Impairment of two types of circulating endothelial progenitor cells in patients with glucocorticoid-induced avascular osteonecrosis of the femoral head

Exosomes from bone marrow mesenchymal stem cells ameliorate glucocorticoid-induced osteonecrosis of femoral head by transferring microRNA-210 into bone microvascular endothelial cells

OBJECTIVES

Bone microvascular endothelial cells (BMECs) played an important role in the pathogenesis of glucocorticoid-induced osteonecrosis of femoral head (GCS-ONFH), and exosomes derived from bone marrow mesenchymal stem cells (BMSC-Exos) may provide an effective treatment. This study aimed to evaluate the effects of BMSC-Exos and internal microRNA-210-3p (miRNA-210) on GCS-ONFH in an in vitro hydrocortisone-induced BMECs injury model and an in vivo rat GCS-ONFH model.

METHODS

BMECs, BMSCs and BMSC-Exos were isolated and validated. BMECs after the treatment of hydrocortisone were cocultured with different concentrations of BMSC-Exos, then proliferation, migration, apoptosis and angiogenesis of BMECs were evaluated by CCK-8, Annexin V-FITC/PI, cell scratch and tube formation assays. BMSCs were transfected with miRNA-210 mimics and miRNA-210 inhibitors, then BMSC-ExosmiRNA-210 mimic and BMSC-ExosmiRNA-210 inhibitor secreted from such cells were collected. The differences between BMSC-Exos, BMSC-ExosmiRNA-210 mimic and BMSC-ExosmiRNA-210 inhibitor in protecting BMECs against GCS treatment were analyzed by methods mentioned above. Intramuscular injections of methylprednisolone were performed on Sprague-Dawley rats to establish an animal model of GCS-ONFH, then tail intravenous injections of BMSC-Exos, BMSC-ExosmiRNA-210 mimic or BMSC-ExosmiRNA-210 inhibitor were conducted after methylprednisolone injection. Histological and immunofluorescence staining and micro-CT were performed to evaluate the effects of BMSC-Exos and internal miRNA-210 on the in vivo GCS-ONFH model.

RESULTS

Different concentrations of BMSC-Exos, especially high concentration of BMSC-Exos, could enhance the proliferation, migration and angiogenesis ability and reduce the apoptosis rates of BMECs treated with GCS. Compared with BMSC-Exos, BMSC-ExosmiRNA-210 mimic could further enhance the proliferation, migration and angiogenesis ability and reduce the apoptosis rates of BMECs, while BMECs in the GCS + BMSC-ExosmiRNA-210 inhibitor group showed reduced proliferation, migration and angiogenesis ability and higher apoptosis rates. In the rat GCS-ONFH model, BMSC-Exos, especially BMSC-ExosmiRNA-210 mimic, could increase microvascular density and enhance bone remodeling of femoral heads.

CONCLUSIONS

BMSC-Exos containing miRNA-210 could serve as potential therapeutics for protecting BMECs and ameliorating the progression of GCS-ONFH.

Tanshinone I alleviates steroid-induced osteonecrosis of femoral heads and promotes angiogenesis: in vivo and in vitro studies

BACKGROUND

The impaired blood supply to the bones is an important pathological feature of steroid-induced osteonecrosis of the femoral head (SIONFH). Danshen is a Chinese herb that shows therapeutic effects on SIONFH, but the effects of one of its major bioactive constituents, Tanshinone I (TsI), on SIONFH remain unknown. Here, we evaluated the effects of TsI on SIONFH, particularly focusing on its effects on angiogenesis, in in vivo and in vitro research.

METHODS

SIONFH was induced in Sprague-Dawley rats by an intramuscular injection of methylprednisolone (40 mg/kg) in combination with an intraperitoneal injection of lipopolysaccharide (20 μg/kg). Morphological alterations of the femoral head were observed by dual-energy X-ray absorptiometry and HE staining. Western blot, qRT-PCR, and immunohistochemical/immunofluorescence staining were used to determine gene expression.

RESULTS

TsI (10 mg/kg) alleviated bone loss and rescued the expression of angiogenesis-related molecules (CD31, VWF, VEGF, and VEGFR2) in the femoral heads of SIONFH rats. Notably, TsI rescued the down-regulated expression of SRY-box transcription factor 11 (SOX11) in CD31⁺ endothelial cells in the femoral heads of SIONFH rats. In vitro studies showed that TsI preserved the dexamethasone-harmed angiogenic property (migration and tube formation) of human umbilical vein cells (EA.hy926), suppressed dexamethasone-induced cell apoptosis, reduced pro-apoptotic proteins (cytosolic cytochrome C, Bax, and caspase 3/9) and increased anti-apoptotic protein Bcl-2, whereas silencing of SOX11 reversed these beneficial effects.

CONCLUSIONS

This study demonstrates that TsI alleviates SIONFH and promotes angiogenesis by regulating SOX11 expression. Our work would provide new evidence for the application of TsI to treat SIONFH.

FAR591 promotes the pathogenesis and progression of SONFH by regulating Fos expression to mediate the apoptosis of bone microvascular endothelial cells

The specific pathogenesis of steroid-induced osteonecrosis of the femoral head (SONFH) is still not fully understood, and there is currently no effective early cure. Understanding the role and mechanism of long noncoding RNAs (lncRNAs) in the pathogenesis of SONFH will help reveal the pathogenesis of SONFH and provide new targets for its early prevention and treatment. In this study, we first confirmed that glucocorticoid (GC)-induced apoptosis of bone microvascular endothelial cells (BMECs) is a pre-event in the pathogenesis and progression of SONFH. Then, we identified a new lncRNA in BMECs via lncRNA/mRNA microarray, termed Fos-associated lincRNA ENSRNOT00000088059.1 (FAR591). FAR591 is highly expressed during GC-induced BMEC apoptosis and femoral head necrosis. Knockout of FAR591 effectively blocked the GC-induced apoptosis of BMECs, which then alleviated the damage of GCs to the femoral head microcirculation and inhibited the pathogenesis and progression of SONFH. In contrast, overexpression of FAR591 significantly promoted the GC-induced apoptosis of BMECs, which then aggravated the damage of GCs to the femoral head microcirculation and promoted the pathogenesis and progression of SONFH. Mechanistically, GCs activate the glucocorticoid receptor, which translocates to the nucleus and directly acts on the FAR591 gene promoter to induce FAR591 gene overexpression. Subsequently, FAR591 binds to the Fos gene promoter (-245∼-51) to form a stable RNA:DNA triplet structure and then recruits TATA-box binding protein associated factor 15 and RNA polymerase II to promote Fos expression through transcriptional activation. Fos activates the mitochondrial apoptotic pathway by regulating the expression of Bcl-2 interacting mediator of cell death (Bim) and P53 upregulated modulator of apoptosis (Puma) to mediate GC-induced apoptosis of BMECs, which leads to femoral head microcirculation dysfunction and femoral head necrosis. In conclusion, these results confirm the mechanistic link between lncRNAs and the pathogenesis of SONFH, which helps reveal the pathogenesis of SONFH and provides a new target for the early prevention and treatment of SONFH.

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.

Advances in experimental models of osteonecrosis of the femoral head

Background

Osteonecrosis of the femoral head (ONFH) is a devastating disease affecting young adults, resulting in significant pain, articular surface collapse, and disabling dysfunction. ONFH can be divided into two broad categories: traumatic and non-traumatic. It has been established that ONFH results from an inadequate blood supply that causes the death of osteocytes and bone marrow cells. Nonetheless, the precise mechanism of ONFH remains to be elucidated. In this regard, preclinical animal and cell models to study ONFH have been established to assess the efficacy of various modalities for preventing and treating ONFH. Nevertheless, it should be borne in mind that many models do not share the same physiologic and metabolic characteristics as humans. Therefore, it is necessary to establish a reproducible model that better mimics human disease.

Methods

We systematically reviewed the literatures in regard to ONFH experimental models over the past 30 years. The search was performed in PubMed and Web of Science. Original animal, cell studies with available full-text were included. This review summarizes different methods for developing animal and cell experimental models of ONFH. The advantages, disadvantages and success rates of ONFH models are also discussed. Finally, we provide experimental ONFH model schemes as a reference.

Results

According to the recent literatures, animal models of ONFH include traumatic, non-traumatic and traumatic combined with non-traumatic models. Most researchers prefer to use small animals to establish non-traumatic ONFH models. Indeed, small animal-based non-traumatic ONFH modeling can more easily meet ethical requirements with large samples. Otherwise, gradient concentration or a particular concentration of steroids to induce MSCs or EPCs, through which researchers can develop cell models to study ONFH.

Conclusions

Glucocorticoids in combination with LPS to induce ONFH animal models, which can guarantee a success rate of more than 60% in large samples. Traumatic vascular deprivation combines with non-traumatic steroids to induce ONFH, obtaining success rates ranging from 80% to 100%. However, animals that undergo vascular deprivation surgery may not survive the glucocorticoid induction process. As for cell models, 10-6mol/L Dexamethasone (Dex) to treat bone marrow stem cells, which is optimal for establishing cell models to study ONFH.

The translational potential of this article

This review aims to summarize recent development in experimental models of ONFH and recommended the modeling schemes to verify new models, mechanisms, drugs, surgeries, and biomaterials of ONFH to contribute to the prevention and treatment of ONFH.

C/EBPα regulates the fate of bone marrow mesenchymal stem cells and steroid-induced avascular necrosis of the femoral head by targeting the PPARγ signalling pathway

BACKGROUND

The imbalance of osteogenic/adipogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) is closely related to steroid-induced avascular necrosis of the femoral head (SANFH). We aimed to investigate the epigenetic mechanism of intramedullary fat accumulation and continuous osteonecrosis after glucocorticoid (GC) withdrawal in SANFH.

METHODS

An SANFH model was established in SD rats, which received an intermittent high GC dose for the first 4 weeks followed by an additional 4 weeks without GC. We explored the synergistic effects and mechanisms of C/EBPα and PPARγ on the differentiation of BMSCs by lentivirus-mediated gene knockdown and overexpression assays. A chromatin immunoprecipitation assay was performed to identify epigenetic modification sites on PPARγ in vivo and in vitro.

RESULTS

In the SANFH model, intramedullary fat was significantly increased, and the transcription factors C/EBPα and PPARγ were upregulated simultaneously in the femoral head. In vitro, C/EBPα promoted adipogenic differentiation of BMSCs by targeting the PPARγ signalling pathway, while overexpression of C/EBPα significantly impaired osteogenic differentiation. Further studies demonstrated that histone H3K27 acetylation of PPARγ played an important role in the epigenetic mechanism underlying SANFH. C/EBPα upregulates the histone H3K27 acetylation level in the PPARγ promoter region by inhibiting HDAC1. Additionally, inhibiting the histone acetylation level of PPARγ effectively prevented adipogenic differentiation, thus slowing the progression of SANFH.

CONCLUSIONS

Our results demonstrate the molecular mechanism by which C/EBPα regulates PPARγ expression by acetylating histones and revealed the epigenetic phenomenon in SANFH for the first time.

Steroid-Induced Osteonecrosis of the Femoral Head: Novel Insight Into the Roles of Bone Endothelial Cells in Pathogenesis and Treatment

Steroid-induced osteonecrosis of the femoral head (SONFH) is a disease characterized by the collapse of the femoral head. SONFH occurs due to the overuse of glucocorticoids (GCs) in patients with immune-related diseases. Among various pathogenesis proposed, the mechanism related to impaired blood vessels is gradually becoming the most convincing hypothesis. Bone endothelial cells including bone microvascular endothelial cells (BMECs) and endothelial progenitor cells (EPCs) play a crucial role in the maintenance of vascular homeostasis. Therefore, bone endothelial cells are key regulators in the occurrence and progression of SONFH. Impaired angiogenesis, abnormal apoptosis, thrombosis and fat embolism caused by the dysfunctions of bone endothelial cells are considered to be the pathogenesis of SONFH. In addition, even with high disability rates, SONFH lacks effective therapeutic approach. Icariin (ICA, a flavonoid extracted from Epimedii Herba), pravastatin, and VO-OHpic (a potent inhibitor of PTEN) are candidate reagents to prevent and treat SONFH through improving above pathological processes. However, these reagents are still in the preclinical stage and will not be widely used temporarily. In this case, bone tissue engineering represented by co-transplantation of bone endothelial cells and bone marrow mesenchymal stem cells (BMSCs) may be another feasible therapeutic strategy.

Protective Effect of Human Umbilical Cord Mesenchymal Stem Cells in Glucocorticoid-induced Osteonecrosis of Femoral Head

OBJECTIVE

To evaluate the effect of human umbilical cord mesenchymal stem cells (hUC-MSCs) on preventing rats from glucocorticoid-induced osteonecrosis of femoral head (GCONFH) in the early stage in vivo and to investigate the possible mechanism of hUC-MSCs in regulating the balance of osteogenesis and adipogenesis.

METHODS

All rats were randomly divided into 3 groups: control group (C group), model group (M group), and intervention group (I group). The model of GC-ONFH was developed by a sequential administration of lipopolysaccharide and methylprednisolone. The rats in the I group were treated with caudal vein injection of hUC-MSCs. Six weeks later, the blood samples were obtained to measure the activity of alkaline phosphatase (ALP) and the content of triglyceride (TG) in serum, and the femoral heads were harvested and observed by hematoxylin-eosin staining, Micro-CT, Western blot and real-time quantitative polymerase chain reaction.

RESULTS

After intervention of hUC-MSCs, the necrosis rate of femoral head decreased from 83% (10/12) to 33% (4/12), the rate of empty bone lacuna was significantly decreased, the activity of ALP increased significantly, the content of TG decreased significantly, the bone density increased obviously, the expression of RUNX2 and Col I increased significantly and the expression of PPARγ decreased significantly.

CONCLUSION

These results revealed that caudal vein injection of hUC-MSCs can effectively reduce the incidence of GC-ONFH in rats by increasing ALP activity and reducing TG content in serum, increasing bone mineral density, promoting the expression of RUNX2 and Col I, and inhibiting the expression of PPARγ.

Calycosin modulates inflammation via suppressing TLR4/NF-κB pathway and promotes bone formation to ameliorate glucocorticoid-induced osteonecrosis of the femoral head in rat

Glucocorticoid (GC) administration is one of the main causes of osteonecrosis of the femoral head (ONFH). Inflammation, especially the TLR4/NF-κB pathway, has been demonstrated to play a pivotal role in the pathogenesis of GC-induced ONFH. Calycosin, the main bioactive extract of Astragali Radix, could substantially regulate the TLR4/NF-κB pathway. Therefore, in this study, we hypothesized that calycosin could exert beneficial effects in GC-induced ONFH. In vitro, effects of calycosin on the osteogenic differentiation of human bone mesenchymal stem cells (hBMSCs) were determined using Alizarin red staining, alkaline phosphatase activity examination, and osteogenic-related gene assay. Meanwhile, inflammatory cytokines were detected by enzyme-linked immunosorbent assay. In vivo, 60 male Sprague-Dawley rats were randomly separated into three groups: the control group, the methylprednisolone (MPS) group, and the MPS + calycosin group. The results showed that calycosin could significantly promote dynamic bone formation and retard TLR4/NF-κB pathway. in vivo investigations indicated that calycosin could decrease the morbidity of ONFH and alleviate pathological manifestations within the femoral head. Meanwhile, calycosin could protect osseous blood supply and facilitate dynamic bone formation. The findings collectively demonstrated that calycosin could ameliorate GC-induced ONFH in rat and might become a potential candidate for pharmaceutical prevention of this intractable disease.

Japanese Orthopaedic Association 2019 Guidelines for osteonecrosis of the femoral head

PURPOSE

The Clinical Practice Guidelines for Osteonecrosis of the Femoral Head (ONFH) 2019 Edition, written by the working group for ONFH guidelines of the Japanese Investigation Committee (JIC) for ONFH under the auspices of the Japanese Ministry of Health, Labour, and Welfare and endorsed by the Japanese Orthopaedic Association, were published in Japanese in October 2019. The objective of this guideline is to provide a support tool for decision-making between doctors and patients.

METHODS

Procedures for developing this guideline were based on the Medical Information Network Distribution Service Handbook for Clinical Practice Guideline Development 2014, which proposed an appropriate method for preparing clinical guidelines in Japan.

RESULTS

This clinical practice guideline consists of 7 chapters: epidemiology; pathology; diagnosis; conservative therapy; surgical treatment: bone transplantation/cell therapy; surgical treatment: osteotomy; and surgical treatment: hip replacement. Twelve background questions and 13 clinical questions were determined to define the basic features of the disease and to be addressed when deciding treatment in daily practice, respectively.

CONCLUSIONS

The clinical practice guidelines for the ONFH 2019 edition will be useful for physicians, investigators, and medical staff in clinical practice, as well as for patients, during the decision-making process when defining how to treat ONFH.

Effects of hypoxia environment on osteonecrosis of the femoral head in Sprague-Dawley rats

INTRODUCTION

Osteonecrosis of the femoral head (ONFH) is a disease in which the blood supply of the femoral head is interrupted or damaged, resulting in joint dysfunction. Hypoxic environments increase the expression of EPO, VEGF, and HIF causes vascular proliferation and increases the blood supply. It also causes the organism to be in a state of hypercoagulability and increases thrombosis. Therefore, the purpose of this study was to explore the occurrence of ONFH after the use of glucocorticoids (GCs) under conditions of hypoxia tolerance for a long time.

MATERIALS AND METHODS

Sprague-Dawley rats were fed in a hypobaric hypoxic chamber at an altitude of 4000 m, the whole blood viscosity, and plasma viscosity were determined to analyze the blood flow and hemagglutination. Western blotting, polymerase chain reaction, and immunohistochemistry were used to detect EPO, VEGF, CD31, and osteogenesis related proteins. Femoral head angiography was used to examine the local blood supply and micro-CT scanning was used to detect the structure of the bone trabecula.

RESULTS

Under hypoxic environments, the expression of EPO and VEGF increased, which increased the local blood supply of the femoral head, but due to more severe thrombosis, the local blood supply of the femoral head decreased.

CONCLUSIONS

Hypoxic environments can aggravate ONFH in SD rats; this aggravation may be related to the hypercoagulable state of the blood. We suggest that long-term hypoxia should be regarded as one of the risk factors of ONFH and we need to conduct a more extensive epidemiological investigation on the occurrence of ONFH in hypoxic populations.

miR-155-5p regulates mesenchymal stem cell osteogenesis and proliferation by targeting GSK3B in steroid-associated osteonecrosis

microRNAs (miRNAs) have recently been recognized as playing an important role in bone-associated diseases. This study investigated whether the reduced miR-155-5p in steroid-associated osteonecrosis of the femoral head (ONFH) attenuated osteogenic differentiation and cell proliferation by targeting GSK3B. Bone marrow was collected from the proximal femurs of patients with steroid-associated ONFH (n = 10) and patients with new femoral neck fracture (n = 10) and mesenchymal stem cells (MSCs) were isolated. The expression profile, the biological function of miR-155-5p, and the interaction between miR-155-5p and GSK3B were investigated by cell viability measurement, western blot, real-time polymerase chain reaction, luciferase reporter assay, and Alizarin Red S (ARS) staining of MSCs. The MSCs that were obtained from the femoral neck fracture group and from the steroid-associated ONFH group were transfected with or without miR-155-5p. We found that, in ONFH samples, the level of mature miR-155-5p was significantly lower than that of control samples. By inhibiting GSK3B, miR-155-5p promoted the nuclear translocation of β-catenin, increased the expression of osteogenesis-related genes, and facilitated the proliferation and differentiation of MSCs. Restoring the expression of GSK3B in MSCs partially reversed the effect of miR-155-5p. These findings suggest that reduced miR-155-5p in steroid-associated ONFH attenuates osteogenic differentiation and cell proliferation by increased levels of GSK3B and inhibition of Wnt signaling.

PTEN inhibitor VO-OHpic attenuates GC-associated endothelial progenitor cell dysfunction and osteonecrosis of the femoral head via activating Nrf2 signaling and inhibiting mitochondrial apoptosis pathway

Background

Glucocorticoid (GC)-associated osteonecrosis of the femoral head (ONFH) is the most common in non-traumatic ONFH. Despite a strong relationship between GC and ONFH, the detailed mechanisms have remained elusive. Recent studies have shown that GC could directly injure the blood vessels and reduce blood supply in the femoral head. Endothelial progenitor cells (EPCs), which were inhibited quantitatively and functionally during ONFH, play an important role in maintaining the normal structure and function of vascular endothelium. Phosphatase and tensin homolog (PTEN) is a tumor suppressor gene that promotes cell apoptosis, and its expression was found to be elevated in GC-associated ONFH patients. However, whether direct inhibition of PTEN attenuates GC-associated apoptosis and dysfunction of the EPCs remains largely unknown.

Methods

We investigated the effect of, VO-OHpic, a potent inhibitor of PTEN, in attenuating GC-associated apoptosis and dysfunction of EPCs and the molecular mechanism. SD rats were used to study the effect of VO-OHpic on angiogenesis and osteonecrosis in vivo.

Results

The results revealed that methylprednisolone (MPS) obviously inhibit angiogenesis of EPCs by inducing apoptosis, destroying the normal mitochondrial structure, and disrupting function of mitochondria. VO-OHpic treatment is able to reverse the harmful effects by inhibiting the mitochondrial apoptosis pathway and activating the NF-E2-related factor 2 (Nrf2) signaling. Si-Nrf2 transfection significantly reduced the protective effects of VO-OHpic on EPCs. Our in vivo studies also showed that intraperitoneal injection of VO-OHpic obviously attenuates the osteonecrosis of the femoral head induced by MPS and potently increases the blood supply in the femoral head.

Conclusion

Taken together, the data suggests that inhibition of PTEN with VO-OHpic attenuates apoptosis and promotes angiogenesis of EPCs in vitro via activating Nrf2 signaling pathway and inhibiting the mitochondrial apoptosis pathway. Moreover, VO-OHpic also mitigates GC-associated ONFH and potentiates angiogenesis in the femoral head.

Therapeutic Applications of Genes and Gene-Engineered Mesenchymal Stem Cells for Femoral Head Necrosis

Osteonecrosis of the femoral head (ONFH) is a common and disabling joint disease. Although there is no clear consensus on the complex pathogenic mechanism of ONFH, trauma, abuse of glucocorticoids, and alcoholism are implicated in its etiology. The therapeutic strategies are still limited, and the clinical outcomes are not satisfactory. Mesenchymal stem cells (MSCs) have been shown to exert a positive impact on ONFH in preclinical experiments and clinical trials. The beneficial properties of MSCs are due, at least in part, to their ability to home to the injured tissue, secretion of paracrine signaling molecules, and multipotentiality. Nevertheless, the regenerative capacity of transplanted cells is impaired by the hostile environment of necrotic tissue in vivo, limiting their clinical efficacy. Recently, genetic engineering has been introduced as an attractive strategy to improve the regenerative properties of MSCs in the treatment of early-stage ONFH. This review summarizes the function of several genes used in the engineering of MSCs for the treatment of ONFH. Further, current challenges and future perspectives of genetic manipulation of MSCs are discussed. The notion of genetically engineered MSCs functioning as a "factory" that can produce a significant amount of multipotent and patient-specific therapeutic product is emphasized.

Silencing MicroRNA-137-3p, which Targets RUNX2 and CXCL12 Prevents Steroid-induced Osteonecrosis of the Femoral Head by Facilitating Osteogenesis and Angiogenesis

The main pathogenesis of steroid-induced osteonecrosis of the femoral head (SONFH) includes decreased osteogenic capacity of bone marrow-derived mesenchymal stem cells (BMSCs) and damaged blood supply to the femoral head. MicroRNAs (miRNAs) have been shown to play prominent roles in SONFH development. However, there is no report that a specific miRNA targeting two genes in two different pathogenic pathways has been applied to this disease. The present study investigated the effects of transplantation of miR-137-3p-silenced BMSCs on the prevention and early treatment of SONFH. First, western blotting and dual luciferase assays were employed to verify that miR-137-3p directly targets Runx2 and CXCL12. Then, silencing of miR-137-3p was found to facilitate osteogenic differentiation of BMSCs, which was confirmed by alkaline phosphatase (ALP) staining, alizarin red staining and qRT-PCR. Silencing of miR-137-3p also promoted angiogenesis by human umbilical vein endothelial cells (HUVECs) in the presence or absence of glucocorticoids. Thereafter, overexpression of Runx2 and CXCL12 without the 3′ untranslated region (3′UTR) partially rescued the effects of miR-137-3p on osteogenesis and angiogenesis, respectively. This finding further supported the hypothesis that miR-137-3p exerts its functions partly by regulating the genes, Runx2 and CXCL12. We also demonstrated that SONFH was partially prevented by transplantation of miR-137-3p-silenced BMSCs into a rat model. Micro-CT and histology showed that the transplantation of miR-137-3p-silenced BMSCs significantly improved bone regeneration. Additionally, the results of enzyme-linked immunosorbent assays (ELISA) and flow cytometry suggested that stromal cell-derived factor-1α (SDF-1α) and endothelial progenitor cells (EPCs) participated in the process of vascular repair. Taken together, these findings show that silencing of miR-137-3p directly targets the genes, Runx2 and CXCL12, which can play critical roles in SONFH repair by facilitating osteogenic differentiation and mobilizing EPCs.

Expression Profile Analysis of Differentially Expressed Circular RNAs in Steroid-Induced Osteonecrosis of the Femoral Head

Background

A growing number of studies have suggested that circular RNAs (circRNAs) serve as potential diagnostic biomarkers in many diseases. However, the role of circRNAs in steroid-induced osteonecrosis of the femoral head (SONFH) has not been reported.

Methods

Secondary sequencing was performed to profile circRNA expression in peripheral blood samples from three SONFH patients and three healthy individuals. We confirmed our preliminary findings by qRT-PCR. Bioinformatics analysis was conducted to predict their functions.

Results

The result showed 345 dysregulated circRNAs. qRT-PCR of eight selected circRNAs preliminarily confirmed the results, which were consistent with RNA sequencing. Bioinformatics analyses were performed to predict the functions of circRNAs to target the genes of miRNAs and the networks of circRNA-miRNA-mRNA interactions.

Conclusions

This study provides a new and fundamental circRNA profile of SONFH and a theoretical basis for further studies on the functions of circRNAs in SONFH.

Dexamethasone impairs neurofunctional recovery in rats following traumatic brain injury by reducing circulating endothelial progenitor cells and angiogenesis

The administration of glucocorticoids (GCs) after traumatic brain injury (TBI) is controversial. Clinical evidence reveals the deleterious effects of GCs, but the mechanism remains unclear. Previous studies indicate that GCs impair wound healing by affecting endothelial progenitor cell (EPC) function and inhibiting angiogenesis after skin injury. Thus, we hypothesize that the central deleterious effect of GCs is associated with reduced EPCs and angiogenesis after TBI. Using a controlled cortical impact model, we examined the dynamic changes in circulating EPCs and in the regional microcirculation within 14 days of TBI by flow cytometry analysis and contrast-enhanced ultrasound, respectively. The modified neurological severity score (mNSS) and Morris water maze assay were used to assess neurological recovery. Angiogenesis and hippocampal neuron counts were assessed using immunohistochemistry analysis and hematoxylin and eosin staining 14 days after TBI. Compared with the TBI control group, dexamethasone treatment significantly reduced the number of circulating EPCs on days 1, 3, 7 and 14 (P < 0.05); decreased the number of CD31+ cells, the peak intensity and the number of hippocampal neurons on day 14 (P < 0.05); increased the latency on days 12 and 13 (P < 0.05); and reduced the percentage of time spent in the goal quadrant (P < 0.05) on day 14. Similarly, dexamethasone increased the mNSS on days 7 and 14 (P < 0.05). A strong correlation was observed between these results at 14 days after TBI (r = 0.815-0.892, P < 0.05). These data indicate that DEX inhibits the mobilization of EPC levels and angiogenesis around the lesion after TBI, which may contribute to neuronal cell loss and impaired neurofunction.

Impairment of circulating endothelial progenitor cells (EPCs) in patients with glucocorticoid-induced avascular necrosis of the femoral head and changes of EPCs after glucocorticoid treatment in vitro

Background

Avascular necrosis of the femoral head (ANFH) is a severe complication after high-dose glucocorticoid (GC) administration. The pathogenesis of GC-induced ANFH remains unclear. Though the important role of endothelial progenitor cells (EPCs) in the progression of GC-induced ANFH has been noticed, the effects of GCs on EPCs and the underlying mechanism still need further study.

Methods

Circulating EPCs were obtained from the peripheral blood of ANFH patients and healthy controls by Ficoll-density gradient centrifugation. CD133⁺CD34⁺ cells with DiI-Ac-LDL uptake and FITC-UEA-1 binding were considered as EPCs. Number and functions of EPCs were analyzed by flow cytometry, chemotaxis assay, and tube formation assay. EPCs from healthy controls were also treated by different concentrations of methylprednisolone and prednisolone in vitro, and cell growth and angiogenic function were evaluated. Expression of CXCR7 and its downstream Akt/GSK-3β/Fyn pathway were also analyzed by western blots after cells treated by methylprednisolone in vitro.

Results

The number and functions of EPCs in patients with GC-induced ANFH were significantly decreased. In vitro study showed for the first time that except extremely high concentrations, low to medium concentrations of GCs did not have significant effects on EPCs’ growth. Methylprednisolone and prednisolone both inhibited angiogenesis of EPCs even at low concentrations. Mechanism studies found CXCR7 was downregulated in EPCs after methylprednisolone treatment in vitro. Expression and phosphorylation of Akt and GSK-3β were also decreased with an upregulation of Fyn expression after steroid treatment.

Conclusions

Our study showed that GC-induced ANFH patients have reduced the number and impaired functions of circulating EPCs. GCs did not show a significant effect on the growth of EPCs in vitro except extremely high concentrations of GCs. However, GCs significantly impaired EPC angiogenic function in vitro, even at low concentrations. Our study also suggested that downregulation of CXCR7 and its downstream Akt/GSK-3β/Fyn pathway in EPCs might be a novel mechanism of how GCs suppress EPCs’ angiogenesis.

Hypermethylation of Frizzled1 is associated with Wnt/β-catenin signaling inactivation in mesenchymal stem cells of patients with steroid-associated osteonecrosis

The Wnt/β-catenin signaling pathway is associated with the pathogenesis of steroid-induced osteonecrosis. Our investigation studied whether aberrant CpG island hypermethylation of the FZD1 gene was present in patients with osteonecrosis of the femoral head (ONFH), which results in Wnt/β-catenin signaling inactivation and subsequent cell dysfunction. Bone marrow was collected from the proximal femurs of patients with steroid-associated ONFH (n = 21) and patients with new femoral neck fractures (n = 22), and then mesenchymal stem cells (MSCs) were isolated. We investigated cell viability, the transcription and translation levels of Wnt/β-catenin signaling-related genes, the extent of methylation at CpG islands of the FZD1 promoter, and the osteogenic and adipogenic differentiation abilities of MSCs from the control group and from the ONFH group treated with or without 5′-Aza-dC. According to the results, MSCs from the ONFH group showed a reduced proliferation ability, low transcription and translation levels of FZD1, inhibition of the Wnt/β-catenin signaling pathway, weakened osteogenesis and enhanced adipogenesis ability. Aberrant CpG island hypermethylation of FZD1 was observed in the ONFH group. Treatment with 5’-Aza-dC resulted in de novo FZD1 expression, reactivation of the Wnt/β-catenin signaling pathway and promotion of osteogenesis. Taken together, our study not only provides novel insights into the regulation of the Wnt/β-catenin signaling pathway in this disease but also reveals potential for the use of demethylating agents for the treatment of GC-associated ONFH.

Studies of genetic and molecular signaling processes in the bone disease osteonecrosis, when it is associated with steroid use, reveal insights into disease development and suggest new approaches for treatment. Steroid drugs increase the risk of osteonecrosis, in which bone tissue dies due to insufficient blood supply, but the mechanism of this effect is unclear. Researchers in China, led by Zhibo Sun at Wuhan University, investigated a link between the aberrant addition of methyl groups (CH₃) to the DNA of a specific gene and the onset of the disease. They identified an important molecular signaling pathway in cultured bone marrow cells from patients that is inhibited by the gene methylation. Treating these cells with a drug that inhibits methylation led to reactivation of the gene and the associated signalling pathway that promotes healthy bone formation.

Multiscale Stem Cell Technologies for Osteonecrosis of the Femoral Head

The last couple of decades have seen brilliant progress in stem cell therapies, including native, genetically modified, and engineered stem cells, for osteonecrosis of the femoral head (ONFH). In vitro studies evaluate the effect of endogenous or exogenous factor or gene regulation on osteogenic phenotype maintenance and/or differentiation towards osteogenic lineage. The preclinical and clinical outcomes accelerate the clinical translation. Bone marrow mesenchymal stem cells and adipose-derived stem cells have demonstrated better effects in the treatment of femoral head necrosis. Various materials have been used widely in the ONFH treatment in both preclinical and clinical trials. In a word, in vivo and multiscale efforts are expected to overcome obstacles in the approaches for treating ONFH and provide clinical relevance and commercial strategies in the future. Therefore, we will discuss the above aspects in this paper and present our opinions.

MiR-217 promotes cell proliferation and osteogenic differentiation of BMSCs by targeting DKK1 in steroid-associated osteonecrosis

MicroRNAs (miRNAs) have recently been recognized to play an important role in bone-associated diseases. This study aims to explore the expression profile and biological function of miR-217, which is known to be related to tumor cell proliferation and migration, to the proliferation and osteogenic differentiation of MSCs from the patients with steroid-associated osteonecrosis (ONFH). Bone marrow was obtained from the proximal femur of 10 patients with ONFH and 10 patients with femoral neck fractures. Bone marrow-derived mesenchymal stem cells (MSCs) were isolated and cultured. The expression profile, biological function of miR-217 and the interaction between miR-217 and DKK1 were assayed using cell viability measurement, western blot, Real-time PCR, luciferase reporter assay, Alizarin Red S (ARS) staining. We noted that the expression level of miR-217 was significantly decreased in the ONFH samples compared to the control samples (P < 0.0001). By targeting DKK1, miR-217 promoted nuclear translocation of β-catenin, increased expression of RUNX2, COL1A1 and obviously promoted the proliferation and differentiation of MSCs. Restoring the expression of DKK1 in the MSCs partially reversed the role of miR-217. These findings suggest that miR-217 promotes cell proliferation and osteogenic differentiation by inhibiting DKK1 during the development of steroid-associated osteonecrosis.

Glucocorticoid Impaired the Wound Healing Ability of Endothelial Progenitor Cells by Reducing the Expression of CXCR4 in the PGE2 Pathway

Background: Endothelial progenitor cells (EPCs) can be used to treat ischemic disease in cell-based therapy owing to their neovascularization potential. Glucocorticoids (GCs) have been widely used as strong anti-inflammatory reagents. However, despite their beneficial effects, side effects, such as impairing wound healing are commonly reported with GC-based therapy, and the effects of GC therapy on the wound healing function of EPCs are unclear.

Methods: In this study, we investigated how GC treatment affects the characteristics and wound healing function of EPCs.

Results: We found that GC treatment reduced the proliferative ability of EPCs. In addition, the expression of CXCR4 was dramatically impaired, which suppressed the migration of EPCs. A transplantation study in a flap mouse model revealed that GC-treated EPCs showed a poor homing ability to injured sites and a low activity for recruiting inflammatory cells, which led to wound healing dysfunction. Impairment of prostaglandin E2 (PGE2) synthases, cyclooxygenase (COX2) and microsomal PGE2 synthase 1 (mPEGS1) were identified as being involved in the GC-induced impairment of the CXCR4 expression in EPCs. Treatment with PGE2 rescued the expression of CXCR4 and restored the migration ability of GC-treated EPCs. In addition, the PGE2 signal that activated the PI3K/AKT pathway was identified to be involved in the regulation of CXCR4 in EPCs under the effects of GCs. In addition, similar negative effects of GCs were observed in EPCs under hypoxic conditions. Under hypoxic conditions, GCs independently impaired the PGE2 and HIF2α pathways, which downregulated the expression of CXCR4 in EPCs. Our findings highlighted the influences of GCs on the characteristics and functions of EPCs, suggesting that the use of EPCs for autologous cell transplantation in patients who have used GCs for a long time should be considered carefully.

Role of coagulopathy in glucocorticoid-induced osteonecrosis of the femoral head

The two major theories of glucocorticoid (GC)-induced osteonecrosis of the femoral head (ONFH) are apoptosis and ischaemia. The traditional theory implicates ischaemia as the main aetiological factor because the final common pathway of ONFH is interruption of blood supply to the bone. The most common causes of interruption of blood supply include fat embolism and coagulation disorders. GCs can directly or indirectly lead to coagulation disorders, producing a hypercoagulable state, followed by poor blood flow, ischaemia, and eventually ONFH. This review summarizes the existing knowledge on coagulation disorders in the context of GC-induced ONFH, including hypofibrinolysis and thrombophilia, endothelial cell dysfunction and damage, endothelial cell apoptosis, lipid metabolism, platelet activation, and the effect of anticoagulant treatment.

Neuromuscular electrical stimulation acutely mobilizes endothelial progenitor cells in critically ill patients with sepsis

BACKGROUND

Endothelial progenitor cells (EPCs) have been suggested to constitute a restoration index of the disturbed endothelium in ICU patients. Neuromuscular electric stimulation (NMES) is increasingly employed in ICU to prevent comorbidities such as ICU-acquired weakness, which is related to endothelial dysfunction. The role of NMES to mobilize EPCs has not been investigated yet. The purpose of this study was to explore the NMES-induced effects on mobilization of EPCs in septic ICU patients.

METHODS

Thirty-two septic mechanically ventilated patients (mean ± SD, age 58 ± 14 years) were randomized to one of the two 30-min NMES protocols of different characteristics: a high-frequency (75 Hz, 6 s on-21 s off) or a medium-frequency (45 Hz, 5 s on-12 s off) protocol both applied at maximally tolerated intensity. Blood was sampled before and immediately after the NMES sessions. Different EPCs subpopulations were quantified by cytometry markers CD34(+)/CD133(+)/CD45(-), CD34(+)/CD133(+)/CD45(-)/VEGFR2 (+) and CD34(+)/CD45(-)/VEGFR2 (+).

RESULTS

Overall, CD34(+)/CD133(+)/CD45(-) EPCs increased from 13.5 ± 10.2 to 20.8 ± 16.9 and CD34(+)/CD133(+)/CD45(-)/VEGFR2 (+) EPCs from 3.8 ± 5.2 to 6.4 ± 8.5 cells/10(6) enucleated cells (mean ± SD, p < 0.05). CD34(+)/CD45(-)/VEGFR2 (+) EPCs also increased from 16.5 ± 14.5 to 23.8 ± 19.2 cells/10(6) enucleated cells (mean ± SD, p < 0.05). EPCs mobilization was not affected by NMES protocol and sepsis severity (p > 0.05), while it was related to corticosteroids administration (p < 0.05).

CONCLUSIONS

NMES acutely mobilized endothelial progenitor cells, measures of the endothelial restoration potential, in septic ICU patients.

Cirrhosis is a risk factor for total hip arthroplasty for avascular necrosis

Background and purpose - There are limited data on risk factors for avascular necrosis of the hip, but cirrhosis has been proposed as a risk factor. We examined the association between cirrhosis and incidence of total hip arthroplasty for avascular necrosis. Methods - We used nationwide healthcare data to identify all Danish residents diagnosed with cirrhosis in 1994-2011, and matched them 1:5 by age and sex to non-cirrhotic reference individuals from the general population. We excluded people with a previous total hip arthroplasty, a previous hip fracture, or a previous diagnosis of avascular necrosis. We used stratified Cox regression to estimate the hazard ratio (HR) for cirrhosis patients relative to reference individuals, adjusting for potential confounders. We used the cumulative incidence function to compute 5-year risks. Results - We included 25,421 cirrhosis patients and 114,052 reference individuals. Their median age was 57 years, and 65% were men. 45 cirrhosis patients and 44 reference individuals underwent total hip arthroplasty for avascular necrosis. Cirrhosis patients' HR for a total hip arthroplasty for avascular necrosis was 10 (95% CI: 6-17), yet their 5-year risk of avascular necrosis was only 0.2%. For the reference individuals, the 5-year risk was 0.02%. Interpretation - Cirrhosis is a strong risk factor for avascular necrosis of the hip, but it is rare even in cirrhosis patients.

MicroRNA-134 Contributes to Glucose-Induced Endothelial Cell Dysfunction and This Effect Can Be Reversed by Far-Infrared Irradiation

Diabetes mellitus (DM) is a metabolic disease that is increasing worldwide. Furthermore, it is associated with the deregulation of vascular-related functions, which can develop into major complications among DM patients. Endothelial colony forming cells (ECFCs) have the potential to bring about medical repairs because of their post-natal angiogenic activities; however, such activities are impaired by high glucose- (HG) and the DM-associated conditions. Far-infrared radiation (FIR) transfers energy as heat that is perceived by the thermoreceptors in human skin. Several studies have revealed that FIR improves vascular endothelial functioning and boost angiogenesis. FIR has been used as anti-inflammatory therapy and as a clinical treatment for peripheral circulation improvement. In addition to vascular repair, there is increasing evidence to show that FIR can be applied to a variety of diseases, including cardiovascular disorders, hypertension and arthritis. Yet mechanism of action of FIR and the biomarkers that indicate FIR effects remain unclear. MicroRNA-134 (miR-134-5p) was identified by small RNA sequencing as being increased in high glucose (HG) treated dfECFCs (HG-dfECFCs). Highly expressed miR-134 was also validated in dmECFCs by RT-qPCR and it is associated with impaired angiogenic activities of ECFCs. The functioning of ECFCs is improved by FIR treatment and this occurs via a reduction in the level of miR-134 and an increase in the NRIP1 transcript, a direct target of miR-134. Using a mouse ischemic hindlimb model, the recovery of impaired blood flow in the presence of HG-dfECFCs was improved by FIR pretreatment and this enhanced functionality was decreased when there was miR-134 overexpression in the FIR pretreated HG-dfECFCs. In conclusion, our results reveal that the deregulation of miR-134 is involved in angiogenic defects found in DM patients. FIR treatment improves the angiogenic activity of HG-dfECFCs and dmECFCs and FIR has potential as a treatment for DM. Detection of miR-134 expression in FIR-treated ECFCs should help us to explore further the effectiveness of FIR therapy.

Nontraumatic Osteonecrosis of the Femoral Head: Where Do We Stand Today? A Ten-Year Update

➤ Although multiple theories have been proposed, no one pathophysiologic mechanism has been identified as the etiology for the development of osteonecrosis of the femoral head. However, the basic mechanism involves impaired circulation to a specific area that ultimately becomes necrotic.➤ A variety of nonoperative treatment regimens have been evaluated for the treatment of precollapse disease, with varying success. Prospective, multicenter, randomized trials are needed to evaluate the efficacy of these regimens in altering the natural history of the disease.➤ Joint-preserving procedures are indicated in the treatment of precollapse disease, with several studies showing successful outcomes at mid-term and long-term follow-up.➤ Studies of total joint arthroplasty, once femoral head collapse is present, have described excellent outcomes at greater than ten years of follow-up, which is a major advance and has led to a paradigm shift in treating these patients.➤ The results of hemiresurfacing and total resurfacing arthroplasty have been suboptimal, and these procedures have restricted indications in patients with osteonecrosis of the femoral head.

Nitric oxide content and apoptosis rate in steroid-induced avascular necrosis of the femoral head

The aim of the present study was to explore the effect on nitric oxide (NO) content and osteocyte apoptosis of steroid-induced avascular necrosis of the femoral head (SANFH) in an animal model of SANFH. A total of 40 Japanese white rabbits, 5 months of age and weighing 2.5±0.5 kg, were randomly divided into groups A (hormone + endotoxin group), B (endotoxin + normal saline group), C (normal saline + hormone group) and D (control group). Following the establishment of the model, a blood sample was taken from the heart of each animal and centrifuged; the levels of NO in the serum were detected. The bilateral femoral heads were conventionally dissected, fixed, decalcified and stained with hematoxylin and eosin. Subsequently, the empty bone lacunae were counted under an optical microscope. Changes in osteocyte morphology were observed using electron microscopy and osteocyte apoptosis was detected with a terminal deoxynucleotidyl transferase dUTP nick end labeling assay. The percentage of empty bone lacunae in group A was significantly higher compared with that in groups B, C and D (P<0.01); however, there was no significant difference in percentage among groups B, C and D. The NO content in group A was significantly higher compared with that in groups B, C and D (P<0.01); however, there was no significant difference in NO content among groups B, C and D. The osteocyte apoptosis index in group A was significantly higher compared with that in the other groups (P<0.01); there was no significant difference among groups B, C and D. NO content was positively correlated with osteocyte apoptosis index (r=0.707). Thus, the present study found that NO content and the osteocyte apoptosis index were increased in SANFH, and that they play an important role in SANFH. The content of NO was positively correlated with the osteocyte apoptosis index, indicating that NO induces apoptosis.

Icariin may benefit the mesenchymal stem cells of patients with steroid-associated osteonecrosis by ABCB1-promoter demethylation: a preliminary study

In this study, we found out a previously undefined function of icariin which restored the dynamic balance between osteogenic and adipogenic differentiation of mesenchymal stem cells (MSCs) in patients with osteonecrosis of femoral head (ONFH) via ABCB1-promoter demethylation. These findings provided important information regarding potential implication of icariin targeting epigenetic changes for the treatment of steroid -associated ONFH.

INTRODUCTION

Here, we investigated whether icariin can also exert a beneficial role in the reactivation of MSCs in the patients with steroid-associated ONFH via ABCB1-promoter demethylation.

METHODS

Bone marrow was collected from the proximal femur in patients with steroid-associated ONFH (n = 20) and patients with new femoral neck fractures (n = 22), and then MSCs were isolated. We investigated cell viability, intracellular reactive oxygen species (ROS) level, mitochondrial membrane potential (MMP), P-glycoprotein (P-gp) activity, the transcript levels of ABCB1 and oxidative stress-related genes, methylation extent at CpG islands of ABCB1 promoter, and osteogenic and adipogenic differentiation ability of MSCs from the femoral neck fractures group and from the steroid-associated ONFH group treated with or without icariin.

RESULTS

We observed that MSCs from the steroid-associated ONFH group showed reduced proliferation ability, elevated ROS level, depressed MMP, weakened osteogenesis, and enhanced adipogenesis while low P-gp activity, transcription level of ABCB1, and oxidative stress-related genes as well as aberrant CpG islands hypermethylation of ABCB1 were also noted in steroid-associated ONFH group. Treatment with icariin obviously induced de novo P-gp expression, decreased oxidative stress, and promoted osteogenesis.

CONCLUSION

Icariin may be a potential drug targeting epigenetic changes for the treatment of steroid-associated ONFH.

ABCB1 gene polymorphisms and glucocorticoid-induced avascular necrosis of the femoral head susceptibility: a meta-analysis

BACKGROUND

The results of studies on association between ABCB1 gene polymorphisms and glucocorticoid-induced avascular necrosis of the femoral head (GANFH) are controversial. This study aimed to assess the association of ABCB1 gene polymorphisms with the risk of GANFH by conducting a meta-analysis.

MATERIAL AND METHODS

The PubMed, Cochrane Library, and Embase databases were searched for papers that describe the association between ABCB1 polymorphisms and GANFH risk. Summary odds ratios and 95% confidence intervals (CI) were estimated based on a fixed-effects model or random-effects model, depending on the absence or presence of significant heterogeneity.

RESULTS

A total of 5 studies and 833 patients were included in the final analysis. Significant differences were found for rs1045642 polymorphism in the comparisons of CC vs. CT+TT (OR, 1.462; 95% CI, 1.066-2.007; P=0.019), and rs2032582 polymorphism in the comparisons of GG vs. G(TA)+(TA)(TA) (OR, 1.548; 95% CI,1.063-2.255; P=0.023).

CONCLUSIONS

The study demonstrated that the ABCB1 polymorphisms (rs1045642 and rs2032582) significantly reduced the risk of GANFH.

Aberrant CpG islands' hypermethylation of ABCB1 in mesenchymal stem cells of patients with steroid-associated osteonecrosis

OBJECTIVE

Patients carrying an ABCB1 polymorphism have a higher risk of developing osteonecrosis of the femoral head (ONFH). We investigated whether aberrant dinucleotide CpG islands' hypermethylation of ABCB1 gene existed in mesenchymal stem cells (MSC) of patients with ONFH, which results in cell dysfunction.

METHODS

Bone marrow was collected from the proximal femur of patients with glucocorticoid (GC)-associated ONFH (n = 22) and patients with new femoral neck fractures (n = 25). MSC were isolated by density gradient centrifugation. We investigated cell viability, intracellular reactive oxygen species (ROS) level, mitochondrial membrane potential (MMP), the amount of P-glycoprotein (P-gp) and ABCB1 transcripts, and methylation at CpG islands of ABCB1 promoter from both the femoral neck fractures group and the GC-associated ONFH group treated with or without the DNA methyltransferase inhibitor, 5'-Aza-2-deoxycytidine (5'-Aza-dC).

RESULTS

We observed that MSC from GC-associated ONFH groups showed reduced proliferation ability, elevated ROS levels, and depressed MMP when compared with the other 2 groups. Low levels of P-gp and ABCB1 transcript, as well as ABCB1 gene hypermethylation, in patients with GC-associated ONFH were also noted. Treatment with 5'-Aza-dC rapidly restored ABCB1 expression. Analysis of general expression revealed that aberrant CpG islands' hypermethylation of ABCB1 caused sensitivity to GC and induced changes in the proliferation and oxidative stress of MSC under GC administration.

CONCLUSION

These data suggest that aberrant CpG islands' hypermethylation of ABCB1 gene may be responsible for individual differences in the development of GC-associated ONFH.