Ontogeny of rat chondrocyte proliferation: studies in embryo, adult and osteoarthritic (OA) cartilage

Enhancing intrinsic TGF-β signaling via heparan sulfate glycosaminoglycan regulation to promote mesenchymal stem cell capabilities and chondrogenesis for cartilage repair

Osteoarthritis burdens patients due to the limited regenerative capacity of chondrocytes. Traditional cartilage repair often falls short, necessitating innovative approaches. Mesenchymal stem cells (MSCs) show promise for regeneration. Heparan sulfate glycosaminoglycans (HS-GAGs) regulate cellular functions, making them a target for cartilage repair. This study highlights how Heparinase III (HepIII) cleaves intact HS-GAGs in bone marrow-derived MSCs (BM-MSCs), enhancing their capabilities and specifically promoting chondrogenesis. HepIII-treated BM-MSCs cultured in a hanging drop device for three days, significantly increased cell number and aggregation into a cell sphere with early chondrogenesis. HepIII promoted BM-MSCs toward chondrogenesis, increasing type II collagen, intact HS-GAGs, and sulfated GAG content, while upregulating chondrogenic and heparan sulfate proteoglycan genes. Treatment with the TGF-β inhibitor (SB-431542) in HepIII-treated BM-MSCs demonstrated enhanced intrinsic transforming growth factor-β (TGF-β) signaling and fibronectin expression. This approach also boosted BM-MSC self-renewal, immunosuppressive potential, and modified acetylated histone signatures, offering a cost-effective strategy for cartilage repair by addressing inflammation, metabolic changes, and the high costs of traditional TGF-β methods. From the results, HepIII-treated BM-MSCs show potential for use in combination with other biopolymers as injectable gels to improve cartilage repair in osteoarthritis patients in the near future.

Cartilage tissue from sites of weight bearing in patients with osteoarthritis exhibits a differential phenotype with distinct chondrocytes subests

OBJECTIVE

Osteoarthritis (OA) is a degenerative joint disease associated with excessive mechanical loading. The aim here was to elucidate whether different subpopulations of chondrocytes exhibit distinct phenotypes in response to variations in loading conditions. Furthermore, we seek to investigate the transcriptional switches and cell crosstalk among these chondrocytes subsets.

METHODS

Proteomic analysis was performed on cartilage tissues isolated from weight-bearing and non-weight-bearing regions. Additionally, single-cell RNA sequencing was employed to identify different subsets of chondrocytes. For disease-specific cells, in vitro differentiation induction was performed, and their presence was confirmed in human cartilage tissue sections using immunofluorescence. The molecular mechanisms underlying transcriptional changes in these cells were analysed through whole-transcriptome sequencing.

RESULTS

In the weight-bearing regions of OA cartilage tissue, a subpopulation of chondrocytes called OA hypertrophic chondrocytes (OAHCs) expressing the marker genes SLC39A14 and COL10A1 are present. These cells exhibit unique characteristics of active cellular interactions mediated by the TGFβ signalling pathway and express OA phenotypes, distinct from hypertrophic chondrocytes in healthy cartilage. OAHCs are mainly distributed in the superficial region of damaged cartilage in human OA tissue, and on TGFβ stimulation, exhibit activation of transcriptional expression of iron metabolism-related genes, along with enrichment of associated pathways.

CONCLUSION

This study identified and validated the existence of a subset of OAHCs in the weight-bearing area of OA cartilage tissue. Our findings provide a theoretical basis for targeting OAHCs to slow down the progression of OA and facilitate the repair of cartilage injuries.

Melatonin Prevents Cartilage Degradation in Early-Stage Osteoarthritis Through Activation of miR-146a/NRF2/HO-1 Axis

Reactive oxygen species (ROS) are implicated in induction of inflammatory response and cartilage degradation in osteoarthritis (OA). Melatonin has been shown to improve the chondrogenic differentiation and promote cartilage matrix synthesis in mesenchymal stem cells. However, the underlying mechanisms of melatonin-regulated antioxidant activity in OA cartilage are not known. The aim of this study was to explore the effect of melatonin on nuclear factor-erythroid 2-related factor 2 (NRF2), a key antioxidant transcription factor, and its target antioxidant genes in early-stage OA cartilage. Primary chondrocytes were isolated from rats with surgically induced OA. In vitro treatment of melatonin significantly increased cartilage matrix synthesis and upregulated antioxidant enzymes, mainly heme oxygenase 1 (HO-1), while decreasing matrix degradation enzymes and intracellular ROS. In vivo intraarticular injection of melatonin effectively ameliorated cartilage degeneration in an experimental rat OA model. Inhibition of melatonin membrane receptors by Luzindole or 4-P-PDOT reversed the beneficial effects of melatonin on cartilage matrix synthesis, implying that melatonin receptor-mediated pathway is involved in its anti-arthritic effects. Interestingly, melatonin showed no significant effect on the mRNA level of Nrf2 but significantly increased its protein level. Silencing of Nrf2 or HO-1 expression abolished the protective effects of melatonin, as shown by increased ROS levels and matrix degradation enzyme expression. Microarray assays revealed that miR-146a, a predicted target for Nrf2, was significantly upregulated in OA chondrocytes but was markedly reduced by melatonin treatment. Overexpression of miR-146a diminished the protective effects of melatonin by inhibiting NRF2 expression and aggravating OA-induced cartilage degradation. These findings demonstrate that melatonin supports the anabolic metabolism of cartilage matrix in OA chondrocytes by enhancing the protein levels of NRF2 via suppressing miR-146a. Melatonin-mediated activation of the NRF2/HO-1 axis prevents cartilage degeneration and represents a promising therapeutic target for treatment of early-stage OA. © 2022 American Society for Bone and Mineral Research (ASBMR).

An In Vivo Stable Isotope Labeling Method to Investigate Individual Matrix Protein Synthesis, Ribosomal Biogenesis, and Cellular Proliferation in Murine Articular Cartilage

Targeting chondrocyte dynamics is a strategy for slowing osteoarthritis progression during aging. We describe a stable-isotope method using in vivo deuterium oxide labeling and mass spectrometry to measure protein concentration, protein half-life, cell proliferation, and ribosomal biogenesis in a single sample of murine articular cartilage. We hypothesized that a 60-d labeling period would capture age-related declines in cartilage matrix protein content, protein synthesis rates, and cellular proliferation. Knee cartilage was harvested to the subchondral bone from 25- to 90-wk-old female C57BL/6J mice treated with deuterium oxide for 15, 30, 45, and 60 d. We measured protein concentration and half-lives using targeted high resolution accurate mass spectrometry and d2ome data processing software. Deuterium enrichment was quantified in isolated DNA and RNA to measure cell proliferation and ribosomal biogenesis, respectively. Most collagen isoforms were less abundant in aged animals, with negligible collagen synthesis at either age. In contrast, age altered the concentration and half-lives of many proteoglycans and other matrix proteins, including several with greater concentration and half-lives in older mice such as proteoglycan 4, clusterin, and fibronectin-1. Cellular proteins were less abundant in older animals, consistent with reduced cellularity. Nevertheless, deuterium was maximally incorporated into 60% of DNA and RNA by 15 d of labeling in both age groups, suggesting the presence of two large pools of either rapidly (<15 d) or slowly (>60 d) proliferating cells. Our findings indicate that age-associated changes in cartilage matrix protein content and synthesis occur without detectable changes in the relative number of proliferating cells.

Identification of Pivotal Genes and Pathways in Osteoarthritic Degenerative Meniscal Lesions via Bioinformatics Analysis of the GSE52042 Dataset

Background

To better understand the process of osteoarthritic degenerative meniscal lesions (DMLs) formation, this study analyzed the dataset GSE52042 using bioinformatics methods to identify the pivotal genes and pathways related to osteoarthritic DMLs.

Material/Methods

The GSE52042 dataset, comprising diseased meniscus samples and healthier meniscus samples, was downloaded and the differentially-expressed genes (DEGs) were extracted. The reactome pathways assessment and functional analysis were performed using the “ClusterProfiler” package and “ReactomePA” package of Bioconductor. The protein–protein interaction network was constructed, followed by the extraction of hub genes and modules.

Results

A set of 154 common DEGs, including 64 upregulated DEGs and 90 downregulated DEGs, were obtained. GO analysis suggested that the DEGs primarily participated in positive regulation of the mitotic cell cycle and extracellular matrix organization. Reactome pathway analysis showed that the DEGs were predominantly enriched in TP53, which regulates transcription of genes involved in G2 cell cycle arrest and extracellular matrix organization. The top 10 hub genes were TYMS, AURKA, CENPN, NUSAP1, CENPM, TPX2, CDK1, UBE2C, BIRC5, and CCNB1. The genes in the 2 modules were primarily associated with M Phase and keratan sulfate degradation.

Conclusions

A series of pivotal genes and reactome pathways were identified elucidate the molecular mechanisms involved in the formation of osteoarthritic DMLs and to discover potential therapeutic targets.

Menisectomized miniature Vietnamese pigs develop articular cartilage pathology resembling osteoarthritis

Animal models have been used to understand the basic biology of osteoarthritis (OA) and have helped to identify new candidate biomarkers for the early diagnosis and treatment of this condition. Small animals cannot sufficiently mimic human diseases; therefore, large animal models are needed. Pigs have been used as models for human diseases because they are similar to humans in terms of their anatomy, physiology and genome. Hence, we analyzed articular cartilage and synovial membrane pathology in miniature Vietnamese pigs after a unilateral partial menisectomy and 20-day exercise regimen to determine if the pigs developed pathological characteristics similar to human OA. Histological and protein expression analysis of articular cartilage from menisectomized pigs revealed the following pathologic changes resembling OA: fibrillation, fissures, chondrocyte cluster formation, decrease in proteoglycan content and upregulation of the OA-associated proteins MMP-3, MMP-13, procaspase-3 and IL-1β. Moreover, histological analysis of synovial membrane revealed mild synovitis, characterized by hyperplasia, cell infiltration and neoangiogenesis. Pathological changes were not observed in the contralateral joints or the joints of sham-operated pigs. Further studies are required to validate such an OA model; however, our results can encourage the use of pigs to study early stages of OA physiopathology. Based on their similarities to humans, pigs may be useful for preclinical studies to identify new candidate biomarkers and novel treatments for OA.

Proliferative remodeling of the spatial organization of human superficial chondrocytes distant from focal early osteoarthritis

OBJECTIVE

Human superficial chondrocytes show distinct spatial organizations, and they commonly aggregate near osteoarthritic (OA) fissures. The aim of this study was to determine whether remodeling or destruction of the spatial chondrocyte organization might occur at a distance from focal (early) lesions in patients with OA.

METHODS

Samples of intact cartilage (condyles, patellofemoral groove, and proximal tibia) lying distant from focal lesions of OA in grade 2 joints were compared with location-matched nondegenerative (grade 0-1) cartilage samples. Chondrocyte nuclei were stained with propidium iodide, examined by fluorescence microscopy, and the findings were recorded in a top-down view. Chondrocyte arrangements were tested for randomness or significant grouping via point pattern analyses (Clark and Evans Aggregation Index) and were correlated with the OA grade and the surface cell densities.

RESULTS

In grade 2 cartilage samples, superficial chondrocytes were situated in horizontal patterns, such as strings, clusters, pairs, and singles, comparable to the patterns in nondegenerative cartilage. In intact cartilage samples from grade 2 joints, the spatial organization included a novel pattern, consisting of chondrocytes that were aligned in 2 parallel lines, building double strings. These double strings correlated significantly with an increased number of chondrocytes per group and an increased corresponding superficial zone cell density. They were observed in all grade 2 condyles and some grade 2 tibiae, but never in grade 0-1 cartilage.

CONCLUSION

This study is the first to identify a distinct spatial reorganization of human superficial chondrocytes in response to distant early OA lesions, suggesting that proliferation had occurred distant from focal early OA lesions. This spatial reorganization may serve to recruit metabolically active units as an attempt to repair focal damage.

Chondrocyte proliferation in a new culture system

OBJECTIVE

This study has aimed to study different culture systems that might stimulate an increase in cell proliferation of normal and osteoarthritis chondrocytes from articular cartilage in rat model.

MATERIAL AND METHODS

Three culture systems using chondrocytes embedded in alginate beads were tested: chondrocytes cultured in Dulbecco's modified Eagle's medium (DMEM) as control, a co-culture system consisting of a monolayer of de-differentiated chondrocytes as a source of mitotic factors, and an enriched medium containing culture medium obtained from a monolayer of chondrocytes and DMEM. Normal and osteoarthritis chondrocytes were stained with 5-carboxyfluorescein diacetate succinimidyl ester and were cultured in each of the three systems. After 5 days of culture cell, proliferation was detected by flow cytometry. Chondrocyte phenotype was confirmed by collagen type II and MMP-3 expression. To determine possible molecules released into the medium by the cultured chondrocyte monolayer and which would probably be involved in cell proliferation, a study of mRNA and expression of transforming growth factor-beta1 (TGF-beta1), fibroblastic growth factor-2 (FGF-2), epidermal growth factor (EGF), platelet derived growth factor-A (PDGF-A) and insulin-like growth factor-1 (IGF-1) proteins was conducted.

RESULTS AND CONCLUSIONS

Chondrocytes in the co-culture system or in enriched medium showed an increase in proliferation; only when osteoarthritis chondrocytes were cultured in enriched medium would they display a statistically significant increase in their proliferation rate and in their viability. When chondrocytes from the monolayer were analysed, differential mRNA expression of TGF-beta1 and IGF-1 was found during all passages, which suggests that these two growth factors might be involved in chondrocyte proliferation.

Anti-apoptotic effect of transforming growth factor-beta1 on human articular chondrocytes: role of protein phosphatase 2A

OBJECTIVE

To study whether transforming growth factor-beta1 (TGF-beta1) is able to protect human chondrocytes from apoptosis and to analyze the role of phosphatases in the possible anti-apoptotic effect of TGF-beta1.

METHODS

Cartilage was obtained from patients with osteoarthritis (OA) who were undergoing joint replacement; normal cartilage was obtained from cadavers who had no history of joint disease. Chondrocytes stimulated with tumor necrosis factor-alpha (TNF-alpha) plus Ro 31-8220 (a specific inhibitor of mitogen-activated kinase phosphatase-1 - MKP-1) were employed as an in vitro model of apoptosis. Apoptosis was assessed by flow cytometry and a cell death immunoassay. Protein phosphatase 2A (PP2A) activity was estimated by measuring the absorbance of a molybdate:malachite green:phosphate reaction complex. MKP-1, bcl-2 and bax expressions were quantified by western blot.

RESULTS

In OA cells, TGF-beta1 significantly reduced the percentage of hypo-diploid chondrocytes, as well as the percentage of internucleosomal DNA breakage. However, in normal chondrocytes, TGF-beta1 did not reduce apoptosis, as assessed by both the percentage of hypo-diploid chondrocytes and internucleosomal DNA breakage. MKP-1 expression did not show significant modulation in OA or normal chondrocytes. However, PP2A activity was differentially modulated in normal and OA chondrocytes. In OA chondrocytes, PP2A activity was not altered by TGF-beta1 stimulation; however in normal chondrocytes PP2A activity was significantly activated by TGF-beta1. The preincubation of normal chondrocytes with TGF-beta1 plus the PP2A inhibitor protein, IPP2A, reduced internucleosomal DNA breakage when compared with TGF-beta1 stimulation alone. The bcl-2/bax protein ratio was significantly higher in TGF-beta1 plus IPP2A preincubated normal chondrocytes than in cells stimulated with TGF-beta1 alone.

CONCLUSION

By manipulating the degree of PP2A activity, these results show the major role that PP2A plays in the outcome of TGF-beta1 signal transduction. These data suggest that PP2A could be a pivotal regulator of anti-apoptotic TGF-beta1-induced effects.

The beneficial effect of delayed compressive loading on tissue-engineered cartilage constructs cultured with TGF-beta3

OBJECTIVE

To determine whether the functional properties of tissue-engineered constructs cultured in a chemically-defined medium supplemented briefly with TGF-beta3 can be enhanced with the application of dynamic deformational loading.

METHODS

Primary immature bovine cells (2-3 months old) were encapsulated in agarose hydrogel (2%, 30 x 10(6)cells/ml) and cultured in chemically-defined medium supplemented for the first 2 weeks with transforming growth factor beta 3 (TGF-beta3) (10 microg/ml). Physiologic deformational loading (1 Hz, 3 h/day, 10% unconfined deformation initially and tapering to 2% peak-to-peak deformation by day 42) was applied either concurrent with or after the period of TGF-beta3 supplementation. Mechanical and biochemical properties were evaluated up to day 56.

RESULTS

Dynamic deformational loading applied concurrently with TGF-beta3 supplementation yielded significantly lower (-90%) overall mechanical properties when compared to free-swelling controls. In contrast, the same loading protocol applied after the discontinuation of the growth factor resulted in significantly increased (+10%) overall mechanical properties relative to free-swelling controls. Equilibrium modulus values reach 1306+/-79 kPa and glycosaminoglycan levels reach 8.7+/-1.6% w.w. during this 8-week period and are similar to host cartilage properties (994+/-280 kPa, 6.3+/-0.9% w.w.).

CONCLUSIONS

An optimal strategy for the functional tissue engineering of articular cartilage, particularly to accelerate construct development, may incorporate sequential application of different growth factors and applied deformational loading.

Transforming growth factor-beta2 suppresses collagen cleavage in cultured human osteoarthritic cartilage, reduces expression of genes associated with chondrocyte hypertrophy and degradation, and increases prostaglandin E(2) production

Articular cartilage degeneration in osteoarthritis (OA) involves type II collagen degradation and chondrocyte differentiation (hypertrophy). Because these changes resemble growth plate remodeling, we hypothesized that collagen degradation may be inhibitable by growth factors known to suppress growth plate hypertrophy, namely transforming growth factor (TGF)-beta2, fibroblast growth factor (FGF)-2, and insulin. Full-depth explants of human OA knee articular cartilage from arthroplasty were cultured with TGF-beta2, FGF-2, and insulin in combination (growth factors) or individually. In cultured explants from five OA patients, collagenase-mediated type II collagen cleavage was significantly down-regulated by combined growth factors as measured by enzyme-linked immunosorbent assay. Individually, FGF-2 and insulin failed to inhibit collagen cleavage in some OA explants whereas TGF-beta2 reduced collagen cleavage in these 5 explants and in 19 additional explants. Moreover, TGF-beta2 effectively suppressed cleavage at low concentrations. Together or individually these growth factors did not inhibit glycosaminoglycan (primarily aggrecan) degradation while TGF-beta2 occasionally did. Semiquantitative reverse transcriptase-polymerase chain reaction of articular cartilage from six OA patients revealed that TGF-beta2 suppressed expression of matrix metalloproteinase-13 and matrix metalloproteinase-9, early (PTHrP) and late (COL10A1) differentiation-related genes, and proinflammatory cytokines (interleukin-1beta, tumor necrosis factor-alpha). In contrast, TGF-beta2 up-regulated PGES-1 expression and prostaglandin E(2) release. These observations show that TGF-beta2 can suppress collagen resorption and chondrocyte differentiation in OA cartilage and that this may be mediated by prostaglandin E(2). Therefore TGF-beta2 could provide therapeutic control of type II collagen degeneration in OA.

Reduced transforming growth factor-beta signaling in cartilage of old mice: role in impaired repair capacity

Osteoarthritis (OA) is a common joint disease, mainly effecting the elderly population. The cause of OA seems to be an imbalance in catabolic and anabolic factors that develops with age. IL-1 is a catabolic factor known to induce cartilage damage, and transforming growth factor (TGF)-beta is an anabolic factor that can counteract many IL-1-induced effects. In old mice, we observed reduced responsiveness to TGF-beta-induced IL-1 counteraction. We investigated whether expression of TGF-beta and its signaling molecules altered with age. To mimic the TGF-beta deprived conditions in aged mice, we assessed the functional consequence of TGF-beta blocking. We isolated knee joints of mice aged 5 months or 2 years, half of which were exposed to IL-1 by intra-articular injection 24 h prior to knee joint isolation. Immunohistochemistry was performed, staining for TGF-beta1, -2 or -3, TGF-betaRI or -RII, Smad2, -3, -4, -6 and -7 and Smad-2P. The percentage of cells staining positive was determined in tibial cartilage. To mimic the lack of TGF-beta signaling in old mice, young mice were injected with IL-1 and after 2 days Ad-LAP (TGF-beta inhibitor) or a control virus were injected. Proteoglycan (PG) synthesis (³⁵S-sulfate incorporation) and PG content of the cartilage were determined. Our experiments revealed that TGF-beta2 and -3 expression decreased with age, as did the TGF-beta receptors. Although the number of cells positive for the Smad proteins was not altered, the number of cells expressing Smad2P strongly dropped in old mice. IL-1 did not alter the expression patterns. We mimicked the lack of TGF-beta signaling in old mice by TGF-beta inhibition with LAP. This resulted in a reduced level of PG synthesis and aggravation of PG depletion. The limited response of old mice to TGF-beta induced-IL-1 counteraction is not due to a diminished level of intracellular signaling molecules or an upregulation of intracellular inhibitors, but is likely due to an intrinsic absence of sufficient TGF-beta receptor expression. Blocking TGF-beta distorted the natural repair response after IL-1 injection. In conclusion, TGF-beta appears to play an important role in repair of cartilage and a lack of TGF-beta responsiveness in old mice might be at the root of OA development.