Maintaining Cartilage Homeostasis Research Articles

The role of targeting glucose metabolism in chondrocytes in the pathogenesis and therapeutic mechanisms of osteoarthritis: a narrative review.

Osteoarthritis (OA) is a common degenerative joint disease that can affect almost any joint, mainly resulting in joint dysfunction and pain. Worldwide, OA affects more than 240 million people and is one of the leading causes of activity limitation in adults. However, the pathogenesis of OA remains elusive, resulting in the lack of well-established clinical treatment strategies. Recently, energy metabolism alterations have provided new insights into the pathogenesis of OA. Accumulating evidence indicates that glucose metabolism plays a key role in maintaining cartilage homeostasis. Disorders of glucose metabolism can lead to chondrocyte hypertrophy and extracellular matrix degradation, and promote the occurrence and development of OA. This article systematically summarizes the regulatory effects of different enzymes and factors related to glucose metabolism in OA, as well as the mechanism and potential of various substances in the treatment of OA by affecting glucose metabolism. This provides a theoretical basis for a better understanding of the mechanism of OA progression and the development of optimal prevention and treatment strategies.

Gli1 labels progenitors during chondrogenesis in postnatal mice

Skeletal growth promoted by endochondral ossification is tightly coordinated by self-renewal and differentiation of chondrogenic progenitors. Emerging evidence has shown that multiple skeletal stem cells (SSCs) participate in cartilage formation. However, as yet, no study has reported the existence of common long-lasting chondrogenic progenitors in various types of cartilage. Here, we identify Gli1+ chondrogenic progenitors (Gli1+ CPs), which are distinct from PTHrP+ or FoxA2+ SSCs, are responsible for the lifelong generation of chondrocytes in the growth plate, vertebrae, ribs, and other cartilage. The absence of Gli1+ CPs leads to cartilage defects and dwarfishness phenotype in mice. Furthermore, we show that the BMP signal plays an important role in self-renewal and maintenance of Gli1+ CPs. Deletion of Bmpr1α triggers Gli1+ CPs quiescence exit and causes the exhaustion of Gli1+ CPs, consequently disrupting columnar cartilage. Collectively, our data demonstrate that Gli1+ CPs are common long-term chondrogenic progenitors in multiple types of cartilage and are essential to maintain cartilage homeostasis.

Mitoquinone alleviates osteoarthritis progress by activating the NRF2-Parkin axis

Osteoarthritis (OA) is a prevalent degenerative disease of the elderly. The NRF2 antioxidant system plays a critical role in maintaining redox balance. Mitoquinone (MitoQ) is a mitochondria-targeted antioxidant. This research aimed to determine whether MitoQ alleviated OA and the role of the NRF2/Parkin axis in MitoQ-mediated protective effects. In interleukin (IL)-1β-induced OA chondrocytes, MitoQ activated the NRF2 pathway, reducing extracellular matrix (ECM) degradation and inflammation. MitoQ also increased glutathione peroxidase 4 (GPX4) expression, leading to decreased levels of reactive oxygen species (ROS) and lipid ROS. Silencing NRF2 weakened MitoQ's protective effects, while knockdown of Parkin upregulated the NRF2 pathway, inhibiting OA progression. Intra-articular injection of MitoQ mitigated cartilage destruction in destabilized medial meniscus (DMM)-induced OA mice. Our study demonstrates that MitoQ maintains cartilage homeostasis invivo and invitro through the NRF2/Parkin axis. We supplemented the negative feedback regulation mechanism between NRF2 and Parkin. These findings highlight the therapeutic potential of MitoQ for OA treatment.

Revealing the Key MSCs Niches and Pathogenic Genes in Influencing CEP Homeostasis: A Conjoint Analysis of Single-Cell and WGCNA.

Degenerative disc disease (DDD), a major contributor to discogenic pain, which is mainly resulted from the dysfunction of nucleus pulposus (NP), annulus fibrosis (AF) and cartilage endplate (CEP) cells. Genetic and cellular components alterations in CEP may influence disc homeostasis, while few single-cell RNA sequencing (scRNA-seq) report in CEP makes it a challenge to evaluate cellular heterogeneity in CEP. Here, this study conducted a first conjoint analysis of weighted gene co-expression network analysis (WGCNA) and scRNA-seq in CEP, systematically analyzed the interested module, immune infiltration situation, and cell niches in CEP. WGCNA and protein-protein interaction (PPI) network determined a group of gene signatures responsible for degenerative CEP, including BRD4, RAF1, ANGPT1, CHD7 and NOP56; differentially immune analysis elucidated that CD4+ T cells, NK cells and dendritic cells were highly activated in degenerative CEP; then single-cell resolution transcriptomic landscape further identified several mesenchymal stem cells and other cellular components focused on human CEP, which illuminated niche atlas of different cell subpopulations: 8 populations were identified by distinct molecular signatures. Among which, NP progenitor/mesenchymal stem cells (NPMSC), also served as multipotent stem cells in CEP, exhibited regenerative and therapeutic potentials in promoting bone repair and maintaining bone homeostasis through SPP1, NRP1-related cascade reactions; regulatory and effector mesenchymal chondrocytes could be further classified into 2 different subtypes, and each subtype behaved potential opposite effects in maintaining cartilage homeostasis; next, the potential functional differences of each mesenchymal stem cell populations and the possible interactions with different cell types analysis revealed that JAG1, SPP1, MIF and PDGF etc. generated by different cells could regulate the CEP homeostasis by bone formation or angiogenesis, which could be served as novel therapeutic targets for degenerative CEP. In brief, this study mainly revealed the mesenchymal stem cells populations complexity and phenotypic characteristics in CEP. In brief, this study filled the gap in the knowledge of CEP components, further enhanced researchers’ understanding of CEP and their cell niches constitution.

Dual functions of microRNA-17 in maintaining cartilage homeostasis and protection against osteoarthritis

Damaged hyaline cartilage has no capacity for self-healing, making osteoarthritis (OA) “difficult-to-treat”. Cartilage destruction is central to OA patho-etiology and is mediated by matrix degrading enzymes. Here we report decreased expression of miR-17 in osteoarthritic chondrocytes and its deficiency contributes to OA progression. Supplementation of exogenous miR-17 or its endogenous induction by growth differentiation factor 5, effectively prevented OA by simultaneously targeting pathological catabolic factors including matrix metallopeptidase-3/13 (MMP3/13), aggrecanase-2 (ADAMTS5), and nitric oxide synthase-2 (NOS2). Single-cell RNA sequencing of hyaline cartilage revealed two distinct superficial chondrocyte populations (C1/C2). C1 expressed physiological catabolic factors including MMP2, and C2 carries synovial features, together with C3 in the middle zone. MiR-17 is highly expressed in both superficial and middle chondrocytes under physiological conditions, and maintains the physiological catabolic and anabolic balance potentially by restricting HIF-1α signaling. Together, this study identified dual functions of miR-17 in maintaining cartilage homeostasis and prevention of OA.

MIR-544A: A NEW MODULATOR OF THE WNT/β-CATENIN PATHWAY IN ARTICULAR CHONDROCYTES

Purpose: A balanced activation of the Wnt/β-catenin pathway is pivotal to maintain cartilage homeostasis and prevent the onset of osteoarthritis (OA). While the role of ligands and inhibitors of the pathway has already been well explored in the articular cartilage, the effect of fine-tuned modulators such as micro-RNAs has been less investigated. A microarray analysis of human articular chondrocytes stimulated with Wnt3a showed miR-544a, a known modulator of the Wnt/β-catenin pathway in different biological contexts, as the most downregulated gene.

PPAR\u03b1\u2212ACOT12 axis is responsible for maintaining cartilage homeostasis through modulating de novo lipogenesis

Here, in Ppara−/− mice, we found that an increased DNL stimulated the cartilage degradation and identified ACOT12 as a key regulatory factor. Suppressed level of ACOT12 was observed in cartilages of OA patient and OA-induced animal. To determine the role and association of ACOT12 in the OA pathogenesis, we generated Acot12 knockout (KO) (Acot12−/−) mice using RNA-guided endonuclease. Acot12−/− mice displayed the severe cartilage degradation with the stimulation of matrix MMPs and chondrocyte apoptosis through the accumulation of acetyl CoA. Delivery of acetyl CoA-conjugated chitosan complex into cartilage stimulated DNL and cartilage degradation. Moreover, restoration of ACOT12 into human OA chondrocytes and OA-induced mouse cartilage effectively rescued the pathophysiological features of OA by regulating DNL. Taken together, our study suggested ACOT12 as a novel regulatory factor in maintaining cartilage homeostasis and targeting ACOT12 could contribute to developing a new therapeutic strategy for OA.

Comparison of Curative Effect of Human Umbilical Cord-Derived Mesenchymal Stem Cells and Their Small Extracellular Vesicles in Treating Osteoarthritis.

IntroductionHuman umbilical cord-derived mesenchymal stem cells (hUC-MSCs) and their small extracellular vesicles (hUC-MSC-sEVs) have shown attractive prospects applying in regenerative medicine. This study aimed to compare the therapeutic effects of two agents on osteoarthritis (OA) and investigate underlying mechanism using proteomics.MethodsIn vitro, the proliferation and migration abilities of chondrocytes treated with hUC-MSCs or hUC-MSC-sEVs were detected by Cell Counting Kit-8 assay and scratch wound assay. In vivo, hUC-MSCs (a single dose of 5 × 105) or hUC-MSC-sEVs (30 μg/time) were injected into the knee joints of anterior cruciate ligament transection-induced OA model. Hematoxylin and eosin, Safranin O/Fast Green staining were used to observe cartilage degeneration. The levels of cartilage matrix metabolic molecules (Collagen II, MMP13 and ADAMTS5) and macrophage polarization markers (CD14, IL-1β, IL-10 and CD206) were assessed by immunohistochemistry. Finally, proteomics analysis was performed to characterize the proteinaceous contents of two agents.ResultsIn vitro data showed that hUC-MSC-sEVs were taken up by chondrocytes. A total of 15 μg/mL of sEVs show the greatest proliferative and migratory capacities among all groups. In the animal study, hUC-MSCs and hUC-MSC-sEVs alleviated cartilage damage. This effect was mediated via maintaining cartilage homeostasis, as was confirmed by upregulation of the COL II and downregulation of the MMP13 and ADAMTS5. Moreover, the M1 macrophage markers (CD14) were significantly reduced, while the M2 macrophage markers (CD206 and IL-10) were increased in the hUC-MSCs and hUC-MSC-sEVs relative to the untreated group. Mechanistically, we found that many proteins connected to cartilage repair were more abundant in sEVs. Notably, compared to hUC-MSCs, the upregulated proteins in sEVs were mostly involved in the regulation of immune effector process, extracellular matrix organization, PI3K-AKT signaling pathways, and Rap1 signaling pathway.ConclusionOur study indicated that hUC-MSC-sEVs protect cartilage from damage and many cartilage repair-related proteins are probably involved in the restoration process. These data suggest the promising potential of hUC-MSC-sEVs as a therapeutic agent for OA.

BNIP3-Dependent Mitophagy via PGC1α Promotes Cartilage Degradation.

Since mitochondria are suggested to be important regulators in maintaining cartilage homeostasis, turnover of mitochondria through mitochondrial biogenesis and mitochondrial degradation may play an important role in the pathogenesis of osteoarthritis (OA). Here, we found that mitochondrial dysfunction is closely associated with OA pathogenesis and identified the peroxisome proliferator-activated receptor-gamma co-activator 1-alpha (PGC1α) as a potent regulator. The expression level of PGC1α was significantly decreased under OA conditions, and knockdown of PGC1α dramatically elevated the cartilage degradation by upregulating cartilage degrading enzymes and apoptotic cell death. Interestingly, the knockdown of PGC1α activated the parkin RBR E3 ubiquitin protein ligase (PRKN)-independent selective mitochondria autophagy (mitophagy) pathway through the upregulation of BCL2 and adenovirus E1B 19-kDa-interacting protein 3 (BNIP3). The overexpression of BNIP3 stimulated mitophagy and cartilage degradation by upregulating cartilage-degrading enzymes and chondrocyte death. We identified microRNA (miR)-126-5p as an upstream regulator for PGC1α and confirmed the direct binding between miR-126-5p and 3′ untranslated region (UTR) of PGC1α. An in vivo OA mouse model induced by the destabilization of medial meniscus (DMM) surgery, and the delivery of antago-miR-126 via intra-articular injection significantly decreased cartilage degradation. In sum, the loss of PGC1α in chondrocytes due to upregulation of miR-126-5p during OA pathogenesis resulted in the activation of PRKN-independent mitophagy through the upregulation of BNIP3 and stimulated cartilage degradation and apoptotic death of chondrocytes. Therefore, the regulation of PGC1α:BNIP3 mitophagy axis could be of therapeutic benefit to cartilage-degrading diseases.

TGFβ1-Induced Transglutaminase-2 Triggers Catabolic Response in Osteoarthritic Chondrocytes by Modulating MMP-13.

Transforming growth factor beta 1 (TGFβ1) plays an essential role in maintaining cartilage homeostasis. TGFβ1 is known to upregulate anabolic processes in articular cartilage, but the role of TGFβ1 in chondrocyte catabolism remains unclear. Thus, we examined whether TGFβ1 increases catabolic processes in the osteoarthritic joint via transglutaminase 2 (TG2). In this study, we investigated whether interplay between TGFβ1 and TG2 mediates chondrocyte catabolism and cartilage degeneration in osteoarthritis. To investigate the role of TGFβ1 and TG2 in osteoarthritis, we performed immunostaining to measure the levels of TGFβ1 and TG2 in 6 human non-osteoarthritic and 16 osteoarthritic joints. We conducted quantitative reverse transcription polymerase chain reaction and western blot analysis to investigate the relationship between TGFβ1 and TG2 in chondrocytes and determined whether TG2 regulates the expressions of matrix metalloproteinase (MMP)-13, type II, and type X collagen. We also examined the extent of cartilage degradation after performing anterior cruciate ligament transection (ACLT) and destabilization of the medial meniscus (DMM) surgery in TG2 knock-out mice. We confirmed the overexpression of TGFβ1 and TG2 in human osteoarthritic cartilage compared with non-osteoarthritic cartilage. TGFβ1 treatment significantly increased the expression of TG2 via p38 and ERK activation. TGFβ1-induced TG2 also elevated the level of MMP-13 and type X collagen via NF-κB activation in chondrocytes. Cartilage damage after ACLT and DMM surgery was less severe in TG2 knock-out mice compared with wild-type mice. TGFβ1 modulated catabolic processes in chondrocytes in a TG2-dependent manner. TGFβ1-induced TG2 might be the therapeutic target for treating cartilage degeneration and osteoarthritis.

Ubiquitin-protein ligase Ubr5 cooperates with hedgehog signalling to promote skeletal tissue homeostasis.

Mammalian Hedgehog (HH) signalling pathway plays an essential role in tissue homeostasis and its deregulation is linked to rheumatological disorders. UBR5 is the mammalian homologue of the E3 ubiquitin-protein ligase Hyd, a negative regulator of the Hh-pathway in Drosophila. To investigate a possible role of UBR5 in regulation of the musculoskeletal system through modulation of mammalian HH signaling, we created a mouse model for specific loss of Ubr5 function in limb bud mesenchyme. Our findings revealed a role for UBR5 in maintaining cartilage homeostasis and suppressing metaplasia. Ubr5 loss of function resulted in progressive and dramatic articular cartilage degradation, enlarged, abnormally shaped sesamoid bones and extensive heterotopic tissue metaplasia linked to calcification of tendons and ossification of synovium. Genetic suppression of smoothened (Smo), a key mediator of HH signalling, dramatically enhanced the Ubr5 mutant phenotype. Analysis of HH signalling in both mouse and cell model systems revealed that loss of Ubr5 stimulated canonical HH-signalling while also increasing PKA activity. In addition, human osteoarthritic samples revealed similar correlations between UBR5 expression, canonical HH signalling and PKA activity markers. Our studies identified a crucial function for the Ubr5 gene in the maintenance of skeletal tissue homeostasis and an unexpected mode of regulation of the HH signalling pathway.

Compressive loading modulates the effect of insulin-like growth factor-1 in type II collagen processing in bovine cartilage explants

Purpose: Despite extensive success of novel drugs in preclinical models of osteoarthritis (OA), none have successfully been translated into approved interventions effective at restoring cartilage or modifying the onset of joint structural damage. It is possible that the lack of disease-modifying OA drugs (DMOADs) may in part be explained by the inadequate ability of present preclinical OA models to reflect the physiological environment of the joint. Joint tissues, in particular cartilage, are subject to mechanical loading, which is a critical component in maintaining cartilage homeostasis.

Identifying factors that regulate ANP32A expression using a novel bioinformatic analysis pipeline

Purpose: Osteoarthritis (OA) is the most common chronic joint disease and is a leading cause of disability. It has a complex pathogeny and causes damage to the articular cartilage, increased joint-associated bone remodelling, and synovial inflammation. Currently, no cure exists and the molecular mechanisms maintaining cartilage homeostasis remain incompletely defined. Previously, an association between polymorphisms in the acidic leucine-rich nuclear phosphoprotein-32A (ANP32A) gene and OA was described. Then, our group showed that ANP32A plays a key protective role in OA by preventing oxidative stress via increasing the transcription of the ATM kinase. Also, we demonstrated that ANP32A is downregulated in OA cartilage as compared to non-OA cartilage. Therefore, maintaining the levels of ANP32A seems to be of crucial importance to preserve joint health and prevent the development and progression of OA. Yet the factors that regulate ANP32A in the joint remain unknown. In this study, we aim to investigate factors that regulate ANP32A expression since such knowledge may lead to the identification of specific novel targets for OA therapy. Methods: An in-house developed bioinformatic pipeline was used in which four bioinformatic tools (BindDB, CONSITE, PROMO and TFsitescan) were interrogated for regulatory factors that are predicted to interact with the ANP32A promotor. The sequence of the ANP32A promotor was obtained using the Eukaryotic Promotor Database (EPD). The Results from these four tools were assembled and then corrected for occurring synonyms. After this, we selected hits that were predicted by two or more databases. An in silico specificity analysis was performed to identify genes with predicted specificity for ANP32A regulation. In this analysis, we excluded hits that also seemed to modulate genes that characterize the chondrocyte identity, namely Aggrecan and Collagen2a1, as well as hits modulating the housekeeping gene Actin. Afterwards, network analysis using StringDB and Humanbase tools was performed, as well as pathway enrichment analysis using the Ingenuity Pathway Analysis (IPA) software. Results: We retrieved 209 hits that were predicted to interact with the ANP32A promoter in silico, of which 49 hits were simultaneously predicted by at least two different bioinformatic tools. After applying the specificity analysis, 16 hits were retained. Network analysis suggested several interesting pathways that may potentially modulate the expression of ANP32A. First, Wnt signaling appeared in the analysis using both the StringDB tool and the IPA software for the 49 hits. Of note, two Wnt signaling TCF/LEF transcription factors were present among the 16 final hits obtained after applying the specificity analysis. Wnt hyper-activation is known to contribute to OA and targeting this pathway is becoming increasingly interesting in the treatment of OA. Second, the network analysis indicated the hypoxia pathway as a potential regulator for ANP32A expression. This pathway is noteworthy since the oxygen gradients in OA cartilage are known to be disturbed. Lastly, network analysis further pointed out cellular senescence (StringDB tool and IPA analysis) and histone modifications (StringDB tool) among the enriched pathways. Both the senescence pathway and alterations in histone modifications have been linked to OA. Conclusions: The bioinformatic pipeline suggested 16 potential regulatory factors for ANP32A expression. Combined with the network analysis, we identified Wnt signaling, hypoxia, cellular senescence and histone modifications as potential regulatory networks for ANP32A transcription. In our future experiments, we will further investigate the significance of these in silico findings and their potential clinical implications in OA.

Investigating the molecular control of deer antler extract on articular cartilage

BackgroundDeer antler is considered as a precious traditional Chinese medicinal material and has been widely used to reinforce kidney’s yang, nourish essence, and strengthen bone function. The most prominent bioactive components in deer antler are water-soluble proteins that play potential roles in bone formation and repair. The aim of this study was to explore the molecular control and therapeutic targets of deer antler extract (DAE) on articular cartilage.MethodsDAE was prepared as previously described. All rats were randomly divided into Blank group and DAE group (10 rats per group) after 7-day adaptive feeding. The rats in DAE group were orally administrated with DAE at a dose of 0.2 g/kg per day for 3 weeks, and the rats in Blank group were fed with drinking water. Total RNA was isolated from the articular cartilage of knee joints. RNA sequencing (RNA-seq) experiment combined with quantitative real-time polymerase chain reaction (qRT-PCR) verification assay was carried out to explore the molecular control and therapeutic targets of DAE on articular cartilage.ResultsWe demonstrated that DAE significantly increased the expression levels of functional genes involved in cartilage formation, growth, and repair and decreased the expression levels of susceptibility genes involved in the pathophysiology of osteoarthritis.ConclusionsDAE might serve as a candidate supplement for maintaining cartilage homeostasis and preventing cartilage degeneration and inflammation. These effects were possibly achieved by accelerating the expression of functional genes involved in chondrocyte commitment, survival, proliferation, and differentiation and suppressing the expression of susceptibility genes involved in the pathophysiology of osteoarthritis. Thus, our findings will contribute towards deepening the knowledge about the molecular control and therapeutic targets of DAE on the treatment of cartilage-related diseases.

Melatonin: Effects on Cartilage Homeostasis and Therapeutic Prospects in Cartilage-related Diseases

Cartilage is a relatively simple connective tissue that plays a variety of roles in the human body, including joint support and protection, load bearing of the intervertebral discs, joint lubrication, formation of the external structure of the ears and nose and support of the trachea. The maintenance of cartilage homeostasis is therefore crucial. Cartilage-related diseases are difficult to diagnose and treat because their molecular and pathological mechanisms are not fully understood. Melatonin, which has a wide range of physiological effects, is an endocrine hormone mainly secreted by the pineal gland. Its biological effects include its antioxidant, antiaging, analgesic, and hypnotic effects and its ability to stabilize the circadian rhythm. In recent years, research on cartilage homeostasis and melatonin has been increasing, and melatonin has gradually been used in the treatment of cartilage-related diseases. Therefore, this article will briefly review the role of melatonin in cartilage homeostasis, including its anti-inflammatory effects and effects in protecting cartilage from damage by other factors and promoting chondrocyte growth and the expression of cartilage-related genes. Based on the above, the current status and future developmental direction of melatonin in the treatment of cartilage-related diseases are also discussed, demonstrating the broad prospects of melatonin in maintaining cartilage homeostasis and treating cartilage injury-related diseases.

Progranulin modulates cartilage-specific gene expression via sirtuin 1–mediated deacetylation of the transcription factors SOX9 and P65

Progranulin (PGRN) is an autocrine growth factor that exerts crucial roles within cartilage tissue; however, the molecular mechanisms underlying PGRN-mediated cartilage homeostasis remain elusive. In the present study, we investigated the role of PGRN in regulating chondrocyte homeostasis and its therapeutic potential for managing osteoarthritis (OA). We found that PGRN levels are significantly increased in human cartilage in mild OA and that its expression is decreased in the cartilage in severe OA. In vitro, treatment of primary rat chondrocytes with recombinant PGRN significantly enhanced the levels of collagen type II α 1 chain (COL2A1) and aggrecan, and attenuated TNFα-induced up-regulation of matrix metallopeptidase 13 (MMP13) and ADAM metallopeptidase with thrombospondin type 1 motif 5 (ADAMTS5) in chondrocytes. These effects were abrogated in SIRT1-/- cells, indicating a causative role of SIRT1 in the effects of PGRN on protein expression in chondrocytes. Mechanistically, PGRN increased SIRT1 expression and activity, which reduced the acetylation levels of SRY-box transcription factor (SOX9) and transcription factor P65 (P65) and thereby promoted nuclear translocation of SOX9 and inhibited TNFα-induced P65 nuclear accumulation to maintain chondrocyte homeostasis. In conclusion, our findings reveal a mechanism of action for PGRN that maintains cartilage homeostasis and supports the notion that PGRN up-regulation may be a promising strategy for managing OA.

TAT-Beclin-1 induces severe synovial hyperplasia and does not protect from injury-induced osteoarthritis in mice

Autophagy maintains cartilage homeostasis and is compromised during osteoarthritis (OA), contributing to cartilage degeneration. We sought to determine if D-isomer TAT-Beclin-1, a potent inducer of autophagy, could attenuate post-traumatic OA in mice. 10-week-old mice underwent destabilization of the medial meniscus (DMM) surgery to induce post-traumatic OA, or sham surgery (control), and injected intra-articularly with D-isomer TAT-Beclin-1 (0.5-2mg/kg) or PBS 1 week post-surgery for up to 9 weeks. Mice were sacrificed at 2 or 10 weeks post-surgery. Knee joint sections were evaluated by histopathology for cartilage degeneration and synovitis, and immunostaining for key markers of autophagy (LC3B), cell proliferation (nuclear Ki67), activated fibroblasts (αSMA), and cells of hematopoietic origin (CD45). All D-isomer TAT-Beclin-1-treated DMM mice had no difference in the degree of cartilage degeneration compared to PBS-injected DMM mice. Surprisingly, all D-isomer TAT-Beclin-1-treated mice exhibited substantial synovial hyperplasia, with increased cellularity and ECM deposition (fibrosis-like phenotype), as compared to PBS-injected mice. Synovial effects of D-isomer TAT-Beclin-1 were dose- and injection frequency-dependent. An increased percentage of cells positive for LC3B and nuclear Ki67 were found in the synovial intima early after injection, which persisted after frequent injections. D-isomer TAT-Beclin-1 did not attenuate cartilage degeneration, but rather induced synovial hyperplasia associated with increased expression of key markers of autophagy and cell proliferation and a fibrosis-like phenotype, independent of markers of fibroblast activation or persistent hematopoietic-origin cell infiltration. These data suggest that, if not tissue-targeted, caution should be taken using autophagy activators due to diverse cellular responses in the joint.

Runx3 regulates chondrocyte phenotype by controlling multiple genes involved in chondrocyte proliferation and differentiation.

Chondrocytes are the sole cell type present within cartilage, and play pivotal roles in controlling the formation and composition of health cartilage. Chondrocytes maintain cartilage homeostasis through proliferating, differentiating and synthesizing different types of extracellular matrices. Thus, the coordinated proliferation and differentiation of chondrocytes are essential for cartilage growth, repair and the conversion from cartilage to bone during the processes of bone formation and fracture healing. Runx3, a transcription factor that belongs to the Runx family, is significantly upregulated at the onset of cartilage mineralization and regulates both early and late markers of chondrocyte maturation. Therefore, Runx3 may serve as an accelerator of chondrocyte differentiation and maturation. However, the underlying molecular mechanism of Runx3 in regulating chondrocyte proliferation and differentiation remains largely to be elucidated. In the present study, we used state-of-the-art RNA-seq technology combined with validation methods to investigate the effect of Runx3 overexpression or silencing on primary chondrocyte proliferation and differentiation, and demonstrated that Runx3 overexpression possibly inhibited chondrocyte proliferation but accelerated differentiation, whereas Runx3 silencing possibly promoted chondrocyte proliferation but suppressed differentiation. Furthermore, Runx3 overexpression possibly decreased the expression levels of Sox9 and its downstream genes via Sox9 cartilage-specific enhancers, and vice versa for Runx3 silencing.

Effect of cadmium on the concentration of essential metals in a human chondrocyte micromass culture

BackgroundAn essential element imbalance in the joint might favor gradual degeneration of the articular cartilage. It has been reported that cadmium (Cd) plays an antagonistic role with regards to the presence of essential elements, such as zinc (Zn), iron (Fe), and manganese (Mn), which may favor the development of disabling diseases, like osteoarthritis (OA) and osteoporosis. Methods3D cultures of human chondrocytes were phenotyped with the Western blot technique and structurally evaluated with histological staining. The samples were exposed to 1, 5, and 10 μM of CdCl2 for 12 h, with a non-exposed culture as control. The concentration of Cd, Fe, Mn, Zn, chromium (Cr), and nickel (Ni) was quantified through plasma mass spectrometry (ICP-MS). The data were analyzed with a Kruskal Wallis test, a Kendall’s Tau test and Spearman’s correlation coefficient with the Stata program, version 14. ResultsOur results suggest that Cd exposure affects the structure of micromass cultures and plays an antagonistic role on the concentration of essential metals, such as Zn, Ni, Fe, Mn, and Cr. ConclusionCd exposure may be a risk factor for developing joint diseases like OA, as it can interfere with cartilage absorption of other essential elements that maintain cartilage homeostasis.

Cartilage/Bone Crosstalk in Joint Health and Disease

Purpose: Understanding the mechanisms that maintain cartilage homeostasis and disease requires consideration of how spatial and physical features of the joint, across multiple length scales, shift the activity of biological signaling pathways. With a focus on well-known participants in cartilage health and disease, TGF-beta and MMP13, this talk will explore these concepts in joint crosstalk between cartilage and bone.