Bone marrow fat

Effects of Thermal Environment on Bone Microenvironment: A Narrative Review

Research findings reveal that thermal environments precisely regulate the skeletal system through a triple regulation of "structural morphology-cellular dynamics-molecular mechanisms": At the tissue morphology level, moderate heat exposure can promote increased bone density and longitudinal growth, as well as improved fracture load and yield point, but may negatively affect geometric shape and cortical bone thickness. Continuous high-temperature exposure harms bone structure, manifested as changes in biomechanical characteristics such as decreased toughness and rigidity. At the cellular level, thermal environments directly affect the proliferation/apoptosis balance of osteoblasts and osteoclasts, and by regulating osteocyte network activity and bone marrow mesenchymal stem cell fate decisions, these four cell populations form temperature-dependent metabolic regulatory circuits. At the molecular dimension, heat stress can activate the release of neural factors such as CGRP and NPY, which possess dual regulatory functions promoting both bone formation and resorption; simultaneously achieving coordinated regulation of angiogenesis and fat inhibition through VEGF and TGFβ. The thermal environment-bone regulatory mechanisms revealed in this study have important translational value: they not only provide theoretical basis for biomechanical protection strategies for high-temperature workers and athletes, but also offer innovative entry points for analyzing the pathological mechanisms of heat stroke secondary bone injury and osteoporosis through heat stress-related signaling pathways, while establishing a theoretical foundation for the development of temperature-responsive functionalized biomaterials in bone tissue engineering.

Mid-Term Outcomes of Screw Loosening in Lumbar Dynamic Stabilization with Polyetheretherketone Rods versus Titanium Rods: A Minimum 4-Year Follow-Up

OBJECTIVE

To retrospectively analyze screw loosening rates following dynamic fixation with polyetheretherketone (PEEK) rods and rigid fixation with titanium rods and assess mid-term outcomes of loosened screws.

METHODS

This retrospective analysis included 203 patients who underwent lumbar pedicle screw fixation between March 2017 and June 2020 (57 with PEEK rods, 146 with titanium rods). Patients were followed for at least 48 months to evaluate screw loosening postoperatively and investigate outcomes of loosened screws. Multivariate logistic regression identified factors influencing screw restabilization.

RESULTS

Both PEEK rod and titanium rod groups exhibited peak screw loosening rates approximately 1 year after surgery, decreasing with longer follow-up. At 48 months, screw loosening rates were 5.3% and 15.8% for PEEK and titanium rods, respectively (P < 0.05). Among patients experiencing early loosening (within 12 months), the proportion of stabilized screws was significantly higher with PEEK rods (84% vs. 34%, P < 0.001). Regression analysis revealed dynamic fixation (odds ratio 4.579; 95% confidence interval 1.611-12.519), lowest fixed vertebra S1 (odds ratio 3.151; 95% confidence interval 1.352-9.233), and L1-L4 average computed tomography value (odds ratio 1.132; 95% confidence interval 1.015-1.263) as independent risk factors for screw restabilization. The area under the receiver operating characteristic curve for L1-L4 average computed tomography value predicting restabilization was 0.713 (P < 0.05), with an optimal threshold of 106 Hounsfield units (sensitivity 0.771, specificity 0.803).

CONCLUSIONS

Following PEEK rod dynamic fixation surgery, a certain proportion of screw loosening may occur in the short term. With prolonged follow-up, screws gradually restabilize at the bone interface, with most loosened screws returning to a stable state.

Association between vertebral bone quality score and residual back pain following percutaneous vertebroplasty for osteoporotic vertebral compression fractures

BACKGROUND

Residual back pain (RBP) is one of the complications following percutaneous vertebroplasty (PVP) in older people with osteoporotic vertebral compression fractures (OVCFs). The vertebral bone quality (VBQ) score obtained from magnetic resonance imaging (MRI) can be used to evaluate bone quality. The objective of this study aimed to explore the potential relationship between the VBQ score and RBP after PVP.

METHODS

From January 2018 to January 2022, patients with OVCFs who underwent PVP in our hospital were retrospectively reviewed. Each patient's lumbar VBQ score was recorded. The RBP was defined as a visual analog scale (VAS) score ≥ 4 for back pain postoperatively. Other variables included demographic, clinical, radiological, and surgical data. The univariate and multivariate logistic regression analyses were used to determine the independent risk factors.

RESULTS

The incidence of RBP was 8.0% among 598 patients. The results of the multivariate regression analysis showed that preoperative VBQ score (OR 3.295, P < 0.001), BMD (OR 0.545, P = 0.007), lumbodorsal fascia contusion (OR 4.297, P = 0.034), and cement distribution (OR 4.556, P = 0.006) were risk factors associated with RBP after PVP.

CONCLUSIONS

The preoperative high VBQ score was an independent risk factor associated with RBP after PVP. Moreover, other risk factors included low BMD, lumbodorsal fascia contusion, and cement distribution. The MRI-VBQ score may serve as a useful tool for assisting in evaluating patients at risk of RBP following PVP.

Pathological mechanisms and related markers of steroid-induced osteonecrosis of the femoral head

BACKGROUND

Osteonecrosis of the femoral head (ONFH) is a refractory orthopedic disease with a high disability rate. Long-term administration of steroids is the most common pathogenic factor for non-traumatic ONFH. Early diagnosis of steroid-induced osteonecrosis of the femoral head (SONFH) is difficult and mainly depends on imaging.

OBJECTIVES

The objectives of this review were to examine the pathological mechanisms of SONFH, summarize related markers of SONFH, and identify areas for future studies.

METHODS

We reviewed studies on pathological mechanisms and related markers of SONFH and discussed the relationship between them, as well as clinical applications and the outlook of potential markers.

RESULTS

The pathological mechanisms of SONFH included decreased osteogenesis, lipid accumulation, increased intraosseous pressure, and microcirculation disruption. Differential proteomics and genomics play crucial roles in the occurrence, progression, and outcome of SONFH, providing novel insights into SONFH. Additionally, the biological functions of mesenchymal stem cells (MSCs) and exosomes (Exos) in SONFH have attracted increasing attention.

CONCLUSIONS

The pathological mechanisms of SONFH are complex. The related markers mentioned in the current review can predict the occurrence and progression of SONFH, which will help provide effective early clinical prevention and treatment strategies for SONFH.

More accurate trabecular bone imaging using UTE MRI at the resonance frequency of fat

High-resolution magnetic resonance imaging (HR-MRI) has been increasingly used to assess the trabecular bone structure. High susceptibility at the marrow/bone interface may significantly reduce the marrow's apparent transverse relaxation time (T2*), overestimating trabecular bone thickness. Ultrashort echo time MRI (UTE-MRI) can minimize the signal loss caused by susceptibility-induced T2* shortening. However, UTE-MRI is sensitive to chemical shift artifacts, which manifest as spatial blurring and ringing artifacts partially due to non-Cartesian sampling. In this study, we proposed UTE-MRI at the resonance frequency of fat to minimize marrow-related chemical shift artifacts and the overestimation of trabecular thickness. Cubes of trabecular bone from six donors (75 ± 4 years old) were scanned using a 3 T clinical scanner at the resonance frequencies of fat and water, respectively, using 3D UTE sequences with five TEs (0.032, 1.1, 2.2, 3.3, and 4.4 ms) and a clinical 3D gradient echo (GRE) sequence at 0.2 × 0.2 × 0.4 mm3 voxel size. Trabecular bone thickness was measured in 30 regions of interest (ROIs) per sample. MRI results were compared with thicknesses obtained from micro-computed tomography (μCT) at 50 μm3 voxel size. Linear regression models were used to calculate the coefficient of determination between MRI- and μCT-based trabecular thickness. All MRI-based trabecular thicknesses showed significant correlations with μCT measurements. The correlations were higher (examined with paired Student's t-test, P < 0.01) for 3D UTE images performed at the fat frequency (R2 = 0.59-0.74, P < 0.01) than those at the water frequency (R2 = 0.18-0.52, P < 0.01) and clinical GRE images (R2 = 0.39-0.47, P < 0.01). Significantly reduced correlations were observed with longer TEs. This study highlighted the feasibility of UTE-MRI at the fat frequency for a more accurate assessment of trabecular bone thickness.

Prediction of Screw Loosening After Dynamic Pedicle Screw Fixation With Lumbar Polyetheretherketone Rods Using Magnetic Resonance Imaging-Based Vertebral Bone Quality Score

OBJECTIVE

To investigate the correlation between magnetic resonance imaging-based vertebral bone quality (VBQ) score and screw loosening after dynamic pedicle screw fixation with polyetheretherketone (PEEK) rods, and evaluate its predictive value.

METHODS

A retrospective analysis was conducted on the patients who underwent dynamic pedicle screw fixation with PEEK rods from March 2017 to June 2022. Data on age, sex, body mass index, hypertension, diabetes, hyperlipidemia history, long-term smoking, alcohol consumption, VBQ score, L1-4 average Hounsfield unit (HU) value, surgical fixation length, and the lowest instrumented vertebra were collected. Logistic regression analysis was employed to assess the relationship between VBQ score and pedicle screw loosening (PSL).

RESULTS

A total of 24 patients experienced PSL after surgery (20.5%). PSL group and non-PSL group showed statistical differences in age, number of fixed segments, fixation to the sacrum, L1-4 average HU value, and VBQ score (p < 0.05). The VBQ score in the PSL group was higher than that in the non-PSL group (3.56 ± 0.45 vs. 2.77 ± 0.31, p < 0.001). In logistic regression analysis, VBQ score (odds ratio, 3.425; 95% confidence interval, 1.552-8.279) were identified as independent risk factors for screw loosening. The area under the receiver operating characteristic curve for VBQ score predicting PSL was 0.819 (p < 0.05), with the optimal threshold of 3.15 (sensitivity, 83.1%; specificity, 80.5%).

CONCLUSION

The VBQ score can independently predict postoperative screw loosening in patients undergoing lumbar dynamic pedicle screw fixation with PEEK rods, and its predictive value is comparable to HU value.

Demonstration of magnetic resonance Z-spectral imaging for fatty acid characterization of bone marrow at 3 T

Magnetic resonance Z-spectral imaging (ZSI) has emerged as a new approach to measure fat fraction (FF). However, its feasibility for fat spectral imaging remains to be elucidated. In this study, a single-slice ZSI sequence dedicated to fat spectral imaging was designed, and its capability for fatty acid characterization was investigated on peanut oil samples, a multiple-vial fat-water phantom with varied oil volumes, and vertebral body marrow in healthy volunteers and osteoporosis patients at 3 T. The peanut oil spectrum was also recorded with a 400-MHz NMR spectrometer. A Gaussian-Lorentzian sum model was used to resolve water and six fat signals of the pure oil sample or four fat signals of the fat-water phantom or vertebral bone marrow from Z spectra. Fat peak amplitudes were normalized to the total peak amplitude of water and all fat signals. Normalized fat peak amplitudes and FF were quantified and compared among vials of the fat-water phantom or between healthy volunteers and osteoporosis patients. An unpaired student's t-test and Pearson's correlation were conducted, with p less than 0.05 considered statistically significant. The results showed that the peanut oil spectra measured with the ZSI technique were in line with respective NMR spectra, with amplitudes of the six fat signal peaks significantly correlated between the two methods (y = x + 0.001, r = 0.996, p < 0.001 under a repetition time of 1.6 s; and y = 1.026x - 0.003, r = 0.996, p < 0.001 under a repetition time of 3.1 s). Moreover, ZSI-measured FF exhibited a significant correlation with prepared oil volumes (y = 0.876x + 1.290, r = 0.996, p < 0.001). The osteoporosis patients showed significantly higher normalized fat peak amplitudes and FF in the L4 vertebral body marrow than the healthy volunteers (all p < 0.01). In summary, the designed ZSI sequence is feasible for fatty acid characterization, and has the potential to facilitate the diagnosis and evaluation of diseases associated with fat alterations at 3 T.

Bone Marrow Adipose Tissue

Bone marrow (BM) acts as a dynamic organ within the bone cavity, responsible for hematopoiesis, skeletal remodeling, and immune system control. Bone marrow adipose tissue (BMAT) was long simply considered a filler of space, but now it is known that it instead constitutes an essential element of the BM microenvironment that participates in homeostasis, influences bone health and bone remodeling, alters hematopoietic stem cell functions, contributes to the commitment of mesenchymal stem cells, provides effects to immune homeostasis and defense against infections, and participates in energy metabolism and inflammation. BMAT has emerged as a significant contributor to the development and progression of various diseases, shedding light on its complex relationship with health. Notably, BMAT has been implicated in metabolic disorders, hematological malignancies, and skeletal conditions. BMAT has been shown to support the proliferation of tumor cells in acute myeloid leukemia and niche adipocytes have been found to protect cancer cells against chemotherapy, contributing to treatment resistance. Moreover, BMAT's impact on bone density and remodeling can lead to conditions like osteoporosis, where high levels of BMAT are inversely correlated with bone mineral density, increasing the risk of fractures. BMAT has also been associated with diabetes, obesity, and anorexia nervosa, with varying effects on individuals depending on their weight and health status. Understanding the interaction between adipocytes and different diseases may lead to new therapeutic strategies.

Utility of MRI-based vertebral bone quality scores and CT-based Hounsfield unit values in vertebral bone mineral density assessment for patients with diffuse idiopathic skeletal hyperostosis

This study investigated bone mineral density assessment for patients with DISH. DXA-based T-scores overestimated bone quality, while MRI-based VBQ scores and CT-based HU values provided accurate assessments, particularly for advanced degenerative cases. This enhances accurate evaluation of BMD, crucial for clinical decision-making.

PURPOSE

To investigate the diagnostic effectiveness of DXA, MRI, and CT in assessing bone mineral density (BMD) for diffuse idiopathic skeletal hyperostosis (DISH) patients.

METHODS

Retrospective analysis of 105 DISH patients and 116 age-matched controls with lumbar spinal stenosis was conducted. BMD was evaluated using DXA-based T-scores, MRI-based vertebral bone quality (VBQ) scores, and CT-based Hounsfield unit (HU) values. Patients were categorized into three BMD subgroups. Lumbar osteophyte categories were determined by Mata score. Demographics, clinical data, T-scores, VBQ scores, and HU values were collected. Receiver operating characteristic (ROC) analysis identified VBQ and HU thresholds for diagnosing normal BMD using DXA in controls. Correlations between VBQ, HU, and lumbar T-score were analyzed.

RESULTS

Age, gender, and BMI showed no significant differences between DISH and control groups. DISH patients had higher T-score (L1-4), the lowest T-score, and Mata scores. VBQ and HU did not significantly differ between groups. In controls, VBQ and HU effectively diagnosed normal BMD (AUC = 0.857 and 0.910, respectively) with cutoffs of 3.0 for VBQ and 104.3 for HU. DISH had higher normal BMD prevalence using T-scores (69.5% vs. 58.6%, P < 0.05), but no significant differences using VBQ (57.1% vs. 56.2%, P > 0.05) and HU (58.1% vs. 57.8%, P > 0.05). Correlations revealed moderate correlations between HU and T-scores (L1-4) in DISH (r = 0.642, P < 0.001) and strong in controls (r = 0.846, P < 0.001). Moderate negative correlations were observed between VBQ and T-scores (L1-4) in DISH (r =  - 0.450, P < 0.001) and strong in controls (r =  - 0.813, P < 0.001).

CONCLUSION

DXA-based T-scores may overestimate BMD in DISH. VBQ scores and HU values could effectively complement BMD assessment, particularly in DISH patients or those with advanced lumbar degeneration.

Bone marrow adipocytes and lung cancer bone metastasis: unraveling the role of adipokines in the tumor microenvironment

Bone is a common site of metastasis for lung cancer. The "seed and soil" hypothesis suggests that the bone marrow microenvironment ("soil") may provide a conducive survival environment for metastasizing tumor cells ("seeds"). The bone marrow microenvironment, comprising a complex array of cells, includes bone marrow adipocytes (BMAs), which constitute about 70% of the adult bone marrow volume and may play a significant role in tumor bone metastasis. BMAs can directly provide energy for tumor cells, promoting their proliferation and migration. Furthermore, BMAs participate in the tumor microenvironment's osteogenesis regulation, osteoclast(OC) regulation, and immune response through the secretion of adipokines, cytokines, and inflammatory factors. However, the precise mechanisms of BMAs in lung cancer bone metastasis remain largely unclear. This review primarily explores the role of BMAs and their secreted adipokines (leptin, adiponectin, Nesfatin-1, Resistin, chemerin, visfatin) in lung cancer bone metastasis, aiming to provide new insights into the mechanisms and clinical treatment of lung cancer bone metastasis.

Emerging factors affecting peri-implant bone metabolism

Implant dentistry has evolved to the point that standard implant osseointegration is predictable. This is attributed in part to the advancements in material sciences that have led toward improvements in implant surface technology and characteristics. Nonetheless, there remain several cases where implant therapy fails (specifically at early time points), most commonly attributed to factors affecting bone metabolism. Among these patients, smokers are known to have impaired bone metabolism and thus be subject to higher risks of early implant failure and/or late complications related to the stability of the peri-implant bone and mucosal tissues. Notably, however, emerging data have unveiled other critical factors affecting osseointegration, namely, those related to the metabolism of bone tissues. The aim of this review is to shed light on the effects of implant-related factors, like implant surface or titanium particle release; surgical-related factors, like osseodensification or implanted biomaterials; various drugs, like selective serotonin reuptake inhibitors, proton pump inhibitors, anti-hypertensives, nonsteroidal anti-inflammatory medication, and statins, and host-related factors, like smoking, diet, and metabolic syndrome on bone metabolism, and aseptic peri-implant bone loss. Despite the infectious nature of peri-implant biological complications, these factors must be surveyed for the effective prevention and management of peri-implantitis.

Effects of Hyperlipidemia on Osseointegration of Dental Implants and Its Strategies

Hyperlipidemia refers to the abnormal increase in plasma lipid level exceeding the normal range. At present, a large number of patients require dental implantation. However, hyperlipidemia affects bone metabolism, promotes bone loss, and inhibits the osseointegration of dental implants through the mutual regulation of adipocytes, osteoblasts, and osteoclasts. This review summarized the effects of hyperlipidemia on dental implants and addressed the potential strategies of dental implants to promote osseointegration in a hyperlipidemic environment and to improve the success rate of dental implants in patients with hyperlipidemia. We summarized topical drug delivery methods to solve the interference of hyperlipidemia in osseointegration, which were local drug injection, implant surface modification and bone-grafting material modification. Statins are the most effective drugs in the treatment of hyperlipidemia, and they also encourage bone formation. Statins have been used in these three methods and have been found to be positive in promoting osseointegration. Directly coating simvastatin on the rough surface of the implant can effectively promote osseointegration of the implant in a hyperlipidemic environment. However, the delivery method of this drug is not efficient. Recently, a variety of efficient methods of simvastatin delivery, such as hydrogels and nanoparticles, have been developed to boost bone formation, but few of them were applied to dental implants. Applicating these drug delivery systems using the three aforementioned ways, according to the mechanical and biological properties of materials, could be promising ways to promote osseointegration under hyperlipidemic conditions. However, more research is needed to confirm.

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.

Novel micro-MRI approach for subchondral trabecular bone analysis in patients with hip osteoarthritis is comparable to micro-CT approach

AIM

To test the agreement between a newly developed micro-magnetic resonance imaging (MRI) analysis of the subchondral bone and the micro-computed tomography (CT) approach.

METHODS

Samples obtained from 10 patients with osteoarthritis undergoing total hip arthroplasty were scanned with a 7.0 T micro-MRI. Proton density-weighted images and proton density-weighted images with fat suppression were obtained. The results were validated with a micro-CT device. Micro-MRI and micro-CT scans of the same sample were aligned, and regions of interest were delineated on equal areas of the sample. Bone volume fraction was calculated by using in-house plugins. The agreement between the methods was tested with Bland-Altman analysis.

RESULTS

The agreement between the methods was good, with average difference of 2.167%. The differences between the methods were not significant (P=0.272, t test).

CONCLUSION

The novel micro-MRI approach could be used for subchondral bone analysis. With further optimization for clinical MRI machines, the approach can be also used in the diagnostics of hip osteoarthritis.

Recent advances in engineering hydrogels for niche biomimicking and hematopoietic stem cell culturing

Hematopoietic stem cells (HSCs) provide a life-long supply of haemopoietic cells and are indispensable for clinical transplantation in the treatment of malignant hematological diseases. Clinical applications require vast quantities of HSCs with maintained stemness characteristics. Meeting this demand poses often insurmountable challenges for traditional culture methods. Creating a supportive artificial microenvironment for the culture of HSCs, which allows the expansion of the cells while maintaining their stemness, is becoming a new solution for the provision of these rare multipotent HSCs. Hydrogels with good biocompatibility, excellent hydrophilicity, tunable biochemical and biophysical properties have been applied in mimicking the hematopoietic niche for the efficient expansion of HSCs. This review focuses on recent progress in the use of hydrogels in this specialized application. Advanced biomimetic strategies use for the creation of an artificial haemopoietic niche are discussed, advances in combined use of hydrogel matrices and microfluidics, including the emerging organ-on-a-chip technology, are summarized. We also provide a brief description of novel stimulus-responsive hydrogels that are used to establish an intelligent dynamic cell microenvironment. Finally, current challenges and future perspectives of engineering hydrogels for HSC biomedicine are explored.

Lipidomics Profiling of Patients with Low Bone Mineral Density (LBMD)

The relationship between lipid metabolism and bone mineral density (BMD) is still not fully elucidated. Despite the presence of investigations using osteoporotic animal models, clinical studies in humans are limited. In this work, untargeted lipidomics profiling using liquid chromatography-mass spectrometry (LC-MS) analysis of human serum samples was performed to identify the lipidomics profile associated with low bone mineral density (LBMD), with a subsequent examination of potential biomarkers related to OP risk prediction or progression. A total of 69 participants were recruited for this cohort study, including the osteoporotic group (OP, n = 25), osteopenia group (ON, n = 22), and control (Ctrl, n = 22). The LBMD group included OP and ON patients. The lipidomics effect of confounding factors such as age, gender, lipid profile, body mass index (BMD), chronic diseases, and medications was excluded from the dataset. The results showed a clear group separation and clustering between LBMD and Ctrl (Q² = 0.944, R² = 0.991), indicating a significant difference in the lipids profile. In addition, 322 putatively identified lipid molecules were dysregulated, with 163 up- and 159 down-regulated in LBMD, compared with the Ctrl. The most significantly dysregulated subclasses were phosphatidylcholines (PC) (n = 81, 25.16% of all dysregulated lipids 322), followed by triacylglycerol (TG) (n = 65, 20.19%), and then phosphatidylethanolamine (PE) (n = 40, 12.42%). In addition, groups of glycerophospholipids, including LPC (7.45%), LPE (5.59%), and PI (2.48%) were also dysregulated as of LBMD. These findings provide insights into the lipidomics alteration involved in bone remodeling and LBMD. and may drive the development of therapeutic targets and nutritional strategies for OP management.

An integrative bioinformatics approach to decipher adipocyte-induced transdifferentiation of osteoblast

In human, bone loss is associated with increased marrow adipose tissue and recent data suggest that medullary adipocytes could play a role in osteoporosis by acting on neighboring bone-forming osteoblasts. Supporting this hypothesis, we previously showed, in a coculture model based on human bone marrow stromal cells, that factors secreted by adipocytes induced the conversion of osteoblasts towards an adipocyte-like phenotype. In this work, we employed an original integrative bioinformatics approach connecting proteomic and transcriptomic data from adipocytes and osteoblasts, respectively, to investigate the mechanisms underlying their crosstalk. Our analysis identified a total of 271 predicted physical interactions between adipocyte-secreted proteins and osteoblast membrane protein coding genes and proposed three pathways for their potential contribution to osteoblast transdifferentiation, the PI3K-AKT, the JAK2-STAT3 and the SMAD pathways. Our findings demonstrated the effectiveness of our integrative omics strategy to decipher cell-cell communication events.

Growth Hormone Receptor Controls Adipogenic Differentiation of Chicken Bone Marrow Mesenchymal Stem Cells by Affecting Mitochondrial Biogenesis and Mitochondrial Function

Growth hormone receptor (GHR) can activate several signaling pathways after binding to growth hormone (GH) to regulate cell growth and development. Sex-linked dwarf (SLD) chickens, normal protein functions are prevented because of exon mutations in the GHR gene, have more severe fat deposition. However, the specific molecular mechanisms responsible for this phenotype remains unclear. We therefore investigated the effect of the GHR gene on adipogenic differentiation of chicken bone marrow mesenchymal stem cells (BMSCs). We found that bone marrow fat deposition was more severe in SLD chickens compared to normal chickens, and the expression of genes related to adipogenic differentiation was enhanced in SLD chicken BMSCs. We also detected enhanced mitochondrial function of BMSCs in SLD chickens. In vitro, overexpression of GHR in chicken BMSCs increased mitochondrial membrane potential but decreased reactive oxygen and ATP contents, oxidative phosphorylation complex enzyme activity, and mitochondrial number. Expression of genes associated with mitochondrial biogenesis and function was repressed during adipogenic differentiation in chicken BMSCs, the adipogenic differentiation capacity of chicken BMSCs was also repressed. With knockdown of GHR, opposite results were observed. We concluded that GHR inhibited adipogenic differentiation of chicken BMSCs by suppressing mitochondrial biogenesis and mitochondrial function.

The ATF3-OPG Axis Contributes to Bone Formation by Regulating the Differentiation of Osteoclasts, Osteoblasts, and Adipocytes

Activating transcription factor 3 (ATF3) has been identified as a negative regulator of osteoblast differentiation in in vitro study. However, it was not associated with osteoblast differentiation in in vivo study. To provide an understanding of the discrepancy between the in vivo and in vitro findings regarding the function of ATF3 in osteoblasts, we investigated the unidentified roles of ATF3 in osteoblast biology. ATF3 enhanced osteoprotegerin (OPG) production, not only in osteoblast precursor cells, but also during osteoblast differentiation and osteoblastic adipocyte differentiation. In addition, ATF3 increased nodule formation in immature osteoblasts and decreased osteoblast-dependent osteoclast formation, as well as the transdifferentiation of osteoblasts to adipocytes. However, all these effects were reversed by the OPG neutralizing antibody. Taken together, these results suggest that ATF3 contributes to bone homeostasis by regulating the differentiation of various cell types in the bone microenvironment, including osteoblasts, osteoclasts, and adipocytes via inducing OPG production.

Characterization of multi-biomarkers for bone health assessment based on photoacoustic physicochemical analysis method

Photoacoustic (PA) techniques are potential alternatives to histopathology. The physicochemical spectrogram (PCS) generated by the PA measurement at multiple wavelengths can presents the morphology and chemical composition target at multi-biomarkers simultaneously. In this work, via multi-wavelength PA measurements performed on rabbit bone models, we investigated the feasibility of using PCSs for bone health assessment. A comprehensive analysis of the PCSs, termed PA physicochemical analysis (PAPCA), was conducted. The "slope" and "relative content" were used as the PAPCA-quantified parameters to characterize the changes in the physical and chemical properties of bone tissue, respectively. The findings are consistent well with the gold-standard imaging results. It demonstrated that the PAPCA can be used to characterize both the microstructure and content of multi-biomarkers which highly related with bone health. Considering the PA technique is noninvasive and radiation-free, it has great potential in the implementation and monitoring of bone diseases progression.

Study of bone marrow microstructure in healthy young adults using intravoxel incoherent motion diffusion-weighted MRI

Bone marrow is one of the most important organs in the human body. The evaluation of bone marrow microstructure and gender-related cellular and capillary networks in healthy young adults can help to better understand the process of bone metabolism. Intravoxel incoherent motion (IVIM) provides both diffusion and perfusion quantifications without requiring intravenous contrast agent injection. In this prospective study, 60 healthy young age-matched volunteers (30 men and 30 women) underwent MRI scans at 1.5 T using multi-b-value diffusion-weighted imaging on sagittal planes covering the lumbar bone marrow. The apparent diffusion coefficient (ADC), true ADC (D), pseudo-ADC (D*), and perfusion fraction (f) were calculated from the diffusion-weighted images using the mono- and bi-exponential models. Lumbar cancellous bone (L2-L4) was selected as the region of interest. An independent t-test was used to detect significant differences in ADC values and IVIM parameters between men and women. The differences in IVIM parameters among the L2, L3, and L4 groups were compared with analysis of variance. The D and f values in women were significantly higher than that in men (p = 0.001, 0.026). However, D* was significantly lower in women than that in men (p = 0.001). Furthermore, there was no significant gender difference for the conventional ADC value (p = 0.186). Moreover, there were no significant differences in the D, f, and D* values among the L2, L3, and L4 vertebras of women or men. IVIM parameters can show differences in bone marrow between young women and men. As a non-invasive method, it can assess bone marrow microstructure, such as cellularity and perfusion.

Stimulatory Effect of Tofacitinib on Bone Marrow Adipocytes Differentiation

BACKGROUND

Systemic inflammation is the main factor underlying secondary osteoporosis in patients with rheumatoid arthritis (RA). Janus kinase inhibitors (JAKi), such as tofacitinib (Tofa), can control systemic inflammation and may have beneficial effects on bone in various models. This might be due to direct effects on the bone microenvironment and not exclusively based on their anti-inflammatory function. Bone marrow adipocytes (BMAds) are abundant in the bone microenvironment. The effect of JAKi on BMAds is unknown, but evidence suggests that there is competition between human bone marrow-derived stromal cell (hBMSC) differentiation routes towards BMAds and osteoblasts (Ob) in osteoporosis.

OBJECTIVES

The aims of the study are to determine whether Tofa influences BMAds and Ob derived from hBMSCs and to investigate the potential effects of Tofa on bone marrow adiposity in RA patients.

METHODS

To determine the effect of Tofa on cellular commitment, hBMSCs were differentiated to BMAds or OBs for 3 days together with Tofa at 200, 400, or 800 nM and TNFα. This study was also conducted using differentiated BMAds. The impact of Tofa was determined by gene and protein expression analysis and cell density monitoring. In parallel, in a pilot study of 9 RA patients treated with Tofa 5 mg twice a day (NCT04175886), the proton density fat fraction (PDFF) was measured using MRI at the lumbar spine at baseline and at 6 months.

RESULTS

In non-inflammatory conditions, the gene expression of Runx2 and Dlx5 decreased in Ob treated with Tofa (p <0.05). The gene expression of PPARγ2, C/EBPα, and Perilipin 1 were increased compared to controls (p <0.05) in BMAds treated with Tofa. Under inflammatory conditions, Tofa did not change the expression profiles of Ob compared to TNFα controls. In contrast, Tofa limited the negative effect of TNFα on BMAd differentiation (p <0.05). An increase in the density of differentiated BMAds treated with Tofa under TNFα was noted (p <0.001). These findings were consolidated by an increase in PDFF at 6 months of treatment with Tofa in RA patients (46.3 ± 7.0% versus 53.2 ± 9.2% p <0.01).

CONCLUSION

Together, these results suggest a stimulatory effect of Tofa on BMAd commitment and differentiation, which does not support a positive effect of Tofa on bone.

The Cross-Talk between Myeloid and Mesenchymal Stem Cells of Human Bone Marrow Represents a Biomarker of Aging That Regulates Immune Response and Bone Reabsorption

One of the mechanisms that characterizes the aging process of different organs is the accumulation of fat. Different authors have demonstrated that adipose tissue replaces the loss of other cell types, deriving from mesenchymal cells. During aging, there is substitution or trans-differentiation of mesenchymal cells with other cells having the same embryological origin. Newly formed adipocytes were also observed in the trabecular matrix of elderly people’s bones, associated with myeloid cells. In this study, we have investigated the relationship between immature myeloid-derived suppressor cells (I-MDSCs) and mesenchymal stem cells (MSCs) in bone marrow (BM) samples harvested from 57 patients subjected to different orthopedic surgeries. Patients aged from 18 to 92 years were considered in order to compare the cellular composition of bone marrow of young and elderly people, considered a biomarker of immunity, inflammation, and bone preservation. The I-MDSC percentage was stable during aging, but in elderly people, it was possible to observe a strong basal immunosuppression of autologous and heterologous T cells’ proliferation. We hypothesized that this pattern observed in elders depends on the progressive accumulation in the BM of activating stimuli, including cell–cell contact, or the production of different cytokines and proteins that induce the differentiation of bone marrow mesenchymal stem cells in adipocytes. The collected data provided underline the importance of specific biomarkers of aging that promote a reduction in immune response and incremented inflammatory pathways, leading to bone reabsorption in elderly people.

Aging of the Hematopoietic Stem Cell Niche: New Tools to Answer an Old Question

The hematopoietic stem cell (HSC) niche is a specialized microenvironment, where a complex and dynamic network of interactions across multiple cell types regulates HSC function. During the last years, it became progressively clearer that changes in the HSC niche are responsible for specific alterations of HSC behavior. The aging of the bone marrow (BM) microenvironment has been shown to critically contribute to the decline in HSC function over time. Interestingly, while upon aging some niche structures within the BM are degenerated and negatively affect HSC functionality, other niche cells and specific signals are preserved and essential to retaining HSC function and regenerative capacity. These new findings on the role of the aging BM niche critically depend on the implementation of new technical tools, developed thanks to transdisciplinary approaches, which bring together different scientific fields. For example, the development of specific mouse models in addition to coculture systems, new 3D-imaging tools, ossicles, and ex-vivo BM mimicking systems is highlighting the importance of new technologies to unravel the complexity of the BM niche on aging. Of note, an exponential impact in the understanding of this biological system has been recently brought by single-cell sequencing techniques, spatial transcriptomics, and implementation of artificial intelligence and deep learning approaches to data analysis and integration. This review focuses on how the aging of the BM niche affects HSCs and on the new tools to investigate the specific alterations occurring in the BM upon aging. All these new advances in the understanding of the BM niche and its regulatory function on HSCs have the potential to lead to novel therapeutical approaches to preserve HSC function upon aging and disease.

Bone marrow adipose tissue: Role in bone remodeling and energy metabolism

Bone marrow adipose tissue (BMAT) has been considered for several decades as a silent bystander that fills empty space left in bone marrow following age-related decrease in hematopoiesis. However, recently new discoveries revealed BMAT as a secretory and metabolically active organ contributing to bone and whole-body energy metabolism. BMAT exhibits metabolic functions distinct from extramedullary adipose depots, relevant to its role in regulation of energy metabolism and its contribution to fracture risk observed in metabolic bone diseases. This review discusses novel insights of BMAT with particular emphasis on its contribution to the regulation of bone homeostasis. We also discuss the role of BMAT in regulation of fuel utilization and energy use that affect skeletal stem cell functions.

Effects of Sex and Age on Fat Fraction, Diffusion-Weighted Image Signal Intensity and Apparent Diffusion Coefficient in the Bone Marrow of Asymptomatic Individuals: A Cross-Sectional Whole-Body MRI Study

We aimed to describe the relationships between the relative fat fraction (%FF), muscle-normalized diffusion-weighted (DW) image signal intensity and water apparent diffusion coefficient (ADC), sex and age for normal bone marrow, in the normal population. Our retrospective cohort consisted of 100 asymptomatic individuals, equally divided by sex and 10-year age groups, who underwent whole-body MRI at 1.5 T for early cancer detection. Semi-automated segmentation of global bone marrow volume was performed using the DW images and the resulting segmentation masks were projected onto the ADC and %FF maps for extraction of parameter values. Differences in the parameter values between sexes at age ranges were assessed using the Mann–Whitney and Kruskal–Wallis tests. The Spearman correlation coefficient r was used to assess the relationship of each imaging parameter with age, and of %FF with ADC and normalized DW signal intensity values. The average %FF of normal bone marrow was 65.6 ± 7.2%, while nSI_b50, nSI_b900 and ADC were 1.7 ± 0.5, 3.2 ± 0.9 and 422 ± 67 μm²/s, respectively. The bone marrow %FF values increased with age in both sexes (r = 0.63 and r = 0.64, respectively, p < 0.001). Values of nSI_b50 and nSI_b900 were higher in younger women compared to men of the same age groups (p < 0.017), but this difference decreased with age. In our cohort of asymptomatic individuals, the values of bone marrow relative %FF, normalized DW image signal intensity and ADC indicate higher cellularity in premenopausal women, with increasing bone marrow fat with aging in both sexes.

Adipocyte-induced transdifferentiation of osteoblasts and its potential role in age-related bone loss

Our preliminary findings have lead us to propose bone marrow adipocyte secretions as new contributors to bone loss. Indeed, using a coculture model based on human bone marrow stromal cells, we previously showed that soluble factors secreted by adipocytes induced the conversion of osteoblasts towards an adipocyte-like phenotype. In this study, microarray gene expression profiling showed profound transcriptomic changes in osteoblasts following coculture and confirmed the enrichment of the adipocyte gene signature. Double immunofluorescence microscopic analyses demonstrated the coexpression of adipogenic and osteoblastic specific markers in individual cells, providing evidence for a transdifferentiation event. At the molecular level, this conversion was associated with upregulated expression levels of reprogramming genes and a decrease in the DNA methylation level. In line with these in vitro results, preliminary immunohistochemical analysis of bone sections revealed adipogenic marker expression in osteoblasts from elderly subjects. Altogether, these data suggest that osteoblast transdifferentiation could contribute to decreased bone mass upon ageing.

Vertebral bone quality score predicts fragility fractures independently of bone mineral density

BACKGROUND

Current evidence suggests that dual-energy x-ray absorptiometry (DXA) scans, the conventional method defining osteoporosis, is underutilized and, when used, may underestimate patient risk for skeletal fragility. It has recently been suggested that other imaging modalities may better estimate bone quality, such as the magnetic resonance imaging (MRI)-based vertebral bone quality (VBQ) score which also may assess vertebral compression fracture risk in patients with spine metastases.

PURPOSE

To evaluate whether VBQ score is predictive of fragility fractures in a population with pre-existing low bone density and at high-risk for fracture.

STUDY DESIGN/SETTING

Retrospective single-center cohort.

PATIENT SAMPLE

Patients followed at a metabolic bone clinic for osteopenia and/or osteoporosis.

OUTCOME MEASURES

Radiographically-documented new-onset fragility fracture.

METHODS

Patients with a DXA and MRI scans at the time of consultation and ≥2-year follow-up were included. Details were gathered about patient demographics, health history, current medication use, and serological studies of kidney function and bone turnover. For each patient, VBQ score was calculated using T1-weighted lumbar MRI images. Univariable and multivariable analyses were used to identify the independent predictors of a new fragility fracture. To support the construct validity of VBQ, patient VBQ scores were compared to those in a cohort of 45 healthy adults.

RESULTS

Seventy-two (39.1%) study participants suffered fragility fractures, the occurrence of which was associated with higher VBQ score (3.50 vs. 3.01; p<.001), chronic glucocorticoid use (30.6% vs. 15.2%; p=.014), and a history of prior fragility fracture (36.1% vs. 21.4%; p=.030). Mean VBQ score across all patients in the study cohort was significantly higher than the mean VBQ score in the healthy controls (p<.001). In multivariable analysis, new-onset fracture was independently associated with history of prior fracture (OR=6.94; 95% confidence interval [2.48-19.40]; p<.001), higher VBQ score (OR=2.40 per point; [1.30-4.44]; p=.003), higher body mass index (OR=1.09 per kg/m²; [1.01-1.17]; p=.03), and chronic glucocorticoid use (OR=2.89; [1.03-8.17]; p=0.043). Notably, DXA bone mineral density (BMD) was not found to be significantly predictive of new-onset fractures in the multivariable analysis (p=.081).

CONCLUSIONS

Here we demonstrate the novel, MRI-derived VBQ score is both an independent predictor of fragility fracture in at-risk patients and a superior predictor of fracture risk than DXA-measured BMD. Given the frequency with which MRIs are obtained by patients undergoing spine surgery consultation, we believe the VBQ score could be a valuable tool for estimating bone quality in order to optimize the management of these patients.

Obesity induced by high-fat diet is associated with critical changes in biological and molecular functions of mesenchymal stromal cells present in visceral adipose tissue

The mesenchymal stromal cells (MSCs) residing within the stromal component of visceral adipose tissue appear to be greatly affected by obesity, with impairment of their functions and presence of senescence. To gain further insight into these phenomena, we analyzed the changes in total proteome content and secretome of mouse MSCs after a high-fat diet (HFD) treatment compared to a normal diet (ND). In healthy conditions, MSCs are endowed with functions mainly devoted to vesicle trafficking. These cells have an immunoregulatory role, affecting leukocyte activation and migration, acute inflammation phase response, chemokine signaling, and platelet activities. They also present a robust response to stress. We identified four signaling pathways (TGF-β, VEGFR2, HMGB1, and Leptin) that appear to govern the cells' functions. In the obese mice, MSCs showed a change in their functions. The immunoregulation shifted toward pro-inflammatory tasks with the activation of interleukin-1 pathway and of Granzyme A signaling. Moreover, the methionine degradation pathway and the processing of capped intronless pre-mRNAs may be related to the inflammation process. The signaling pathways we identified in ND MSCs were replaced by MET, WNT, and FGFR2 signal transduction, which may play a role in promoting inflammation, cancer, and aging.

Hyperplasia and accelerated hypertrophy of marrow adipocytes with knee immobilization were sustained despite remobilization

Skeletal disuse can cause an accumulation of bone marrow adipose tissue (MAT) characterized by a combination of marrow adipocyte hyperplasia and/or hypertrophy. The malleability of MAT accumulation and of the hyperplasia and hypertrophy upon remobilization is unknown. In this study, we showed extensive hyperplasia and accelerated hypertrophy of bone marrow adipocytes in the proximal tibia epiphysis of rat knees immobilized for durations between 1 and 32 wk. Similar histomorphometric measures of adipocytes carried out in unoperated controls allowed distinguishing the effects of immobilization from the effects of aging. Although both knee immobilization and aging led to adipocyte hypertrophy, adipocyte hyperplasia was the hallmark signature effect of immobilization on MAT. Both bone marrow adipocyte hyperplasia and hypertrophy were sustained despite knee remobilization for durations up to four times the duration of immobilization. These results suggest that adipocyte hyperplasia is the predominant mechanism explaining MAT accumulation in skeletal disuse. In this model, the changes were unremitting for the investigated time points. Investigating the cellular and molecular mechanisms of marrow adipocyte mechanoregulation will be important to better understand how adipocytes adapt to changes in mechanical environments.NEW & NOTEWORTHY This longitudinal study elucidates the response of marrow adipose tissue adipocytes in weight-bearing joints to changes in different mechanical environments, and we provide insight on the malleability of the changes over time. In a rat animal model, knee immobilization induced hyperplasia and accelerated the age-dependent hypertrophy of adipocytes. Changes in adipocyte number and size were sustained despite unassisted remobilization. Multimodal distributions of cell size were characteristic of bone marrow adipocytes.

Characterization of bony anatomic regions in pediatric and adult healthy volunteers using diffuse optical spectroscopic imaging

SIGNIFICANCE

Diffuse optical spectroscopic imaging (DOSI) measures quantitative functional and molecular information in thick tissue in a noninvasive manner using near-infrared light. DOSI may be useful for diagnosis and prognosis of bone pathologies including osteosarcoma and Ewing's sarcoma, but little is currently known about DOSI-derived parameters in bony anatomic locations where this disease occurs.

AIM

Our goal is to quantify the optical characteristics and chromophore content of bony anatomic locations of healthy volunteers and assess differences due to anatomic region, age, sex, ethnicity, race, and body fat.

APPROACH

Fifty-five healthy volunteers aged 4 to 72 were enrolled in the study. The optical properties and quantitative tissue concentrations of oxyhemoglobin, deoxyhemoglobin, water, and lipids were assessed at the distal humerus, distal femur, and proximal tibia. Body fat was assessed using skinfold calipers. One volunteer underwent a more comprehensive body scan from neck to foot to explore chromophore distributions within an individual. Regression analysis was used to identify the most important sources of variation in the measured data set.

RESULTS

Statistical differences between bony locations were found for scattering, water, and lipids, but not for hemoglobin. All chromophores had statistical differences with sex, but there were no significant age-related correlations. Regression analysis revealed that body fat measured with skinfold calipers was the most important predictor of oxy-, deoxy-, total hemoglobin, and lipids. Hemoglobin and lipid levels were highly correlated (ρ  ≥  0.7) over the subject population and within the single-subject body scan.

CONCLUSIONS

DOSI can successfully measure bony anatomic sites where osteosarcomas and Ewing's sarcomas commonly occur. Future studies of bone pathology using DOSI should account for the variation caused by anatomic region, sex, race and ethnicity, and body fat as these cause substantial variations in DOSI-derived metrics.

Fat and bone: the multiperspective analysis of a close relationship

The study of bone has for many years been focused on the study of its mineralized component, and one of the main objects of study as radiology developed as a medical specialty. The assessment has until recently been almost limited to its role as principal component of the scaffolding of the human body. Bone is a very active tissue, in continuous cross-talk with other organs and systems, with functions that are endocrine and paracrine and that have an important involvement in metabolism, ageing and health in general. Bone is also the continent for the bone marrow, in the form of "yellow marrow" (mainly adipocytes) or "red marrow" (hematopoietic cells and adipocytes). Recently, numerous studies have focused on these adipocytes contained in the bone marrow, often referred to as marrow adipose tissue (MAT). Bone marrow adipocytes do not only work as storage tissue, but are also endocrine and paracrine cells, with the potential to contribute to local bone homeostasis and systemic metabolism. Many metabolic disorders (osteoporosis, obesity, diabetes) have a complex and still not well-established relationship with MAT. The development of imaging methods, in particular the development of cross-sectional imaging has helped us to understand how much more laid beyond our classical way to look at bone. The impact on the mineralized component of bone in some cases (e.g., osteoporosis) is well-established, and has been extensively analyzed and quantified through different radiological methods. The application of advanced magnetic resonance techniques has unlocked the possibility to access the detailed study, characterization and quantification of the bone marrow components in a non-invasive way. In this review, we will address what is the evidence on the physiological role of MAT in normal skeletal health (interaction with the other bone components), during the process of normal aging and in the context of some metabolic disorders, highlighting the role that imaging methods play in helping with quantification and diagnosis.

A comparative study on normal and obese mice indicates that the secretome of mesenchymal stromal cells is influenced by tissue environment and physiopathological conditions

BACKGROUND

The term mesenchymal stromal cells (MSCs) designates an assorted cell population comprised of stem cells, progenitor cells, fibroblasts, and stromal cells. MSCs contribute to the homeostatic maintenance of many organs through paracrine and long-distance signaling. Tissue environment, in both physiological and pathological conditions, may affect the intercellular communication of MSCs.

METHODS

We performed a secretome analysis of MSCs isolated from subcutaneous adipose tissue (sWAT) and visceral adipose tissue (vWAT), and from bone marrow (BM), of normal and obese mice.

RESULTS

The MSCs isolated from tissues of healthy mice share a common core of released factors: components of cytoskeletal and extracellular structures; regulators of basic cellular functions, such as protein synthesis and degradation; modulators of endoplasmic reticulum stress; and counteracting oxidative stress. It can be hypothesized that MSC secretome beneficially affects target cells by the horizontal transfer of many released factors. Each type of MSC may exert specific signaling functions, which could be determined by looking at the many factors that are exclusively released from every MSC type. The vWAT-MSCs release factors that play a role in detoxification activity in response to toxic substances and drugs. The sWAT-MSC secretome contains proteins involved in in chondrogenesis, osteogenesis, and angiogenesis. Analysis of BM-MSC secretome revealed that these cells exert a signaling function by remodeling extracellular matrix structures, such as those containing glycosaminoglycans. Obesity status profoundly modified the secretome content of MSCs, impairing the above-described activity and promoting the release of inflammatory factors.

CONCLUSION

We demonstrated that the content of MSC secretomes depends on tissue microenvironment and that pathological condition may profoundly alter its composition. Video abstract.

Obesity is associated with senescence of mesenchymal stromal cells derived from bone marrow, subcutaneous and visceral fat of young mice

White adipose tissue (WAT) is distributed in several depots with distinct metabolic and inflammatory functions. In our body there are subcutaneous (sWAT), visceral (vWAT) and bone marrow (bWAT) fat depots. Obesity affects the size, function and inflammatory state of WATs. In particular, obesity may affect the activity of mesenchymal stromal cells (MSCs) present in WAT. MSCs are a heterogeneous population containing stromal cells, progenitor cells, fibroblasts and stem cells that are able to differentiate among adipocytes, chondrocytes, osteocytes and other mesodermal derivatives.In the first study of this kind, we performed a comparison of the effects of obesity on MSCs obtained from sWAT, vWAT and bWAT. Our study showed that obesity affects mainly the biological functions of MSCs obtained from bone marrow and vWAT by decreasing the proliferation rate, reducing the percentage of cells in S phase and triggering senescence. The onset of senescence was confirmed by expression of genes belonging to RB and P53 pathways.Our study revealed that the negative consequences of obesity on body physiology may also be related to impairment in the functions of the stromal compartment present in the several adipose tissues. This finding provides new insights as to the targets that should be considered for an effective treatment of obesity-related diseases.

Effects of short- and long-term glucocorticoid-induced osteoporosis on plasma metabolome and lipidome of ovariectomized sheep

BACKGROUND

Understanding the metabolic and lipidomic changes that accompany bone loss in osteoporosis might provide insights about the mechanisms behind molecular changes and facilitate developing new drugs or nutritional strategies for osteoporosis prevention. This study aimed to examine the effects of short- or long-term glucocorticoid-induced osteoporosis on plasma metabolites and lipids of ovariectomized (OVX) sheep.

METHODS

Twenty-eight aged ewes were divided randomly into four groups: an OVX group, OVX in combination with glucocorticoids for two months (OVXG2), and OVX in combination with five doses of glucocorticoids (OVXG5) to induce bone loss, and a control group. Liquid chromatography-mass spectrometry untargeted metabolomic analysis was applied to monthly plasma samples to follow the progression of osteoporosis over five months.

RESULTS

The metabolite profiles revealed significant differences in the plasma metabolome of OVX sheep and OVXG when compared with the control group by univariate analysis. Nine metabolites were altered, namely 5-methoxytryptophan, valine, methionine, tryptophan, glutaric acid, 2-pyrrolidone-5-carboxylic acid, indole-3-carboxaldehyde, 5-hydroxylysine and malic acid. Similarly, fifteen lipids were perturbed from multiple lipid classes such as lysophoslipids, phospholipids and ceramides.

CONCLUSION

This study showed that OVX and glucocorticoid interventions altered the metabolite and lipid profiles of sheep, suggesting that amino acid and lipid metabolisms are potentially the main perturbed metabolic pathways regulating bone loss in OVX sheep.

Vertebral Bone Marrow Fat Is independently Associated to VAT but Not to SAT: KORA FF4-Whole-Body MR Imaging in a Population-Based Cohort

The objective of the current study was to assess the relationship of bone marrow adipose tissue (BMAT) content to abdominal fat depots, including visceral adipose tissue (VAT) and subcutaneous adipose tissue (SAT), as well as cardiovascular risk factors (CVRF) beyond physical activity in a population-based cohort study undergoing whole-body magnetic resonance (MR) imaging. Subjects of the Cooperative Health Research in the Augsburg Region (KORA) FF4 study without known cardiovascular disease underwent fat fraction quantification in vertebrae (BMAT_L1/L2) via a 2-point T1-weighted volumetric interpolated breath-hold examination (VIBE) Dixon sequence. The same MR sequence was applied to quantify VAT and SAT volume. Subjects’ characteristics, including physical activity, were determined through standardized exams and self-assessment questionnaires. Univariate and multivariate linear regression were applied. In the cohort of 378 subjects (56 ± 9.1years; 42.1% female), BMAT_L1/L2 was 54.3 ± 10.1%, VAT was 4.54 ± 2.71 L, and SAT was 8.10 ± 3.68 L. VAT differed significantly across BMAT_L1/L2 tertiles (3.60 ± 2.76 vs. 4.92 ± 2.66 vs. 5.11 ± 2.48; p < 0.001), there was no significant differences for SAT (p = 0.39). In the fully adjusted model, VAT remained positively associated with BMAT_L1/L2 (β = 0.53, p = 0.03). Furthermore, BMAT_L1/L2 was associated with age (β = 5.40 per 10-years, p < 0.001), hemoglobin A1c (HbA1c; β = 1.55 per 1%, p = 0.04), lipids (β = 0.20 per 10 mg/dL triglycerides; β = 0.40 per 10 mg/dL low-density lipoprotein (LDL); β =−3.21 lipid-lowering medication; all p < 0.05), and less physical activity (β = 3.7 “no or nearly no exercise” as compared to “≥2 h per week, regularly”, p = 0.003); gender was not significantly different (p = 0.57). In the population-based cohort, VAT but not SAT were associated with higher BMAT_L1/L2 independently of physical activity and other cardiovascular risk factors. Further, BMAT_L1/L2 increased with older age, less physical activity, higher HbA1c, and increased lipids but decreased with lipid-lowering medication.

Diffusion MRI for Assessment of Bone Quality; A Review of Findings in Healthy Aging and Osteoporosis

Diffusion MRI (dMRI) is a growing imaging technique with the potential to provide biomarkers of tissue variation, such as cellular density, tissue anisotropy, and microvascular perfusion. However, the role of dMRI in characterizing different aspects of bone quality, especially in aging and osteoporosis, has not yet been fully established, particularly in clinical applications. The reason lies in the complications accompanied with implementation of dMRI in assessment of human bone structure, in terms of acquisition and quantification. Bone is a composite tissue comprising different elements, each contributing to the overall quality and functional competence of bone. As diffusion is a critical biophysical process in biological tissues, early changes of tissue microstructure and function can affect diffusive properties of the tissue. While there are multiple MRI methods to detect variations of individual properties of bone quality due to aging and osteoporosis, dMRI has potential to serve as a superior method for characterizing different aspects of bone quality within the same framework but with higher sensitivity to early alterations. This is mainly because several properties of the tissue including directionality and anisotropy of trabecular bone and cell density can be collected using only dMRI. In this review article, we first describe components of human bone that can be potentially detected by their diffusivity properties and contribute to variations in bone quality during aging and osteoporosis. Then we discuss considerations and challenges of dMRI in bone imaging, current status, and suggestions for development of dMRI in research studies and clinics to segregate different contributing components of bone quality in an integrated acquisition. Level of Evidence: 5 Technical Efficacy Stage: 2 J. Magn. Reson. Imaging 2020;51:975-992.

Specific Biological Features of Adipose Tissue, and Their Impact on HIV Persistence

Although white AT can contribute to anti-infectious immune responses, it can also be targeted and perturbed by pathogens. The AT's immune involvement is primarily due to strong pro-inflammatory responses (with both local and paracrine effects), and the large number of fat-resident macrophages. Adipocytes also exert direct antimicrobial responses. In recent years, it has been found that memory T cells accumulate in AT, where they provide efficient secondary responses against viral pathogens. These observations have prompted researchers to re-evaluate the links between obesity and susceptibility to infections. In contrast, AT serves as a reservoir for several persistence pathogens, such as human adenovirus Ad-36, Trypanosoma gondii, Mycobacterium tuberculosis, influenza A virus, and cytomegalovirus (CMV). The presence and persistence of bacterial DNA in AT has led to the concept of a tissue-specific microbiota. The unexpected coexistence of immune cells and pathogens within the specific AT environment is intriguing, and its impact on anti-infectious immune responses requires further evaluation. AT has been recently identified as a site of HIV persistence. In the context of HIV infection, AT is targeted by both the virus and the antiretroviral drugs. AT's intrinsic metabolic features, large overall mass, and wide distribution make it a major tissue reservoir, and one that may contribute to the pathophysiology of chronic HIV infections. Here, we review the immune, metabolic, viral, and pharmacological aspects that contribute to HIV persistence in AT. We also evaluate the respective impacts of both intrinsic and HIV-induced factors on AT's involvement as a viral reservoir. Lastly, we examine the potential consequences of HIV persistence on the metabolic and immune activities of AT.

Anorexia Nervosa and the Immune System-A Narrative Review

The pathogenesis of an increasing number of chronic diseases is being attributed to effects of the immune system. However, its role in the development and maintenance of anorexia nervosa is seemingly under-appreciated. Yet, in examining the available research on the immune system and genetic studies in anorexia nervosa, one becomes increasingly suspicious of the immune system’s potential role in the pathophysiology of anorexia nervosa. Specifically, research is suggestive of increased levels of various pro-inflammatory cytokines as well as the spontaneous production of tumor necrosis factor in anorexia nervosa; genetic studies further support a dysregulated immune system in this disorder. Potential contributors to this dysregulated immune system are discussed including increased oxidative stress, chronic physiological/psychological stress, changes in the intestinal microbiota, and an abnormal bone marrow microenvironment, all of which are present in anorexia nervosa.

Mandibular bone is protected against microarchitectural alterations and bone marrow adipose conversion in ovariectomized rats

Osteoporosis is a disease that leads to a loss of bone mass and to alterations in the bone microarchitecture that occur in a site-specific manner; however it remains controversial in the jaw. The involvement of bone marrow adipose tissue (BMAT) in the bone metabolism has been suggested in several physiopathological contexts, such as in aging and osteoporosis. To test whether the BMAT content is related to mandibular bone loss, this study aimed to investigate the potential correlations between the trabecular bone microarchitecture on one hand and BMAT content and its spatial distribution in relation to bone surface on the other hand during aging and ovariectomy (OVX) during a long-term follow-up in a mature rat model. No age-related microarchitectural or BMAT changes were observed in the mandible. The OVX-induced bone loss was three-fold lower in the mandible than in the tibia and was observed only in the alveolar bone (not in the condyle). We also report a delayed increase in the mandibular BMAT content that remained 4-6-fold lower compared to tibia. This low BMAT content in the mandible was located at a distance from the trabecular bone surface (only 5% in contact with the bone surface versus 87% in the tibia). These findings highlight a specific mandibular response to OVX, in particular fewer microarchitectural alterations compared to that in the tibia. For the latter, the trabecular bone thickness and surface were correlated with the BMAT content. Oral functions may have a protective effect on the mandibular BMAT conversion in an OVX context.

Cinacalcet attenuated bone loss via inhibiting parathyroid hormone-induced endothelial-to-adipocyte transition in chronic kidney disease rats

Background

Recently, cinacalcet (CINA) has been shown to be effective for attenuating bone loss in the treatment of secondary hyperparathyroidism (SHPT) in patients with chronic kidney disease (CKD), which might be associated with the reduction in serum parathyroid hormone (PTH) levels. However, the exact mechanism is largely unclear. Emerging studies have revealed that an increased number of bone marrow adipocytes (BMAs) are involved in bone loss and the endothelial-to-adipocyte transition via the endothelial-to-mesenchymal transition (EndMT) might play a key role in this pathological process. Here, we assessed whether CINA could attenuate bone loss via inhibiting endothelial-to-adipocyte transition in CKD rats.

Methods

A rat model of CKD was induced by adenine and a high phosphorus diet. CINA was orally administrated to CKD animals (10 mg/kg once a day). Dual energy X-ray absorptiometry, micro-computed tomography, bone histomorphometry, and bone mechanical tests were used to determine the skeletal changes. The bone marrow expression of EndMT markers was also examined. The effect of elevated PTH levels on the endothelial-to-adipocyte transition was studied in endothelial cells (ECs).

Results

Elevation of serum PTH levels, remarkable bone loss and increased numbers of BMAs were observed in rats with CKD compared with the controls, and these changes were attenuated after treatment with CINA. Furthermore, the CINA treatment abolished the upregulation of mesenchymal markers (FSP1 and α-SMA) and the downregulation of an endothelial marker (CD31) in bone tissues from rats with CKD. The serum PTH concentrations were correlated with the bone marrow protein levels of these EndMT-related proteins. An in vitro treatment in ECs demonstrated that PTH induced the EndMT in a concentration- and time-dependent manner. Accordingly, ECs treated with PTH exhibited adipogenic potential following growth in adipogenic culture medium.

Conclusions

Our study indicated CINA treatment attenuated bone loss in CKD rats, which might be associated with inhibiting PTH-induced endothelial-to-adipocyte transition in CKD rats.

Aging and lineage allocation changes of bone marrow skeletal (stromal) stem cells

Aging is associated with decreased bone mass and accumulation of bone marrow adipocytes. Both bone forming osteoblastic cells and bone marrow adipocytes are derived from a stem cell population within the bone marrow stroma called bone marrow stromal (skeletal or mesenchymal) stem cells (BMSC). In the present review, we provide an overview, based on the current literature, regarding the physiological aging processes that cause changes in BMSC lineage allocation, enhancement of adipocyte and defective osteoblast differentiation, leading to gradual exhaustion of stem cell regenerative potential and defects in bone tissue homeostasis and metabolism. We discuss strategies to preserve the "youthful" state of BMSC, to reduce bone marrow age-associated adiposity, and to counteract the overall negative effects of aging on bone tissues with the aim of decreasing bone fragility and risk of fractures.

Increase of Glucose Uptake in Human Bone Marrow With Increasing Exercise Intensity

Human bone marrow is a metabolically active tissue that responds to acute low-intensity exercise by having increased glucose uptake (GU). Here, the authors studied whether bone marrow GU increases more with increased exercise intensities. Femoral bone marrow GU was measured using positron emission tomography and [18F]-fluorodeoxyglucose in six healthy young men during cycling at intensities of 30% (low), 55% (moderate), and 75% (high) of maximal oxygen consumption on three separate days. Bone marrow GU at low was 17.2 µmol·kg−1·min−1 (range 9.0–25.4) and increased significantly (p = .003) at moderate (31.2 µmol·kg−1·min−1, 22.9–39.4) but was not significant from moderate to high (37.4 µmol·kg−1·min−1, 29.0–45.7, p = .26). Furthermore, the ratio between bone and muscle GU decreased from low to moderate exercise intensity (p < .01) but not (p = .99) from moderate to high exercise intensity. In conclusion, these results show that although the increase is not as large as observed in exercising skeletal muscle, GU in femoral bone marrow increases with increasing exercise intensity at least from low- to moderate-intensity effort, which may be important for bone and whole-body metabolic health.

Marrow adiposity and bone: Review of clinical implications

There is growing interest in the relationship between bone marrow fat (BMF) and skeletal health. Progress in clinical studies of BMF and skeletal health has been greatly enhanced by recent technical advances in our ability to measure BMF non-invasively. Magnetic resonance imagery (MRI) with or without spectroscopy is currently the standard technique for evaluating BMF content and composition in humans. This review focuses on clinical studies of marrow fat and its relationship with bone. The amount of marrow fat is associated with bone mineral density (BMD). Several studies have reported a significant negative association between marrow fat content and BMD in both healthy and osteoporotic populations. There may also be a relationship between marrow fat and fracture (mostly vertebral fracture), but data are scarce and further studies are needed. Furthermore, a few studies suggest that a lower proportion of unsaturated lipids in vertebral BMF may be associated with reduced BMD and greater prevalence of fracture. Marrow fat might be influenced by metabolic diseases associated with bone loss and fractures, such as diabetes mellitus, obesity and anorexia nervosa. An intriguing aspect of bariatric (weight loss) surgery is that it induces bone loss and fractures, but with different impacts on marrow fat depending on diabetic status. In daily practice, the usefulness for clinicians of assessing marrow fat using MRI is still limited. However, the perspectives are exciting, particularly in terms of improving the diagnosis and management of osteoporosis. Further studies are needed to better understand the regulators involved in the marrow fat-bone relationship and the links between marrow fat, other fat depots and energy metabolism.

Bone marrow adipose amount influences vertebral bone strength

Association of bone marrow adipose and microstructure with bone strength in osteoporotic rats using MR Dixon analysis and micro-CT was evaluated. A total of 40 female Sprague-Dawley rats (6-month-old) were divided randomly into sham-operated (SHAM, n=20) group and ovariectomized (OVX, n=20) group. Fat fraction (FF) was measured by two-point Dixon method with MR imaging at the baseline, 4th, 8th and 12th week, respectively. After sacrifice by anesthesia, the fifth lumbar vertebrae bone was sampled for micro-CT scanning. The biomechanical analysis was also performed. FF in osteoporotic rats significantly increases with time, which correlates with bone microstructure parameters. Compared with biomechanical test, FF showed negative correlation with break stress and elastic modulus. It also suggested that loss of bone mass was accompanied with the increase of adipose tissue content in vertebrae bone marrow. The impairment of bone strength leads to the risk of brittle fracture. In conclusion, the bone marrow adipose amount obtained by MR Dixon and microstructure by micro-CT correlates to bone strength in osteoporotic rats.

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

OBJECTIVE

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

DESIGN

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Autophagy protects bone marrow mesenchymal stem cells from palmitate‑induced apoptosis through the ROS‑JNK/p38 MAPK signaling pathways

In recent years, the association between saturated fatty acids (FA) and bone cells has received a high level of attention. Previous studies have shown that palmitate (PA), a common saturated FA, can cause apoptosis in bone marrow mesenchymal stem cells (BMSCs). However, whether PA can induce autophagy, an important intracellular protection mechanism that is closely associated with apoptosis, in BMSCs is still unknown; the association between autophagy and apoptosis is also unclear. The aim of the present study was to determine whether PA can induce autophagy in BMSCs. When BMSCs were treated with PA for >18 h, p62 began to accumulate, indicating that autophagic flux was impaired by prolonged exposure to PA. In addition, the proportion of apoptotic cells was increased when autophagy was inhibited by the autophagy inhibitor 3‑methyladenine. Furthermore, inducing autophagy by pretreating cells with rapamycin, a known inducer of autophagy, markedly reduced PA‑induced apoptosis, suggesting that autophagy may serve a protective role in PA‑induced apoptosis in BMSCs. PA also increased intracellular reactive oxygen species (ROS) production, which was decreased by the antioxidant N‑Acetyl‑cysteine, and promoted the activation of c‑Jun N‑terminal kinases (JNKs) and p38 mitogen‑activated protein kinase (MAPK). The addition of JNK and p38 MAPK inhibitors substantially reduced autophagy. Therefore, the results indicated that PA can induce autophagy in BMSCs and protect cells from PA‑induced apoptosis through the ROS‑JNK/p38 MAPK signaling pathways. These results may improve the general understanding of the mechanisms through which BMSCs adapt to PA‑induced apoptosis. The present study also provides a novel approach for the prevention and treatment of PA‑induced lipotoxicity.