Adipocytic proportion of bone marrow is inversely related to bone formation in osteoporosis

Influence of sleeve gastrectomy on bone marrow fat in metabolic syndrome patients with and without diabetes: a prospective follow-up study

OBJECTIVES

To evaluate bone marrow fat concentration changes after sleeve gastrectomy in metabolic syndrome patients with and without diabetes.

METHODS

A total of 58 metabolic syndrome patients (29 metabolic syndrome patients with diabetes (35.10 years ± 6.62) and 29 metabolic syndrome patients without diabetes (35.07 years ± 6.47)) who underwent sleeve gastrectomy received prospective follow-up for 2 years. Echo asymmetry, least square estimation-MRI, and laboratory tests were performed on all patients before and 2 years after surgery. The differences between baseline and end-of-study parameters were analyzed with the paired Student's t test. In addition, the associations of vertebral bone marrow fat concentration (denoted by proton density fat fraction, PDFF) with other variables were determined using multiple linear regression analysis.

RESULTS

Bone proton density fat fraction decreased significantly among patients with diabetes (from 38.62 ± 8.01 to 34.54 ± 7.54, P = 0.003) and without diabetes (from 36.82 ± 8.80 to 35.09 ± 8.33, P = 0.011) after sleeve gastrectomy. Among patients with diabetes, multivariable predictors of changes in proton density fat fraction by descending order of standardized coefficient were changes in HbA1c (2.690, P < 0.001), baseline HbA1c (2.354, P < 0.001), changes in insulin (0.627, P < 0.001), changes in low-density lipoprotein cholesterol (0.597, P = 0.013), and changes in C-peptide (-0.664, P = 0.001). Among patients without diabetes, multivariable predictors of changes in proton density fat fraction were changes in low-density lipoprotein cholesterol (1.486, P < 0.001), changes in high-density lipoprotein cholesterol (0.460, P = 0.003), baseline low-density lipoprotein cholesterol (0.438, P = 0.014), changes in triglyceride (0.383, P = 0.007), and changes in total cholesterol (-1.614, P < 0.001).

CONCLUSIONS

Sleeve gastrectomy may decrease bone marrow fat concentration of MetS patients regardless of diabetes status. Changes in bone marrow fat concentration may be influenced by different factors based on diabetes status.

SARS-CoV-2 Impairs Osteoblast Differentiation Through Spike Glycoprotein and Cytokine Dysregulation

Pulmonary and extrapulmonary manifestations have been reported following infection with SARS-CoV-2, the causative agent of COVID-19. The virus persists in multiple organs due to its tropism for various tissues, including the skeletal system. This study investigates the effects of SARS-CoV-2 infection, including both ancestral and Omicron viral strains, on differentiating mesenchymal stem cells (MSCs), the precursor cells, into osteoblasts. Although both viral strains can productively infect osteoblasts, precursor cell infection remained abortive. Viral exposure during osteoblast differentiation demonstrates that both variants inhibit mineral and organic matrix deposition. This is accompanied by reduced expression of runt-related transcription factor 2 (RUNX2) and increased levels of interleukin-6 (IL-6), a cytokine that negatively regulates osteoblast differentiation. Furthermore, the upregulation of receptor activator of nuclear factor kappa B ligand (RANKL) strongly suggests that the ancestral and Omicron variants may disrupt bone homeostasis by promoting osteoclast differentiation, ultimately leading to the formation of bone-resorbing cells. This process is dependent of spike glycoprotein since its neutralization significantly reduced the effect of infective SARS-CoV-2 and UV-C inactivated virus. This study underscores the capacity of ancestral and Omicron SARS-CoV-2 variants to disrupt osteoblast differentiation, a process essential for preserving the homeostasis and functionality of bone tissue.

Association of proton-density fat fraction with osteoporosis: a systematic review and meta-analysis

This study aimed to evaluate the correlation between measuring proton-density fat fraction (PDFF) in bone marrow using multi-echo chemical shift-encoded MRI and osteoporosis, assessing its effectiveness as a biomarker for osteoporosis. A systematic review was conducted by two independent researchers using Cochrane, PubMed, EMBASE, and Web of Science databases up to December 2023. Quality assessments were evaluated using the Cochrane risk of bias tool and the Agency for Healthcare Research and Quality (AHRQ) checklist. Fourteen studies involving 1495 patients were analyzed. The meta-analysis revealed a significant difference in PDFF values between the osteoporosis/osteopenia group and the normal control group, with a mean difference of 11.04 (95% CI: 9.17 to 12.92, Z=11.52, P < 0.00001). Measuring PDFF via MRI shows potential as an osteoporosis biomarker and may serve as a risk factor for osteoporosis. This insight opens new avenues for future diagnostic and therapeutic strategies, potentially improving osteoporosis management and patient care.

OBJECTIVE

This study aims to assess the correlation between measuring proton-density fat fraction (PDFF) in bone marrow using multi-echo chemical shift-encoded MRI and osteoporosis, evaluating its effectiveness as a biomarker for osteoporosis.

MATERIALS AND METHODS

This systematic review was carried out by two independent researchers using Cochrane, PubMed, EMBASE, and Web of Science databases up to December 2023. Quality assessments were evaluated using the Cochrane risk of bias tool and the Agency for Healthcare Research and Quality (AHRQ) checklist.

RESULTS

Fourteen studies involving 1495 patients were analyzed. The meta-analysis revealed a significant difference in PDFF values between the osteoporosis/osteopenia group and the normal control group, with a (MD = 11.04, 95% CI: 9.17 to 12.92, Z = 11.52, P < 0.00001). Subgroup analyses indicated that diagnostic methods, gender, and echo length did not significantly impact the PDFF-osteoporosis association.

CONCLUSION

PDFF measurement via MRI shows potential as an osteoporosis biomarker and may serve as a risk factor for osteoporosis. This insight opens new avenues for future diagnostic and therapeutic strategies, potentially improving osteoporosis management and patient care.

PET/CT for the Opportunistic Screening of Osteoporosis and Fractures in Cancer Patients

PURPOSE OF REVIEW

In this review, we outline the different etiologies of osteoporosis in the oncologic setting and describe the basis for using PET/CT as screening tool for osteoporosis with a focus on the radiotracers [18F]FDG and [18F]NaF.

RECENT FINDINGS

Osteoporosis is a condition commonly affecting cancer patients due to their age, cancer-specific treatment agents, and effects of cancer. In terms of the unifying mechanism, decreased ratio of osteoblast-bone formation to osteoclast-bone resorption is responsible for causing osteoporosis. PET/CT, a crucial metabolic imaging modality in the oncologic imaging, could be a useful tool for the opportunistic screening of osteoporosis. There are two approaches with which osteoporosis could be identified with PET/CT-using either the (1) CT- based or (2) PET- based approaches. While the CT-based approach has been used with [18F]FDG PET/CT, both CT- and PET-based approaches can be employed with [18F]NaF-PET/CT as [18F]NaF is a radiotracer specific for osteoblast activity.

Sex Differences in Fat Distribution and Muscle Fat Infiltration in the Lower Extremity: A Retrospective Diverse-Ethnicity 7T MRI Study in a Research Institute Setting in the USA

Background: Fat infiltration in skeletal muscle is related to declining muscle strength, whereas excess subcutaneous fat is implicated in the development of metabolic diseases. Methods: Using multi-slice axial T2-weighted (T2w) MR images, this retrospective study characterized muscle fat infiltration (MFI) and fat distribution in the lower extremity of 107 subjects (64M/43F, age 11-79 years) with diverse ethnicities (including White, Black, Latino, and Asian subjects). Results: MRI data analysis shows that MFI, evaluated by the relative intensities of the pixel histogram profile in the calf muscle, tends to increase with both age and BMI. However, statistical significance was found only for the age correlation in women (p < 0.002), and the BMI correlation in men (p = 0.04). Sex disparities were also seen in the fat distribution, which was assessed according to subcutaneous fat thickness (SFT) and the fibula bone marrow cross-sectional area (BMA). SFT tends to decrease with age in men (p < 0.01), whereas SFT tends to increase with BMI only in women (p < 0.01). In contrast, BMA tends to increase with age in women (p < 0.01) and with BMI in men (p = 0.04). Additionally, MFI is positively correlated with BMA but not with SFT, suggesting that compromised bone structure may contribute to fat infiltration in the surrounding skeletal muscle. Conclusions: The findings of this study highlight a sex factor affecting MFI and fat distribution, which may offer valuable insights into effective strategies to prevent and treat MFI in women versus men.

Effects of tetrahedral DNA nanostructures on the treatment of osteoporosis

Osteoporosis (OP) is a common disease characterized by bone loss and bone tissue microstructure degradation. Drug treatment is a common clinical treatment that aims to increase bone mass and bone density. Tetrahedral DNA nanostructures (TDNs) are three-dimensional tetrahedral frames formed by folding four single-stranded DNA molecules, which have good biological safety and can promote bone regeneration. In this study, a mouse model of OP was established by ovariectomy (OVX) and TDN was injected into the tail vein for 8 weeks. We found that ovariectomized mice could simulate some physiological changes in OP. After treatment with TDNs, some of this destruction in mice was significantly improved, including an increase in the bone volume fraction (BV/TV) and bone trabecular number (Tb. N), decrease in bone separation (Tb. SP), reduction in the damage to the mouse cartilage layer, reduction in osteoclast lacunae in bone trabecula, and reduction in the damage to the bone dense part. We also found that the expression of ALP, β-Catenin, Runx2, Osterix, and bone morphogenetic protein (BMP)2 significantly decreased in OVX mice but increased after TDN treatment. Therefore, this study suggests that TDNs may regulate the Wnt/β-Catenin and BMP signalling pathways to improve the levels of some specific markers of osteogenic differentiation, such as Runx2, ALP, and Osterix, to promote osteogenesis, thus showing a therapeutic effect on OP mice.

Carboxypeptidase M modulates BMSCs osteogenesis-adipogenesis via the MAPK/ERK pathway: An integrated single-cell and bulk transcriptomic study

The pathogenesis of osteoporosis (OP) is closely associated with the disrupted balance between osteogenesis and adipogenesis in bone marrow-derived mesenchymal stem cells (BMSCs). We analyzed published single-cell RNA sequencing (scRNA-seq) data to dissect the transcriptomic profiles of bone marrow-derived cells in OP, reviewing 56 377 cells across eight scRNA-seq datasets from femoral heads (osteoporosis or osteopenia n = 5, osteoarthritis n = 3). Seventeen genes, including carboxypeptidase M (CPM), were identified as key osteogenesis-adipogenesis regulators through comprehensive gene set enrichment, differential expression, regulon activity, and pseudotime analyses. In vitro, CPM knockdown reduced osteogenesis and promoted adipogenesis in BMSCs, while adenovirus-mediated CPM overexpression had the reverse effects. In vivo, intraosseous injection of CPM-overexpressing BMSCs mitigated bone loss in ovariectomized mice. Integrated scRNA-seq and bulk RNA sequencing analyses provided insight into the MAPK/ERK pathway's role in the CPM-mediated regulation of BMSC osteogenesis and adipogenesis; specifically, CPM overexpression enhanced MAPK/ERK signaling and osteogenesis. In contrast, the ERK1/2 inhibitor binimetinib negated the effects of CPM overexpression. Overall, our findings identify CPM as a pivotal regulator of BMSC differentiation, which provides new clues for the mechanistic study of OP.

Chronic di(2-ethylhexyl) phthalate exposure at environmental-relevant doses induces osteoporosis by disturbing the differentiation of bone marrow mesenchymal stem cells

Di(2-ethylhexyl) phthalate (DEHP) is a widely used plastic additive with persistent characteristics in the environment. This study was designed to investigate the detrimental effects of chronic DEHP exposure at environmental-relevant doses on bone metabolism and the underlying mechanisms. It was found that exposure to 25 μg/kg bw and 50 μg/kg bw DEHP for 29 weeks led to a reduction of whole-body bone mineral density (BMD), femur microstructure damage, decreased femur new bone formation, and increased femur bone marrow adipogenesis in C57BL/6 female mice, which was not observed in mice exposed to 5000 μg/kg bw DEHP. Further in vitro study showed that DEHP treatment robustly promoted adipogenic differentiation and suppressed osteogenic differentiation of the bone marrow mesenchymal stem cells (BMSCs). Mechanistically, DEHP exposure resulted in elevated expressions of DYRK1B, CDK5, PPARγ, and p-PPARγSer273 in both bone tissue and BMSCs. Interestingly, co-IP analysis showed potential interactions among DYRK1B, PPARγ, and CDK5. Lastly, antagonists of DYRK1B and CDK5 effectively alleviated the BMSCs differentiation disturbance induced by DEHP. These results suggest that DEHP may disturb the BMSCs differentiation by upregulating the PPARγ signaling which may be associated with the activation of DYRK1B and CDK5.

Effect of Tempeh and Daidzein on Calcium Status, Calcium Transporters, and Bone Metabolism Biomarkers in Ovariectomized Rats

Menopause marks a critical life stage characterized by hormonal changes that significantly impact bone health, leading to a heightened susceptibility to bone fractures. This research seeks to elucidate the impact of daidzein and tempeh on calcium status, calcium transporters, and bone metabolism in an ovariectomized rat model. Forty female Wistar rats, aged 3 months, participated in a two-phase experiment. The initial phase involved inducing a calcium deficit, while the second phase comprised dietary interventions across five groups: Sham (S) and Ovariectomy (O) with a standard diet, O with bisphosphonate (OB), O with pure daidzein (OD), and O with tempeh (OT). Multiple parameters, encompassing calcium levels, calcium transporters, bone histopathology, and serum bone metabolism markers, were evaluated. The findings revealed that the OT group showcased heightened levels of bone turnover markers, such as pyridinoline, C-telopeptide of type I collagen, bone alkaline phosphatase, and procollagen type I N-terminal propeptide, in contrast to S and O groups, with statistical significance (p < 0.05). Histopathologically, both the OD and OT groups exhibited effects akin to the OB group, indicating a decrease in the surface area occupied by adipocytes in the femoral bone structure, although statistically non-equivalent, supporting the directionally similar trends. Although TRPV5 and TRPV6 mRNA expression levels in the jejunum and duodenum did not display statistically significant differences (p > 0.05), the OD and OT groups exhibited increased expression compared to the O group. We hypothesized that obtained results may be related to the effect of isoflavones on estrogen pathways because of their structurally similar to endogenous estrogen and weak estrogenic properties. In conclusion, the daily consumption of pure daidzein and tempeh could potentially improve and reinstate calcium status, calcium transport, and bone metabolism in ovariectomized rats. Additionally, isoflavone products demonstrate effects similar to bisphosphonate drugs on these parameters in ovariectomized rats.

Chromium Picolinate Regulates Bone Metabolism and Prevents Bone Loss in Diabetic Rats

Diabetic osteoporosis (DOP) is an abnormal metabolic disease caused by long-term hyperglycemia. In this study, a model rat of streptozotocin (STZ)-induced diabetes was established, and chromium picolinate (5 mg·kg-1) was given; the changes in blood glucose and body weight were detected before and after administration; and bone mineral density (BMD), bone morphology, bone turnover markers, inflammatory cytokines, and oxidative stress indicators were observed in each group. We found that after chromium picolinate (CP) intervention for 8 weeks, the blood glucose level was decreased; the BMD, the bone histomorphology parameters, and the pathological structure were improved; the expression of bone resorption-related proteins was downregulated; and the expression of bone formation-related proteins was upregulated. Meanwhile, serum antioxidant activity was increased, and inflammatory cytokine levels were decreased. In conclusion, CP could alleviate DOP by anti-oxidation, inhibition of bone turnover, anti-inflammation, and regulation of the OPG/RANKL/RANK signaling pathway. Therefore, CP has important application values for further development as a functional food or active medicine in DOP treatment.

Targeted Overexpression of Claudin 11 in Osteoblasts Increases Trabecular Bone Mass by Stimulating Osteogenesis at the Expense of Adipogenesis in Mice

Mice lacking Claudin11 (Cldn11) manifest reduced trabecular bone mass. However, the impact of Cldn11 expression in osteoblasts in vivo remains understudied. Herein, we generated osteoblast-specific transgenic (Tg) mice expressing Cldn11 and characterized their skeletal phenotype. Micro-CT analyses of the distal metaphysis of the femur showed a 50% and a 38% increase in trabecular bone mass in Tg male and female mice, respectively, due to a significant increase in trabecular number and a reduction in trabecular separation. Histomorphometry and serum biomarker studies uncovered that increased trabecular bone mass in Cldn11 Tg mice was the consequence of enhanced bone formation. Accordingly, an abundance of bone formation (Alp, Bsp), but not bone resorption (Ctsk), markers were augmented in the femurs of Cldn11 Tg mice. Since the trabecular bone density is known to inversely correlate with the amount of marrow adipose tissue (MAT), we measured the MAT in osmium-tetroxide-labeled bones by micro-CT scanning. We found 86% less MAT in the proximal tibia of the Tg males. Consistently, the expression levels of the adipogenic markers, adiponectin and leptin, were 50% lower in the femurs of the Tg males. Our data are consistent with the possibility that claudin11 exerts anabolic effects in osteoblastic lineage cells that act via promoting the differentiation of marrow stem cells towards osteoblasts at the expense of adipocytes.

Idiosyncratic bone responses to blood flow restriction exercise: new insights and future directions

Applying blood flow restriction (BFR) during low-load exercise induces beneficial adaptations of the myotendinous and neuromuscular systems. Despite the low mechanical tension, BFR exercise facilitates a localized hypoxic environment and increase in metabolic stress, widely regarded as the primary stimulus for tissue adaptations. First evidence indicates that low-load BFR exercise is effective in promoting an osteogenic response in bone, although this has previously been postulated to adapt primarily during high-impact weight-bearing exercise. Besides studies investigating the acute response of bone biomarkers following BFR exercise, first long-term trials demonstrate beneficial adaptations in bone in both healthy and clinical populations. Despite the increasing number of studies, the physiological mechanisms are largely unknown. Moreover, heterogeneity in methodological approaches such as biomarkers of bone metabolism measured, participant and study characteristics, and time course of measurement renders it difficult to formulate accurate conclusions. Furthermore, incongruity in the methods of BFR application (e.g., cuff pressure) limits the comparability of datasets and thus hinders generalizability of study findings. Appropriate use of biomarkers, effective BFR application, and befitting study design have the potential to progress knowledge on the acute and chronic response of bone to BFR exercise and contribute toward the development of a novel strategy to protect or enhance bone health. Therefore, the purpose of the present synthesis review is to 1) evaluate current mechanistic evidence; 2) discuss and offer explanations for similar and contrasting data findings; and 3) create a methodological framework for future mechanistic and applied research.

Mitochondrial permeability transition regulator, cyclophilin D, is transcriptionally activated by C/EBP during adipogenesis

Age-related bone loss is associated with decreased bone formation, increased bone resorption, and accumulation of bone marrow fat. During aging, differentiation potential of bone marrow stromal (a.k.a. mesenchymal stem) cells (BMSCs) is shifted toward an adipogenic lineage and away from an osteogenic lineage. In aged bone tissue, we previously observed pathological opening of the mitochondrial permeability transition pore (MPTP) which leads to mitochondrial dysfunction, oxidative phosphorylation uncoupling, and cell death. Cyclophilin D (CypD) is a mitochondrial protein that facilitates opening of the MPTP. We found earlier that CypD is downregulated during osteogenesis of BMSCs leading to lower MPTP activity and, thus, protecting mitochondria from dysfunction. However, during adipogenesis, a fate alternative to osteogenesis, the regulation of mitochondrial function and CypD expression is still unclear. In this study, we observed that BMSCs have increased CypD expression and MPTP activity, activated glycolysis, and fragmented mitochondrial network during adipogenesis. Adipogenic C/EBPα acts as a transcriptional activator of expression of the CypD gene, Ppif, during this process. Inflammation-associated transcription factor NF-κB shows a synergistic effect with C/EBPα inducing Ppif expression. Overall, we demonstrated changes in mitochondrial morphology and function during adipogenesis. We also identified C/EBPα as a transcriptional activator of CypD. The synergistic activation of CypD by C/EBPα and the NF-κB p65 subunit during this process suggests a potential link between adipogenic signaling, inflammation, and MPTP gain-of-function, thus altering BMSC fate during aging.

The Janus-Faced Role of Lipid Droplets in Aging: Insights from the Cellular Perspective

It is widely accepted that nine hallmarks-including mitochondrial dysfunction, epigenetic alterations, and loss of proteostasis-exist that describe the cellular aging process. Adding to this, a well-described cell organelle in the metabolic context, namely, lipid droplets, also accumulates with increasing age, which can be regarded as a further aging-associated process. Independently of their essential role as fat stores, lipid droplets are also able to control cell integrity by mitigating lipotoxic and proteotoxic insults. As we will show in this review, numerous longevity interventions (such as mTOR inhibition) also lead to strong accumulation of lipid droplets in Saccharomyces cerevisiae, Caenorhabditis elegans, Drosophila melanogaster, and mammalian cells, just to name a few examples. In mammals, due to the variety of different cell types and tissues, the role of lipid droplets during the aging process is much more complex. Using selected diseases associated with aging, such as Alzheimer's disease, Parkinson's disease, type II diabetes, and cardiovascular disease, we show that lipid droplets are "Janus"-faced. In an early phase of the disease, lipid droplets mitigate the toxicity of lipid peroxidation and protein aggregates, but in a later phase of the disease, a strong accumulation of lipid droplets can cause problems for cells and tissues.

Pharmaceutical treatment of bone loss: From animal models and drug development to future treatment strategies

Animal models are fundamental to advance our knowledge of the underlying pathophysiology of bone loss and to study pharmaceutical countermeasures against it. The animal model of post-menopausal osteoporosis from ovariectomy is the most widely used preclinical approach to study skeletal deterioration. However, several other animal models exist, each with unique characteristics such as bone loss from disuse, lactation, glucocorticoid excess, or exposure to hypobaric hypoxia. The present review aimed to provide a comprehensive overview of these animal models to emphasize the importance and significance of investigating bone loss and pharmaceutical countermeasures from perspectives other than post-menopausal osteoporosis only. Hence, the pathophysiology and underlying cellular mechanisms involved in the various types of bone loss are different, and this might influence which prevention and treatment strategies are the most effective. In addition, the review sought to map the current landscape of pharmaceutical countermeasures against osteoporosis with an emphasis on how drug development has changed from being driven by clinical observations and enhancement or repurposing of existing drugs to today's use of targeted anti-bodies that are the result of advanced insights into the underlying molecular mechanisms of bone formation and resorption. Moreover, new treatment combinations or repurposing opportunities of already approved drugs with a focus on dabigatran, parathyroid hormone and abaloparatide, growth hormone, inhibitors of the activin signaling pathway, acetazolamide, zoledronate, and romosozumab are discussed. Despite the considerable progress in drug development, there is still a clear need to improve treatment strategies and develop new pharmaceuticals against various types of osteoporosis. The review also highlights that new treatment indications should be explored using multiple animal models of bone loss in order to ensure a broad representation of different types of skeletal deterioration instead of mainly focusing on primary osteoporosis from post-menopausal estrogen deficiency.

B. abortus Infection Promotes an Imbalance in the Adipocyte-Osteoblast Crosstalk Favoring Bone Resorption

Osteoarticular injury is the most common presentation of active brucellosis in humans. Osteoblasts and adipocytes originate from mesenchymal stem cells (MSC). Since those osteoblasts are bone-forming cells, the predilection of MSC to differentiate into adipocytes or osteoblasts is a potential factor involved in bone loss. In addition, osteoblasts and adipocytes can be converted into each other according to the surrounding microenvironment. Here, we study the incumbency of B. abortus infection in the crosstalk between adipocytes and osteoblasts during differentiation from its precursors. Our results indicate that soluble mediators present in culture supernatants from B. abotus-infected adipocytes inhibit osteoblast mineral matrix deposition in a mechanism dependent on the presence of IL-6 with the concomitant reduction of Runt-related transcription factor 2 (RUNX-2) transcription, but without altering organic matrix deposition and inducing nuclear receptor activator ligand kβ (RANKL) expression. Secondly, B. abortus-infected osteoblasts stimulate adipocyte differentiation with the induction of peroxisome proliferator-activated receptor γ (PPAR-γ) and CCAAT enhancer binding protein β (C/EBP-β). We conclude that adipocyte-osteoblast crosstalk during B. abortus infection could modulate mutual differentiation from its precursor cells, contributing to bone resorption.

CCL3 in the bone marrow microenvironment causes bone loss and bone marrow adiposity in aged mice

The central physiological role of the bone marrow renders bone marrow stromal cells (BMSCs) particularly sensitive to aging. With bone aging, BMSCs acquire a differentiation potential bias in favor of adipogenesis over osteogenesis, and the underlying molecular mechanisms remain unclear. Herein, we investigated the factors underlying age-related changes in the bone marrow and their roles in BMSCs' differentiation. Antibody array revealed that CC chemokine ligand 3 (CCL3) accumulation occurred in the serum of naturally aged mice along with bone aging phenotypes, including bone loss, bone marrow adiposity, and imbalanced BMSC differentiation. In vivo Ccl3 deletion could rescue these phenotypes in aged mice. CCL3 improved the adipogenic differentiation potential of BMSCs, with a positive feedback loop between CCL3 and C/EBPα. CCL3 activated C/EBPα expression via STAT3, while C/EBPα activated CCL3 expression through direct promoter binding, facilitated by DNA hypomethylation. Moreover, CCL3 inhibited BMSCs' osteogenic differentiation potential by blocking β-catenin activity mediated by ERK-activated Dickkopf-related protein 1 upregulation. Blocking CCL3 in vivo via neutralizing antibodies ameliorated trabecular bone loss and bone marrow adiposity in aged mice. This study provides insights regarding age-related bone loss and bone marrow adiposity pathogenesis and lays a foundation for the identification of new targets for senile osteoporosis treatment.

Osteoblast-Specific Overexpression of Nucleolar Protein NO66/RIOX1 in Mouse Embryos Leads to Osteoporosis in Adult Mice

In previous study, we showed that nucleolar protein 66 (NO66) is a chromatin modifier and negatively regulates Osterix activity as well as mesenchymal progenitor differentiation. Genetic ablation of the NO66 (RIOX1) gene in cells of the Prx1-expressing mesenchymal lineage leads to acceleration of osteochondrogenic differentiation and a larger skeleton in adult mice, whereas mesenchyme-specific overexpression of NO66 inhibits osteochondrogenesis resulting in dwarfism and osteopenia. However, the impact of NO66 overexpression in cells of the osteoblast lineage in vivo remains largely undefined. Here, we generated osteoblast-specific transgenic mice overexpressing a FLAG-tagged NO66 transgene driven by the 2.3 kB alpha-1type I collagen (Col1a1) promoter. We found that overexpression of NO66 in cells of the osteoblast lineage did not cause overt defects in developmental bones but led to osteoporosis in the long bones of adult mice. This includes decreased bone volume (BV), bone volume density (bone volume/total volume, BV/TV), and bone mineral density (BMD) in cancellous compartment of long bones, along with the accumulation of fatty droplets in bone marrow. Ex vivo culture of the bone marrow mesenchymal stem/stromal cells (BMSCs) from adult Col1a1-NO66 transgenic mice showed an increase in adipogenesis and a decrease in osteogenesis. Taken together, these data demonstrate a crucial role for NO66 in adult bone formation and homeostasis. Our Col1a1-NO66 transgenic mice provide a novel animal model for the mechanistic and therapeutic study of NO66 in osteoporosis.

Operative treatment of nonunions in the elderly: Clinical and radiographic outcomes in patients at minimum 75 years of age

BACKGROUND

Limited information exists on nonunion treatment in the elderly. This retrospective study evaluates whether results of operative treatment of nonunion of the humerus or femur in patients aged ≥ 75 years are comparable to those in younger patients.

METHODS

We identified patients age ≥ 75 years with a nonunion of humerus or femur treated with open reduction and internal fixation. The Non-Union Scoring System was calculated. Complications, clinical outcome, and radiographic findings were assessed. Primary endpoint was nonunion healing. A literature review compared time to healing of humeral and femoral nonunion in younger populations.

RESULTS

We identified 45 patients treated for a nonunion of humerus or femur with > 12 months follow-up. Median age was 79 years (range 75-96). Median time to presentation was 12 months (range 4-127) after injury, median number of prior surgeries was 1 (range 0-4). Union rate was 100%, with median time to union 6 months (range 2-42). Six patients underwent revision for persistent nonunion and healed without further complications.

CONCLUSIONS

Using a protocol of debridement, alignment, compression, stable fixation, bone grafting and early motion, patients aged 75 years or older can reliably achieve healing when faced with a nonunion of the humerus or femur.

LEVEL OF EVIDENCE

IV.

The role of bone marrow on the mechanical properties of trabecular bone: a systematic review

Background

Accurate evaluation of the mechanical properties of trabecular bone is important, in which the internal bone marrow plays an important role. The aim of this systematic review is to investigate the roles of bone marrow on the mechanical properties of trabecular bone to better support clinical work and laboratory research.

Methods

A systematic review of the literature published up to June 2022 regarding the role of bone marrow on the mechanical properties of trabecular bone was performed, using PubMed and Web of Science databases. The journal language was limited to English. A total of 431 articles were selected from PubMed (n = 186), Web of Science (n = 244) databases, and other sources (n = 1).

Results

After checking, 38 articles were finally included in this study. Among them, 27 articles discussed the subject regarding the hydraulic stiffening of trabecular bone due to the presence of bone marrow. Nine of them investigated the effects of bone marrow on compression tests with different settings, i.e., in vitro experiments under unconfined and confined conditions, and computer model simulations. Relatively few controlled studies reported the influence of bone marrow on the shear properties of trabecular bone.

Conclusion

Bone marrow plays a non-neglectable role in the mechanical properties of trabecular bone, its contribution varies depending on the different loading types and test settings. To obtain the mechanical properties of trabecular bone comprehensively and accurately, the solid matrix (trabeculae) and fluid-like component (bone marrow) should be considered in parallel rather than tested separately.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12938-022-01051-1.

Imputation of Human Primary Osteoblast Single Cell RNA-Seq Data Identified Three Novel Osteoblastic Subtypes

BACKGROUND

Recently, single-cell RNA sequencing (scRNA-seq) technology was increasingly used to study transcriptomics at a single-cell resolution, scRNA-seq analysis was complicated by the "dropout", where the data only captures a small fraction of the transcriptome. This phenomenon can lead to the fact that the actual expressed transcript may not be detected. We previously performed osteoblast subtypes classification and dissection on freshly isolated human osteoblasts.

MATERIALS AND METHODS

Here, we used the scImpute method to impute the missing values of dropout genes from a scRNA-seq dataset generated on freshly isolated human osteoblasts.

RESULTS

Based on the imputed gene expression patterns, we discovered three new osteoblast subtypes. Specifically, these newfound osteoblast subtypes are osteoblast progenitors, and two undetermined osteoblasts. Osteoblast progenitors showed significantly high expression of proliferation related genes (FOS, JUN, JUNB and JUND). Analysis of each subtype showed that in addition to bone formation, these undetermined osteoblasts may involve osteoclast and adipocyte differentiation and have the potential function of regulate immune activation.

CONCLUSIONS

Our findings provided a new perspective for studying the osteoblast heterogeneity and potential biological functions of these freshly isolated human osteoblasts at the single-cell level, which provides further insight into osteoblasts subtypes under various (pathological) physiological conditions.

Predicting Lumbar Vertebral Osteopenia Using LvOPI Scores and Logistic Regression Models in an Exploratory Study of Premenopausal Taiwanese Women

Purpose

To propose hybrid predicting models integrating clinical and magnetic resonance imaging (MRI) features to diagnose lumbar vertebral osteopenia (LvOPI) in premenopausal women.

Methods

This prospective study enrolled 101 Taiwanese women, including 53 before and 48 women after menopause. Clinical information, including age, body height, body weight and body mass index (BMI), were recorded. Bone mineral density (BMD) was measured by the dual-energy X-ray absorptiometry. Lumbar vertebral fat fraction (LvFF) was measured by MRI. LvOPI scores (LvOPISs) comprising different clinical features and LvFF were constructed to diagnose LvOPI. Statistical analyses included normality tests, linear regression analyses, logistic regression analyses, group comparisons, and diagnostic performance. A P value less than 0.05 was considered as statistically significant.

Results

The post-menopausal women had higher age, body weight, BMI, LvFF and lower BMD than the pre-menopausal women (all P < 0.05). The lumbar vertebral osteoporosis group had significantly higher age, longer MMI, and higher LvFF than the LvOPI group (all P < 0.05) and normal group (all P < 0.005). LvOPISs (AUC, 0.843 to 0.864) outperformed body weight (0.747; P = 0.0566), BMI (0.737; P < 0.05), age (0.649; P < 0.05), and body height (0.5; P < 0.05) in diagnosing LvOPI in the premenopausal women. Hybrid predicting models using logistic regression analysis (0.894 to 0.9) further outperformed all single predictors in diagnosing LvOPI in the premenopausal women (P < 0.05).

Conclusion

The diagnostic accuracy of the LvOPI can be improved by using our proposed hybrid predicting models in Taiwanese premenopausal women.

Magnetic resonance imaging at 3.0-T in postmenopausal osteoporosis: a prospective study and review of the literature

Objective

To promote advanced research using magnetic resonance imaging (MRI) in the diagnosis of and screening for osteoporosis by looking for correlations among the T-scores measured by dual-energy X-ray absorptiometry (DEXA), the apparent diffusion coefficient (ADC) values on diffusion-weighted imaging (DWI), and the T1-weighted signal intensity values.

Materials and Methods

This was a prospective study of postmenopausal women with no contraindications to MRI and no history of cancer who underwent DEXA within 30 days before or after the MRI examination. A 3.0-T scanner was used in order to acquire sagittal sequences targeting the lumbar spine.

Results

Thirteen women underwent DEXA and MRI. In two cases, the MRI was discontinued early. Therefore, the final sample comprised 11 patients. The ADC values and T1-weighted signal intensity were found to be higher in patients with osteoporosis. However, among the patients > 60 years of age with osteoporosis, ADC values were lower and T1-weighted signal intensity was even higher.

Conclusion

It is unlikely that MRI will soon replace DEXA for the diagnostic workup of osteoporosis. Although DWI and ADC mapping are useful for understanding the pathophysiology of osteoporosis, we believe that T1-weighted sequences are more sensitive than is DWI as a means of performing a qualitative analysis of vertebral alterations.

Serum biomarker-based osteoporosis risk prediction and the systemic effects of Trifolium pratense ethanolic extract in a postmenopausal model

Background

Recent years, a soaring number of marketed Trifolium pratense (red clover) extract products have denoted that a rising number of consumers are turning to natural alternatives to manage postmenopausal symptoms. T. pratense ethanolic extract (TPEE) showed immense potential for their uses in the treatment of menopause complications including osteoporosis and hormone dependent diseases. Early diagnosis of osteoporosis can increase the chance of efficient treatment and reduce fracture risks. Currently, the most common diagnosis of osteoporosis is performed by using dual-energy x-ray absorptiometry (DXA). However, the major limitation of DXA is that it is inaccessible and expensive in rural areas to be used for primary care inspection. Hence, serum biomarkers can serve as a meaningful and accessible data for osteoporosis diagnosis.

Methods

The present study systematically elucidated the anti-osteoporosis and estrogenic activities of TPEE in ovariectomized (OVX) rats by evaluating the bone microstructure, uterus index, serum and bone biomarkers, and osteoblastic and osteoclastic gene expression. Leverage on a pool of serum biomarkers obtained from this study, recursive feature elimination with a cross-validation method (RFECV) was used to select useful biomarkers for osteoporosis prediction. Then, using the key features extracted, we employed five classification algorithms: extreme gradient boosting (XGBoost), random forest, support vector machine, artificial neural network, and decision tree to predict the bone quality in terms of T-score.

Results

TPEE treatments down-regulated nuclear factor kappa-B ligand, alkaline phosphatase, and up-regulated estrogen receptor β gene expression. Additionally, reduced serum C-terminal telopeptides of type 1 collagen level and improvement in the estrogen dependent characteristics of the uterus on the lining of the lumen were observed in the TPEE intervention group. Among the tested classifiers, XGBoost stood out as the best performing classification model with the highest F1-score and lowest standard deviation.

Conclusions

The present study demonstrates that TPEE treatment showed therapeutic benefits in the prevention of osteoporosis at the transcriptional level and maintained the estrogen dependent characteristics of the uterus. Our study revealed that, in the case of limited number of features, RFECV paired with XGBoost model could serve as a powerful tool to readily evaluate and diagnose postmenopausal osteoporosis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13020-022-00622-7.

Bone Marrow Adiposity, Bone Mineral Density and Wnt/β-catenin Pathway Inhibitors Levels in Hemodialysis Patients

Background

Marrow adipose tissue (MAT) is known to accumulate in patients with chronic kidney disease. This pilot study aimed to evaluate bone mineral density (BMD), MAT, visceral adipose tissue (VAT), and subcutaneous adipose tissue (SAT) using computed tomography (CT) scans and to explore correlations between bone parameters, circulating Wnt/β-catenin pathway inhibitor levels, and adipose tissue parameters.

Methods

Single-center cross-sectional pilot study conducted in hemodialysis patients at the Centre Universitaire de Québec, Hôtel-Dieu de Québec hospital, Canada. CT-scan slices were acquired at the levels of the hip, L3 vertebra, and tibia. Volumetric and areal BMD, tibia cortical thickness, VAT and SAT area, and fat marrow index (FMI) were analyzed using the Mindways QCT Pro software. Blood levels of sclerostin, dickkopf-related protein 1 (DKK1), fibroblast growth factor 23, and α-Klotho were assessed. Spearman’s rho test was used to evaluate correlations.

Results

Fifteen hemodialysis patients (median age, 75 [66–82] years; 80% male; dialysis vintage, 39.3 [27.4–71.0] months) were included. While inverse correlations were obtained between L3 FMI and BMD, positive correlations were found between proximal tibial FMI and vertebral and tibial BMD, as well as with tibial (proximal and distal) cortical thickness. VAT had a positive correlation with α-Klotho levels, whereas L3 FMI had a negative correlation with DKK1 levels.

Conclusions

CT-scan allows simultaneous evaluation of bone and marrow adiposity in dialysis patients. Correlations between MAT and BMD vary depending on the bone site evaluated. DKK1 and α-Klotho levels correlate with adipose tissue accumulation in dialysis patients.

MRI-based vertebral bone quality score effectively reflects bone quality in patients with osteoporotic vertebral compressive fractures

OBJECTIVE

The present study is aimed to validate the ability of the vertebral bone quality (VBQ) score to evaluate bone quality in patients with osteoporotic vertebral compression fractures (OVCF) and to compare it with the ability of T-score by DXA. In addition, the sensitivity of VBQ score with cerebrospinal fluid (CSF) of L2 and L3 segments as baseline is evaluated.

METHODS

196 inpatients were collected and assigned into OVCF and Non-OVCF groups, respectively. For each patient, the VBQ score was calculated by the signal intensity of the L1-L4 vertebral bodies and CSF at L3 or L2 level from T1-weighted MRIs, while T-score from DXA was also obtained. The VBQ and T-score was compared between OVCF and non-OVCF groups, and among age groups. The OVCF ORs by VBQ score and T-score were calculated using logistic regression.

RESULTS

OVCF group was significantly different to the non-OVCF group in the T-score (- 2.9 vs. - 0.7) and VBQ score (4.0 vs. 3.5). VBQ score and T-score in patient aged 60-79 years old could indicate the bone quality, but only T-score in patients aged 50-59 years old. OVCF are associated with both higher VBQ score and lower T-score. The VBQ scores calculated by L2 CSF and L3 CSF were similar.

CONCLUSIONS

The VBQ score is an effective indicator of bone quality in OVCF patients and comparable to T-score, particularly in people over 60 years old. The VBQ score is not sensitive to CSF of different segments as a baseline.

In premenopausal women with idiopathic osteoporosis, lower bone formation rate is associated with higher body fat and higher IGF-1

We examined serum IGF-1 in premenopausal IOP, finding relationships that were opposite to those expected: higher IGF-1 was associated with lower bone formation and higher body fat, and lower BMD response to teriparatide. These paradoxical relationships between serum IGF-1, bone, and fat may contribute to the mechanism of idiopathic osteoporosis in premenopausal women.

INTRODUCTION

Premenopausal women with idiopathic osteoporosis (IOP) have marked deficits in bone microarchitecture but variable bone remodeling. We previously reported that those with low tissue-level bone formation rate (BFR) are less responsive to teriparatide and have higher serum IGF-1, a hormone anabolic for osteoblasts and other tissues. The IGF-1 data were unexpected because IGF-1 is low in other forms of low turnover osteoporosis-leading us to hypothesize that IGF-1 relationships are paradoxical in IOP. This study aimed to determine whether IOP women with low BFR have higher IGF-1 and paradoxical IGF-1 relationships in skeletal and non-skeletal tissues, and whether IGF-1 and the related measures predict teriparatide response.

METHODS

This research is an ancillary study to a 24 month clinical trial of teriparatide for IOP. Baseline assessments were related to trial outcomes: BMD, bone remodeling.

SUBJECTS

 Premenopausal women with IOP(n = 34); bone remodeling status was defined by baseline cancellous BFR/BS on bone biopsy.

MEASURES

 Serum IGF-1 parameters, compartmental adiposity (DXA, CT, MRI), serum hormones, and cardiovascular-risk-markers related to fat distribution.

RESULTS

As seen in other populations, lower BFR was associated with higher body fat and poorer teriparatide response. However, in contrast to observations in other populations, low BFR, higher body fat, and poorer teriparatide response were all related to higher IGF-1: IGF-1 Z-score was inversely related to BFR at all bone surfaces (r =  - 0.39 to - 0.46; p < 0.05), directly related to central fat (p = 0.05) and leptin (p = 0.03). IGF-1 inversely related to 24 month hip BMD %change (r =  - 0.46; p = 0.01).

CONCLUSIONS

Paradoxical IGF-1 relationships suggest that abnormal or atypical regulation of bone and fat may contribute to osteoporosis mechanisms in premenopausal IOP.

Validation of a Semiautomatic Image Analysis Software for the Quantification of Musculoskeletal Tissues

Accurate quantification of bone, muscle, and their components is still an unmet need in the musculoskeletal field. Current methods to quantify tissue volumes in 3D images are expensive, labor-intensive, and time-consuming; thus, a reliable, valid, and quick application is highly needed. Tissue Compass is a standalone software for semiautomatic segmentation and automatic quantification of musculoskeletal organs. To validate the software, cross-sectional micro-CT scans images of rat femur (n = 19), and CT images of hip and abdomen (n = 100) from the Osteoporotic Fractures in Men (MrOS) Study were used to quantify bone, hematopoietic marrow (HBM), and marrow adipose tissue (MAT) using commercial manual software as a comparator. Also, abdominal CT scans (n = 100) were used to quantify psoas muscle volumes and intermuscular adipose tissue (IMAT) using the same software. We calculated Pearson's correlation coefficients, individual intra-class correlation coefficients (ICC), and Bland-Altman limits of agreement together with Bland-Altman plots to show the inter- and intra-observer agreement between Tissue Compass and commercially available software. In the animal study, the agreement between Tissue Compass and commercial software was r > 0.93 and ICC > 0.93 for rat femur measurements. Bland-Altman limits of agreement was - 720.89 (- 1.5e+04, 13,074.00) for MAT, 4421.11 (- 1.8e+04, 27,149.73) for HBM and - 6073.32 (- 2.9e+04, 16,388.37) for bone. The inter-observer agreement for QCT human study between two observers was r > 0.99 and ICC > 0.99. Bland-Altman limits of agreement was 0.01 (- 0.07, 0.10) for MAT in hip, 0.02 (- 0.08, 0.12) for HBM in hip, 0.05 (- 0.15, 0.25) for bone in hip, 0.02 (- 0.18, 0.22) for MAT in L1, 0.00 (- 0.16, 0.16) for HBM in L1, and 0.02 (- 0.23, 0.27) for bone in L1. The intra-observer agreement for QCT human study between the two applications was r > 0.997 and ICC > 0.99. Bland-Altman limits of agreement was 0.03 (- 0.13, 0.20) for MAT in hip, 0.05 (- 0.08, 0.18) for HBM in hip, 0.05 (- 0.24, 0.34) for bone in hip, - 0.02 (- 0.34, 0.31) for MAT in L1, - 0.14 (- 0.44, 0.17) for HBM in L1, - 0.29 (- 0.62, 0.05) for bone in L1, 0.03 (- 0.08, 0.15) for IMAT in psoas, and 0.02 (- 0.35, 0.38) for muscle in psoas. Compared to a conventional application, Tissue Compass demonstrated high accuracy and non-inferiority while also facilitating easier analyses. Tissue Compass could become the tool of choice to diagnose tissue loss/gain syndromes in the future by requiring a small number of CT sections to detect tissue volumes and fat infiltration.

Promoting osteointegration effect of Cu alloyed titanium (TiCu) in ovariectomized rats

Osteoporosis is a common skeletal disease making patients be prone to the osteoporotic fracture. However, the clinical implants made of titanium and its alloys with a poor osseointegration need a long time for healing and easily to loosening. Thus, a new class of Cu-alloyed titanium (TiCu) alloys with excellent mechanical properties and bio-functionalization has been developed. In this study, the osteoporosis modeled rats were used to study the osteointegration effect and underlying mechanism of TiCu. The results showed that after implantation for 4 weeks, TiCu alloy could promote the reconstruction of vascular network around the implant by up-regulating vascular endothelial growth factor expression. After 8 weeks, it could further promote the proliferation and differentiation of osteoblasts, mineralization and deposition of collagens, and then significantly increasing bone mineral density around the implant. In conclusion, TiCu alloy would enhance the fixation stability, accelerate the osteointegration, and thus reduce the risk of aseptic loosening during the long-term implantation in the osteoporosis environment. This study was the first to report the role and mechanism of a Cu-alloyed metal in promoting osteointegration in osteoporosis environment, which provides a new attractive support for the improvement of future clinical applications of Cu-alloyed antibacterial titanium alloys.

Alkbh1-mediated DNA N6-methyladenine modification regulates bone marrow mesenchymal stem cell fate during skeletal aging

Objectives

DNA N6‐methyladenine (N6‐mA) demethylase Alkbh1 participates in regulating osteogenic differentiation of mesenchymal stem cell (MSCs) and vascular calcification. However, the role of Alkbh1 in bone metabolism remains unclear.

Materials and Methods

Bone marrow mesenchymal stem cells (BMSCs)‐specific Alkbh1 knockout mice were used to investigate the role of Alkbh1 in bone metabolism. Western blot, qRT‐PCR, and immunofluorescent staining were used to evaluate the expression of Alkbh1 or optineurin (optn). Micro‐CT, histomorphometric analysis, and calcein double‐labeling assay were used to evaluate bone phenotypes. Cell staining and qRT‐PCR were used to evaluate the osteogenic or adipogenic differentiation of BMSCs. Dot blotting was used to detect the level of N6‐mA in genomic DNA. Chromatin immunoprecipitation (Chip) assays were used to identify critical targets of Alkbh1. Alkbh1 adeno‐associated virus was used to overexpress Alkbh1 in aged mice.

Results

Alkbh1 expression in BMSCs declined during aging. Knockout of Alkbh1 promoted adipogenic differentiation of BMSCs while inhibited osteogenic differentiation. BMSC‐specific Alkbh1 knockout mice exhibited reduced bone mass and increased marrow adiposity. Mechanistically, we identified optn as the downstream target through which Alkbh1‐mediated DNA m6A modification regulated BMSCs fate. Overexpression of Alkbh1 attenuated bone loss and marrow fat accumulation in aged mice.

Conclusions

Our findings demonstrated that Alkbh1 regulated BMSCs fate and bone‐fat balance during skeletal aging and provided a potential target for the treatment of osteoporosis.

PTHG2 Reduces Bone Loss in Ovariectomized Mice by Directing Bone Marrow Mesenchymal Stem Cell Fate

Teriparatide, also known as 1-34 parathyroid hormone (PTH (1-34)), is commonly used for the treatment of osteoporosis in postmenopausal women. But its therapeutic application is restricted by poor metabolic stability, low bioavailability, and rapid clearance. Herein, PTHG2, a glycosylated teriparatide derivative, is designed and synthesized to improve PTH stability and exert more potent antiosteoporosis effect. Surface plasmon resonance (SPR) analysis shows that PTHG2 combines to PTH 1 receptor. Additional acetylglucosamine covalent bonding in the first serine at the N terminal of PTH (1-34) improves stability and increases protein hydrolysis resistance. Intermittent administration of PTHG2 preserves bone quality in ovariectomy- (OVX-) induced osteoporosis mice model, along with increased osteoblastic differentiation and bone formation, and reduced marrow adipogenesis. In vitro, PTHG2 inhibits adipogenic differentiation and promotes osteoblastic differentiation of bone marrow mesenchymal stem cells (BMSCs). For molecular mechanism, PTHG2 directs BMSCs fate through stimulating the cAMP-PKA signaling pathway. Blocking PKA abrogates the pro-osteogenic effect of PTHG2. In conclusion, our study reveals that PTHG2 can accelerate osteogenic differentiation of BMSCs and inhibit adipogenic differentiation of BMSCs and show a better protective effect than PTH (1-34) in the treatment of osteoporosis.

Leptin and environmental temperature as determinants of bone marrow adiposity in female mice

Bone marrow adipose tissue (BMAT) levels are higher in distal femur metaphysis of female mice housed at thermoneutral (32°C) than in mice housed at 22°C, as are abdominal white adipose tissue (WAT) mass, and serum leptin levels. We performed two experiments to explore the role of increased leptin in temperature-enhanced accrual of BMAT. First, we supplemented 6-week-old female C57BL/6J (B6) mice with leptin for 2 weeks at 10 µg/d using a subcutaneously implanted osmotic pump. Controls consisted of ad libitum (ad lib) fed mice and mice pair fed to match food intake of leptin-supplemented mice. The mice were maintained at 32°C for the duration of treatment. At necropsy, serum leptin in leptin-supplemented mice did not differ from ad lib mice, suggesting suppression of endogenous leptin production. In support, Ucp1 expression in BAT, percent body fat, and abdominal WAT mass were lower in leptin-supplemented mice. Leptin-supplemented mice also had lower BMAT and higher bone formation in distal femur metaphysis compared to the ad lib group, changes not replicated by pair-feeding. In the second experiment, BMAT response was evaluated in 6-week-old female B6 wild type (WT), leptin-deficient ob/ob and leptin-treated (0.3 μg/d) ob/ob mice housed at 32°C for the 2-week duration of the treatment. Compared to mice sacrificed at baseline (22°C), BMAT increased in ob/ob mice as well as WT mice, indicating a leptin independent response to increased temperature. However, infusion of ob/ob mice with leptin, at a dose rate having negligible effects on either energy metabolism or serum leptin levels, attenuated the increase in BMAT. In summary, increased housing temperature and increased leptin have independent but opposing effects on BMAT in mice.

Expression of long noncoding RNA Xist is induced by glucocorticoids

Glucocorticoids (GCs) are potent anti-inflammatory and immunosuppressive agents. However, their clinical usage is limited by severe multisystemic side effects. Glucocorticoid induced osteoporosis results in significant morbidity and mortality but the cellular and molecular mechanisms underlying GC-induced bone loss are not clear. GC use results in decreased osteoblast differentiation with increased marrow adiposity through effects on bone marrow stem cells. GC effects are transduced through its receptor (GR). To identify novel GR regulated genes, we performed RNA sequencing (RNA-Seq) analysis comparing conditional GR knockout mouse made by crossing the floxed GR animal with the Col I promoter-Cre, versus normal floxed GR without Cre, and that testing was specific for Col I promoter active cells, such as bone marrow mesenchymal stem/osteoprogenitor cells (MSCs) and osteoblasts. Results showed 15 upregulated genes (3- to 10-fold) and 70 downregulated genes (-2.7- to -10-fold), with the long noncoding RNA X-inactive specific transcript (Xist) downregulated the most. The differential expression of genes measured by RNA-Seq was validated by qRT-PCR analysis of selected genes and the GC/GR signaling-dependent expression of Xist was further demonstrated by GC (dexamethasone) treatment of GR-deficient MSCs in vitro and by GC injection of C57BL/6 mice (wild-type males and females) in vivo. Our data revealed that the long noncoding RNA Xist is a GR regulated gene and its expression is induced by GC both in vitro and in vivo. To our knowledge, this is the first evidence showing that Xist is transcriptionally regulated by GC/GR signaling.

Mechanically-regulated bone repair

Fracture healing is a complex, multistep process that is highly sensitive to mechanical signaling. To optimize repair, surgeons prescribe immediate weight-bearing as-tolerated within 24 hours after surgical fixation; however, this recommendation is based on anecdotal evidence and assessment of bulk healing outcomes (e.g., callus size, bone volume, etc.). Given challenges in accurately characterizing the mechanical environment and the ever-changing properties of the regenerate, the principles governing mechanical regulation of repair, including their cell and molecular basis, are not yet well defined. However, the use of mechanobiological rodent models, and their relatively large genetic toolbox, combined with recent advances in imaging approaches and single-cell analyses is improving our understanding of the bone microenvironment in response to loading. This review describes the identification and characterization of distinct cell populations involved in bone healing and highlights the most recent findings on mechanical regulation of bone homeostasis and repair with an emphasis on osteo-angio coupling. A discussion on aging and its impact on bone mechanoresponsiveness emphasizes the need for novel mechanotherapeutics that can re-sensitize skeletal stem and progenitor cells to physical rehabilitation protocols.

Dietary organosulfur compounds: Emerging players in the regulation of bone homeostasis by plant-derived molecules

The progressive decline of bone mass and the deterioration of bone microarchitecture are hallmarks of the bone aging. The resulting increase in bone fragility is the leading cause of bone fractures, a major cause of disability. As the frontline pharmacological treatments for osteoporosis suffer from low patients' adherence and occasional side effects, the importance of diet regimens for the prevention of excessive bone fragility has been increasingly recognized. Indeed, certain diet components have been already associated to a reduced fracture risk. Organosulfur compounds are a broad class of molecules containing sulfur. Among them, several molecules of potential therapeutic interest are found in edible plants belonging to the Allium and Brassica botanical genera. Polysulfides derived from Alliaceae and isothiocyanates derived from Brassicaceae hold remarkable nutraceutical potential as anti-inflammatory, antioxidants, vasorelaxant and hypolipemic. Some of these effects are linked to the ability to release the gasotrasmitter hydrogen sulfide (H₂S). Recent preclinical studies have investigated the effect of organosulfur compounds in bone wasting and metabolic bone diseases, revealing a strong potential to preserve skeletal health by exerting cytoprotection and stimulating the bone forming activity by osteoblasts and attenuating bone resorption by osteoclasts. This review is intended for revising evidence from preclinical and epidemiological studies on the skeletal effects of organosulfur molecules of dietary origin, with emphasis on the direct regulation of bone cells by plant-derived polysulfides, glucosinolates and isothiocyanates. Moreover, we highlight the potential molecular mechanisms underlying the biological role of these compounds and revise the importance of the so-called 'H₂S-system' on the regulation of bone homeostasis.

Finite Element Analysis of Osteoporotic and Osteoblastic Vertebrae and Its Association With the Proton Density Fat Fraction From Chemical Shift Encoding-Based Water-Fat MRI - A Preliminary Study

PURPOSE

Osteoporosis is prevalent and entails alterations of vertebral bone and marrow. Yet, the spine is also a common site of metastatic spread. Parameters that can be non-invasively measured and could capture these alterations are the volumetric bone mineral density (vBMD), proton density fat fraction (PDFF) as an estimate of relative fat content, and failure displacement and load from finite element analysis (FEA) for assessment of bone strength. This study's purpose was to investigate if osteoporotic and osteoblastic metastatic changes in lumbar vertebrae can be differentiated based on the abovementioned parameters (vBMD, PDFF, and measures from FEA), and how these parameters correlate with each other.

MATERIALS AND METHODS

Seven patients (3 females, median age: 77.5 years) who received 3-Tesla magnetic resonance imaging (MRI) and multi-detector computed tomography (CT) of the lumbar spine and were diagnosed with either osteoporosis (4 patients) or diffuse osteoblastic metastases (3 patients) were included. Chemical shift encoding-based water-fat MRI (CSE-MRI) was used to extract the PDFF, while vBMD was extracted after automated vertebral body segmentation using CT. Segmentation masks were used for FEA-based failure displacement and failure load calculations. Failure displacement, failure load, and PDFF were compared between patients with osteoporotic vertebrae versus patients with osteoblastic metastases, considering non-fractured vertebrae (L1-L4). Associations between those parameters were assessed using Spearman correlation.

RESULTS

Median vBMD was 59.3 mg/cm³ in osteoporotic patients. Median PDFF was lower in the metastatic compared to the osteoporotic patients (11.9% vs. 43.8%, p=0.032). Median failure displacement and failure load were significantly higher in metastatic compared to osteoporotic patients (0.874 mm vs. 0.348 mm, 29,589 N vs. 3,095 N, p=0.034 each). A strong correlation was noted between PDFF and failure displacement (rho -0.679, p=0.094). A very strong correlation was noted between PDFF and failure load (rho -0.893, p=0.007).

CONCLUSION

PDFF as well as failure displacement and load allowed to distinguish osteoporotic from diffuse osteoblastic vertebrae. Our findings further show strong associations between PDFF and failure displacement and load, thus may indicate complimentary pathophysiological associations derived from two non-invasive techniques (CSE-MRI and CT) that inherently measure different properties of vertebral bone and marrow.

Relationship between Osteopontin and Bone Mineral Density

Recent studies suggest that osteopontin (OPN) could be used as an early marker for the diagnosis of bone disorders. Considering the contradictory opinions in the literature, the objective of this systematic review is to analyse the current information regarding the relationship between OPN and bone mineral density (BMD), which represents an important process in the development of osteoporosis. We performed a literature search of clinical trials using the PubMed database, published between 1999-2020, and identified 7 studies that were eligible for analysis. The eligibility criteria were based on studies that analysed the relationship between osteopontin and bone mineral density on human subjects. Conclusion: serum OPN levels might be used as a biomarker of the early diagnosis of osteoporosis in postmenopausal women, with or without osteoporotic vertebral fractures.

Forkhead box P1 (Foxp1) in osteoblasts regulates bone mass accrual and adipose tissue energy metabolism

Adiponectin (AdipoQ), a hormone abundantly secreted by adipose tissues, has multiple beneficial functions, including insulin sensitization as well as lipid and glucose metabolism. It has been reported that bone controls energy metabolism through an endocrine-based mechanism. In this study, we observed that bone also acts as an important endocrine source for AdipoQ, and its capacity in osteoblasts is controlled by the forkhead box P1 (FOXP1) transcriptional factor. Deletion of the Foxp1 gene in osteoblasts led to augmentation of AdipoQ levels accompanied by fueled energy expenditure in adipose tissues. In contrast, overexpression of Foxp1 in bones impaired AdipoQ secretion and restrained energy consumption. Chromatin immunoprecipitation sequencing (ChIP-seq) analysis revealed that AdipoQ expression, which increases as a function of bone age, is directly controlled by FOXP1. Our results indicate that bones, especially aged bones, provide an important source of a set of endocrine factors, including AdipoQ, that control body metabolism. © 2021 American Society for Bone and Mineral Research (ASBMR).

LncRNA PART1/miR-185-5p/RUNX3 feedback loop modulates osteogenic differentiation of bone marrow mesenchymal stem cells

BACKGROUND

Osteogenic differentiation of human bone marrow-derived mesenchymal stem cells (hBMSCs) is essential for bone formation, and its dysfunction is reported to be associated with osteoporosis (OP). Recent researches have determined that lncRNA PART1 participates in the pathogenesis of multiple diseases. However, its role in modulating osteogenic differentiation of hBMSCs is unclear.

METHODS

PART1, miR-185-5p, and RUNX3 levels were assessed via RT-qPCR. The protein levels of OCN, OSN, and COL1A1 were measured by western blotting. The osteoblastic phenotype was evaluated via ALP activity and ARS staining. The relationship between miR-185-5p and PART1 or RUNX3 was validated by luciferase reporter, RIP assays.

RESULTS

PART1 and RUNX3 expression were enhanced during hBMSC osteogenic differentiation. PART1 deletion decreased OCN, OSN, and COL1A1 levels and weakened ALP activity, but promoted the apoptosis of hBMSCs. Moreover, PART1 served as a ceRNA to influence the RUNX3 level via targeting miR-185-5p. In addition, RUNX3 was verified to activate the transcription of PART1 in hBMSCs. Finally, rescue assays indicated that suppression of miR-185-5p or addition of RUNX3 partially abolished the effects of PART1 knockdown on the levels of OCN, OSX, and COL1A1 levels, ALP activity, and apoptosis.

CONCLUSION

Our study elaborated that PART1/miR-185-5p/RUNX3 feedback contributed to osteogenic differentiation and inhibited the hBMSCs apoptosis, suggesting that PART1 might be a novel target for OP treatment.

Bone marrow adiposity inversely correlates with bone turnover in pediatric renal osteodystrophy

Bone marrow adiposity is associated with bone disease in the general population. Although chronic kidney disease (CKD) is associated with increased bone fragility, the correlation between marrow adiposity and bone health in CKD is unknown. We evaluated the relationship between bone marrow adipocytes and bone histomorphometry in 32 pediatric patients. We also evaluated the effects of growth hormone and calcitriol (1,25(OH)₂D₃)—two therapies commonly prescribed for pediatric bone disease—on marrow adiposity and bone histomorphometry. Finally, the adipogenic potential of primary human osteoblasts from CKD patients was assessed in vitro, both alone and in the presence of 1,25(OH)₂D₃. In cross-sectional analysis, marrow adipocyte number per tissue area (Adi.N/T.Ar) correlated with bone formation rate/bone surface (BFR/BS) in patients with high bone turnover (r = −0.55, p = 0.01) but not in those with low/normal bone turnover. Changes in bone formation rate correlated with changes Adi.N/T.Ar on repeat bone biopsy(r = −0.48, p = 0.02). In vitro, CKD and control osteoblasts had a similar propensity to transition into an adipocyte-like phenotype; 1,25(OH)₂D₃ had very little effect on this propensity. In conclusion, marrow adiposity correlates inversely with bone turnover in pediatric patients with high turnover renal osteodystrophy. The range of adiposity observed in pediatric patients with low/normal bone turnover is not explained by intrinsic changes to precursor cells or by therapies but may reflect the effects of circulating factors on bone cell health in this population.

•

Marrow adipocyte numbers correlate with bone formation in high turnover renal osteodystrophy.

•

Marrow adipocyte numbers do not correlate with osteoid accumulation in CKD.

•

Circulating toxins may impair adipogenesis in low turnover osteodystrophy.

Deficiency of PPARγ in Bone Marrow Stromal Cells Does not Prevent High-Fat Diet-Induced Bone Deterioration in Mice

BACKGROUND

Bone marrow osteoblasts and adipocytes are derived from a common mesenchymal stem cell and have a reciprocal relationship. Peroxisome proliferator-activated receptor gamma (PPARγ), a regulator for adipocyte differentiation, may be a potential target for reducing obesity and increasing bone mass.

OBJECTIVES

This study tested the hypothesis that bone-specific Pparg conditional knockout (cKO), via deletion of Pparg from bone marrow stromal cells (BMSC) using Osterix 1 (Osx1)-Cre, would prevent high-fat (HF) diet-induced bone deterioration in mice.

METHODS

PPARγ cKO (PPARγfl/fl: Osx1-Cre) and floxed littermate control (PPARγfl/fl Osx1-Cre- ) mice that were 6 weeks old were randomly assigned to 4 groups (n = 12/group, 6 male and 6 female) and fed ad libitum with either a normal-fat (NF) purified diet (3.85 kcal/g; 10% energy as fat) or an HF diet (4.73 kcal/g; 45% energy as fat) for 6 mo. Bone structure, body composition, and serum bone-related cytokines were measured. Data were analyzed by 2-way ANOVA with Tukey post hoc comparison.

RESULTS

The HF diet decreased the tibial and lumbar vertebrae trabecular bone volume/total volume (BV/TV) by 28% and 18%, respectively, compared to the NF diet (P < 0.01). PPARγ cKO mice had 23% lower body fat mass and 9% lower lean mass than control mice. PPARγ cKO mice had 41% greater tibial trabecular BV/TV compared to control mice. None of trabecular bone parameters at the second lumbar vertebra were affected by genotype. PPARγ cKO mice had decreased cortical thickness compared to control mice. PPARγ cKO mice had a 14% lower (P < 0.01) serum concentration of leptin and a 35% higher (P < 0.05) concentration of osteocalcin compared with control mice.

CONCLUSIONS

These data indicate that PPARγ has site-specific impacts on bone structures in mice and that knockout PPARγ in BMSC increased bone mass (BV/TV) in the tibia but not the lumbar vertebrae. PPARγ disruption in BMSC did not prevent HF diet-induced bone deterioration in mice.

Association between Visceral and Bone Marrow Adipose Tissue and Bone Quality in Sedentary and Physically Active Ovariectomized Wistar Rats

Background: Obesity is considered protective for bone mass, but this view has been progressively challenged. Menopause is characterized by low bone mass and increased adiposity. Our aim was to determine how visceral and bone marrow adiposity change following ovariectomy (OVX), how they correlate with bone quality and if they are influenced by physical activity. Methods: Five-month-old Wistar rats were OVX or sham-operated and maintained in sedentary or physically active conditions for 9 months. Visceral and bone marrow adiposity as well as bone turnover, femur bone quality and biomechanical properties were assessed. Results: OVX resulted in higher weight, visceral and bone marrow adiposity. Visceral adiposity correlated inversely with femur Ct.Th (r = −0.63, p < 0.001), BV/TV (r = −0.67, p < 0.001), Tb.N (r = −0.69, p < 0.001) and positively with Tb.Sp (r = 0.58, p < 0.001). Bone marrow adiposity also correlated with bone resorption (r = 0.47, p < 0.01), bone formation rate (r = −0.63, p < 0.01), BV/TV (r = −0.85, p < 0.001), Ct.Th (r = −0.51, p < 0.0.01), and with higher empty osteocyte lacunae (r = 0.39, p < 0.05), higher percentage of osteocytes with oxidative stress (r = 0.64, p < 0.0.01) and lower femur maximal stress (r = −0.58, p < 0.001). Physical activity correlated inversely with both visceral (r = −0.74, p < 0.01) and bone marrow adiposity (r = −0.92, p < 0.001). Conclusions: OVX increases visceral and bone marrow adiposity which are associated with inferior bone quality and biomechanical properties. Physical activity could contribute to reduce adipose tissue and thereby improve bone quality.

Ubiquitin specific peptidase Usp53 regulates osteoblast versus adipocyte lineage commitment

We have previously shown that parathyroid hormone (PTH) induces the phosphorylation of the DNA-binding protein Nascent polypeptide associated complex And Coregulator alpha (NACA), leading to nuclear translocation of NACA and activation of target genes. Using ChIP-Seq against NACA in parallel with RNA-sequencing, we report the identification of Ubiquitin Specific Peptidase 53 (Usp53) as a target gene of PTH-activated NACA in osteoblasts. A binding site for NACA within the ChIP fragment from the Usp53 promoter was confirmed by electrophoretic mobility shift assay. Activity of the Usp53 promoter (− 2325/+ 238 bp) was regulated by the JUN-CREB complex and this activation relied on activated PKA and the presence of NACA. Usp53 knockdown in ST2 stromal cells stimulated expression of the osteoblastic markers Bglap2 (Osteocalcin) and Alpl (Alkaline phosphatase) and inhibited expression of the adipogenic markers Pparg and Cebpa. A similar effect was measured when knocking down Naca. During osteoblastogenesis, the impact of Usp53 knockdown on PTH responses varied depending on the maturation stage of the cells. In vivo implantation of Usp53-knockdown bone marrow stromal cells in immunocompromised mice showed an increase in osteoblast number and a decrease in adipocyte counts. Our data suggest that Usp53 modulates the fate of mesenchymal cells by impacting lineage selection.

Identification of co-expression network correlated with different periods of adipogenic and osteogenic differentiation of BMSCs by weighted gene co-expression network analysis (WGCNA)

BACKGROUND

The differentiation of bone marrow mesenchymal stem cells is a complex and dynamic process. The gene expression pattern and mechanism of different periods of adipogenic and osteogenic differentiation remain unclear. Additionally, the interaction between these two lineage determination requires further exploration.

RESULTS

Five modules that were most significantly associated with osteogenic or adipogenic differentiation of BMSCs were selected for further investigation. Biological terms (e.g. ribosome biogenesis, TNF-α signalling pathway, glucose import and fatty acid metabolism) along with hub transcription factors (e.g. PPARG and YY1) and hub miRNAs (e.g. hsa-mir-26b-5p) were enriched in different modules. The expression pattern of 6 hub genes, ADIPOQ, FABP4, SLC7A5, SELPLG, BIRC3, and KLHL30 was validated by RT-qPCR. Finally, cell staining experiments extended the findings of bioinformatics analysis.

CONCLUSION

This study identified the key genes, biological functions, and regulators of each time point of adipogenic and osteogenic differentiation of BMSCs and provided novel evidence and ideas for further research on the differentiation of BMSCs.

In vivo quantitative imaging biomarkers of bone quality and mineral density using multi-band-SWIFT magnetic resonance imaging

Bone is a composite biomaterial of mineral crystals, organic matrix, and water. Each contributes to bone quality and strength and may change independently, or together, with disease progression and treatment. Even so, there is a near ubiquitous reliance on ionizing x-ray-based approaches to measure bone mineral density (BMD) which is unable to fully characterize bone strength and may not adequately predict fracture risk. Characterization of treatment efficacy in bone diseases of altered remodeling is complicated by the lack of imaging modality able to safely monitor material-level and biochemical changes in vivo. To improve upon the current state of bone imaging, we tested the efficacy of Multi Band SWeep Imaging with Fourier Transformation (MB-SWIFT) magnetic resonance imaging (MRI) as a readout of bone derangement in an estrogen deficient ovariectomized (OVX) rat model during growth. MB-SWIFT MRI-derived BMD correlated significantly with BMD measured using micro-computed tomography (μCT). In this rodent model, growth appeared to overcome estrogen deficiency as bone mass continued to increase longitudinally over the duration of the study. Nonetheless, after 10 weeks of intervention, MB-SWIFT detected significant changes consistent with estrogen deficiency in cortical water, cortical matrix organization (T₁), and marrow fat. Findings point to MB-SWIFT's ability to quantify BMD in good agreement with μCT while providing additive quantitative outcomes about bone quality in a manner consistent with estrogen deficiency. These results indicate MB-SWIFT as a non-ionizing imaging strategy with value for bone imaging and may be a promising technique to progress to the clinic for monitoring and clinical management of patients with bone diseases such as osteoporosis.

Deletion of PPARγ in Mesenchymal Lineage Cells Protects Against Aging-Induced Cortical Bone Loss in Mice

Bone loss in aging is linked with chronic low-grade inflammation and the accumulation of marrowfat in animals and humans. Peroxisome proliferator-activated receptor gamma (PPARγ), an adipogenic regulator, plays key roles in these biological processes. However, studies of the roles of PPARγ in age-related bone loss and inflammation are lacking. We hypothesized that deletion of PPARγ in bone marrow mesenchymal lineage cells would reduce bone loss with aging, potentially through a reduction in fat-generated inflammatory responses and an increase in osteoblastic activity. In the present study, we show that mice deficient of PPARγ in Dermo1-expressing mesenchymal lineage cells (Dermo1-Cre:PPARγ fl/fl) have reduced fat mass and increased cortical bone thickness but that deficiency of PPARγ had limited effect on protection of trabecular bone with aging as demonstrated by dual-energy X-ray absorptiometry, µCT, and histomorphometric analyses. Conditional knockout of PPARγ reduced serum concentrations of adipokines, including adiponectin, resistin, and leptin, and reduced marrow stromal cell expression levels of inflammation-related genes. Inflammation genes involved in the interferon signaling pathway were reduced the most. These results demonstrate that disruption of the master adipogenic regulator, PPARγ, has a certain protective effect on aging-induced bone loss, suggesting that regulation of adipose function and modulation of interferon signaling are among the key mechanisms by which PPARγ regulates bone homeostasis during aging process.

Do polyunsaturated fatty acids protect against bone loss in our aging and osteoporotic population?

Age-related bone loss is inevitable in both men and women and there will soon be more people of extreme old age than ever before. Osteoporosis is a common chronic disease and as the proportion of older people, rate of obesity and the length of life increases, a rise in age-related degenerating bone diseases, disability, and prolonged dependency is projected. Fragility fractures are one of the most severe complications associated with both primary and secondary osteoporosis and current treatment strategies target weight-bearing exercise and pharmacological intervention, both with limited long-term success. Obesity and osteoporosis are intimately interrelated, and diet is a variable that plays a significant role in bone regeneration and repair. The Western Diet is characterized by its unhealthy components, specifically excess amounts of saturated fat intake. This review examines the impact of saturated and polyunsaturated fatty acid consumption on chronic inflammation, osteogenesis, bone architecture, and strength and explores the hypothesis that dietary polyunsaturated fats have a beneficial effect on osteogenesis, reducing bone loss by decreasing chronic inflammation, and activating bone resorption through key cellular and molecular mechanisms in our aging population. We conclude that aging, obesity and a diet high in saturated fatty acids significantly impairs bone regeneration and repair and that consumption of ω-3 polyunsaturated fatty acids is associated with significantly increased bone regeneration, improved microarchitecture and structural strength. However, ω-6 polyunsaturated fatty acids were typically pro-inflammatory and have been associated with an increased fracture risk. This review suggests a potential role for ω-3 fatty acids as a non-pharmacological dietary method of reducing bone loss in our aging population. We also conclude that contemporary amendments to the formal nutritional recommendations made by the Food and Nutrition Board may be necessary such that our aging population is directly considered.

Deletion of phospholipase D1 decreases bone mass and increases fat mass via modulation of Runx2, β-catenin-osteoprotegerin, PPAR-γ and C/EBPα signaling axis

In osteoporosis, mesenchymal stem cells (MSCs) prefer to differentiate into adipocytes at the expense of osteoblasts. Although the balance between adipogenesis and osteogenesis has been closely examined, the mechanism of commitment determination switch is unknown. Here we demonstrate that phospholipase D1 (PLD1) plays a key switch in determining the balance between bone and fat mass. Ablation of Pld1 reduced bone mass but increased fat in mice. Mechanistically, Pld1^/- MSCs inhibited osteoblast differentiaion with diminished Runx2 expression, while osteoclast differentiation was accelerated in Pld1^-/- bone marrow-derived macrophages. Pld1^-/- osteoblasts showed decreased expression of osteogenic makers. Increased number and resorption activity of osteoclasts in Pld1^-/- mice were corroborated with upregulation of osteoclastogenic markers. Moreover, Pld1^-/- osteoblasts reduced β-catenin mediated-osteoprotegerin (OPG) with increased RANKL/OPG ratio which resulted in accelerated osteoclast differentiation. Thus, low bone mass with upregulated osteoclasts could be due to the contribution of both osteoblasts and osteoclasts during bone remodeling. Moreover, ablation of Pld1 further increased bone loss in ovariectomized mice, suggesting that PLD1 is a negative regulator of osteoclastogenesis. Furthermore, loss of PLD1 increased adipogenesis, body fat mass, and hepatic steatosis along with upregulation of PPAR-γ and C/EBPα. Interestingly, adipocyte-specific Pld1 transgenic mice rescued the compromised phenotypes of fat mass and adipogenesis in Pld1 knockout mice. Collectively, PLD1 regulated the bifurcating pathways of mesenchymal cell lineage into increased osteogenesis and decreased adipogenesis, which uncovered a previously unrecognized role of PLD1 in homeostasis between bone and fat mass.

Quantitative CT Detects Undiagnosed Low Bone Mineral Density in Oncologic Patients Imaged With 18F-FDG PET/CT

PURPOSE

We assessed the prevalence of low bone mineral density (BMD) in oncologic patients undergoing F-FDG PET/CT.

PATIENTS AND METHODS

This is a retrospective analysis of 100 patients who underwent F-FDG PET/CT at a single center from October 2015 till May 2016. Quantitative CT (QCT) was used to assess BMD at the lumbar spine (BMDQCT) and femoral necks (BMDCTXA). SUVmax was used to evaluate metabolic activity of the bone marrow. Risk of osteoporosis-related fractures was calculated with femoral neck BMDCTXA and the FRAX algorithm, which was compared against measurements of CT attenuation of the trabecular bone at L1 (L1HU).

RESULTS

Osteoporosis and osteopenia were respectively present in 16% and 46% of patients 50 years and older. Bone marrow SUVmax was correlated with BMD at the lumbar spine (ρ = 0.36, P < 0.001). Increased age and low marrow SUVmax were associated with low BMDQCT at the lumbar spine (both P < 0.001), whereas increased age, female sex, and low marrow SUVmax were associated with low BMDCTXA at the femoral necks (P < 0.001, P < 0.001, P = 0.01, respectively). L1HU had an area under the curve of 0.95 (95% confidence interval [CI], 0.90-0.99) for detecting increased risk for osteoporosis-related fracture, with best threshold of 125.8 HU (95% CI, 115.7-144.9) yielding sensitivity of 100% (95% CI, 0.92-1.00), specificity of 0.90 (95% CI, 0.76-0.97), and accuracy of 0.91 (95% CI, 0.79-0.97).

CONCLUSIONS

Low BMD is frequent in oncologic patients undergoing F-FDG PET/CT. Decreased F-FDG avidity of the bone marrow correlates with decreased BMD, validating the link between osteoporosis and bone marrow fat. L1HU could be a simple and accurate approach for detecting patients at risk for osteoporosis-related fractures using PET/CTdata.