Osteoprotegerin promotes the proliferation of chondrocytes and affects the expression of ADAMTS-5 and TIMP-4 through MEK/ERK signaling

CircRSU1 contributes to the development of osteoarthritis via the miR-345-3p/TRAF6 signaling

OBJECTIVE

Osteoarthritis (OA) is a common type of prevalent joint diseases in the elderly. At present, circular RNAs receive more attention due to their roles during the progression of OA. In this paper, the expression profiles of circRSU1 and relevant molecules in OA patients and cell models were evaluated, and the underlying regulatory mechanisms of circRSU1-modulated OA development were also explored.

METHODS

The proliferation of chondrocytes was examined using CCK-8 assay. The levels of relevant proteins were evaluated by western blotting. The production of pro-inflammatory cytokines were measured by ELISA.

RESULTS

The results revealed upregulation of circRSU1 in OA samples, and IL-1β treatment could elevate the expression of circRSU1 in human chondrocytes. In addition, knockdown of circRSU1 abolished the dysfunctions caused by IL-1β in chondrocytes. Furthermore, miR-345-3p was identified as the novel downstream molecule of circRSU1. The levels of miR-345-3p were notably decreased in cells transfected with oe-circRSU1 and elevated in cells treated with si-circRSU1, respectively. Moreover, si-circRSU1 was able to attenuate IL-1β-induced impairments in chondrocyte via miR-345-3p. In addition, to verify the downstream mechanisms of circRSU1-modulated OA progression, TRAF6 was identified as the putative target of miR-345-3p, and miR-345-3p inhibition abolished circRSU1 knockdown-triggered downregulation of TRAF6 in IL-1β-induced OA cell model. In addition, miR-345-3p protected chondrocytes from IL-1β-induced dysfunction such as impaired ECM, reduced proliferation and upregulated apoptosis of chondrocytes, and elevated production of proinflammatory cytokines through regulating TRAF6.

CONCLUSION

In summary, circRSU1 was able to contribute to the progression of OA through regulating the miR-345-3p/TRAF6 pathway, and this novel signalling could be novel candidate for targeted therapy for OA patients.

Angiotensin II Induces Aortic Rupture and Dissection in Osteoprotegerin-Deficient Mice

Background

The biological mechanism of action for osteoprotegerin, a soluble decoy receptor for the receptor activator of nuclear factor‐kappa B ligand in the vascular structure, has not been elucidated. The study aim was to determine if osteoprotegerin affects aortic structural integrity in angiotensin II (Ang II)‐induced hypertension.

Methods and Results

Mortality was higher (P<0.0001 by log‐rank test) in 8‐week‐old male homozygotes of osteoprotegerin gene‐knockout mice given subcutaneous administration of Ang II for 28 days, with an incidence of 21% fatal aortic rupture and 23% aortic dissection, than in age‐matched wild‐type mice. Ang II‐infused aorta of wild‐type mice showed that osteoprotegerin immunoreactivity was present with proteoglycan. The absence of osteoprotegerin was associated with decreased medial and adventitial thickness and increased numbers of elastin breaks as well as with increased periostin expression and soluble receptor activator of nuclear factor‐kappa B ligand concentrations. PEGylated human recombinant osteoprotegerin administration decreased all‐cause mortality (P<0.001 by log‐rank test), the incidence of fatal aortic rupture (P=0.08), and aortic dissection (P<0.001) with decreasing numbers of elastin breaks, periostin expressions, and soluble receptor activator of nuclear factor‐kappa B ligand concentrations in Ang II‐infused osteoprotegerin gene‐knockout mice.

Conclusions

These data suggest that osteoprotegerin protects against aortic rupture and dissection in Ang II‐induced hypertension by inhibiting receptor activator of nuclear factor‐kappa B ligand activity and periostin expression.

PRIMUS: Comprehensive proteomics of mouse intervertebral discs that inform novel biology and relevance to human disease modelling

•

Proteomics of healthy mouse IVDs differentiating compartments and spine levels.

•

NP cells feature vacuoles with lysosomal, transport and cell–cell communication functions.

•

Collagen XII, decorin and other ECM proteins contribute to function of the AF.

•

Distinct proteomics between lumbar and tail discs.

•

Mouse is a relevant model for human disc biology but care is needed in its use.

Mice are commonly used to study intervertebral disc (IVD) biology and related diseases such as IVD degeneration. Discs from both the lumbar and tail regions are used. However, little is known about compartmental characteristics in the different regions, nor their relevance to the human setting, where a functional IVD unit depends on a homeostatic proteome. Here, we address these major gaps through comprehensive proteomic profiling and in-depth analyses of 8-week-old healthy murine discs, followed by comparisons with human. Leveraging on a dataset of over 2,700 proteins from 31 proteomic profiles, we identified key molecular and cellular differences between disc compartments and spine levels, but not gender. The nucleus pulposus (NP) and annulus fibrosus (AF) compartments differ the most, both in matrisome and cellularity contents. Differences in the matrisome are consistent with the fibrous nature required for tensile strength in the AF and hydration property in the NP. Novel findings for the NP cells included an enrichment in cell junction proteins for cell–cell communication (Cdh2, Dsp and Gja1) and osmoregulation (Slc12a2 and Wnk1). In NP cells, we detected heterogeneity of vacuolar organelles; where about half have potential lysosomal function (Vamp3, Copb2, Lamp1/2, Lamtor1), some contain lipid droplets and others with undefined contents. The AF is enriched in proteins for the oxidative stress responses (Sod3 and Clu). Interestingly, mitochondrial proteins are elevated in the lumbar than tail IVDs that may reflect differences in metabolic requirement. Relative to the human, cellular and structural information are conserved for the AF. Even though the NP is more divergent between mouse and human, there are similarities at the level of cell biology. Further, common cross-species markers were identified for both NP (KRT8/19, CD109) and AF (COL12A1). Overall, mouse is a relevant model to study IVD biology, and an understanding of the limitation will facilitate research planning and data interpretation, maximizing the translation of research findings to human IVDs.

Monocyte chemoattractant protein‑1 promotes the proliferation, migration and differentiation potential of fibroblast‑like synoviocytes via the PI3K/P38 cellular signaling pathway

Rheumatoid arthritis (RA) is an autoimmune disease characterized by chronic inflammation of the joints and joint destruction. Monocyte chemoattractant protein 1 (MCP‑1) is highly expressed in the joints of patients suffering from RA. The present study aimed to evaluate the effects of MCP‑1 on the phenotype of fibroblast‑like synoviocytes (FLSs) and their differentiation potential towards vascular endothelial cells. The expression of MCP‑1 in collagen‑induced arthritis (CIA) rats was investigated by PCR, ELISA and immunohistology. Cell proliferation induced by MCP‑1 was measured using a Cell Counting Kit‑8 (CCK‑8) and 5‑Bromo‑2‑deoxyuridine ELISA assay. In addition, the effects of MCP‑1 on the migration of FLSs was examined using a Transwell assay. Activation of PI3K and P38 were investigated by western blotting following MCP‑1 treatment. The vascular endothelial cell markers, tumor necrosis factor alpha (TNF‑α) and interleukin‑1 beta (IL‑β), were also examined by western blotting. LY294002 [PI3K inhibitor, (LY)] and SB203580 [P38 inhibitor, (SB)] were used to examine the proliferative and pro‑differentiation effect of PI3K and P38. The present findings showed that the expression level of MCP‑1 in the synovium of CIA rats was significantly higher compared with controls. The present in vitro study suggested that MCP‑1 increased the FLSs cell numbers with a maximal effect at 200 ng/ml, and induced the maximal phosphorylation of PI3K at 15 min and P38 at 30 min. In addition, MCP‑1 stimulation significantly increased the migration of FLSs. Furthermore, MCP‑1‑induced the expression of vascular endothelial growth factor and CD31 in FLSs. Suppression of PI3K and P38 was found to reduce MCP‑1 induced FLSs proliferation and migration, and decreased the expression levels of angiogenesis markers increased following MCP‑1 treatment. MCP‑1 was also found to increase the expression levels of both TNF‑α and IL‑β. Therefore, MCP‑1 could promote the proliferation and migration of FLSs, and was found to increase the expression levels of various angiogenesis markers via PI3K/P38, suggesting a role for this pathway in synovium hyperplasia in RA.

17β-Estradiol Induces Mitophagy Upregulation to Protect Chondrocytes via the SIRT1-Mediated AMPK/mTOR Signaling Pathway

Increasing evidence reveals that estrogen, especially 17β-estradiol (17β-E2), is associated with articular cartilage metabolism disorder and postmenopausal osteoarthritis (OA). SIRT1, AMPK, and mTOR are regarded as critical mitophagy regulators. Recent studies have shown that mitophagy displays a protective effect against OA, but the molecular mechanism is not well known. This study aimed to investigate the effect of 17β-E2 on Sirtuin-1 (SIRT1) expression and the induction of mitophagy upregulation by 17β-E2 via the SIRT1-mediated AMP-activated protein kinase (AMPK)/mammalian target of the rapamycin (mTOR) signaling pathway to protect chondrocytes. ATDC5 chondrocytes were treated with different concentrations of 17β-E2 (0 M, 1 × 10^-9 M, 1 × 10^-8 M, and 1 × 10^-7 M) for 24 h or pretreatment with or without NAM (SIRT1 inhibitor), Compound C (AMPK inhibitor) and S1842 (mTOR inhibitor) for 30 min prior to treatment with 17β-E2 (1 × 10^-7 M) for 24 in each groups. Expression of SIRT1 was evaluated by real-time PCR, Western blotting and confocal immunofluorescence staining. Then, the mitophagosomes in cells were observed under a transmission electron microscopy (TEM), and the AMPK/mTOR signaling pathway was detected by Western blotting. The mitophagy-related proteins, p-AMPK, p-mTOR, p-JNK, and p-p38 were also identified by Western blot analysis. The chondrocytes viability and proliferation were determined by MTT and 5-Bromo-2'-deoxyuridine (BrdU) assay. These experiments were independently repeated 3 times The study found that 17β-E2 increased the expression level of SIRT1, p-AMPK, and mitophagy-related proteins but decreased p-mTOR expression, and then induced mitophagy upregulation in chondrocytes. More mitochondrial autophagosomes were observed in 17β-E2-treated chondrocytes under a transmission electron microscope. Also, 17β-E2 improved cell viability and proliferation with the higher expression of SIRT1 and activation of the AMPK/mTOR signaling pathway. However, SIRT1 inhibitor nicotinamide (NAM) and AMPK inhibitor Compound C blocked the beneficial effect of 17β-E2. In summary, this study was novel in demonstrating that 17β-E2 induced mitophagy upregulation to protect chondrocytes via the SIRT1-mediated AMPK/mTOR signaling pathway.

Association of TIMP4 gene variants with steroid-induced osteonecrosis of the femoral head in the population of northern China

Background

In clinical treatment, the use of steroid hormones is an important etiological factor of non-traumatic osteonecrosis of the femoral head (ONFH) risk. As an endogenous inhibitor of matrix metalloproteinases (MMPs) in the extracellular matrix, the expression of tissue inhibitors of metalloprotease-4 (TIMP4) plays an essential role in cartilage and bone tissue damage and remodeling, vasculitis formation, intravascular thrombosis, and lipid metabolism.

Methods

This study aimed to detect the association between TIMP4 polymorphism and steroid-induced ONFH. We genotyped seven single-nucleotide polymorphisms (SNPs) in TIMP4 genes and analyzed the association with steroid-induced ONFH from 286 steroid-induced ONFH patients and 309 normal individuals.

Results

We performed allelic model analysis and found that the minor alleles of five SNPs (rs99365, rs308952, rs3817004, rs2279750, and rs3755724) were associated with decreased steroid-induced ONFH (p = 0.02, p = 0.03, p = 0.04, p = 0.01, p = 0.04, respectively). rs2279750 showed a significant association with decreased risk of steroid-induced ONFH in the Dominant and Log-additive models (p = 0.042, p = 0.028, respectively), and rs9935, rs30892, and rs3817004 were associated with decreased risk in the Log-additive model (p = 0.038, p = 0.044, p = 0.042, respectively). In further stratification analysis, TIMP4 gene variants showed a significant association with steroid-induced ONFH in gender under the genotypes. Haplotype analysis also revealed that “TCAGAC” and “CCGGAA” sequences have protective effect on steroid-induced ONFH.

Conclusion

Our results indicate that five TIMP4 SNPs (rs99365, rs308952, rs3817004rs2279750, and rs3755724) are significantly associated with decreased risk of steroid-induced ONFH in the population of northern China.

Mutations in osteoprotegerin account for the CCAL1 locus in calcium pyrophosphate deposition disease

OBJECTIVE

Mutations on chromosomes 5p (CCAL2) and 8q (CCAL1) have been linked to familial forms of calcium pyrophosphate deposition disease (CPDD). Mutations in the ANKH gene account for CCAL2, but the identity of CCAL1 has been elusive. Recently, a single Dutch kindred with a mutation in the Tumor Necrosis Factor Receptor Super Family member 11B (TNFRSF11B) gene coding for osteoprotegerin (OPG) was described as a gain-of-function mutation. Affected family members had premature generalized osteoarthritis (PGOA) and CPDD. As the TNFRSF11B gene is on 8q, we sought additional evidence that TNFRSF11B was CCAL1, and investigated potential disease mechanisms.

DESIGN

DNA from two novel PGOA/CPDD families was screened for sequence variants in the TNFRSF11B gene. Mutations were verified by genotype analysis of affected and unaffected family members. We also investigated effects of normal and mutant OPG on regulators of CPP crystal formation in porcine cartilage.

RESULTS

The identical TNFRSF11B mutation described in the Dutch family was present in two novel PGOA/CPDD families. ANKH was normal in affected patient fibroblasts. Exogenous OPG did not alter ANKH mRNA or protein levels, affect translocation of ANKH to the membrane, nor increase [pyrophosphate (PPi)] or other key regulators of CPDD.

CONCLUSION

We have firmly established the identity of CCAL1 as TNFRSF11B (OPG). Our findings suggest that this mutation produces disease in an ANKH-independent manner via novel mechanisms not primarily targeting cartilage. This work rationalizes further investigation of OPG pathway components as potential druggable targets for CPDD.

A Human Chondrocyte-Derived In Vitro Model of Alcohol-Induced and Steroid-Induced Femoral Head Necrosis

BACKGROUND Worldwide, femoral head necrosis (FHN), which is also known as avascular necrosis of the femoral head or osteonecrosis of the femoral head, affects millions of people. Excess alcohol intake and steroid use are two common associations with FHN, but their pathogenesis remains unknown. The aim of this study was to develop an in vitro model using human chondrocytes to study alcohol-induced and steroid-induced FHN. MATERIAL AND METHODS In this study, the in vitro model used a monolayer culture of articular chondrocytes derived from patients with non-traumatic FHN (Ficat and Arlet, Stage III). Normal chondrocytes were obtained from patients with femoral neck fracture resulting from road traffic accident (Garden, Stage IV). Alcohol-stimulated and steroid-stimulated articular chondrocytes were evaluated by a cell proliferation assay, measurement of calcium levels (alizarin red), measurement of alkaline phosphatase (ALP) levels, detection of glycosaminoglycan (GAG) secretion using safranin O histochemical staining, and analysis of cartilage-specific genes, ACAN, SOX9, OPG, TGF-β, RANKL, and RUNX2, using quantitative real-time polymerase chain reaction (qRT-PCR). RESULTS Both alcohol and steroids, but especially steroids, accelerated the degradation of cartilage by suppression of chondrogenesis while promoting chondrocyte hypertrophy and activating osteogenic differentiation, as assessed by cell proliferation assay, detection of glycosaminoglycan (GAG) secretion, and analysis of cartilage-specific genes. CONCLUSIONS A human chondrocyte-derived in vitro model of alcohol-induced and steroid-induced FHN demonstrated chondrocyte hypertrophy and activated osteogenic differentiation.

Parathyroid hormone (1-34) promotes fracture healing in ovariectomized rats with type 2 diabetes mellitus

Ovariectomized (OVX) rats with type 2 diabetes mellitus (T2DM) with femur fracture received vehicle, insulin, or insulin plus parathyroid hormone (PTH) treatment for 2 and 3 weeks. Radiography, histomorphometry, histology, and immunohistochemistry in callus were evaluated.

INTRODUCTION

Reports about effects of PTH plus insulin on callus formation of osteoporotic fracture with T2DM were limited. This study was designed to investigate the effects of the combination of PTH and insulin on fracture healing in OVX rats with T2DM.

METHODS

Two-month-old female rats were randomly divided into five groups: normal fracture (F), OVX fracture (OF), T2DM + OVX fracture (DOF), insulin-treated (2-4 u/daylight, 4-6 u/night, DOFI), and treated with insulin and PTH (50 μg/kg/day, 5 days/week, DOFIP). A closed mid-shaft fracture was established in the right femurs of all rats after 6 weeks of OVX. Rats were euthanized at 2 and 3 weeks post-fracture according to the time schedule, respectively.

RESULTS

The administration of insulin alone or insulin combined with PTH significantly increased mineralized bone volume fraction (BV/TV) and connectivity density (Conn.D) compared with those of the DOF group at 3 weeks post-fracture and also increased cartilaginous callus area ratio in the DOFI and DOFIP groups at 2 weeks and bony callus area ratio in the DOFIP groups at both the 2 and 3 weeks post-fracture.

CONCLUSIONS

OVX rats with T2DM exhibited a marked delay in the fracture healing process; insulin treatment ameliorated these effects, and the healing process was enhanced following treatment with a combination of insulin and PTH.

Effects of miR-145 on the inhibition of chondrocyte proliferation and fibrosis by targeting TNFRSF11B in human osteoarthritis

Osteoarthritis (OA) is a common cause of functional deterioration in older adults, and altered chondrogenesis is the most common pathophysiological process involved in the development of OA. MicroRNA‑145 (miR‑145) has been shown to regulate chondrocyte homeostasis. However, the function of miR‑145 in OA remains to be elucidated. In the present study, the expression levels of miR‑145 were examined in cartilage specimens from 25 patients with knee OA using reverse transcription‑quantitative polymerase chain reaction analysis. The effects of miR‑145 on the proliferation and fibrosis of the C‑20/A4 and CH8 cell lines were also investigated using 3-(4,5-dimethylth-iazol-2-yl)-2,5-diphenyltetrazolium bromide and western blot assays in vitro. The results revealed that the expression of miR-145 was decreased in the OA cartilage tissues, compared with normal cartilage tissues. The overexpression of miR‑145 by transfection of cells with miR‑145 mimics significantly inhibited C‑20/A4 and CH8 cell proliferation and fibrosis. Furthermore, tumor necrosis factor receptor superfamily, member 11b (TNFRSF11B) was identified as a direct target of miR‑145 in chondrocytes, which was confirmed using a dual‑luciferase reporter assay. The expression level of TNFRSF11B was markedly upregulated in the patients with OA, and the ectopic expression of miR‑145 was capable of suppressing the expression of TNFRSF11B. In addition, the knock down of TNFRSF11B using specific small interfering RNA also inhibited the proliferation and fibrosis of C‑20/A4 and CH8 cells in vitro. These data provide the first evidence, to the best of our knowledge, to suggest the critical function of miR‑145 in regulating the expression of TNFRSF11B, which may have important implications on the regulation of chondrocyte proliferation and fibrosis in OA.

Bone-cartilage crosstalk: a conversation for understanding osteoarthritis

Although cartilage degradation is the characteristic feature of osteoarthritis (OA), it is now recognized that the whole joint is involved in the progression of OA. In particular, the interaction (crosstalk) between cartilage and subchondral bone is thought to be a central feature of this process. The interface between articular cartilage and bone of articulating long bones is a unique zone, which comprises articular cartilage, below which is the calcified cartilage sitting on and intercalated into the subchondral bone plate. Below the subchondral plate is the trabecular bone at the end of the respective long bones. In OA, there are well-described progressive destructive changes in the articular cartilage, which parallel characteristic changes in the underlying bone. This review examines the evidence that biochemical and biomechanical signaling between these tissue compartments is important in OA disease progression and asks whether such signaling might provide possibilities for therapeutic intervention to halt or slow disease development.

Mitral valve endothelial cells secrete osteoprotegerin during endothelial mesenchymal transition

AIMS

Mitral valve prolapse (MVP) has a prevalence of 3% in the general population, affecting >176 million people worldwide. Despite this, little is known about the molecular and cellular mechanisms involved in the progression of MVP and surgical intervention is the only available option. In this study we investigated the role of osteoprotegerin (OPG) during endothelial to mesenchymal transition (EndMT) in MVP.

METHODS AND RESULTS

VECs and VICs were isolated from posterior mitral valve leaflets of patients undergoing mitral valve repair (n=25). Plasma was collected from 57 subjects (29 controls and 28 MVP patients). Overexpression of OPG during EndMT followed by autocrine effects characterised by reactive oxygen species increment and accelerated migration was documented. In addition, OPG increased VIC proliferation. Finally, OPG plasma levels were significantly higher in MVP patients compared to control subjects and the area under the ROC curve was 0.92.

CONCLUSION

EndMT has been recognised as a possible pathological mechanism for MVP. For the first time, we report the involvement of OPG in cellular and molecular changes in MVP isolated cells. In addition, we detected elevated circulating OPG levels in MVP patients when compared to controls, which supports the hypothesis that OPG is involved in MVP development and progression.

Serum Osteoprotegerin Is Associated With Calcified Carotid Plaque: A Strobe-Compliant Observational Study

Osteoprotegerin (OPG) is a kind of tumor necrosis factor, which is related to bone metabolism and vascular calcification. The increase of Osteoprotegerin concentration in serum is related to cardiovascular diseases in humans. The purpose of this study was to figure out the relevance between osteoprotegerin in serum and carotid calcification. Serum OPG concentrations were compared in 145 patients who underwent carotid sonography (average age: 68 ± 9 years old, male: female = 81:64). A calcified plaque (CP) (37 people [27%]), a noncalcified plaque (NCP) (54 people [37%]), and a nonplaque (NP) (54 people [37%]) were classified for this study. No significant differences among 3 groups were demonstrated in the distribution of age, diabetes, high blood pressure, and hyperlipidemia. Serum osteoprotegerin concentrations were significantly increased in CP group rather than NCP group or NP group; (median [interquartile range], 4016 [1410] vs 3210 [1802] pg/mL, P < 0.05 and 4016 [1410] vs 3204 [1754] pg/mL, P < 0.05). Serum osteoprotegerin concentrations did not indicate a significant difference between NCP Group or NP Group. This study had proved that patient group accompanied with carotid calcification in carotid artery disease had an increased serum OPG concentration, so it could consider that OPG plays an important function on calcification related to arteriosclerosis.

Effects of icariin on the regulation of the OPG-RANKL-RANK system are mediated through the MAPK pathways in IL-1β-stimulated human SW1353 chondrosarcoma cells

Arthrodial cartilage degradation and subchondral bone remodeling comprise the most predominant pathological changes in osteoarthritis (OA). Moreover, accumulating evidence indicates that the abnormal expression of osteoprotegerin (OPG), receptor activator of nuclear factor kappa-B ligand (RANKL) and receptor activator of nuclear factor kappa-B (RANK) plays a vital role in the collapse of cartilage and subchondral bone. In the present study, the effects of icariin on the expression levels of these 3 factors in interleukin (IL)-1β-stimulated SW1353 chondrosarcoma cells were investigated. The SW1353 chondrosarcoma cells were cultured in the presence or absence of icariin and mitogen-activated protein kinase signaling pathway inhibitors, and were then stimulated with IL-1β. Cell viability was assessed by MTT assay. The mRNA and protein expression of OPG, RANKL and RANK was analyzed by quantitative reverse transcription polymerase chain reaction (RT-qPCR) and ELISA, respectively. In addition, the levels of phosphorylated p38 (p-p38) and phosphorylated extracellular signal-regulated kinase (p-ERK)1/2 were detected by western blot analysis. The results from western blot analysis revealed that treatment with icariin decreased the levels of p-p38 and increased the levels of p-ERK1/2 in the IL-1β-stimulated SW1353 cells. In addition, treatment with icariin decreased the levels of RANK and RANKL. Furthermore, the suppressive effects of icariin on OPG and OPG/RANKL were greater than those exhibited by the p38 signaling pathway inhibitor (SB203580). The findings of the the present study suggest that icariin has therapeutic potential for use in the treatment of OA.