Attenuation of the progression of articular cartilage degeneration by inhibition of TGF-β1 signaling in a mouse model of osteoarthritis

Intra-articular sustained-release of pirfenidone as a disease-modifying treatment for early osteoarthritis

Osteoarthritis (OA) is a major clinical challenge, and effective disease-modifying drugs for OA are still lacking due to the complicated pathology and scattered treatment targets. Effective early treatments are urgently needed to prevent OA progression. The excessive amount of transforming growth factor β (TGFβ) is one of the major causes of synovial fibrosis and subchondral bone sclerosis, and such pathogenic changes in early OA precede cartilage damage. Herein we report a novel strategy of intra-articular sustained-release of pirfenidone (PFD), a clinically-approved TGFβ inhibitor, to achieve disease-modifying effects on early OA joints. We found that PFD effectively restored the mineralization in the presence of excessive amount of TGFβ1 (as those levels found in patients' synovial fluid). A monthly injection strategy was then designed of using poly lactic-co-glycolic acid (PLGA) microparticles and hyaluronic acid (HA) solution to enable a sustained release of PFD (the "PLGA-PFD + HA" strategy). This strategy effectively regulated OA progression in destabilization of the medial meniscus (DMM)- induced OA mice model, including preventing subchondral bone loss in early OA and subchondral bone sclerosis in late OA, and reduced synovitis and pain with cartilage preservation effects. This finding suggests the promising clinical application of PFD as a novel disease-modifying OA drug.

Mesenchymal stem cells for cartilage regeneration: Insights into molecular mechanism and therapeutic strategies

The use of mesenchymal stem cells (MSCs) in cartilage regeneration has gained significant attention in regenerative medicine. This paper reviews the molecular mechanisms underlying MSC-based cartilage regeneration and explores various therapeutic strategies to enhance the efficacy of MSCs in this context. MSCs exhibit multipotent capabilities and can differentiate into various cell lineages under specific microenvironmental cues. Chondrogenic differentiation, a complex process involving signaling pathways, transcription factors, and growth factors, plays a pivotal role in the successful regeneration of cartilage tissue. The chondrogenic differentiation of MSCs is tightly regulated by growth factors and signaling pathways such as TGF-β, BMP, Wnt/β-catenin, RhoA/ROCK, NOTCH, and IHH (Indian hedgehog). Understanding the intricate balance between these pathways is crucial for directing lineage-specific differentiation and preventing undesirable chondrocyte hypertrophy. Additionally, paracrine effects of MSCs, mediated by the secretion of bioactive factors, contribute significantly to immunomodulation, recruitment of endogenous stem cells, and maintenance of chondrocyte phenotype. Pre-treatment strategies utilized to potentiate MSCs, such as hypoxic conditions, low-intensity ultrasound, kartogenin treatment, and gene editing, are also discussed for their potential to enhance MSC survival, differentiation, and paracrine effects. In conclusion, this paper provides a comprehensive overview of the molecular mechanisms involved in MSC-based cartilage regeneration and outlines promising therapeutic strategies. The insights presented contribute to the ongoing efforts in optimizing MSC-based therapies for effective cartilage repair.

Silymarin and MSC-exosomes ameliorate thioacetamide-evoked renal fibrosis by inhibiting TGF-β/SMAD pathway in rats

BACKGROUND

TGF-β1 and SMAD3 are particularly pathogenic in the progression of renal fibrosis.

AIM

This study aimed to evaluate the kidney protective potentials of silymarin (SM) and exosomes of mesenchymal stem cells against the nephrotoxin thioacetamide (TAA) in rats.

METHODS

32 female rats were randomly assigned into four groups: the control group, the TAA group, the TAA + SM group, and the TAA + Exosomes group. The kidney homogenates from all groups were examined for expression levels of TGF-β receptors I and II using real-time PCR, expression levels of collagen type I and CTGF proteins using ELISA, and the expression levels of nuclear SMAD2/3/4, cytoplasmic SMAD2/3, and cytoplasmic SMAD4 proteins using the western blot technique.

RESULTS

Compared to the control group, the injection of TAA resulted in a significant increase in serum levels of urea and creatinine, gene expression levels of TβRI and TβRII, protein expression levels of both collagen I and CTGF proteins, cytoplasmic SMAD2/3 complex, and nuclear SMAD2/3/4 (p-value < 0.0001), with significantly decreased levels of the co-SMAD partner, SMAD4 (p-value < 0.0001). Those effects were reversed considerably in both treatment groups, with the superiority of the exosomal treatment regarding the SMAD proteins and the expression levels of the TβRI gene, collagen I, and CTGF proteins returning to near-control values (p-value > 0.05).

CONCLUSION

Using in vitro and in vivo experimental approaches, the research discovered a reno-protective role of silymarin and exosomes of BM-MSCs after thioacetamide-induced renal fibrosis in rats, with the advantage of exosomes.

Towards disease modification in osteoarthritis

In December 2022, Gerwin et al published in Nature Medicine that the C-terminal portion of angiopoietin-like 3, called LNA043, has chondroprotective and cartilage-regenerative properties. Molecular data from an experimental medicine phase I study suggested potential efficacy in humans. Here, we respond to and complement a commentary from Vincent and Conaghan and discuss unresolved issues and the potential of this molecule as a disease-modifying osteoarthritis drug.

The effects of losartan or angiotensin II receptor antagonists on cartilage: a systematic review

OBJECTIVE

The aim of this study is to analyze the latest evidence on the effects of losartan or Ang II receptor antagonists on cartilage repair, with a focus on their clinical relevance.

DESIGN

The PubMed, Embase, and Cochrane Library databases were searched up to November 12th 2021 to evaluate the effects of losartan or Ang II receptor antagonists on cartilage repair in in vitro studies and in vivo animal studies. Study design, sample characteristics, treatment type, duration, and outcomes were analyzed. The risk of bias and the quality of the eligible studies were assessed using the Systematic Review Centre for Laboratory Animal Experimentation (SYRCLE) risk of bias assessment tool and Collaborative Approach to Meta-Analysis and Review of Animal Data from Experimental Studies (CAMARADES).

RESULTS

A total of 12 studies were included in this systematic review. Of the 12 eligible studies, two studies were in vitro human studies, three studies were in vitro animal studies, one study was an in vitro human and animal study, and six studies were in vivo animal studies. The risk bias and quality assessments were predominantly classified as moderate. Since meta-analysis was difficult due to differences in treatment type, dosage, route of administration, and method of outcome assessment among the eligible studies, qualitative evaluation was conducted for each study.

CONCLUSIONS

Both in vitro and in vivo studies provide evidence to demonstrate beneficial effects of Ang II receptor antagonists on osteoarthritis and cartilage defect models across animal species.

Sustained-release losartan from peptide nanofibers promotes chondrogenesis

Introduction: The central pathologic feature of osteoarthritis (OA) is the progressive loss of articular cartilage, which has a limited regenerative capacity. The TGF-β1 inhibitor, losartan, can improve cartilage repair by promoting hyaline rather that fibrous cartilage tissue regeneration. However, there are concerns about side effects associated with oral administration and short retention within the joint following intra-articular injections. To facilitate local and sustained intra-articular losartan delivery we have designed an injectable peptide amphiphile (PA) nanofiber that binds losartan. The aims of this study are to characterize the release kinetics of losartan from two different PA nanofiber compositions followed by testing pro-regenerative bioactivity on chondrocytes. Methods: We tested the impact of electrostatic interactions on nanostructure morphology and release kinetics of the negatively charged losartan molecule from either a positively or negatively charged PA nanofiber. Subsequently, cytotoxicity and bioactivity were evaluated in vitro in both normal and an IL-1β-induced OA chondrocyte model using ATDC5. Results: Both nanofiber systems promoted cell proliferation but that the positively-charged nanofibers also significantly increased glycosaminoglycans production. Furthermore, gene expression analysis suggested that losartan-encapsulated nanofibers had significant anti-inflammatory, anti-degenerative, and cartilage regenerative effects by significantly blocking TGF-β1 in this in vitro system. Discussion: The results of this study demonstrated that positively charged losartan sustained-release nanofibers may be a novel and useful treatment for cartilage regeneration and OA by blocking TGF-β1.

Effectiveness of losartan on infrapatellar fat pad/synovial fibrosis and pain behavior in the monoiodoacetate-induced rat model of osteoarthritis pain

Infrapatellar fat pad (IFP)/ synovial fibrosis is closely associated with the clinical symptoms of joint pain and stiffness, which contribute to locomotor restriction in osteoarthritis (OA) patients. Hence, this study was designed to gain insight on whether losartan, a selective angiotensin II type 1 receptor (AT1R) antagonist, has therapeutic benefit to reverse IFP/synovial fibrosis and secondarily to attenuate pain behavior. In male Wistar rats with monoiodoacetic acid (MIA)-induced IFP/synovial fibrosis, a possible role for increased AT1R expression in the pathogenesis of IFP/synovial fibrosis was assessed over an 8-week period. Pain behavior comprised static weight bearing and von Frey paw withdrawal thresholds (PWTs), which were assessed once or twice weekly, respectively. Groups of MIA-rats received oral losartan (30-mg/kg; n = 8 or 100-mg/kg; n = 9) or vehicle (n = 9) for 28-days according to a prevention protocol. Animals were euthanized on day 28 and various tissues (IFP/synovium, cartilage and lumbar dorsal root ganglia (DRGs)) were collected for histological, immunohistochemical and western blot analyses. Administration of once-daily losartan for 28-days dose-dependently attenuated the development of static weight bearing. This was accompanied by reduced IFP/synovial fibrosis and suppression of TGF-β1 expression. Chronic treatment of MIA-rats with losartan had an anti-fibrotic effect and it attenuated pain behavior in this animal model.

Cellular therapy and tissue engineering for cartilage repair

Articular cartilage (AC) has limited capacity for repair. The first attempt to repair cartilage using tissue engineering was reported in 1977. Since then, cell-based interventions have entered clinical practice in orthopaedics, and several tissue engineering approaches to repair cartilage are in the translational pipeline towards clinical application. Classically, these involve a scaffold, substrate or matrix to provide structure, and cells such as chondrocytes or mesenchymal stromal cells to generate the tissue. We discuss the advantages and drawbacks of the use of various cell types, natural and synthetic scaffolds, multiphasic or gradient-based scaffolds, and self-organizing or self-assembling scaffold-free systems, for the engineering of cartilage constructs. Several challenges persist including achieving zonal tissue organization and integration with the surrounding tissue upon implantation. Approaches to improve cartilage thickness, organization and mechanical properties include mechanical stimulation, culture under hypoxic conditions, and stimulation with growth factors or other macromolecules. In addition, advanced technologies such as bioreactors, biosensors and 3D bioprinting are actively being explored. Understanding the underlying mechanisms of action of cell therapy and tissue engineering approaches will help improve and refine therapy development. Finally, we discuss recent studies of the intrinsic cellular and molecular mechanisms of cartilage repair that have identified novel signals and targets and are inspiring the development of molecular therapies to enhance the recruitment and cartilage reparative activity of joint-resident stem and progenitor cells. A one-fits-all solution is unrealistic, and identifying patients who will respond to a specific targeted treatment will be critical.

Effects of oral losartan administration on homeostasis of articular cartilage and bone in a rabbit model

Background and aims

Previous work has shown that oral losartan can enhance microfracture-mediated cartilage repair in a rabbit osteochondral defect injury model. In this study, we aimed to determine whether oral losartan would have a detrimental effect on articular cartilage and bone homeostasis in the uninjured sides.

Methods

New Zealand rabbits were divided into 4 groups including normal uninjured (Normal), contralateral uninjured side of osteochondral defect (Defect), osteochondral defect plus microfracture (Microfracture) and osteochondral defect plus microfracture and losartan oral administration (10 mg/kg/day) (Losartan). Rabbits underwent different surgeries and treatment and were sacrificed at 12 weeks. Both side of the normal group and uninjured side of treatment groups tibias were harvested for Micro-CT and histological analysis for cartilage and bone including H&E staining, Herovici's staining (bone and cartilage) Alcian blue and Safranin O staining (cartilage) as well as immunohistochemistry of losartan related signaling pathways molecules for both cartilage and bone.

Results

Our results showed losartan oral treatment at 10 mg/kg/day slightly increase Alcian blue positive matrix as well as decrease collagen type 3 in articular cartilage while having no significant effect on articular cartilage structure, cellularity, and other matrix. Losartan treatment also did not affect angiotensin receptor type 1 (AGTR1), angiotensin receptor type 2 (AGTR2) and phosphorylated transforming factor β1 activated kinase 1 (pTAK1) expression level and pattern in the articular cartilage. Furthermore, losartan treatment did not affect microarchitecture of normal cancellous bone and cortical bone of tibias compared to normal and other groups. Losartan treatment slightly increased osteocalcin positive osteoblasts on the surface of cancellous bone and did not affect bone matrix collagen type 1 content and did not change AGTR1, AGTR2 and pTAK1 signal molecule expression.

Conclusion

Oral losartan used as a microfracture augmentation therapeutic does not have significant effect on uninjured articular cartilage and bone based on our preclinical rabbit model. These results provided further evidence that the current regimen of using losartan as a microfracture augmentation therapeutic is safe with respect to bone and cartilage homeostasis and support clinical trials for its application in human cartilage repair.

Optimization of the Duration of the Administration of Mesenchymal Stem Cells Wharton’s Jelly to the Level of Matrix Metalloproteinase-1 and Transforming Growth Factor-β in Osteoarthritis Rat Model

BACKGROUND: Mesenchymal Stem Cell Wharton’s Jelly (MSC-WJ) is promising candidates for osteoarthritis (OA) therapy since they have chondrogenic potential and the ability to form the extracellular matrix. AIM: This study aimed to determine the effect of the time giving MSC-WJ on bioactive markers of osteoarthritis. METHODS: The osteoarthritis rat model was treated by intra-articular injection with MSC-WJ and α _MEM as a control. Four and 8 weeks later performed a histological analysis of cartilage and the determination of the levels of Matrix Metalloproteinase-1(MMP-1) and Transforming growth factor β1 (TGF-β1) in serum by ELISA. RESULTS: The results showed that administration of MSC-WJ showed improvement in the histological picture of knee joints in experimental animals characterized by an increase in cartilage thickness on the joint surface. The administration of MSC-WJ showed a tendency to decrease MMP-1 serum levels of OA rats treated for 8 weeks, although statistically did not show a significant difference. Whereas, administration of MSC-WJ showed a decrease in serum levels of TGF-β1 OA rat treated for 8 weeks. CONCLUSION: MSC-WJ can repair damaged knee OA cartilage tissue. The administration of MSC-WJ can reduce serum levels of TGF-β1 OA rats treated for 8 weeks.

Inhibition of transforming growth factor-β in osteoarthritis. Discrepancy with reduced TGFβ signaling in normal joints

Objective

Transforming growth factor-β (TGFβ) is a pleiotropic cytokine that is central in the regulation of joint health and disease. Inhibition of TGFβ activity/signaling in experimental osteoarthritis (OA) has been performed to modulate OA severity and progression. In this narrative review we discuss the potential reasons for the variable results of TGFβ inhibition in these models.

Design

A literature study was performed using the search terms; experimental osteoarthritis and TGFβ. Papers were selected that describe the effect TGFβ activity/signaling inhibition on experimental OA. Based on the selected papers a narrative review has been written about the potential therapeutic role of TGFβ inhibition in OA and potential causes for its variable effects are discussed.

Results

Inhibition of TGFβ activity in experimental models of OA does not result in either straightforward protection or deleterious effects. More than half of the studies (13/19), but not all, report that inhibition of TGFβ in experimental OA reduces OA severity. This is in contrast with the protective role of TGFβ in healthy joints.

Conclusions

The effect of TGFβ inhibition on joint damage in experimental OA is variable. Most likely this is a consequence of the changing function of TGFβ in normal and OA joints. As a result, the overall outcome of TGFβ modulation in OA will be unpredictable. To develop OA therapies based on modulation of TGFβ activity specific protective and damaging signaling routes should be identified and tools developed to block the damaging ones.

Pleiotropic Effects of Simvastatin and Losartan in Preclinical Models of Post-Traumatic Elbow Contracture

Elbow trauma can lead to post-traumatic joint contracture (PTJC), which is characterized by loss of motion associated with capsule/ligament fibrosis and cartilage damage. Unfortunately, current therapies are often unsuccessful or cause complications. This study aimed to determine the effects of prophylactically administered simvastatin (SV) and losartan (LS) in two preclinical models of elbow PTJC: an in vivo elbow-specific rat injury model and an in vitro collagen gel contraction assay. The in vivo elbow rat (n = 3-10/group) injury model evaluated the effects of orally administered SV and LS at two dosing strategies [i.e., low dose/high frequency/short duration (D1) vs. high dose/low frequency/long duration (D2)] on post-mortem elbow range of motion (via biomechanical testing) as well as capsule fibrosis and cartilage damage (via histopathology). The in vitro gel contraction assay coupled with live/dead staining (n = 3-19/group) evaluated the effects of SV and LS at various concentrations (i.e., 1, 10, 100 µM) and durations (i.e., continuous, short, or delayed) on the contractibility and viability of fibroblasts/myofibroblasts [i.e., NIH3T3 fibroblasts with endogenous transforming growth factor-beta 1 (TGFβ1)]. In vivo, no drug strategy prevented elbow contracture biomechanically. Histologically, only SV-D2 modestly reduced capsule fibrosis but maintained elevated cellularity and tissue hypertrophy, and both SV strategies lessened cartilage damage. SV modest benefits were localized to the anterior region, not the posterior, of the joint. Neither LS strategy had meaningful benefits in capsule nor cartilage. In vitro, irrespective of the presence of TGFβ1, SV (≥10 μM) prevented gel contraction partly by decreasing cell viability (100 μM). In contrast, LS did not prevent gel contraction or affect cell viability. This study demonstrates that SV, but not LS, might be suitable prophylactic drug therapy in two preclinical models of elbow PTJC. Results provide initial insight to guide future preclinical studies aimed at preventing or mitigating elbow PTJC.

Transforming growth factor-β receptors mediates matrix degradation and abnormal hypertrophy in T-2 toxin-induced hypertrophic chondrocytes

This study investigated whether transforming growth factor-β receptor I (TGF-βRI) and TGF-βRII mediate matrix degradation and abnormal hypertrophy in T-2 toxin-induced hypertrophic chondrocytes. Hypertrophic chondrocytes were exposed to TGF-βRI and TGF-βRII binding inhibitor (GW788388) for 24 h prior to exposure to different concentrations of T-2 toxin (0, 10, 25, and 50 ng/mL for 48 h). Hypertrophic chondrocytes were assessed based on the expression of matrix-degrading and terminal differentiation-related genes and cell viability. Matrix metalloproteinases (MMPs, MMP-13, MMP-1, and MMP-9) were reduced in the GW788388+T-2 toxin group compared to the T-2 toxin group. The expression of terminal differentiation-related genes (MMP-2, MMP-10, and collagen X) was increased in hypertrophic chondrocytes in the inhibited groups compared to that in the T-2 toxin group. The survival rate of chondrocytes decreased significantly in a dose-dependent manner. GW788388 did not significantly block the reduced cell viability in hypertrophic chondrocytes exposed to T-2 toxin. The upregulated expression of TGF-βRI and TGF-βRII mediates the abnormal chondrocyte hypertrophy and extracellular matrix degeneration observed in T-2 toxin-induced hypertrophic chondrocytes.

Noggin, an inhibitor of bone morphogenetic protein signaling, antagonizes TGF-β1 in a mouse model of osteoarthritis

Osteoarthritis (OA) is the most common joint disease worldwide; however, disease-modifying treatments are lacking because of the complicated pathological mechanisms. As a breakthrough, aberrant activation of transforming growth factor-β 1 (TGF-β1)in subchondral bone has been confirmed as an essential pathomechanism for OA progression, and has become a potential therapeutic target. In addition to R&D on neutralizing antibodies, small-molecule antagonists and chemical medicines, native antagonists of TGF-β1 could be exploited as another promising approach. Noggin (NOG) is an antagonist of bone morphogenetic proteins (BMPs) and was reported to effectively attenuate OA by protecting cartilage and preventing pathological subchondral bone remodeling. However, the underlying mechanisms have not been fully clarified. We first detected the distribution of NOG in knee joints of an OA mouse model, which showed upregulation at early stage of OA but downregulation later in the subchondral bone and no significant change in the articular cartilage. Furthermore, the interaction between NOG and TGF-β1 was verified, which in turn suppressed the downstream SMAD2/3 activity of TGF-β1. Moreover, the proliferation and chondrogenesis of mesenchymal stem cells (MSCs) were not significantly influenced by NOG. Taken together, the results showed that NOG antagonized TGF-β1 but did not repress MSC proliferation and chondrogenesis; thus, it seems promising for OA treatment.

Losartan protects against osteoarthritis by repressing the TGF-β1 signaling pathway via upregulation of PPARγ

OBJECTIVE

Losartan and activation of the peroxisome proliferator-activated receptor-γ (PPARγ) have been previously reported to alleviate the progression of osteoarthritis (OA). However, the nature of the interaction between losartan and PPARγ in OA remains elusive. Therefore, we aimed to investigate the mechanism of the regulation of PPARγ by losartan in the context of OA.

METHODS

Clinical samples of OA patients were collected and the chondrocytes were further isolated, and used to construct OA chondrocyte model via induction with IL-1β. An OA mouse model was developed by the surgical destabilization of the medial meniscus (DMM). OA chondrocytes were treated with losartan, PPARγ siRNA and the PPAR-γ agonist GW1929 alone or in combination. Furthermore, the OA mice were treated with varying doses of losartan to determine the best mode of administration and treatment dose. Subsequently, the DMM mice were treated with losartan and GW9662. Expression of PPARγ, key proteins of the transforming growth factor-beta1 (TGF-β1) signaling pathway and the markers of OA degeneration were evaluated by the Western blot analysis, while effects on OA inflammatory factors were determined by ELISA.

RESULTS

The downregulation of PPARγ and the upregulation of TGF-β1 signaling pathway were detected in the OA cartilage tissues and chondrocytes. Losartan treatment or PPARγ activation contributes to reduced levels of IL-6, IL-1β, TNF-α, and COX-2, expression of TGF-β1, MMP-13, ADAMTS-4, ADAMTS-5, HtrA1, and iNOS, along with reduced Smad2 and Smad3 phosphorylation, but elevated PPARγ and Collagen II expression in vivo and in vitro. Additionally, the intraarticular injection of losartan into the knee joint proved to be the best mode of administration, and 10 ​mg/mL being the optimal treatment concentration.

CONCLUSION

Our results show that losartan could arrest the progression of OA by upregulating PPARγ expression and inactivating the TGF-β1 signaling pathway.The translational potential of this article: Our results provide a biological rationale for the use of losartan as a potential candidate for OA treatment.

The Beneficial Effect of an Intra-articular Injection of Losartan on Microfracture-Mediated Cartilage Repair Is Dose Dependent

BACKGROUND

A previous publication demonstrated that the oral intake of losartan promoted microfracture-mediated hyaline-like cartilage repair in osteochondral defects of a rabbit knee model. However, an intra-articular (IA) injection of losartan may have direct beneficial effects on cartilage repair and has not been studied.

PURPOSE

To determine the dosage and beneficial effects of an IA injection of losartan on microfracture-mediated cartilage repair and normal cartilage homeostasis.

STUDY DESIGN

Controlled laboratory study.

METHODS

Rabbits were divided into 5 groups (n = 6 each): a microfracture group (MFX group) and 4 different losartan treatment groups that received varying doses of IA losartan (0.1, 1, 10, and 100 mg per knee). An osteochondral defect (5 mm) was created in the trochlear groove cartilage of 1 limb in each rabbit, and 5 microfracture perforations were made in the osteochondral defect. Both the injured and the contralateral knee joints were injected with IA losartan immediately after microfracture and at 2 and 4 weeks after surgery. Rabbits were sacrificed at 6 weeks after surgery for analysis including gross observation, micro-computed tomography, histology, and reverse transcription quantitative polymerase chain reaction.

RESULTS

Micro-computed tomography and gross observation demonstrated comparable subchondral bone healing and hyaline-like cartilage morphology in the 0.1-, 1-, and 10-mg losartan groups relative to the MFX group. Conversely, the 100-mg losartan group showed neither bony defect healing nor cartilage repair. Histology revealed higher O'Driscoll scores and hyaline-like cartilage regeneration in the 1-mg losartan group compared with the MFX group. In contrast, the 100-mg losartan group showed the lowest histology score and no cartilage repair. An IA injection of losartan at the doses of 0.1, 1, and 10 mg did not cause adverse effects on uninjured cartilage, while the 100-mg dose induced cartilage damage. Quantitative polymerase chain reaction results showed downregulation of the transforming growth factor β (TGF-β) signaling pathway after IA losartan injection.

CONCLUSION

An IA injection of losartan at the dose of 1 mg was most effective for the enhancement of microfracture-mediated cartilage repair without adversely affecting uninjured cartilage. Conversely, a high dose (100 mg) IA injection of losartan inhibited cartilage repair in the osteochondral defect and was chondrotoxic to normal articular cartilage.

CLINICAL RELEVANCE

An IA injection of losartan at an optimal dosage represents a novel microfracture enhancement therapy and warrants a clinical trial for future clinical applications.

A Molecular Cascade Underlying Articular Cartilage Degeneration

Preserving of articular cartilage is an effective way to protect synovial joints from becoming osteoarthritic (OA) joints. Understanding of the molecular basis of articular cartilage degeneration will provide valuable information in the effort to develop cartilage preserving drugs. There are currently no disease-modifying OA drugs (DMOADs) available to prevent articular cartilage destruction during the development of OA. Current drug treatments for OA focus on the reduction of joint pain, swelling, and inflammation at advanced stages of the disease. However, based on discoveries from several independent research laboratories and our laboratory in the past 15 to 20 years, we believe that we have a functional molecular understanding of articular cartilage degeneration. In this review article, we present and discuss experimental evidence to demonstrate a sequential chain of the molecular events underlying articular cartilage degeneration, which consists of transforming growth factor beta 1, high-temperature requirement A1 (a serine protease), discoidin domain receptor 2 (a cell surface receptor tyrosine kinase for native fibrillar collagens), and matrix metalloproteinase 13 (an extracellularmatrix degrading enzyme). If, as we strongly suspect, this molecular pathway is responsible for the initiation and acceleration of articular cartilage degeneration, which eventually leads to progressive joint failure, then these molecules may be ideal therapeutic targets for the development of DMOADs.

Brucella-Induced Downregulation of lncRNA Gm28309 Triggers Macrophages Inflammatory Response Through the miR-3068-5p/NF-κB Pathway

Objectives

The underlying mechanism of the inflammatory response against Brucellosis caused by Brucella remains poorly understood. This study aimed to determine the role of long non-coding RNAs (lncRNAs) in regulating of inflammatory and anti-Brucella responses.

Materials and methods

Microarray analysis was performed to detect differentially expressed lncRNAs in THP-1 cells infected with an S2308 Brucella strain. The candidate lncRNAs were screened using bioinformatic analysis and siRNAs; bioinformatic prediction and luciferase reporter assay were also conducted, while inflammatory responses was assessed using RT‐qPCR, western blot, immunofluorescence, ELISA, HE, and immunohistochemistry.

Results

The lncRNA Gm28309 was identified to be involved in regulating inflammation induced by Brucella. Gm28309, localized in the cytoplasm, was down-expressed in RAW264.7 cells infected with S2308. Overexpression of Gm28309 or inhibition of miR-3068-5p repressed p65 phosphorylation and reduced NLRP3 inflammasome and IL-1β and IL-18 secretion. Mechanistically, Gm28309 acted as a ceRNA of miR-3068-5p to activate NF-κB pathway by targeting κB-Ras2, an inhibitor of NF-κB signaling. Moreover, the number of intracellular Brucella was higher when Gm28309 was overexpressed or when miR-3068-5p or p65 was inhibited. However, these effects were reversed by the miR-3068-5p mimic.

Conclusions

Our study demonstrates, for the first time, that LncRNAs are involved in regulating immune responses during Brucella infection, and Gm28309, an lncRNA, plays a crucial role in activating NF-κB/NLRP3 inflammasome signaling pathway.

miR-296-5p inhibits IL-1β-induced apoptosis and cartilage degradation in human chondrocytes by directly targeting TGF-β1/CTGF/p38MAPK pathway

Osteoarthritis (OA) is characterized by apoptosis of chondrocytes and an imbalance of extracellular matrix (ECM) synthesis and catabolism. Emerging evidence has demonstrated that miRNAs are involved in OA pathologies, but the role of miR-296-5p in OA remains unclear. The present study proposes to reveal the functions and mechanisms of miR-296-5p in a cell model of OA. In this study, human chondrocytes were treated with 5 ml interleukin-1 beta (IL-1β) to induce apoptosis and cartilage degradation. Our results showed that miR-296-5p was downregulated in chondrocytes stimulated with IL-1β. Overexpressed miR-296-5p enhanced cell proliferation and inhibited apoptosis and matrix degrading enzyme expression in response to IL-1β stimulation, and knockdown of miR-296-5p showed the opposite effect. Further, we found that miR-296-5p directly targeted the 3'-untranslated region (3'-UTR) of TGF-β1 mRNA, and miR-296-5p inactivated the TGF-β1/CTGF/p38MAPK signaling pathway. Overexpression of TGF-β1 alleviated the inhibition of miR-296-5p on chondrocyte apoptosis and cartilage degradation. In conclusion, miR-296-5p inhibited the progression of OA through the CTGF/p38MAPK pathway by directly targeting TGF-β1.

Resistance training decreases matrix metalloproteinase-2 activity in quadriceps tendon in a rat model of osteoarthritis

BACKGROUND

Osteoarthritis (OA) is a degenerative disease that induces peri-articular tissue degradation. OA induces an imbalance between synthesis and degradation of the extracellular matrix components in favor of catabolic events, promoting pathological remodeling and involving degradative enzymes, such as matrix metalloproteinases (MMPs).

OBJECTIVE

This study aimed to investigate the effects of 8-weeks resistance training (RT) on MMP-2 activity in the quadriceps tendon and patellar tendon in an OA model.

METHODS

Twenty-four Wistar rats were randomly divided into six groups: Control, Exercise, Sham, Sham with Exercise, OA, and OA with Exercise (OAE). The OA model was performed by anterior cruciate ligament transection surgery on the left knee. The 8-week RT consisted of climbing a 1.1-m vertical ladder three times per week with progressive weights secured to the animals' tails. MMP-2 activity was analyzed by zymography.

RESULTS

The OAE group displayed lower pro, intermediate, and active MMP-2 activity in the quadriceps tendon compared with the OA group (p<0.05). For the patellar tendon, there was no significant difference between the OAE group compared with the other groups (p>0.05) for pro, intermediate, and active MMP-2 activity. Moreover, MMP-2 activity differed between tissues, the OA and OAE groups presented lower pro, intermediate, and active MMP-2 activity in the quadriceps tendon compared to the patellar tendon.

CONCLUSION

RT induced down-regulated MMP-2 activity in the quadriceps tendon. RT is a potential therapeutic approach to minimize the deleterious effects of extracellular matrix degeneration.

Biologically Regulated Marrow Stimulation by Blocking TGF-β1 With Losartan Oral Administration Results in Hyaline-like Cartilage Repair: A Rabbit Osteochondral Defect Model

BACKGROUND

Microfracture or bone marrow stimulation (BMS) is often the first choice for clinical treatment of cartilage injuries; however, fibrocartilage, not pure hyaline cartilage, has been reported because of the development of fibrosis in the repair tissue. Transforming growth factor β1 (TGF-β1), which can promote fibrosis, can be inhibited by losartan and potentially be used to reduce fibrocartilage.

HYPOTHESIS

Blocking TGF-β1 would improve cartilage healing in a rabbit knee BMS model via decreasing the amount of fibrocartilage and increasing hyaline-like cartilage formation.

STUDY DESIGN

Controlled laboratory study.

METHODS

An osteochondral defect was made in the patellar groove of 48 New Zealand White rabbits. The rabbits were divided into 3 groups: a defect group (defect only), a BMS group (osteochondral defect + BMS), and a BMS + losartan group (osteochondral defect + BMS + losartan). For the rabbits in the BMS + losartan group, losartan was administrated orally from the day after surgery through the day of euthanasia. Rabbits were sacrificed 6 or 12 weeks postoperatively. Macroscopic appearance, microcomputed tomography, histological assessment, and TGF-β1 signaling pathway were evaluated at 6 and 12 weeks postoperatively.

RESULTS

The macroscopic assessment of the repair revealed that the BMS + losartan group was superior to the other groups tested. Microcomputed tomography showed superior healing of the bony defect in the BMS + losartan group in comparison with the other groups. Histologically, fibrosis in the repair tissue of the BMS + losartan group was significantly reduced when compared with the other groups. Results obtained with the modified O'Driscoll International Cartilage Repair Society grading system yielded significantly superior scores in the BMS + losartan group as compared with both the defect group and the BMS group (F value: 15.8, P < .001, P = .012, respectively). TGF-β1 signaling and TGF-β-activated kinase 1 of the BMS + losartan group were significantly suppressed in the synovial tissues.

CONCLUSION

By blocking TGF-β1 with losartan, the repair cartilage tissue after BMS was superior to the other groups and consisted primarily of hyaline cartilage. These results should be easily translated to the clinic because losartan is a Food and Drug Administration-approved drug and it can be combined with the BMS technique for optimal repair of chondral defects.

CLINICAL RELEVANCE

Biologically regulated marrow stimulation by blocking TGF-β1 (oral intake of losartan) provides superior repair via decreasing fibrocartilage formation and resulting in hyaline-like cartilage as compared with outcomes from BMS only.

Dual roles of misshapen/NIK-related kinase (MINK1) in osteoarthritis subtypes through the activation of TGFβ signaling

OBJECTIVE

To identify the role of misshapen/NIK-related kinase (MINK1) in age-related Osteoarthritis (OA) and injury-induced OA, and the effects of enhanced TGFβ signaling in these progresses.

DESIGN

The effect of MINK1 was analyzed with MINK1 knock out (Mink1-/-) mice and C57BL/6J mice. OA progress was studied in age-related OA and instability-associated OA (destabilization of the medial meniscus, DMM) models. The murine knee joint was evaluated through histological staining, Osteoarthritis Research Society International (OARSI) scores, immunohistochemistry, and μCT analysis. Primary chondrocytes were isolated from wild type and Mink1-/- mice and subjected to osteogenic induction and Western blot analysis.

RESULTS

MINK1 is highly expressed during cartilage development and in normal cartilage. Mink1-/- mice displayed markedly lower OARSI scores, aggrecan degradation neoepitope positive cells and increased Safranin O and pSMAD2 staining in aging-related OA model. However, in injury-induced OA, loss of MINK1 accelerates extracellular matrix (ECM) destruction, osteophyte formation, and subchondral bone sclerosis. Accelerated subchondral bone remodeling in Mink1-/- mice was accompanied with increased numbers of nestin-positive mesenchymal stem cells (MSCs) and osterix-positive osteoprogenitors. pSMAD2 staining was increased in the subchondral bone marrow of Mink1-/- mice and overexpression of MINK1 inhibited SMAD2 phosphorylation in vitro.

CONCLUSIONS

This study shows for the first time that activation of TGFβ/SMAD2 by MINK1 deficiency plays opposite roles in aging-related and injury-induced OA. MINK1 deficiency protects cartilage from degeneration in aging joints through increased SMAD2 activation in chondrocytes, while accelerating OA progress in injury-induced model through enhanced osteogenesis of MSCs in the subchondral bone. These findings provide insights for developing precision OA therapeutics targeting TGFβ/SMAD2 signaling.

TGFβ/BMP Signaling Pathway in Cartilage Homeostasis

Cartilage homeostasis is governed by articular chondrocytes via their ability to modulate extracellular matrix production and degradation. In turn, chondrocyte activity is regulated by growth factors such as those of the transforming growth factor β (TGFβ) family. Members of this family include the TGFβs, bone morphogenetic proteins (BMPs), and growth and differentiation factors (GDFs). Signaling by this protein family uniquely activates SMAD-dependent signaling and transcription but also activates SMAD-independent signaling via MAPKs such as ERK and TAK1. This review will address the pivotal role of the TGFβ family in cartilage biology by listing several TGFβ family members and describing their signaling and importance for cartilage maintenance. In addition, it is discussed how (pathological) processes such as aging, mechanical stress, and inflammation contribute to altered TGFβ family signaling, leading to disturbed cartilage metabolism and disease.

The TGFβ type I receptor TGFβRI functions as an inhibitor of BMP signaling in cartilage

The TGFβ signaling pathway is activated when TGFβ ligands induce formation of TGFβRI and TGFβRII receptor complexes. However, loss of TGFβRI in mouse cartilage led to more severe defects than did loss of TGFβRII. Most of the defects were rescued by deletion of the BMP receptor ACVRL1, suggesting that a major role of TGFβRI in cartilage development is to suppress BMP signaling by ACVRL1. TGFβRI prevents the formation of ACVRL1/ACTRIIB complexes, which have high affinity for BMP9, the most abundant BMP in circulation. These results demonstrate a form of cross talk between BMP and TGFβ signaling pathways in cartilage that may also operate in other tissues where the relative output of these 2 pathways is required.

The type I TGFβ receptor TGFβRI (encoded by Tgfbr1) was ablated in cartilage. The resulting Tgfbr1^Col2 mice exhibited lethal chondrodysplasia. Similar defects were not seen in mice lacking the type II TGFβ receptor or SMADs 2 and 3, the intracellular mediators of canonical TGFβ signaling. However, we detected elevated BMP activity in Tgfbr1^Col2 mice. As previous studies showed that TGFβRI can physically interact with ACVRL1, a type I BMP receptor, we generated cartilage-specific Acvrl1 (Acvrl1^Col2) and Acvrl1/Tgfbr1 (Acvrl1/Tgfbr1^Col2) knockouts. Loss of ACVRL1 alone had no effect, but Acvrl1/Tgfbr1^Col2 mice exhibited a striking reversal of the chondrodysplasia seen in Tgfbr1^Col2 mice. Loss of TGFβRI led to a redistribution of the type II receptor ACTRIIB into ACVRL1/ACTRIIB complexes, which have high affinity for BMP9. Although BMP9 is not produced in cartilage, we detected BMP9 in the growth plate, most likely derived from the circulation. These findings demonstrate that the major function of TGFβRI in cartilage is not to transduce TGFβ signaling, but rather to antagonize BMP signaling mediated by ACVRL1.

Genome-wide microRNA screening reveals miR-582-5p as a mesenchymal stem cell-specific microRNA in subchondral bone of the human knee joint

Emerging evidence suggests that microRNAs (miRNAs) may be pathologically involved in osteoarthritis (OA). Subchondral bone (SCB) sclerosis is accounted for the knee osteoarthritis (KOA) development and progression. In this study, we aimed to screen the miRNA biomarkers of KOA and investigated whether these miRNAs regulate the differentiation potential of mesenchymal stem cells (MSCs) and thus contributing to SCB. We identified 48 miRNAs in the blood samples in KOA patients (n = 5) through microarray expression profiling detection. After validation with larger sample number, we confirmed hsa-miR-582-5p and hsa-miR-424-5p were associated with the pathology of SCB sclerosis. Target genes prediction and pathway analysis were implemented with online databases, indicating these two candidate miRNAs were closely related to the pathways of pluripotency of stem cells and pathology of OA. Surprisingly, mmu-miR-582-5p (homology of hsa-miR-582-5p) was downregulated in osteogenic differentiation and upregulated in adipogenic differentiation of mesenchymal progenitor C3H10T1/2 cells, whereas mmu-mir-322-5p (homology of hsa-miR-424-5p) showed no change through the in vitro study. Supplementing mmu-miR-582-5p mimics blocked osteogenic and induced adipogenic differentiation of C3H10T1/2 cells, whereas silencing of the endogenous mmu-miR-582-5p enhanced osteogenic and repressed adipogenic differentiation. Further mechanism studies showed that mmu-miR-582-5p was directly targeted to Runx2. Mutation of putative mmu-miR-582-5p binding sites in Runx2 3' untranslated region (3'UTR) could abolish the response of the 3'UTR-luciferase construct to mmu-miR-582-5p supplementation. Generally speaking, our data suggest that miR-582-5p is an important biomarker of KOA and is able to regulate osteogenic and adipogenic differentiation of MSCs via targeting Runx2. The study also suggests that miR-582-5p may play a crucial role in SCB sclerosis of human KOA.

Characterization of articular cartilage homeostasis and the mechanism of superior cartilage regeneration of MRL/MpJ mice

This study investigated articular cartilage (AC) homeostasis and different signaling pathways involved in the superior cartilage regeneration of Murphy Roths large (MRL/MpJ) mice previously reported. We collected uninjured and destabilized medial meniscus (DMM)-injured knees from 8-wk-old C57BL/6J and MRL/MpJ mice. We used micro-computed tomography (microCT), histology, and immunohistochemistry to evaluate AC homeostasis and repair. We used the ear punch model to investigate the role of angiogenesis and inflammation in the superior healing of MRL/MpJ mice. We found fewer β-catenin and more pSMAD5 positive cells in the uninjured AC of MRL/MpJ mice than that from C57BL/6J mice. MRL/MpJ mice exhibited better AC repair in DMM-induced OA, as indicated by microCT results, Alcian blue, and Safranin O staining. Mechanistically, fewer β-catenin, pSMAD2-, pSMAD3-, a disintegrin and metalloproteinase with thrombospondin motifs 4-, matrix metalloproteinase (MMP) 9-, and MMP13-positive cells and more proliferating cell nuclear antigen- and pSMAD5-positive cells were found in the DMM-injured AC in MRL/MpJ mice than in normal mice. The accelerated ear wound healing of MRL/MpJ mice correlated with enhanced angiogenesis and macrophage polarization toward the M2a phenotype through elevated IL-10 and IL-4 expressing cells. Collectively, our study revealed that down-regulation of pSMAD2/3, β-catenin, and MMPs and up-regulation of pSMAD5 and M2a macrophage polarization contribute to the enhanced cartilage repair observed in MRL/MpJ mice.-Deng, Z., Gao, X., Sun, X., Amra, S., Lu, A., Cui, Y., Eltzschig, H. K., Lei, G., Huard, J. Characterization of articular cartilage homeostasis and the mechanism of superior cartilage regeneration of MRL/MpJ mice.

High-Temperature Requirement A1 Protease as a Rate-Limiting Factor in the Development of Osteoarthritis

Preserving the mature articular cartilage of joints is a critical focus in the prevention and treatment of osteoarthritis. We determined whether the genetic inactivation of high-temperature requirement A1 (HtrA1) can significantly attenuate the degradation of articular or condylar cartilage. Two types of mouse models of osteoarthritis were used, a spontaneous mutant mouse model [type XI collagen-haploinsufficient (Col11a1^+/-) mice] and two post-traumatic mouse models [destabilization of the medial meniscus (DMM) on the knee and a partial discectomy (PDE) on the temporomandibular joint]. Three different groups of mice were generated: i) HtrA1 was genetically deleted from Col11a1^+/- mice (HtrA1^-/-;Col11a1^+/-), ii) HtrA1-deficient mice (HtrA1^-/-) were subjected to DMM, and iii) HtrA1^-/- mice were subjected to PDE. Knee and temporomandibular joints from the mice were characterized for evidence of cartilage degeneration. The degradation of articular or condylar cartilage was significantly delayed in HtrA1^-/-;Col11a1^+/- mice and HtrA1^-/- mice after DMM or PDE. The amount of collagen type VI was significantly higher in the articular cartilage in HtrA1^-/-;Col11a1^+/- mice, compared with that in Col11a1^+/- mice. The genetic removal of HtrA1 may delay the degradation of articular or condylar cartilage in mice.

Losartan attenuates progression of osteoarthritis in the synovial temporomandibular and knee joints of a chondrodysplasia mouse model through inhibition of TGF-β1 signaling pathway

OBJECTIVE

Transforming growth factor beta 1 (TGF-β1) is implicated in osteoarthritis (OA). The purpose of this study was to explore the ability of Losartan to inhibit the inflammatory signaling pathway of TGF-β1 observed during osteoarthritic progression in the temporomandibular joint (TMJ) and knee joint using a genetic mouse model.

METHODS

A murine OA model displaying the heterozygous chondrodysplasia gene (cho/+), a col11a1 mutation, was used to test this hypothesis. Following a 7-month treatment period with Losartan, the synovial joints were analyzed for histopathological improvement comparing two experimental groups. Tissues were fixed in paraformaldehyde, processed to paraffin section, and stained with Safranin O and Fast Green to visualize proteoglycans and collagen proteins in cartilage. Using the Modified Mankin scoring system, the degree of staining and OA progression were evaluated.

RESULTS

Results show heterozygous animals receiving Losartan having diminished degeneration of TMJ condylar and knee joint articular cartilage. This was confirmed in the TMJ and knee by a statistically significant decrease in the Mankin histopathology score. Decreased expression of HtrA1, a key regulator to the TGF-β1 signaling pathway, was demonstrated in vitro as well as in vivo, via Losartan inhibition.

CONCLUSION

Using a genetic mouse model of OA, this study demonstrated the utility of Losartan to improve treatment of human OA in the TMJ and knee joint through inhibition of the TGF-β1 signaling cascade. We further demonstrated inhibition of HtrA1, the lowering of Mankin scores to wild type control levels, and the limiting of OA progressive damage with treatment of Losartan.

Understanding chondrodysplasia (cho): A comprehensive review of cho as an animal model of birth defects, disorders, and molecular mechanisms

BACKGROUND

The mutant chondrodysplasia (cho) is a cartilage-targeting disorder in C57BL mice that results in dwarfing and other malformations stemming from this collagenopathy. Clarke Fraser made the discovery of the mutation accidentally in the early 1960s during the thalidomide tragedy.

METHODS

For this review we identified key research on cho as since its discovery. Relevant data were compiled to make a comprehensive review that details discoveries associated with the cho mutation, that describes the associated phenotypes and molecular mechanisms, and that provides a discussion surrounding its current clinical relevance.

RESULTS

Mechanistically, cho acts by hindering chondrogenesis and endochondral bone formation. The phenotype results from a 1-nt deletion in the gene encoding the alpha 1 chain of type XI collagen. For more than half a century, researchers have studied the pathogenesis of the cho mutation in relation to a variety of mouse models of human birth defects and disease. These studies have resulted in several discoveries linking cho with such human disorders as dwarfism, tracheal stenosis, cleft palate, pulmonary hypoplasia, and osteoarthritis (OA).

CONCLUSION

The study of cho has led to numerous advances in understanding human birth defects, congenital disorders, and adult human disease. The most recent studies have suggested a role for the TGF-Beta, HtrA1, Ddr2, and Mmp-13 pathway in the degradation of articular cartilage and the development of OA in cho/+ mice. We have shown that the anti-hypertension drug Losartan is a TGF-Beta blocker that could be used to treat OA in Stickler syndrome, and thereby rescue the WT phenotype.

Dehydroepiandrosterone: Molecular mechanisms and therapeutic implications in osteoarthritis

Dehydroepiandrosterone (DHEA), a 19-carbon steroid hormone primarily synthesized in the adrenal gland, exerts a chondroprotective effect against osteoarthritis (OA) and has been considered an effective candidate of disease-modifying OA drugs (DMOADs) that slow disease progression. We and others previously demonstrated that DHEA exerted a beneficial effect on osteoarthritic cartilage by positively modulating the balance between anabolic and catabolic factors (e.g., MMPs/TIMP-1, ADAMTS/TIMP-3 and cysteine proteinases/cystatin C), inhibiting catabolic signaling pathways (e.g., Wnt/β-catenin), and suppressing proinflammatory cytokines-mediated low-grade synovial inflammation (e.g., IL-1β). However, the full picture of the pharmacological molecular mechanism(s) underlying the activity of DHEA against OA is still incomplete, and a comprehensive and up-to-date review article in this field is unavailable. In this review, recent findings (apart from the well documented pathogenesis of OA) regarding disease-related mechanisms involving low grade synovial inflammation, cartilage matrix stiffness, chondrocyte autophagy and the roles of a variety of catabolic cellular signaling pathways are discussed. Moreover, the possible relationship between these disease-related mechanisms and DHEA action is discussed. Emerging evidence from in vivo and in vitro studies were scrutinized and are concisely presented to demonstrate the investigational and putative mechanisms underlying the anti-OA potential of DHEA.

Effects of TGF-β Overexpression via rAAV Gene Transfer on the Early Repair Processes in an Osteochondral Defect Model in Minipigs

BACKGROUND

Application of the chondrogenic transforming growth factor beta (TGF-β) is an attractive approach to enhance the intrinsic biological activities in damaged articular cartilage, especially when using direct gene transfer strategies based on the clinically relevant recombinant adeno-associated viral (rAAV) vectors.

PURPOSE

To evaluate the ability of an rAAV-TGF-β construct to modulate the early repair processes in sites of focal cartilage injury in minipigs in vivo relative to control (reporter lacZ gene) vector treatment.

STUDY DESIGN

Controlled laboratory study.

METHODS

Direct administration of the candidate rAAV-human TGF-β (hTGF-β) vector was performed in osteochondral defects created in the knee joint of adult minipigs for macroscopic, histological, immunohistochemical, histomorphometric, and micro-computed tomography analyses after 4 weeks relative to control (rAAV- lacZ) gene transfer.

RESULTS

Successful overexpression of TGF-β via rAAV at this time point and in the conditions applied here triggered the cellular and metabolic activities within the lesions relative to lacZ gene transfer but, at the same time, led to a noticeable production of type I and X collagen without further buildup on the subchondral bone.

CONCLUSION

Gene therapy via direct, local rAAV-hTGF-β injection stimulates the early reparative activities in focal cartilage lesions in vivo.

CLINICAL RELEVANCE

Local delivery of therapeutic (TGF-β) rAAV vectors in focal defects may provide new, off-the-shelf treatments for cartilage repair in patients in the near future.

Aberrant TGF-β activation in bone tendon insertion induces enthesopathy-like disease

Enthesopathy is a disorder of bone, tendon, or ligament insertion. It represents one-fourth of all tendon-ligament diseases and is one of the most difficult tendon-ligament disorders to treat. Despite its high prevalence, the exact pathogenesis of this condition remains unknown. Here, we show that TGF-β was activated in both a semi-Achilles tendon transection (SMTS) mouse model and in a dorsiflexion immobilization (DI) mouse model of enthesopathy. High concentrations of active TGF-β recruited mesenchymal stromal stem cells (MSCs) and led to excessive vessel formation, bone deterioration, and fibrocartilage calcification. Transgenic expression of active TGF-β1 in bone also induced enthesopathy with a phenotype similar to that observed in SMTS and DI mice. Systemic inhibition of TGF-β activity by injection of 1D11, a TGF-β-neutralizing antibody, but not a vehicle antibody, attenuated the excessive vessel formation and restored uncoupled bone remodeling in SMTS mice. 1D11-treated SMTS fibrocartilage had increased proteoglycan and decreased collagen X and matrix metalloproteinase 13 expression relative to control antibody treatment. Notably, inducible knockout of the TGF-β type II receptor in mouse MSCs preserved the bone microarchitecture and fibrocartilage composition after SMTS relative to the WT littermate controls. Thus, elevated levels of active TGF-β in the enthesis bone marrow induce the initial pathological changes of enthesopathy, indicating that TGF-β inhibition could be a potential therapeutic strategy.

What drives osteoarthritis?-synovial versus subchondral bone pathology

Subchondral bone and the synovium play an important role in the initiation and progression of OA. MRI often permits an early detection of synovial hypertrophy and bone marrow lesions, both of which can precede cartilage damage. Newer imaging modalities including CT osteoabsorptiometry and hybrid SPECT-CT have underlined the importance of bone in OA pathogenesis. The subchondral bone in OA undergoes an uncoupled remodelling process, which is notably characterized by macrophage infiltration and osteoclast formation. Concomitant increased osteoblast activity leads to spatial remineralization and osteosclerosis in end-stage disease. A plethora of metabolic and mechanical factors can lead to synovitis in OA. Synovial tissue is highly vascularized and thus exposed to systemic influences such as hypercholesterolaemia or low grade inflammation. This review aims to describe the current understanding of synovitis and subchondral bone pathology and their connection in OA.

Inhibition of the TGF-β1/Smad signaling pathway protects against cartilage injury and osteoarthritis in a rat model

Transforming growth factor-β1 (TGF-β1) in osteoblastic cells triggers pathological changes observed in osteoarthritis (OA). Thus, we hypothesized that the inhibition of the TGF-β1/Smad signaling pathway could act to protect against cartilage injury in rats with OA. After establishment of rat models induced by papain and L-cysteine, rats were subsequently assigned into the TβRI inhibitors, normal control (NC) and OA model groups. RT-qPCR and western blotting were performed to determine mRNA and protein expressions of TGFβ1, Smad2, Smad3 and Activin receptor-like kinase 5 (ALK5), respectively. Immunofluorescence staining was used to detect the expression of collagen X (COLX). Immunohistochemical staining was used to determine the expression of the specific transcription factor Osterix as well as TGF-β1 related factors. Increased expression levels of TGFβ1, Smad2, Smad3 and ALK5in the OA model group were higher than those in the TβRI inhibitors group. Compared with the NC group, the OA model groups exhibited elevated expressions of TGF-β1, p-Smad2/3 and ALK5 in the TGF-β1 signaling pathway, and elevated numbers of COLX and Osterix positive cells. The rats in the TβRI inhibitors group had decreased expressions of p-Smad2/3 and ALK5, as well as decreased COLX and Osterix positive cells when compared with OA model group. However, these levels were still higher than that of the NC group. Our findings suggested that up-regulation of TGF-β1 inhibited the TGF-β1/Smad signaling pathway acting to alleviate OA, thus highlighting the potential of the TGF-β1/Smad signaling pathway as a therapeutic target for treatment of OA.

Recent developments in emerging therapeutic targets of osteoarthritis

Purpose of review

Despite the tremendous individual suffering and socioeconomic burden caused by osteoarthritis, there are currently no effective disease-modifying treatment options. This is in part because of our incomplete understanding of osteoarthritis disease mechanism. This review summarizes recent developments in therapeutic targets identified from surgical animal models of osteoarthritis that provide novel insight into osteoarthritis pathology and possess potential for progression into preclinical studies.

Recent findings

Several candidate pathways and processes that have been identified include chondrocyte autophagy, growth factor signaling, inflammation, and nociceptive signaling. Major strategies that possess therapeutic potential at the cellular level include inhibiting autophagy suppression and decreasing reactive oxygen species (ROS) production. Cartilage anabolism and prevention of cartilage degradation has been shown to result from growth factor signaling modulation, such as TGF-β, TGF-α, and FGF; however, the results are context-dependent and require further investigation. Pain assessment studies in rodent surgical models have demonstrated potential in employing anti-NGF strategies for minimizing osteoarthritis-associated pain.

Summary

Studies of potential therapeutic targets in osteoarthritis using animal surgical models are helping to elucidate osteoarthritis pathology and propel therapeutics development. Further studies should continue to elucidate pathological mechanisms and therapeutic targets in various joint tissues to improve overall joint health.

Conditional removal of the canonical TGF-β1 signaling delays condylar cartilage degeneration induced by a partial discectomy in mice

Recent emerging data indicate that the increase in the expression and activity of the transforming growth factor beta 1 (Tgf-β1) signaling may have detrimental effect to mature articular cartilage of knee joints. However, there is no information about whether or not this is the case in condylar cartilages. The objective of this study is to investigate the protein expression and activity of Tgf-β1 signaling in degenerative condylar cartilages. We also investigate biological effects of the conditional deletion of transforming growth factor receptor type II (Tgfbr2) in condylar cartilage of adult mice after a partial discectomy. Two mouse models of osteoarthritis (OA) were used to examine protein expressions of Tgf-β1 and p-Smad2/3 in condylar cartilages at early degenerative stages. In addition, cartilage specific Tgfbr2-deficient adult mice were subjected to a partial discectomy. The morphological condition of condylar cartilages was evaluated in mice at 4 and 12 weeks after the surgery. We found that protein levels of Tgf-β1 and p-Smad2/3 were increased in the degenerative condylar cartilage of the mouse models. The conditional removal of Tgfbr2 in mature condylar cartilage significantly delayed the progressive progression of the cartilage degeneration induced by a partial discectomy. We conclude that the increase in the expression and activity of Tgf-β1 signaling may have detrimental effect to mature condylar cartilages. Therefore, inhibition of Tgf-β1 signaling may be able to protect condylar cartilages from being degraded in mature temporomandibular joints.

Effects of aluminum trichloride on the cartilage stimulatory growth factors in rats

Aluminum (Al) is considered to be a potentially toxic metal and inhibits cartilage formation. Transforming growth factor β1 (TGF-β1) and bone morphogenetic protein 2 (BMP-2) are cartilage stimulatory growth factors, which play important roles in regulating the cartilage formation. To investigate the effects of aluminum trichloride (AlCl₃) on the regulation of cartilage formation. Eighty Wistar rats were orally exposed to 0 (control group), 0.4 g/L (low-dose group), 0.8 g/L (mid-dose group) and 1.6 g/L (high-dose group) AlCl₃ for 120 days, respectively. The rats body weight were decreased, the cartilage histological structure were disrupted, the cartilage and serum contents of Al and the serum level of C-telopeptide of type II collagen were all increased, the serum level of type II collagen (Col II) and alkaline phosphatase (ALP), and the mRNA expressions of TGF-β1, BMP-2, ALP and Col II were all decreased in the AlCl₃-treated groups compared with those in control group. These results indicate that AlCl₃ inhibits the cartilage formation through inhibition of the cartilage stimulatory growth factors expressions.

Discoidin Domain Receptor 2 as a Potential Therapeutic Target for Development of Disease-Modifying Osteoarthritis Drugs

Osteoarthritis (OA) is the most common form of arthritis disorders, but the identification of therapeutic targets to effectively prevent OA has been increasingly difficult. The goal of this investigation is to provide experimental evidence that discoidin domain receptor 2 (DDR2) may be an ideal target for the development of disease-modifying OA drugs. Ddr2 was conditionally deleted from articular cartilage of adult mouse knee joints. Aggrecan-CreERT2;floxed Ddr2 mice, which were generated by crossing Aggrecan-CreERT2 mice with floxed Ddr2 mice, then received tamoxifen injections at the age of 8 weeks. The mice were then subjected to destabilization of the medial meniscus (DMM) surgery. At 8 and 16 weeks after DMM, mice were euthanized for the collection of knee joints. In a separate experiment, Aggrecan-CreERT2;floxed Ddr2 mice were subjected to DMM at the age of 10 weeks. The mice then received tamoxifen injections at 8 weeks after DMM. The mice were euthanized for the collection of knee joints at 16 weeks after DMM. The progressive process of articular cartilage degeneration was significantly delayed in the knee joints of Ddr2-deficient mice in comparison to their control littermates. Articular cartilage damage in the knee joints of the mice was associated with increased expression profiles of both Ddr2 and matrix metalloproteinase 13. These findings suggest that DDR2 may be an ideal target for the development of disease-modifying OA drugs.