Osteoblast-chondrocyte interactions in osteoarthritis

The emerging role of the semaphorin family in cartilage and osteoarthritis

In the pathogenesis of osteoarthritis, various signaling pathways may influence the bone joint through a common terminal pathway, thereby contributing to the pathological remodeling of the joint. Semaphorins (SEMAs) are cell-surface proteins actively involved in and primarily responsible for regulating chondrocyte function in the pathophysiological process of osteoarthritis (OA). The significance of the SEMA family in OA is increasingly acknowledged as pivotal. This review aims to summarize the mechanisms through which different members of the SEMA family impact various structures within joints. The findings indicate that SEMA3A and SEMA4D are particularly relevant to OA, as they participate in cartilage injury, subchondral bone remodeling, or synovitis. Additionally, other elements such as SEMA4A and SEMA5A may also contribute to the onset and progression of OA by affecting different components of the bone and joint. The mentioned mechanisms demonstrate the indispensable role of SEMA family members in OA, although the detailed mechanisms still require further exploration.

Is RANKL a potential molecular target in osteoarthritis?

OBJECTIVE

Osteoarthritis (OA) is a disease of joints, in which the bone under the articular cartilage undergoes increased remodelling activity. The question is whether a better understanding of the causes and mechanisms of bone remodelling can predict disease-modifying treatments.

DESIGN

This review summarises the current understanding of the aetiology of OA, with an emphasis on events in the subchondral bone (SCB), and the cells and cytokines involved, to seek an answer to this question.

RESULTS

SCB remodelling across OA changes the microstructure of the SCB, which alters the load-bearing properties of the joint and seems to have an important role in the initiation and progression of OA. Bone remodelling is tightly controlled by numerous cytokines, of which Receptor Activator of NFκB ligand (RANKL) and osteoprotegerin are central factors in almost all known bone conditions. In terms of finding therapeutic options for OA, an important question is whether controlling the rate of SCB remodelling would be beneficial. The role of RANKL in the pathogenesis and progression of OA and the effect of its neutralisation remain to be clarified.

CONCLUSIONS

This review further makes the case for SCB remodelling as important in OA and for additional study of RANKL in OA, both its pathophysiological role and its potential as an OA disease target.

Potential therapeutic strategies for osteoarthritis via CRISPR/Cas9 mediated gene editing

Osteoarthritis (OA) is an incapacitating and one of the most common physically degenerative conditions with an assorted etiology and a highly complicated molecular mechanism that to date lacks an efficient treatment. The capacity to design biological networks and accurately modify existing genomic sites holds an apt potential for applications across medical and biotechnological sciences. One of these highly specific genomes editing technologies is the CRISPR/Cas9 mechanism, referred to as the clustered regularly interspaced short palindromic repeats, which is a defense mechanism constituted by CRISPR associated protein 9 (Cas9) directed by small non-coding RNAs (sncRNA) that bind to target DNA through Watson-Crick base pairing rules where subsequent repair of the target DNA is initiated. Up-to-date research has established the effectiveness of the CRISPR/Cas9 mechanism in targeting the genetic and epigenetic alterations in OA by suppressing or deleting gene expressions and eventually distributing distinctive anti-arthritic properties in both in vitro and in vivo osteoarthritic models. This review aims to epitomize the role of this high-throughput and multiplexed gene editing method as an analogous therapeutic strategy that could greatly facilitate the clinical development of OA-related treatments since it's reportedly an easy, minimally invasive technique, and a comparatively less painful method for osteoarthritic patients.

Effects of alendronate on cartilage lesions and micro-architecture deterioration of subchondral bone in patellofemoral osteoarthritic ovariectomized rats with patella-baja

BACKGROUND

Patellofemoral osteoarthritis (PFJOA) is a subtype of knee OA, which is one of the main causes of anterior knee pain. The current study found an increased prevalence of OA in postmenopausal women, called postmenopausal OA. Therefore, we designed the ovariectomized rat model of patella baja-induced PFJOA. Alendronate (ALN) inhibits osteoclast-mediated bone loss, and has been reported the favorable result of a potential intervention option of OA treatment. However, the potential effects of ALN treatment on PFJOA in the ovariectomized rat model are unknown and need further investigation prior to exploration in the clinical research setting. In this study, the effects of ALN on articular cartilage degradation and subchondral bone microstructure were assessed in the ovariectomized PFJOA rat model for 10 weeks.

METHODS

Patella baja and estrogen withdrawal were induced by patellar ligament shortening (PLS) and bilateral ovariectmomy surgeries in 3-month-old female Sprague-Dawley rats, respectively. Rats were randomly divided into five groups (n = 8): Sham + V; OVX + V, Sham + PLS + V, OVX + PLS + V, OVX + PLS + ALN (ALN: 70 μg/kg/week). Radiography was performed to evaluate patellar height ratios, and the progression of PFJOA was assessed by macroscopic and microscopic analyses, immunohistochemistry and micro-computed tomography (micro-CT).

RESULTS

Our results found that the patella baja model prepared by PLS can successfully cause degeneration of articular cartilage and subchondral bone, resulting in changes of PFJOA. OVX caused a decrease in estrogen levels in rats, which aggravated the joint degeneration caused by PFJOA. Early application of ALN can delay the degenerative changes of articular cartilage and subchondral bone microstructure in castrated PFJOA rat to a certain extent, improve and maintain the micrometabolism and structural changes of cartilage and subchondral bone.

CONCLUSION

The early application of ALN can delay the destruction of articular cartilage and subchondral bone microstructure in castrated PFJOA rat to a certain extent.

Tranexamic Acid Attenuates the Progression of Posttraumatic Osteoarthritis in Mice

BACKGROUND

Posttraumatic osteoarthritis (OA) is a common disorder associated with a high socioeconomic burden, particularly in young, physically active, and working patients. Tranexamic acid (TXA) is commonly used in orthopaedic trauma surgery as an antifibrinolytic agent to control excessive bleeding. Previous studies have reported that TXA modulates inflammation and bone cell function, both of which are dysregulated during posttraumatic OA disease progression.

PURPOSE

To evaluate the therapeutic effects of systemic and topical TXA treatment on the progression of posttraumatic OA in the knee of mice.

STUDY DESIGN

Controlled laboratory study.

METHODS

OA was induced via anterior cruciate ligament (ACL) transection on the right knee of female mice. Mice were treated with TXA or vehicle intraperitoneally daily or intra-articularly weekly for 4 weeks, starting on the day of surgery. Articular cartilage degeneration, synovitis, bone erosion, and osteophyte formation were scored histologically. Micro-computed tomography evaluation was conducted to measure the subchondral bone microstructure and osteophyte volume. Cartilage thickness and bone remodeling were assessed histomorphometrically.

RESULTS

Both systemic and topical TXA treatment significantly reduced cartilage degeneration, synovitis, and bone erosion scores and increased the ratio of hyaline to calcified cartilage thickness in posttraumatic OA. Systemic TXA reversed ACL transection-induced subchondral bone loss and osteophyte formation, whereas topical treatment had no effect. Systemic TXA decreased the number and surface area of osteoclasts, whereas those of osteoblasts were not affected. No effect of topical TXA on osteoblast or osteoclast parameters was observed.

CONCLUSION

Both systemic and topical TXA exerted protective effects on the progression of posttraumatic OA. Drug repurposing of TXA may, therefore, be useful for the prevention or treatment of posttraumatic OA, particularly after ACL surgery.

CLINICAL RELEVANCE

TXA might be beneficial in patients with posttraumatic OA of the knee.

Integrated comparison of the mRNAome in cartilage, synovium, and macrophages in osteoarthritis

The precise molecular mechanisms associated with osteoarthritis (OA), the most common musculoskeletal disorder, are poorly understood. There are currently no effective treatments to prevent the initiation and progression of the disease. In recent years, the development of mRNAome has made it possible to identify new mechanisms and therapeutic targets. However, the differentially expressed genes screened by different microarrays are not completely the same. In order to avoid this shortcoming, we integrate the different genes from different tissues and data sets, and select the commonly expressed genes for further studies.

Microstructural and cellular characterisation of the subchondral trabecular bone in human knee and hip osteoarthritis using synchrotron tomography

OBJECTIVE

It is unclear if different factors influence osteoarthritis (OA) progression and degenerative changes characterising OA disease in hip and knee. We investigated the difference between hip OA and knee OA at the subchondral bone (SCB) tissue and cellular level, relative to the degree of cartilage degeneration.

DESIGN

Bone samples were collected from 11 patients (aged 70.4 ± 10.7years) undergoing knee arthroplasty and 8 patients (aged 62.3 ± 13.4years) undergoing hip arthroplasty surgery. Trabecular bone microstructure, osteocyte-lacunar network, and bone matrix vascularity were evaluated using synchrotron micro-CT imaging. Additionally, osteocyte density, viability, and connectivity were determined histologically.

RESULTS

The associations between severe cartilage degeneration and increase of bone volume fraction (%) [- 8.7, 95% CI (-14.1, -3.4)], trabecular number (#/mm) [- 1.5, 95% CI (-0.8, -2.3)], osteocyte lacunar density (#/mm3) [4714.9; 95% CI (2079.1, 7350.6)] and decrease of trabecular separation (mm) [- 0.07, 95% CI (0.02, 0.1)] were found in both knee and hip OA. When compared to knee OA, hip OA was characterised by larger (µm3) but less spheric osteocyte lacunae [47.3; 95% CI (11.2, 83.4), - 0.04; 95% CI (-0.06, -0.02), respectively], lower vascular canal density (#/mm3) [- 22.8; 95% CI (-35.4, -10.3)], lower osteocyte cell density (#/mm2) [- 84.2; 95% CI (-102.5, -67.4)], and less senescent (#/mm2) but more apoptotic osteocytes (%) [- 2.4; 95% CI (-3.6, -1.2), 24.9; 95% CI (17.7, 32.1)], respectively.

CONCLUSION

SCB from hip OA and knee OA exhibits different characteristics at the tissue and cellular levels, suggesting different mechanisms of OA progression in different joints.

Hypoxia-induced Wnt/β-catenin signaling activation in subchondral bone osteoblasts leads to an osteoarthritis-like phenotype of chondrocytes in articular cartilage

Background: Osteoarthritis (OA) is a whole-joint disease and characterized by alterations in the articular cartilage, subchondral bone, ligaments, and synovial membrane. The crosstalk between cartilage and subchondral bone plays a crucial role in the pathogenesis and progression of OA. Hypoxia has been reported to play an important role in cartilage degradation and subchondral bone remodeling in OA. In this study, we aimed to identify the involvement of hypoxia in modifying the osteoblast phenotypes and determine whether these alterations could influence the metabolism of chondrocytes. Methods: First, the levels of Hif-1α in subchondral bone of different compartments in patients with OA were assessed using immunohistochemistry (IHC). In in vitro, human primary osteoblasts were cultured under hypoxic and normoxic conditions, and the hypoxic or normoxic conditioned media (HCM and NCM) were used to culture human primary chondrocytes. Then, phenotypic changes in osteoblasts were assessed using reverse transcription-polymerase chain reaction (RT-PCR), Western blotting, and enzyme-linked immunosorbent assay (ELISA). Furthermore, the expression of type II collagen (COL2A1), aggrecan (ACAN), SRY-related high-mobility group-box gene 9 (SOX9), matrix metalloproteinase 13 (MMP13), and matrix metalloproteinase 3 (MMP3) in chondrocytes was measured using RT-PCR. Finally, the serum levels of Wnt-related proteins were determined using ELISA. Results: Hif-1α was significantly increased in severely sclerotic subchondral bone compared to less damaged subchondral bone. β-Catenin and SOST were identified as upregulated and downregulated in hypoxic osteoblasts, respectively. The hypoxia-induced results were confirmed by ELISA. Stimulating human primary chondrocytes with HCM significantly induced MMP13 and MMP3 and inhibited COL2A1, ACAN, and SOX9 mRNA expression. The serum levels of DKK-1 were significantly increased in human OA. Conclusion: Together, these findings revealed that hypoxia in subchondral bone is a key factor in the crosstalk between chondrocytes and osteoblasts and facilitates the shift of chondrocytes toward an OA-like phenotype probably by activating the Wnt/β-catenin signaling pathway in osteoblasts.

Increased Sparc release from subchondral osteoblasts promotes articular chondrocyte degeneration under estrogen withdrawal

OBJECTIVE

The incidence of osteoarthritis (OA) in menopausal women is significantly higher than in same-aged men. Investigating the role of subchondral osteoblasts in estrogen deficiency-induced OA may help elucidate the pathological mechanism, providing new insights for the diagnosis and treatment of menopausal OA.

METHODS

A classical ovariectomy-induced OA (OVX-OA) rat model was utilized to isolate primary articular chondrocytes and subchondral osteoblasts, which were identified and then cocultured in Transwell. The expression of chondrocyte anabolic and catabolic indicators was evaluated. The differentially expressed proteins in the conditioned medium (CM) of osteoblasts were identified by Liquid Chromatograph-Mass Spectrometer (LC-MS/MS). Normal chondrocytes were treated with osteoblast CM, and then RNA sequencing was performed on the treated chondrocytes. KEGG was used to identify significant enrichment of signaling pathways, and Simple Western was used to verify the expression of related proteins in the signaling pathways.

RESULTS

Coculture of OVX-OA subchondral osteoblasts with chondrocytes significantly downregulated the expression of the anabolic indicators and upregulated the expression of the catabolic indicators in chondrocytes. 1,601 proteins were identified in both normal and OVX osteoblast culture supernatants. Protein-protein interaction network analysis revealed that Sparc was one of the hub proteins. The AMPK/Foxo3a signaling pathway of chondrocytes was downregulated by OVX-OA osteoblasts CM. AICAR, the AMPK agonist, partially reversed the catabolic effect of OVX-OA osteoblasts on chondrocytes.

CONCLUSIONS

Sparc secreted by OVX-OA subchondral osteoblasts can downregulate the AMPK/Foxo3a signaling pathway of chondrocytes, thereby promoting chondrocyte degeneration.

Epigallocatechin-3-O-gallate promotes extracellular matrix and inhibits inflammation in IL-1β stimulated chondrocytes by the PTEN/miRNA-29b pathway

CONTEXT

Epigallocatechin-3-O-gallate (EGCG) exhibits anti-arthritic activity. MiR-29b-3p provokes chondrocyte apoptosis and promotes the initiation and development of osteoarthritis (OA).

OBJECTIVE

To explore the roles of EGCG and miR-29b-3p in interleukin-1β (IL-1β)-stimulated chondrocytes.

MATERIALS AND METHODS

HE and Safranin O staining were used to detect the pathological changes of cartilage tissue in OA patients and healthy people. OA-like chondrocyte injury was mimicked by 5 ng/mL IL-1β stimulation for 24 h in vitro, and after transfection with miR-29b-3p mimics and pcDNA-PTEN, IL-1β-stimulated chondrocytes were pre-treated with EGCG (20 and 50 μM) for 2 h. Cell viability, colony numbers, apoptosis rate, the levels of IL-6 and matrix metalloproteinase-13 (MMP-13), miR-19b-3p, PTEN and apoptosis-associated proteins in chondrocytes were evaluated.

RESULTS

MiR-29b-3p level was upregulated in cartilage tissues of OA patients (3.5-fold change, p < 0.001) and IL-1β stimulated chondrocytes (two fold change, p < 0.001). The matrix staining was weakened and unevenly distributed, and the chondrocytes were arranged disorderly in the tissues of patients with OA. EGCG (20 and 50 μM) increases viability and decreases the levels of miR-29b-3p and MMP-13 and IL-6 in IL-1β stimulated chondrocytes (p < 0.05). MiR-29b-3p mimics reversed the effects above 50 μM EGCG (p < 0.05). Furthermore, PTEN overexpression abrogated the effects of miR-29b-3p mimics on viability, colony numbers, apoptosis rate and the levels of Bcl-2, MMP-13, IL-6, Bax and cleaved caspase 3 in IL-1β-stimulated chondrocytes (p < 0.01).

DISCUSSION AND CONCLUSIONS

EGCG is a potential candidate for the treatment of OA, which also can be explored in a novel therapeutic method for other degenerative or inflammatory disorders.

Conventional MRI-derived subchondral trabecular biomarkers and their association with knee cartilage volume loss as early as 1 year: a longitudinal analysis from Osteoarthritis Initiative

OBJECTIVE

To study associations between MRI-derived subchondral trabecular biomarkers obtained from conventional MRI sequences and knee cartilage loss over 12 and 24 months, using the FNIH osteoarthritis (OA) biomarkers consortium.

MATERIALS AND METHODS

Data of the 600 subjects in the FNIH OA biomarkers consortium (a nested case-control study within Osteoarthritis Initiative [OAI]) were extracted from the online database. Baseline knee MRI (intermediate-weighted (IW) sequences) were evaluated to determine conventional MRI-derived trabecular thickness (cTbTh) and bone-to-total ratio (cBV/TV). The measurements for medial and lateral volumes of cartilages using baseline, 12-, and 24-month knee MRI were extracted from the OAI database, and cartilage volume loss over 12 and 24 months of follow-up were determined using Relative Change Index. The association between conventional MRI-based subchondral trabecular biomarkers and cartilage volume loss were studied using logistic regression models, adjusted for relevant confounders including age, sex, body mass index (BMI), vitamin D use, Kellgren Lawrence grade (KLG), and tibiofemoral alignment.

RESULTS

Higher medial cTbTh and cBV/TV at baseline were associated with increased odds of medial tibial cartilage volume loss over 12 months (ORs: 1.01 [1.00-1.02] and 1.24 [1.10-1.39] per 1-SD change) and 24 months (ORs: 1.01 [1.00-1.02] and 1.22 [1.08-1.37], per 1-SD change). No significant association was observed between medial subchondral trabecular biomarkers and lateral tibial or femoral (medial or lateral) cartilage volume loss over the first and second follow-up years.

CONCLUSIONS

Conventional MRI-derived subchondral trabecular biomarkers (higher medial cTbTh and cBV/TV) may be associated with increased medial tibial cartilage volume loss as early as 1 year.

Elucidation of the Underlying Mechanism of Gujian Oral Liquid Acting on Osteoarthritis through Network Pharmacology, Molecular Docking, and Experiment

Gujian oral liquid (GJ), a traditional herbal formula in China, has been widely used to treat patients with osteoarthritis (OA). Nevertheless, the active component and potential mechanism of GJ are not fully elucidated. Thus, we investigate the effect of GJ and explore its underlying mechanism on OA through network pharmacology and experimental validation. First, a total of 175 bioactive compounds were identified, and 134 overlapping targets were acquired after comparing the targets of the GJ with those of OA. 8 hub targets, including IL6 and AKT1, were obtained in PPI network analysis. Then, we built up GJ-target-OA network and protein-protein interaction (PPI) network, followed by Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses. The results underlined inflammatory tumor necrosis factor (TNF) as a promising signaling pathway of GJ for OA treatment. Moreover, molecular docking also verified the top two active compounds had direct bindings with the top three target genes. Finally, we verified the effect of GJ on OA in vivo and in vitro. In vivo experiments validated that GJ not only significantly attenuated OA phenotypes including articular cartilage degeneration and subchondral bone sclerosis but also reduced the expressions of tumor necrosis factor-α (TNF-α) and p-p65 in articular chondrocytes. Besides, GJ serum also had a protective effect on chondrocytes against inflammation caused by TNF-α in vitro. Hence, our study predicted and verified that GJ could exert anti-inflammation and anticatabolism effects partially via regulating TNF-α/NF-kappa B (NF-κB) signaling.

Senescent preosteoclast secretome promotes metabolic syndrome associated osteoarthritis through cyclooxygenase 2

Background

Metabolic syndrome-associated osteoarthritis (MetS-OA) is a distinct osteoarthritis phenotype defined by the coexistence of MetS or its individual components. Despite the high prevalence of MetS-OA, its pathogenic mechanisms are unclear. The aim of this study was to determine the role of cellular senescence in the development of MetS-OA.

Methods

Analysis of the human osteoarthritis initiative (OAI) dataset was conducted to investigate the MRI subchondral bone features of MetS-human OA participants. Joint phenotype and senescent cells were evaluated in two MetS-OA mouse models: high-fat diet (HFD)-challenged mice and STR/Ort mice. In addition, the molecular mechanisms by which preosteoclasts become senescent as well as how the senescent preosteoclasts impair subchondral bone microenvironment were characterized using in vitro preosteoclast culture system.

Results

Humans and mice with MetS are more likely to develop osteoarthritis-related subchondral bone alterations than those without MetS. MetS-OA mice exhibited a rapid increase in joint subchondral bone plate and trabecular thickness before articular cartilage degeneration. Subchondral preosteoclasts undergo senescence at the pre- or early-osteoarthritis stage and acquire a unique secretome to stimulate osteoblast differentiation and inhibit osteoclast differentiation. Antagonizing preosteoclast senescence markedly mitigates pathological subchondral alterations and osteoarthritis progression in MetS-OA mice. At the molecular level, preosteoclast secretome activates COX2-PGE2, resulting in stimulated differentiation of osteoblast progenitors for subchondral bone formation. Administration of a selective COX2 inhibitor attenuated subchondral bone alteration and osteoarthritis progression in MetS-OA mice. Longitudinal analyses of the human Osteoarthritis Initiative (OAI) cohort dataset also revealed that COX2 inhibitor use, relative to non-selective nonsteroidal antiinflammatory drug use, is associated with less progression of osteoarthritis and subchondral bone marrow lesion worsening in participants with MetS-OA.

Conclusions

Our findings suggest a central role of a senescent preosteoclast secretome-COX2/PGE2 axis in the pathogenesis of MetS-OA, in which selective COX2 inhibitors may have disease-modifying potential.

Funding

This work was supported by the National Institutes of Health grant R01AG068226 and R01AG072090 to MW, R01AR079620 to SD, and P01AG066603 to XC.

Zoledronic acid does not slow spinal radiographic progression of osteoarthritis in postmenopausal women with osteoporosis and radiographic osteoarthritis

Introduction:

Post hoc analyses of osteoporosis trials have suggested that alendronate and strontium ranelate may be associated with a reduction in the progression of spinal radiographic osteoarthritis (OA). We performed an analysis on a subgroup of participants in the horizon PFT trial (a 3-year randomized controlled trial (RCT) of yearly zoledronic acid (ZA) in postmenopausal women with osteoporosis), to evaluate the effect of ZA on the structural progression of spinal osteophytes (OPh) and disk space narrowing (DN).

Methods:

Paired lateral spinal X-rays (baseline and 36 months) were selected from the horizon PFT trial records restricted to those with radiographic OA at baseline. The X-rays were analyzed by two readers blinded to the treatment allocation. OPh and DN were scored separately using the Lane atlas (0–3 for increasing severity at each vertebral level) at all evaluable levels from T4–12 and L1–5.

Results:

A total of 504 sets of paired radiographs were included in the analysis, 245 in the ZA group and 259 in the placebo group. Overall, the rates of change of OPh and DN scores were low, and they were not statistically different between the groups (change in the whole spine OPh ZA 1.0 ± 1.6, placebo 0.8 ± 1.3, p = 0.1; DN ZA 0.3 ± 1.0, placebo 0.3 ± 0.8, p = 0.7).

Conclusion:

Yearly ZA for 3 years was not associated with a slowing of progression of OPh or DN in the thoracolumbar spine in patients with pre-existing radiographic OA.

The Mechanism and Role of ADAMTS Protein Family in Osteoarthritis

Osteoarthritis (OA) is a principal cause of aches and disability worldwide. It is characterized by the inflammation of the bone leading to degeneration and loss of cartilage function. Factors, including diet, age, and obesity, impact and/or lead to osteoarthritis. In the past few years, OA has received considerable scholarly attention owing to its increasing prevalence, resulting in a cumbersome burden. At present, most of the interventions only relieve short-term symptoms, and some treatments and drugs can aggravate the disease in the long run. There is a pressing need to address the safety problems due to osteoarthritis. A disintegrin-like and metalloprotease domain with thrombospondin type 1 repeats (ADAMTS) metalloproteinase is a kind of secretory zinc endopeptidase, comprising 19 kinds of zinc endopeptidases. ADAMTS has been implicated in several human diseases, including OA. For example, aggrecanases, ADAMTS-4 and ADAMTS-5, participate in the cleavage of aggrecan in the extracellular matrix (ECM); ADAMTS-7 and ADAMTS-12 participate in the fission of Cartilage Oligomeric Matrix Protein (COMP) into COMP lyase, and ADAMTS-2, ADAMTS-3, and ADAMTS-14 promote the formation of collagen fibers. In this article, we principally review the role of ADAMTS metalloproteinases in osteoarthritis. From three different dimensions, we explain how ADAMTS participates in all the following aspects of osteoarthritis: ECM, cartilage degeneration, and synovial inflammation. Thus, ADAMTS may be a potential therapeutic target in osteoarthritis, and this article may render a theoretical basis for the study of new therapeutic methods for osteoarthritis.

Acupotomy inhibits aberrant formation of subchondral bone through regulating osteoprotegerin/receptor activator of nuclear factor-κB ligand pathway in rabbits with knee osteoarthritis induced by modified Videman method

OBJECTIVE

To investigate the effects of acupotomy on inhibiting abnormal formation of subchondral bone in rabbits with knee osteoarthritis (KOA).

METHODS

A total of 24 New Zealand rabbits were randomly divided into four groups of 6 rabbits each [control, model, electroacupuncture (EA) and acupotomy]. Eighteen KOA model rabbits were established using a modified Videman method. Rabbits in EA and acupotomy groups received the intervention for 3 weeks. Then, the cartilage and subchondral bone unit were obtained and the histomorphological changes were recorded. Osteo-protegerin (OPG) and receptor activator of nuclear factor-κB ligand (RANKL) in subchondral bone were evaluated by Western blotting, real-time polymerase chain reaction and immunohistochemistry.

RESULTS

Compared with the model group, both the acupotomy and EA groups showed a significant decrease in the Lequesne index (both 0.01) and Mankin score ( 0.01, < 0.05). In addition, both EA and acupotomy groups had a higher expression of total articular cartilage (TAC) ( 0.05, < 0.01) and lower expression of articular calcified cartilage (ACC)/TAC ( 0.05, < 0.05) compared with the model group. The thickness of the subchondral bone plate in EA and acupotomy groups were decreased (both 0.01) compared to the model group. Moreover, trabecular bone volume (BV/TV), protein and relative expression of OPG and the ratio of OPG/RANKL in the subchondral bone of acupotomy group were decreased statistically significant, while these parameters were not significantly changed in the EA group compared with the model group.

CONCLUSIONS

In the rabbit model of KOA, acupotomy inhibits aberrant formation of subchondral bone by suppressing OPG/RANKL ratio as a potential therapy for KOA.

Biochanin A as a modulator of the inflammatory response: an updated overview and therapeutic potential

Uncontrolled inflammation and failure to resolve the inflammatory response are crucial factors involved in the progress of inflammatory diseases. Current therapeutic strategies aimed at controlling excessive inflammation are effective in some cases, though they may be accompanied by severe side effects, such as immunosuppression. Phytochemicals as a therapeutic alternative can have a fundamental impact on the different stages of inflammation and its resolution. Biochanin A (BCA) is an isoflavone known for its wide range of pharmacological properties, especially its marked anti-inflammatory effects. Recent studies have provided evidence of BCA's abilities to activate events essential for resolving inflammation. In this review, we summarize the most recent findings from pre-clinical studies of the pharmacological effects of BCA on the complex signaling network associated with the onset and resolution of inflammation and BCA's potential protective functionality in several models of inflammatory diseases, such as arthritis, pulmonary disease, neuroinflammation, and metabolic disease.

Insight into the potential pathogenesis of human osteoarthritis via single-cell RNA sequencing data on osteoblasts

Osteoarthritis (OA) is the most common degenerative joint disease caused by osteoblastic lineage cells. However, a comprehensive molecular program for osteoblasts in human OA remains underdeveloped. The single-cell gene expression of osteoblasts and microRNA array data were from human. After processing the single-cell RNA sequencing (scRNA-seq) data, it was subjected to principal component analysis (PCA) and T-Stochastic neighbor embedding analysis (TSNE). Differential expression analysis was aimed to find marker genes. Gene-ontology (GO) enrichment, Kyoto encyclopedia of genes and genomes (KEGG) pathway enrichment analysis and Gene set enrichment analysis (GSEA) were applied to characterize the molecular function of osteoblasts with marker genes. Protein-protein interaction (PPI) networks and core module were established for marker genes by using the STRING database and Cytoscape software. All nodes in the core module were considered to be hub genes. Subsequently, we predicted the potential miRNA of hub genes through the miRWalk, miRDB and TargetScan database and experimentally verified the miRNA by GSE105027. Finally, miRNA-mRNA regulatory network was constructed using the Cytoscape software. We characterized the single-cell expression profiling of 4387 osteoblasts from normal and OA sample. The proportion of osteoblasts subpopulations changed dramatically in the OA, with 70.42% of the pre-osteoblasts. 117 marker genes were included and the results of GO analysis show that up-regulated marker genes enriched in collagen-containing extracellular matrix were highly expressed in the pre-osteoblasts cluster. Both KEGG and GSEA analyses results indicated that IL-17 and NOD-like receptor signaling pathways were enriched in down-regulated marker genes. We visualize the weight of marker genes and constructed the core module in PPI network. In potential mRNA-miRNA regulatory network, hsa-miR-449a and hsa-miR-218-5p may be involved in the development of OA. Our study found that alterations in osteoblasts state and cellular molecular function in the subchondral bone region may be involved in the pathogenesis of osteoarthritis.

[Co-Culturing of Osteoblasts and Chondrocytes Upregulates HIF-1 Pathway of Chondrocytes via MAPK Signaling]

OBJECTIVE

To study the effect of co-culturing chondrocytes with osteoblasts on hypoxia-inducible factor (HIF)-1 pathway of chondrocytes and its mechanism.

METHODS

Chondrocytes and osteoblasts were separately extracted from the knee joint and skull of newborn mice by trypsin digestion. The co-culturing system of osteoblasts and chondrocytes was constructed by using Transwell inserts to culture the osteoblasts and 6-well plate to culture the chondrocytes. We used qRT-PCR to examine changes in the mRNA expression of HIFs and its target gene pyruvate dehydrogenase kinase 1 ( PDK1) in chondrocytes co-cultured for 24 h. Western blot was used to analyze changes in the protein expression of HIFs and PDK1 and the changes in the activation of mitogen activated protein kinase (MAPK) signaling pathway after the cells were co-cultured for 48 h. Reactive oxygen species (ROS) staining was done to show the changes of ROS production in chondrocytes co-cultured for 48 h.

RESULTS

The results of qRT-PCR and Western blot showed upregulated levels of HIF-1α gene and protein expression ( P<0.05) in the chondrocytes after they were co-cultured with osteoblasts. The gene and protein expression levels of PDK1 , the target gene of HIF-1, were also upregulated ( P<0.05). ROS staining showed that co-culturing of chondrocytes with osteoblasts decreased ROS production in chondrocytes. Western blot revealed that extracellular signal-regulated kinase (ERK) 1/2 and p38 signaling of co-cultured chondrocytes were enhanced ( P<0.05).

CONCLUSION

Co-culturing with osteoblasts enhanced the ERK1/2 and p38 signaling of chondrocytes and upregulated the HIF-1 pathway of chondrocytes.

Osteochondral tissue engineering: Perspectives for clinical application and preclinical development

The treatment of osteochondral defects (OCD) remains challenging. Among currently available surgical treatments for OCDs, scaffold-based treatments are promising to regenerate the osteochondral unit. However, there is still no consensus regarding the clinical effectiveness of these scaffold-based therapies for OCDs. Previous reviews have described the gradient physiological characteristics of osteochondral tissue and gradient scaffold design for OCD, tissue engineering strategies, biomaterials, and fabrication technologies. However, the discussion on bridging the gap between the clinical need and preclinical research is still limited, on which we focus in the present review, providing an insight into what is currently lacking in tissue engineering methods that failed to yield satisfactory outcomes, and what is needed to further improve these techniques. Currently available surgical treatments for OCDs are firstly summarized, followed by a comprehensive review on experimental animal studies in recent 5 years on osteochondral tissue engineering. The review will then conclude with what is currently lacking in these animal studies and the recommendations that would help enlighten the community in developing more clinically relevant implants.

The translational potential of this article

This review is attempting to summarize the lessons from clinical and preclinical failures, providing an insight into what is currently lacking in TE methods that failed to yield satisfactory outcomes, and what is needed to further improve these implants.

Cellular alterations and crosstalk in the osteochondral joint in osteoarthritis and promising therapeutic strategies

Osteoarthritis (OA) is a joint disorder involving cartilage degeneration and subchondral bone sclerosis. The bone-cartilage interface is implicated in OA pathogenesis due to its susceptibility to mechanical and biological factors. The crosstalk between cartilage and the underlying subchondral bone is elevated in OA due to multiple factors, such as increased vascularization, porosity, microcracks and fissures. Changes in the osteochondral joint are traceable to alterations in chondrocytes and bone cells (osteoblasts, osteocytes and osteoclasts). The phenotypes of these cells can change with the progression of OA. Aberrant intercellular communications among bone cell-bone cell and bone cell-chondrocyte are of great importance and might be the factors promoting OA development. An appreciation of cellular phenotypic changes in OA and the mechanisms by which these cells communicate would be expected to lead to the development of targeted drugs with fewer side effects.

Characterization and miRNA Profiling of Extracellular Vesicles from Human Osteoarthritic Subchondral Bone Multipotential Stromal Cells (MSCs)

Osteoarthritis (OA) is a heterogeneous disease in which the cross-talk between the cells from different tissues within the joint is affected as the disease progresses. Extracellular vesicles (EVs) are known to have a crucial role in cell-cell communication by means of cargo transfer. Subchondral bone (SB) resident cells and its microenvironment are increasingly recognised to have a major role in OA pathogenesis. The aim of this study was to investigate the EV production from OA SB mesenchymal stromal cells (MSCs) and their possible influence on OA chondrocytes. Small EVs were isolated from OA-MSCs, characterized and cocultured with chondrocytes for viability and gene expression analysis, and compared to small EVs from MSCs of healthy donors (H-EVs). OA-EVs enhanced viability of chondrocytes and the expression of chondrogenesis-related genes, although the effect was marginally lower compared to that of the H-EVs. miRNA profiling followed by unsupervised hierarchical clustering analysis revealed distinct microRNA sets in OA-EVs as compared to their parental MSCs or H-EVs. Pathway analysis of OA-EV miRNAs showed the enrichment of miRNAs implicated in chondrogenesis, stem cells, or other pathways related to cartilage and OA. In conclusion, OA SB MSCs were capable of producing EVs that could support chondrocyte viability and chondrogenic gene expression and contained microRNAs implicated in chondrogenesis support. These EVs could therefore mediate the cross-talk between the SB and cartilage in OA potentially modulating chondrocyte viability and endogenous cartilage regeneration.

Diagnostic and Therapeutic Role of Extracellular Vesicles in Articular Cartilage Lesions and Degenerative Joint Diseases

Two leading contributors to the global disability are cartilage lesions and degenerative joint diseases, which are characterized by the progressive cartilage destruction. Current clinical treatments often fail due to variable outcomes and an unsatisfactory long-term repair. Cell-based therapies were once considered as an effective solution because of their anti-inflammatory and immunosuppression characteristics as well as their differentiation capacity to regenerate the damaged tissue. However, stem cell-based therapies have inherent limitations, such as a high tumorigenicity risk, a low retention, and an engraftment rate, as well as strict regulatory requirements, which result in an underwhelming therapeutic effect. Therefore, the non-stem cell-based therapy has gained its popularity in recent years. Extracellular vesicles (EVs), in particular, like the paracrine factors secreted by stem cells, have been proven to play a role in mediating the biological functions of target cells, and can achieve the therapeutic effect similar to stem cells in cartilage tissue engineering. Therefore, a comprehensive review of the therapeutic role of EVs in cartilage lesions and degenerative joint diseases can be discussed both in terms of time and favorability. In this review, we summarized the physiological environment of a joint and its pathological alteration after trauma and consequent changes in EVs, which are lacking in the current literature studies. In addition, we covered the potential working mechanism of EVs in the repair of the cartilage and the joint and also discussed the potential therapeutic applications of EVs in future clinical use.

Excessive mechanical stretch‑mediated osteoblasts promote the catabolism and apoptosis of chondrocytes via the Wnt/β‑catenin signaling pathway

Excessive biomechanical loading is considered an important cause of osteoarthritis. Although the mechanical responses of chondrocytes and osteoblasts have been investigated, their communication during mechanical loading and the underlying molecular mechanisms are not yet fully known. The present study investigated the effects of excessive mechanically stretched osteoblasts on the metabolism and apoptosis of chondrocytes, and also assessed the involvement of the Wnt/β‑catenin signaling pathway. In the present study, rat chondrocytes and osteoblasts were subjected to mechanical tensile strain, and an indirect chondrocyte‑osteoblast co‑culture model was established. Reverse transcription‑quantitative PCR and western blotting were performed to determine the expression levels of genes and proteins of interest. An ELISA was performed to investigate the levels of cytokines, including matrix metalloproteinase (MMP) 13, MMP 3, interleukin‑6 (IL‑6) and prostaglandin E2 (PG E2), released from osteoblasts. Flow cytometry was performed to detect the apoptosis of chondrocytes exposed to stretched osteoblast conditioned culture medium. The levels of MMP 13, IL‑6 and PG E2 increased significantly in the supernatants of stretched osteoblasts compared with the un‑stretched group. By contrast, the mRNA expression levels of Collagen 1a and alkaline phosphatase were significantly decreased in osteoblasts subjected to mechanical stretch compared with the un‑stretched group. The mRNA expression level of Collagen 2a was significantly decreased, whereas the expression levels of MMP 13 and a disintegrin and metalloproteinase with thrombospondin‑like motifs 5 were significantly increased in chondrocytes subjected to mechanical stretch compared with the un‑stretched group. In the co‑culture model, the results indicated that excessive mechanically stretched osteoblasts induced the catabolism and apoptosis of chondrocytes, which was partly inhibited by Wnt inhibitor XAV‑939. The results of the present study demonstrated that excessive mechanical stretch led to chondrocyte degradation and inhibited osteoblast osteogenic differentiation; furthermore, excessive mechanically stretched osteoblasts induced the catabolism and apoptosis of chondrocytes via the Wnt/β‑catenin signaling pathway.

An In Vitro System to Study the Effect of Subchondral Bone Health on Articular Cartilage Repair in Humans

Chondrocyte-based cartilage repair strategies, such as articular chondrocyte implantation, are widely used, but few studies addressed the communication between native subchondral bone cells and the transplanted chondrocytes. An indirect co-culture model was developed, representing a chondrocyte/scaffold-construct repair of a cartilage defect adjoining bone, where the bone could have varying degrees of degeneration. Human BM-MSCs were isolated from two areas of subchondral bone in each of five osteochondral tissue specimens from five patients undergoing knee arthroplasty. These two areas underlaid the macroscopically and histologically best and worst cartilage, representing early and late-stage OA, respectively. BM-MSCs were co-cultured with normal chondrocytes suspended in agarose, with the two cell types separated by a porous membrane. After 0, 7, 14 and 21 days, chondrocyte-agarose scaffolds were assessed by gene expression and biochemical analyses, and the abundance of selected proteins in conditioned media was assessed by ELISA. Co-culture with late-OA BM-MSCs resulted in a reduction in GAG deposition and a decreased expression of genes encoding matrix-specific proteins (COL2A1 and ACAN), compared to culturing with early OA BM-MSCs. The concentration of TGF-β1 was significantly higher in the early OA conditioned media. The results of this study have clinical implications for cartilage repair, suggesting that the health of the subchondral bone may influence the outcomes of chondrocyte-based repair strategies.

Macro, Micro, and Molecular. Changes of the Osteochondral Interface in Osteoarthritis Development

Osteoarthritis (OA) is a long-term condition that causes joint pain and reduced movement. Notably, the same pathways governing cell growth, death, and differentiation during the growth and development of the body are also common drivers of OA. The osteochondral interface is a vital structure located between hyaline cartilage and subchondral bone. It plays a critical role in maintaining the physical and biological function, conveying joint mechanical stress, maintaining chondral microenvironment, as well as crosstalk and substance exchange through the osteochondral unit. In this review, we summarized the progress in research concerning the area of osteochondral junction, including its pathophysiological changes, molecular interactions, and signaling pathways that are related to the ultrastructure change. Multiple potential treatment options were also discussed in this review. A thorough understanding of these biological changes and molecular mechanisms in the pathologic process will advance our understanding of OA progression, and inform the development of effective therapeutics targeting OA.

MiR-30b-5p Influences Chronic Exercise Arthritic Injury by Targeting Hoxa1

We identified the role of miR-30b-5p in chronic exercise arthritic injury. Rats with chronic exercise arthritic injury received treatment with miR-30b-5p antagomiR. H&E and Safranin O-fast green staining were performed. The levels of tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) were detected. The binding relationship between homeobox A1 (Hoxa1) and miR-30b-5p was revealed. After manipulating the expressions of miR-30b-5p and/or Hoxa1 in chondrocytes, the viability, apoptosis and migration of chondrocytes were assessed. The levels of molecules were determined by qRT-PCR or Western blot. MiR-30b-5p antagomiR ameliorated articular cartilage lesion and destruction, reduced Mankin's score and the levels of TNF-α, IL-1β, miR-30b-5p, matrix metallopeptidase 13 (MMP-13), and cleaved caspase-3, and increased relative thickness and the levels of Hoxa1, Aggrecan and type II collagen (COLII) in model rats. MiR-30b-5p up-regulation decreased Hoxa1 level, viability, migration and induced apoptosis, whereas miR-30b-5p down-regulation produced the opposite effects. MiR-30b-5p up-regulation increased the levels of MMP-13 and cleaved caspase-3, but decreased those of Aggrecan and COLII in chondrocytes. However, the action of miR-30b-5p up-regulation on chondrocytes was reversed by Hoxa1 overexpression. In conclusion, miR-30b-5p is involved in cartilage degradation in rats with chronic exercise arthritic injury and regulates chondrocyte apoptosis and migration by targeting Hoxa1.

Acupotomy Contributes to Suppressing Subchondral Bone Resorption in KOA Rabbits by Regulating the OPG/RANKL Signaling Pathway

Subchondral bone lesions, as the crucial inducement for accelerating cartilage degeneration, have been considered as the initiating factor and the potential therapeutic target of knee osteoarthritis (KOA). Acupotomy, the biomechanical therapy guided by traditional Chinese meridians theory, alleviates cartilage deterioration by correcting abnormal mechanics. Whether this mechanical effect of acupotomy inhibits KOA subchondral bone lesions is indistinct. This study aimed to investigate the effects of acupotomy on inhibiting subchondral bone resorption and to define the possible mechanism in immobilization-induced KOA rabbits. After KOA modeling, 8 groups of rabbits (4w/6w acupotomy, 4w/6w electroacupuncture, 4w/6w model, and 4w/6w control groups) received the indicated intervention for 3 weeks. Histological and bone histomorphometry analyses revealed that acupotomy prevented both cartilage surface erosion and subchondral bone loss. Further, acupotomy suppressed osteoclast activity and enhanced osteoblast activity in KOA subchondral bone, showing a significantly decreased expression of tartrate-resistant acid phosphatase (TRAP), matrix metalloproteinases-9 (MMP-9), and cathepsin K (Ctsk) and a significantly increased expression of osteocalcin (OCN); this regulation may be mediated by blocking the decrease in osteoprotegerin (OPG) and the increase in NF-κB receptor activated protein ligand (RANKL). These findings indicated that acupotomy inhibited osteoclast activity and promoted osteoblast activity to ameliorate hyperactive subchondral bone resorption and cartilage degeneration in immobilization-induced KOA rabbits, which may be mediated by the OPG/RANKL signaling pathway. Taken together, our results indicate that acupotomy may have therapeutic potential in KOA by restoring the balance between bone formation and bone resorption to attenuate subchondral bone lesions.

Ectopic models recapitulating morphological and functional features of articular cartilage

BACKGROUND

Articular cartilage is an extremely specialized connective tissue which covers all diarthrodial joints. Implantation of chondrogenic cells without or with additional biomaterial scaffolds in ectopic locationsin vivo generates substitutes of cartilage with structural and functional characteristics that are used in fundamental investigations while also serving as a basis for translational studies.

METHODS

Literature search in Pubmed.

RESULTS AND DISCUSSION

This narrative review summarizes the most relevant ectopic models, among which subcutaneous, intramuscular, and kidney capsule transplantation and elaborates on implanted cells and biomaterial scaffolds and on their use to recapitulate morphological and functional features of articular cartilage. Although the absence of a physiological joint environment and biomechanical stimuli is the major limiting factor, ectopic models are an established component for articular cartilage research aiming to generate a bridge between in vitro data and the clinically more relevant translational orthotopic in vivo models when their limitations are considered.

Low-intensity pulsed ultrasound inhibits IL-6 in subchondral bone of temporomandibular joint osteoarthritis by suppressing the TGF-β1/Smad3 pathway

OBJECTIVE

This study aimed to provide further information on the exact mechanisms involved in the anti-inflammatory effect of low-intensity pulsed ultrasound (LIPUS) on rabbit temporomandibular joint osteoarthritis (TMJOA) on interleukin-6 (IL-6) production in subchondral bone, IL-6 production in IL-1β stimulated via inhibition of the TGF-β1/Smad3 pathway in mouse embryo osteoblast precursor (MC3T3-E1) cells.

DESIGN

Bilateral joints were injected with type II collagenase to establish TMJOA models in two male and four female rabbits. The left joint was continuously stimulated by LIPUS, while the right joint was treated with the power off in this model. One male and two female rabbits were used as normal healthy controls without treatment. The histological features of subchondral bone were examined by Safranin-O/Fast staining. Immunohistochemistry was conducted to evaluate IL-6 expression. Then, cells were stimulated by LIPUS with IL-1β. IL-6 expression and activity of the TGF-β1/Smad3 pathway were evaluated by Enzyme-linked immunosorbent assay (ELISA), Immunofluorescence and Western blotting, respectively. Specific inhibition of the TGF-β1/Smad3 pathway was conducted by transfecting with small interfering RNA (siRNA) of type II receptor (siTβRII).

RESULTS

LIPUS significantly ameliorated the production of IL-6 in vitro and in vivo. Its inhibitory effect on the production of IL-6 induced by IL-1β in MC3T3-E1 cells was partly reversed by siTβRII knockdown.

CONCLUSIONS

LIPUS inhibited IL-6 production by suppressing the TGF-β1/Smad3 pathway of subchondral bone in TMJOA. These data revealed the part of the pathways involved in the anti-inflammatory effect of LIPUS and provided a possible treatment strategy for TMJOA patients and other inflammatory diseases.

Investigating the protective effect of tanshinone IIA against chondrocyte dedifferentiation: a combined molecular biology and network pharmacology approach

Background

Osteoarthritis (OA) is a common degenerative disease with multifactorial etiology. The dedifferentiation of chondrocytes can accelerate the progress of OA. Tanshinone IIA (TIIA) has been widely used to treat OA for many years and has proved to be effective in inhibiting chondrocyte dedifferentiation. Until now, the precise mechanism of TIIA’s effect against dedifferentiation has not been well understood.

Methods

The targets of TIIA were explored from public databases using various methods. The related targets of OA were obtained from the GeneCards database and the Online Mendelian Inheritance in Man (OMIM) database. The potential targets and signaling pathways were determined using protein-protein interaction (PPI), Gene Ontology (GO), and the Kyoto Encyclopedia of Genes and Genomes (KEGG). Cell viability, proliferation, and metabolic activity were analyzed in vitro. The effects of TIIA on chondrocyte dedifferentiation were evaluated by assessing morphological changes, glycosaminoglycan (GAG) production, and messenger RNA (mRNA) levels of cartilage-related genes. After 48 hours of culture in medium with 100 μg/mL TIIA, chondrocytes/hydrogel spheres were implanted to repair cartilage defects in a rat model. The harvested specimens were examined with hematoxylin and eosin (H&E) staining and immunohistochemistry to evaluate cartilage regeneration.

Results

The results showed that there were 28 genes potentially interacting in the TIIA-chondrocyte dedifferentiation network, and nine hub genes were identified. In vitro experiments showed an inhibitory effect of TIIA on chondrocyte dedifferentiation. The proliferation and viability of chondrocytes were promoted by TIIA at a concentration of 100–200 μg/mL, but inhibited by TIIA at 400 μg/mL. Furthermore, the histology results showed that chondrocyte/hydrogel spheres pre-treated with TIIA had better cartilage repair.

Conclusions

This study revealed a systematic network pharmacology approach and provided a basis for the future study of TIIA as an effective treatment for cartilage regeneration. Moreover, in vitro and in vivo results confirmed the protective effects of TIIA against chondrocyte dedifferentiation.

Inhibition of mTORC1 in the rat condyle subchondral bone aggravates osteoarthritis induced by the overly forward extension of the mandible

The present study aimed to investigate the role of mammalian target of rapamycin complex 1 (mTORC1) in the remodeling of the condyle subchondral bone in rats with temporomandibular joint osteoarthritis (TMJ OA) and explore the mechanisms involved. In this study, we used rats fitted with appliances to overly extend the mandible forward as an animal model of TMJ OA. Bone samples were collected 2, 4, and 8 weeks after appliance fixation. Histological changes in the condyle subchondral bone were assessed by staining with hematoxylin and eosin, safranin O, and tartrate-resistant acid phosphatase. Real-time polymerase chain reaction and immunohistochemical analyses were performed to evaluate the expression levels of osterix, runt-related transcription factor 2 (RUNX2), osteocalcin (OCN), and mTORC1 in the condyle subchondral bone. The dissected condyles were analyzed using a micro-CT scanner. We also investigated changes in the condyle subchondral bone after mTORC1 pathway inhibition. In the early stages of TMJ OA, preosteoblasts, osteoblasts, and osteoclasts of the condyle subchondral bone were activated, which stimulated subchondral bone loss. MTORC1 was activated in subchondral bone preosteoblasts in rats with TMJ OA. The mTORC1 pathway was inhibited by a local injection of rapamycin, and the number of osteoblasts and mRNA levels of osteogenic markers in the condyle subchondral bone decreased, but the number of osteoclasts was basically unchanged. As a result, in the early stages of TMJ OA, subchondral bone loss and aggravation of OA were observed. These findings suggest that the mTORC1 signaling pathway plays an important role in subchondral bone remodeling during early stages of TMJ OA.

Feasibility of an Inversion Recovery-Prepared Fat-Saturated Zero Echo Time Sequence for High Contrast Imaging of the Osteochondral Junction

PURPOSE

The osteochondral junction (OCJ) region-commonly defined to include the deep radial uncalcified cartilage, tidemark, calcified cartilage, and subchondral bone plate-functions to absorb mechanical stress and is commonly associated with the pathogenesis of osteoarthritis. However, magnetic resonance imaging of the OCJ region is difficult due to the tissues' short transverse relaxation times (i.e., short T₂ or T₂*), which result in little or no signal with conventional MRI. The goal of this study is to develop a 3D adiabatic inversion recovery prepared fat saturated zero echo time (IR-FS-ZTE) sequence for high-contrast imaging of the OCJ.

METHOD

An IR-FS-ZTE MR sequence was developed to image the OCJ on a clinical 3T MRI scanner. The IR-FS-ZTE sequence employed an adiabatic inversion pulse followed by a fat saturation pulse that suppressed signals from the articular cartilage and fat. At an inversion time (TI) that was matched to the nulling point of the articular cartilage, continuous ZTE imaging was performed with a smoothly rotating readout gradient, which enabled time-efficient encoding of the OCJ region's short T₂ signal with a minimal echo time (TE) of 12 μs. An ex vivo experiment with six cadaveric knee joints, and an in vivo experiment with six healthy volunteers and three patients with OA were performed to evaluate the feasibility of the proposed approach for high contrast imaging of the OCJ. Contrast-to-noise ratios (CNRs) between the OCJ and its neighboring femoral and tibial cartilage were measured.

RESULTS

In the ex vivo experiment, IR-FS-ZTE produced improved imaging of the OCJ region over the clinical sequences, and significantly improved the contrast compared to FS-ZTE without IR preparation (p = 0.0022 for tibial cartilage and p = 0.0019 for femoral cartilage with t-test). We also demonstrated the feasibility of high contrast imaging of the OCJ region in vivo using the proposed IR-FS-ZTE sequence, thereby providing more direct information on lesions in the OCJ. Clinical MRI did not detect signal from OCJ due to the long TE (>20 ms).

CONCLUSION

IR-FS-ZTE allows direct imaging of the OCJ region of the human knee and may help in elucidating the role of the OCJ in cartilage degeneration.

Vertebral Fractures Associated with Spinal Sagittal Imbalance and Quality of Life in Acromegaly: A Radiographic Study with EOS 2D/3D Technology

INTRODUCTION

Acromegaly is commonly complicated by arthropathy and skeletal fragility with high risk of vertebral fractures (VFs).

OBJECTIVE

This study aimed to assess whether VFs may be associated with sagittal spine deformities, arthropathy, impaired quality of life (QoL), pain, and disability.

METHODS

Thirty-eight patients with acromegaly (median age: 55 years, 20 males) and 38 matched control subjects were evaluated by a low-dose sagittal and coronal planes, X-ray imaging system (EOS®-2D/3D) for morphometric VFs, radiological signs of spine arthropathy, and spine deformities (Cobb thoracic index ≥40°, pelvic incidence minus lumbar lordosis ≥10°, pelvic tilt >20°, and sagittal vertical axis ≥4 cm) determining sagittal spine imbalance. Acromegalic patients were also evaluated by questionnaires for QoL (Acromegaly QoL Questionnaire [AcroQoL] and Short Form-36 [SF-36]) and pain and disability (Western Ontario and McMaster University [WOMAC]).

RESULTS

Acromegalic patients showed higher prevalence of thoracic hyperkyphosis (i.e., Cobb thoracic index ≥40°; p = 0.04) and pelvic tilt >20° (p = 0.02) than control subjects. VFs were found in 34.2% of acromegalic patients (p = 0.003 vs. control subjects), in relationship with higher prevalence of hyperkyphosis (p = 0.03), pelvic tilt >20° (p = 0.04), sagittal vertical axis ≥4 cm (p = 0.03), and moderate/severe subchondral degeneration (p = 0.01). Moreover, patients with VFs had lower AcroQoL general health (p = 0.007) and SF-36 general health (p = 0.002) scores and higher WOMAC pain (p = 0.003) and global (p = 0.009) scores than patients who did not fracture.

CONCLUSIONS

In acromegaly, VFs may be associated with spine deformities and sagittal imbalance, spine arthropathy, impaired QoL, and disability.

Overexpression of HIF-1alpha in Bone Marrow Mesenchymal Stem Cells Promote the Repair of Mandibular Condylar Osteochondral Defect in a Rabbit Model

PURPOSE

The self-repair ability of temporomandibular joint (TMJ) cartilage is limited. Hypoxia-inducible factor-1 alpha (HIF-1alpha) may induce stem cells to promote chondrogenic repair. The purpose of this study was to systematically evaluate the effect of HIF-1alpha overexpression in bone marrow mesenchymal stem cells (BMSCs) combined with collagen scaffolds on the repair of TMJ condylar osteochondral defects in a rabbit model.

METHODS

Osteochondral defects of 3-mm diameter × 2-mm depth were created at the right side of the mandibular condyle in 40 New Zealand white rabbits. The defect sites were treated with simple empty, collagen scaffolds (COL), BMSCs/COL, and HIF-1alpha overexpression BMSCs/COL groups. The histomorphologic features of condylar cartilage were monitored by gross examination, safranin O-fast green staining (Solarbio, Beijing, China), and immunohistochemical staining. The changes in subchondral bone were examined by microcomputed tomography. Immunofluorescence staining was used to trace the transplanted BMSCs in vivo.

RESULTS

At 12 weeks postimplantation, histologic staining showed that the osteochondral defects in the simple empty and COL groups were mainly filled with fibrous tissue, whereas the BMSCs/COL and HIF-1alpha overexpression BMSCs/COL groups repaired the defect with fibrocartilage. Furthermore, the cartilage was better organized in the HIF-1alpha overexpression BMSCs/COL group compared with the BMSCs/COL group. Microcomputed tomography showed that osteochondral defects can cause abnormal hyperosteogeny in subchondral bone, and the transplantation of BMSCs, especially HIF-1alpha overexpression BMSCs, may alleviate osteosclerosis. Immunofluorescence staining showed that HIF-1alpha overexpression can promote the survival of transplanted BMSCs.

CONCLUSIONS

The transplantation of HIF-1alpha overexpression BMSCs combined with a COL scaffold promotes cartilaginous repair of condylar cartilage and inhibits subchondral bone sclerosis in TMJ condylar osteochondral defect rabbits.

Low-intensity pulsed ultrasound protects subchondral bone in rabbit temporomandibular joint osteoarthritis by suppressing TGF-β1/Smad3 pathway

Transforming growth factor β1(TGF-β1)/Smad3 pathway promotes the pathological progression of subchondral bone in osteoarthritis. The aim of this study is to determine the effect of low-intensity pulsed ultrasound (LIPUS) on the pathological progression and TGF-β1/Smad3 pathway of subchondral bone in temporomandibular joint osteoarthritis (TMJOA). Rabbit TMJOA model was established by type II collagenase induction. The left joint in this model was continuously stimulated with LIPUS for 3 and 6 weeks (1 MHz; 30 mW/cm² ) for 20 min/day. The morphological and histological features of subchondral bone were respectively examined by microcomputed tomography and Safranin-O staining. The number of osteoclasts was quantitatively assessed by tartrate-resistant acid phosphatase staining. Immunohistochemistry and Western blot analysis were conducted to evaluate the protein expression of Cathepsin K and TGF-β1/Smad3 pathway. The results indicated that LIPUS could improve the trabecular microstructure and histological characteristics of subchondral bone in rabbit TMJOA. It also suppressed abnormal subchondral bone resorption and activation of TGF-β1/Smad3 pathway, characterized by the number of osteoclasts, protein expression levels of Cathepsin K, TGF-β1, type II TGFβ receptor, and phosphorylated Smad3 (pSmad3) were decreased. In conclusion, LIPUS promoted the quality of subchondral bone by suppressing osteoclast activity and TGF-β1/Smad3 pathway in rabbit TMJOA.

Knee osteochondral junction imaging using a fast 3D T1-weighted ultrashort echo time cones sequence at 3T

The osteochondral junction (OCJ) of the knee joint is comprised of multiple tissue components, including a portion of the deep layer cartilage, calcified cartilage, and subchondral bone. The OCJ is of increasing radiological interest as it may be relevant in the early pathogenesis of osteoarthritis (OA). Due to its short transverse relaxation, the OCJ is invisible to clinical MR sequences. The purpose of this study was to develop a fast 3D T₁-weighted ultrashort echo time cones sequence with fat saturation (FS-UTE-Cones) for high resolution and high contrast imaging of the OCJ on a clinical 3T scanner. First, numerical simulations were performed to investigate how the flip angle affected the signal intensities and contrasts of both short and long T₁ tissues. The results from these simulations demonstrated that higher short T₁ contrast could be achieved with higher flip angle. Next, T₁ relaxation was measured for the different layers of a human patellar cartilage sample, and the results showed that the deepest layer had a significantly shorter T₁ value than other layers. Finally, a healthy knee joint was scanned with different flip angles and the OCJ was highlighted in the T₁-weighted FS-UTE-Cones sequence using a flip angle greater than 20°. The clinical T₂-weighted and proton density-weighted FSE sequences were also included for comparison, revealing a dark OCJ region. Representative T₁-weighted FS-UTE-Cones images of the whole knee of a healthy volunteer showed high signal intensity bands in the OCJ regions of the patella, femur, and tibia. On the other hand, T₁-weighted FS-UTE-Cones imaging of the knee joints of OA patients revealed regions with reduction or loss of these high signal intensity bands in the OCJ regions, indicating abnormal OCJ tissue composition. The proposed 3D T₁-weighted FS-UTE-Cones sequence with a 3-min scan time may be very useful for demonstrating the involvement of the OCJ regions in early OA.

Role of the SDF-1/CXCR4 signaling pathway in cartilage and subchondral bone in temporomandibular joint osteoarthritis induced by overloaded functional orthopedics in rats

OBJECTIVES

To (i) use a mandibular advancement appliance in rats to investigate the role of the stromal cell-derived factor/CXC receptor 4 (SDF-1/CXCR4) signaling pathway in temporomandibular joint osteoarthritis (TMJ OA) induced by overloaded functional orthopedics (OFO) and (ii) provide a cellular and molecular basis for efficacious treatment of skeletal class-II malocclusion and avoidance of TMJ OA.

METHOD

Male Sprague-Dawley rats (6 weeks) were divided randomly into control + normal saline (NS), EXP + ADM3100 (SDF-1 antagonist), EXP + NS, and control + ADM3100 groups. Changes in articular cartilage and subchondral bone after TMJ OA in these four groups were observed by hematoxylin and eosin (H&E), immunofluorescence double staining (IDS), Safranin-O staining, immunohistochemical (IHC) staining, real-time polymerase chain reaction, and micro-computed tomography at 2, 4, and 8 weeks.

RESULTS

OFO led to increased expression of SDF-1, CXCR4, and matrix metalloproteinase (MMP) 13 and decreased expression of collagen II. The thickness of the hypertrophic cartilage layer was reduced at 4 weeks in the EXP + NS group, and damage to subchondral bone was observed at 2 weeks. Using ADM3100 to inhibit SDF-1 signaling could attenuate expression of MMP13, cartilage damage, and osteoblast differentiation. IDS showed that the areas of expression of SDF-1 and OSX in subchondral bone overlapped.

CONCLUSIONS

Overloaded functional orthopedics (OFO) induced TMJ OA. The destruction of subchondral bone in TMJ OA caused by OFO occurred before damage to cartilage. SDF-1/CXCR4 may induce the osteogenic differentiation and cause cartilage degradation in TMJ OA caused by OFO.

Biphasic Double-Network Hydrogel With Compartmentalized Loading of Bioactive Glass for Osteochondral Defect Repair

Periarticular injury usually causes the defects of superficial cartilage and the underlying subchondral bone. Although some efficacious outcomes have been achieved by the existing therapeutic methods both in clinics and research, like symptomatic treatment, microfracture surgery, and tissue engineering technology, they still present specific disadvantages and complications. To improve this situation, we designed a biphasic (bi-) scaffold aiming to repair the structure of cartilage and subchondral bone synchronously. The scaffold consisted of a superior double-network (DN) hydrogel layer and a lower bioactive glass (BG) reinforced hydrogel layer, and the DN hydrogel included glycol chitosan (GC) and dibenzaldhyde functionalized poly(ethylene oxide) network, and sodium alginate (Alg) and calcium chloride (CaCl₂) network. To investigate its effectiveness, we applied this biphasic scaffold to repair osteochondral full-thickness defects in rabbit models. We set up six observation groups in total, including Untreated group, Microfracture group, BG only group, DN gel group, bi-DN gel group, and bi-DN/TGF-β gel group. With a follow-up period of 24 weeks, we evaluated the treatment effects by gross observation, micro-CT scan and histological staining. Besides, we further fulfilled the quantitative analysis of the data from ICRS score, O’Driscoll score and micro-CT parameters. The results revealed that neat GC/Alg DN hydrogel scaffold was only conductive to promoting cartilage regeneration and neat BG scaffold merely showed the excellent ability to reconstruct subchondral bone. While the biphasic scaffold performed better in repairing osteochondral defect synchronously, exhibiting more well-integrated cartilage-like tissue with positive staining of toluidine blue and col II immunohistochemistry, and more dense trabecular bone connecting closely with the surrounding host bone. Therefore, this method possessed the clinical application potential in treating articular injury, osteochondral degeneration, osteochondral necrosis, and sclerosis.

Joint Fluid Proteome after Anterior Cruciate Ligament Rupture Reflects an Acute Posttraumatic Inflammatory and Chondrodegenerative State

OBJECTIVE

The purpose of this study was to evaluate changes in the synovial fluid proteome following acute anterior cruciate ligament (ACL) injury.

DESIGN

This study represents a secondary analysis of synovial fluid samples collected from the placebo group of a previous randomized trial. Arthrocentesis was performed twice on 6 patients with an isolated acute ACL tear at a mean of 6 and 14 days postinjury. Synovial fluid was analyzed by a highly multiplexed assay of 1129 proteins (SOMAscan version 3, SomaLogic, Inc., Boulder, CO). Pathway analysis using DAVID was performed; genes included met 3 criteria: significant change between the 2 study time points using a paired t test, significant change between the 2 study time points using a Mann-Whitney nonparametric test, and significant Benjamini post hoc analysis.

RESULTS

Fifteen analytes demonstrated significant increases between time points. Five of the 15 have been previously associated with the onset and/or severity of rheumatoid arthritis, including apoliopoprotein E and isoform E3, vascular cell adhesion protein 1, interleukin-34, and cell surface glycoprotein CD200 receptor 1. Chondrodegenerative enzymes and products of cartilage degeneration all increased over time following injury: MMP-1 (P = 0.08, standardized response mean [SRM] = 1.00), MMP-3 (P = 0.05, SRM = 0.90), ADAM12 (P = 0.03, SRM = 1.31), aggrecan (P = 0.08, SRM = 1.13), and CTX-II (P = 0.07, SRM = 0.56). Notable pathways that were differentially expressed following injury were the cytokine-cytokine receptor interaction and osteoclast differentiation pathways.

CONCLUSIONS

The proteomic results and pathway analysis demonstrated a pattern of cartilage degeneration, not only consistent with previous findings but also changes consistent with an inflammatory arthritogenic process post-ACL injury.

Identification of Cartilage Microbial DNA Signatures and Associations With Knee and Hip Osteoarthritis

OBJECTIVE

Alterations of the gut microbiota have been implicated in many forms of arthritis, but an examination of cartilage microbial patterns has not been performed. This study was undertaken to characterize the microbial DNA profile of articular cartilage and determine changes associated with osteoarthritis (OA).

METHODS

We performed 16S ribosomal RNA gene deep sequencing on eroded and intact cartilage samples from knee OA patients (n = 21 eroded and 21 intact samples) and hip OA patients (n = 34 eroded and 33 intact samples) and cadaver controls (n = 10 knee samples and 10 hip samples). Microbial DNA diversity was assessed, groups were compared, and metagenomic profiles were reconstructed. Confirmation was performed in an independent cohort by clade-specific quantitative polymerase chain reaction. Findings in human cartilage were compared to those in cartilage from OA-susceptible C57BL/6 (B6) mice and OA-resistant MRL/MpJ (MRL) mice. Germ-free B6 mouse cartilage was analyzed as a methodologic control.

RESULTS

Alpha diversity was reduced in human OA versus control samples (P < 0.0001), and in hip versus knee samples (P < 0.0001). Numerous clades were different in human OA versus control samples, and similar findings were noted in comparisons of murine B6 versus MRL mice. Hip samples were microbiologically distinct from knee samples. OA microbial DNA demonstrated increased gram-negative constituents (P = 0.02). Functional analysis demonstrated increases in lipopolysaccharide production (P = 9.9 × 10-3 ), phosphatidylinositol signaling (P = 4.2 × 10-4 ), and nitrogen metabolism (P = 8 × 10-3 ) and decreases in sphingolipid metabolism (P = 7.7 × 10-4 ) associated with OA.

CONCLUSION

Our study reveals a microbial DNA signature in human and mouse cartilage. Alterations in this signature, including increases in gram-negative constituents, occur during the development and progression of human OA. Furthermore, our findings indicate that strain-specific signatures exist within mouse cartilage that mirror human patterns. Further study of the establishment and potential pathogenic role of these DNA signatures is needed.

Stabilization of HIF-1α alleviates osteoarthritis via enhancing mitophagy

Mitochondrial dysfunction leads to osteoarthritis (OA) and disc degeneration. Hypoxia inducible factor-1α (HIF-1α) mediated mitophagy has a protective role in several diseases. However, the underlying mechanism of HIF-1α mediated mitophagy in OA remains largely unknown. This current study was performed to determine the effect of HIF-1α mediated mitophagy on OA. Therefore, X-ray and tissue staining including HE staining, safranin O-fast green (S-O) and Alcian Blue were used to assess imageology and histomorphology differences of mouse knee joint. Transcriptional analysis was used to find the possible targets in osteoarthritis. Western blot analysis, RT-qPCR and immunofluorescence staining were used to detect the changes in gene and protein levels in the vitro experiment. The expression of HIF-1α was increased in human and mouse OA cartilage. HIF-1α knockdown by siRNA further impair the hypoxia-induced mitochondrial dysfunction; In contrast, HIF-1α mediated protective role was reinforced by prolylhydroxylase (PHD) inhibitor dimethyloxalylglycine (DMOG). In addition, HIF-1α stabilization could alleviate apoptosis and senescence via mitophagy in chondrocytes under hypoxia condition, which could also ameliorate surgery-induced cartilage degradation in mice OA model. In conclusion, HIF-1α mediated mitophagy could alleviate OA, which may serve as a promising strategy for OA treatment.

Triiodothyronine potentiates angiogenesis-related factor expression through PI3K/AKT signaling pathway in human osteoarthritic osteoblasts

Objective(s):

Previous study has indicated that triiodothyronine (T3) facilitated cartilage degeneration in osteoarthritis (OA). This study aimed to investigate the effects of T3 on angiogenesis-related factor expression in human osteoblasts of OA subchondral bone.

Materials and Methods:

The subchondral bone specimens were obtained from OA patients and healthy participants. The expressions of VEGF, HIF-1α, AKT, and phosphorylated AKT was detected by immunohistochemistry, Western blotting, and RT-qPCR in OA. Angiogenesis-related factor expression in OA osteoblasts was measured by treating different concentrations of T3. The hypoxia model and PX-478 (HIF-1α inhibitor) were employed to confirm the regulative role of HIF-1α for VEGF expression. The level of VEGF secretion was examined in osteoblasts supernatant using ELISA.

Results:

Immunohistochemistry showed strong staining of VEGF and HIF-1α in OA subchondral bone. The expression of VEGF, HIF-1α, and p-AKT in OA osteoblasts was higher than that of normal osteoblasts at protein and mRNA levels. The physiological concentration of T3 (10-7 M) in OA osteoblasts up-regulated the expression of VEGF, HIF-1α, and p-AKT after 24 hr and 48 hr culture, while a higher dose of T3 displayed the adverse effects. Additionally, VEGF and p-AKT expression was down-regulated when PX-478 inhibited HIF-1α protein.

Conclusion:

Our results suggested that local T3 could effectively increase angiogenesis-related factor expression by PI3K/AKT signaling pathway, and HIF-1α regulated the VEGF expression in OA osteoblasts.

Transcriptional Regulation of Osteoclastogenesis: The Emerging Role of KLF2

Dysregulation of osteoclastic differentiation and its activity is a hallmark of various musculoskeletal disease states. In this review, the complex molecular factors underlying osteoclastic differentiation and function are evaluated. The emerging role of KLF2 in regulation of osteoclastic differentiation is examined, specifically in the context of rheumatoid arthritis in which it has been most extensively studied among the musculoskeletal diseases. The therapies that exist to manage diseases associated with osteoclastogenesis are numerous and diverse. They are varied in their mechanisms of action and in the outcomes they produce. For this review, therapies targeting osteoclasts will be emphasized, though it should be noted that many therapies exist which bolster the action of osteoblasts. A new targeted molecular approach is under investigation for the future potential therapeutic development of rheumatoid arthritis.

Interleukin-1-Interleukin-17 Signaling Axis Induces Cartilage Destruction and Promotes Experimental Osteoarthritis

Osteoarthritis (OA), which is the most common degenerative joint disorder, has been considered a non-inflammatory disease with abnormal mechanics. Interleukin (IL)-17 is a pleiotropic cytokine involved in inflammatory diseases and their production is driven by the cytokine including IL-1 and IL-23. However, little is known about the mechanism of IL-17 in the development of OA. Here, we investigated the role of IL-17 in the pathogenesis of OA using monosodium iodoacetate (MIA)-injected IL-17 and IL-1 receptor antagonist (IL-1Ra) double-deficient mice. In MIA-injected IL-1Ra KO mice, nociceptive properties, degree of cartilage damage, and the level of inflammatory factors in articular cartilage were increased compared to MIA-injected wild-type mice. Interestingly, the intestinal architecture was impaired in IL-1Ra KO mice compared to wild-type mice and the damage was further exacerbated by MIA injection. Deficiency of IL-17 reduced nociceptive properties and cartilage destruction, as well as inflammation-related factors in MIA-injected IL-1Ra KO mice compared to MIA-injected wild-type mice. Furthermore, IL-17-treated chondrocytes from OA patients showed enhanced expression of catabolic factors that are involved in the destruction of cartilage in OA. IL-17 accelerates the destruction of cartilage and small intestine via regulation of several inflammatory mediators in an OA murine model. These results suggest that IL-17 plays a critical role in the development of OA.

Angiogenesis stimulated by elevated PDGF-BB in subchondral bone contributes to osteoarthritis development

Increased subchondral bone angiogenesis with blood vessels breaching the tidemark into the avascular cartilage is a diagnostic feature of human osteoarthritis. However, the mechanisms that initiate subchondral bone angiogenesis remain unclear. We show that abnormally increased platelet-derived growth factor-BB (PDGF-BB) secretion by mononuclear preosteoclasts induces subchondral bone angiogenesis, contributing to osteoarthritis development. In mice after destabilization of the medial meniscus (DMM), aberrant joint subchondral bone angiogenesis developed during an early stage of osteoarthritis, before articular cartilage damage occurred. Mononuclear preosteoclasts in subchondral bone secrete excessive amounts of PDGF-BB, which activates platelet-derived growth factor receptor-β (PDGFR-β) signaling in pericytes for neo-vessel formation. Selective knockout of PDGF-BB in preosteoclasts attenuates subchondral bone angiogenesis and abrogates joint degeneration and subchondral innervation induced by DMM. Transgenic mice that express PDGF-BB in preosteoclasts recapitulate pathological subchondral bone angiogenesis and develop joint degeneration and subchondral innervation spontaneously. Our study provides the first evidence to our knowledge that PDGF-BB derived from preosteoclasts is a key driver of pathological subchondral bone angiogenesis during osteoarthritis development and offers a new avenue for developing early treatments for this disease.

The Role of Chondrocyte Hypertrophy and Senescence in Osteoarthritis Initiation and Progression

Osteoarthritis (OA) is the most common joint disease that causes pain and disability in the adult population. OA is primarily caused by trauma induced by an external force or by age-related cartilage damage. Chondrocyte hypertrophy or chondrocyte senescence is thought to play a role in the initiation and progression of OA. Although chondrocyte hypertrophy and cell death are both crucial steps during the natural process of endochondral bone formation, the abnormal activation of these two processes after injury or during aging seems to accelerate the progression of OA. However, the exact mechanisms of OA progression and these two processes remain poorly understood. Chondrocyte senescence and hypertrophy during OA share various markers and processes. In this study, we reviewed the changes that occur during chondrocyte hypertrophy or senescence in OA and the attempts that were made to regulate them. Regulation of hypertrophic or senescent chondrocytes might be a potential therapeutic target to slow down or stop OA progression; thus, a better understanding of the processes is required for management.

Esculentoside A protects against osteoarthritis by ameliorating inflammation and repressing osteoclastogenesis

Osteoarthritis is a relatively common disorder of articular deterioration related to cartilage damage, subchondral bone remodelling, inflammation and metabolism. Agents that can inhibit cartilage degradation and osteoclastogenesis are required for the prevention and treatment of osteoarthritis. Esculentoside A, the highest concentration triterpene saponin isolated from the root of Phytolacca esculenta, has commonly been used for the treatment of chronic bronchitis. However, the role esculentoside A plays in ameliorating osteoarthritis has not been reported. We found that esculentoside A suppresses the expression of IL-1β-induced inflammatory and metabolic factors (IL-6, IL-8, TNF-α, MMP2, MMP3 and MMP13). In addition, esculentoside A restrains osteoclast formation by inhibiting the marker gene expression of NFATc1 and c-Fos. Our results indicate that esculentoside A markedly suppresses IL-1β-induced NF-κB and MAPK signalling pathway activation in chondrocytes, and inhibits RANKL-induced osteoclast precursor generation. Finally, treatment with esculentoside A inhibits the progressive cartilage degeneration and osteoclastogenesis in osteoarthritis mouse models. In summary, these results demonstrate that esculentoside A could be a latent therapeutic reagent for the treatment of osteoarthritis.