Involvement of MicroRNA-210 Demethylation in Steroid-associated 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.

SOX17 is a Critical Factor in Maintaining Endothelial Function in Pulmonary Hypertension by an Exosome-Mediated Autocrine Manner

Endothelial dysfunction is considered a predominant driver for pulmonary vascular remodeling in pulmonary hypertension (PH). SOX17, a key regulator of vascular homoeostasis, has been found to harbor mutations in PH patients, which are associated with PH susceptibility. Here, this study explores whether SOX17 mediates the autocrine activity of pulmonary artery ECs to maintain endothelial function and vascular homeostasis in PH and its underlying mechanism. It is found that SOX17 expression is downregulated in the endothelium of remodeled pulmonary arteries in IPH patients and SU5416/hypoxia (Su/hypo)-induced PH mice as well as dysfunctional HPAECs. Endothelial knockdown of SOX17 accelerates the progression of Su/hypo-induced PH in mice. SOX17 overexpression in the pulmonary endothelium of mice attenuates Su/hypo-induced PH. SOX17-associated exosomes block the proliferation, apoptosis, and inflammation of HPAECs, preventing pulmonary arterial remodeling and Su/hypo-induced PH. Mechanistic analyses demonstrates that overexpressing SOX17 promotes the exosome-mediated release of miR-224-5p and miR-361-3p, which are internalized by injured HPAECs in an autocrine manner, ultimately repressing the upregulation of NR4A3 and PCSK9 genes and improving endothelial function. These results suggest that SOX17 is a key gene in maintaining endothelial function and vascular homeostasis in PH through regulating exosomal miRNAs in an autocrine manner.

miR-210-3p protects against osteoarthritis through inhibiting subchondral angiogenesis by targeting the expression of TGFBR1 and ID4

Excessive subchondral angiogenesis is a key pathological feature of osteoarthritis (OA), as it alters the balance of subchondral bone remodeling and causes progressive cartilage degradation. We previously found that miR-210-3p correlates negatively with angiogenesis, though the specific mechanism of miR-210-3p-related angiogenesis in subchondral bone during OA progression remains unclear. This study was conducted to identify the miR-210-3p-modulating subchondral angiogenesis mechanism in OA and investigate its therapeutic effect. We found that miR-210-3p expression correlated negatively with subchondral endomucin positive (Emcn+) vasculature in the knee joints of OA mice. miR-210-3p overexpression regulated the angiogenic ability of endothelial cells (ECs) under hypoxic conditions in vitro. Mechanistically, miR-210-3p inhibited ECs angiogenesis by suppressing transforming growth factor beta receptor 1 (TGFBR1) mRNA translation and degrading DNA-binding inhibitor 4 (ID4) mRNA. In addition, TGFBR1 downregulated the expression of ID4. Reduced ID4 levels led to a negative feedback regulation of TGFBR1, enhancing the inhibitory effect of miR-210-3p on angiogenesis. In OA mice, miR-210-3p overexpression in ECs via adeno-associated virus (AAV) alleviated cartilage degradation, suppressed the type 17 immune response and relieved symptoms by attenuating subchondral Emcn+ vasculature and subchondral bone remodeling. In conclusion, we identified a miR-210-3p/TGFBR1/ID4 axis in subchondral ECs that modulates OA progression via subchondral angiogenesis, representing a potential OA therapy target.

Therapeutic perspectives of exosomes in glucocorticoid-induced osteoarthrosis

Exosomes are widely involved in a variety of physiological and pathological processes. These important roles are also hidden in the physiological processes related to bone. Chondrocytes, osteoblasts, synovial fibroblasts, and bone marrow mesenchymal stem cells produce and secrete exosomes, thereby affecting the biology process of target cells. Furthermore, in the primary pathogenesis of osteoarthrosis induced by steroid hormones, mainly involve glucocorticoid (GC), the exosomes have also widely participated. Therefore, exosomes may also play an important role in glucocorticoid-induced osteoarthrosis and serve as a promising treatment for early intervention of osteoarthrosis in addition to playing a regulatory role in malignant tumors. This review summarizes the previous results on this direction, systematically combs the role and therapeutic potential of exosomes in GC-induced osteoarthrosis, discusses the potential role of exosomes in the treatment and prevention of GC-induced osteoarthrosis, and reveals the current challenges we confronted.

Lipid metabolism analysis for peripheral blood in patients with alcoholinduced and steroidinduced osteonecrosis of the femoral head

OBJECTIVES

Osteonecrosis of the femoral head (ONFH), also known as vascular necrosis of the femoral head, is combined with lipid metabolism disorders in most patients. This study aims to explore the lipid metabolism profiles in different subtypes of ONFH.

METHODS

The subjects were divided into an alcohol-induced osteonecrosis of the femoral head (AONFH) group, a steroid-induced osteonecrosis of the femoral head (SONFH) group, and a normal control (NC) group (n=16, 29, and 32, respectively). Ultra-performance liquid chromatography-mass spectrometry/mass spectrometry (UPLC-MS/MS) was used to detect the lipidomics analysis in the peripheral blood samples of subjects and identify the underlying biomarkers. The samples were preprocessed, the partial least squares discriminant analysis (PLS-DA) was adopted, and the variable importance for the projection (VIP) values were calculated to measure the expression pattern of each lipid metabolite and observe the influence and explanatory power of the expression pattern of each lipid metabolite on the classification and discrimination between the different groups. The lipid metabolites with fold change (FC)>2, P<0.05 and VIP>1 in the different groups were screened as differential lipids. Among them, the differential lipids co-existing in the AONFH group and the SONFH group were regarded as common differential lipids for ONFH, and the differential lipids that exist separately were regarded as specific differential lipids in the AONFH group or the SONFH group. Binary logistic regression was used to evaluate the diagnostic value of differential lipid metabolites on the basis of the receiver operator characteristic (ROC) curve analysis. Based on the disease stage information, the correlation between the differential lipids and the disease stage was analyzed in the AONFH group and the SONFH group.

RESULTS

In this study, 1 358 lipid metabolites were detected in each plasma sample. Compared with the NC group, there were significant difference in the expression patterns of lipid metabolism profiles in the AONFH group and the SONFH group. A total of 62 and 64 differential lipid metabolites were screened in the AONFH and SONFH patients (FC>2, P<0.05, VIP>1) respectively, and these differential lipids were mainly up-regulated in the disease samples. Nine differential lipid metabolites were further identified, which were shared by the AONFH group and the SONFH group; the area under the curve (AUC) in 6 kinds of lipid components was greater than 0.7, including 1-myristoyl-2-docosahexaenoyl-sn-glycero-3-phosphocholine, hypoxanthin, serotonin, PE (19:0/22:5), PE (19:0/22:5), and cholest-5-en-3-yl beta-D-glucopyranosiduronic acid. Fifty-three specific differential lipid metabolites were identified in the AONFH group, and 55 specific differential lipid metabolites were identified in the SONFH group. The AUC in 6 kinds of lipid components was greater than 0.9, including 1D-myo-Inositol 1,2-cyclic phosphate, L-pyroglutamic acid, DL-carnitine, 8-amino-7-oxononanoic acid, Clobetasol, and presqualene diphosphate. In the AONFH group, there were 9 differential lipid metabolites related to the disease stages, including LPG 18:1, serotonin, PC (22:4e/23:0), PC (19:2/18:5), hypoxanthin, PE (18:1/20:3), LPE 18:1, 1-stearoyl-2-arachidonoyl-sn-glycerol, and PE (16:0/18:1); with AONFH disease progresses from I/II stages to III/IV stages, the relative content of these 9 differential lipid metabolites was increased. In the SONFH group, 8 differential lipid metabolites were found to be related to the stage of the disease, including TM6076000, 4-(1,1-dimethylpropyl)phenol, D-617, asarone, phenylac-gln-OH, creatine, leu-pro, and 8-amino-7-oxononanoic acid; and with the SONFH progressed from stage I/II to stage III/IV, the content of these 8 differential lipid metabolites were gradually increased.

CONCLUSIONS

This study analyzes the characteristics of the plasma lipid metabolism profile in the AONFH and SONFH patients, and which identifies the differential lipid metabolites related to disease diagnosis and evaluation. These results provide evidence for exploring lipid metabolism alterations and the mining of novel lipid biomarkers for the ONFH.

miR-210 hypoxamiR in Angiogenesis and Diabetes

Significance: microRNA-210 (miR-210) is the master hypoxia-inducible miRNA (hypoxamiR) since it has been found to be significantly upregulated under hypoxia in a wide range of cell types. Recent advances: Gene ontology analysis of its targets indicates that miR-210 modulates several aspects of cellular response to hypoxia. Due to its high pleiotropy, miR-210 not only plays a protective role by fine-tuning mitochondrial metabolism and inhibiting red-ox imbalance and apoptosis, but it can also promote cell proliferation, differentiation, and migration, substantially contributing to angiogenesis. Critical issues: As most miRNAs, modulating different gene pathways, also miR-210 can potentially lead to different and even opposite effects, depending on the physio-pathological contexts in which it acts. Future direction: The use of miRNAs as therapeutics is a fast growing field. This review aimed at highlighting the role of miR-210 in angiogenesis in the context of ischemic cardiovascular diseases and diabetes in order to clarify the molecular mechanisms underpinning miR-210 action. Particular attention will be dedicated to experimentally validated miR-210 direct targets involved in cellular processes related to angiogenesis and diabetes mellitus, such as mitochondrial metabolism, redox balance, apoptosis, migration, and adhesion. Antioxid. Redox Signal. 36, 685-706.

Novel miR-5088-5p promotes malignancy of breast cancer by inhibiting DBC2

Breast cancer is the most common female cancer in the world. Despite the active research on metastatic breast cancer, the treatment of breast cancer patients is still difficult because the mechanism is not well known. Therefore, research on new targets and mechanisms for diagnosis and treatment of breast cancer patients is required. On the other hand, microRNA (miRNA) has the advantage of simultaneously regulating the expression of many target genes, so it has been proposed as an effective biomarker for the treatment of various diseases including cancer. This study analyzed the role and mechanism of DBC2 (deleted in breast cancer 2), which is known to inhibit its expression in breast cancer, and proposed microRNA (miR)-5088-5p, which regulates its expression. It was revealed that the biogenesis of miR-5088-5p was upregulated by hypomethylation of its promoter, promoted by Fyn, and was involved in malignancy in breast cancer. With the use of the cellular level, clinical samples, and published data, we verified that the expression patterns of DBC2 and miR-5088-5p were negatively related, suggesting the potential as novel biomarkers for the diagnosis of breast cancer patients.

Histopathological and immunohistochemical aspects of bone tissue in aseptic necrosis of the femoral head

Femoral head osteonecrosis, also known as avascular necrosis, is a disease with a multifactorial etiology, characterized by a profound change of bone architecture, which leads to the diminishing of bone resistance and femoral head collapse. The main causes that lead to femoral head necrosis are represented by the decrease of local blood perfusion and increase of intraosseous pressure, because of an excessive development of adipose tissue in the areolas of the trabecular bone tissue in the femoral head. The histopathological and immunohistochemical (IHC) study performed by us showed that most of bone trabeculae were damaged by necrotic-involutive processes, their sizes being reduced, both regarding their length and their diameter; generally, the spans were thin, fragmented, distanced among them, which led to the occurrence of some large areolar cavities, full of conjunctive tissue, rich in adipocytes. Some of the residual bone spans even presented microfractures. In the structure of the trabecular bone tissue, numerous cavities showed lack of content, which indicates the death of osteocytes inside, while the endosteum appeared very thin, with few osteoprogenitor, flattened, difficult to highlight cells. The IHC study showed a low reaction of the bone reparatory processes and a reduced multiplication capacity of bone cells involved in the remodeling and remake of the diseased bone tissue. Nevertheless, there were identified numerous young conjunctive cells (fibroblasts, myofibroblasts), positive to proliferating cell nuclear antigen (PCNA), cells that have a high capacity of multiplication, participating in the formation of a fibrous conjunctive tissue (sclerous) instead of the damaged bone trabeculae. The formation of fibrous conjunctive tissue causes the reduction of mechanical resistance of the femoral head and its collapse. The IHC study of the microvascularization in the femoral head damaged by aseptic osteonecrosis showed the presence of a very low vascular system, both in the residual bone trabeculae and in the sclerous conjunctive tissue. Of the inflammatory cells present in the spongy bone tissue of the femoral head affected by osteonecrosis, the most numerous ones were the macrophages. Both macrophages and T- and B-lymphocytes had a heterogenous distribution.

Non-coding RNA Identification in Osteonecrosis of the Femoral Head Using Competitive Endogenous RNA Network Analysis

OBJECTIVE

To investigate the regulatory network of long non-coding RNA (lncRNA) as competing endogenous RNAs (ceRNAs) in osteonecrosis of the femoral head (ONFH).

METHODS

The gene expression profile GSE74089 of ONFH and microRNA (miRNA) expression profile of GSE89587 were obtained from the Gene Expression Omnibus (GEO) database. The GSE74089 contained four ONFH samples and four controls. The GSE89587 included 10 ONFH samples and 10 control samples. The differentially expressed lncRNAs (DE-lncRNAs) and DE-mRNAs between ONFH group and control group were identified from GSE74089 using the limma package based on criteria of adjusted P value <0.05 and |log fold change (FC)| ≥2. The DEmiRNAs between ONFH group and control group were screened from GSE89587 on the basis of adjusted P value <0.05. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway for DE-mRNAs were analyzed using DAVID 6.7 and GSEA 3.0, respectively. Coexpressed lncRNA-mRNA pairs were identified by corr.test method in R based on the criteria of adjusted P value <0.01 and |r| ≥ 0.9. A ceRNA network was constructed and visualized using cytoscape 3.7.0 by integrating the DE-lncRNA, DE-miRNA, and DEmRNA data. The key mRNAs and lncRNAs in the ceRNA network were further validated in an independent dataset of GSE123568.

RESULTS

Based on our analysis, a total of 28 DE-lncRNAs, 1403 DE-mRNAs, and 134 DE-miRNAs were identified, respectively. The DE-mRNAs were significantly enriched in the function of "skeletal system development," "collagen fibril organization," "blood vessel development," and "regulation of nervous system development." Besides, 72 KEGG pathways, including eight active pathways and 64 suppressed pathways were identified, including which immune pathway was the most significantly activated one and which ribosome-related function was the most suppressed. A co-expression network including 161 DE-mRNAs and 16 DE-lncRNAs was built. Highly connected nodes were identified among lncRNAs such as H19, C20orf203, LINC00355, SFTA3, CRNDE, CASC2, LINC00494, C9orf163, C10orf91, and LINC00301. The ceRNA network indicated that lncRNA H19 functioned as a ceRNA of hsa-miR-519b-3p and hsa-miR-296-5p in ANKH and ECHDC1 regulation; lncRNA C9orf163 functioned as a ceRNA of hsa-miR-424-5p in CCNT1 regulation. The expression trends of ANKH, CCNT1, and C9orf163 were successfully validated in independent dataset of GSE123568.

CONCLUSION

The ceRNAs of lncRNA H19- hsa-miR-519b-3p/hsa-miR-296-5p-ANKH and lncRNA c9orf163- hsa-miR-424-5p-CCNT1 might play important roles in ONFH development. Our research provided an understanding of the important role of lncRNA-related ceRNAs in ONFH.

Osteogenic Effect of tsRNA-10277-Loaded Exosome Derived from Bone Mesenchymal Stem Cells on Steroid-Induced Osteonecrosis of the Femoral Head

Purpose

Steroids are known to inhibit osteogenic differentiation and subsequent bone formation in bone mesenchymal stem cells (BMSCs). However, little is known about the role of BMSC exosomes (Exos) and tRNA-derived small RNAs (tsRNAs) in steroid-induced osteonecrosis of the femoral head (SONFH). The objective of this study was to characterize the tsRNA expression profiles of plasma Exos collected from SONFH patients and healthy individuals using small RNA sequencing and further explore the effect of BMSC Exos carrying specific tsRNAs on osteogenic differentiation.

Materials and Methods

Based on insights from small RNA sequencing, five differentially expressed (DE) tsRNAs were selected for quantitative real-time polymerase chain reaction (qRT-PCR). The regulatory networks associated with interactions of the tsRNAs-mRNA-pathways were reconstructed. The osteogenesis and adipogenesis in BMSCs were detected via ALP and oil red O staining methods, respectively.

Results

A total of 345 DE small RNAs were screened, including 223 DE tsRNAs. The DE tsRNAs were enriched in Wnt signaling pathway and osteogenic differentiation. We identified five DE tsRNAs, among which tsRNA-10277 was significantly downregulated in plasma Exos of SONFH patients compared to that in healthy individuals. Dexamethasone-induced BMSCs were associated with an increased fraction of lipid droplets and decreased osteogenic differentiation, whereas BMSC Exos restored the osteogenic differentiation of that. After treatment of tsRNA-10277-loaded BMSC Exos, the lipid droplets and osteogenic differentiation ability were found to be decreased and enhanced in dexamethasone-induced BMSCs, respectively.

Conclusion

An altered tsRNA profile might be involved in the pathophysiology of SONFH. tsRNA-10277-loaded BMSC Exos enhanced osteogenic differentiation ability of dexamethasone-induced BMSCs. Our results provide novel insights into the osteogenic effect of BMSC Exos carrying specific tsRNAs on SONFH.

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.

Epigenetic Regulation of Skeletal Tissue Integrity and Osteoporosis Development

Bone turnover is sophisticatedly balanced by a dynamic coupling of bone formation and resorption at various rates. The orchestration of this continuous remodeling of the skeleton further affects other skeletal tissues through organ crosstalk. Chronic excessive bone resorption compromises bone mass and its porous microstructure as well as proper biomechanics. This accelerates the development of osteoporotic disorders, a leading cause of skeletal degeneration-associated disability and premature death. Bone-forming cells play important roles in maintaining bone deposit and osteoclastic resorption. A poor organelle machinery, such as mitochondrial dysfunction, endoplasmic reticulum stress, and defective autophagy, etc., dysregulates growth factor secretion, mineralization matrix production, or osteoclast-regulatory capacity in osteoblastic cells. A plethora of epigenetic pathways regulate bone formation, skeletal integrity, and the development of osteoporosis. MicroRNAs inhibit protein translation by binding the 3'-untranslated region of mRNAs or promote translation through post-transcriptional pathways. DNA methylation and post-translational modification of histones alter the chromatin structure, hindering histone enrichment in promoter regions. MicroRNA-processing enzymes and DNA as well as histone modification enzymes catalyze these modifying reactions. Gain and loss of these epigenetic modifiers in bone-forming cells affect their epigenetic landscapes, influencing bone homeostasis, microarchitectural integrity, and osteoporotic changes. This article conveys productive insights into biological roles of DNA methylation, microRNA, and histone modification and highlights their interactions during skeletal development and bone loss under physiological and pathological conditions.

The pathogenesis, diagnosis and clinical manifestations of steroid-induced osteonecrosis

Corticosteroid associated osteonecrosis is bone death resulting from the use of chronic glucocorticoids and most commonly affects the femoral head, although the bones such as around knee joint, wrist joint and ankle joint can be affected. The pathogenesis is likely multifactorial, with genetic and environmental factors playing a role. Epigenetics may be the mechanism by which environment exerts it effects. In spite of recent discoveries, the exact pathogenesis of corticosteroid associated osteonecrosis is unknown. Over the past few years, more miRNA's have been found to be associated with osteonecrosis. The older mechanisms such as a coagulopathy, abnormalities in apoptosis and lipid metabolism dysfunction are still believed to play a role. The role of inflammatory pathways including the PDK1/AKT/mTOR signaling pathway, the PERK and Parkin pathways have been increasingly recognized as playing a mechanistic role. Histological damage to the joint can occur before the presence of symptoms. The most common symptoms are pain and an inability to bear weight. Differential diagnosis includes infection, bone marrow edema syndrome or subchondral fracture. Early detection is important for successful management of the condition. MRI is the best radiologic technique to diagnosis femoral head osteonecrosis. Multiple staging systems for osteonecrosis have been used over the years, including the Ficat and Arlet system and the Steinberg criteria. The later stages of these staging systems are irreversible. Both non-surgical (conservative) and surgical modes of therapy are used in the treatment of osteonecrosis.

Therapeutic potential of KLF2-induced exosomal microRNAs in pulmonary hypertension

Pulmonary arterial hypertension (PAH) is a severe disorder of lung vasculature that causes right heart failure. Homoeostatic effects of flow-activated transcription factor Krüppel-like factor 2 (KLF2) are compromised in PAH. Here, we show that KLF2-induced exosomal microRNAs, miR-181a-5p and miR-324-5p act together to attenuate pulmonary vascular remodelling and that their actions are mediated by Notch4 and ETS1 and other key regulators of vascular homoeostasis. Expressions of KLF2, miR-181a-5p and miR-324-5p are reduced, while levels of their target genes are elevated in pre-clinical PAH, idiopathic PAH and heritable PAH with missense p.H288Y KLF2 mutation. Therapeutic supplementation of miR-181a-5p and miR-324-5p reduces proliferative and angiogenic responses in patient-derived cells and attenuates disease progression in PAH mice. This study shows that reduced KLF2 signalling is a common feature of human PAH and highlights the potential therapeutic role of KLF2-regulated exosomal miRNAs in PAH and other diseases associated with vascular remodelling.

Microarray profiling of circular RNAs in steroid-associated osteonecrosis of the femoral head: Observational study

The aim of this study was to elucidate the molecular mechanisms and to identify the differential expression of circular RNAs (circRNAs) for steroid-associated osteonecrosis of the femoral head (SONFH) using bioinformatics analysis.circRNA microarray was performed with 3 SONFH tissues and the adjacent normal tissues, and differentially expressed circRNA were identified by limma package in R. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses were performed using the Database for Annotation, Visualization and Integrated Discovery database. In addition, a differentially expressed genes (DEG)-associated circRNA/microRNA (miRNA) interaction was predicted by combination of TargetScan and miRanda, and the circRNA/miRNA interaction network generated by the cytoscape software.A total of 647 differentially expressed circRNAs, including 433 upregulated and 214 downregulated circRNA were identified. The most enriched GO terms for upregulated and downregulated circRNA were extracellular matrix organization and leukocyte activation in biological process; extracellular matrix and spindle pole in cellular component; integrin binding and ATP binding in molecular function, and KEGG pathway enrichment analyses showed that the upregulated and downregulated circRNA were strongly associated with Protein digestion and absorption and Cell cycle. Moreover, a total of 212 differentially expressed messenger RNAs (mRNAs), including 113 upregulated and 99 downregulated genes were identified. In addition, from the analysis of miRNA, long noncoding RNAs, mRNA, and circRNA networks, we found that hsa_circ_0008136 and hsa_circ_0074758 were respectively the upregulated and downregulated circRNA with highest degrees.The identified circRNA and mRNA could be implicated in the progression of human SONFH. The findings could lead to a better understanding of SONFH pathogenesis.

Serum exosomal hsa-miR-135b-5p serves as a potential diagnostic biomarker in steroid-induced osteonecrosis of femoral head

Accumulating studies have demonstrated serum exosomal microRNAs (miRNAs) represent novel biomarkers for various diseases. In this study, we aimed to explore the feasibility of using serum exosomal miRNAs as novel serological biomarkers for steroid-induced osteonecrosis of femoral head (SONFH). We identified the characters of exosomes which were obtained from fresh serum of 5 systemic lupus erythematosus (SLE) patients without SONFH, 5 SLE patients with SONFH (SLE-SONFH) and 5 healthy ones. Comprehensive exosomal miRNA sequencing was performed to profile the differentially expressed miRNAs in the three groups. We then validated the expression levels of selected miRNAs by qRT-PCR. Furthermore, KEGG pathway, GO annotation, protein-protein interaction (PPI) network, module analysis and miRNAs-mRNAs interaction network were built to analyze the potential targets and mechanism. Sequencing data conveyed that hsa-miR-135b-5p, hsa-miR-150-5p, hsa-miR-509-3-5p, hsa-miR-514a-3p and hsa-miR-708-5p were significantly differentially expressed in the three groups. The results of qRT-PCR for the first time confirmed that the expression of hsa-miR-135b-5p was strikingly up-regulated in SLE-SONFH group which were consistent with miRNA sequencing results. In addition, bioinformatics analysis indicated that the enriched functions and pathways of the most differentially expressed miRNAs including Wnt, MAPK as well as Hippo signaling pathway. The top five hub genes (FGF2, PTEN, HACE1, VAMP2, and CBL) were part of module of the PPI network, which consisted of 713 nodes and 2191 edges. In conclusion, this study provides a novel and fundamental serum exosomal miRNAs profile of SONFH and hsa-miR-135b-5p may be identified as a unique diagnostic biomarker for SONFH.

Noncoding RNAs in Steroid-Induced Osteonecrosis of the Femoral Head

Steroid-induced osteonecrosis of the femoral head (ONFH) is a severe orthopedic disease caused by the long-term administration of glucocorticoids. The main pathological feature of ONFH is the gradually progressive necrosis of bone cells and the bone marrow, ultimately resulting in structural changes or even complete collapse of the femoral head. However, the exact pathogenic mechanism of ONFH remains unknown. Noncoding RNAs (ncRNAs) have emerged as very powerful regulators of gene expression, functioning at both transcriptional and posttranscriptional levels in the pathogenesis of ONFH. Here, we review the current knowledge of the role of ncRNAs, including microRNAs, long noncoding RNAs, and circular RNAs, in the pathogenesis of steroid-induced ONFH. Further focus and validation of these associations can provide new insight into the pathogenic mechanisms at the molecular level to suggest targets for treatment and prevention.

Analysis of circulating microRNAs aberrantly expressed in alcohol-induced osteonecrosis of femoral head

Serum miRNAs are potential biomarkers for predicting the progress of bone diseases, but little is known about miRNAs in alcohol-induced osteonecrosis of femoral head (AIONFH). This study evaluated disease-prevention value of specific serum miRNA expression profiles in AIONFH. MiRNA PCR Panel was taken to explore specific miRNAs in serum of AIONFH cases. The top differentially miRNAs were further validated by RT-qPCR assay in serum and bone tissues of two independent cohorts. Their biofunction and target genes were predicted by bioinformatics databases. Target genes related with angiogenesis and osteogenesis were quantified by RT-qPCR in necrotic bone tissue. Our findings demonstrated that multiple miRNAs were evaluated to be differentially expressed with high dignostic values. MiR-127-3p, miR-628-3p, and miR-1 were downregulated, whereas miR-885-5p, miR-483-3p, and miR-483-5p were upregulated in serum and bone samples from the AIONFH patients compared to those from the normal control individuals (p < 0.01). The predicted target genes of the indicated miRNAs quantified by qRT-PCR, including IGF2, PDGFA, RUNX2, PTEN, and VEGF, were presumed to be altered in necrotic bone tissue of AIONFH patients. The presence of five altered miRNAs in AIONFH patients may serve as non-invasive biomarkers and potential therapeutic targets for the early diagnosis of AIONFH.

S100 Calcium Binding Protein A9 Represses Angiogenic Activity and Aggravates Osteonecrosis of the Femoral Head

Ischemic damage aggravation of femoral head collapse is a prominent pathologic feature of osteonecrosis of the femoral head (ONFH). In this regard, S100 calcium binding protein A9 (S100A9) is known to deteriorate joint integrity, however, little is understood about which role S100A9 may play in ONFH. In this study, a proteomics analysis has revealed a decrease in the serum S100A9 level in patients with ONFH upon hyperbaric oxygen therapy. Serum S100A9 levels, along with serum vascular endothelial growth factor (VEGF), soluble vascular cell adhesion molecule-1 (sVCAM-1), interleukin-6 (IL-6), and tartrate-resistant acid phosphatase 5b levels were increased in patients with ONFH, whereas serum osteocalcin levels were decreased as compared to healthy controls. Serum S100A9 levels were increased with the Ficat and Arlet stages of ONFH and correlated with the patients with a history of being on glucocorticoid medication and alcohol consumption. Osteonecrotic tissue showed hypovasculature histopathology together with weak immunostaining for vessel marker CD31 and von Willrbrand factor (vWF) as compared to femoral head fracture specimens. Thrombosed vessels, fibrotic tissue, osteocytes, and inflammatory cells displayed strong S100A9 immunoreactivity in osteonecrotic lesion. In vitro, ONFH serum and S100A9 inhibited the tube formation of vessel endothelial cells and vessel outgrowth of rat aortic rings, whereas the antibody blockade of S100A9 improved angiogenic activities. Taken together, increased S100A9 levels are relevant to the development of ONFH. S100A9 appears to provoke avascular damage, ultimately accelerating femoral head deterioration through reducing angiogenesis. This study provides insight into the molecular mechanism underlying the development of ONFH. Here, analysis also highlights that serum S100A9 is a sensitive biochemical indicator of ONFH.

BMSC-derived exosomes carrying microRNA-122-5p promote proliferation of osteoblasts in osteonecrosis of the femoral head

Mesenchymal stem cells (MSCs) with multipotential differentiation capacity can differentiate into bone cells under specific conditions and can be used to treat osteonecrosis (ON) of the femoral head (ONFH) through cell transplantation. The current study aims to explore the role of bone marrow (BM) MSCs (BMSCs)-derived exosomes carrying microRNA-122-5p (miR-122-5p) in ONFH rabbit models.First, rabbit models with ONFH were established. ONFH-related miRNAs were screened using the Gene Expression Omnibus (GEO) database. A gain-of-function study was performed to investigate the effect of miR-122-5p on osteoblasts and BMSCs and effects of exosomes carrying miR-122-5p on ONFH. Co-culture experiments for osteoblasts and BMSCs were performed to examine the role of exosomal miR-122-5p in osteoblast proliferation and osteogenesis. The target relationship between miR-122-5p and Sprouty2 (SPRY2) was tested.MiR-122, significantly decreased in ONFH in the GSE89587 expression profile, was screened. MiR-122-5p negatively regulated SPRY2 and elevated the activity of receptor tyrosine kinase (RTK), thereby promoting the proliferation and differentiation of osteoblasts. In vivo experiments indicated that bone mineral density (BMD), trabecular bone volume (TBV), and mean trabecular plate thickness (MTPT) of femoral head were increased after over-expressing miR-122-5p in exosomes. Significant healing of necrotic femoral head was also observed.Exosomes carrying over-expressed miR-122-5p attenuated ONFH development by down-regulating SPRY2 via the RTK/Ras/mitogen-activated protein kinase (MAPK) signaling pathway. Findings in the present study may provide miR-122-5p as a novel biomarker for ONFH treatment.

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.

miR-10a-5p, miR-99a-5p and miR-21-5p are steroid-responsive circulating microRNAs

Steroid-induced osteonecrosis of the femoral head (ONFH) is a common orthopedic disease. The lack of specific manifestations and effective diagnostic methods make it difficult for this disease to be diagnosed at early stages. Recent studies have shown that microRNAs (miRNA) participate in the development of steroid-induced ONFH, but there is limited research into the diagnostic use of circulating miRNAs. Blood samples from 23 human subjects (7 systemic lupus erythematosus (SLE) patients with steroid-induced ONFH; 7 SLE controls without ONFH; and 9 healthy controls) and 71 rats (19 with steroid-induced ONFH; 28 receiving steroids without ONFH; and 24 untreated controls) were collected to verify the abundance of changes of 6 previously identified ONFH-associated plasma miRNAs (miR-423-5p, miR-99a-5p, miR-10a-5p, miR-21-5p, miR-130a-3p and miR-6787-5p) by quantitative RT-PCR (Reverse Transcription-Polymerase Chain Reaction). In humans, the circulating levels of miR-10a-5p, miR-99a-5p and miR-21-5p were increased in SLE patients treated with cortico steroid regardless of ONFH status when compared with healthy controls. However, miR-423-5p, miR-6787-5p and miR-130a-3p showed no significant differences between the three groups. In the rat model, the success rate of steroid-induced ONFH was 40.4% (19/47) based on pathological examination and confirmation by micro-CT scan. Similar to human plasma, the circulating levels of miR-10a-5p, miR-99a-5p and miR-21-5p were increased in steroid-treated rats independent of ONFH development. The serum levels of miR-10a-5p, miR-99a-5p and miR-21-5p were increased by steroid treatment regardless of ONFH development in both humans and rats. These data suggested that miR-10a-5p, miR-99a-5p and miR-21-5p are steroid-responsive circulating miRNAs, but they are not specific for diagnosing steroid-induced ONFH.

Differential expression of miR-195-5p in collapse of steroid-induced osteonecrosis of the femoral head

Background

Femoral head collapse is a key reference point for determining a treatment regimen of femoral head osteonecrosis. However, there are no effective preventive measures and the efficacy of hip-preserving surgery is unsatisfactory due to the unclear mechanism of collapse. This study aimed to identify and validate miRNAs differentially expressed in collapse and non-collapse areas of the osteonecrotic femoral head, and to predict the target genes and pathways of these miRNAs.

Results

Nine samples passed the quality control test. A total of 2085 differentially expressed miRNAs were detected, among which 433 miRNAs showed differential expression in the T1 group compared to the W1 group; 344 miRNAs showed differential expression in the T2 group compared to the W2 group; 107 miRNAs showed differential expression in the T3 group compared to the W3 group. After combining data from all three patients, 10 miRNAs showed differential expression in the collapse area (T1+T2+T3) compared to the non-collapse area (W1+W2+W3). Compared to the normal area, has-miR-195-5p showed the most significant downregulation. Expression results from RT-PCR revealed that the expression of hsa-miR-195-5p in the collapse area (T1+T2+T3) was significantly lower than that in the non-collapse area (W1+W2+W3) and normal area (Z1+Z2+Z3). 157 genes were perdicted as the target gene of hsa-miR-195-5p.

Materials and Methods

Femoral heads of three patients (2 males and 1 female) treated by total hip arthroplasty surgery for steroid-induced femoral head osteonecrosis were selected based on inclusion and exclusion criteria. Bone tissue samples were obtained from the collapse area (T), non-collapse area (W), and normal area (Z) according to the anatomical structure of osteonecrotic femoral heads. Total RNA was extracted from the samples and the microarray chip was scanned. miRNAs showing differential expressions of more than 1.5-fold were selected and was validated by RT-PCR. TargetScan, mirBase and miRanda bioinformatics software was used to predict target genes and identify possible pathways involving these genes.

Conclusions

miR-195-5p showed the most significant difference in the collapse area of osteonecrotic femoral heads, suggesting that collapse may be related to the downregulation of miR-195-5p.

Altered microRNA expression profile in the peripheral lymphoid compartment of multiple myeloma patients with bisphosphonate-induced osteonecrosis of the jaw

Bisphosphonates are formidable inhibitors of osteoclast-mediated bone resorption employed for therapy of multiple myeloma (MM) subjects with osteolytic lesions. Osteonecrosis of the jaw (ONJ) is an uncommon drug-induced adverse event of these agents. MicroRNAs (miRNAs) are a group of small, noncoding RNAs nucleotides, which are essential post-transcriptional controllers of gene expression. They have a central role in the normal bone development. The goal of our study was to investigate 18 miRNAs, whose targets were previously validated and described in MM subjects without ONJ, in peripheral lymphocytes of MM subjects with bisphosphonate-induced ONJ. Utilizing reverse transcription quantitative polymerase chain reaction, we evaluated miRNAs in five healthy subjects and in five MM patients with ONJ. Our experimental data revealed that a diverse miRNA signature for ONJ subjects emerged with respect to control subjects. Using the filter for in silico analysis, among the 18 miRNAs, we recognized 14 dysregulated miRNAs. All these miRNAs were significantly over-expressed in patients vs controls (MIR-16-1, MIR-21, MIR-23A, MIR-28, MIR-101-1, MIR-124-1, MIR-129, MIR-139, MIR-145, MIR-149, MIR-202, MIR-221, MIR-424, MIR-520). Among them, six were strongly upregulated (fourfold upregulated and more). These miRNAs target numerous pathways and genes implicated in calcium ion binding, bone resorption, mineralization of bone matrix, and differentiation and maintenance of bone tissue. A modified microRNA expression profile after zoledronate therapy could participate to the onset of ONJ. Targeting these miRNAs could provide a new opportunity for the prevention or treatment of ONJ.

Analysis of early stage osteonecrosis of the human femoral head and the mechanism of femoral head collapse

We explored the mechanism of early stage osteonecrotic femoral head collapse by analyzing and comparing different regions in human osteonecrotic femoral head samples. Eight osteonecrotic femoral heads (ARCO II-III) were obtained from patients undergoing total hip arthroplasty. Bone structure was observed and evaluated by micro-computed tomography (CT) scans and pathology. Osteoblast and osteoclast activities were detected by tartrate-resistant acid phosphatase, alkaline phosphatase, and immunofluorescent staining. Some trabeculae had microfractures in the subchondral bone and necrotic region, which had lower bone mineral density, as well as trabecular thickness and number, but greater osteoclast activity. A sclerotic band had already appeared in certain samples which had greater trabecular thickness and number, bone mineral density, and osteoblast activity. The appearance of the femoral head did not change significantly in the early stage of osteonecrosis of the femoral head. However, osteoblast and osteoclast activities had already changed in different regions of the osteonecrotic femoral head, which may lead to eventual collapse of the femoral head. Therefore, osteonecrosis of the femoral head must be treated during the early stage. In addition, osteoblast activity should be promoted and osteoclast activity inhibited as early as possible to prevent collapse of an osteonecrotic femoral head.

Herbal Fufang Xian Ling Gu Bao prevents corticosteroid-induced osteonecrosis of the femoral head-A first multicentre, randomised, double-blind, placebo-controlled clinical trial

Background/Objective

This is a multicentre, randomised, double-blind, placebo-controlled clinical trial to investigate the safety and efficacy of Chinese herbal Fufang Xian Ling Gu Bao (XLGB) with antiadipogenic compounds for the prevention of corticosteroid (CS)-induced osteonecrosis of femoral head (ONFH).

Methods

Patients of both genders, aged between 18 and 65 years, with diseases such as systemic lupus erythematosus, nephrosis, dermatosis and rheumatoid arthritis indicated for CS treatment and who did not show magnetic resonance imaging of ONFH at baseline were recruited into the study and then randomised into either XLGB group (n = 129) with daily oral administration of XLGB or placebo group (n = 146).

Results

Magnetic resonance imaging revealed a total of 30 ONFH cases at 6 months after CS treatment, with 6.98% (9 of 129 cases) and 14.4% (21 of 146 cases) in the XLGB group and placebo group, respectively, (p < 0.05), i.e., a 2-fold significantly less ONFH identified in the XLGB treatment group. Blood tests suggested that XLGB significantly inhibited the elevation of activated protein C resistance induced by CS treatment.

Conclusion

This is the first multicentre clinical study to demonstrate that the antiadipogenic compounds–rich herbal Fufang (formula) XLGB is effective in preventing CS-associated ONFH in patients with immune-inflammatory diseases under CS treatment.

The translational potential of this article

The translation potential of this clinical trial is that the initially officially approved clinical indication for XLGB for treatment of osteoporosis has been now also proven to be effective for a new clinical application.

Circulating microRNA signature of steroid-induced osteonecrosis of the femoral head

OBJECTIVES

Steroid-induced osteonecrosis of the femoral head (ONFH) is a common orthopaedic disease of which early detection remains clinically challenging. Accumulating evidences indicated that circulating microRNAs (miRNAs) plays vital roles in the development of several bone diseases. However, the association between circulating miRNAs and steroid-induced ONFH remains elusive.

MATERIALS AND METHODS

miRNA microarray was performed to identify the differentially abundant miRNAs in the serums of systemic lupus erythematosus (SLE) patients with steroid-induced ONFH as compared with SLE control and healthy control group. We predicted the potential functions of these differentially abundant miRNAs using Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses and reconstructed the regulatory networks of miRNA-mRNA interactions.

RESULTS

Our data indicated that there were 11 differentially abundant miRNAs (2 upregulated and 9 downregulated) between SLE-ONFH group and healthy control group and 42 differentially abundant miRNAs (14 upregulated and 28 downregulated) between SLE-ONFH group and SLE control group. We also predicted the potential functions of these differentially abundant miRNAs using Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses and reconstructed the regulatory networks of miRNA-mRNA interactions.

CONCLUSIONS

These findings corroborated the idea that circulating miRNAs play significant roles in the development of ONFH and may serve as diagnostic markers and therapeutic targets.

Emerging roles of MicroRNAs in osteonecrosis of the femoral head

Osteonecrosis of the femoral head (ONFH) is one of the most common orthopaedic diseases. The exact pathogenic mechanism of ONFH is still unknown. MicroRNAs (miRNAs) are a class of non-coding RNAs that negatively modulate gene expression at post-transcriptional level. An increasing number of studies have shown that miRNAs play crucial roles in different physiological processes, including development, cell proliferation, differentiation and metabolism. Recently, multiple studies demonstrated that miRNAs are involved in the pathogenesis of ONFH. In this review, we summarize dysregulated miRNAs and their functions in ONFH. Furthermore, we discuss their potential clinical applications for diagnosis and treatment of ONFH.

Cardioprotective effects of anisodamine against myocardial ischemia/reperfusion injury through the inhibition of oxidative stress, inflammation and apoptosis

The aim of the present study was to investigate the cardioprotective effects of anisodamine against myocardial ischemia/reperfusion (I/R) injury and the molecular mechanisms involved. The present results demonstrated that anisodamine attenuated myocardial infarct sizes, decreased the levels of creatine kinase and lactate dehydrogenase, whereas it increased the left ventricular (LV) systolic pressure, the LV end‑diastolic pressure, and the LV pressure maximum rising and falling rates in a myocardial I/R rat model. In addition, anisodamine was revealed to suppress oxidative stress, inflammatory factor production and myocardial cell apoptosis, as demonstrated by the downregulation of caspase‑3 and apoptosis regulator BAX protein expression. The production of reactive oxygen species was decreased and the protein expression of inducible nitric oxide synthase (iNOS) was downregulated, whereas the expression of endothelial NOS was enhanced. In addition, the activity of nicotinamide‑adenine dinucleotide phosphate oxidase (Nox) was suppressed and the expression of Nox4 was downregulated in rats with myocardial I/R injury. In conclusion, the results of the present study suggested that anisodamine exerted a cardioprotective effect against myocardial I/R injury in rats, through the inhibition of oxidative stress, the suppression of inflammatory processes and the inhibition of myocardial cell apoptosis.

ErbB2 signaling epigenetically suppresses microRNA-205 transcription via Ras/Raf/MEK/ERK pathway in breast cancer

We previously reported that microRNA-205 (miR-205) is downregulated by overexpression of the receptor tyrosine kinase ErbB2 and that ectopic transfection of miR-205 precursor decreases ErbB2 tumorigenicity in soft agar. In this study, we further analyzed the regulatory mechanisms linking ErbB2 overexpression and miR-205 downregulation. In ErbB2-overexpressing breast epithelial cells, miR-205 expression was significantly increased by treatment with MEK inhibitor U0126 or PD98059, Raf-1 inhibitor ZM-336372, and ERK inhibitor SCH772984, but PI3K inhibitor LY294002 and p38 MAPK inhibitor SB203580 had no effect. We established breast epithelial cells overexpressing RafCAAX, a constitutively active form of Raf-1, and showed that overexpression of RafCAAX dramatically reduced miR-205 expression. In RafCAAX-overexpressing cells, miR-205 expression was also significantly increased by SCH772984. Moreover, miR-205 expression was significantly increased by treatment with DNA methyltransferase (DNMT) inhibitor 5-aza-2'-deoxycytidine and expression of several DNMT family members was increased in both ErbB2- and RafCAAX-overexpressing cells. DNA methylation analysis by bisulfite sequencing revealed that the putative miR-205 promoters were predominantly hypermethylated in both ErbB2- and RafCAAX-overexpressing cells. Reporter activity of the putative miR-205 promoters was reduced in both ErbB2-overexpressing and RafCAAX-overexpressing cells. Together, these findings indicate that ErbB2 signaling epigenetically suppresses miR-205 transcription via the Ras/Raf/MEK/ERK pathway.

Regulatory mechanisms of microRNA expression

MicroRNAs (miRs, miRNAs) are small molecules of 18-22 nucleotides that serve as important regulators of gene expression at the post-transcriptional level. One of the mechanisms through which miRNAs regulate gene expression involves the interaction of their "seed" sequences primarily with 3'-end and more rarely with 5'-end, of mRNA transcribed from target genes. Numerous studies over the past decade have been devoted to quantitative and qualitative assessment of miRNAs expression and have shown remarkable changes in miRNA expression profiles in various diseases. Thus, profiling of miRNA expression can be an important tool for diagnostics and treatment of disease. However, less attention has been paid towards understanding the underlying reasons for changes in miRNA expression, especially in cancer cells. The purpose of this review is to analyze and systematize current data that explains reasons for changes in the expression of miRNAs. The review will cover both transcriptional (changes in gene expression and promoter hypermethylation) and post-transcriptional (changes in miRNA processing) mechanisms of regulation of miRNA expression, as well as effects of endogenous (hormones, cytokines) and exogenous (xenobiotics) compounds on the miRNA expression. The review will summarize the complex multilevel regulation of miRNA expression, in relation to cell type, physiological state of the body and various external factors.