Alterations of Subchondral Bone Progenitor Cells in Human Knee and Hip Osteoarthritis Lead to a Bone Sclerosis Phenotype

Systematic narrative review of modalities in physiotherapy for managing pain in hip and knee osteoarthritis: A review

Osteoarthritis (OA) affects 528 million individuals globally, predominantly in knee and hip joints, with a notable impact on females aged over 55, resulting in a substantial economic burden. However, the efficacy of modalities used in physiotherapy to manage OA pain for reducing the need for joint replacement remains an open question, and guidelines differ. Our systematic narrative review, drawing from reputable databases (e.g., PubMed, Cochrane, and CINAHL) with specific Mesh terms investigated evidence from 23 Randomized Controlled Trials (that included a control or a sham group in 30 different protocols) using therapeutic modalities like ultrasound, diathermy, and electrical stimulation for knee and hip OA pain, involving a total of 1055 subjects. We investigated the attainment of minimal clinically important differences in pain reduction, operationalized through a 20% decrement in the Western Ontario and McMaster University Arthritis Index or Visual Analog Scale (VAS) score. Our results indicated that 15 protocols out of 30 reach that level, but there were no statistical differences among modalities. Half of the protocol presented in the literature reached clinical efficiency but studies on hip remains scarce. We recommend a comprehensive, sequential, and multimodal intervention plan for individuals with joint OA with initial transcutaneous electrical nerve stimulation and progressing to a 2-week protocol of continuous ultrasound, potentially combined with deep microwave diathermy. Long-term intervention involves the use of pulsed electrical stimulation. For hip OA, a cautious approach and discussions with healthcare providers about potential benefits of spinal cord nerve stimulation.

SDF-1α promotes subchondral bone sclerosis and aggravates osteoarthritis by regulating the proliferation and osteogenic differentiation of bone marrow mesenchymal stem cells

BACKGROUND

Subchondral bone sclerosis is a major feature of osteoarthritis (OA), and bone marrow mesenchymal stem cells (BMSCs) are presumed to play an important role in subchondral bone sclerosis. Accumulating evidence has shown that stromal cell-derived factor-1α (SDF-1α) plays a key role in bone metabolism-related diseases, but its role in OA pathogenesis remains largely unknown. The purpose of this study was to explore the role of SDF-1α expressed on BMSCs in subchondral bone sclerosis in an OA model.

METHODS

In the present study, C57BL/6J mice were divided into the following three groups: the sham control, destabilization of the medial meniscus (DMM), and AMD3100-treated DMM (DMM + AMD3100) groups. The mice were sacrificed after 2 or 8 weeks, and samples were collected for histological and immunohistochemical analyses. OA severity was assessed by performing hematoxylin and eosin (HE) and safranin O-fast green staining. SDF-1α expression in the OA model was measured using an enzyme-linked immunosorbent assay (ELISA), quantitative real-time polymerase chain reaction (q-PCR), and immunohistochemistry. Micro-CT was used to observe changes in subchondral bone in the OA model. CD44, CD90, RUNX2, and OCN expression in subchondral bone were measured using q-PCR and immunohistochemistry. In vitro, BMSCs were transfected with a recombinant lentivirus expressing SDF-1α, an empty vector (EV), or siRNA-SDF-1α. Western blot analysis, q-PCR, and immunofluorescence staining were used to confirm the successful transfection of BMSCs. The effect of SDF-1α on BMSC proliferation was evaluated by performing a CCK-8 assay and cell cycle analysis. The effect of SDF-1α on the osteogenic differentiation of BMSCs was assessed by performing alkaline phosphatase (ALP) and alizarin red S (ARS) staining. Cyclin D1, RUNX2 and OCN expression were measured using Western blot analysis, q-PCR, and immunofluorescence staining.

RESULTS

SDF-1α expression in the DMM-induced OA model increased. In the DMM + AMD3100 group, subchondral bone sclerosis was alleviated, OA was effectively relieved, and CD44, CD90, RUNX2, and OCN expression in subchondral bone was decreased. In vitro, high levels of SDF-1α promoted BMSC proliferation and increased osteogenic differentiation. Cyclin D1, RUNX2, and OCN expression increased.

CONCLUSION

The results of this study reveal a new molecular mechanism underlying the pathogenesis of OA. The targeted regulation of SDF-1α may be clinically effective in suppressing OA progression.

The crucial role of LncRNA MIR210HG involved in the regulation of human cancer and other disease

Long noncoding RNAs (lncRNAs) have evoked considerable interest in recent years due to their critical functions in the regulation of disease processes. Abnormal expression of lncRNAs is found in multiple diseases, and lncRNAs have been exploited for diverse medical applications. The lncRNA MIR210HG is a recently discovered lncRNA that is widely dysregulated in human disease. MIR210HG was described to have biological functions with potential roles in disease development, including cell proliferation, invasion, migration, and energy metabolism. And MIR210HG dysregulation was confirmed to have promising clinical values in disease diagnosis, treatment, and prognosis. In this review, we systematically summarize the expression profiles, roles, underlying mechanisms, and clinical applications of MIR210HG in human disease.

Temporomandibular Joint Osteoarthritis: Pathogenic Mechanisms Involving the Cartilage and Subchondral Bone, and Potential Therapeutic Strategies for Joint Regeneration

The temporomandibular joint (TMJ) is a specialized synovial joint that is crucial for the movement and function of the jaw. TMJ osteoarthritis (TMJ OA) is the result of disc dislocation, trauma, functional overburden, and developmental anomalies. TMJ OA affects all joint structures, including the articular cartilage, synovium, subchondral bone, capsule, ligaments, periarticular muscles, and sensory nerves that innervate the tissues. The present review aimed to illustrate the main pathomechanisms involving cartilage and bone changes in TMJ OA and some therapeutic options that have shown potential restorative properties regarding these joint structures in vivo. Chondrocyte loss, extracellular matrix (ECM) degradation, and subchondral bone remodeling are important factors in TMJ OA. The subchondral bone actively participates in TMJ OA through an abnormal bone remodeling initially characterized by a loss of bone mass, followed by reparative mechanisms that lead to stiffness and thickening of the condylar osteochondral interface. In recent years, such therapies as intraarticular platelet-rich plasma (PRP), hyaluronic acid (HA), and mesenchymal stem cell-based treatment (MSCs) have shown promising results with respect to the regeneration of joint structures or the protection against further damage in TMJ OA. Nevertheless, PRP and MSCs are more frequently associated with cartilage and/or bone repair than HA. According to recent findings, the latter could enhance the restorative potential of other therapies (PRP, MSCs) when used in combination, rather than repair TMJ structures by itself. TMJ OA is a complex disease in which degenerative changes in the cartilage and bone develop through intricate mechanisms. The regenerative potential of such therapies as PRP, MSCs, and HA regarding the cartilage and subchondral bone (alone or in various combinations) in TMJ OA remains a matter of further research, with studies sometimes obtaining discrepant results.

Immune and stem cell compartments of acetabular and femoral bone marrow in hip osteoarthritis patients

OBJECTIVE

Hip osteoarthritis (OA) affects all components of the osteochondral unit, leading to bone marrow (BM) lesions, and unknown consequences on BM cell functionality. We analyzed the cellular composition in OA-affected acetabula compared to proximal femur shafts obtained of hip OA patients to reveal yet not explored immune and stem cell compartments.

DESIGN

Combining flow cytometry, cellular assays and transcription analyses, we performed extensive ex vivo phenotyping of acetabular BM cells from 18 hip OA patients, comparing them with their counterparts from patient-matched femoral shaft BM samples. Findings were related to differences in skeletal sites and age.

RESULTS

Acetabular BM had a greater frequency of T-lymphocytes, non-hematopoietic cells and colony-forming units fibroblastic potential than femoral BM. The incidence of acetabular CD45⁺CD3⁺ T-lymphocytes increased (95% CI: 0.1770 to 0.0.8416), while clonogenic hematopoietic progenitors declined (95% CI: -0.9023 to -0.2399) with age of patients. On the other side, in femoral BM, we observed higher B-lymphocyte, myeloid and erythroid cell frequencies. Acetabular mesenchymal stromal cells (MSCs) showed a senescent profile associated with the expression of survival and inflammation-related genes. Efficient osteogenic and chondrogenic differentiation was detected in acetabular MSCs, while adipogenesis was more pronounced in their femoral counterparts.

CONCLUSION

Our results suggest that distinctions in BM cellular compartments and MSCs may be due to the influence of the OA-stressed microenvironment, but also acetabular vs femoral shaft-specific peculiarities cannot be excluded. These results bring new knowledge on acetabular BM cell populations and may be addressed as novel pathogenic mechanisms and therapeutic targets in OA.

The repair effect and mechanism of continuous passive motion on osteoarthritis in a rabbit model

OBJECTIVE

To observe the effect of continuous passive motion (CPM) on osteoarthritis in a rabbit model and explore its mechanism.

METHODS

Thirty healthy rabbits with a total of 60 knee joints were randomized into three groups. Group A had CPM for 8 h daily, starting on postoperative day 1 and free movement in the cage, group B received CPM for 2 h daily, starting on postoperative day 1 and free movement in the cage, and group C only had free movement in the cage. Mankin's score was used to compare the gross morphology of the rabbit's knee joint. Malondialdehyde (MDA) and superoxide dismutase (SOD) were measured by RT-PCR and western blot method before and after intervention.

RESULTS

The Mankin's scores of rabbits in groups A and B were significantly lower than those in group C, and those in group A were lower than those in group B at week 4 and week 12 of intervention (P<0.05). At week 4 of the CPM intervention, the gross morphological scores were the highest in group A, followed by group B, and the lowest in group C (P<0.05). At week 12 of CPM intervention, the gross morphological scores of the knee joints in groups A and B were increased again, which were the highest in group A, followed by group B, and the lowest in group C (P<0.05). At week 12 of intervention, MDA levels in group A were lower than those in groups B and C, whereas SOD levels in group A were higher than those in groups B and C.

CONCLUSION

CPM can effectively improve the symptoms of knee osteoarthritis in rabbits and increase the mobility of the joints, and the mechanism may be related to the ability of CPM to reduce the overproduction of peroxide at the lesion site.

Alpha-7 Nicotinic Receptor Dampens Murine Osteoblastic Response to Inflammation and Age-Related Osteoarthritis

Introduction

Osteoarthritis (OA) is a whole-joint disease characterized by a low-grade inflammation that is involved in both cartilage degradation and subchondral bone remodeling. Since subchondral bone has a cholinergic innervation and that acetylcholine (Ach) might have an anti-inflammatory effect through the α7 nicotinic Ach receptor (α7nAchR), we aimed (i) to determine the expression of non-neuronal cholinergic system and nicotinic receptor subunits by murine and human osteoblasts, (ii) to address the role of α7nAchR in osteoblastic response to inflammation, and (iii) to study the role of α7nAchR in a spontaneous aging OA model.

Methods

Primary cultures of WT and α7nAchR knock-out mice (Chrna7^-/-) murine osteoblasts and of subchondral bone human OA osteoblasts were performed. The expressions of the non-neuronal cholinergic system and of the nAchR subunits were assessed by PCR. In vitro, IL1β-stimulated WT, Chrna7^-/-, and human osteoblasts were pretreated with nicotine. At 24 h, expressions of interleukin-6 (IL6) and metalloproteinase-3 and -13 (MMP), RANK-ligand (RANKL), and osteoprotegerin (OPG) were quantified by qPCR and ELISA. Spontaneous aging OA was evaluated and compared between male WT and Chrna7^-/- mice of 9 and 12 months.

Results

Murine WT osteoblasts express the main components of the cholinergic system and α7 subunit composing α7nAchR. Nicotine partially prevented the IL1β-induced expression and production of IL6, MMP3, and RANKL in WT osteoblasts. The effect for IL6 and MMP was mediated by α7nAchR since nicotine had no effect on Chrna7^-/- osteoblasts while the RANKL decrease persisted. Chrna7^-/- mice displayed significantly higher cartilage lesions than their WT counterparts at 9 and 12 months, without difference in subchondral bone remodeling. Human OA osteoblasts also expressed the non-neuronal cholinergic system and α7 subunit as well as CHRFAM7A, the dominant negative duplicate of Chrna7. Nicotine pretreatment did not significantly reduce IL6 and MMP3 production in IL-1β-stimulated human osteoarthritic osteoblasts (n = 4), possibly due to CHRFAM7A.

Conclusion

Cholinergic system counteracts murine osteoblastic response to IL-1β through α7nAchR. Since α7nAchR deletion may limit cartilage degradation during murine age-related OA, enhancing cholinergic system could be a new therapeutic target in OA but may depend on CHRFAM7A expression.

Alpha-7 Nicotinic Receptor Dampens Murine Osteoblastic Response to Inflammation and Age-Related Osteoarthritis

INTRODUCTION

Osteoarthritis (OA) is a whole-joint disease characterized by a low-grade inflammation that is involved in both cartilage degradation and subchondral bone remodeling. Since subchondral bone has a cholinergic innervation and that acetylcholine (Ach) might have an anti-inflammatory effect through the α7 nicotinic Ach receptor (α7nAchR), we aimed (i) to determine the expression of non-neuronal cholinergic system and nicotinic receptor subunits by murine and human osteoblasts, (ii) to address the role of α7nAchR in osteoblastic response to inflammation, and (iii) to study the role of α7nAchR in a spontaneous aging OA model.

METHODS

Primary cultures of WT and α7nAchR knock-out mice (Chrna7^-/-) murine osteoblasts and of subchondral bone human OA osteoblasts were performed. The expressions of the non-neuronal cholinergic system and of the nAchR subunits were assessed by PCR. In vitro, IL1β-stimulated WT, Chrna7^-/-, and human osteoblasts were pretreated with nicotine. At 24 h, expressions of interleukin-6 (IL6) and metalloproteinase-3 and -13 (MMP), RANK-ligand (RANKL), and osteoprotegerin (OPG) were quantified by qPCR and ELISA. Spontaneous aging OA was evaluated and compared between male WT and Chrna7^-/- mice of 9 and 12 months.

RESULTS

Murine WT osteoblasts express the main components of the cholinergic system and α7 subunit composing α7nAchR. Nicotine partially prevented the IL1β-induced expression and production of IL6, MMP3, and RANKL in WT osteoblasts. The effect for IL6 and MMP was mediated by α7nAchR since nicotine had no effect on Chrna7^-/- osteoblasts while the RANKL decrease persisted. Chrna7^-/- mice displayed significantly higher cartilage lesions than their WT counterparts at 9 and 12 months, without difference in subchondral bone remodeling. Human OA osteoblasts also expressed the non-neuronal cholinergic system and α7 subunit as well as CHRFAM7A, the dominant negative duplicate of Chrna7. Nicotine pretreatment did not significantly reduce IL6 and MMP3 production in IL-1β-stimulated human osteoarthritic osteoblasts (n = 4), possibly due to CHRFAM7A.

CONCLUSION

Cholinergic system counteracts murine osteoblastic response to IL-1β through α7nAchR. Since α7nAchR deletion may limit cartilage degradation during murine age-related OA, enhancing cholinergic system could be a new therapeutic target in OA but may depend on CHRFAM7A expression.

Modeling In Vitro Osteoarthritis Phenotypes in a Vascularized Bone Model Based on a Bone-Marrow Derived Mesenchymal Cell Line and Endothelial Cells

The subchondral bone and its associated vasculature play an important role in the onset of osteoarthritis (OA). Integration of different aspects of the OA environment into multi-cellular and complex human, in vitro models is therefore needed to properly represent the pathology. In this study, we exploited a mesenchymal stromal cell line/endothelial cell co-culture to produce an in vitro human model of vascularized osteogenic tissue. A cocktail of inflammatory cytokines, or conditioned medium from mechanically-induced OA engineered microcartilage, was administered to this vascularized bone model to mimic the inflamed OA environment, hypothesizing that these treatments could induce the onset of specific pathological traits. Exposure to the inflammatory factors led to increased network formation by endothelial cells, reminiscent of the abnormal angiogenesis found in OA subchondral bone, demineralization of the constructs, and increased collagen production, signs of OA related bone sclerosis. Furthermore, inflammation led to augmented expression of osteogenic (alkaline phosphatase (ALP) and osteocalcin (OCN)) and angiogenic (vascular endothelial growth factor (VEGF)) genes. The treatment, with a conditioned medium from the mechanically-induced OA engineered microcartilage, also caused increased demineralization and expression of ALP, OCN, ADAMTS5, and VEGF; however, changes in network formation by endothelial cells were not observed in this second case, suggesting a possible different mechanism of action in inducing OA-like phenotypes. We propose that this vascularized bone model could represent a first step for the in vitro study of bone changes under OA mimicking conditions and possibly serve as a tool in testing anti-OA drugs.

An implementation study of periarticular knee osteotomy in the treatment of knee osteoarthritis

OBJECTIVE

To analyze the clinical effects of periarticular knee osteotomy (PKO) in the treatment of knee osteoarthritis (KOA).

METHODS

A total of 180 patients with KOA admitted to our hospital were selected as the study subjects, and were divided into study group (90 cases) and control group (90 cases) in accordance with different intervention measures. The study group was treated with PKO, while the control group was treated with joint replacement. The perioperative indices, and postoperative pain degrees, knee joint function, quality of life, inflammatory factors and complications were compared between the two groups.

RESULTS

The control group was superior to the study group regarding the amount of preoperative bleeding, surgical duration, and incidence rate of complications, while the study group was superior to the control group regarding the long-term (over 2 years) knee joint function and quality of life (P < 0.05). There was no marked difference in the postoperative pain degrees and preoperative and postoperative levels of inflammatory factors between the two groups (P < 0.05).

CONCLUSION

PKO, exhibiting a high safety profile, can remarkably improve the joint pain symptoms, knee joint function, quality of life and symptoms of KOA in patients with KOA. Therefore, PKO is worthy of clinical promotion and implementation.

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.

From Pathogenesis to Therapy in Knee Osteoarthritis: Bench-to-Bedside

Osteoarthritis (OA) is currently the most widespread musculoskeletal condition and primarily affects weight-bearing joints such as the knees and hips. Importantly, knee OA remains a multifactorial whole-joint disease, the appearance and progression of which involves the alteration of articular cartilage as well as the synovium, subchondral bone, ligaments, and muscles through intricate pathomechanisms. Whereas it was initially depicted as a predominantly aging-related and mechanically driven condition given its clear association with old age, high body mass index (BMI), and joint malalignment, more recent research identified and described a plethora of further factors contributing to knee OA pathogenesis. However, the pathogenic intricacies between the molecular pathways involved in OA prompted the study of certain drugs for more than one therapeutic target (amelioration of cartilage and bone changes, and synovial inflammation). Most clinical studies regarding knee OA focus mainly on improvement in pain and joint function and thus do not provide sufficient evidence on the possible disease-modifying properties of the tested drugs. Currently, there is an unmet need for further research regarding OA pathogenesis as well as the introduction and exhaustive testing of potential disease-modifying pharmacotherapies in order to structure an effective treatment plan for these patients.

Printing the Pathway Forward in Bone Metastatic Cancer Research: Applications of 3D Engineered Models and Bioprinted Scaffolds to Recapitulate the Bone-Tumor Niche

Breast cancer commonly metastasizes to bone, resulting in osteolytic lesions and poor patient quality of life. The bone extracellular matrix (ECM) plays a critical role in cancer cell metastasis by means of the physical and biochemical cues it provides to support cellular crosstalk. Current two-dimensional in-vitro models lack the spatial and biochemical complexities of the native ECM and do not fully recapitulate crosstalk that occurs between the tumor and endogenous stromal cells. Engineered models such as bone-on-a-chip, extramedullary bone, and bioreactors are presently used to model cellular crosstalk and bone-tumor cell interactions, but fall short of providing a bone-biomimetic microenvironment. Three-dimensional bioprinting allows for the deposition of biocompatible materials and living cells in complex architectures, as well as provides a means to better replicate biological tissue niches in-vitro. In cancer research specifically, 3D constructs have been instrumental in seminal work modeling cancer cell dissemination to bone and bone-tumor cell crosstalk in the skeleton. Furthermore, the use of biocompatible materials, such as hydroxyapatite, allows for printing of bone-like microenvironments with the ability to be implanted and studied in in-vivo animal models. Moreover, the use of bioprinted models could drive the development of novel cancer therapies and drug delivery vehicles.

Subchondral Bone Remodeling: A Therapeutic Target for Osteoarthritis

There is emerging awareness that subchondral bone remodeling plays an important role in the development of osteoarthritis (OA). This review presents recent investigations on the cellular and molecular mechanism of subchondral bone remodeling, and summarizes the current interventions and potential therapeutic targets related to OA subchondral bone remodeling. The first part of this review covers key cells and molecular mediators involved in subchondral bone remodeling (osteoclasts, osteoblasts, osteocytes, bone extracellular matrix, vascularization, nerve innervation, and related signaling pathways). The second part of this review describes candidate treatments for OA subchondral bone remodeling, including the use of bone-acting reagents and the application of regenerative therapies. Currently available clinical OA therapies and known responses in subchondral bone remodeling are summarized as a basis for the investigation of potential therapeutic mediators.

Knee Osteoarthritis: A Review of Pathogenesis and State-Of-The-Art Non-Operative Therapeutic Considerations

Being the most common musculoskeletal progressive condition, osteoarthritis is an interesting target for research. It is estimated that the prevalence of knee osteoarthritis (OA) among adults 60 years of age or older is approximately 10% in men and 13% in women, making knee OA one of the leading causes of disability in elderly population. Today, we know that osteoarthritis is not a disease characterized by loss of cartilage due to mechanical loading only, but a condition that affects all of the tissues in the joint, causing detectable changes in tissue architecture, its metabolism and function. All of these changes are mediated by a complex and not yet fully researched interplay of proinflammatory and anti-inflammatory cytokines, chemokines, growth factors and adipokines, all of which can be measured in the serum, synovium and histological samples, potentially serving as biomarkers of disease stage and progression. Another key aspect of disease progression is the epigenome that regulates all the genetic expression through DNA methylation, histone modifications, and mRNA interference. A lot of work has been put into developing non-surgical treatment options to slow down the natural course of osteoarthritis to postpone, or maybe even replace extensive surgeries such as total knee arthroplasty. At the moment, biological treatments such as platelet-rich plasma, bone marrow mesenchymal stem cells and autologous microfragmented adipose tissue containing stromal vascular fraction are ordinarily used. Furthermore, the latter two mentioned cell-based treatment options seem to be the only methods so far that increase the quality of cartilage in osteoarthritis patients. Yet, in the future, gene therapy could potentially become an option for orthopedic patients. In the following review, we summarized all of the latest and most important research in basic sciences, pathogenesis, and non-operative treatment.

Knee Osteoarthritis: A Review of Pathogenesis and State-Of-The-Art Non-Operative Therapeutic Considerations

Being the most common musculoskeletal progressive condition, osteoarthritis is an interesting target for research. It is estimated that the prevalence of knee osteoarthritis (OA) among adults 60 years of age or older is approximately 10% in men and 13% in women, making knee OA one of the leading causes of disability in elderly population. Today, we know that osteoarthritis is not a disease characterized by loss of cartilage due to mechanical loading only, but a condition that affects all of the tissues in the joint, causing detectable changes in tissue architecture, its metabolism and function. All of these changes are mediated by a complex and not yet fully researched interplay of proinflammatory and anti-inflammatory cytokines, chemokines, growth factors and adipokines, all of which can be measured in the serum, synovium and histological samples, potentially serving as biomarkers of disease stage and progression. Another key aspect of disease progression is the epigenome that regulates all the genetic expression through DNA methylation, histone modifications, and mRNA interference. A lot of work has been put into developing non-surgical treatment options to slow down the natural course of osteoarthritis to postpone, or maybe even replace extensive surgeries such as total knee arthroplasty. At the moment, biological treatments such as platelet-rich plasma, bone marrow mesenchymal stem cells and autologous microfragmented adipose tissue containing stromal vascular fraction are ordinarily used. Furthermore, the latter two mentioned cell-based treatment options seem to be the only methods so far that increase the quality of cartilage in osteoarthritis patients. Yet, in the future, gene therapy could potentially become an option for orthopedic patients. In the following review, we summarized all of the latest and most important research in basic sciences, pathogenesis, and non-operative treatment.

Osteocyte TGFβ1‑Smad2/3 is positively associated with bone turnover parameters in subchondral bone of advanced osteoarthritis

Subchondral sclerosis is considered the main characteristic of advanced osteoarthritis, in which bone remodeling mediated by transforming growth factor β (TGFβ) signaling plays an indispensable role in the metabolism. Osteocytes have been identified as pivotal regulators of bone metabolism, due to their mechanosensing and endocrine function. Therefore, the aim of the present study was to investigate the association between osteocyte TGFβ signal and subchondral sclerosis. Knee tibia plateau samples were collected from osteoarthritic patients and divided into three groups: The full cartilage, partial cartilage and full defect groups. Next, changes in osteocyte TGFβ signaling and subchondral bone structure underlying various types of cartilage erosion were detected. Bone mineral density (BMD) assay, histology [hematoxylin and eosin, Safranin‑O/Fast green, and tartrate resistant acid phosphatase (TRAP) staining], and reverse transcription‑quantitative PCR mainly detected structural alterations, osteogenic and osteoclastic activity in the cartilage and subchondral bone. The activation of the TGFβ signaling pathway in the subchondral bone was detected by immunohistochemistry and western blotting. The association between osteocyte TGFβ and the regulation of bone metabolism was analyzed by correlation analysis, and further proven in vitro. It was confirmed that the BMD of the subchondral bone increased and underwent sclerosis in the partial cartilage and full defect groups. Additional observation included the thinning of the area of calcified cartilage, in which a bone island formed locally, with subchondral bone plate thickening and increased trabecular bone volume. TRAP staining suggested an increase in bone resorption in subchondral underlying areas of the partial cartilage and full defect groups. Immunohistochemistry results confirmed the activation of osteocyte TGFβ in subchondral underlying areas with severe cartilage erosion. Moreover, osteocyte phosphorylated‑Smad2/3 was positively correlated with subchondral BMD, alkaline phosphatase and osteopontin mRNA expression, but it was negatively correlated with TRAP+ cells. Furthermore, it was confirmed in vitro that osteocyte TGFβ signaling could regulate the osteogenic and osteoclastic activity of the mesenchymal stem cells. This study illustrated that osteocyte TGFβ signaling is positively associated with the remodeling of subchondral bone in advanced osteoarthritis and provides a preliminary theoretical basis for further investigations of the role and mechanism of osteocyte TGFβ in subchondral of osteoarthritis.

Subchondral bone dysplasia mediates susceptibility to osteoarthritis in female adult offspring rats induced by prenatal caffeine exposure

Our previous studies confirmed that prenatal caffeine exposure (PCE) could induce susceptibility to osteoarthritis in adult offspring rats due to poor chondrocyte differentiation, but its mechanism remains to be further investigated. This study aimed to explore whether subchondral bone dysplasia mediates susceptibility to osteoarthritis in adult offspring rats induced by PCE. Pregnant Wistar rats were treated with caffeine (120 mg/kg.d) or saline from gestational day (GD) 9 to 20. The female offspring were euthanized to collect femurs at GD20, postnatal week (PW) 6, and PW28 (non-ovariectomy and ovariectomy groups) to detect osteoarthritis-like phenotype, subchondral bone mass, ossification center development, and other evidence. The results showed that PCE increased the Mankin score of pathological articular cartilage, but decreased articular cartilage thickness and subchondral bone mass, which were more obvious after ovariectomy. Meanwhile, the correlation analysis results demonstrated that the Mankin score of articular cartilage was significantly negatively correlated with subchondral bone mass, and the thickness of articular cartilage was significantly positively correlated with subchondral bone mass. Further, the length and area of the primary and secondary ossification centers, the number of osteoblasts, and the related genes' expression of osteogenic differentiation (e.g., Runx2, BSP, ALP, and OCN) were all significantly decreased in the PCE group before and after birth. Taken together, PCE induced susceptibility to osteoarthritis in adult female offspring, which was likely related to the subchondral bone dysplasia and reduction of subchondral bone mass production due to developmental disorder of primary and secondary ossification centers caused by osteoblast differentiation disability before and after birth.

Association of IL-6, IL-8, MMP-13 gene polymorphisms with knee osteoarthritis susceptibility in the Chinese Han population

Objective: To identify the association between the interleukin (IL) 6 (IL-6) rs1800795 (-174 G>C), IL-8 rs4073 (-251T>A), and matrix metalloproteinase-13 (MMP-13) rs2252070 (-77G>A) gene polymorphisms and knee osteoarthritis (KOA) susceptibility in the Chinese Han population. Methods: Genomic DNA was extracted from a total of 400 KOA patients and 400 healthy subjects. Sanger sequencing was performed to determine the genotypes of the IL-6 rs1800795 (-174 G/C), IL-8 rs4073 (-251A/T), and MMP-13 rs2252070 (-77A/G) loci. The mRNA expression levels of IL-6, IL-8, and MMP-13 in osteoblasts and the protein expression levels of IL-6, IL-8, and MMP-13 in the synovial fluids of KOA patients were analyzed. Results: The recessive model of IL-6 rs1800795 locus was found to be associated with KOA risk (adjusted odds ratio (OR) = 1.657, 95% confidence interval (CI) = 1.396-1.866, P<0.001). The IL-8 rs4073 locus dominant and recessive model showed no significant association with KOA risk (P>0.05). The dominant and recessive models of the MMP-13 rs2252070 locus showed higher risk for developing KOA (dominant model: adjusted OR = 1.271, 95%CI = 1.095-1.480, P=0.001; recessive model: adjusted OR = 1.361 95%CI = 1.151-1.569, P<0.001). The G>C mutation in IL-6 rs1800795 and the G>A mutation in MMP-13 rs2252070 were associated with significantly higher KOA disease severity. The G>C mutation in the IL-6 rs1800795 locus was associated with up-regulation of IL-6 expression. The G>A mutation in the MMP-13 rs2252070 locus was associated with up-regulation of MMP-13 expression. Conclusion: The IL-8 rs4073 (-251T>A) mutation was not associated with KOA susceptibility. The IL-6 rs1800795 (-174 G>C) and MMP-13 rs2252070 (-77G>A) mutations were associated with KOA susceptibility, increased disease severity, and up-regulation of IL-6 and MMP-13 expression levels.

Glucocorticoid signaling and osteoarthritis

Glucocorticoids are steroid hormones synthesized and released by the adrenal cortex. Their main function is to maintain cell homeostasis through a variety of signaling pathways, responding to changes in an organism's environment or developmental status. Mimicking the actions of natural glucocorticoids, synthetic glucocorticoids have been recruited to treat many diseases that implicate glucocorticoid receptor signaling such as osteoarthritis. In osteoarthritis, synthetic glucocorticoids aim to alleviate inflammation and pain. The variation of patients' response and the possibility of complications associated with their long-term use have led to a need for a better understanding of glucocorticoid receptor signaling in osteoarthritis. In this review, we performed a literature search in the molecular pathways that link the osteoarthritic joint to the glucocorticoid receptor signaling. We hope that this information will advance research in the field and propose new molecular targets for the development of more optimized therapies for osteoarthritis.

Cancer Metastases to Bone: Concepts, Mechanisms, and Interactions with Bone Osteoblasts

The skeleton is a unique structure capable of providing support for the body. Bone resorption and deposition are controlled in a tightly regulated balance between osteoblasts and osteoclasts with no net bone gain or loss. However, under conditions of disease, the balance between bone resorption and deposition is upset. Osteoblasts play an important role in bone homeostasis by depositing new bone osteoid into resorption pits. It is becoming increasingly evident that osteoblasts additionally play key roles in cancer cell dissemination to bone and subsequent metastasis. Our laboratory has evidence that when osteoblasts come into contact with disseminated breast cancer cells, the osteoblasts produce factors that initially reduce breast cancer cell proliferation, yet promote cancer cell survival in bone. Other laboratories have demonstrated that osteoblasts both directly and indirectly contribute to dormant cancer cell reactivation in bone. Moreover, we have demonstrated that osteoblasts undergo an inflammatory stress response in late stages of breast cancer, and produce inflammatory cytokines that are maintenance and survival factors for breast cancer cells and osteoclasts. Advances in understanding interactions between osteoblasts, osteoclasts, and bone metastatic cancer cells will aid in controlling and ultimately preventing cancer cell metastasis to bone.