for further research in the field.

Thermoneutral Housing has Limited Effects on Social Isolation-Induced Bone Loss in Male C57BL/6J Mice.

Social isolation stress has numerous known negative health effects, including increased risk for cardiovascular disease, dementia, as well as overall mortality. The impacts of social isolation on skeletal health, however, have not been thoroughly investigated. We previously found that four weeks of social isolation through single housing led to a significant reduction in trabecular and cortical bone in male, but not female, mice. One possible explanation for these changes in male mice is thermal stress due to sub-thermoneutral housing. Single housing at room temperature (~20-25°C)-below the thermoneutral range of mice (~26-34°C)-may lead to cold stress, which has known negative effects on bone. Therefore, the aim of this study was to test the hypothesis that housing mice near thermoneutrality, thereby ameliorating cold-stress, will prevent social isolation-induced bone loss in male C57BL/6J mice. 16-week-old mice were randomized into social isolation (1 mouse/cage) or grouped housing (4 mice/cage) at either room temperature (~23°C) or in a warm temperature incubator (~28°C) for four weeks (N=8/group). As seen in our previous studies, isolated mice at room temperature had significantly reduced bone parameters, including femoral bone volume fraction (BV/TV), bone mineral density (BMD), and cortical thickness. Contrary to our hypothesis, these negative effects on bone were not ameliorated by thermoneutral housing. Social isolation increased glucocorticoid-related gene expression in bone and Ucp1 and Pdk4 expression in BAT across temperatures, while thermoneutral housing increased percent lipid area and decreased Ucp1 and Pdk4 expression in BAT across housing conditions. Overall, our data suggest social isolation-induced bone loss is not a result of thermal stress from single housing and provides a key insight into the mechanism mediating the effects of isolation on skeletal health.

Social Isolation Causes Cortical and Trabecular Bone Loss in Adult Male, but not Female, C57BL/6J Mice.

Social isolation is a potent form of psychosocial stress and is a growing public health concern, particularly among older adults. Even prior to the onset of the COVID-19 pandemic, which has significantly increased the prevalence of isolation and loneliness, researchers have been concerned about a rising "epidemic" of loneliness. Isolation is associated with an increased risk for many physical and mental health disorders and increased overall mortality risk. In addition to social isolation, older adults are also at greater risk for osteoporosis and related fractures. While researchers have investigated the negative effects of other forms of psychosocial stress on bone, including depression and PTSD, the effects of social isolation on bone have not been thoroughly investigated. The aim of this study was to test the hypothesis that social isolation would lead to bone loss in male and female C57BL/6J mice. 16-week-old mice were randomized into social isolation (1 mouse/cage) or grouped housing (4 mice/cage) for four weeks (N=16/group). Social isolation significantly decreased trabecular (BV/TV, BMD, Tb. N., Tb. Th.) and cortical bone (Ct.Th., Ct.Ar., Ct.Ar./Tt.Ar., pMOI, Ct.Por.) parameters in male, but not female mice. Isolated male mice had signs of reduced bone remodeling represented by reduced osteoblast numbers, osteoblast-related gene expression and osteoclast-related gene expression. However, isolated females had increased bone resorption-related gene expression, without any change in bone mass. Overall, our data suggest that social isolation has negative effects on bone in males, but not females, although females showed suggestive effects on bone resorption. These results provide critical insight into the effects of isolation on bone and have key clinical implications as we grapple with the long-term health impacts of the rise in social isolation related to the COVID-19 pandemic.

Social isolation through single housing negatively affects trabecular and cortical bone in adult male, but not female, C57BL/6J mice.

Social isolation is a potent form of psychosocial stress and is a growing public health concern, particularly among older adults. Even prior to the onset of the COVID-19 pandemic, which has significantly increased the prevalence of isolation and loneliness, researchers have been concerned about a rising "epidemic" of loneliness. Isolation is associated with an increased risk for many physical and mental health disorders and increased overall mortality risk. In addition to social isolation, older adults are also at greater risk for osteoporosis and related fractures. While researchers have investigated the negative effects of other forms of psychosocial stress on bone, including depression and PTSD, the effects of social isolation on bone have not been thoroughly investigated. The aim of this study was to test the hypothesis that social isolation would lead to bone loss in male and female C57BL/6J mice. 16-week-old mice were randomized into social isolation (1 mouse/cage) or grouped housing (4 mice/cage) for four weeks. Social isolation significantly decreased trabecular (BV/TV, BMD, Tb. N., Tb. Th.) and cortical bone (Ct.Th., Ct.Ar., Ct.Ar./Tt.Ar., pMOI) parameters in male, but not female mice. Isolated male mice had signs of reduced bone remodeling represented by reduced osteoblast numbers, osteoblast-related gene expression and osteoclast-related gene expression. However, isolated females had increased bone resorption-related gene expression, without any change in bone mass. Overall, our data suggest that social isolation has negative effects on bone in male, but not female mice, although females showed suggestive effects on bone resorption. These results provide critical insight into the effects of isolation on bone and have key clinical implications as we grapple with the long-term health impacts of the rise in social isolation related to the COVID-19 pandemic.

Thermoneutral housing does not rescue olanzapine-induced trabecular bone loss in C57BL/6J female mice.

Antipsychotic drugs are prescribed to a wide range of individuals to treat mental health conditions including schizophrenia. However, antipsychotic drugs cause bone loss and increase fracture risk. We previously found that the atypical antipsychotic (AA) drug risperidone causes bone loss through multiple pharmacological mechanisms, including activation of the sympathetic nervous system in mice treated with clinically relevant doses. However, bone loss was dependent upon housing temperature, which modulates sympathetic activity. Another AA drug, olanzapine, has substantial metabolic side effects, including weight gain and insulin resistance, but it is unknown whether bone and metabolic outcomes of olanzapine are also dependent upon housing temperature in mice. We therefore treated eight week-old female mice with vehicle or olanzapine for four weeks, housed at either room temperature (23 °C) or thermoneutrality (28-30 °C), which has previously been shown to be positive for bone. Olanzapine caused significant trabecular bone loss (-13% BV/TV), likely through increased RANKL-dependent osteoclast resorption, which was not suppressed by thermoneutral housing. Additionally, olanzapine inhibited cortical bone expansion at thermoneutrality, but did not alter cortical bone expansion at room temperature. Olanzapine also increased markers of thermogenesis within brown and inguinal adipose depots independent of housing temperature. Overall, olanzapine causes trabecular bone loss and inhibits the positive effect of thermoneutral housing on bone. Understanding how housing temperature modulates the impact of AA drugs on bone is important for future pre-clinical studies, as well as for the prescription of AA drugs, particularly to older adults and adolescents who are most vulnerable to the effects on bone.

Amelioration of type I diabetes-induced osteoporosis by parathyroid hormone is associated with improved osteoblast survival.

Type 1 diabetic osteoporosis results from impaired osteoblast activity and death. Therefore, anti-resorptive treatments may not effectively treat bone loss in this patient population. Intermittent parathyroid hormone (PTH) treatment stimulates bone remodeling and increases bone density in healthy subjects. However, PTH effects may be limited in patients with diseases that interfere with its signaling. Here, we examined the ability of 8 and 40 µg/kg intermittent PTH to counteract diabetic bone loss. PTH treatment reduced fat pad mass and blood glucose levels in non-diabetic PTH-treated mice, consistent with PTH-affecting glucose homeostasis. However, PTH treatment did not significantly affect general body parameters, including the blood glucose levels, of type 1 diabetic mice. We found that the high dose of PTH significantly increased tibial trabecular bone density parameters in control and diabetic mice, and the lower dose elevated trabecular bone parameters in diabetic mice. The increased bone density was due to increased mineral apposition and osteoblast surface, all of which are defective in type 1 diabetes. PTH treatment suppressed osteoblast apoptosis in diabetic bone, which could further contribute to the bone-enhancing effects. In addition, PTH treatment (40 µg/kg) reversed preexisting bone loss from diabetes. We conclude that intermittent PTH may increase type 1 diabetic trabecular bone volume through its anabolic effects on osteoblasts.

Sustained Morphine Delivery Suppresses Bone Formation and Alters Metabolic and Circulating miRNA Profiles in Male C57BL/6J Mice.

Opioid use is detrimental to bone health, causing both indirect and direct effects on bone turnover. Although the mechanisms of these effects are not entirely clear, recent studies have linked chronic opioid use to alterations in circulating miRNAs. Here, we developed a model of opioid-induced bone loss to understand bone turnover and identify candidate miRNA-mediated regulatory mechanisms. We evaluated the effects of sustained morphine treatment on male and female C57BL/6J mice by treating with vehicle (0.9% saline) or morphine (17 mg/kg) using subcutaneous osmotic minipumps for 25 days. Morphine-treated mice had higher energy expenditure and respiratory quotient, indicating a shift toward carbohydrate metabolism. Micro-computed tomography (µCT) analysis indicated a sex difference in the bone outcome, where male mice treated with morphine had reduced trabecular bone volume fraction (Tb.BV/TV) (15%) and trabecular bone mineral density (BMD) (14%) in the distal femur compared with vehicle. Conversely, bone microarchitecture was not changed in females after morphine treatment. Histomorphometric analysis demonstrated that in males, morphine reduced bone formation rate compared with vehicle, but osteoclast parameters were not different. Furthermore, morphine reduced bone formation marker gene expression in the tibia of males (Bglap and Dmp1). Circulating miRNA profile changes were evident in males, with 14 differentially expressed miRNAs associated with morphine treatment compared with two differentially expressed miRNAs in females. In males, target analysis indicated hypoxia-inducible factor (HIF) signaling pathway was targeted by miR-223-3p and fatty acid metabolism by miR-484, -223-3p, and -328-3p. Consequently, expression of miR-223-3p targets, including Igf1r and Stat3, was lower in morphine-treated bone. In summary, we have established a model where morphine leads to a lower trabecular bone formation in males and identified potential mediating miRNAs. Understanding the sex-specific mechanisms of bone loss from opioids will be important for improving management of the adverse effects of opioids on the skeleton. © 2022 American Society for Bone and Mineral Research (ASBMR).

Propranolol Promotes Bone Formation and Limits Resorption Through Novel Mechanisms During Anabolic Parathyroid Hormone Treatment in Female C57BL/6J Mice.

Although the nonselective ß-blocker, propranolol, improves bone density with parathyroid hormone (PTH) treatment in mice, the mechanism of this effect is unclear. To address this, we used a combination of in vitro and in vivo approaches to address how propranolol influences bone remodeling in the context of PTH treatment. In female C57BL/6J mice, intermittent PTH and propranolol administration had complementary effects in the trabecular bone of the distal femur and fifth lumbar vertebra (L5 ), with combination treatment achieving microarchitectural parameters beyond that of PTH alone. Combined treatment improved the serum bone formation marker, procollagen type 1 N propeptide (P1NP), but did not impact other histomorphometric parameters relating to osteoblast function at the L5 . In vitro, propranolol amplified the acute, PTH-induced, intracellular calcium signal in osteoblast-like cells. The most striking finding, however, was suppression of PTH-induced bone resorption. Despite this, PTH-induced receptor activator of nuclear factor κ-B ligand (RANKL) mRNA and protein levels were unaltered by propranolol, which led us to hypothesize that propranolol could act directly on osteoclasts. Using in situ methods, we found Adrb2 expression in osteoclasts in vivo, suggesting ß-blockers may directly impact osteoclasts. Consistent with this, we found propranolol directly suppresses osteoclast differentiation in vitro. Taken together, this work suggests a strong anti-osteoclastic effect of nonselective ß-blockers in vivo, indicating that combining propranolol with PTH could be beneficial to patients with extremely low bone density. © 2022 American Society for Bone and Mineral Research (ASBMR).

CCAAT/enhancer binding protein ß-deficiency enhances type 1 diabetic bone phenotype by increasing marrow adiposity and bone resorption.

Bone loss in type 1 diabetes is accompanied by increased marrow fat, which could directly reduce osteoblast activity or result from altered bone marrow mesenchymal cell lineage selection (adipocyte vs. osteoblast). CCAAT/enhancer binding protein beta (C/EBPß) is an important regulator of both adipocyte and osteoblast differentiation. C/EBPß-null mice have delayed bone formation and defective lipid accumulation in brown adipose tissue. To examine the balance of C/EBPß functions in the diabetic context, we induced type 1 diabetes in C/EBPß-null (knockout, KO) mice. We found that C/EBPß deficiency actually enhanced the diabetic bone phenotype. While KO mice had reduced peripheral fat mass compared with wild-type mice, they had 5-fold more marrow adipocytes than diabetic wild-type mice. The enhanced marrow adiposity may be attributed to compensation by C/EBPδ, peroxisome proliferator-activated receptor-γ2, and C/EBPα. Concurrently, we observed reduced bone density. Relative to genotype controls, trabecular bone volume fraction loss was escalated in diabetic KO mice (-48%) compared with changes in diabetic wild-type mice (-22%). Despite greater bone loss, osteoblast markers were not further suppressed in diabetic KO mice. Instead, osteoclast markers were increased in the KO diabetic mice. Thus, C/EBPß deficiency increases diabetes-induced bone marrow (not peripheral) adipose depot mass, and promotes additional bone loss through stimulating bone resorption. C/EBPß-deficiency also reduced bone stiffness and diabetes exacerbated this (two-way ANOVA P < 0.02). We conclude that C/EBPß alone is not responsible for the bone vs. fat phenotype switch observed in T1 diabetes and that suppression of CEBPß levels may further bone loss and decrease bone stiffness by increasing bone resorption.

Housing Temperature Influences Atypical Antipsychotic Drug-Induced Bone Loss in Female C57BL/6J Mice.

Atypical antipsychotic (AA) drugs, such as risperidone, are associated with endocrine and metabolic side effects, including impaired bone mineral density (BMD) acquisition and increased fracture risk. We have previously shown that risperidone causes bone loss through the sympathetic nervous system and that bone loss is associated with elevated markers of thermogenesis in brown and white adipose tissue. Because rodents are normally housed in sub-thermoneutral conditions, we wanted to test whether increasing housing temperature would protect against bone loss from risperidone. Four weeks of risperidone treatment in female C57BL/6J mice at thermoneutral (28°C) housing attenuated risperidone-induced trabecular bone loss and led to a low-turnover bone phenotype, with indices of both bone formation and resorption suppressed in mice with risperidone treatment at thermoneutrality, whereas indices of bone resorption were elevated by risperidone at room temperature. Protection against trabecular bone loss was not absolute, however, and additional evidence of cortical bone loss emerged in risperidone-treated mice at thermoneutrality. Taken together, these findings suggest thermal challenge may be in part responsible for bone loss with risperidone treatment and that housing temperature should be considered when assessing bone outcomes of treatments that impact thermogenic pathways. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

TRPM8 modulates temperature regulation in a sex-dependent manner without affecting cold-induced bone loss.

Trpm8 (transient receptor potential cation channel, subfamily M, member 8) is expressed by sensory neurons and is involved in the detection of environmental cold temperatures. TRPM8 activity triggers an increase in uncoupling protein 1 (Ucp1)-dependent brown adipose tissue (BAT) thermogenesis. Bone density and marrow adipose tissue are both influenced by rodent housing temperature and brown adipose tissue, but it is unknown if TRPM8 is involved in the co-regulation of thermogenesis and bone homeostasis. To address this, we examined the bone phenotypes of one-year-old Trpm8 knockout mice (Trpm8-KO) after a 4-week cold temperature challenge. Male Trpm8-KO mice had lower bone mineral density than WT, with smaller bone size (femur length and cross-sectional area) being the most striking finding, and exhibited a delayed cold acclimation with increased BAT expression of Dio2 and Cidea compared to WT. In contrast to males, female Trpm8-KO mice had low vertebral bone microarchitectural parameters, but no genotype-specific alterations in body temperature. Interestingly, Trpm8 was not required for cold-induced trabecular bone loss in either sex, but bone marrow adipose tissue in females was significantly suppressed by Trpm8 deletion. In summary, we identified sex differences in the role of TRPM8 in maintaining body temperature, bone microarchitecture and marrow adipose tissue. Identifying mechanisms through which cold temperature and BAT influence bone could help to ameliorate potential bone side effects of obesity treatments designed to stimulate thermogenesis.

miRNA Mechanisms Underlying the Association of Beta Blocker Use and Bone Mineral Density.

Osteoporosis is a debilitating and costly disease that causes fractures in 33% of women and 20% of men over the age of 50 years. Recent studies have shown that beta blocker (BB) users have higher bone mineral density (BMD) and decreased risk of fracture compared with non-users. The mechanism underlying this association is thought to be due to suppression of adrenergic signaling in osteoblasts, which leads to increased BMD in rodent models; however, the mechanism in humans is unknown. Also, several miRNAs are associated with adrenergic signaling and BMD in separate studies. To investigate potential miRNA mechanisms, we performed a cross-sectional analysis using clinical data, dual-energy X-ray absorptiometry (DXA) scans, and miRNA and mRNA profiling of whole blood from the Framingham Study's Offspring Cohort. We found nine miRNAs associated with BB use and increased BMD. In parallel network analyses, we discovered a subnetwork associated with BMD and BB use containing two of these nine miRNAs, miR-19a-3p and miR-186-5p. To strengthen this finding, we showed that these two miRNAs had significantly higher expression in individuals without incident fracture compared with those with fracture in an external data set. We also noted a similar trend in association between these miRNA and Z-score as calculated from heel ultrasound measures in two external cohorts (SOS-Hip and SHIP-TREND). Because miR-19a directly targets the ADRB1 mRNA transcript, we propose BB use may downregulate ADRB1 expression in osteoblasts through increased miR-19a-3p expression. We used enrichment analysis of miRNA targets to find potential indirect effects through insulin and parathyroid hormone signaling. This analysis provides a starting point for delineating the role of miRNA on the association between BB use and BMD. © 2020 American Society for Bone and Mineral Research (ASBMR).

Pharmacogenomic Effects of ß-Blocker Use on Femoral Neck Bone Mineral Density.

CONTEXT: Recent studies have shown that ß-blocker (BB) users have a decreased risk of fracture and higher bone mineral density (BMD) compared to nonusers, likely due to the suppression of adrenergic signaling in osteoblasts, leading to increased BMD. There is also variability in the effect size of BB use on BMD in humans, which may be due to pharmacogenomic effects. OBJECTIVE: To investigate potential single-nucleotide variations (SNVs) associated with the effect of BB use on femoral neck BMD, we performed a cross-sectional analysis using clinical data, dual-energy x-ray absorptiometry, and genetic data from the Framingham Heart Study's (FHS) Offspring Cohort. We then sought to validate our top 4 genetic findings using data from the Rotterdam Study, the BPROOF Study, the Malta Osteoporosis Fracture Study (MOFS), and the Hertfordshire Cohort Study. METHODS: We used sex-stratified linear mixed models to determine SNVs that had a significant interaction effect with BB use on femoral neck (FN) BMD across 11 gene regions. We also evaluated the association of our top SNVs from the FHS with microRNA (miRNA) expression in blood and identified potential miRNA-mediated mechanisms by which these SNVs may affect FN BMD. RESULTS: One variation (rs11124190 in HDAC4) was validated in females using data from the Rotterdam Study, while another (rs12414657 in ADRB1) was validated in females using data from the MOFS. We performed an exploratory meta-analysis of all 5 studies for these variations, which further validated our findings. CONCLUSION: This analysis provides a starting point for investigating the pharmacogenomic effects of BB use on BMD measures.

Bone and glucose metabolism: a two-way street.

Evidence from rodent models indicates that undercarboxylated osteocalcin (ucOC), a product of osteoblasts, is a hormone affecting insulin production by the pancreas and insulin sensitivity in peripheral tissues, at least in part through enhanced secretion of adiponectin from adipocytes. Clinical research to test whether this relationship is found in humans is just beginning to emerge. Cross-sectional studies confirm associations between total osteocalcin (OC), ucOC and glucose metabolism but cannot distinguish causality. To date, longitudinal studies have not provided a consistent picture of the effects of ucOC or OC on fasting glucose and insulin sensitivity. Further exploration into the physiological and mechanistic effects of ucOC and OC, in rodent models and clinical studies, is necessary to determine to what extent the skeleton regulates energy metabolism in humans.

Association of Beta Blocker Use With Bone Mineral Density in the Framingham Osteoporosis Study: A Cross-Sectional Study.

Some, but not all, prior observational studies have shown that beta blocker (BB) use is associated with lower fracture risk and higher bone mineral density (BMD). Rodent studies show the mechanism to involve the reduction in the effects of beta-adrenergic signaling on bone remodeling. Because previous studies did not have detailed information on dose, duration, and beta-1 selectivity, we examined these in a cross-sectional analysis of the association between BB use and hip and spine BMD using DXA with the Offspring Cohort of the Framingham Heart Study. The sample size was n = 1520, and 397 individuals used BBs. We used propensity score modeling to balance a comprehensive set of covariates using inverse probability of treatment weighting (IPTW) to minimize bias due to treatment indication. We found significant differences in BMD between BB users and non-users for three of four BMD measurements (femoral neck: 3.1%, 95% CI, 1.1% to 5.0%; total femur: 2.9%, 95% CI, 0.9% to 4.9%; femoral trochanter: 2.4%, 95% CI, -0.1% to 5.0%; and lumbar spine: 2.7%, 95% CI, 0.2% to 5.0%). Results were found to be similar between sexes although the magnitude of association was larger for women. Similar differences were estimated for beta-1 selective and nonselective BBs compared with no BB use. We modeled dose in categories (no BB use, low-dose, high-dose) and as a continuous variable and found an increasing dose response that levels off at higher doses. Finally, associations were similar for short-term versus long-term (≤4 years versus >4 years) use. In summary, this large comprehensive study shows that BB use is associated with higher BMD in a dose-related manner regardless of beta-1 specificity and duration of use, which supports the conduct of a randomized clinical trial of BBs for achieving improvements in BMD for individuals at risk of bone loss with aging. © 2020 The Authors. JBMR Plus published by Wiley Periodicals LLC. on behalf of American Society for Bone and Mineral Research.

Leptin treatment prevents type I diabetic marrow adiposity but not bone loss in mice.

Leptin is a hormone secreted by adipocytes that is implicated in the regulation of bone density. Serum leptin levels are decreased in rodent models of type 1 (T1-) diabetes and in diabetic patients. Whether leptin mediates diabetic bone changes is unclear. Therefore, we treated control and T1-diabetic mice with chronic (28 days) subcutaneous infusion of leptin or saline to elucidate the therapeutic potential of leptin for diabetic osteoporosis. Leptin prevented the increase of marrow adipocytes and the increased aP2 expression that we observed in vehicle-treated diabetic mice. However, leptin did not prevent T1-diabetic decreases in trabecular bone volume fraction or bone mineral density in tibia or vertebrae. Consistent with this finding, markers of bone formation (osteocalcin RNA and serum levels) in diabetic mice were not restored to normal levels with leptin treatment. Interestingly, markers of bone resorption (TRAP5 RNA and serum levels) were decreased in diabetic mice by leptin treatment. In summary, we have demonstrated a link between low leptin levels in T1-diabetes and marrow adiposity. However, leptin treatment alone was not successful in preventing bone loss.