Dimethyloxalylglycine prevents bone loss in ovariectomized C57BL/6J mice through enhanced angiogenesis and osteogenesis

A Meta-Analysis Study to Define Variations in Murine Long Bone Biomechanical Testing

A systematic literature search and meta-analysis were performed to evaluate the variability in biomechanical testing of murine long bones, specifically focused on point-bending tests of mice femora. Due to the lack of standardized protocols for these tests, the assessment quantifies the heterogeneity in reported mechanical properties across existing literature. This study followed preferred reporting items for systematic reviews and meta-analyses (PRISMA) and strengthening the reporting of observational studies in epidemiology (STROBE) guidelines to search publicly available databases for relevant studies. After title and abstract screening, full-text reviews identified 73 articles meeting the inclusion criteria. Data was extracted from these studies, including stiffness, maximum load, modulus, and ultimate stress values for both three-point and four-point bending tests. The data were analyzed through ANOVA and metaregression to assess variability caused by age, sex, and genetic strain. The reviewers also assessed the quality of the included studies. The meta-analysis revealed significant heterogeneity in reported mechanical properties, with I2 values ranging from 72% to 100% in the three point-bend tests of pooled genetic strains. This heterogeneity persisted even after accounting for age, sex, and genetic strain differences. The review concludes that nonstandardized testing setups are the likely major source of the observed variability in reported data more than the population characteristics of the mice, highlighting the need for more consistent testing methodologies in future studies.

Sildenafil promotes osteogenic differentiation of human mesenchymal stem cells and inhibits bone loss by affecting the TGF-β signaling pathway

BACKGROUND

Osteoporosis, a common bone disorder, is primarily managed pharmacologically. However, existing medications are associated with non-trivial side-effects. Sildenafil, which already finds many clinical applications, promotes angiogenesis and cellular differentiation. Osteoporotic patients often exhibit a reduced intraosseous vasculature and impaired cellular differentiation; sildenafil may thus usefully treat osteoporosis.

METHODS

Here, the effects of sildenafil on the osteogenic differentiation of human mesenchymal stem cells (hMSCs) were explored, as were the molecular mechanisms in play. We treated hMSCs with varying concentrations of sildenafil and measured cell proliferation and osteogenic differentiation in vitro. We used a mouse model of subcutaneous ectopic osteogenesis to assess sildenafil's effect on hMSC osteogenic differentiation in vivo. We also explored the effects of sildenafil on bone loss in tail-suspended (TS) and ovariectomized (OVX) mice. Mechanistically, we employed RNA-sequencing to define potentially relevant molecular pathways.

RESULTS

The appropriate concentrations of sildenafil significantly enhanced osteogenic hMSC differentiation; the optimal sildenafil concentration may be 10 mg/L. Sildenafil mitigated osteoporosis in OVX and TS mice. The appropriate concentrations of sildenafil probably promoted hMSC osteogenic differentiation by acting on the transforming growth factor-β (TGF-β) signaling pathway.

CONCLUSIONS

In conclusion, sildenafil enhanced hMSC osteogenic differentiation and inhibited bone loss. Sildenafil may usefully treat osteoporosis. Our findings offer new insights into the physiological effects of the medicine.

Roles of lncRNA in the crosstalk between osteogenesis and angiogenesis in the bone microenvironment

Bone is a highly calcified and vascularized tissue. The vascular system plays a vital role in supporting bone growth and repair, such as the provision of nutrients, growth factors, and metabolic waste transfer. Moreover, the additional functions of the bone vasculature, such as the secretion of various factors and the regulation of bone-related signaling pathways, are essential for maintaining bone health. In the bone microenvironment, bone tissue cells play a critical role in regulating angiogenesis, including osteoblasts, bone marrow mesenchymal stem cells (BMSCs), and osteoclasts. Osteogenesis and bone angiogenesis are closely linked. The decrease in osteogenesis and bone angiogenesis caused by aging leads to osteoporosis. Long noncoding RNAs (lncRNAs) are involved in various physiological processes, including osteogenesis and angiogenesis. Recent studies have shown that lncRNAs could mediate the crosstalk between angiogenesis and osteogenesis. However, the mechanism by which lncRNAs regulate angiogenesis‒osteogenesis crosstalk remains unclear. In this review, we describe in detail the ways in which lncRNAs regulate the crosstalk between osteogenesis and angiogenesis to promote bone health, aiming to provide new directions for the study of the mechanism by which lncRNAs regulate bone metabolism.

Hesperidin Nanoformulation: A Potential Strategy for Reducing Doxorubicin-Induced Renal Damage via the Sirt-1/HIF1-α/VEGF/NF-κB Signaling Cascade

Hesperidin (Hes) functions as a strong antioxidant and anti-inflammatory to guard against damage to the heart, liver, and kidneys. Nevertheless, due to its restricted solubility and bioavailability, a delivery method is required for it to reach a specific organ. In this study, ion gelation was used to synthesize a chitosan/hesperidin nanoformulation. Numerous characterization techniques, such as zeta potential, particle size, XRD, TEM, SEM, and FTIR analyses, were used to corroborate the synthesis of hesperidin nanoparticles (Hes-NPs). Male albino mice were given a pretreatment dose of 100 mg/kg, PO, of Hes or Hes-NPs, which was administered daily for 14 days before the induction of doxorubicin nephrotoxicity on the 12th day. Kidney function (urea and creatinine levels) was measured. Lipid peroxidation (MDA) and antioxidant enzyme (CAT and SOD) activities were estimated. TNF-α, IL-1β, and VEGF content; histopathological examination of kidney tissue; and immunohistochemical staining of NF-κB, Caspase-3, BAX, Bcl-2, and TGF-β1 were evaluated. The gene expressions of Sirt-1, Bcl-2, VEGF, HIF1-α, and Kim-1 were also considered. The results showed that pretreatment with Hes or Hes-NPs reduced doxorubicin's nephrotoxic effects, with Hes-NPs showing the greatest reduction. Kidney enzyme and MDA content were lowered in response to the Hes or Hes-NP pretreatment, whereas antioxidant enzyme activities were increased. Hes or Hes-NP pretreatment suppressed the levels of TNF-α, IL-1β, VEGF, NF-κB, Caspase-3, BAX, and TGF-β1; however, pretreatment increased Bcl-2 protein levels. Furthermore, the gene expressions of Sirt-1, Bcl-2, VEGF, HIF1-α, and Kim-1 were considerably higher with Hes-NP than with Hes treatment. These results suggest that Hes-NP treatment might reduce DOX-induced nephrotoxicity in mice via modulating Sirt-1/HIF1-α/VEGF/NF-κB signaling to provide antioxidant, anti-inflammatory, and anti-apoptotic effects.

Potential Antitumor Activity of Combined Lycopene and Sorafenib against Solid Ehrlich Carcinoma via Targeting Autophagy and Apoptosis and Suppressing Proliferation

An FDA-approved kinase inhibitor called sorafenib (SOR) is used to treat primary kidney and liver cancer as well as to stop the spread of advanced breast cancer. Side effects from SOR, such as palmar-plantar erythrodysesthesia syndrome, can negatively impact an individual's quality of life. There are a lot of data supporting the importance of lycopene (LYC) in preventing cancer. The antitumor properties of the combination of sorafenib and lycopene were examined in this study. A viability test against MDA-MB-231 was used to assess the anticancer efficacy of sorafenib, lycopene, and their combination in vitro. Moreover, a cell cycle analysis and Annexin-V/PI double staining were performed by using flow cytometry. In addition, the protein level of JNK-1, ERK-1, Beclin-1, P38, and P53 of the MDA-MB-231 cell line was estimated using ELISA kits. In addition, mice with SEC were divided into four equal groups at random (n = 10) to investigate the possible processes underlying the in vivo antitumor effect. Group IV (SEC-SOR-LYC) received SOR (30 mg/kg/day, p.o.) and LYC (20 mg/kg/day, p.o.); Group I received the SEC control; Group II received SEC-SOR (30 mg/kg/day, p.o.); and Group III received SEC-LYC (20 mg/kg/day, p.o.). The findings demonstrated that the combination of sorafenib and lycopene was superior to sorafenib and lycopene alone in causing early cell cycle arrest, suppressing the viability of cancer cells, and increasing cell apoptosis and autophagy. Likewise, the combination of sorafenib and lycopene demonstrated inhibition of the levels of Bcl-2, Ki-67, VEGF, IL-1β, and TNF-α protein. Otherwise, the quantities of the proteins BAX, P53, and caspase 3 were amplified. Furthermore, the combined treatment led to a substantial increase in TNF-α, caspase 3, and VEGF gene expression compared to the equivalent dosages of monotherapy. The combination of sorafenib and lycopene enhanced apoptosis and reduced inflammation, as seen by the tumor's decreased weight and volume, hence demonstrating its potential anticancer effect.

Effect of Dimethyloxalylglycine on Stem Cells Osteogenic Differentiation and Bone Tissue Regeneration-A Systematic Review

Dimethyloxalylglycine (DMOG) has been found to stimulate osteogenesis and angiogenesis of stem cells, promoting neo-angiogenesis in bone tissue regeneration. In this review, we conducted a comprehensive search of the literature to investigate the effects of DMOG on osteogenesis and bone regeneration. We screened the studies based on specific inclusion criteria and extracted relevant information from both in vitro and in vivo experiments. The risk of bias in animal studies was evaluated using the SYRCLE tool. Out of the 174 studies retrieved, 34 studies met the inclusion criteria (34 studies were analyzed in vitro and 20 studies were analyzed in vivo). The findings of the included studies revealed that DMOG stimulated stem cells' differentiation toward osteogenic, angiogenic, and chondrogenic lineages, leading to vascularized bone and cartilage regeneration. Addtionally, DMOG demonstrated therapeutic effects on bone loss caused by bone-related diseases. However, the culture environment in vitro is notably distinct from that in vivo, and the animal models used in vivo experiments differ significantly from humans. In summary, DMOG has the ability to enhance the osteogenic and angiogenic differentiation potential of stem cells, thereby improving bone regeneration in cases of bone defects. This highlights DMOG as a potential focus for research in the field of bone tissue regeneration engineering.

MMP13 promotes the osteogenic potential of BMP9 by enhancing Wnt/β-catenin signaling via HIF-1α upregulation in mouse embryonic fibroblasts

Bone morphogenetic protein 9 (BMP9) has been validated as one of the most potent osteoinduction factors, but its underlying mechanism remains unclear. As a member of the matrix metalloproteinase (MMP) family, MMP13 may be involved in regulating the lineage-specific differentiation of mouse embryonic fibroblasts (MEFs). The goal of this study was to determine whether MMP13 regulates the osteoinduction potential of BMP9 in MEFs, which are multipotent progenitor cells widely used for stem cell biology research. In vitro and in vivo experiments showed that BMP9-induced osteogenic markers and/or bone were enhanced by exogenous MMP13 in MEFs, but were reduced by MMP13 knockdown or inhibition. The expression of hypoxia inducible factor 1 alpha (HIF-1α) was induced by BMP9, which was enhanced by MMP13. The protein expression of β-catenin and phosphorylation level of glycogen synthase kinase-3 beta (GSK-3β) were increased by BMP9 in MEFs, as was the translocation of β-catenin from the cytoplasm to the nucleus; all these effects of BMP9 were enhanced by MMP13. Furthermore, the MMP13 effects of increasing BMP9-induced β-catenin protein expression and GSK-3β phosphorylation level were partially reversed by HIF-1α knockdown. These results suggest that MMP13 can enhance the osteoinduction potential of BMP9, which may be mediated, at least in part, through the HIF-1α/β-catenin axis. Our findings demonstrate a novel role of MMP13 in the lineage decision of progenitor cells and provide a promising strategy to speed up bone regeneration.

HIF-1α and periodontitis: Novel insights linking host-environment interplay to periodontal phenotypes

Periodontitis, the sixth most prevalent epidemic disease globally, profoundly impacts oral aesthetics and masticatory functionality. Hypoxia-inducible factor-1α (HIF-1α), an oxygen-dependent transcriptional activator, has emerged as a pivotal regulator in periodontal tissue and alveolar bone metabolism, exerts critical functions in angiogenesis, erythropoiesis, energy metabolism, and cell fate determination. Numerous essential phenotypes regulated by HIF are intricately associated with bone metabolism in periodontal tissues. Extensive investigations have highlighted the central role of HIF and its downstream target genes and pathways in the coupling of angiogenesis and osteogenesis. Within this concise perspective, we comprehensively review the cellular phenotypic alterations and microenvironmental dynamics linking HIF to periodontitis. We analyze current research on the HIF pathway, elucidating its impact on bone repair and regeneration, while unraveling the involved cellular and molecular mechanisms. Furthermore, we briefly discuss the potential application of targeted interventions aimed at HIF in the field of bone tissue regeneration engineering. This review expands our biological understanding of the intricate relationship between the HIF gene and bone angiogenesis in periodontitis and offers valuable insights for the development of innovative therapies to expedite bone repair and regeneration.

Hypoxia-Inducible Factor-2α Signaling in the Skeletal System

Hypoxia-inducible factors (HIFs) are oxygen-dependent heterodimeric transcription factors that mediate molecular responses to reductions in cellular oxygen (hypoxia). HIF signaling involves stable HIF-β subunits and labile, oxygen-sensitive HIF-α subunits. Under hypoxic conditions, the HIF-α subunit is stabilized, complexes with nucleus-confined HIF-β subunit, and transcriptionally regulates hypoxia-adaptive genes. Transcriptional responses to hypoxia include altered energy metabolism, angiogenesis, erythropoiesis, and cell fate. Three isoforms of HIF-α-HIF-1α, HIF-2α, and HIF-3α-are found in diverse cell types. HIF-1α and HIF-2α serve as transcriptional activators, whereas HIF-3α restricts HIF-1α and HIF-2α. The structure and isoform-specific functions of HIF-1α in mediating molecular responses to hypoxia are well established across a wide range of cell and tissue types. The contributions of HIF-2α to hypoxic adaptation are often unconsidered if not outrightly attributed to HIF-1α. This review establishes what is currently known about the diverse roles of HIF-2α in mediating the hypoxic response in skeletal tissues, with specific focus on development and maintenance of skeletal fitness. © 2023 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Insight into the effect of biomaterials on osteogenic differentiation of mesenchymal stem cells: A review from a mitochondrial perspective

Bone damage may be triggered by a variety of factors, and the damaged area often requires a bone graft. Bone tissue engineering can serve as an alternative strategy for repairing large bone defects. Mesenchymal stem cells (MSCs), the progenitor cells of connective tissue, have become an important tool for tissue engineering due to their ability to differentiate into a variety of cell types. The precise regulation of the growth and differentiation of the stem cells used for bone regeneration significantly affects the efficiency of this type of tissue engineering. During the process of osteogenic induction, the dynamics and function of localized mitochondria are altered. These changes may also alter the microenvironment of the therapeutic stem cells and result in mitochondria transfer. Mitochondrial regulation not only affects the induction/rate of differentiation, but also influences its direction, determining the final identity of the differentiated cell. To date, bone tissue engineering research has mainly focused on the influence of biomaterials on phenotype and nuclear genotype, with few studies investigating the role of mitochondria. In this review, we provide a comprehensive summary of researches into the role of mitochondria in MSCs differentiation and critical analysis regarding smart biomaterials that are able to "programme" mitochondria modulation was proposed. STATEMENT OF SIGNIFICANCE: : • This review proposed the precise regulation of the growth and differentiation of the stem cells used to seed bone regeneration. • This review addressed the dynamics and function of localized mitochondria during the process of osteogenic induction and the effect of mitochondria on the microenvironment of stem cells. • This review summarized biomaterials which affect the induction/rate of differentiation, but also influences its direction, determining the final identity of the differentiated cell through the regulation of mitochondria.

Dimethyloxalylglycine Attenuates Steroid-Associated Endothelial Progenitor Cell Impairment and Osteonecrosis of the Femoral Head by Regulating the HIF-1α Signaling Pathway

Endothelial impairment and dysfunction are closely related to the pathogenesis of steroid-associated osteonecrosis of the femoral head (SONFH). Recent studies have showed that hypoxia inducible factor-1α (HIF-1α) plays a crucial role in endothelial homeostasis maintenance. Dimethyloxalylglycine (DMOG) could suppress HIF-1 degradation and result in nucleus stabilization by repressing prolyl hydroxylase domain (PHD) enzymatic activity. Our results showed that methylprednisolone (MPS) remarkably undermined biological function of endothelial progenitor cells (EPC) by inhibiting colony formation, migration, angiogenesis, and stimulating senescence of EPCs, while DMOG treatment alleviated these effects by promoting HIF-1α signaling pathway, as evidenced by senescence-associated β-galactosidase (SA-β-Gal) staining, colony-forming unit, matrigel tube formation, and transwell assays. The levels of proteins related to angiogenesis were determined by ELISA and Western blotting. In addition, active HIF-1α bolstered the targeting and homing of endogenous EPCs to the injured endothelium in the femoral head. Histopathologically, our in vivo study showed that DMOG not only alleviated glucocorticoid-induced osteonecrosis but also promoted angiogenesis and osteogenesis in the femoral head as detected by microcomputed tomography (Micro-CT) analysis and histological staining of OCN, TRAP, and Factor Ⅷ. However, all of these effects were impaired by an HIF-1α inhibitor. These findings demonstrate that targeting HIF-1α in EPCs may constitute a novel therapeutic approach for the treatment of SONFH.

Dual antituberculosis drugs-loaded gelatin hydrogel bioimplant for treating spinal tuberculosis

Spinal tuberculosis (TB) represents around 1% of the recorded TB with a high mortality rate due to neurological complications and kyphosis. The current work aimed to develop a bioimplant scaffold to treat spinal TB disease. The scaffold is composed of a biocompatible semi-interpenetrating (semi-IPN) gelatin-based hydrogel incorporating mesoporous silica nanoparticles (MPS-NPs) loaded with rifampicin (RIF) and levofloxacin (LEV) to treat TB. The elastic modulus of the hydrogel was 7.18 ± 0.78 MPa. Minimum inhibitory concentrations (MIC) value against Mycobacterium bovis for LEV-loaded and RIF-loaded MPS-NPs were 6.50 and 1.33 µm/ml, respectively.Sequential release of drugs was observed after 15 days. Loading of the MPS-NPs in the hydrogel matrix governed the amount of released drugs by prolonging the period of release up to 60 days. WST-1 test confirmed the biocompatibility and safety of the developed vertebral hydrogel bioimplant. Histological and immunohistochemistry micrographs showed the progress in healing process with the bioimplant. Besides, loading of LEV and RIF in the implants declined the presence of the giant macrophages clusters as compared to control groups. All the obtained results support the potential use of the developed vertebral hydrogel bioimplant as a scaffold with good mechanical and biocompatible properties along with a good ability to eradicate the TB pathogen.

Hypoxia Pathway in Osteoporosis: Laboratory Data for Clinical Prospects

The hypoxia pathway not only regulates the organism to adapt to the special environment, such as short-term hypoxia in the plateau under normal physiological conditions, but also plays an important role in the occurrence and development of various diseases such as cancer, cardiovascular diseases, osteoporosis. Bone, as a special organ of the body, is in a relatively low oxygen environment, in which the expression of hypoxia-inducible factor (HIF)-related molecules maintains the necessary conditions for bone development. Osteoporosis disease with iron overload endangers individuals, families and society, and bone homeostasis disorder is linked to some extent with hypoxia pathway abnormality, so it is urgent to clarify the hypoxia pathway in osteoporosis to guide clinical medication efficiently. Based on this background, using the keywords "hypoxia/HIF, osteoporosis, osteoblasts, osteoclasts, osteocytes, iron/iron metabolism", a matching search was carried out through the Pubmed and Web Of Science databases, then the papers related to this review were screened, summarized and sorted. This review summarizes the relationship and regulation between the hypoxia pathway and osteoporosis (also including osteoblasts, osteoclasts, osteocytes) by arranging the references on the latest research progress, introduces briefly the application of hyperbaric oxygen therapy in osteoporosis symptoms (mechanical stimulation induces skeletal response to hypoxic signal activation), hypoxic-related drugs used in iron accumulation/osteoporosis model study, and also puts forward the prospects of future research.

Fortified gelatin-based hydrogel scaffold with simvastatin-mixed nanomicelles and platelet rich plasma as a promising bioimplant for tissue regeneration

Treatment of intervertebral disc (IVD) degeneration includes conservative and surgical strategies that have a high risk of recurrence. Consequently, tissue engineering represents a promising alternative treatment. This study aimed at healing damaged IVD with a bioimplant that can maintain the function of defected IVD. The developed IVD scaffold is composed of a fortified biocompatible gelatin-based hydrogel to mimic the ECM mechanical properties of IVD and to allow a sustained release of loaded bioactive agents. The hydrogel is laden with platelet-rich plasma (PRP) and simvastatin (SIM)-loaded mixed pluronics nanomicelles because of their regenerative ability and anti-inflammatory effect, respectively. The gelatin-based hydrogel attained swelling of 508.9 ± 7.9 % to 543.1 ± 5.9 % after 24 h. Increasing crosslinking degree of the hydrogel improved its mechanical elasticity up to 0.3 ± 0.1 N/mm², and retarded its degradation. The optimum mixed nanomicelles had particle size of 84 ± 0.5 nm, a surface charge of -10 ± 7.1 mv, EE% of 84.9 %, and released 88.4 % of SIM after 21 days. Cytotoxicity of IVD components was evaluated using human skin fibroblast for 3 days. WST-test results proved biocompatibility of IVD scaffold. Subcutaneous implantation of the IVD scaffold was performed for 28 days to test in-vivo biocompatibility. Histological and histochemical micrographs depicted normal healing signs such as macrophages, T-cells, angiogenesis and granulation reactions. Introducing PRP in IVD improved healing process and decreased inflammation reactions. The developed multicomponent implant could be used as potential IVD scaffold with desirable mechanical properties, biocompatibility and healing process.

Roxadustat improves renal osteodystrophy by dual regulation of bone remodeling

PURPOSE

Renal osteodystrophy (ROD), a component of chronic kidney disease-mineral and bone disorder (CKD-MBD) can lead to bone loss increasing fracture risks in CKD patients. Therefore, it is important to prevent and treat ROD. Activation of hypoxia-inducible factor-1α (HIF-1α) signaling was reported to prevent osteoporotic bone loss. Roxadustat, which is used to treat renal anemia in the clinic, is a novel HIF stabilizer. In our study, we aimed to investigate the effects of roxadustat on ROD.

METHODS

We established an adenine-induced CKD rat model. Roxadustat was administered intragastrically to normal and CKD rats for 4 weeks. Hemoglobin concentrations and serum biochemical parameters were tested, and bone histomorphometric analysis was performed.

RESULTS

CKD rats exhibited impaired renal function with anemia, secondary hyperparathyroidism and high-turnover ROD-induced significant bone loss. Roxadustat ameliorated renal anemia and attenuated the extreme increase in intact parathyroid hormone (iPTH) and fibroblast growth factor 23 (FGF23) in CKD rats. Bone histomorphometric analysis showed that roxadustat significantly alleviated bone loss and bone microarchitecture deterioration in CKD rats by increasing osteoblast activity and inhibiting osteoclast activity. We did not find that roxadustat had significant effects on bone metabolism in normal rats.

CONCLUSION

Roxadustat can improve ROD via dual regulation of bone remodeling. The use of roxadustat may be a promising strategy to treat osteoporotic bone disorders, such as ROD.

HIF-1α Regulates Bone Homeostasis and Angiogenesis, Participating in the Occurrence of Bone Metabolic Diseases

In the physiological condition, the skeletal system's bone resorption and formation are in dynamic balance, called bone homeostasis. However, bone homeostasis is destroyed under pathological conditions, leading to the occurrence of bone metabolism diseases. The expression of hypoxia-inducible factor-1α (HIF-1α) is regulated by oxygen concentration. It affects energy metabolism, which plays a vital role in preventing bone metabolic diseases. This review focuses on the HIF-1α pathway and describes in detail the possible mechanism of its involvement in the regulation of bone homeostasis and angiogenesis, as well as the current experimental studies on the use of HIF-1α in the prevention of bone metabolic diseases. HIF-1α/RANKL/Notch1 pathway bidirectionally regulates the differentiation of macrophages into osteoclasts under different conditions. In addition, HIF-1α is also regulated by many factors, including hypoxia, cofactor activity, non-coding RNA, trace elements, etc. As a pivotal pathway for coupling angiogenesis and osteogenesis, HIF-1α has been widely studied in bone metabolic diseases such as bone defect, osteoporosis, osteonecrosis of the femoral head, fracture, and nonunion. The wide application of biomaterials in bone metabolism also provides a reasonable basis for the experimental study of HIF-1α in preventing bone metabolic diseases.

Exploration of metabolic responses towards hypoxia mimetic DMOG in cancer cells by using untargeted metabolomics

Hypoxia is considered as one of the most crucial elements of tumor microenvironment. The hypoxia inducible transcription factors (HIF-1/2) are used by the cancer cells to adapt hypoxic microenvironment through regulating the expression of various target genes, including metabolic enzymes. Dimethyloxalylglycine (DMOG), a hypoxic mimetic used for HIF stabilisation in cell and animal models, also demonstrates multiple metabolic effects. In past, it was shown that in cancer cells, DMOG treatment alters mitochondrial ATP production, glycolysis, respiration etc. However, a global landscape of metabolic level alteration in cancer cells during DMOG treatment is still not established. In the current work, the metabolic landscape of cancer cells during DMOG treatment is explored by using untargeted metabolomics approach. Results showed that DMOG treatment primarily alters the one carbon and lipid metabolism. The levels of one-carbon metabolism related metabolites like serine, ornithine, and homomethionine levels significantly altered during DMOG treatment. Further, DMOG treatment reduces the global fatty acyls like palmitic acids, stearic acids, and arachidonic acid levels in cancer cell lines. Additionally, we found an alteration in glycolytic metabolites known to be regulated by hypoxia in cancer cell lines. Collectively, the results provided novel insights into the metabolic impact of DMOG on cancer cells and showed that the use of DMOG to induce hypoxia yields similar metabolic features relative to physiological hypoxia.

Roxadustat promotes osteoblast differentiation and prevents estrogen deficiency-induced bone loss by stabilizing HIF-1α and activating the Wnt/β-catenin signaling pathway

BACKGROUND

Osteoporosis is a very common skeletal disorder that increases the risk of fractures. However, the treatment of osteoporosis is challenging. Hypoxia-inducible factor-1α (HIF-1α) plays an important role in bone metabolism. Roxadustat is a novel HIF stabilizer, and its effects on bone metabolism remain unknown. This study aimed to investigate the effects of roxadustat on osteoblast differentiation and bone remodeling in an ovariectomized (OVX) rat model.

METHODS

In vitro, primary mouse calvarial osteoblasts were treated with roxadustat. Alkaline phosphatase (ALP) activity and extracellular matrix mineralization were assessed. The mRNA and protein expression levels of osteogenic markers were detected. The effects of roxadustat on the HIF-1α and Wnt/β-catenin pathways were evaluated. Furthermore, osteoblast differentiation was assessed again after HIF-1α expression knockdown or inhibition of the Wnt/β-catenin pathway. In vivo, roxadustat was administered orally to OVX rats for 12 weeks. Then, bone histomorphometric analysis was performed. The protein expression levels of the osteogenic markers HIF-1α and β-catenin in bone tissue were detected.

RESULTS

In vitro, roxadustat significantly increased ALP staining intensity, enhanced matrix mineralization and upregulated the expression of osteogenic markers at the mRNA and protein levels in osteoblasts compared with the control group. Roxadustat activated the HIF-1α and Wnt/β-catenin pathways. HIF-1α knockdown or Wnt/β-catenin pathway inhibition significantly attenuated roxadustat-promoted osteoblast differentiation. In vivo, roxadustat administration improved bone microarchitecture deterioration and alleviated bone loss in OVX rats by promoting bone formation and inhibiting bone resorption. Roxadustat upregulated the protein expression levels of the osteogenic markers, HIF-1α and β-catenin in the bone tissue of OVX rats.

CONCLUSION

Roxadustat promoted osteoblast differentiation and prevented bone loss in OVX rats. The use of roxadustat may be a new promising strategy to treat osteoporosis.

Vascularized Tumor Spheroid-on-a-Chip Model Verifies Synergistic Vasoprotective and Chemotherapeutic Effects

Prolyl hydroxylases (PHD) inhibitors have been observed to improve drug distribution in mice tumors via blood vessel normalization, increasing the effectiveness of chemotherapy. These effects are yet to be demonstrated in human cell models. Tumor spheroids are three-dimensional cell clusters that have demonstrated great potential in drug evaluation for personalized medicine. Here, we used a perfusable vascularized tumor spheroid-on-a-chip to simulate the tumor microenvironment in vivo and demonstrated that the PHD inhibitor dimethylallyl glycine prevents the degradation of normal blood vessels while enhancing the efficacy of the anticancer drugs paclitaxel and cisplatin in human esophageal carcinoma (Eca-109) spheroids. Our results point to the potential of this model to evaluate anticancer drugs under more physiologically relevant conditions.

A dual role of HIF1α in regulating osteogenesis–angiogenesis coupling

Objectives

The hypoxia-inducible factor 1-α (HIF1α), a key molecule in mediating bone-vessel crosstalk, has been considered a promising target for treating osteoporosis caused by gonadal hormones. However, senile osteoporosis, with accumulated senescent cells in aged bone, has a distinct pathogenesis. The study aimed at revealing the unknown role of HIF1α in aged bone, thus broadening its practical application in senile osteoporosis.

Materials and methods

Femurs and tibias were collected from untreated mice of various ages (2 months old, 10 months old, 18 months old) and treated mice (2 months old, 18 months old) underwent 4-w gavage of 2-methoxyestradiol (a kind of HIF1α inhibitor). Bone-vessel phenotypes were observed by microfil infusion, micro-CT and HE staining. Markers of senescence, osteogenesis, angiogenesis, oxidative stress and expression of HIF1α were detected by senescence β-galactosidase staining, qRT-PCR, western blot and immunostaining, respectively. Furthermore, bone mesenchymal stem cells from young mice (YBMSCs) and aged mice (ABMSCs) were transfected by knockout siRNA and overexpression plasmid of HIF1α. Senescence β-galactosidase staining, Cell Counting Kit-8, transwell assay, alkaline phosphatase staining, alizarin red-S staining and angiogenesis tests were utilized to assess the biological properties of two cell types. Then, Pifithrin-α and Nutlin-3a were adopted to intervene p53 of the two cells. Finally, H₂O₂ on YBMSCs and NAC on ABMSCs were exploited to change their status of oxidative stress to do a deeper detection.

Results

Senescent phenotypes, impaired osteogenesis–angiogenesis coupling and increased HIF1α were observed in aged bone and ABMSCs. However, 2-methoxyestradiol improved bone-vessel metabolism of aged mice while damaged that of young mice. Mechanically, HIF1α showed opposed effects in regulating the cell migration and osteogenesis–angiogenesis coupling of YBMSCs and ABMSCs, but no remarked effect on the proliferation of either cell type. Pifithrin-α upregulated the osteogenic and angiogenic markers of HIF1α-siRNA-transfected YBMSCs, and Nutlin-3a alleviated those of HIF1α-siRNA-transfected ABMSCs. The HIF1α-p53 relationship was negative in YBMSCs and NAC-treated ABMSCs, but positive in ABMSCs and H₂O₂-treated YBMSCs.

Conclusion

The dual role of HIF1α in osteogenesis–angiogenesis coupling may depend on the ROS-mediated HIF1α-p53 relationship. New awareness about HIF1α will be conducive to its future application in senile osteoporosis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-02742-1.

The osteoprotective role of USP26 in coordinating bone formation and resorption

Bone homeostasis is maintained through a balance of bone formation by osteoblasts and bone resorption by osteoclasts. Ubiquitin-specific proteases (USPs) are involved in regulating bone metabolism by preserving bone formation or antagonizing bone resorption. However, the specific USPs that maintain bone homeostasis by orchestrating bone formation and bone resorption simultaneously are poorly understood. Here, we identified USP26 as a previously unknown regulator of bone homeostasis that coordinates bone formation and resorption. Mechanistically, USP26 stabilizes β-catenin to promote the osteogenic activity of mesenchymal cells (MSCs) and impairs the osteoclastic differentiation of bone myelomonocytes (BMMs) by stabilizing inhibitors of NF-κBα (IκBα). Gain-of-function experiments revealed that Usp26 supplementation significantly increased bone regeneration in bone defects in aged mice and decreased bone loss resulting from ovariectomy. Taken together, these data show the osteoprotective effect of USP26 via the coordination of bone formation and resorption, suggesting that USP26 represents a potential therapeutic target for osteoporosis.

Osteocytic HIF-1α Pathway Manipulates Bone Micro-structure and Remodeling via Regulating Osteocyte Terminal Differentiation

The activation of hypoxia-inducible factor 1α (HIF-1α) signaling has promising implications for the treatment of bone diseases such as osteoporosis and skeletal fractures. However, the effects of manipulating HIF-1α pathway on bone micro-structure and remodeling should be fully studied before the clinical application of therapeutics that interfere with the HIF-1α pathway. In this study, we found that osteocyte-specific HIF-1α pathway had critical role in manipulating bone mass accrual, bone material properties and micro-structures, including bone mineralization, bone collagen fiber formation, osteocyte/canalicular network, and bone remodeling. In addition, our results suggest that osteocyte-specific HIF-1α pathway regulates bone micro-structure and remodeling via impairing osteocyte differentiation and maturation.

Cyclic Tensile Stress to Rat Thoracolumbar Ligamentum Flavum Inducing the Ossification of Ligamentum Flavum: An In Vivo Experimental Study

STUDY DESIGN

Western blot, reverse transcription-polymerase chain reaction (RT-PCR), radiological, and histological analyses of the rat ossification of ligamentum flavum (OLF) induced by cyclic tensile stress.

OBJECTIVE

The aim of this study was to induce the OLF using cyclic tensile stress to rat thoracolumbar ligamentum flavum, and to investigate the possible molecular mechanism of tension-induced OLF.

SUMMARY OF BACKGROUND DATA

Tensile stress has been considered as an important factor leading to the OLF. So far, however, no OLF induced by tension has been reported.

METHODS

Forty rats were randomly divided into five equal groups. For control groups, the blank and anesthesia groups were not subjected to tension. For experimental groups, the 4-, 8-, and 12-week groups were subjected to cyclic tensile stress of ligamentum flavum after abdominal anesthesia for 4 weeks, 8 weeks, and 12 weeks, respectively, using an original stress apparatus for rats. The radiological and morphological changes of rat spine, as well as the protein and mRNA expressions of CD44, bone morphogenetic protein-2 (BMP-2), integrin β3, collagen protein type I (COL1), osteopontin (OPN), runt-related transcription factor 2 (RUNX-2), and vascular endothelial growth factor (VEGF), were concerned.

RESULTS

The micro-CT showed OLF in the 4-, 8-, and 12-week group. The axial maximum occupied area of ossifications was 1.42 mm2, 3.35 mm2, and 7.28 mm2, respectively. In histopathology, chondrocytes proliferated in the experimental model; woven bone arose in the 8- and 12-week groups, and was more noticeable in the 12-week group. According to western blot and RT-PCR, the expressions of seven osteogenesis-related molecules were all increased in three experimental groups.

CONCLUSION

Cyclic tensile stress to the ligamentum flavum in rats can induce the OLF, and the longer the duration, the more visible the osteogenesis. The upregulation and synergism of osteogenesis-related molecules may contribute to the OLF induced by tensile stress.Level of Evidence: N/A.

Effects of Pulsed Electromagnetic Field Therapy at Different Frequencies on Bone Mass and Microarchitecture in Osteoporotic Mice

A pulsed electromagnetic field (PEMF) can promote osteogenesis. However, studies have shown variation in the signal characteristics in terms of waveform type, intensity, frequency, and treatment duration. Among the factors that affect electromagnetic fields, frequency plays a major role. However, few studies have investigated the effects of PEMF at different frequencies in osteoporotic mice. Therefore, our objective was to determine the effect of PEMF frequency in osteoporotic mice. Forty 3-month-old female mice were randomly divided into the following five groups: sham, OVX, and OVX followed by 1.6-mT PEMF exposure groups (8 Hz, 50 Hz, and 75 Hz, 1.6 mT). The PEMF was applied for 1 h/day, 7 days/week, for 4 weeks. After 4 weeks, the micro-computed tomography showed that PEMF with (50 and 75 Hz) ameliorated the deterioration of bone microarchitecture. Improvements in the bone histological analysis were identified for PEMF with 50 and 75 Hz groups compared with the ovariectomy (OVX) controls. Osteoclast numbers were decreased in PEMF with (50 and 75 Hz). Moreover, the real-time PCR demonstrated PEMF with (50 and 75 Hz) significantly promoted the expression of the osteoblast-related genes (ALP, OCN, Runx2), and increased the serum PINP. PEMF with (50 and 75 Hz) exerted significant inhibitory effects on the osteoclast-related mRNA expression (CTSK, NFATc1, TRAP) and bone resorption markers CTX-I and IL-1β. Taken together, our results showed that PEMF at 50 and 75 Hz with 1.6 mT significantly ameliorate the deterioration of bone microarchitecture in OVX mice. The inhibitory effect of PEMF may be associated with IL-1β inhibition. © 2021 Bioelectromagnetics Society.

Macropore design of tissue engineering scaffolds regulates mesenchymal stem cell differentiation fate

Craniosynostosis is a debilitating birth defect characterized by the premature fusion of cranial bones resulting from premature loss of stem cells located in suture tissue between growing bones. Mesenchymal stromal cells in long bone and the cranial suture are known to be multipotent cell sources in the appendicular skeleton and cranium, respectively. We are developing biomaterial constructs to maintain stemness of the cranial suture cell population towards an ultimate goal of diminishing craniosynostosis patient morbidity. Recent evidence suggests that physical features of synthetic tissue engineering scaffolds modulate cell and tissue fate. In this study, macroporous tissue engineering scaffolds with well-controlled spherical pores were fabricated by a sugar porogen template method. Cell-scaffold constructs were implanted subcutaneously in mice for up to eight weeks then assayed for mineralization, vascularization, extracellular matrix composition, and gene expression. Pore size differentially regulates cell fate, where sufficiently large pores provide an osteogenic niche adequate for bone formation, while sufficiently small pores (<125 μm in diameter) maintain stemness and prevent differentiation. Cell-scaffold constructs cultured in vitro followed the same pore size-controlled differentiation fate. We therefore attribute the differential cell and tissue fate to scaffold pore geometry. Scaffold pore size regulates mesenchymal cell fate, providing a novel design motif to control tissue regenerative processes and develop mesenchymal stem cell niches in vivo and in vitro through biophysical features.

Hypoxia-Inducible Factors Regulate Osteoclasts in Health and Disease

Hypoxia-inducible factors (HIFs) have become key transcriptional regulators of metabolism, angiogenesis, erythropoiesis, proliferation, inflammation and metastases. HIFs are tightly regulated by the tissue microenvironment. Under the influence of the hypoxic milieu, HIF proteins allow the tissue to adapt its response. This is especially critical for bone, as it constitutes a highly hypoxic environment. As such, bone structure and turnover are strongly influenced by the modulation of oxygen availability and HIFs. Both, bone forming osteoblasts and bone resorbing osteoclasts are targeted by HIFs and modulators of oxygen tension. Experimental and clinical data have delineated the importance of HIF responses in different osteoclast-mediated pathologies. This review will focus on the influence of HIF expression on the regulation of osteoclasts in homeostasis as well as during inflammatory and malignant bone diseases.

Roles of oxygen level and hypoxia-inducible factor signaling pathway in cartilage, bone and osteochondral tissue engineering

The repair and treatment of articular cartilage injury is a huge challenge of orthopedics. Currently, most of the clinical methods applied in treating cartilage injuries are mainly to relieve pains rather than to cure them, while the strategy of tissue engineering is highly expected to achieve the successful repair of osteochondral defects. Clear understandings of the physiological structures and mechanical properties of cartilage, bone and osteochondral tissues have been established, but the understanding of their physiological heterogeneity still needs further investigation. Apart from the gradients in the micromorphology and composition of cartilage-to-bone extracellular matrixes, an oxygen gradient also exists in natural osteochondral tissue. The response of hypoxia-inducible factor (HIF)-mediated cells to oxygen would affect the differentiation of stem cells and the maturation of osteochondral tissue. This article reviews the roles of oxygen level and HIF signaling pathway in the development of articular cartilage tissue, and their prospective applications in bone and cartilage tissue engineering. The strategies for regulating HIF signaling pathway and how these strategies finding their potential applications in the regeneration of integrated osteochondral tissue are also discussed.

Antineoplastic activity of Salmonella Typhimurium outer membrane nanovesicles

Nano-sized Gram-negative bacterial outer membrane vesicles possess unique structural and immunostimulatory effects that could be exploited to regress tumors by alerting the host immune system and reversing the immunosuppressive tumor microenvironment. The current study was conducted to investigate the antitumor activity of the outer membrane vesicles (ST-OMVs) of Salmonella Typhimurium ATCC 14028, in vitro in human colorectal carcinoma (HTC116), breast cancer (MCF-7), and hepatocellular carcinoma (HepG2) cell lines and in vivo in Ehrlich solid carcinoma-bearing mice model either as a mono-immunotherapy or as an adjuvant to a commonly used conventional chemotherapy. In addition, we investigated the safety of ST-OMVs. Adult Swiss albino female mice with transplanted Ehrlich solid carcinoma were treated with either ST-OMVs, paclitaxel or a combination of both. Tumor volume, growth inhibition rate, quantitative RT-PCR of Bax and VEGF genes expression, histopathology and immune-expression of caspase-3, Beclin-1, CD49b and Ki-67 were all analyzed. Our results showed that ST-OMVs significantly decreased tumor volume, significantly increased tumor growth inhibition rate, up-regulated the immunohistochemical expression of caspase-3, Beclin-1, and CD49b (enhanced recruitment of NK cells). Furthermore, ST-OMVs down-regulated the expression of Ki-67, increased Bax gene expression and decreased VEGF gene expression as detected by qRT-PCR analysis. Histologically, ST-OMVs promoted apoptosis, decreased tumor invasion and mitotic activities. Moreover, ST-OMVs showed a remarkable cytotoxic activity in various investigated in vitro cancer cell lines. Our findings demonstrate potential antitumor activity of ST-OMVs that might be used as a promising safe antitumor immunotherapy or an adjuvant to conventional chemotherapeutic drugs, resolving some of their problems.

Dimethyloxallyl glycine/nanosilicates-loaded osteogenic/angiogenic difunctional fibrous structure for functional periodontal tissue regeneration

The coupled process of osteogenesis-angiogenesis plays a crucial role in periodontal tissue regeneration. Although various cytokines or chemokines have been widely applied in periodontal in situ tissue engineering, most of them are macromolecular proteins with the drawbacks of short effective half-life, poor stability and high cost, which constrain their clinical translation. Our study aimed to develop a difunctional structure for periodontal tissue regeneration by incorporating an angiogenic small molecule, dimethyloxalylglycine (DMOG), and an osteoinductive inorganic nanomaterial, nanosilicate (nSi) into poly (lactic-co-glycolic acid) (PLGA) fibers by electrospinning. The physiochemical properties of DMOG/nSi-PLGA fibrous membranes were characterized. Thereafter, the effect of DMOG/nSi-PLGA membranes on periodontal tissue regeneration was evaluated by detecting osteogenic and angiogenic differentiation potential of periodontal ligament stem cells (PDLSCs) in vitro. Additionally, the fibrous membranes were transplanted into rat periodontal defects, and tissue regeneration was assessed with histological evaluation, micro-computed tomography (micro-CT), and immunohistochemical analysis. DMOG/nSi-PLGA membranes possessed preferable mechanical property and biocompatibility. PDLSCs seeded on the DMOG/nSi-PLGA membranes showed up-regulated expression of osteogenic and angiogenic markers, higher alkaline phosphatase (ALP) activity, and more tube formation in comparison with single application. Further, in vivo study showed that the DMOG/nSi-PLGA membranes promoted recruitment of CD90+/CD34− stromal cells, induced angiogenesis and osteogenesis, and regenerated cementum-ligament-bone complex in periodontal defects. Consequently, the combination of DMOG and nSi exerted admirable effects on periodontal tissue regeneration. DMOG/nSi-PLGA fibrous membranes could enhance and orchestrate osteogenesis-angiogenesis, and may have the potential to be translated as an effective scaffold in periodontal tissue engineering.

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Dual-load fibrous structure possessed preferable mechanical property and biocompatibility.

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Fibrous structure can orchestrate and enhance osteogenesis-angiogenesis coupling.

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Difunctional fibrous structure can recruit CD90+/CD34− stromal cells to periodontal defects.

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Difunctional fibrous structure obtained functional periodontal tissue regeneration.

Delivery of dimethyloxalylglycine in calcined bone calcium scaffold to improve osteogenic differentiation and bone repair

As hypoxia plays a vital role in the angiogenic-osteogenic coupling, using proline hydroxylase inhibitors to manipulate hypoxia-inducible factors has become a strategy to improve the osteogenic properties of biomaterials. Dimethyloxallyl glycine (DMOG) is a 2-ketoglutarate analog, a small molecular compound that competes for 2-ketoglutaric acid to inhibit proline hydroxylase. In order to improve the osteogenic ability of calcined bone calcium (CBC), a new hypoxia-mimicking scaffold (DMOG/Collagen/CBC) was prepared by immersing it in the DMOG-Collagen solution, followed by freeze-drying. All coated CBC scaffolds retained the inherent natural porous architecture and showed excellent biocompatibility. A slow release of DMOG by the DMOG-loaded CBC scaffolds for up to one week was observed in in vitro experiments. Moreover, the DMOG/Collagen/CBC composite scaffold was found to significantly stimulate bone marrow stromal cells to express osteogenic and angiogenic genes in vitro. In addition, the osteogenic properties of three kinds of scaffolds, raw CBC, Collagen/CBC, and DMOG/Collagen/CBC, were evaluated by histology using the rabbit femoral condyle defect model. Histomorphometric analyses showed that the newly formed bone (BV/TV) in the DMOG/Collagen/CBC group was significantly higher than that of the Collagen/CBC group. However, immunostaining of CD31 and Runx2 expression between these two groups showed no significant difference at this time point. Our results indicate that DMOG-coated CBC can promote osteogenic differentiation and bone healing, and show potential for clinical application in bone tissue engineering.

Osteoblast-Osteoclast Coculture Amplifies Inhibitory Effects of FG-4592 on Human Osteoclastogenesis and Reduces Bone Resorption

The link between bone and blood vessels is regulated by hypoxia and the hypoxia‐inducible transcription factor, HIF, which drives both osteogenesis and angiogenesis. The recent clinical approval of PHD enzyme inhibitors, which stabilize HIF protein, introduces the potential for a new clinical strategy to treat osteolytic conditions such as osteoporosis, osteonecrosis, and skeletal fracture and nonunion. However, bone‐resorbing osteoclasts also play a central role in bone remodeling and pathological osteolysis, and HIF promotes osteoclast activation and bone loss in vitro. It is therefore likely that the result of PHD enzyme inhibition in vivo would be mediated by a balance between increased bone formation and increased bone resorption. It is essential that we improve our understanding of the effects of HIF on osteoclast formation and function and consider the potential contribution of inhibitory interactions with other musculoskeletal cells. The PHD enzyme inhibitor FG‐4592 stabilized HIF protein and stimulated osteoclast‐mediated bone resorption, but inhibited differentiation of human CD14+ monocytes into osteoclasts. Formation of osteoclasts in a more physiologically relevant 3D collagen gel did not affect the sensitivity of osteoclastogenesis to FG‐4592, but increased sensitivity to reduced concentrations of RANKL. Coculture with osteoblasts amplified inhibition of osteoclastogenesis by FG‐4592, whether the osteoblasts were proliferating, differentiating, or in the presence of exogenous M‐CSF and RANKL. Osteoblast coculture dampened the ability of high concentrations of FG‐4592 to increase bone resorption. These data provide support for the therapeutic use of PHD enzyme inhibitors to improve bone formation and/or reduce bone loss for the treatment of osteolytic pathologies and indicate that FG‐4592 might act in vivo to inhibit the formation and activity of the osteoclasts that drive osteolysis. © 2020 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

Osteoking improves OP rat by enhancing HSP90‑β expression

Osteoporosis (OP) is a chronic bone disease that affects individuals worldwide. Osteoporosis is primarily asymptomatic, and patients with OP suffer from pain, inconvenience, economic pressure and osteoporotic fracture (OPF). Osteoking, a Traditional Chinese Medicine compound that originates from the Yi ethnic group, has been used for a number of years to treat fractures. In our previous study, osteoking exhibited therapeutic effects on rats with OPF by promoting calcium deposition. Based on bioinformatics and network pharmacology analyses of a component‑target‑disease database, heat shock protein HSP 90‑β (HSP90‑β), also known as HSP90‑β, was identified to be a key target of osteoking in OP. High HSP90‑β expression levels were observed in osteoporotic rats and rat bone mesenchymal stem cells (rBMSCs) following osteoking treatment. After 12 weeks of administration in vivo, there was increased bone mineral density (BMD) (P<0.05), increased bone alkaline phosphatase (P<0.05), and improved bone microstructure in the osteoking group compared with those of the negative control group. In vitro, increased calcium deposition in rBMSCs was observed after 4 weeks of osteoking treatment. These results suggest that the mechanisms of osteoking are closely associated with HSP90‑β and activate the bone morphogenetic protein (BMP) signalling pathway, primarily through BMP‑2. Osteoking treatment improves OP in rats by enhancing HSP90‑β expression.

Semaphorin 3A-hypoxia inducible factor 1 subunit alpha co-overexpression enhances the osteogenic differentiation of induced pluripotent stem cells-derived mesenchymal stem cells in vitro

Background:

Mesenchymal stem or stromal cells (MSCs) derived from the induced pluripotent stem cells (iPSCs) have uniform biological activity, which makes the clinical application of MSCs in bone repair possible. Culturing the iPSC-MSCs onto osteoconductive materials is a promising tissue engineering-based strategy in bone regeneration. The aim of this work was to evaluate the effects of semaphorin 3A (Sema3A) and hypoxia inducible factor 1 subunit alpha (HIF1α) co-overexpression on the survival and osteogenic differentiation of iPSC-MSCs.

Methods:

Sema3A and HIF1α were linked together with the three (GGGGS; G, glycine; S, serine) peptide fragment, and their co-expression in iPSC-MSCs was mediated by a lentiviral vector. The fusion protein retained the immune reactivity for both Sema3A and HIF1α as determined with Western blotting. iPSC-MSCs were infected with overexpression lentivirus (oeLenti) as negative control, oeLenti-Sema3A, oeLenti-HIF1α or oeLenti-Sema3A-HIF1α lentiviruses.

Results:

Sema3A overexpression alone promoted the osteogenic differentiation of iPSC-MSCs (the activity and/or expression of osteoblast markers, such as alkaline phosphatase, osteopontin, and osteocalcin, were upregulated), and suppressed cell survival. The Sema3A-HIF1α fusion protein showed a comparable osteoconductive effect to that of Sema3A without reducing cell survival. We further seeded iPSC-MSCs modified by SemaA-HIF1α overexpression onto hydroxyapatite (HA) scaffolds, and evaluated their growth and differentiation on this three-dimensional material. Additional data indicated that, as compared to iPSC-MSCs cultured in ordinary two-dimensional dishes, cells cultured in HA scaffolds grew (blank vs. HA scaffolds: 0.83 vs. 1.39 for survival) and differentiated better (blank vs. HA scaffolds: 11.29 vs. 16.62 for alkaline phosphatase activity).

Conclusion:

Modifying iPSC-MSCs with pro-osteogenic (Sema3A) and pro-survival (HIF1α) factors may represent a promising strategy to optimize tissue engineering-based strategy in bone repair.

Screening of key candidate genes and pathways for osteocytes involved in the differential response to different types of mechanical stimulation using a bioinformatics analysis

This study aimed to predict the key genes and pathways that are activated when different types of mechanical loading are applied to osteocytes. mRNA expression datasets (series number of GSE62128 and GSE42874) were obtained from Gene Expression Omnibus database (GEO). High gravity-treated osteocytic MLO-Y4 cell-line samples from GSE62128 (Set1), and fluid flow-treated MLO-Y4 samples from GSE42874 (Set2) were employed. After identifying the differentially expressed genes (DEGs), functional enrichment was performed. The common DEGs between Set1 and Set2 were considered as key DEGs, then a protein-protein interaction (PPI) network was constructed using the minimal nodes from all of the DEGs in Set1 and Set2, which linked most of the key DEGs. Several open source software programs were employed to process and analyze the original data. The bioinformatic results and the biological meaning were validated by in vitro experiments. High gravity and fluid flow induced opposite expression trends in the key DEGs. The hypoxia-related biological process and signaling pathway were the common functional enrichment terms among the DEGs from Set1, Set2 and the PPI network. The expression of almost all the key DEGs (Pdk1, Ccng2, Eno2, Egln1, Higd1a, Slc5a3 and Mxi1) were mechano-sensitive. Eno2 was identified as the hub gene in the PPI network. Eno2 knockdown results in expression changes of some other key DEGs (Pdk1, Mxi1 and Higd1a). Our findings indicated that the hypoxia response might have an important role in the differential responses of osteocytes to the different types of mechanical force.

Wnt3a involved in the mechanical loading on improvement of bone remodeling and angiogenesis in a postmenopausal osteoporosis mouse model

Osteoporosis is a major health problem, making bones fragile and susceptible to fracture. Previous works showed that mechanical loading stimulated bone formation and accelerated fracture healing. Focusing on the role of Wnt3a (wingless/integrated 3a), this study was aimed to assess effects of mechanical loading to the spine, using ovariectomized (OVX) mice as a model of osteoporosis. Two-week daily application of this novel loading (4 N, 10 Hz, 5 min/d) altered bone remodeling with an increase in Wnt3a. Spinal loading promoted osteoblast differentiation, endothelial progenitor cell migration, and tube formation and inhibited osteoclast formation, migration, and adhesion. A transient silencing of Wnt3a altered the observed loading effects. Spinal loading significantly increased bone mineral density, bone mineral content, and bone area per tissue area. The loaded OVX group showed a significant increase in the number of osteoblasts and reduction in osteoclast surface/bone surface. Though expression of osteoblastic genes was increased, the levels of osteoclastic genes were decreased by loading. Spinal loading elevated a microvascular volume as well as VEGF expression. Collectively, this study supports the notion that Wnt3a-mediated signaling involves in the effect of spinal loading on stimulating bone formation, inhibiting bone resorption, and promoting angiogenesis in OVX mice. It also suggests that Wnt3a might be a potential therapeutic target for osteoporosis treatment.-Li, X., Liu, D., Li, J., Yang, S., Xu, J., Yokota, H., Zhang, P. Wnt3a involved in the mechanical loading on improvement of bone remodeling and angiogenesis in a postmenopausal osteoporosis mouse model.

Hypoxia Signaling in the Skeleton: Implications for Bone Health

PURPOSE OF REVIEW

We reviewed recent literature on oxygen sensing in osteogenic cells and its contribution to development of a skeletal phenotype, the coupling of osteogenesis with angiogenesis and integration of hypoxia into canonical Wnt signaling, and opportunities to manipulate oxygen sensing to promote skeletal repair.

RECENT FINDINGS

Oxygen sensing in osteocytes can confer a high bone mass phenotype in murine models; common and unique targets of HIF-1α and HIF-2α and lineage-specific deletion of oxygen sensing machinery suggest differentia utilization and requirement of HIF-α proteins in the differentiation from mesenchymal stem cell to osteoblast to osteocyte; oxygen-dependent but HIF-α-independent signaling may contribute to observed skeletal phenotypes. Manipulating oxygen sensing machinery in osteogenic cells influences skeletal phenotype through angiogenesis-dependent and angiogenesis-independent pathways and involves HIF-1α, HIF-2α, or both proteins. Clinically, an FDA-approved iron chelator promotes angiogenesis and osteogenesis, thereby enhancing the rate of fracture repair.

3D-porous β-tricalcium phosphate-alginate-gelatin scaffold with DMOG delivery promotes angiogenesis and bone formation in rat calvarial defects

Hypoxia-inducible factor-1α (HIF-1α), a well-studied angiogenesis pathway, plays an essential role in angiogenesis-osteogenesis coupling. Targeting the HIF-1a pathway frequently leads to successful reconstruction of large-sized bone defects through promotion of angiogenesis. Dimethyloxalylglycine (DMOG) small molecule regulates the stability of HIF-1α at normal oxygen tension by mimicking hypoxia, which subsequently accelerates angiogenesis. The current study aims to develop a novel construct by seeding adipose derived mesenchymal stem cells (ADMSCs) onto a scaffold that contains DMOG to induce angiogenesis and regeneration of a critical size calvarial defect in a rat model. The spongy scaffolds have been synthesized in the presence and absence of DMOG and analyzed in terms of morphology, porosity, pore size, mechanical properties and DMOG release profile. The effect of DMOG delivery on cellular behaviors of adhesion, viability, osteogenic differentiation, and angiogenesis were subsequently evaluated under in vitro conditions. Histological analysis of cell-scaffold constructs were also performed following transplantation into the calvarial defect. Physical characteristics of fabricated scaffolds confirmed higher mechanical strength and surface roughness of DMOG-loaded scaffolds. Scanning electron microscopy (SEM) images and MTT assay demonstrated the attachment and viability of ADMSCs in the presence of DMOG, respectively. Osteogenic activity of ADMSCs that included alkaline phosphatase (ALP) activity and calcium deposition significantly increased in the DMOG-loaded scaffold. Computed tomography (CT) imaging combined with histomorphometry and immunohistochemistry analysis showed enhanced bone formation and angiogenesis in the DMOG-loaded scaffolds. Therefore, spongy scaffolds that contained DMOG and had angiogenesis ability could be utilized to enhance bone regeneration of large-sized bone defects.

Osteocytic oxygen sensing controls bone mass through epigenetic regulation of sclerostin

Preservation of bone mass is crucial for healthy ageing and largely depends on adequate responses of matrix-embedded osteocytes. These cells control bone formation and resorption concurrently by secreting the WNT/β-catenin antagonist sclerostin (SOST). Osteocytes reside within a low oxygen microenvironment, but whether and how oxygen sensing regulates their function remains elusive. Here, we show that conditional deletion of the oxygen sensor prolyl hydroxylase (PHD) 2 in osteocytes results in a high bone mass phenotype, which is caused by increased bone formation and decreased resorption. Mechanistically, enhanced HIF-1α signalling increases Sirtuin 1-dependent deacetylation of the Sost promoter, resulting in decreased sclerostin expression and enhanced WNT/β-catenin signalling. Additionally, genetic ablation of PHD2 in osteocytes blunts osteoporotic bone loss induced by oestrogen deficiency or mechanical unloading. Thus, oxygen sensing by PHD2 in osteocytes negatively regulates bone mass through epigenetic regulation of sclerostin and targeting PHD2 elicits an osteo-anabolic response in osteoporotic models.

Osteocytes reside in a low oxygen environment, but it is not clear if oxygen sensing regulates their function. Here, the authors show that deletion of the oxygen sensor prolyl hydroxylase 2 in osteocytes leads to increased bone mass via regulation of sclerostin, and reduces bone loss in mouse models of osteoporosis.

Bu-Shen-Tong-Luo decoction prevents bone loss via inhibition of bone resorption and enhancement of angiogenesis in ovariectomy-induced osteoporosis of rats

ETHNOPHARMACOLOGICAL RELEVANCE

Gathering three ancient formulas, traditional Chinese medicine Bu-Shen-Tong-Luo decoction (BSTLD) has been used to treat postmenopausal osteoporosis (PMO) at the Jiangsu Province Hospital of Chinese Medicine for decades. However, the effect of BSTLD on angiogenesis and bone resorption as well as its possible mechanism are still unknown.

AIM OF THE STUDY

This study was aimed to evaluate the preventive effect of BSTLD on ovariectomy-induced bone loss and vasculature disorder, and to investigate the possible bone protection mechanism of BSTLD in inhibiting bone resorption by enhancing angiogenesis signaling in ovariectomy-induced osteoporosis of rats.

MATERIALS AND METHODS

The animal experiment was divided into five groups. Rats underwent either sham surgery with intact ovaries (SHAM, n = 10) or bilateral ovariectomy (OVX, n = 40). OVX rats were randomly divided into four groups and gavaged by water (vehicle, 12 mL/kg, n = 10), BSTLD (6 g/kg, n = 10), BSTLD (12 g/kg, n = 10) and 17β-estradiol (E2, 100 μg/kg, n = 10) daily for 12 weeks, respectively. The bone loss and microstructure of the distal femur were observed using micro-computed tomography (μCT). The biomechanical parameters of the femur were detected using three-point bending tests. The distribution of osteoclasts and endothelial cells were analyzed by immunohistochemistry. The mRNA and protein levels of angiogenesis-related hypoxia-inducible factor-1α (HIF-1α) and vascular endothelial growth factor (VEGF), as well as osteoclast activation-related signaling calcitonin receptor (CALCR), cathepsin K (CTSK), receptor activator of NF-κB ligand (RANKL), osteoprotegerin (OPG), and β-catenin were assayed by RT-PCR or Western blot.

RESULTS

BSTLD protected trabecular bone mass density and trabecular bone microstructure from ovariectomy-induced osteoporosis in rats. BSTLD significantly reduced mRNA and protein levels of calcitonin receptor and CTSK in femoral metaphysis and inhibited bone resorption in ovariectomized rats. Furthermore, BSTLD stabilized HIF-1α activity and subsequently increased VEGF expression to enhance angiogenesis and modulated RANKL/OPG signaling in this animal model.

CONCLUSIONS

These results demonstrated that BSTLD reduced osteoclasts activation and bone resorption in ovariectomy-induced osteoporosis. Bone protection by BSTLD may be associated with its stimulation of HIF-1α/VEGF angiogenesis signaling and suppression of RANKL/OPG ratio. This study may provide evidence that BSTLD treats postmenopausal osteoporosis, especially with micro-circulation complication.

Mongolian Medicine echinops prevented postmenopausal osteoporosis and induced ER/AKT/ERK pathway in BMSCs

Hormone replacement medicine such as traditional Chinese medicine has proven to be effective in decreasing the risk of osteoporosis. Mongolian medicine echinops prevents osteoporosis, but its mechanism remains unclear. In this study, we explored the mechanism underlying echinops prevents and treats postmenopausal osteoporosis. Osteoporosis model was established by ovariectomy in rats. Rats were treated to Echinops (16.26, 32.5, or 65 mg/kg/day) by oral gavage for 3 months. Bone mineral density (BMD) was detected by micro-CT detection of left proximal medial metaphyseal tibia. Hematoxylin and eosin (H&E) and toluidine blue O staining were also performed. Serum levels of E2, ALP and testosterone were examined. Bone marrow-derived bone marrow stem cells (BMSCs) were isolated and treated with echinops-containing serum. Estrogen receptors (ER) including ERα and ERβ in bone specimens and BMSCs were detected by qRT-PCR. Cell viability and colon formation of BMSCs were detected. Expressions of ERα, ERβ, AKT, p-AKT, ERK, and p-ERK in BMSCs were detected by western blot. Results showed that echinops significantly increased trabecular interconnectivity, thickness of trabeculae, and connection of trabecula. Echinops significantly increased BMD and E2, but significantly reduced ALP and testosterone in dose-dependent manners. Echinops induced ERα and ERβ in both bone specimens and BMSCs. Echinops enhanced cell viability and ability of colony formation of BMSCs, and increased ERα, ERβ, p-AKT, and p-ERK. Thus, Mongolian echinops reduced bone loss and delayed the occurrence and development of osteoporosis, and increased ERα, ERβ, p-AKT, and P-ERK in BMSCs. These results provide experimental basis for clinical prevention and treatment of postmenopausal osteoporosis by echniops.

Repair of Critical-Sized Mandible Defects in Aged Rat Using Hypoxia Preconditioned BMSCs with Up-regulation of Hif-1α

The repair of bone defects in the geriatric population remains a challenge for modern medicine. Transplantation of bone marrow mesenchymal stem cells (BMSCs) combined with or without biomaterials has been a promising approach to bone restoration and regeneration. Typically, the transplanted BMSCs are cultured under normoxic conditions (21% O2 and 10% serum medium) in vitro. However, the micro-environment of bone defect area is much more severe, in which lower physiological oxygen tension (<1%) and tissue ischemia were present. Therefore, how to improve the survival rate and osteogenesis of transplanted BMSCs at the low oxygenic and ischemic region in vivo is critical. Hypoxia inducible factor-1α (HIF-1α) plays an important role in the tolerance, angiogenesis and osteogenesis of BMSCs during bone regeneration after transplantation. Previous studies have demonstrated that Dimethyloxaloylglycine (DMOG) improves the angiogenic activity of BMSCs. Typically, angiogenesis and osteogenesis are coupled with each other. Therefore, we detected that hypoxia preconditioned BMSCs with the combined treatment of 1% O2 and 0.5mM DMOG showing up-regulation of Hif-1α could enhance the survival rate of BMSCs under severe condition (serum-free medium and 1% O2) in vitro and enhances the angiogenesis and osteogenesis potential of BMSCs under 1% O2 microenvironment in vitro. The hypoxia preconditioned BMSCs were transplanted into critical-sized mandible defects in aged SD rats to test the effectiveness of hypoxic preconditioning approach. We found that hypoxia preconditioned BMSCs improved the repair of critical-sized mandible defects in vivo. These data showed that hypoxia preconditioned BMSCs with the up-regulation of Hif-1α have the potential of enhancing the bone healing process in geriatric individuals.

Sleep apnea and femoral neck BMD among Singaporean mid-life women

The relationship between sleep apnea and bone health remains controversial. This study explored the relationship between sleep apnea and femoral neck BMD in midlife Asian women. Partner-witnessed apnea predicted higher femoral neck BMD, an effect validated by the STOP index. Our findings suggest that sleep apnea may protect bone health.

PURPOSE

The menopause transition is associated with decline in bone mineral density (BMD) and sleep quality. However, any relationship between these two factors remains controversial. This study explored the association between sleep apnea and femoral neck BMD in middle-aged women.

METHODS

Participants (n = 1201) aged 45-69 years attending well-women visits at the National University Hospital, Singapore were recruited. Self-reported breathing discomfort and snoring, partner-witnessed apnea and snoring were assessed from the Pittsburgh Sleep Quality Index. Femoral neck BMD was assessed with dual-energy X-ray absorptiometry scan and classified into tertiles based on T-scores. Factors reported to affect sleep apnea and bone health in medical literature were potential covariates, p < 0.10. Multivariable ordinal regression analyses assessed associations between sleep measures and BMD. To further validate our findings, we analyzed four sleep apnea characteristics from the STOP questionnaire, a screening tool for sleep apnea. All analyses were performed using SPSS version 20.0.

RESULTS

Mean (SD) age of participants was 56.3 (6.2) years. Partner-witnessed apnea predicted higher BMD tertiles (OR per unit increase in severity 1.39, 95% CI [1.02, 1.89]), independent of age, ethnicity, diabetes, BMI, and handgrip strength. This was further corroborated by the STOP index (OR 1.45, 95% CI [1.07, 1.96]).

CONCLUSIONS

This study adds to the literature on sleep apnea and bone health in a non-Caucasian and younger population. Our findings support OSA-associated intermittent hypoxia protecting bone health.

Hypoxia-Inducible Factor-1α Regulates CD55 in Airway Epithelium

Airway epithelial CD55 down-regulation occurs in several hypoxia-associated pulmonary diseases, but the mechanism is unknown. Using in vivo and in vitro assays of pharmacologic inhibition and gene silencing, the current study investigated the role of hypoxia-inducible factor (HIF)-1α in regulating airway epithelial CD55 expression. Hypoxia down-regulated CD55 expression on small-airway epithelial cells in vitro, and in murine lungs in vivo; the latter was associated with local complement activation. Treatment with pharmacologic inhibition or silencing of HIF-1α during hypoxia-recovered CD55 expression in small-airway epithelial cells. HIF-1α overexpression or blockade, in vitro or in vivo, down-regulated CD55 expression. Collectively, these data show a key role for HIF-1α in regulating the expression of CD55 on airway epithelium.

Hypoxia-inducible factor 1-alpha does not regulate osteoclastogenesis but enhances bone resorption activity via prolyl-4-hydroxylase 2

Osteogenic-angiogenic coupling is promoted by the hypoxia-inducible factor 1-alpha (HIF-1α) transcription factor, provoking interest in HIF activation as a therapeutic strategy to improve osteoblast mineralization and treat pathological osteolysis. However, HIF also enhances the bone-resorbing activity of mature osteoclasts. It is therefore essential to determine the full effect(s) of HIF on both the formation and the bone-resorbing function of osteoclasts in order to understand how they might respond to such a strategy. Expression of HIF-1α mRNA and protein increased during osteoclast differentiation from CD14+ monocytic precursors, additionally inducing expression of the HIF-regulated glycolytic enzymes. However, HIF-1α siRNA only moderately affected osteoclast differentiation, accelerating fusion of precursor cells. HIF induction by inhibition of the regulatory prolyl-4-hydroxylase (PHD) enzymes reduced osteoclastogenesis, but was confirmed to enhance bone resorption by mature osteoclasts. Phd2^+/- murine osteoclasts also exhibited enhanced bone resorption, associated with increased expression of resorption-associated Acp5, in comparison with wild-type cells from littermate controls. Phd3^-/- bone marrow precursors displayed accelerated early fusion, mirroring results with HIF-1α siRNA. In vivo, Phd2^+/- and Phd3^-/- mice exhibited reduced trabecular bone mass, associated with reduced mineralization by Phd2^+/- osteoblasts. These data indicate that HIF predominantly functions as a regulator of osteoclast-mediated bone resorption, with little effect on osteoclast differentiation. Inhibition of HIF might therefore represent an alternative strategy to treat diseases characterized by pathological levels of osteolysis. © 2017 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Human type H vessels are a sensitive biomarker of bone mass

Vascularization is fundamental for bone formation and bone tissue homeostasis. However, in human subjects, a direct molecular relationship has not been identified between angiogenesis and agents that promote bone disease or factors related to age. Osteopenia is a condition in which bone mineral density is lower than normal, and it represents a sign of normal aging. Here we tested whether the type H vessel, which was recently identified as strongly positive for CD31 and Endomucin (CD31^hiEmcn^hi) in mice, is an important indicator of aging and osteopenia in human subjects. We found that age-dependent losses of type H vessels in human bone sections conform to the observations in aged mice. The abundance of human type H vessels and osteoprogenitors may be relevant to changes in the skeletal microarchitecture and advanced osteopenia. Furthermore, ovariectomized mice, a widely used model for postmenopausal osteoporosis, exhibited significantly reduced type H vessels accompanied by reduced osteoprogenitors, which is consistent with impaired bone microarchitecture and osteoporosis, suggesting that this feature is an indicator of bone mass independent of aging. More importantly, administration of desferrioxamine led to significantly increased bone mass via enhanced angiogenesis and increased type H vessels in ovariectomized mice. Altogether, these data represent a novel finding that type H vessels are regulated in aged and osteopenia subjects. The abundance of human type H vessels is an early marker of bone loss and represents a potential target for improving bone quality via the induction of type H vessels.

Tumor Necrosis Factor Alpha Promotes Osteoclast Formation Via PI3K/Akt Pathway-Mediated Blimp1 Expression Upregulation

Tumor necrosis factor alpha (TNF-α)-induced osteoclastogenesis have profound effects in states of inflammatory osteolysis such as rheumatoid arthritis, periprosthetic implant loosening, and periodontitis. However, the exact mechanisms by which TNF-α promotes RANKL-induced osteoclast formation remains poorly understood. B lymphocyte-induced maturation protein-1 (Blimp1) is a transcriptional repressor that plays crucial roles in the differentiation and/or function of various kinds of cells including osteoclasts. A novel mechanism was identified where TNF-α-mediated Blimp1 expression, which contributed to RANKL-induced osteoclastogenesis. It is shown that TNF-α could promote the level of Blimp1 expression during osteoclast differentiation. Silencing of Blimp1 in osteoclast precursor cells obviously attenuated the stimulatory effect of TNF-α on osteoclastogenesis. Mechanistically, TNF-α-induced Blimp1 expression was markedly rescued by blocking the PI3K/Akt signaling pathway, which suggested that PI3K/Akt signaling was involved in the regulation of TNF-α-stimulated Blimp1 expression. Taken together, the results established a molecular mechanism of TNF-α-induced osteoclasts differentiation, and provided insights into the potential contribution of Blimp1 in the regulation of osteoclastogenesis by TNF-α. J. Cell. Biochem. 118: 1308-1315, 2017. © 2016 Wiley Periodicals, Inc.

3D-Microarchitectural patterns of Hyperostosis frontalis interna: a micro-computed tomography study in aged women

Although seen frequently during dissections and autopsies, Hyperostosis frontalis interna (HFI) - a morphological pattern of the frontal bone thickening - is often ignored and its nature and development are not yet understood sufficiently. Current macroscopic classification defines four grades/stages of HFI based on the morphological appearance and size of the affected area; however, it is unclear if these stages also depict the successive phases in the HFI development. Here we assessed 3D-microarchitecture of the frontal bone in women with various degrees of HFI expression and in an age- and sex-matched control group, hypothesizing that the bone microarchitecture bears imprints of the pathogenesis of HFI and may clarify the phases of its development. Frontal bone samples were collected during routine autopsies from 20 women with HFI (age: 69.9 ± 11.1 years) and 14 women without HFI (age: 74.1 ± 9.7 years). We classified the HFI samples into four groups, each group demonstrating different macroscopic type or stage of HFI. All samples were scanned by micro-computed tomography to evaluate 3D bone microarchitecture in the following regions of interest: total sample, outer table, diploe and inner table. Our results revealed that, compared to the control group, the women with HFI showed a significantly increased bone volume fraction in the region of diploe, along with significantly thicker and more plate-like shaped trabeculae and reduced trabecular separation and connectivity density. Moreover, the inner table of the frontal bone in women with HFI displayed significantly increased total porosity and mean pore diameter compared to controls. Microstructural reorganization of the frontal bone in women with HFI was also reflected in significantly higher porosity and lower bone volume fraction in the inner vs. outer table due to an increased number of pores larger than 100 μm. The individual comparisons between the control group and different macroscopic stages of HFI revealed significant differences only between the control group and the morphologically most pronounced type of HFI. Our microarchitectural findings demonstrated clear differences between the HFI and the control group in the region of diploe and the inner table. Macroscopic grades of HFI could not be distinguished at the level of bone microarchitecture and their consecutive nature cannot be supported. Rather, our study suggests that only two different types of HFI (moderate and severe HFI) have microstructural justification and should be considered further. It is essential to record HFI systematically in human postmortem subjects to provide more data on the mechanisms of its development.