Osteoclasts degrade bone and cartilage knee joint compartments through different resorption processes

Validity evaluation of a rat model of monoiodoacetate-induced osteoarthritis with clinically effective drugs

BACKGROUND

Knee osteoarthritis (KOA) is the most common type of joint disease in elderly people and is characterized by pain and dysfunction. Although the monoiodoacetate (MIA)-induced model is widely used as a rodent KOA model, it is important to acknowledge the inherent limitations of this model, as the MIA model develops complex pathological phases on a daily basis. An accurate understanding of this model and the selection of an appropriate time point according to the target for drug candidates can lead to the development of clinically effective drugs.

METHODS

Changes in the pathological state of the MIA model were assessed via histopathological evaluation. Clodronate, a bisphosphonate, and diclofenac, a nonsteroidal anti-inflammatory drug (NSAID), were selected as models of clinically effective drugs due to their different mechanisms of action. The analgesic effects of both drugs on the MIA model were evaluated. The long-term effect of clodronate on subchondral bone osteoclasts was also evaluated.

RESULTS

Histopathological evaluation revealed that MIA-induced symptomatic behavior occurred in the early and late phases and was accompanied by synovial inflammation and osteoclast-related joint degeneration, respectively. Although clodronate inhibited symptomatic behavior and prevented cartilage degeneration from the early to late phases, diclofenac inhibited symptomatic behavior only in the early phase. Clodronate acted locally and inhibited the activation of subchondral osteoclasts.

CONCLUSIONS

Pathological changes, such as synovial changes in the early phase and knee joint degeneration in the late phase, in the MIA model are similar to those in human KOA. Our results indicate that the early phase in the MIA model is appropriate for evaluating the effects of anti-inflammatory agents such as NSAIDs and corticosteroids. The late phase in the MIA model is appropriate for evaluating the effects of drugs that act on cartilage and subchondral bone.

Injectable Regenerated Silk Fibroin Micro/Nanosphere with Enhanced Permeability and Stability for Osteoarthritis Therapy

In the therapy of early-stage osteoarthritis, to accomplish full infiltration of subchondral bone and cartilage, and to target osteoclast and chondrocyte simultaneously remain challenges in biomaterials design. Herein, a novel hierarchical drug delivery system is introduced, with micrometer-scale outer layer spheres composed of regenerated silk fibroin, characterized by connected porous structure through the n-butanol and regenerated silk fibroin combined emulsion route and freezing method. The design effectively resists clearance from the joint cavity, ensuring stable delivery and prolonged residence time within the joint space. Additionally, the system incorporates phenylboronic acid-enriched silk fibroin nanoparticles, stabilized through chemical cross-linking, which encapsulate isoliquiritin derived from Glycyrrhiza uralensis. These nanoparticles facilitate complete penetration of the cartilage extracellular matrix, exhibit pH-responsive behavior, neutralize reactive oxygen species, and enable controlled drug release, thereby enhancing therapeutic efficacy. The in vitro and in vivo experiments both demonstrate that the composite micro/nanospheres not only inhibit osteoclastogenesis with bone loss in subchondral bone and osteophyte formation, but also mitigate chondrocytes apoptosis, reduce oxidative stress associated with cartilage degeneration, and ameliorate neuropathic hyperalgesia, with the underlying mechanisms being elucidated. The study indicates that such an injectable strategy combining organic biomaterials with Chinese medicine holds substantial promise for the treatment of early osteoarthritis.

Osteoclasts control endochondral ossification via regulating acetyl-CoA availability

Osteoclast is critical in skeletal development and fracture healing, yet the impact and underlying mechanisms of their metabolic state on these processes remain unclear. Here, by using osteoclast-specific small GTPase Rheb1-knockout mice, we reveal that mitochondrial respiration, rather than glycolysis, is essential for cathepsin K (CTSK) production in osteoclasts and is regulated by Rheb1 in a mechanistic target of rapamycin complex 1 (mTORC1)-independent manner. Mechanistically, we find that Rheb1 coordinates with mitochondrial acetyl-CoA generation to fuel CTSK, and acetyl-CoA availability in osteoclasts is the central to elevating CTSK. Importantly, our findings demonstrate that the regulation of CTSK by acetyl-CoA availability is critical and may confer a risk for abnormal endochondral ossification, which may be the main cause of poor fracture healing on alcohol consumption, targeting Rheb1 could successfully against the process. These findings uncover a pivotal role of mitochondria in osteoclasts and provide a potent therapeutic opportunity in bone disorders.

Postoperative Antiosteoporotic Treatment with Zoledronic Acid Improves Rotator Cuff Healing but Does Not Improve Outcomes in Female Patients with Postmenopausal Osteoporosis: A Prospective, Single-Blinded, Randomized Study

PURPOSE

To investigate the effect of the antiosteoporotic agent zoledronic acid (ZA) on rotator cuff healing and clinical outcomes in patients with postmenopausal osteoporosis.

METHODS

We prospectively enrolled 138 female patients with postmenopausal osteoporosis who were scheduled to undergo arthroscopic rotator cuff repair (ARCR) from March 2020 to March 2021. Patients were randomly allocated to the ZA group (ARCR followed by intravenous ZA infusions at postoperative Day 1 and 1 year later) and the control group (ARCR alone). All patients were followed up for 24 months. Tendon healing was evaluated by ultrasonography at 6 weeks and 24 months after surgery. The American Shoulder and Elbow Surgeons (ASES) score, Western Ontario Rotator Cuff (WORC) index, and Numeric Rating Scale (NRS) for pain were recorded at each follow-up, and the minimal clinically important difference (MCID) was calculated.

RESULTS

A total of 124 patients were included in the final analysis, 61 in the ZA group and 63 in the control group. There was no statistically significant difference in participant characteristics between the 2 groups. The ZA group had a significantly higher tendon healing rate than the control group at 2 years after surgery (odds ratio = 5.0; 95% confidence interval [CI], 1.4-18.7; P = .014). Regarding clinical outcomes, 100% of patients exceeded the MCID in both groups, and no significant differences were found at 2 years after surgery between the 2 groups (ASES: 2.5 [95% CI, -2.2 to 7.2; P = .291]; WORC index: 4.5 [95% CI, -0.117 to 9.117; P = .056]; NRS: -0.1 [95% CI, -0.3 to 0.1; P = .394]).

CONCLUSIONS

Antiosteoporotic treatment with ZA reduced the retear rate but did not significantly influence the clinical outcomes after ARCR in female patients with postmenopausal osteoporosis. Outcomes of ARCR showed good results in both groups and exceeded the MCID.

LEVEL OF EVIDENCE

Level I, randomized controlled trial.

Trachelogenin alleviates osteoarthritis by inhibiting osteoclastogenesis and enhancing chondrocyte survival

BACKGROUND

Osteoarthritis (OA) is a prevalent global health concern associated with the loss of articular cartilage and subchondral bone. The lack of disease-modifying drugs for OA necessitates the exploration of novel therapeutic options. Our previous study has demonstrated that traditional Chinese medical herb Trachelospermum jasminoides (Lindl.) Lem. extract suppressed osteoclastogenesis and identified trachelogenin (TCG) as a representative compound. Here, we delved into TCG's potential to alleviate OA.

METHODS

We initially validated the in vivo efficacy of TCG in alleviating OA using a rat OA model. Subsequently, we isolated primary bone marrow-derived macrophages in vitro to investigate TCG's impact on osteoclastogenesis. We further employed a small molecule pull-down assay to verify TCG's binding target within osteoclasts. Finally, we isolated primary mouse chondrocytes in vitro to study TCG's regulatory effects and mechanisms on chondrocyte survival.

RESULTS

TCG preserved subchondral bone integrity and protected articular cartilage in a rat OA model. Subsequently, in vitro experiments unveiled TCG's capability to inhibit osteoclastogenesis and function through binding to Ras association proximate 1 (Rap1) and inhibiting its activation. Further study demonstrated that TCG inhibited Rap1/integrin αvβ3/c-Src/Pyk2 signaling cascade, and consequently led to failed F-actin ring formation. Besides, TCG promoted the proliferation of mouse primary chondrocytes while suppressing apoptosis in vitro. This is attributed to TCG's ability to upregulate HIF1α, thereby promoting glycolysis.

CONCLUSION

TCG exerted inhibitory effects on osteoclastogenesis through binding to Rap1 and inhibiting Rap1 activation, consequently preventing subchondral bone loss. Moreover, TCG enhanced chondrocyte survival by upregulating HIF1α and promoting glycolysis. These dual mechanisms collectively provide a novel approach to prevented against cartilage degradation.

Long Noncoding RNA lnc-TCEA1-3 Affects Osteoclastic Function by Regulating ATP6V1H

H subunit of V-ATPase (ATP6V1H) is specifically expressed in osteoclasts and its deficiency lead to osteoporosis. Our group previously found four intronic SNPs of ATP6V1H related to reduced bone mineral density, but the mechanisms was not clear. In this study, we found that the above four SNPs were located at lncRNA lnc-TCEA1-3 by using bioinformatics analysis. We further detected the function of lnc-TCEA1-3 on regulating ATP6V1H and osteoclast function using Atp6v1h knockout mice, lentivirus transfection and qPCR analysis. Over expression of lnc-TCEA1-3 up regulated the expression of ATP6V1H in HEK293 cells, HOS cells and primarily cultured osteoclasts, and increased the number of primarily cultured osteoclasts. In addition, over expression of lnc-TCEA1-3 exerted distinct effect on two transcripts of ATP6V1H in HEK293, HOS and osteoclasts. This study will facilitate the in-depth analysis of the effects of ATP6V1H on bone diseases, and discover new therapeutic strategies.

Distinct mast cell subpopulations within and around lymphatic vessels regulate lymph flow and progression of inflammatory-erosive arthritis in TNF-transgenic mice

Objective

Inflammatory-erosive arthritis is exacerbated by dysfunction of joint-draining popliteal lymphatic vessels (PLVs). Synovial mast cells are known to be pro-inflammatory in rheumatoid arthritis (RA). In other settings they have anti-inflammatory and tissue reparative effects. Herein, we elucidate the role of mast cells on PLV function and inflammatory-erosive arthritis in tumor necrosis factor transgenic (TNF-tg) mice that exhibit defects in PLVs commensurate with disease progression.

Methods

Whole mount immunofluorescent microscopy, toluidine blue stained histology, scanning electron microscopy, and in silico bioinformatics were performed to phenotype and quantify PLV mast cells. Ankle bone volumes were assessed by μCT, while corresponding histology quantified synovitis and osteoclasts. Near-infrared indocyanine green imaging measured lymphatic clearance as an outcome of PLV draining function. Effects of genetic MC depletion were assessed via comparison of 4.5-month-old WT, TNF-tg, MC deficient KitW-sh/W-sh (cKit-/-), and TNF-tg x cKit-/- mice. Pharmacological inhibition of mast cells was assessed by treating TNF-tg mice with placebo or cromolyn sodium (3.15mg/kg/day) for 3-weeks.

Results

PLVs are surrounded by MCT+/MCPT1+/MCPT4+ mast cells whose numbers are increased 2.8-fold in TNF-tg mice. The percentage of peri-vascular degranulating mast cells was inversely correlated with ICG clearance. A population of MCT+/MCPT1-/MCPT4- mast cells were embedded within the PLV structure. In silico single-cell RNA-seq (scRNAseq) analyses identified a population of PLV-associated mast cells (marker genes: Mcpt4, Cma1, Cpa3, Tpsb2, Kit, Fcer1a & Gata2) with enhanced TGFβ-related signaling that are phenotypically distinct from known MC subsets in the Mouse Cell Atlas. cKit-/- mice have greater lymphatic defects than TNF-tg mice with exacerbation of lymphatic dysfunction and inflammatory-erosive arthritis in TNF-tg x cKit-/- vs. TNF-Tg mice. Cromolyn sodium therapy stabilized PLV mast cells, increased TNF-induced bone loss, synovitis, and osteoclasts, and decreased ICG clearance.

Conclusions

Mast cells are required for normal lymphatic function. Genetic ablation and pharmacological inhibition of mast cells exacerbates TNF-induced inflammatory-erosive arthritis with decreased lymphatic clearance. Together, these findings support an inflammatory role of activated/degranulated peri-PLV mast cells during arthritic progression, and a homeostatic role of intra-PLV mast cells, in which loss of the latter dominantly exacerbates arthritis secondary to defects in joint-draining lymphatics, warranting investigation into specific cellular mechanisms.

Importance of Metalloproteinase Enzyme Group in Selected Skeletal System Diseases

Bone tissue is a dynamic structure that is involved in maintaining the homeostasis of the body due to its multidirectional functions, such as its protective, endocrine, or immunological role. Specialized cells and the extracellular matrix (ECM) are responsible for the remodeling of specific bone structures, which alters the biomechanical properties of the tissue. Imbalances in bone-forming elements lead to the formation and progression of bone diseases. The most important family of enzymes responsible for bone ECM remodeling are matrix metalloproteinases (MMPs)-enzymes physiologically present in the body's tissues and cells. The activity of MMPs is maintained in a state of balance; disruption of their activity is associated with the progression of many groups of diseases, including those of the skeletal system. This review summarizes the current understanding of the role of MMPs in bone physiology and the pathophysiology of bone tissue and describes their role in specific skeletal disorders. Additionally, this work collects data on the potential of MMPs as bio-markers for specific skeletal diseases.

Bioactivities and Mechanisms of Action of Diphyllin and Its Derivatives: A Comprehensive Systematic Review

Natural products are treasure houses for modern drug discovery. Diphyllin is a natural arylnaphthalene lignan lactone isolated from the leaf of Astilboides tabularis. Studies have found that it possesses plenty of bioactivity characteristics. In this paper, we reviewed the structure, bioactivity, and mechanism of action of diphyllin and its derivatives. The references were obtained from PubMed, Web of Science, and Science Direct databases up to August 2023. Papers without a bio-evaluation were excluded. Diphyllin and its derivatives have demonstrated V-ATPase inhibition, anti-tumor, anti-virus, anti-biofilm, anti-inflammatory, and anti-oxidant activities. The most studied activities of diphyllin and its derivatives are V-ATPase inhibition, anti-tumor activities, and anti-virus activities. Furthermore, V-ATPase inhibition activity is the mechanism of many bioactivities, including anti-tumor, anti-virus, and anti-inflammatory activities. We also found that the galactosylated modification of diphyllin is a common phenomenon in plants, and therefore, galactosylated modification is applied by researchers in the laboratory to obtain more excellent diphyllin derivatives. This review will provide useful information for the development of diphyllin-based anti-tumor and anti-virus compounds.

Leveraging osteoclast genetic regulatory data to identify genes with a role in osteoarthritis

There has been a growing interest in the role of the subchondral bone and its resident osteoclasts in the progression of osteoarthritis (OA). A recent genome-wide association study (GWAS) identified 100 independent association signals for OA traits. Most of these signals are led by noncoding variants, suggesting that genetic regulatory effects may drive many of the associations. We have generated a unique human osteoclast-like cell-specific expression quantitative trait locus (eQTL) resource for studying the genetics of bone disease. Considering the potential role of osteoclasts in the pathogenesis of OA, we performed an integrative analysis of this dataset with the recently published OA GWAS results. Summary data-based Mendelian randomization (SMR) and colocalization analyses identified 38 genes with a potential role in OA, including some that have been implicated in Mendelian diseases with joint/skeletal abnormalities, such as BICRA, EIF6, CHST3, and FBN2. Several OA GWAS signals demonstrated colocalization with more than one eQTL peak, including at 19q13.32 (hip OA with BCAM, PRKD2, and BICRA eQTL). We also identified a number of eQTL signals colocalizing with more than one OA trait, including FAM53A, GCAT, HMGN1, MGAT4A, RRP7BP, and TRIOBP. An SMR analysis identified 3 loci with evidence of pleiotropic effects on OA-risk and gene expression: LINC01481, CPNE1, and EIF6. Both CPNE1 and EIF6 are located at 20q11.22, a locus harboring 2 other strong OA candidate genes, GDF5 and UQCC1, suggesting the presence of an OA-risk gene cluster. In summary, we have used our osteoclast-specific eQTL dataset to identify genes potentially involved with the pathogenesis of OA.

The role of cells and signal pathways in subchondral bone in osteoarthritis

Osteoarthritis (OA) is mainly caused by ageing, strain, trauma, and congenital joint abnormalities, resulting in articular cartilage degeneration. During the pathogenesis of OA, the changes in subchondral bone (SB) are not only secondary manifestations of OA, but also an active part of the disease, and are closely associated with the severity of OA. In different stages of OA, there were microstructural changes in SB. Osteocytes, osteoblasts, and osteoclasts in SB are important in the pathogenesis of OA. The signal transduction mechanism in SB is necessary to maintain the balance of a stable phenotype, extracellular matrix (ECM) synthesis, and bone remodelling between articular cartilage and SB. An imbalance in signal transduction can lead to reduced cartilage quality and SB thickening, which leads to the progression of OA. By understanding changes in SB in OA, researchers are exploring drugs that can regulate these changes, which will help to provide new ideas for the treatment of OA.

Multiple roles of ALK3 in osteoarthritis

Osteoarthritis (OA) is a chronic degenerative joint disease characterized by progressive cartilage degradation, synovial membrane inflammation, osteophyte formation, and subchondral bone sclerosis. Pathological changes in cartilage and subchondral bone are the main processes in OA. In recent decades, many studies have demonstrated that activin-like kinase 3 (ALK3), a bone morphogenetic protein receptor, is essential for cartilage formation, osteogenesis, and postnatal skeletal development. Although the role of bone morphogenetic protein (BMP) signalling in articular cartilage and bone has been extensively studied, many new discoveries have been made in recent years around ALK3 targets in articular cartilage, subchondral bone, and the interaction between the two, broadening the original knowledge of the relationship between ALK3 and OA. In this review, we focus on the roles of ALK3 in OA, including cartilage and subchondral bone and related cells. It may be helpful to seek more efficient drugs or treatments for OA based on ALK3 signalling in future.

Bone marrow lesions in osteoarthritis: From basic science to clinical implications

Osteoarthritis (OA) is the most prevalent musculoskeletal disease characterized by multiple joint structure damages, including articular cartilage, subchondral bone and synovium, resulting in disability and economic burden. Bone marrow lesions (BMLs) are common and important magnetic resonance imaging (MRI) features in OA patients. Basic and clinical research on subchondral BMLs in the pathogenesis of OA has been a hotspot. New evidence shows that subchondral bone degeneration, including BML and angiogenesis, occurs not only at or after cartilage degeneration, but even earlier than cartilage degeneration. Although BMLs are recognized as important biomarkers for OA, their exact roles in the pathogenesis of OA are still unclear, and disputes about the clinical impact and treatment of BMLs remain. This review summarizes the current basic and clinical research progress of BMLs. We particularly focus on molecular pathways, cellular abnormalities and microenvironmental changes of subchondral bone that contributed to the formation of BMLs, and emphasize the crosstalk between subchondral bone and cartilage in OA development. Finally, potential therapeutic strategies targeting BMLs in OA are discussed, which provides novel strategies for OA treatment.

Maintaining hypoxia environment of subchondral bone alleviates osteoarthritis progression

Abnormal subchondral bone remodeling featured by overactivated osteoclastogenesis leads to articular cartilage degeneration and osteoarthritis (OA) progression, but the mechanism is unclear. We used lymphocyte cytosolic protein 1 (Lcp1) knockout mice to suppress subchondral osteoclasts in a mice OA model with anterior cruciate ligament transection (ACLT), and Lcp1^-/- mice showed decreased bone remodeling in subchondral bone and retarded cartilage degeneration. For mechanisms, the activated osteoclasts in subchondral bone induced type-H vessels and elevated oxygen concentration, which ubiquitylated hypoxia-inducible factor 1 alpha subunit (HIF-1α) in chondrocytes and led to cartilage degeneration. Lcp1 knockout impeded angiogenesis, which maintained hypoxia environment in joints and delayed the OA progression. Stabilization of HIF-1α delayed cartilage degeneration, and knockdown of Hif1a abolished the protective effects of Lcp1 knockout. Last, we showed that Oroxylin A, an Lcp1-encoded protein l-plastin (LPL) inhibitor, could alleviate OA progression. In conclusion, maintaining hypoxic environment is an attractive strategy for OA treatment.

The effect of postmenopausal osteoporosis on subchondral bone pathology in a rat model of knee osteoarthritis

This study aimed to investigate the additional effect of ovariectomy-induced osteoporosis (OP) on the pathology of knee osteoarthritis (OA) in a rat meniscectomized model, particularly focusing on subchondral bone changes and pain behaviour. Rats were divided into four groups, sham, OP, OA, OP plus OA, and assessed for histology, osteoclast activity, subchondral bone microstructure, and pain-related behaviour. Rats with OP plus OA had significantly increased calcified cartilage and subchondral bone damage scores, increased densities of subchondral osteoclasts in the weight-bearing area, and more porous subchondral trabecular bone compared with rats with OA. Loss of tidemark integrity was observed most frequently in rats with OP plus OA. The density of subchondral osteoclasts correlated with the calcified cartilage and subchondral bone damage score in rats with OA (OA and OP plus OA). No significant differences in the receptor activator of nuclear factor-kappa B ligand (RANKL)/osteoprotegerin (OPG) expression ratio in subchondral bone and pain-related behavioural tests were observed between rats with OA and rats with OP plus OA. In rats with OA, coexisting OP potentially aggravated OA pathology mainly in calcified cartilage and subchondral trabecular bone by increasing subchondral osteoclast activity.

Structural clues to articular calcified cartilage function: A descriptive review of this crucial interface tissue

Articular calcified cartilage (ACC) has been dismissed, by some, as a remnant of endochondral ossification without functional relevance to joint articulation or weight-bearing. Recent research indicates that morphologic and metabolic ACC features may be important, reflecting knee joint osteoarthritis (OA) predisposition. ACC is less investigated than neighbouring joint tissues, with its component chondrocytes and mineralised matrix often being either ignored or integrated into analyses of hyaline articular cartilage and subchondral bone tissue respectively. Anatomical variation in ACC is recognised between species, individuals and age groups, but the selective pressures underlying this variation are unknown. Consequently, optimal ACC biomechanical features are also unknown as are any potential locomotory roles. This review collates descriptions of ACC anatomy and biology in health and disease, with a view to revealing its structure/function relationship and highlighting potential future research avenues. Mouse models of healthy and OA joint ageing have shown disparities in ACC load-induced deformations at the knee joint. This raises the hypothesis that ACC response to locomotor forces over time may influence, or even underlie, the bony and hyaline cartilage symptoms characteristic of OA. To effectively investigate the ACC, greater resolution of joint imaging and merging of hierarchical scale data will be required. An appreciation of OA as a 'whole joint disease' is expanding, as is the possibility that the ACC may be a key player in healthy ageing and in the transition to OA joint pathology.

The immune microenvironment in cartilage injury and repair

The ability of articular cartilage to repair itself is limited because it lacks blood vessels, nerves, and lymph tissue. Once damaged, it can lead to joint swelling and pain, accelerating the progression of osteoarthritis. To date, complete regeneration of hyaline cartilage exhibiting mechanical properties remains an elusive goal, despite the many available technologies. The inflammatory milieu created by cartilage damage is critical for chondrocyte death and hypertrophy, extracellular matrix breakdown, ectopic bone formation, and progression of cartilage injury to osteoarthritis. In the inflammatory microenvironment, mesenchymal stem cells (MSCs) undergo aberrant differentiation, and chondrocytes begin to convert or dedifferentiate into cells with a fibroblast phenotype, thereby resulting in fibrocartilage with poor mechanical qualities. All these factors suggest that inflammatory problems may be a major stumbling block to cartilage repair. To produce a milieu conducive to cartilage repair, multi-dimensional management of the joint inflammatory microenvironment in place and time is required. Therefore, this calls for elucidation of the immune microenvironment of cartilage repair after injury. This review provides a brief overview of: (1) the pathogenesis of cartilage injury; (2) immune cells in cartilage injury and repair; (3) effects of inflammatory cytokines on cartilage repair; (4) clinical strategies for treating cartilage defects; and (5) strategies for targeted immunoregulation in cartilage repair. STATEMENT OF SIGNIFICANCE: Immune response is increasingly considered the key factor affecting cartilage repair. It has both negative and positive regulatory effects on the process of regeneration and repair. Proinflammatory factors are secreted in large numbers, and necrotic cartilage is removed. During the repair period, immune cells can secrete anti-inflammatory factors and chondrogenic cytokines, which can inhibit inflammation and promote cartilage repair. However, inflammatory factors persist, which accelerate the degradation of the cartilage matrix. Furthermore, in an inflammatory microenvironment, MSCs undergo abnormal differentiation, and chondrocytes begin to transform or dedifferentiate into fibroblast-like cells, forming fibrocartilage with poor mechanical properties. Consequently, cartilage regeneration requires multi-dimensional regulation of the joint inflammatory microenvironment in space and time to make it conducive to cartilage regeneration.

[The Role of Platelet-Derived Growth Factor-AA in the Pathogenesis and Development of Osteoarthritis]

Osteoarthritis (OA) is a chronic degenerative disease involving the entire joint. The pathogenesis and progression of OA bear close connection to the destruction and the abnormal metabolism of cartilage, subchondral bones and synovium. Platelet derived growth factor-AA (PDGF-AA) is a critical mitogenic and chemotactic factor for a variety of cells, including chondrocytes, mesenchymal stem cells, osteoclasts and osteoblasts, and PDGF-AA promotes effective wound repair. This paper reviewed the pathological changes of cartilage, subchondral bones and synovium in the process of OA development, and summarized research progress regarding the effect of PDGF-AA on the tissues and related cells mentioned above. Current studies have basically clarified the pathological changes of cartilage, subchondral bones and synovium in OA patients, and have shown that PDGF-AA serves critical regulatory function in the tissues or cells involved in OA, the internal mechanism of which remains unclear, though. More studies should be done to find ways to apply PDGF-AA for clinic purpose and to diagnose and treat OA on the cellular basis.

Identification of Common Pathogenic Pathways Involved in Hemochromatosis Arthritis and Calcium Pyrophosphate Deposition Disease: a Review

OBJECTIVES

Arthritis is a common clinical manifestation of hereditary hemochromatosis (HH), and HH is one of a handful of conditions linked to calcium pyrophosphate deposition (CPPD) in joints. The connection between these two types of arthritis has not yet been fully elucidated. In light of new pathogenic pathways recently implicated in CPPD involving bone, we reviewed the literature on the etiology of hemochromatosis arthropathy (HHA) seeking shared pathogenic mechanisms.

RESULTS

Clinical observations reinforce striking similarities between HHA and CPPD even in the absence of CPP crystals. They share a similar joint distribution, low grade synovial inflammation, and generalized bone loss. Excess iron damages chondrocytes and bone cells in vitro. While direct effects of iron on cartilage are not consistently seen in animal models of HH, there is decreased osteoblast alkaline phosphatase activity, and increased osteoclastogenesis. These abnormalities are also seen in CPPD. Joint repair processes may also be impaired in both CPPD and HHA.

CONCLUSIONS

Possible shared pathogenic pathways relate more to bone and abnormal damage/repair mechanisms than direct damage to articular cartilage. While additional work is necessary to fully understand the pathogenesis of arthritis in HH and to firmly establish causal links with CPPD, this review provides some plausible hypotheses explaining the overlap of these two forms of arthritis.

Dihydroartemisinin attenuates osteoclast formation and bone resorption via inhibiting the NF‑κB, MAPK and NFATc1 signaling pathways and alleviates osteoarthritis

Osteoarthritis (OA) is a chronic, progressive and degenerative disease, and its incidence is increasing on a yearly basis. However, the pathological mechanism of OA at each stage is still unclear. The present study aimed to explore the underlying mechanism of dihydroartemisinin (DHA) in terms of its ability to inhibit osteoclast activation, and to determine its effects on OA in rats. Bone marrow‑derived macrophages were isolated as osteoclast precursors. In the presence or absence of DHA, osteoclast formation was assessed by tartrate‑resistant acid phosphatase (TRAP) staining, cell viability was assessed by Cell Counting Kit‑8 assay, the presence of F‑actin rings was assessed by immunofluorescence, bone resorption was determined by bone slices, luciferase activities of NF‑κB and nuclear factor of activated T cell cytoplasmic 1 (NFATc1) were determined using luciferase assay kits, the protein levels of biomolecules associated with the NF‑κB, MAPK and NFATc1 signaling pathways were determined using western blotting, and the expression of genes involved in osteoclastogenesis were measured using reverse transcription‑quantitative PCR. A knee OA rat model was designed by destabilizing the medial meniscus (DMM). A total of 36 rats were assigned to three groups, namely the sham‑operated, DMM + vehicle and DMM + DHA groups, and the rats were administered DHA or DMSO. At 4 and 8 weeks postoperatively, the microarchitecture of the subchondral bone was analyzed using micro‑CT, the thickness of the cartilage layers was calculated using H&E staining, the extent of cartilage degeneration was scored using Safranin O‑Fast Green staining, TRAP‑stained osteoclasts were counted, and the levels of receptor activator of NF‑κB ligand (RANKL), C‑X‑C‑motif chemokine ligand 12 (CXCL12) and NFATc1 were measured using immunohistochemistry. DHA was found to inhibit osteoclast formation without cytotoxicity, and furthermore, it did not affect bone formation. In addition, DHA suppressed the expression levels of NF‑κB, MAPK, NFATc1 and genes involved in osteoclastogenesis. Progressive cartilage loss was observed at 8 weeks postoperatively. Subchondral bone remodeling was found to be dominated by bone resorption accompanied by increases in the levels of RANKL, CXCL12 and NFATc1 during the first 4 weeks. DHA was found to delay OA progression by inhibiting osteoclast formation and bone resorption during the early phase of OA. Taken together, the results of the present study demonstrated that the mechanism through which DHA could inhibit osteoclast activation may be associated with the NF‑κB, MAPK and NFATc1 signaling pathways, thereby indicating a potential novel strategy for OA treatment.

Loss of mutual protection between human osteoclasts and chondrocytes in damaged joints initiates osteoclast-mediated cartilage degradation by MMPs

Osteoclasts are multinucleated, bone-resorbing cells. However, they also digest cartilage during skeletal maintenance, development and in degradative conditions including osteoarthritis, rheumatoid arthritis and primary bone sarcoma. This study explores the mechanisms behind the osteoclast–cartilage interaction. Human osteoclasts differentiated on acellular human cartilage expressed osteoclast marker genes (e.g. CTSK, MMP9) and proteins (TRAP, VNR), visibly damaged the cartilage surface and released glycosaminoglycan in a contact-dependent manner. Direct co-culture with chondrocytes during differentiation increased large osteoclast formation (p < 0.0001) except when co-cultured on dentine, when osteoclast formation was inhibited (p = 0.0002). Osteoclasts cultured on dentine inhibited basal cartilage degradation (p = 0.012). RNA-seq identified MMP8 overexpression in osteoclasts differentiated on cartilage versus dentine (8.89-fold, p = 0.0133), while MMP9 was the most highly expressed MMP. Both MMP8 and MMP9 were produced by osteoclasts in osteosarcoma tissue. This study suggests that bone-resident osteoclasts and chondrocytes exert mutually protective effects on their ‘native’ tissue. However, when osteoclasts contact non-native cartilage they cause degradation via MMPs. Understanding the role of osteoclasts in cartilage maintenance and degradation might identify new therapeutic approaches for pathologies characterized by cartilage degeneration.

Non-polar lipid from greenshell mussel (Perna canaliculus) inhibits osteoclast differentiation

The osteoclast-dependent bone resorption process is a crucial part of the bone regulatory system. The excessive function of osteoclasts can cause diseases of bone, joint, and other tissues such as osteoporosis and osteoarthritis. Greenshell mussel oil (GSM), a good source of long chain omega-3 polyunsaturated fatty acids (LCn-3PUFAs), was fractionated into total lipid, polar lipid, and non-polar lipid components and their anti-osteoclastogenic activity tested in RAW 264.7 cell cultures. Osteoclast differentiation process was achieved after 5 days of incubation with RANKL in 24-well culture plates. Introducing the non-polar lipid fraction into the culture caused a lack of cell differentiation, and a reduction in tartrate-resistant acid phosphatase (TRAP) activity and TRAP cell numbers in a dose-dependent manner (50% reduction at the concentration of 20 μg/mL, p < 0.001). Moreover, actin ring formation was significantly diminished by non-polar lipids at 10-20 μg/mL. The bone digestive enzymes released by osteoclasts into the pit formation were also compromised by downregulating gene expression of cathepsin K, carbonic anhydrase II (CA II), matrix metalloproteinase 9 (MMP-9), and nuclear factor of activated T-cells, cytoplasmic 1 (NFATc1). This study revealed that the non-polar lipid fraction of GSM oil contains bioactive substances which possess potent anti-osteoclastogenic activity.

Cell Interplay in Osteoarthritis

Osteoarthritis (OA) is a common chronic disease and a significant health concern that needs to be urgently solved. OA affects the cartilage and entire joint tissues, including the subchondral bone, synovium, and infrapatellar fat pads. The physiological and pathological changes in these tissues affect the occurrence and development of OA. Understanding complex crosstalk among different joint tissues and their roles in OA initiation and progression is critical in elucidating the pathogenic mechanism of OA. In this review, we begin with an overview of the role of chondrocytes, synovial cells (synovial fibroblasts and macrophages), mast cells, osteoblasts, osteoclasts, various stem cells, and engineered cells (induced pluripotent stem cells) in OA pathogenesis. Then, we discuss the various mechanisms by which these cells communicate, including paracrine signaling, local microenvironment, co-culture, extracellular vesicles (exosomes), and cell tissue engineering. We particularly focus on the therapeutic potential and clinical applications of stem cell-derived extracellular vesicles, which serve as modulators of cell-to-cell communication, in the field of regenerative medicine, such as cartilage repair. Finally, the challenges and limitations related to exosome-based treatment for OA are discussed. This article provides a comprehensive summary of key cells that might be targets of future therapies for OA.

Disease-Modifying Potential of Metformin and Alendronate in an Experimental Mouse Model of Osteoarthritis

Osteoarthritis (OA) is the most common degenerative joint disease causing progressive damages of the cartilage and subchondral bone, synovial inflammation, and severe pain. Despite the complex pathomorphological changes that occur in OA, the approach to different forms of OA is standardized. The global results from pharmacological treatment are not satisfactory. Hence, this study aimed to explore the effects of metformin, alendronate, and their combination on OA development and progression in mice with collagenase-induced osteoarthritis (CIOA). Female ICR (CD-2) mice were randomized to five groups: control group, CIOA untreated, CIOA + metformin, CIOA + alendronate, and CIOA + metformin + alendronate. OA was induced by the intra-articular (i.a.) injection of collagenase. OA phenotype was analyzed by flow cytometry (bone marrow cell differentiation), ELISA (serum levels of the adipokines leptin and resistin), and histology (pathological changes of the knee joint). Treatment with metformin, alendronate, or their combination inhibited the expression of RANK and RANKL on osteoblasts and osteoclasts obtained by ex vivo cultivation of bone marrow cells in mineralization or osteoclastogenic media. In addition, metformin treatment was effective for the attenuation of fibroblast differentiation, but not of mesenchymal stem cells (MSCs), while alendronate had an opposite effect. The combination of metformin and alendronate had a suppressive effect on both MSCs and fibroblasts differentiation. Treatment with metformin, alendronate, and their combination decreased serum concentrations of leptin and resistin in the chronic phase of arthritis. The histopathological examination showed that compared with the untreated CIOA group (OA score 9), the groups treated with metformin (OA score 4) or alendronate (OA score 6) had lower scores for cartilage changes. Metformin combined with alendronate significantly decreased the degree of cartilage degeneration (OA score 2), suggesting that this combination might be a useful approach for the treatment of OA patients.

MicroRNA-151a-3p Functions in the Regulation of Osteoclast Differentiation: Significance to Postmenopausal Osteoporosis

BACKGROUND

Studies have found the pivotal role of miRNAs in the progression of postmenopausal osteoporosis (OP). However, the function of miRNAs in OP is unclear. This study aimed to explore the biological functions of microRNA-151a-3p in OP.

METHODS

RT-qPCR was employed to assess the expression of microRNA-151a-3p in serum isolated from OP patients and healthy controls. Dual-energy X-ray absorptiometry (DXA) was used to measure the bone mineral density (BMD) of the lumbar spine. The expression levels of c-Fos, NFATc1, and TRAP were tested by Western blot. Ovariectomized (OVX) rats were treated with antago microRNA-151a-3p or antago NC, and then serum and lumbar vertebrae were collected for ELISA and bone histomorphology analysis.

RESULTS

The expression of microRNA-151a-3p in postmenopausal women with osteoporosis was significantly up-regulated, and microRNA-151a-3p level was negatively correlated with BMD. During osteoclastogenesis, microRNA-151a-3p level was obviously increased. Overexpression of microRNA-151a-3p promoted the differentiation of RANKL-induced THP-1 and RAW264.7 cells into osteoclasts, whereas silencing of microRNA-151a-3p resulted in the opposite results. Silencing of microRNA-151a-3p in OVX rats altered osteoclastogenesis-related factors and raised BMD.

CONCLUSION

MicroRNA-151a-3p could partly regulate osteoporosis by promoting osteoclast differentiation, and miRNA-151a-3p could be a potential therapeutic target for postmenopausal osteoporosis.

Matrix Metalloproteinase 3: A Promoting and Destabilizing Factor in the Pathogenesis of Disease and Cell Differentiation

Cells must alter their expression profiles and morphological characteristics but also reshape the extracellular matrix (ECM) to fulfill their functions throughout their lifespan. Matrix metalloproteinase 3 (MMP-3) is a member of the matrix metalloproteinase (MMP) family, which can degrade multiple ECM components. MMP-3 can activate multiple pro-MMPs and thus initiates the MMP-mediated degradation reactions. In this review, we summarized the function of MMP-3 and discussed its effects on biological activities. From this point of view, we emphasized the positive and negative roles of MMP-3 in the pathogenesis of disease and cell differentiation, highlighting that MMP-3 is especially closely involved in the occurrence and development of osteoarthritis. Then, we discussed some pathways that were shown to regulate MMP-3. By writing this review, we hope to provide new topics of interest for researchers and attract more researchers to investigate MMP-3.

The Effect of Antiosteoporosis Therapy With Risedronate on Rotator Cuff Healing in an Osteoporotic Rat Model

BACKGROUND

Osteoporosis increases the revision rate of rotator cuff repair (RCR). Weak fixation might not be the only cause of high RCR failure rates. The biological mechanism associated with tendon-to-bone healing after RCR in osteoporosis should be investigated.

HYPOTHESIS

(1) Osteoporosis would impair rotator cuff healing through the high osteoclastic activity at the repaired interface. (2) Risedronate would promote rotator cuff healing by reducing osteoclastic activity at the repaired interface.

STUDY DESIGN

Controlled laboratory study.

METHODS

A total of 84 female Sprague Dawley rats were randomly treated using ovariectomy or sham surgeries to establish osteoporotic and nonosteoporotic rat models. After confirming osteoporosis, a chronic rotator cuff tear model was created and RCR was performed. Postoperatively, osteoporotic rats were randomly divided into osteoporosis (OP) and osteoporosis with risedronate administration (OP+RIS) groups. Nonosteoporotic rats were used as the control (CON) group. Osteoclastic activity was measured at 1 and 3 weeks after RCR, and histologic analysis of the tendon-to-bone interface, bone morphometric evaluation, and biomechanical tests were performed at 4 and 8 weeks.

RESULTS

At the early healing stages of 1 and 3 weeks after RCR, the OP group showed the highest osteoclast density at the repaired interface. Compared with the OP group, risedronate administration significantly decreased osteoclast density in the OP+RIS group. At 8 weeks, histologic scores were greater in the OP+RIS group than in the OP group but still lower than in the CON group. Histologic scores at 8 weeks were negatively correlated with osteoclast density at the early healing stage. Additionally, the OP+RIS group showed better bone morphometric parameters and biomechanical properties than did the OP group.

CONCLUSION

Osteoporosis impaired rotator cuff healing, which might be related to the high osteoclast density at the repaired interface at the early healing stage. Postoperative risedronate administration decreased osteoclast density and enhanced rotator cuff healing in osteoporotic rats, although the effect was inferior to that in nonosteoporotic rats.

CLINICAL RELEVANCE

Postoperative risedronate administration can be considered a potential therapy to enhance rotator cuff healing in patients with postmenopausal osteoporosis. However, this needs to be verified in a clinical setting.

Blocking TNFα attenuates progressive cartilage matrix degradation in inflammatory arthritis

Because damage to hyaline cartilage is irreversible, relieving progressive cartilage destruction is an important therapeutic approach for inflammatory arthritis. In the present study, human hyaline chondrocytes were isolated from total knee replacements of 15 patients with osteoarthritis (OA) and three with rheumatoid arthritis (RA). Synovial fluid of OA (n=25) and RA (n=34) were collected to measure tumor necrosis factor α (TNFα) using ELISA. Consistent with previous studies, the synovial fluid exhibited high TNFα levels and hyaline cartilage was severely destroyed in patients with RA. TNFα-treated chondrocytes were used as model for inflammatory arthritis. TNFα did not influence proliferation or extracellular matrix expression in chondrocytes, but induced matrix metalloproteinase (MMP)1, 3 and 13 expression levels in chondrocytes, which was accompanied by activation of nuclear factor-κB signaling. During chondrogenic differentiation, TNFα attenuated mRNA expression levels of anabolic factors (collagen type 2 and aggrecan) and enhanced mRNA expression of catabolic factors (MMP1, MMP3 and MMP13) in chondrocytes. Moreover, anti-TNFα agents (Golimumab) inhibited the TNFα-induced metabolic shift in chondrocytes and chondrogenic differentiation. The present study revealed a mechanism by which TNFα may induce metabolic shift in chondrocytes, leading to progressive chondrocyte destruction.

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.

CB2 agonism controls pain and subchondral bone degeneration induced by mono-iodoacetate: Implications GPCR functional bias and tolerance development

BACKGROUND AND PURPOSE

The endocannabinoid system became a promising target for osteoarthritis (OA) treatment. Functional selectivity of cannabinoids may increase their beneficial properties while reducing side effects. The aim of the present study was to evaluate the analgesic potential of two functionally biased CB2 agonists in different treatment regimens to propose the best pharmacological approach for OA management.

EXPERIMENTAL APPROACH

Two functionally selective CB2 agonists were administered i.p. - JWH133 (cAMP biased) and GW833972A (β-arrestin biased), in a chemically induced model of OA in rats. The drugs were tested in acute and chronic treatment regimens. Analgesic effects were assessed by pressure application measurement and kinetic weight bearing. X-ray microtomography was used for the morphometric analysis of the femur's subchondral bone tissue. Underlying biochemical changes were analysed via RT-qPCR.

KEY RESULTS

Dose-response studies established the effective dose for both JWH133 and GW833972A. In chronic treatment paradigms, JWH133 was able to elicit analgesia throughout the course of the experiment, whereas GW833972A lost its efficacy after 2 days of treatment. Later studies revealed improvement in subchondral bone architecture and decrement of matrix metalloproteinases and proinflammatory factors expression following JWH133 chronic treatment.

CONCLUSION AND IMPLICATIONS

Data presents analgesic and disease-modifying potential of CB2 agonists in OA treatment. Moreover, the study revealed more pronounced tolerance development for analgesic effects of the β-arrestin biased CB2 agonist GW833972A. These results provide a better understanding of the molecular underpinnings of the anti-nociceptive potential of CB2 agonists and may improve drug development processes for any cannabinoid-based chronic pain therapy.

Microenvironment in subchondral bone: predominant regulator for the treatment of osteoarthritis

Osteoarthritis (OA) is a degenerative joint disease in the elderly. Although OA has been considered as primarily a disease of the articular cartilage, the participation of subchondral bone in the pathogenesis of OA has attracted increasing attention. This review summarises the microstructural and histopathological changes in subchondral bone during OA progression that are due, at the cellular level, to changes in the interactions among osteocytes, osteoblasts, osteoclasts (OCs), endothelial cells and sensory neurons. Therefore, we focus on how pathological cellular interactions in the subchondral bone microenvironment promote subchondral bone destruction at different stages of OA progression. In addition, the limited amount of research on the communication between OCs in subchondral bone and chondrocytes (CCs) in articular cartilage during OA progression is reviewed. We propose the concept of 'OC-CC crosstalk' and describe the various pathways by which the two cell types might interact. Based on the 'OC-CC crosstalk', we elaborate potential therapeutic strategies for the treatment of OA, including restoring abnormal subchondral bone remodelling and blocking the bridge-subchondral type H vessels. Finally, the review summarises the current understanding of how the subchondral bone microenvironment is related to OA pain and describes potential interventions to reduce OA pain by targeting the subchondral bone microenvironment.

Comprehensive evaluation of the combined extracts of Epimedii Folium and Ligustri Lucidi Fructus for PMOP in ovariectomized rats based on MLP-ANN methods

ETHNOPHARMACOLOGICAL RELEVANCE

Kidney deficiency is the main pathogenesis of osteoporosis based on the theory of "kidney governing bones" in traditional Chinese medicine (TCM). Osteoporosis is a systemic disease; kidney deficiency influences the growth, aging and reproduction of human body, reflecting in endocrine, nerve, immunity, metabolism and other functions. Multi-target drugs composed of natural non-toxic products from kidney-reinforcing herbs, are being investigated for the treatment of osteoporosis. Therefore, it is necessary and imperative to develop an objective and comprehensive method to evaluate and compare the effects of herbs with listed drugs.

AIM OF THE STUDY

This study was designed to evaluate and compare the therapeutic effects and the underlying molecular mechanism of the combined extracts of Epimedii Folium and Ligustri Lucidi Fructus (EL) with Raloxifene hydrochloride (RH) in ovariectomy (OVX)-induced postmenopausal osteoporosis (PMOP) rats based on the multi-layer perception (MLP)-artificial neural network (ANN) model.

MATERIALS AND METHODS

Female SD rats were subjected to either sham surgery (n = 8) or bilateral OVX (n = 48). One week after recovering from surgery, the OVX-induced rats were randomly divided into three groups: OVX model group (n = 32, every 8 rats were killed at the end of the 5th, 9th, 11th or 13th week after OVX), EL group (treated with EL 0.35 g/kg, n = 8), and RH group (treated with RH 6.25 mg/kg, n = 8). The rats in the treatment groups were administrated once a day for 12 weeks, then sacrificed. We observed bone mass and quality, bone remodeling, the function of estrogen and TGF-β1/Smads pathway in all rats.

RESULTS

Both EL and RH could increase bone mineral density, enhance bone strength, relieve bone micro-structure degeneration, re-balance bone remodeling, regulate estrogen dysfunction, and up-regulate TGF-β1 expression. The evaluation of the MLP-ANN model showed that EL and RH had markedly anti-PMOP effects, and there was no significant difference in the comprehensive evaluation of anti-osteoporosis between the two drugs. However, RH had better effects on bone mass and quality and TGF-β1/Smads pathway than EL; EL had better effects on estrogen function than RH.

CONCLUSION

Combined extracts of Epimedii Folium and Ligustri Lucidi Fructus (EL) exhibited bone-protective effects on PMOP. The MLP-ANN method evaluated the efficacy of drugs more comprehensively, which provided a new direction for the evaluation and comparison of drugs.

Combinatmarion treatment with Lactobacillus acidophilus LA-1, vitamin B, and curcumin ameliorates the progression of osteoarthritis by inhibiting the pro-inflammatory mediators

Disease-modifying osteoarthritis (OA) therapy is not yet available. Several adjuvant therapies have demonstrated promising results in the treatment of OA. The present study aimed to investigate the therapeutic effects and underlying mechanisms of a combination of Lactobacillus acidophilus, vitamin B, and curcumin in the treatment of OA. Monosodium iodoacetate (MIA)-induced arthritis of the knee joint in rat was used as an animal model of human OA. The combination of L. acidophilus LA-1, vitamin B, and curcumin or a saline solution was given orally. Pain was measured according to the paw withdrawal latency, and paw withdrawal threshold. Cartilage destruction was analyzed using histomorphological techniques and the Mankin scoring system. Protein expression in the joint was examined using immunohistochemistry. The effects of the combination of L. acidophilus LA-1, vitamin B, and curcumin on mRNA levels in chondrocytes stimulated with interleukin (IL)-1β were analyzed using real-time polymerase chain reaction. The combination of L. acidophilus, vitamin B, and curcumin effectively downregulated Th17 cells and the related cytokine IL-17, thereby maintained the Treg population, and increased the expression of the Treg-related cytokine IL-10 in human peripheral blood mononuclear cells. The OA animal model exhibited reduced pain and preservation of cartilage in response to the combination treatment. The expression levels of pro-inflammatory cytokines and the catabolic, matrix metalloproteinase-13 (MMP-13), were decreased, whereas the expression of the anabolic tissue inhibitors of metalloproteinases (TIMPs) were upregulated in response to the drug combination. The combination of L. acidophilus, vitamin B, and curcumin was beneficial in OA treatment, controlling the inflammatory response via regulation of the Th17/Treg population and reducing the expression of pro-inflammatory cytokines in human peripheral blood mononuclear cells. The combination treatment also preserved cartilage, suppressed osteoclastogenesis, and regulated the anabolic/catabolic imbalance. These findings indicate the therapeutic potential of combination use of L. acidophilus, vitamin B, and curcumin in patients with OA.

A trans-eQTL network regulates osteoclast multinucleation and bone mass

Functional characterisation of cell-type-specific regulatory networks is key to establish a causal link between genetic variation and phenotype. The osteoclast offers a unique model for interrogating the contribution of co-regulated genes to in vivo phenotype as its multinucleation and resorption activities determine quantifiable skeletal traits. Here we took advantage of a trans-regulated gene network (MMnet, macrophage multinucleation network) which we found to be significantly enriched for GWAS variants associated with bone-related phenotypes. We found that the network hub gene Bcat1 and seven other co-regulated MMnet genes out of 13, regulate bone function. Specifically, global (Pik3cb^-/-, Atp8b2^+/-, Igsf8^-/-, Eml1^-/-, Appl2^-/-, Deptor^-/-) and myeloid-specific Slc40a1 knockout mice displayed abnormal bone phenotypes. We report opposing effects of MMnet genes on bone mass in mice and osteoclast multinucleation/resorption in humans with strong correlation between the two. These results identify MMnet as a functionally conserved network that regulates osteoclast multinucleation and bone mass.

The essential role of osteoclast-derived exosomes in magnetic nanoparticle-infiltrated hydroxyapatite scaffold modulated osteoblast proliferation in an osteoporosis model

Magnetic hydroxyapatite (MHA) scaffolds promoted osteoblast proliferation in a model of osteoporosis through altering the osteoclast-derived exosomal cargo and decreasing the efficiency of exosome uptake by osteoblasts. Noticeably, certain proteins including ubiquitin, ATP and reactive oxygen species decreased in the osteoclast-derived exosomal cargo with MHA stimulation, while Rho kinase increased.

Abundant osteoclasts in the subchondral bone of the juvenile Thoroughbred metacarpus suggest an important role in joint maturation

BACKGROUND

The administration of bisphosphonate medications, which target osteoclastic-bone remodelling, to juvenile and adult racehorses is a matter of debate owing to concerns that these molecules remain bound to the bone-mineralised matrix and may interfere with subsequent bone growth, adaptation to exercise and healing of bone microdamage in equine athletes. Osteoclasts participate in endochondral ossification, subchondral bone remodelling and bone repair. There is a knowledge gap on the role of equine osteoclast biology in the growth and maturation of joint surfaces and this information is important to inform judicious bisphosphonate use.

OBJECTIVES

Measure and compare the osteoclast density in the subchondral bone of Thoroughbred (TB) distal third metacarpi (McIII) at different sites, varying depths from the articular surface and with age (0-84 months).

STUDY DESIGN

Ex vivo cadaveric study.

METHODS

McIIIs from foals, yearlings and adults were collected, fixed in formaldehyde and stored at 4°C. Sections were cut from the lateral hemi-metacarpus, stained and scored for cartilage degeneration. Osteoclasts were counted on immunohistochemically (Cathepsin K) stained sections. Osteoclast density was compared in regions of interest (ROIs-the sagittal ridge, axial and abaxial condyle) and also at two depths (0-3 mm and 3-6 mm) into the subchondral bone below the osteochondral junction.

RESULTS

The osteoclast density was consistently highest in the subchondral cortical bone plate (0-3 mm) when compared with the deeper trabecular bone in all age groups. Furthermore, the osteoclast density was significantly higher in juvenile Thoroughbreds (foals and yearlings) within both sites in the subchondral bone when compared with adults.

MAIN LIMITATIONS

The number of specimens available for study was restricted.

CONCLUSIONS

Osteoclasts are important in normal McIII epiphyseal and articular surface maturation and have a propensity to localise at the osteochondral junction and subchondral cortical bone plate zone in juvenile Thoroughbreds.

Dracorhodin perchlorate inhibits osteoclastogenesis through repressing RANKL-stimulated NFATc1 activity

Osteolytic skeletal disorders are caused by an imbalance in the osteoclast and osteoblast function. Suppressing the differentiation and resorptive function of osteoclast is a key strategy for treating osteolytic diseases. Dracorhodin perchlorate (D.P), an active component from dragon blood resin, has been used for facilitating wound healing and anti‐cancer treatments. In this study, we determined the effect of D.P on osteoclast differentiation and function. We have found that D.P inhibited RANKL‐induced osteoclast formation and resorbed pits of hydroxyapatite‐coated plate in a dose‐dependent manner. D.P also disrupted the formation of intact actin‐rich podosome structures in mature osteoclasts and inhibited osteoclast‐specific gene and protein expressions. Further, D.P was able to suppress RANKL‐activated JNK, NF‐κB and Ca²⁺ signalling pathways and reduces the expression level of NFATc1 as well as the nucleus translocation of NFATc1. Overall, these results indicated a potential therapeutic effect of D.P on osteoclast‐related conditions.

GPDPLQ1237-A Type II Collagen Neo-Epitope Biomarker of Osteoclast- and Inflammation-Derived Cartilage Degradation in vitro

C-telopeptide of type II collagen (CTX-II) has been shown to be a highly relevant biomarker of cartilage degradation in human rheumatic diseases, if measured in synovial fluid or urine. However, serum or plasma CTX-II have not been demonstrated to have any clinical utility to date. Here, we describe the GPDPLQ₁₂₃₇ ELISA which targets the EKGPDPLQ↓ neo-epitope, an elongated version of the CTX-II neo-epitope (EKGPDP↓), speculated to be a blood-precursor of CTX-II generated by the cysteine protease cathepsin K. Human osteoclast cartilage resorption cultures as well as oncostatin M and tumour necrosis factor α-stimulated bovine cartilage explant cultures were used to validate GPDPLQ₁₂₃₇ biologically by treating the cultures with the cysteine protease inhibitor E-64 and/or the matrix metalloproteinase (MMP) inhibitor GM6001 to assess the potential contributions of these two protease classes to GPDPLQ₁₂₃₇ release. Cartilage resorption-derived GPDPLQ₁₂₃₇ release was inhibited by E-64 (72.1% inhibition), GM6001 (75.5%), and E-64/GM6001 (91.5%), whereas CTX-II release was inhibited by GM6001 (87.0%) but not by E-64 (5.5%). Cartilage explant GPDPLQ₁₂₃₇ and CTX-II release were both fully inhibited by GM6001 but were not inhibited by E-64. No clinically relevant GPDPLQ₁₂₃₇ reactivity was identified in human serum, plasma, or urine from healthy donors or arthritis patients. In conclusion, the GPDPLQ₁₂₃₇ biomarker is released during osteoclast-derived cysteine protease- and MMP-mediated cartilage degradation in vitro, whereas CTX-II release is mediated by MMPs and not by cysteine proteases, as well as from MMP-mediated cartilage degradation under a pro-inflammatory stimulus. These findings suggest that GPDPLQ₁₂₃₇ may be relevant in diseases with pathological osteoclast activity and cartilage degradation. Further studies are required to validate the neo-epitope in human samples.

Treatment of Focal Cartilage Defects in Minipigs with Zonal Chondrocyte/Mesenchymal Progenitor Cell Constructs

Despite advances in cartilage repair strategies, treatment of focal chondral lesions remains an important challenge to prevent osteoarthritis. Articular cartilage is organized into several layers and lack of zonal organization of current grafts is held responsible for insufficient biomechanical and biochemical quality of repair-tissue. The aim was to develop a zonal approach for cartilage regeneration to determine whether the outcome can be improved compared to a non-zonal strategy. Hydrogel-filled polycaprolactone (PCL)-constructs with a chondrocyte-seeded upper-layer deemed to induce hyaline cartilage and a mesenchymal stromal cell (MSC)-containing bottom-layer deemed to induce calcified cartilage were compared to chondrocyte-based non-zonal grafts in a minipig model. Grafts showed comparable hardness at implantation and did not cause visible signs of inflammation. After 6 months, X-ray microtomography (µCT)-analysis revealed significant bone-loss in both treatment groups compared to empty controls. PCL-enforcement and some hydrogel-remnants were retained in all defects, but most implants were pressed into the subchondral bone. Despite important heterogeneities, both treatments reached a significantly lower modified O'Driscoll-score compared to empty controls. Thus, PCL may have induced bone-erosion during joint loading and misplacement of grafts in vivo precluding adequate permanent orientation of zones compared to surrounding native cartilage.

Osteoporosis of the vertebra and osteochondral remodeling of the endplate causes intervertebral disc degeneration in ovariectomized mice

Background

Studies on the relationship between osteoporosis and intervertebral disc degeneration (IVDD) are inconsistent. Therefore, we assessed whether IVDD is affected by vertebral osteoporosis in ovariectomized mice and investigated the underlying pathogenesis of IVDD related to osteoporosis.

Methods

Thirty healthy female C57BL/6 J mice aged 8 weeks were randomly divided into two groups: a control group (sham operation, n = 15) and an ovariectomy group (OVX; bilateral ovariectomy, n = 15). At 12 weeks after surgery, the bone quantity and microstructure in the lumbar vertebra and endplate as well as the volume of the L4/5 disc space were evaluated by microcomputed tomography (micro-CT). The occurrence and characteristic alterations of IVDD were identified via histopathological staining. The osteoclasts were detected using tartrate-resistant acid phosphatase (TRAP) staining. Type II collagen (Col II), osterix (OSX), osteopontin (OPN), and vascular endothelial growth factor (VEGF) expression in the intervertebral disc were detected by immunohistochemical analysis.

Results

OVX significantly increased the body weight and decreased the uterus weight. Micro-CT analysis showed that osteoporosis of the vertebra and osteochondral remodeling of the endplate were accompanied by an increase in the endplate porosity and a decrease in the disc volume in the OVX group. Likewise, histological evaluation revealed that IVDD occurred at 12 weeks after ovariectomy, with features of endochondral ossification of the endplate, loose and broken annulus fibrosus, and degeneration of nucleus pulposus. TRAP staining showed that numerous active osteoclasts appeared in the subchondral bone and cartilaginous endplate of OVX mice, whereas osteoclasts were rarely detected in control mice. Immunohistochemical analysis demonstrated that the expression of osterix was significantly increased, notably in the endplate of OVX mice. In addition, Col II was decreased in the ossification endplate and the degenerative annulus fibrosus, where OPN and VEGF expressions were elevated in OVX mice.

Conclusions

OVX induced vertebral osteoporosis and osteochondral remodeling of the cartilaginous endplate contributing to the angiogenesis and an increase in porosity of the bone-cartilage surface, and also affected the matrix metabolism which consequently had detrimental effects on the intervertebral disc. Our study suggests that preserving the structural integrity and the function of the adjacent structures, including the vertebrae and endplates, may protect the disc against degeneration.

Electronic supplementary material

The online version of this article (10.1186/s13075-018-1701-1) contains supplementary material, which is available to authorized users.