The bone-fat interface: basic and clinical implications of marrow adiposity

Liuwei Dihuang pills attenuate ovariectomy-induced bone loss by alleviating bone marrow mesenchymal stem cell (BMSC) senescence via the Yes-associated protein (YAP)-autophagy axis

CONTEXT

Liuwei Dihuang pill (LWDH) has been used to treat postmenopausal osteoporosis (PMOP).

OBJECTIVE

To explore the effects and mechanisms of action of LWDH in PMOP.

MATERIALS AND METHODS

Forty-eight female Sprague-Dawley rats were divided into four groups: sham-operated (SHAM), ovariectomized (OVX), LWDH high dose (LWDH-H, 1.6 g/kg/d) and LWDH low dose (LWDH-L, 0.8 g/kg/d); the doses were administered after ovariectomy via gavage for eight weeks. After eight weeks, the bone microarchitecture was evaluated. The effect of LWDH on the differentiation of bone marrow mesenchymal stem cells (BMSCs) was assessed via osteogenesis- and lipogenesis-induced BMSC differentiation. The senescence-related biological indices were also detected using senescence staining, cell cycle analysis, quantitative real-time polymerase chain reaction and western blotting. Finally, the expression levels of autophagy-related proteins and Yes-associated protein (YAP) were evaluated.

RESULTS

LWDH-L and LWDH-H significantly modified OVX-induced bone loss. LWDH promoted osteogenesis and inhibited adipogenesis in OVX-BMSCs. Additionally, LWDH decreased the positive ratio of senescence OVX-BMSCs and improved cell viability, cell cycle, and the mRNA and protein levels of p53 and p21. LWDH upregulated the expression of autophagy-related proteins, LC3, Beclin1 and YAP, in OVX-BMSCs and downregulated the expression of p62.

DISCUSSION AND CONCLUSIONS

LWDH improves osteoporosis by delaying the BMSC senescence through the YAP-autophagy axis.

Obesity and periodontitis: a comprehensive review of their interconnected pathophysiology and clinical implications

Obesity and periodontitis are significant health problems with a complex bidirectional relationship. Excess body fat is linked to systemic diseases and can lead to persistent inflammation, potentially harming periodontal health. Periodontitis, a chronic inflammatory condition affecting the supporting structures of teeth, poses substantial health risks. Both conditions share pathological processes such as inflammation and oxidative stress, which aggravate health status and make treatment more challenging. Understanding this interaction is crucial for developing effective management strategies for both diseases. This study explores the multifaceted aspects of obesity and periodontitis and their reciprocal relationship.

Spinal Cord Injury Associated Disease of the Skeleton, an Unresolved Problem with Need for Multimodal Interventions

Spinal cord injury is associated with skeletal unloading, sedentary behavior, decreases in skeletal muscle mass, and exercise intolerance, which results in rapid and severe bone loss. To date, monotherapy with physical interventions such as weight-bearing in standing frames, computer-controlled electrically stimulated cycling and ambulation exercise, and low-intensity vibration are unsuccessful in maintaining bone density after SCI. Strategies to maintain bone density with commonly used osteoporosis medications also fail to provide a significant clinical benefit, potentially due to a unique pathology of bone deterioration in SCI. In this review, the available data is discussed on evaluating and monitoring bone loss, fracture, and physical and pharmacological therapeutic approaches to SCI-associated disease of the skeleton. The treatment of SCI-associated disease of the skeleton, the implications for clinical management, and areas of need are considered for future investigation.

Microbial Tryptophan Metabolites Ameliorate Ovariectomy-Induced Bone Loss by Repairing Intestinal AhR-Mediated Gut-Bone Signaling Pathway

Microbial tryptophan (Trp) metabolites acting as aryl hydrocarbon receptor (AhR) ligands are shown to effectively improve metabolic diseases via regulating microbial community. However, the underlying mechanisms by which Trp metabolites ameliorate bone loss via gut-bone crosstalk are largely unknown. In this study, supplementation with Trp metabolites, indole acetic acid (IAA), and indole-3-propionic acid (IPA), markedly ameliorate bone loss by repairing intestinal barrier integrity in ovariectomy (OVX)-induced postmenopausal osteoporosis mice in an AhR-dependent manner. Mechanistically, intestinal AhR activation by Trp metabolites, especially IAA, effectively repairs intestinal barrier function by stimulating Wnt/β-catenin signaling pathway. Consequently, enhanced M2 macrophage by supplementation with IAA and IPA secrete large amount of IL-10 that expands from intestinal lamina propria to bone marrow, thereby simultaneously promoting osteoblastogenesis and inhibiting osteoclastogenesis in vivo and in vitro. Interestingly, supplementation with Trp metabolites exhibit negligible ameliorative effects on both gut homeostasis and bone loss of OVX mice with intestinal AhR knockout (VillinCreAhrfl/fl). These findings suggest that microbial Trp metabolites may be potential therapeutic candidates against osteoporosis via regulating AhR-mediated gut-bone axis.

Fgf9 regulates bone marrow mesenchymal stem cell fate and bone-fat balance in osteoporosis by PI3K/AKT/Hippo and MEK/ERK signaling

Bone-fat balance is crucial to maintain bone homeostasis. As common progenitor cells of osteoblasts and adipocytes, bone marrow mesenchymal stem cells (BMSCs) are delicately balanced for their differentiation commitment. However, the exact mechanisms governing BMSC cell fate are unclear. In this study, we discovered that fibroblast growth factor 9 (Fgf9), a cytokine expressed in the bone marrow niche, controlled bone-fat balance by influencing the cell fate of BMSCs. Histomorphology and cytodifferentiation analysis showed that Fgf9 loss-of-function mutation (S99N) notably inhibited bone marrow adipose tissue (BMAT) formation and alleviated ovariectomy-induced bone loss and BMAT accumulation in adult mice. Furthermore, in vitro and in vivo investigations demonstrated that Fgf9 altered the differentiation potential of BMSCs, shifting from osteogenesis to adipogenesis at the early stages of cell commitment. Transcriptomic and gene expression analyses demonstrated that FGF9 upregulated the expression of adipogenic genes while downregulating osteogenic gene expression at both mRNA and protein levels. Mechanistic studies revealed that FGF9, through FGFR1, promoted adipogenic gene expression via PI3K/AKT/Hippo pathways and inhibited osteogenic gene expression via MAPK/ERK pathway. This study underscores the crucial role of Fgf9 as a cytokine regulating the bone-fat balance in adult bone, suggesting that FGF9 is a potentially therapeutic target in the treatment of osteoporosis.

Pyroptosis: A spoiler of peaceful coexistence between cells in degenerative bone and joint diseases

BACKGROUND

As people age, degenerative bone and joint diseases (DBJDs) become more prevalent. When middle-aged and elderly people are diagnosed with one or more disorders such as osteoporosis (OP), osteoarthritis (OA), and intervertebral disc degeneration (IVDD), it often signals the onset of prolonged pain and reduced functionality. Chronic inflammation has been identified as the underlying cause of various degenerative diseases, including DBJDs. Recently, excessive activation of pyroptosis, a form of programed cell death (PCD) mediated by inflammasomes, has emerged as a primary driver of harmful chronic inflammation. Consequently, pyroptosis has become a potential target for preventing and treating DBJDs.

AIM OF REVIEW

This review explored the physiological and pathological roles of the pyroptosis pathway in bone and joint development and its relation to DBJDs. Meanwhile, it elaborated the molecular mechanisms of pyroptosis within individual cell types in the bone marrow and joints, as well as the interplay among different cell types in the context of DBJDs. Furthermore, this review presented the latest compelling evidence supporting the idea of regulating the pyroptosis pathway for DBJDs treatment, and discussed the potential, limitations, and challenges of various therapeutic strategies involving pyroptosis regulation.

KEY SCIENTIFIC CONCEPTS OF REVIEW

In summary, an interesting identity for the unregulated pyroptosis pathway in the context of DBJDs was proposed in this review, which was undertaken as a spoiler of peaceful coexistence between cells in a degenerative environment. Over the extended course of DBJDs, pyroptosis pathway perpetuated its activity through crosstalk among pyroptosis cascades in different cell types, thus exacerbating the inflammatory environment throughout the entire bone marrow and joint degeneration environment. Correspondingly, pyroptosis regulation therapy emerged as a promising option for clinical treatment of DBJDs.

Dietary restriction plus exercise change gene expression of Cxcl12 abundant reticular cells in female mice

INTRODUCTION

Low energy availability due to excessive exercise lowers bone mass and impairs various physiological functions, including immunity and hematopoiesis. We focused on Cxcl12 abundant reticular (CAR) cells, which are bone marrow mesenchymal stem cells and are essential for the maintenance of hematopoietic and immune cells in bone marrow. We examine the functional changes in CAR cells resulting from dietary restriction combined with exercise.

MATERIALS AND METHODS

Five-week-old wild-type female mice were divided into an ad libitum group (CON), a 60% dietary restriction group (DR), an ad libitum with exercise group (CON + ex), and a 60% dietary restriction with exercise group (DR + ex). Blood parameters, bone structure parameters, and bone marrow fat volume were evaluated after 5 weeks. In addition, bone marrow CAR cells were isolated by cell sorting and analyzed for gene expression by RT-qPCR.

RESULTS

Bone mineral density (BMD) was significantly decreased in DR and DR + ex compared to CON and CON + ex. Especially, cortical bone mass and thickness were significantly decreased in DR and DR + ex groups, whereas trabecular bone mass was significantly increased. Bone marrow fat volume was significantly increased in DR and DR + ex groups compared to CON and CON + ex. The number of leukocytes in the blood was significantly decreased in the DR + ex group compared to the other three groups. RT-qPCR showed a significant decrease in gene expression of both Foxc1 and Runx2 in CAR cells of the DR + ex group compared to CON.

CONCLUSION

Dietary restriction combined with exercise promotes CAR cell differentiation into bone marrow adipocyte and suppresses osteoblast differentiation.

IFT20 and WWTR1 govern bone homeostasis via synchronously regulating the expression and stability of TβRII in osteoblast lineage cells

Balance of bone and marrow fat formation is critical for bone homeostasis. The imbalance of bone homeostasis will cause various bone diseases, such as osteoporosis. However, the precise mechanisms governing osteoporotic bone loss and marrow adipose tissue (MAT) accumulation remain poorly understood. By analysis of publicly available databases from bone samples of osteoporosis patients, we found that the expression of intraflagellar transport 20 (IFT20) and WW domain containing transcription regulator 1 (WWTR1) were significantly downregulated in osteoblast lineage cells. Additionally, we found that double deletions of IFT20 and WWTR1 in osteoblasts resulted in a significant accumulation of MAT and bone loss. Moreover, IFT20 and WWTR1 deficiency in osteoblasts exacerbated bone-fat imbalance in ovariectomy (OVX)- and high-fat-diet (HFD)-induced osteoporosis mouse models. Mechanistically, we found that deletions of IFT20 and WWTR1 in osteoblasts synergistically inhibited osteogenesis and promoted adipogenesis and osteoclastogenesis. We also found that IFT20 interacted with TGF-β receptor type II (TβRII) to enhance TβRII stability by blocking c-Cbl-mediated ubiquitination and degradation of TβRII. WWTR1 transcriptionally upregulated TβRII expression by directly binding its promoter. These findings indicate that targeting IFT20/WWTR1 may be a potential therapeutic strategy for the treatment of osteoporosis.

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.

A DNA tetrahedron-based ferroptosis-suppressing nanoparticle: superior delivery of curcumin and alleviation of diabetic osteoporosis

Diabetic osteoporosis (DOP) is a significant complication that poses continuous threat to the bone health of patients with diabetes; however, currently, there are no effective treatment strategies. In patients with diabetes, the increased levels of ferroptosis affect the osteogenic commitment and differentiation of bone mesenchymal stem cells (BMSCs), leading to significant skeletal changes. To address this issue, we aimed to target ferroptosis and propose a novel therapeutic approach for the treatment of DOP. We synthesized ferroptosis-suppressing nanoparticles, which could deliver curcumin, a natural compound, to the bone marrow using tetrahedral framework nucleic acid (tFNA). This delivery system demonstrated excellent curcumin bioavailability and stability, as well as synergistic properties with tFNA. Both in vitro and in vivo experiments revealed that nanoparticles could enhance mitochondrial function by activating the nuclear factor E2-related factor 2 (NRF2)/glutathione peroxidase 4 (GPX4) pathway, inhibiting ferroptosis, promoting the osteogenic differentiation of BMSCs in the diabetic microenvironment, reducing trabecular loss, and increasing bone formation. These findings suggest that curcumin-containing DNA tetrahedron-based ferroptosis-suppressing nanoparticles have a promising potential for the treatment of DOP and other ferroptosis-related diseases.

Effects of Tenofovir Disoproxil Fumarate on Bone Quality beyond Bone Density-A Scoping Review of the Literature

Tenofovir disoproxil fumarate (TDF) is a widely used pharmacological agent for the treatment of human immunodeficiency virus infection. While prolonged exposure to TDF has been associated with a decrease in bone mineral density (BMD) and increased fracture risk, limited discussion exists on its effects on various aspects of bone quality. This scoping review aims to provide a comprehensive overview of the impact of TDF on bone quality beyond BMD. A literature search was conducted using the PubMed and Scopus databases to identify studies investigating the effects of TDF on bone quality. Original research articles written in English, irrespective of study type or publication year, were included in the review. Seven articles met the inclusion criteria. Findings indicate that prolonged exposure to TDF adversely affects bone microarchitecture and strength, impeding fracture healing and skeletal microdamage repair. The observed effects suggest a complex interplay involving bone cell signalling, cytokines and bone remodelling processes as potential mechanisms underlying TDF's impact on bone quality. As a conclusion, TDF impairs bone remodelling and microarchitecture by influencing dynamic bone cell behaviour and signalling pathways. Future studies should delve deeper into understanding the intricate negative effects of TDF on bone and explore strategies for reversing these effects.

Effects of Aging on Osteosynthesis at Bone-Implant Interfaces

Joint replacement is a common surgery and is predominantly utilized for treatment of osteoarthritis in the aging population. The longevity of many of these implants depends on bony ingrowth. Here, we provide an overview of current techniques in osteogenesis (inducing bone growth onto an implant), which is affected by aging and inflammation. In this review we cover the biologic underpinnings of these processes as well as the clinical applications. Overall, aging has a significant effect at the cellular and macroscopic level that impacts osteosynthesis at bone-metal interfaces after joint arthroplasty; potential solutions include targeting prolonged inflammation, preventing microbial adhesion, and enhancing osteoinductive and osteoconductive properties.

Deletion of Mettl3 in mesenchymal stem cells promotes acute myeloid leukemia resistance to chemotherapy

Acute myeloid leukemia (AML) cell survival and chemoresistance are influenced by the existence of bone marrow mesenchymal stem cells (BMMSCs); however, the pathways by which BMMSCs contribute to these processes remain unclear. We earlier revealed that methyltransferase-like 3 (METTL3) expression is significantly reduced in AML BMMSCs and that METTL3 mediates BMMSC adipogenesis to promote chemoresistance in human AML cell lines in vitro. In this investigation, we evaluated the METTL3 function in vivo. Mice exhibiting a conditional removal of Mettl3 in BMMSCs were developed by mating Prrx1-CreERT2;Mettl3fl/+ mice with Mettl3fl/fl mice using the CRISPR-Cas9 system. The Mettl3 deletion increased bone marrow adiposity, enhanced disease progression in the transplantation-induced MLL-AF9 AML mouse model, and chemoresistance to cytarabine. The removal of Mettl3 in BMMSCs resulted in a significant increase in BMMSC adipogenesis. This effect was attributed to the downregulation of AKT1 expression, an AKT serine/threonine kinase 1, in an m6A-dependent manner. The development of chemoresistance in AML is linked to the promoted adipogenesis of BMMSCs. We conclude that METTL3 expression in BMMSCs has a critical function in limiting AML progression and chemoresistance, providing a basis for the progression of therapeutic approaches for AML.

Bone Marrow Adiposity Alterations in Type 2 Diabetes Are Sex-Specific and Associated with Serum Lipid Levels

Type 2 diabetes (T2D) has negative effects on skeletal health. A proposed mechanism of diabetic bone disease connects hyperlipidemia to increased bone marrow adiposity and decreased bone quality. Previous research on Type 1 diabetes reported positive associations between serum lipid levels and marrow adiposity, but no data exist for T2D. In addition, marrow adiposity is sex-dependent in healthy populations, but sex has not been addressed adequately in previous reports of marrow adiposity in T2D. The purpose of this study was to quantify associations of marrow adiposity and composition with T2D status, serum lipid levels, and sex. T2D patients and normoglycemic controls (n = 39/37) were included. Single-voxel magnetic resonance spectroscopy (MRS) was performed at the spine and tibia. Quantitative MRS outcomes of marrow adiposity and composition were calculated. Linear regression models were used to compare MRS outcomes among groups and to evaluate associations of MRS outcomes with serum lipid levels. All analyses were performed on sex-stratified subgroups. Total, unsaturated, and saturated fat content at the spine were lower in T2D participants compared to controls in age-adjusted models; these differences were significant in men but not in women. In our study cohort, total cholesterol, low-density lipoprotein (LDL), and high-density lipoprotein (HDL) were lower in T2D participants compared to controls. Adjustment for LDL, HDL, and statin use attenuated the association of T2D status with unsaturated fat but not saturated fat in men. Further analysis confirmed significant associations between serum lipid levels and MRS outcomes. Specifically, we found a positive association between LDL cholesterol and total marrow fat in the male T2D group and a negative association between HDL and total marrow fat in the female T2D group. In conclusion, our results suggest that marrow adiposity and composition are associated with lipid levels as well as T2D status, and these relationships are sex-specific. © 2023 American Society for Bone and Mineral Research (ASBMR).

Novel role for alpha-2-macroglobulin (A2M) as a disease modifying protein in senile osteoporosis

Introduction: In the rapidly aging U.S. population, age-induced bone loss (senile osteoporosis) represents a major public health concern that is associated with a significant increased risk for low trauma fragility fractures, which are debilitating to patients, cause significant morbidity and mortality, and are costly to treat and manage. While various treatments exist to slow bone loss in osteoporosis patients, these suffer from poor tolerability and label restrictions that limit their overall effectiveness. Over the past decade, skeletal stem/progenitor cells (SSPCs), which are the main precursor of osteoblasts and adipocytes in adult bone marrow (BM), have emerged as important players in osteoporosis. Methods: Age-induced skeletal pathology was quantified in elderly (24-month-old) vs. mature (3-month-old) mice by micro-CT and changes in SSPC abundance in the BM of these mice was quantified by fluorescence-activated cell sorting (FACS). SSPCs from elderly vs. mature mice were also analyzed by RNA-Seq to identify differentially expressed genes (DEGs), and gain and loss-of-function studies were performed in human BM-derived mesenchymal stromal cells (BM-MSCs) to assess A2M function. Results: Elderly mice were shown to exhibit significant age-induced skeletal pathology, which correlated with a significant increase in SSPC abundance in BM. RNA-seq analysis identified alpha-2-macroglobulin (A2M), a pan-protease inhibitor that also binds inflammatory cytokines, as one of the most downregulated transcripts in SSPCs isolated from the BM of elderly vs. mature mice, and silencing of A2M expression in human BM-MSCs induced their proliferation and skewed their lineage bifurcation toward adipogenesis at the expense of osteogenesis thereby recapitulating critical aspects of age-induced stem cell dysfunction. Conclusion: These findings identify A2M as a novel disease modifying protein in osteoporosis, downregulation of which in bone marrow promotes SSPC dysfunction and imbalances in skeletal homeostasis.

Dominoes with interlocking consequences triggered by zinc: involvement of microelement-stimulated MSC-derived exosomes in senile osteogenesis and osteoclast dialogue

As societal aging intensifies, senile osteoporosis has become a global public health concern. Bone microdamage is mainly caused by processes such as enhancing osteoclast activity or reducing bone formation by osteoblast-lineage cells. Compared with young individuals, extracellular vesicles derived from senescent bone marrow mesenchymal stem cells(BMSCs) increase the transient differentiation of bone marrow monocytes (BMMs) to osteoclasts, ultimately leading to osteoporosis and metal implant failure. To address this daunting problem, an exosome-targeted orthopedic implant composed of a nutrient coating was developed. A high-zinc atmosphere used as a local microenvironmental cue not only could inhibit the bone resorption by inhibiting osteoclasts but also could induce the reprogramming of senile osteogenesis and osteoclast dialogue by exosome modification. Bidirectional regulation of intercellular communication via cargoes, including microRNAs carried by exosomes, was detected. Loss- and gain-of-function experiments demonstrated that the key regulator miR-146b-5p regulates the protein kinase B/mammalian target of rapamycin pathway by targeting the catalytic subunit gene of PI3K-PIK3CB. In vivo evaluation using a naturally-aged osteoporotic rat femoral defect model further confirmed that a nutrient coating substantially augments cancellous bone remodeling and osseointegration by regulating local BMMs differentiation. Altogether, this study not only reveals the close link between senescent stem cell communication and age-related osteoporosis but also provides a novel orthopedic implant for elderly patients with exosome modulation capability.

Bone Marrow Adiposity and Fragility Fractures in Postmenopausal Women: The ADIMOS Case-Control Study

CONTEXT

Noninvasive assessment of proton density fat fraction (PDFF) by magnetic resonance imaging (MRI) may improve the prediction of fractures.

OBJECTIVE

This work aimed to determine if an association exists between PDFF and fractures.

METHODS

A case-control study was conducted at Lille University Hospital, Lille, France, with 2 groups of postmenopausal women: one with recent osteoporotic fractures, and the other with no fractures. Lumbar spine and proximal femur (femoral head, neck, and diaphysis) PDFF were determined using chemical shift-based water-fat separation MRI (WFI) and dual-energy x-ray absorptiometry scans of the lumbar spine and hip. Our primary objective was to determine the relationship between lumbar spine PDFF and osteoporotic fractures in postmenopausal women. Analysis of covariance was used to compare PDFF measurements between patient cases (overall and according to the type of fracture) and controls, after adjusting for age, Charlson comorbidity index (CCI) and BMD.

RESULTS

In 199 participants, controls (n = 99) were significantly younger (P < .001) and had significantly higher BMD (P < 0.001 for all sites) than patient cases (n = 100). A total of 52 women with clinical vertebral fractures and 48 with nonvertebral fractures were included. When PDFFs in patient cases and controls were compared, after adjustment on age, CCI, and BMD, no statistically significant differences between the groups were found at the lumbar spine or proximal femur. When PDFFs in participants with clinical vertebral fractures (n = 52) and controls were compared, femoral neck PDFF and femoral diaphysis PDFF were detected to be lower in participants with clinical vertebral fractures than in controls (adjusted mean [SE] 79.3% [1.2] vs 83.0% [0.8]; P = 0.020, and 77.7% [1.4] vs 81.6% [0.9]; P = 0.029, respectively).

CONCLUSION

No difference in lumbar spine PDFF was found between those with osteoporotic fractures and controls. However, imaging-based proximal femur PDFF may discriminate between postmenopausal women with and without clinical vertebral fractures, independently of age, CCI, and BMD.

A novel small molecule effectively ameliorates estrogen deficiency-induced osteoporosis by targeting the gut-bone signaling axis

Postmenopausal osteoporosis stems mainly from estrogen deficiency leading to a gut microbiome-dependent disruption of host systemic immunity. However, the underlying mechanisms of estrogen deficiency-induced bone loss remain elusive and novel pharmaceutical intervention strategies for osteoporosis are needed. Here we reveal that ovariectomy (ovx)-induced estrogen deficiency in C57BL/6 mice causes significant disruption of gut microbiota composition, consequently leading to marked destruction of intestinal barrier function and gut leakage. As a result, signals transportation between intestinal microbiota and T cells from the gut to bone marrow is identified to contribute to osteoclastogenesis in ovx mice. Notably, we show that icariside I (GH01), a novel small molecule naturally occurring in Herbal Epimedium, has potential to alleviate or prevent ovx-induced bone loss in mice through regulation of gut-bone signaling axis. We find that GH01 treatment can effectively restore the gut microbiota composition, intestinal barrier function and host immune status markedly altered in ovx mice, thus significantly ameliorating bone loss and osteoporosis. These findings not only provide systematic understanding of the gut-immunity-bone axis-associated pathophysiology of osteoporosis, but also demonstrate the high potential of GH01 for osteoporosis treatment by targeting the gut-bone signaling axis.

[Lipocalin 2 induces self-limited inhibition of osteoblast differentiation of mesenchymal stem cells]

OBJECTIVE

To explore the role of lipocalin 2 (Lcn2) in bone development and senile osteoporosis.

METHODS

Chromatin immunoprecipitation with H3K27AC and H3K9Me3 antibodies coupled with massively parallel sequencing (ChIP-Seq) was performed to analyze the changes in binding of modified histones at the Lcn2 gene locus in C3H10T1/2 mesenchymal stem cells (MSCs) induced with osteogenic induction medium for 3 days. ITRAQ-MS/MS and ELISA were used to compare Lcn2 protein expressions in the cancellous bone and the serum between 16- and 3-month-old male mice. The effect of treatment with recombinant Lcn2 protein on osteogenic differentiation of C3H10T1/2 cells was evaluated by detecting changes in ALP expression, and Western blotting was performed to examine the changes in OSX and OCN expression.

RESULTS

The expression of Lcn2 protein in the cancellous bone and its serum levels were significantly higher in 16-month-old than in 3-month-old male mice (P < 0.01). In C3H10T1/2 cells, ALP expression level decreased significantly after treatment with recombinant Lcn2 protein (P < 0.05) accompanied by lowered protein expressions of OSX and OCN (P < 0.05). Analysis with ROSE software revealed a super enhancer in the Lcn2 gene region of C3H10T1/2 cells after osteogenesis induction. RNA-seq results confirmed that Lcn2 was among the top 4 up-regulated genes in C3H10T1/2 cells following osteogenic induction, and a super enhancer was also detected in Zbtb16 gene, which showed the highest up- regulation after osteogenic induction. Real- time quantitative PCR further confirmed that the mRNA level of Lcn2 increased sharply in C3H10T1/2 cells after osteogenic induction (P < 0.001).

CONCLUSION

Lcn2 is essential for normal osteogenic differentiation of MSCs, but its overexpression and excessive secretion in aging induce self-limited inhibition of osteogenic differentiation of MSCs.

Exploring cellular senescence in the musculoskeletal system: Any insights for biomarkers discovery?

The locomotor system comprises skeletal muscles and bones with active metabolism and cellular turnover. Chronic locomotor system disorders gradually arising with aging are inversely associated with the correct function of bone and muscles. Senescent cells appear more frequently in advanced ages or pathological conditions, and the accumulation of senescent cells in muscle tissue negatively correlates with muscle regeneration, which is crucial for maintaining strength and preventing frailty. Senescence in the bone microenvironment, osteoblasts, and osteocytes affects bone turnover favoring osteoporosis. It is likely that in response to injury and age-related damage over the lifetime, a subset of niche cells accumulates oxidative stress and DNA damage beyond the threshold that primes the onset of cellular senescence. These senescent cells may acquire resistance to apoptosis that, combined with the weakened immune system, results in impaired clearance of senescent cells and their accumulation. The secretory profile of senescent cells causes local inflammation, further spreading senescence in neighboring niche cells and impairing tissue homeostasis. The resulting impairment of turnover/tissue repair in the musculoskeletal system reduces the efficiency of the organ in response to environmental needs that finally lead to functional decline. Management of the musculoskeletal system at the cellular level can benefit the quality of life and reduce early aging. This work discusses current knowledge of cellular senescence of musculoskeletal tissues to conclude with biologically active biomarkers effective enough to reveal the underlying mechanisms of tissue flaws at the earliest possible.

Assessment of osteoporosis in patients with type 2 diabetes mellitus: A study from the central region of Saudi Arabia

OBJECTIVES

To understand the impact of diabetes on bone mineral density and whether it increases the likelihood of osteoporosis.

METHODS

This study was performed on 327 Saudis (aged >40 years) who were screened for osteoporosis and diabetes mellitus (DM). The levels of osteoporosis were determined by an estimation of Bone mineral density (BMD) using a DEXA scan examination. The data on BMD from diabetic subjects were compared with healthy nondiabetic controls.

RESULTS

Out of 327 enrolled subjects, 38 (11.6%) were found to be osteoporotic, whereas 138 (42.2%) had DM. The data showed that the number of patients with osteoporosis in the DM group was 14 (36.8%), significantly lower than in nondiabetic patients, 21 (55.2%) (p=0.0015). Notably, the data showed no significant difference in the mean BMD of the femur in patients with DM (0.926 g/cm2) and non-diabetes (0.936 g/cm2) (p=0.280; T-score p=0.4746). The mean BMD levels in the spine of the DM study group (1.049 g/cm2) were significantly higher when compared with nondiabetic healthy controls (0.990 g/cm2) (p=0.0031).

CONCLUSION

Patients with diabetes had higher lumbar BMD than nondiabetics, although femoral BMD was similar. Patients with diabetes have a lower osteoporosis risk than nondiabetics.

Prolonged Antibiotic Exposure during Adolescence Dysregulates Liver Metabolism and Promotes Adiposity in Mice

Antibiotic administration during early life has been shown to have lasting effects on the gut microbiota, which have been linked to sustained alterations in liver metabolism and adiposity. Recent investigations have discerned that the gut microbiota continues to develop toward an adult-like profile during adolescence. However, the impact of antibiotic exposure during adolescence on metabolism and adiposity is unclear. Herein, a retrospective analysis of Medicaid claims data was performed, which indicated that tetracycline class antibiotics are commonly prescribed for the systemic treatment of adolescent acne. The purpose of this was to discern the impact of a prolonged tetracycline antibiotic exposure during adolescence on the gut microbiota, liver metabolism, and adiposity. Male C57BL/6T specific pathogen-free mice were administered a tetracycline antibiotic during the pubertal/postpubertal adolescent growth phase. Groups were euthanized at different time points to assess immediate and sustained antibiotic treatment effects. Antibiotic exposure during adolescence caused lasting genera-level shifts in the intestinal bacteriome and persistent dysregulation of metabolic pathways in the liver. Dysregulated hepatic metabolism was linked to sustained disruption of the intestinal farnesoid X receptor-fibroblast growth factor 15 axis, a gut-liver endocrine axis that supports metabolic homeostasis. Antibiotic exposure during adolescence increased subcutaneous, visceral, and marrow adiposity, which intriguingly manifested following antibiotic therapy. This preclinical work highlights that prolonged antibiotic courses for the clinical treatment of adolescent acne may have unintended deleterious effects on liver metabolism and adiposity.

HSPB7 oppositely regulates human mesenchymal stromal cell-derived osteogenesis and adipogenesis

BACKGROUND

Recent evidence suggests that accumulation of marrow adipose tissue induced by aberrant lineage allocation of bone marrow-derived mesenchymal stromal cells (BMSCs) contributes to the pathophysiologic processes of osteoporosis. Although master regulators of lineage commitment have been well documented, molecular switches between osteogenesis and adipogenesis are largely unknown.

METHODS

HSPB7 gene expression during osteogenic and adipogenic differentiation of BMSCs was evaluated by qPCR and Western blot analyses. Lentiviral-mediated knockdown or overexpression of HSPB7 and its deletion constructs were used to assess its function. The organization of cytoskeleton was examined by immunofluorescent staining. ALP activity, calcium assay, Alizarin Red S staining and Oil Red O staining were performed in vitro during osteoblast or adipocyte differentiation. SB431542 and Activin A antibody were used to identify the mechanism of Activin A in the regulation of osteogenic differentiation in BMSCs.

RESULTS

In this study, we identified HSPB7 capable of oppositely regulating osteogenic and adipogenic differentiation of BMSCs. HSPB7 silencing promoted adipogenesis while reducing osteogenic differentiation and mineralization. Conversely, overexpression of HSPB7 strongly enhanced osteogenesis, but no effect was observed on adipogenic differentiation. Deletion of the N-terminal or C-terminal domain of HSPB7 led to decreased osteoblastic potency and mineralization. Mechanistically, our data showed that Activin A is a downstream target participating in HSPB7 knockdown-mediated osteogenic inhibition.

CONCLUSIONS

Our findings suggest that HSPB7 plays a positive role in driving osteoblastic differentiation, and with the capability in maintaining the osteo-adipogenesis balance. It holds great promise as a potential therapeutic target in the treatment of bone metabolic diseases.

Turning the spotlight on bone marrow adipocytes in haematological malignancy and non-malignant conditions

Whilst bone marrow adipocytes (BMAd) have long been appreciated by clinical haemato-pathologists, it is only relatively recently, in the face of emerging data, that the adipocytic niche has come under the watchful eye of biologists. There is now mounting evidence to suggest that BMAds are not just a simple structural entity of bone marrow microenvironments but a bona fide driver of physio- and pathophysiological processes relevant to multiple aspects of health and disease. Whilst the truly multifaceted nature of BMAds has only just begun to emerge, paradigms have shifted already for normal, malignant and non-malignant haemopoiesis incorporating a view of adipocyte regulation. Major efforts are ongoing, to delineate the routes by which BMAds participate in health and disease with a final aim of achieving clinical tractability. This review summarises the emerging role of BMAds across the spectrum of normal and pathological haematological conditions with a particular focus on its impact on cancer therapy.

Association between clinical use of nifedipine and the risk of osteoporosis: a nationwide retrospective cohort study

Nifedipine is one of the common calcium channel blockers (CCBs) for hypertension that induce peroxisome-proliferator-activated receptor γ coactivator 1-α, which is envisioned as a potential therapeutic target in bone disease. The findings of this retrospective cohort study suggest that patients who receive nifedipine may have a potential protective effect on osteoporosis in comparison to other CCBs.

INTRODUCTION

Nifedipine was one L-type dihydropyridine calcium channel blocker (CCB) that can improve bone loss. However, epidemiological studies on the association between the use of nifedipine and osteoporosis risk are limited. Thus, this study aimed to evaluate the association between the clinical use of nifedipine and the risk of osteoporosis.

METHODS

This retrospective cohort was conducted using the National Health Insurance Research Database of Taiwan from 2000 to 2013. The study includes 1225 patients receiving nifedipine (the exposed cohort) and 4900 patients receiving other CCBs (the comparison cohort). The primary outcome was the diagnosis of osteoporosis. The hazard ratios (HRs) and 95% confidence intervals (CIs) were used to assess the association between the use of nifedipine and the risk of osteoporosis.

RESULTS

Patients receiving nifedipine treatment had a reduced risk of osteoporosis as compared with those undergoing other CCB treatments (adjusted HR, 0.44; 95% CI, 0.37-0.53). Moreover, this inverse association is evident in both sexes and various age groups.

CONCLUSIONS

This population-based cohort study demonstrated that nifedipine may have potential protective effect on osteoporosis compared with other CCBs. The clinical implications of the present study need further investigation.

Bone Marrow Adipose Tissue: Regulation of Osteoblastic Niche, Hematopoiesis and Hematological Malignancies

Bone marrow adipose tissue (BMAT) creates a specific microniche within multifunctional bone marrow (BM) ecosystem which imposes changes in surrounding cells and at systemic level. Moreover, BMAT contributes to spatial and temporal separation and metabolic compartmentalization of BM, thus regulating BM homeostasis and diseases. Recent findings have identified novel progenitor subsets of bone marrow adipocytes (BMAd)s recruited during the BM adipogenesis within different skeletal and hematopoietic stem cell niches. Potential of certain mesenchymal BM cells to differentiate into both osteogenic and adipogenic lineages, contributes to the complex interplay of BMAT with endosteal (osteoblastic) niche compartments as an important cellular player in bone tissue homeostasis. Targeting and ablation of BMAT cells at certain states might be an optional and promising strategy for improvement of bone health. Additionally, recent findings demonstrated spatial distribution of BMAds related to hematopoietic cells and pointed out important functional roles in the vital processes such as long-term hematopoiesis. BM adipogenesis appears to be an emergency phenomenon that follows the production of hematopoietic stem and progenitor cell niche factors, thus regulating physiological, stressed, and malignant hematopoiesis. Lipolytic and secretory activity of BMAds can influence survival and proliferation of hematopoietic cells at different maturation stages. Due to their different lipid status, constitutive and regulated BMAds are important determinants of normal and malignant hematopoietic cells. Further elucidation of cellular and molecular players involved in BMAT expansion and crosstalk with malignant cells is of paramount importance for conceiving the new therapies for improvement of BM health.

Update on the Role of Glucocorticoid Signaling in Osteoblasts and Bone Marrow Adipocytes During Aging

PURPOSE OF REVIEW

Bone marrow adipose tissue (BMAT) in the skeleton likely plays a variety of physiological and pathophysiological roles that are not yet fully understood. In elucidating the complex relationship between bone and BMAT, glucocorticoids (GCs) are positioned to play a key role, as they have been implicated in the differentiation of bone marrow mesenchymal stem cells (BMSCs) between osteogenic and adipogenic lineages. The purpose of this review is to illuminate aspects of both endogenous and exogenous GC signaling, including the influence of GC receptors, in mechanisms of bone aging including relationships to BMAT.

RECENT FINDINGS

Harmful effects of GCs on bone mass involve several cellular pathways and events that can include BMSC differentiation bias toward adipogenesis and the influence of mature BMAT on bone remodeling through crosstalk. Interestingly, BMAT involvement remains poorly explored in GC-induced osteoporosis and warrants further investigation. This review provides an update on the current understanding of the role of glucocorticoids in the biology of osteoblasts and bone marrow adipocytes (BMAds).

Age and gender differences in vertebral bone marrow adipose tissue and bone mineral density, based on MRI and quantitative CT

PURPOSE

To investigate the age and gender differences in vertebral bone marrow adipose tissue (BMAT) and volumetric bone mineral density (vBMD).

METHOD

A total of 427 healthy adults, including 175 males (41 %) and 252 females (59 %) with an age range of 21-82 years, underwent MRI and quantitative CT examinations of the lumbar spine (L2-L4), and the corresponding BMAT and vBMD values were measured. The age-related progressions of BMAT and vBMD in men and women were evaluated and compared.

RESULTS

In males, vertebral BMAT rose gradually throughout life, while in females, BMAT increased sharply between 41 and 60 years of age. In participants aged < 40 years, BMAT was greater in males compared to females (p ≤ 0.01), while after the age of 60, BMAT was higher in females (p < 0.05). In males, vBMD decreased gradually with age, while in females, there was a sharp decrease in vBMD after the age of 40 years. At age of 31-40 years, vBMD was higher in females (P < 0.002), while at age > 60 years, vBMD was higher in males (61-70 years, P < 0.01; > 70 years, P = 0.02).

CONCLUSIONS

We found significant age and gender differences in lumbar BMAT and vBMD. These findings will help to improve our understanding of the interaction between bone marrow fat content and bone mineral density in the ageing process.

Skeletal diseases caused by mutations in PTH1R show aberrant differentiation of skeletal progenitors due to dysregulation of DEPTOR

Alterations in the balance between skeletogenesis and adipogenesis is a pathogenic feature in multiple skeletal disorders. Clinically, enhanced bone marrow adiposity in bones impairs mobility and increases fracture risk, reducing the quality of life of patients. The molecular mechanism that underlies the balance between skeletogenesis and adipogenesis is not completely understood but alterations in skeletal progenitor cells' differentiation pathway plays a key role. We recently demonstrated that parathyroid hormone (PTH)/PTH-related peptide (PTHrP) control the levels of DEPTOR, an inhibitor of the mechanistic target of rapamycin (mTOR), and that DEPTOR levels are altered in different skeletal diseases. Here, we show that mutations in the PTH receptor-1 (PTH1R) alter the differentiation of skeletal progenitors in two different skeletal genetic disorders and lead to accumulation of fat or cartilage in bones. Mechanistically, DEPTOR controls the subcellular localization of TAZ (transcriptional co-activator with a PDZ-binding domain), a transcriptional regulator that governs skeletal stem cells differentiation into either bone and fat. We show that DEPTOR regulation of TAZ localization is achieved through the control of Dishevelled2 (DVL2) phosphorylation. Depending on nutrient availability, DEPTOR directly interacts with PTH1R to regulate PTH/PTHrP signaling or it forms a complex with TAZ, to prevent its translocation to the nucleus and therefore inhibit its transcriptional activity. Our data point DEPTOR as a key molecule in skeletal progenitor differentiation; its dysregulation under pathologic conditions results in aberrant bone/fat balance.

Metformin increases bone marrow adipose tissue by promoting mesenchymal stromal cells apoptosis

Bone marrow adipose tissue (MAT) has the potential to exert both local and systemic effects on metabolic homeostasis. As a first-line drug used to treat type 2 diabetes mellitus, metformin has conflicting effects on MAT and bone marrow mesenchymal stem cell (BM-MSC) differentiation. Through a series of experiments in vivo and in vitro, we found that except improving the glucose and lipid metabolism disorder in ob/ob mice, 200 mg/kg metformin increased MAT in mice tibia, and prompted osteogenic genes (RunX2, OPN, OCN) and lipogenic genes (Ppar-γ, Cebpα, Scd1) expression in mice bone marrow. However, metformin promoted osteogenesis and inhibited lipogenesis of MSC in vitro, which is inconsistent with the results in vivo. Given MAT being considered the "filler" of the space after the apoptosis of bone marrow stroma, the effect of metformin on MSC apoptosis was examined. We discovered that metformin induces MSC apoptosis in vivo and in vitro. Therefore, we speculated that the increased MAT in mice tibia may be attributed to the filling of adipose tissue after apoptosis of bone marrow stromal cells induced by metformin. The increased MAT may be involved in the regulation of metformin on glucose, lipid, and bone metabolism in diabetic mice, providing a new way to understand the metabolic regulation of metformin. While increased MAT-associated insulin resistance and metabolic disorders may account for the poorer clinical benefits in patients with intensive glucose control.

Genome-Wide Methylation Changes Associated with Replicative Senescence and Differentiation in Endothelial and Bone Marrow Mesenchymal Stromal Cells

Bone marrow mesenchymal stromal cells (BMSCs) are multipotent cells able to self-renew and differentiate, depending on the microenvironment, into adipocytes and osteoblasts. These cells have a limited number of replications and enter replicative senescence during in vitro expansion. The role of DNA methylation (DNAm) assumes importance in cell function and commitment; however, its exact contribution to BMSC differentiation and replicative senescence is still unclear. We performed a genome-wide DNAm analysis on BMSCs cultured in vitro at early passages and induced to differentiate into adipocytes and osteoblasts, and on replicative senescent BMSCs and HUVECs, to identify DNAm patterns of senescence and differentiation. We also compared BMSCs and HUVECs in replicative senescence and found that, in both cellular systems, genome-wide hypomethylation was accompanied by a higher-than-expected overlap of differentially methylated positions (DMPs) and concordance in terms of direction of the change. A Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis on lineage-independent senescence-associated DMPs revealed 16 common pathways, including Insulin resistance, Molecule adhesion, and Wnt/β-catenin signaling. In both adipogenesis and osteogenesis, we observed a general demethylation of CpG sites compared with undifferentiated BMSCs with a higher number of DMPs in osteogenesis. KEGG analysis resulted in 30 pathways enriched in osteoblasts and only 2 in adipocytes when compared to undifferentiated cells. When comparing differentiated BMSCs with senescent ones, osteogenesis exhibited a greater overlap with senescence in terms of number of DMPs and direction of methylation change compared to adipogenesis. In conclusion, this study may be useful for future research on general mechanisms that occur in replicative senescence and furthermore to identify trajectories of BMSC differentiation and common aspects of differentiated and senescent cells.

Amount and composition of total fatty acids in red and yellow bone marrow are altered with changes in bone mineral density

There is general consent that with decreasing bone mineral density the amount of marrow adipose tissue increases. While image-based techniques, claim an increase in saturated fatty acids responsible for this effect, this study shows an increase in both saturated and unsaturated fatty acids in the bone marrow. Using fatty acid methyl ester gas chromatography-mass spectrometry, characteristic fatty acid patterns for patients with normal BMD (N = 9), osteopenia (N = 12), and osteoporosis (N = 9) have been identified, which differ between plasma, red bone marrow and yellow bone marrow. Selected fatty acids, e.g. FA10:0, FA14:1, or FA16:1 n-7 in the bone marrow or FA18:0, FA18:1 n-9, FA18:1 n-7, FA20:0, FA20:1 n-9, or FA20:3 n-6 in the plasma, correlated with osteoclast activity, suggesting a possible mechanism how these fatty acids may interfere with BMD. Although several fatty acids correlated well with the osteoclast activity and BMD, there was not a single fatty acid contained in our fatty acid profile that can be claimed for controlling BMD, a fact that may be attributed to the genetic heterogeneity of the patients.

Leptin's Immune Action: A Review Beyond Satiety

The adipose tissue is an endocrine organ that secretes adipokines such as leptin, which is one of the most important hormones for controlling satiety, metabolism, and energy homeostasis. This hormone acts in the regulation of innate and adaptive immune responses since immune cells have leptin receptors from which this hormone initiates its biological action. These receptors have been identified in hematopoietic stem cells in the bone marrow and mature immune cells, inducing signaling pathways mediated by JAK/STAT, PI3K, and ERK 1/2. It is known that the bone marrow also contains leptin-producing adipocytes, which are crucial for regulating hematopoiesis through largely unknown mechanisms. Therefore, we have reviewed the roles of leptin inside and outside the bone marrow, going beyond its action in the control of satiety.

Exercise Promotes Bone Marrow Microenvironment by Inhibiting Adipsin in Diet-Induced Male Obese Mice

Obesity is a growing global epidemic linked to many diseases, including diabetes, cardiovascular diseases, and musculoskeletal disorders. Exercise can improve bone density and decrease excess bone marrow adipose tissue (BMAT) in obese individuals. However, the mechanism of exercise regulating bone marrow microenvironment remains unclear. This study examines how exercise induces bone marrow remodeling in diet-induced obesity. We employed unbiased RNA-Seq to investigate the effect of exercise on the bone marrow of diet-induced obese male mice. Bone mesenchymal stem cells (BMSCs) were isolated to explore the regulatory effects of exercise in vitro. Our data demonstrated that exercise could slow down the progression of obesity and improve trabecular bone density. RNA-seq data revealed that exercise inhibited secreted phosphoprotein 1 (Spp1), which was shown to mediate bone resorption through mechanosensing mechanisms. Interactome analysis of Spp1 using the HINT database showed that Spp1 interacted with the adipokine adipsin. Moreover, exercise decreased BMAT, which induced osteoclast differentiation and promoted bone loss. Our study reveals that exercise improves the bone marrow microenvironment by at least partially inhibiting the adipsin-Spp1 signaling pathway so as to inhibit the alternative complement system from activating osteoclasts in diet-induced obese mice.

Bone, fat, and muscle interactions in health and disease

Energy metabolism is a point of integration among the various organs and tissues of the human body, not only in terms of consumption of energy substrates but also because it concentrates a wide interconnected network controlled by endocrine factors. Thus, not only do tissues consume substrates, but they also participate in modulating energy metabolism. Soft mesenchymal tissues, in particular, play a key role in this process. The recognition that high energy consumption is involved in bone remodeling has been accompanied by evidence showing that osteoblasts and osteocytes produce factors that influence, for example, insulin sensitivity and appetite. Additionally, there are significant interactions between muscle, adipose, and bone tissues to control mutual tissue trophism. Not by chance, trophic and functional changes in these tissues go hand in hand from the beginning of an individual's development until aging. Likewise, metabolic and nutritional diseases deeply affect the musculoskeletal system and adipose tissue. The present narrative review highlights the importance of the interaction of the mesenchymal tissues for bone development and maintenance and the impact on bone from diseases marked by functional and trophic disorders of adipose and muscle tissues.

Docosahexaenoic Acid-Enriched Phosphatidylcholine Exerted Superior Effects to Triglyceride in Ameliorating Obesity-Induced Osteoporosis through Up-Regulating the Wnt/β-Catenin Pathway

A growing number of studies reported that obesity is one of the major inducements for osteoporosis by promoting excessive adipogenic differentiation of bone marrow mesenchymal stem cells (BMSCs). Marine-derived DHA-enriched phosphatidylcholine (DHA-PC) exhibited activities to improve ovariectomized-induced osteoporosis and kidney damage. However, the potential effect of DHA-PC and efficacy differences between DHA-PC and traditional DHA (DHA-triglyceride, DHA-TG) on BMSCs differentiation in obesity-induced osteoporosis were not clear. In the present study, obesity-induced osteoporotic mice were supplemented with DHA-TG and DHA-PC for 120 days. Results showed that supplementing with DHA-PC improved the bone mineral density and biomechanical properties, increased the new bone formation rate by 55.2%, and reduced the amount of bone marrow fat to a greater extent than DHA-TG. Further in vitro results showed that DHA-PC significantly promoted the osteogenic differentiation and inhibited the adipogenic differentiation of BMSCs. Mechanistically, DHA-PC supplement up-regulated Wnt/β-catenin pathway in BMSCs and up-regulated the expression of osteogenic transcription factors, thereby promoting osteogenic differentiation. In summary, DHA-PC exerted a superior effect to DHA-TG in improving obesity-induced osteoporosis. The results provided new evidence for the application of different molecular forms of DHA in treatment of osteoporosis.

Oestrogen enforces the integrity of blood vessels in the bone during pregnancy and menopause

The mammalian skeletal system shows sex differences in structure, functions, ageing and disease incidences. The role of blood vessels in physiological, regenerative and pathological bone functions indicates the requisite to understanding their sex specificity. Here, we find oestrogen regulates blood vessel physiology during pregnancy and menopause through oestrogen receptor alpha (ERα) and G-protein coupled oestrogen receptor-1 (Gper1) but not ERβ-dependent signalling in mice. Oestrogen regulates BECs' lipid use and promotes lipolysis of adipocytes and FA uptake from the microenvironment. Low oestrogen conditions skew endothelial FA metabolism to accumulate lipid peroxides (LPO), leading to vascular ageing. High ferrous ion levels in female BECs intensify LPO accumulation and accelerate the ageing process. Importantly, inhibiting LPO generation using liproxstatin-1 in aged mice significantly improved bone heath. Thus, our findings illustrate oestrogen's effects on BECs and suggest LPO targeting could be an efficient strategy to manage blood and bone health in females.

Can Iron Play a Crucial Role in Maintaining Cardiovascular Health in the 21st Century?

In the 21st century the heart is facing more and more challenges so it should be brave and iron to meet these challenges. We are living in the era of the COVID-19 pandemic, population aging, prevalent obesity, diabetes and autoimmune diseases, environmental pollution, mass migrations and new potential pandemic threats. In our article we showed sophisticated and complex regulations of iron metabolism. We discussed the impact of iron metabolism on heart diseases, treatment of heart failure, diabetes and obesity. We faced the problems of constant stress, climate change, environmental pollution, migrations and epidemics and showed that iron is really essential for heart metabolism in the 21st century.

Associations of Texture Features of Proton Density Fat Fraction Maps between Lumbar Vertebral Bone Marrow and Paraspinal Musculature

Chemical shift encoding-based water−fat MRI (CSE-MRI)-derived proton density fat fraction (PDFF) has been used for non-invasive assessment of regional body fat distributions. More recently, texture analysis (TA) has been proposed to reveal even more detailed information about the vertebral or muscular composition beyond PDFF. The aim of this study was to investigate associations between vertebral bone marrow and paraspinal muscle texture features derived from CSE-MRI-based PDFF maps in a cohort of healthy subjects. In this study, 44 healthy subjects (13 males, 55 ± 30 years; 31 females, 39 ± 17 years) underwent 3T MRI including a six-echo three-dimensional (3D) spoiled gradient echo sequence used for CSE-MRI at the lumbar spine and the paraspinal musculature. The erector spinae muscles (ES), the psoas muscles (PS), and the vertebral bodies L1-4 (LS) were manually segmented. Mean PDFF values and texture features were extracted for each compartment. Features were compared between males and females using logistic regression analysis adjusted for age and body mass index (BMI). All texture features of ES except for Sum Average were significantly (p < 0.05) different between men and women. The three global texture features (Variance, Skewness, Kurtosis) for PS as well as LS showed a significant difference between male and female subjects (p < 0.05). Mean PDFF measured in PS and ES was significantly higher in females, but no difference was found for the vertebral bone marrow’s PDFF. Partial correlation analysis between the texture features of the spine and the paraspinal muscles revealed a highly significant correlation for Variance(global) (r = 0.61 for ES, r = 0.62 for PS; p < 0.001 respectively). Texture analysis using PDFF maps based on CSE-MRI revealed differences between healthy male and female subjects. Global texture features in the lumbar vertebral bone marrow allowed for differentiation between men and women, when the overall PDFF was not significantly different, indicating that PDFF maps may contain detailed and subtle textural information beyond fat fraction. The observed significant correlation of Variance(global) suggests a metabolic interrelationship between vertebral bone marrow and the paraspinal muscles.

Pharmacological Inhibition of Inositol Hexakisphosphate Kinase 1 Protects Mice against Obesity-Induced Bone Loss

Obesity and type II diabetes mellitus (T2DM) are prominent risk factors for secondary osteoporosis due to the negative impacts of hyperglycemia and excessive body fat on bone metabolism. While the armamentarium of anti-diabetic drugs is expanding, their negative or unknown impacts on bone metabolism limits effectiveness. The inactivation of inositol hexakisphosphate kinase 1 (IP6K1) protects mice from high-fat-diet (HFD)-induced obesity (DIO) and insulin resistance by enhancing thermogenic energy expenditure, but the role of this kinase and the consequences of its inhibition on bone metabolism are unknown. To determine if IP6K1 inhibition in obese mice affords protection against obesity-induced metabolic derangements and bone loss, we maintained 2-month-old mice on a normal chow control diet or HFD under thermal neutral conditions for 100 d. Beginning on day 40, HFD-fed mice were divided into two groups and administered daily injections of vehicle or the pan-IP6K inhibitor TNP [N2-(m-Trifluorobenzyl), N6-(p-nitrobenzyl) purine]. HFD-fed mice developed obesity, hyperglycemia, hyperlipidemia, and secondary osteoporosis, while TNP administration protected mice against HFD-induced metabolic and lipid derangements and preserved bone mass, mineral density, and trabecular microarchitecture, which correlated with reduced serum leptin levels, reduced marrow adiposity, and preservation of marrow resident skeletal stem/progenitor cells (SSPCs). TNP also exhibited hypotensive activity, an unrealized benefit of the drug, and its prolonged administration had no adverse impacts on spermatogenesis. Together, these data indicate that the inhibition of IP6K1 using selective inhibitors, such as TNP, may provide an effective strategy to manage obesity and T2DM due to its bone sparing effects.

Effects of Extracellular Vesicles from Osteogenic Differentiated Human BMSCs on Osteogenic and Adipogenic Differentiation Capacity of Naïve Human BMSCs

Osteoporosis, or steroid-induced osteonecrosis of the hip, is accompanied by increased bone marrow adipogenesis. Such a disorder of adipogenic/osteogenic differentiation, affecting bone-marrow-derived mesenchymal stem cells (BMSCs), contributes to bone loss during aging. Here, we investigated the effects of extracellular vesicles (EVs) isolated from human (h)BMSCs during different stages of osteogenic differentiation on the osteogenic and adipogenic differentiation capacity of naïve (undifferentiated) hBMSCs. We observed that all EV groups increased viability and proliferation capacity and suppressed the apoptosis of naïve hBMSCs. In particular, EVs derived from hBMSCs at late-stage osteogenic differentiation promoted the osteogenic potential of naïve hBMSCs more effectively than EVs derived from naïve hBMSCs (naïve EVs), as indicated by the increased gene expression of COL1A1 and OPN. In contrast, the adipogenic differentiation capacity of naïve hBMSCs was inhibited by treatment with EVs from osteogenic differentiated hBMSCs. Proteomic analysis revealed that osteogenic EVs and naïve EVs contained distinct protein profiles, with pro-osteogenic and anti-adipogenic proteins encapsulated in osteogenic EVs. We speculate that osteogenic EVs could serve as an intercellular communication system between bone- and bone-marrow adipose tissue, for transporting osteogenic factors and thus favoring pro-osteogenic processes. Our data may support the theory of an endocrine circuit with the skeleton functioning as a ductless gland.

Differential blood counts do not consistently predict clinical measurements of bone mineral density and microarchitecture at homeostasis

The hematopoietic stem cell niche constitutes a complex bone marrow (BM) microenvironment. Osteoporosis is characterized by both reduced bone mineral density (BMD) and microarchitectural deterioration, constituting the most frequent alteration of the BM microenvironment. It is unclear to which extent modifications of the BM microenvironment, including in the context of osteoporosis, influence blood cell production. We aimed to describe the association between lumbar spine and total hip BMD and microarchitecture (assessed by trabecular bone score [TBS]) and differential blood counts. Data were collected at two time points from 803 (first assessment) and 901 (second assessment) postmenopausal women participating in the CoLaus/OsteoLaus cohort, a population‐based sample in Lausanne, Switzerland. Participants with other active disease or treatment that could influence hematopoiesis or osteoporosis were excluded. Bivariate and multivariate associations between each peripheral blood cell count and BMD or TBS were performed. Additionally, participants in the highest BMD and TBS tertiles were compared with participants in the lowest BMD and TBS tertiles. At first assessment, only neutrophils were significantly different in the lowest BMD and TBS tertile (3.18 ± 0.09 versus 3.47 ± 0.08 G/L, p = 0.028). At the second assessment, leucocytes (5.90 ± 0.11 versus 5.56 ± 0.10 G/L, p = 0.033), lymphocytes (1.87 ± 0.04 versus 1.72 ± 0.04 G/L p = 0.033), and monocytes (0.49 ± 0.01 versus 0.46 ± 0.1 G/L, p = 0.033) were significantly different. Power analysis did not identify quasi‐significant associations missed due to sample size. Although significant associations between blood counts and BMD or TBS were found, none was consistent across bone measurements or assessments. This study suggests that, at homeostasis and in postmenopausal women, there is no clinically significant association between the osteoporotic microenvironment and blood production output as measured by differential blood counts. In the context of conflicting reports on the relationship between osteoporosis and hematopoiesis, our study represents the first prospective two time‐point analysis of a large, homogenous cohort at steady state. © 2022 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Obesity, Bone Loss, and Periodontitis: The Interlink

Obesity and periodontitis are both common health concerns that have given rise to considerable economic and societal burden worldwide. There are established negative relationships between bone metabolism and obesity, obesity and diabetes mellitus (DM), and DM and periodontitis, to name a few, with osteoporosis being considered a long-term complication of obesity. In the oral cavity, bone metabolic disorders primarily display as increased risks for periodontitis and alveolar bone loss. Obesity-driven alveolar bone loss and mandibular osteoporosis have been observed in animal models without inoculation of periodontopathogens. Clinical reports have also indicated a possible association between obesity and periodontitis. This review systematically summarizes the clinical periodontium changes, including alveolar bone loss in obese individuals. Relevant laboratory-based reports focusing on biological interlinks in obesity-associated bone remodeling via processes like hyperinflammation, immune dysregulation, and microbial dysbiosis, were reviewed. We also discuss the potential mechanism underlying obesity-enhanced alveolar bone loss from both the systemic and periodontal perspectives, focusing on delineating the practical considerations for managing periodontal disease in obese patients.

Frequency-specific sensitivity of 3T3-L1 preadipocytes to low-intensity vibratory stimulus during adipogenesis

Adipocyte accumulation in the bone marrow is a severe complication leading to bone defects and reduced regenerative capacity. Application of external mechanical signals to bone marrow cellular niche is a non-invasive and non-pharmaceutical methodology to improve osteogenesis and suppress adipogenesis. However, in the literature, the specific parameters related to the nature of low-intensity vibratory (LIV) signals appear to be arbitrarily selected for amplitude, bouts, and applied frequency. In this study, we performed a LIV frequency sweep ranging from 30 to 120 Hz with increments of 15 Hz applied onto preadipocytes during adipogenesis for 10 d. We addressed the effect of LIV with different frequencies on single-cell density, adipogenic gene expression, lipid morphology, and triglycerides content. Results showed that LIV signals with 75-Hz frequency had the most significant suppressive effect during adipogenesis. Our results support the premise that mechanical-based interventions for suppressing adipogenesis may benefit from optimizing input parameters.

Skeletal Aging

Aging represents the single greatest risk factor for chronic diseases, including osteoporosis, a skeletal fragility syndrome that increases fracture risk. Optimizing bone strength throughout life reduces fracture risk. Factors critical for bone strength include nutrition, physical activity, and vitamin D status, whereas unhealthy lifestyles, illnesses, and certain medications (eg, glucocorticoids) are detrimental. Hormonal status is another important determinant of skeletal health, with sex steroid concentrations, particularly estrogen, having major effects on bone remodeling. Aging exacerbates bone loss in both sexes and results in imbalanced bone resorption relative to formation; it is associated with increased marrow adiposity, osteoblast/osteocyte apoptosis, and accumulation of senescent cells. The mechanisms underlying skeletal aging are as diverse as the factors that determine the strength (and thus fragility) of bone. This review updates our current understanding of the epidemiology, pathophysiology, and treatment of osteoporosis and provides an overview of the underlying hallmark mechanisms that drive skeletal aging.

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.

Bone Marrow Adiposity in Models of Radiation- and Aging-Related Bone Loss Is Dependent on Cellular Senescence

Oxidative stress-induced reactive oxygen species, DNA damage, apoptosis, and cellular senescence have been associated with reduced osteoprogenitors in a reciprocal fashion to bone marrow adipocyte tissue (BMAT); however, a direct (causal) link between cellular senescence and BMAT is still elusive. Accumulation of senescent cells occur in naturally aged and in focally radiated bone tissue, but despite amelioration of age- and radiation-associated bone loss after senescent cell clearance, molecular events that precede BMAT accrual are largely unknown. Here we show by RNA-Sequencing data that BMAT-related genes were the most upregulated gene subset in radiated bones of C57BL/6 mice. Using focal radiation as a model to understand age-associated changes in bone, we performed a longitudinal assessment of cellular senescence and BMAT. Using real-time quantitative reverse transcription polymerase chain reaction (qRT-PCR), RNA in situ hybridization of p21 transcripts and histological assessment of telomere dysfunction as a marker of senescence, we observed an increase in senescent cell burden of bone cells from day 1 postradiation, without the presence of BMAT. BMAT was significantly elevated in radiated bones at day 7, confirming the qRT-PCR data in which most BMAT-related genes were elevated by day 7, and the trend continued until day 42 postradiation. Similarly, elevation in BMAT-related genes was observed in bones of aged mice. The senolytic cocktail of Dasatinib (D) plus Quercetin (Q) (ie, D + Q), which clears senescent cells, reduced BMAT in aged and radiated bones. MicroRNAs (miRNAs or miRs) linked with senescence marker p21 were downregulated in radiated and aged bones, whereas miR-27a, a miR that is associated with increased BMAT, was elevated both in radiated and aged bones. D + Q downregulated miR-27a in radiated bones at 42 days postradiation. Overall, our study provides evidence that BMAT occurrence in oxidatively stressed bone environments, such as radiation and aging, is induced following a common pathway and is dependent on the presence of senescent cells. © 2022 American Society for Bone and Mineral Research (ASBMR).

Targeted clearance of p21- but not p16-positive senescent cells prevents radiation-induced osteoporosis and increased marrow adiposity

Cellular senescence, which is a major cause of tissue dysfunction with aging and multiple other conditions, is known to be triggered by p16Ink4a or p21Cip1 , but the relative contributions of each pathway toward inducing senescence are unclear. Here, we directly addressed this issue by first developing and validating a p21-ATTAC mouse with the p21Cip1 promoter driving a "suicide" transgene encoding an inducible caspase-8 which, upon induction, selectively kills p21Cip1 -expressing senescent cells. Next, we used the p21-ATTAC mouse and the established p16-INK-ATTAC mouse to directly compare the contributions of p21Cip1 versus p16Ink4a in driving cellular senescence in a condition where a tissue phenotype (bone loss and increased marrow adiposity) is clearly driven by cellular senescence-specifically, radiation-induced osteoporosis. Using RNA in situ hybridization, we confirmed the reduction in radiation-induced p21Cip1 - or p16Ink4a -driven transcripts following senescent cell clearance in both models. However, only clearance of p21Cip1 +, but not p16Ink4a +, senescent cells prevented both radiation-induced osteoporosis and increased marrow adiposity. Reduction in senescent cells with dysfunctional telomeres following clearance of p21Cip1 +, but not p16Ink4a +, senescent cells also reduced several of the radiation-induced pro-inflammatory senescence-associated secretory phenotype factors. Thus, by directly comparing senescent cell clearance using two parallel genetic models, we demonstrate that radiation-induced osteoporosis is driven predominantly by p21Cip1 - rather than p16Ink4a -mediated cellular senescence. Further, this approach can be used to dissect the contributions of these pathways in other senescence-associated conditions, including aging across tissues.

The m6A demethylase FTO promotes the osteogenesis of mesenchymal stem cells by downregulating PPARG

N⁶-methyladenosine (m⁶A) is the most abundant posttranscriptional methylation modification that occurs in mRNA and modulates the fine-tuning of various biological processes in mammalian development and human diseases. In this study we investigated the role of m⁶A modification in the osteogenesis of mesenchymal stem cells (MSCs), and the possible mechanisms by which m⁶A modification regulated the processes of osteoporosis and bone necrosis. We performed systematic analysis of the differential gene signatures in patients with osteoporosis and bone necrosis and conducted m⁶A-RNA immunoprecipitation (m⁶A-RIP) sequencing to identify the potential regulatory genes involved in osteogenesis. We showed that fat mass and obesity (FTO), a primary m⁶A demethylase, was significantly downregulated in patients with osteoporosis and osteonecrosis. During the differentiation of human MSCs into osteoblasts, FTO was markedly upregulated. Both depletion of FTO and application of the FTO inhibitor FB23 or FB23-2 impaired osteogenic differentiation of human MSCs. Knockout of FTO in mice resulted in decreased bone mineral density and impaired bone formation. PPARG, a biomarker for osteoporosis, was identified as a critical downstream target of FTO. We further revealed that FTO mediated m⁶A demethylation in the 3'UTR of PPARG mRNA, and reduced PPARG mRNA stability in an YTHDF1-dependent manner. Overexpression of PPARG alleviated FTO-mediated osteogenic differentiation of MSCs, whereas knockdown of PPARG promoted FTO-induced expression of the osteoblast biomarkers ALPL and OPN during osteogenic differentiation. Taken together, this study demonstrates the functional significance of the FTO-PPARG axis in promoting the osteogenesis of human MSCs and sheds light on the role of m⁶A modification in mediating osteoporosis and osteonecrosis.