Matrix stiffening promotes chondrocyte senescence and the osteoarthritis development through downregulating HDAC3

Extracellular matrix(ECM)stiffening is a typical characteristic of cartilage aging,which is a quintessential feature of knee osteoarthritis(KOA).However,little is known about how ECM stiffening affects chondrocytes and other molecules downstream.This study mimicked the physiological and pathological stiffness of human cartilage using polydimethylsiloxane(PDMS)substrates.It demonstrated that epigenetic Parkin regulation by histone deacetylase 3(HDAC3)represents a new mechanosensitive mechanism by which the stiffness matrix affected chondrocyte physiology.We found that ECM stiffening accelerated cultured chondrocyte senescence in vitro,while the stiffness ECM downregulated HDAC3,prompting Parkin acetylation to activate excessive mitophagy and accelerating chondrocyte senescence and osteoarthritis(OA)in mice.Contrarily,intra-articular injection with an HDAC3-expressing adeno-associated virus restored the young phenotype of the aged chondrocytes stimulated by ECM stiffening and alleviated OA in mice.The findings indicated that changes in the mechanical ECM properties initiated pathogenic mechanotransduction signals,promoted the Parkin acetylation and hyperactivated mitophagy,and damaged chondrocyte health.These results may provide new insights into chondrocyte regulation by the mechanical properties of ECM,suggesting that the modification of the physical ECM properties may be a potential OA treatment strategy.

Exploring the effect of Bushen Bitong recipe-containing serum on IL-1β-induced chondrocyte apoptosis based on SOX9/NF-κB/MMP-13 signaling pathway

Objective:To observe the effect and possible mechanism of action of Bushen Bitong recipe(BSBT)containing serum on IL-1β-induced chondrocyte apoptosis.Methods:Generation 3 rat chondrocytes were randomized into Control,IL-1β,IL-1β+BSBT(L),IL-1β+BSBT(M),and IL-1β+BSBT(H)groups(5%,10%and 15%BSBT-containing serum),and then 24h after intervention respectively,the cell proliferation and Apoptosis rate;Western blot detected the expression levels of Bcl-2,BAX,Caspase-3,SOX9,NF-κB p65,MMP-13 proteins in chondrocytes.ELISA detected the levels of TNF-α,IL-6,and bFGF in the supernatants of chondrocyte culture.Results:Compared with Control group,cell proliferation activity decreased,apoptosis rate increased,NF-κB p65,MMP-13 protein level and TNF-α,IL-6 level increased,and SOX9 protein level and bFGF level decreased in IL-1βgroup;compared with IL-1βgroup,different concentrations of BSBT-containing serum group,cell proliferation activity increased,and apoptosis rate decreased.NF-κB p65,MMP-13 protein level and TNF-α,IL-6 level decreased,SOX9 protein level and bFGF level increased;compared with IL-1β+BSBT(L)group,cell proliferation activity increased,apoptosis rate decreased in IL-1β+BSBT(M)and IL-1β+BSBT(H)groups,and NF-κB p65,MMP-13 protein level and TNF-αlevel decreased.13 protein levels and TNF-αand IL-6 levels decreased,and SOX9 protein levels and bFGF levels increased.Conclusion:BSBT-containing serum may promote IL-1β-induced proliferation of chondrocytes,reduce apoptosis,improve the microenvironment of chondrocytes,and promote cartilage repair through the SOX9/NF-κB/MMP-13 signaling pathway.

α-parvin controls chondrocyte column formation and regulates long bone development

Endochondral ossification requires proper control of chondrocyte proliferation,differentiation,survival,and organization.Here we show that knockout ofα-parvin,an integrin-associated focal adhesion protein,from murine limbs causes defects in endochondral ossification and dwarfism.The mutant long bones were shorter but wider,and the growth plates became disorganized,especially in the proliferative zone.With two-photon time-lapse imaging of bone explant culture,we provide direct evidence showing thatα-parvin regulates chondrocyte rotation,a process essential for chondrocytes to form columnar structure.Furthermore,loss ofα-parvin increased binucleation,elevated cell death,and caused dilation of the resting zones of mature growth plates.Single-cell RNA-seq analyses revealed alterations of transcriptome in all three zones(i.e.,resting,proliferative,and hypertrophic zones)of the growth plates.Our results demonstrate a crucial role ofα-parvin in long bone development and shed light on the cellular mechanism through whichα-parvin regulates the longitudinal growth of long bones.

LOXL3 Inhibits Autophagy of Chondrocytes by Activating Rheb in Osteoarthritis

Objective This study aimed to investigate the potential mechanisms by which lysyl oxidase like 3(LOXL3)affects the autophagy in chondrocytes in osteoarthritis(OA),specifically through the activation of mammalian target of rapamycin complex 1(mTORC1).Methods To establish an OA model,rats underwent anterior cruciate ligament transection(ACLT).Chondrocytes were isolated from cartilage tissues and cultured.Western blotting was performed to assess the expression of LOXL3,Rheb,phosphorylation of p70S6K(p-p70S6K,a downstream marker of mTORC1),and autophagy markers.The autophagy of chondrocytes was observed using an immunofluorescence assay.Results The expression levels of both LOXL3 and Rheb proteins were upregulated in chondrocytes isolated from the OA model cartilage,in comparison to those from the normal cartilage.The silencing of LOXL3 resulted in a decrease in the protein levels of Rheb and p-p70S6K,as well as an increase in the expression of autophagy-related proteins.Additionally,the effect of LOXL3 could be reversed through the silencing of Rheb.The results of the immunofluorescence assay confirmed the impact of LOXL3 and Rheb on chondrocyte autophagy.Conclusion LOXL3 inhibits chondrocyte autophagy by activating the Rheb and mTORC1 signaling pathways.

Regulatory role of NFAT1 signaling in articular chondrocyteactivities and osteoarthritis pathogenesis

Osteoarthritis (OA), the most common form of joint disease, is characterized clinically by joint pain, stiffness,and deformity. OA is now considered a whole joint disease;however, the breakdown of the articular cartilage remains themajor hallmark of the disease. Current treatments targeting OA symptoms have a limited impact on impeding orreversing the OA progression. Understanding the molecular and cellular mechanisms underlying OA development isa critical barrier to progress in OA therapy. Recent studies by the current authors’ group and others have revealedthat the nuclear factor of activated T cell 1 (NFAT1), a member of the NFAT family of transcription factors, regulatesthe expression of many anabolic and catabolic genes in articular chondrocytes of adult mice. Mice lacking NFAT1exhibit normal skeletal development but display OA in both appendicular and spinal facet joints as adults. Thisreview mainly focuses on the recent advances in the regulatory role of NFAT1 transcription factor in the activities ofarticular chondrocytes and its implication in the pathogenesis of OA.

Increase of TNFα-stimulated Osteoarthritic Chondrocytes Apoptosis and Decrease of Matrix Metalloproteinases 9 by NF-κB Inhibition

Objective To investigate the in vitro effect of caffeic acid phenethyl ester （CAPE）, a NF-KB inhibitor, on the apoptosis of osteoarthritic （OA） chondrocytes and on the regulation of the gelatinases matrix metalloproteinase 2 （MMP-2） and matrix metalloproteinase 9 （MMP-9）. Methods Annexin V-FITC/propidium iodide （PI） labeling and western blotting were used to observe and determine the apoptosis in TNFa-stimulated primary cultured osteoarthritic chondrocytes. Also, gelatin zymography was applied to examine MMP-2 and MMP-9 activities in supernatants. Results it was confirmed by both flow cytometry and western blotting that chondrocytes from OA patients have an apoptotic background. Use of CAPE in combination with 10 ng/mL of TNFa for 24 h facilitated the apoptosis. MMP-9 in the supernatant could be autoactivated （from proMMP-9 to active MMP-9）, and the physiologic calcium concentration （2.5 mmol/L） could delay the autoactivation of MMP-9. The activities of MMP-2 and MMP-9 in the fresh supernatant increased significantly in response to stimulation by 10 ng/mL of TNFa for 24 h. The stimulatory effect of TNFa just on proMMP-9 was counteracted significantly by CAPE. Conclusion NF-KB could prevent chondrocytes apoptosis though its activation was attributed to the increase of proMMP-9 activity induced by TNFa （a pro-apoptotic factor）. Therefore, therapeutic NF-KB inhibitor was a ＇double-edged swords＇ to the apoptosis of chondrocytes and the secretion of MMP-9.

Expression of miRNA-140 in Chondrocytes and Synovial Fluid of Knee Joints in Patients with Osteoarthritis

Objective To investigate the expression of miRNA-140 in chondrocytes and synovial fluid of osteoarthritis(OA) patients, and explore the relationship between the miRNA-140 expression and OA severity. Methods This study enrolled 30 OA patients who underwent total knee arthroplasty for chondrocytes sampling and 30 OA patients who underwent intra-articular injection for synovial fluid sampling. All OA patients were grouped into mild [Kellgren and Lawrence(KL) grade 1-2], moderate(KL grade 3) and severe(KL grade 4), with 10 in each subgroups for each sampling purposes. 7 non-OA patients and 10 patients with knee injury were collected for cartilage and synovial fluid sampling respectively as control groups. Chondrocytes were isolated from the cartilage tissue and cultured in vitro. Quantitative real time PCR for miRNA-140 in chondrocytes and synovial fluid were performed, and the U6 sn RNA was used as internal control. The expression difference of miRNA-140 among groups and correlation between the expression and the KL grade of OA were analysed using one-way ANOVA and Spearman test respectively. Results The expression of miRNA-140 in chondrocytes of knees in OA patients was reduced than that in normal knees, and the between-group difference was statistically significant(F=305.464, P<0.001). miRNA-140 could be detected in synovial fluid of both normal knees and OA knees, its relative expression level was reduced in synovial fluid of OA group compared with normal group, and the between-group difference was statistically significant as well(F=314.245, P<0.001). The relative expression level of miRNA-140 in both chondrocytes and synovial fluid were negatively correlated with the KL grade of OA(r=-0.969, P<0.001; r=-0.970, P<0.001). Conclusion miRNA-140 could be detected in chondrocytes and synovial fluid of OA patients, and its expression was negatively correlated with the severity of OA.

The effects of interleukin-1β in modulating osteoclast-conditioned medium's influence on gelatinases in chondrocytes through mitogen-activated protein kinases

Osteoarthritis is recognised to be an interactive pathological process involving the cartilage, subchondral bone and synovium. The signals from the synovium play an important role in cartilage metabolism, but little is known regarding the influence of the signalling from bone. Additionally, the collagenases and stromelysin-1 are involved in cartilage catabolism through mitogen-activated protein kinase （MAPK） signalling, but the role of the gelatinases has not been elucidated. Here, we studied the influence of osteoclastic signals on chondrocytes by characterising the expression of interleukin-1β （IL-1β）-induced gelatinases through MAPK signalling. We found that osteoclast-conditioned media attenuated the gelatinase activity in chondrocytes. However, IL-1β induced increased levels of gelatinase activity in the conditioned media group relative to the mono-cultured chondrocyte group. More specifically, IL-1β restored high levels of gelatinase activity in c-Jun N-terminal kinase inhibitor-pretreated chondrocytes in the conditioned media group and led to lower levels of gelatinase activity in extracellular signal-regulated kinase or p38 inhibitor-pretreated chondrocytes. Gene expression generally correlated with protein expression. Taken together, these results show for the first time that signals from osteoclasts can influence gelatinase activity in chondrocytes. Furthermore, these data show that IL-11~ restores gelatinase activity through MAPK inhibitors; this information can help to increase the understanding of the gelatinase modulation in articular cartilage.

Sustained Akt signaling in articular chondrocytes causes osteoarthritis via oxidative stress-induced senescence in mice

Osteoarthritis(OA) is an age-related disorder that is strongly associated with chondrocyte senescence. The causal link between disruptive PTEN/Akt signaling and chondrocyte senescence and the underlying mechanism are unclear. In this study, we found activated Akt signaling in human OA cartilage as well as in a mouse OA model with surgical destabilization of the medial meniscus.Genetic mouse models mimicking sustained Akt signaling in articular chondrocytes via PTEN deficiency driven by either Col2a1-Cre or Col2a1-Cre^(ERT2) developed OA, whereas restriction of Akt signaling reversed the OA phenotypes in PTEN-deficient mice.Mechanistically, prolonged activation of Akt signaling caused an accumulation of reactive oxygen species and triggered chondrocyte senescence as well as a senescence-associated secretory phenotype, whereas chronic administration of the antioxidant N-acetylcysteine suppressed chondrocyte senescence and mitigated OA progression in PTEN-deficient mice. Therefore,inhibition of Akt signaling by PTEN is required for the maintenance of articular cartilage. Disrupted Akt signaling in articular chondrocytes triggers oxidative stress-induced chondrocyte senescence and causes OA.

Gene expression profile of hypertrophic chondrocytes treated with H2O2:A Preliminary investigation

To identify the osteogenesis genes whose expression is altered in hypertrophic chondrocytes treated with H2O2.Methods Murine chondrogenitor cells(ATDC5)were differentiated into hypertrophic chondrocytes by Insulin-Transferrin-Selenium(ITS)treatment,and then treated with H2O2.Suitable conditions(concentration,time)were determined by using the MTT assay.After total RNA isolation and cDNA synthesis,the levels of 84 genes were determined using the PCR array,whereas quantitative RT-PCR was carried out to validate the PCR array data.Results We identified 9 up-regulated genes and 12 down-regulated genes,encoding proteins with various functions,such as collagen proteins,transcription factors,proteins involved in skeletal development and bone mineral metabolism,as well as cell adhesion molecules.Quantitative RT-PCR confirmed the altered expression of 5 down-regulated genes(Smad2,Smad4,transforming growth factorβreceptor 1,transforming growth factorβreceptor 3,and matrix metalloproteinase 10).Conclusions H2O2 significantly changed the expression of several genes involved in a variety of biological functions.Because of the link between oxidative damage and Kashin-Beck disease,these genes may also be involved in the deep-zone necrosis of the cartilage observed in Kashin-Beck disease.

Effect of Lentivirus-mediated uPA Silencing on the Proliferation and Apoptosis of Chondrocytes and the Expression of MMPs

The lentivirus-mediated u PA interference in the proliferation, apoptosis, and secretion of osteoarthritic chondrocytes was examined in this study. Cells were obtained from the cartilage tissues of New Zealand white rabbits. They were cultured with interleukin（IL）-1β（10 ng/m L） for 24 h and then divided into three groups： u PA-si RNA group（cells transfected with u PA-si RNA lentiviruses）, blank control group（untreated cells）, and negative control group（cells transfected with empty vectors）. Western blotting and real-time quantitative reverse transcription-PCR（RT-QPCR） were performed to detect the protein and m RNA expression levels of u PA, MMP-1, MMP-3, MMP-9, MMP-10, MMP-13 and MMP-14 in osteoarthritic chondrocytes. Cell Counting Kit-8, flow cytometry, and colony formation assay were used to examine the proliferation and apoptosis of chondrocytes. The results showed that after u PA-si RNA transfection, the protein and mR NA expression levels of uP A, MMP-1, MMP-3, MMP-9, MMP-10, MMP-13, and MMP-14 were significantly decreased（P〈0.05 for MMP-1, MMP-9, MMP-10 and MMP-14, P〈0.01 for u PA, MMP-3 and MMP-13）. Cell proliferation and colony formation rate were significantly higher and the cell apoptosis rate was significantly lower in u PA-si RNA group than in control groups（P〈0.01）. The proportion of cells in G0/G1 phase was markedly increased and that in the S phase decreased, and the cell cycle was arrested at the G1/S phase in the control group. In the u PAsi RNA group, the proportion of cells in the S phase was significantly increased, resulting in a different proportion of cells in cell cycle phase（P〈0.01）. It was suggested that the down-regulation of uP A gene could inhibit the expression of MMPs protein and cell apoptosis, increase the proliferation and colony formation of osteoarthritic chondrocytes.

In vitro effects of sodium hyaluronate on the proliferation and the apoptosis in chondrocytes from patients with Kashin-Beck disease and osteoarthritis

Objective：To identify the in vitro effects of sodium hyaluronate（HA） on the proliferation and the apoptosis of chondrocytes from patients with Kashin-Beck disease（KBD） and osteoarthritis（OA）. Methods：Samples of articular cartilages from KBD and OA patients, as well as healthy volunteers（6 subjects in each of the 3 groups） were dissected, digested with collagenase and the cells cultured in monolayers. Chondrocytes from each sample were assigned to an untreated group and two HA-treated groups： H0（no HA）, H100（HA, 0.1 g/L） and H500（HA, 0.5 g/L）. The first passage chondrocytes were used to observe proliferation using the MTT assay, and apoptosis by flow cytometry through Annexin V/PI staining. Results：HA promoted proliferation of chondrocytes in all the three groups, and.in KBD and OA groups, for cells cultured for 4 and 6 days, H500 significantly promoted the cell proliferation. The apoptotic rates of both KBD and OA group chondrocytes were in the order H500 〈 HA100 〈 H0. Conclusion：Sodium hyaluronate administration has a dosedependent in vitro effect to promote proliferation and inhibit apoptosis of chondrocytes from patients with KBD and OA.

Inhibitory Effects of SRT1720 on the Apoptosis of Rabbit Chondrocytes by Activating SIRT1 via p53/bax and NF-κB/PGC-1αPathways

SRT1720, a new discovered drug, was reported to activate silent information regulator 1（SIRT1） and inhibit the chondrocyte apoptosis. However, the underlying mechanism remains elusive. In the present study, the chondrocytes were extracted from the cartilage tissues of New Zealand white rabbits, cultured in the presence of sodium nitroprusside（SNP）（2.5 mmol/L） and divided into five groups： 1, 5, 10, and 20 μmol/L SRT1720 groups and blank control group（0 μmol/L SRT1720）. MTT assay was used to detect the chondrocyte viability and proliferation, and DAPI staining and flow cytometry to measure the chondrocyte apoptosis. The expression levels of SIRT1, p53, NF-κB/p65, Bax, and peroxisome proliferator-activated receptor gamma coactivator 1-α（PGC-1α） were detected by Western blotting and the expression levels of SIRT1, type Ⅱ collagen, and aggrecan m RNA by RT-PCR. The results showed that in the SRT1720-treated groups, the nuclei of chondrocytes were morphologically intact and had uniform chromatin. In the blank control group, nuclear rupture into debris was observed in chondrocytes. With the SRT1720 concentration increasing, the chondrocyte viability increased, the apoptosis rate decreased, the protein expression levels of SIRT1 and PGC-1α and the m RNA expression levels of type Ⅱ collagen and aggrecan increased（P〈0.05）, and the expression levels of p53, NF-κB and bax decreased（P〈0.05）. It was suggested that SRT1720 inhibits chondrocyte apoptosis by activating the expression of SIRT1 via p53/bax and NF-κB/PGC-1α pathways.

The art of building bone: emerging role of chondrocyte-to-osteoblast transdifferentiation in endochondral ossification

There is a worldwide epidemic of skeletal diseases causing not only a public health issue but also accounting for a sizable portion of healthcare expenditures. The vertebrate skeleton is known to be formed by mesenchymal cells condensing into tissue elements(patterning phase) followed by their differentiation into cartilage(chondrocytes) or bone(osteoblasts) cells within the condensations. During the growth and remodeling phase, bone is formed directly via intramembranous ossification or through a cartilage to bone conversion via endochondral ossification routes. The canonical pathway of the endochondral bone formation process involves apoptosis of hypertrophic chondrocytes followed by vascular invasion that brings in osteoclast precursors to remove cartilage and osteoblast precursors to form bone. However, there is now an emerging role for chondrocyte-to-osteoblast transdifferentiation in the endochondral ossification process. Although the concept of "transdifferentiation" per se is not recent,new data using a variety of techniques to follow the fate of chondrocytes in different bones during embryonic and post-natal growth as well as during fracture repair in adults have identified three different models for chondrocyte-to-osteoblast transdifferentiation(direct transdifferentiation, dedifferentiation to redifferentiation, and chondrocyte to osteogenic precursor). This review focuses on the emerging models of chondrocyte-to-osteoblast transdifferentiation and their implications for the treatment of skeletal diseases as well as the possible signaling pathways that contribute to chondrocyte-to-osteoblast transdifferentiation processes.

Increased Chondrocyte Apoptosis in Kashin-Beck Disease and Rats Induced by T-2 Toxin and Selenium Deficiency

Objective To investigate chondrocyte apoptosis and the expression of biochemical markers associated with apoptosis in Kashin-Beck disease（KBD） and in an established T-2 toxin-and selenium（Se） deficiency-induced rat model. Methods Cartilages were collected from the hand phalanges of five patients with KBD and five healthy children. Sprague-Dawley rats were administered a selenium-deficient diet for 4 weeks prior to T-2 toxin exposure. The apoptotic chondrocytes were observed by terminal deoxynucleotidyl transferase d UTP nick end labeling staining. Caspase-3, p53, Bcl-2, and Bax proteins in the cartilages were visualized by immunohistochemistry, their protein levels were determined by Western blotting, and m RNA levels were determined by real-time reverse transcription polymerase chain reaction. Results Increased chondrocyte apoptosis was observed in the cartilages of children with KBD. Increased apoptotic and caspase-3-stained cells were observed in the cartilages of rats fed with normal and Se-deficient diets plus T-2 toxin exposure compared to those in rats fed with normal and Se-deficient diets. Caspase-3, p53, and Bax proteins and m RNA levels were higher, whereas Bcl-2 levels were lower in rats fed with normal or Se-deficiency diets supplemented with T-2 toxin than the corresponding levels in rats fed with normal diet. Conclusion T-2 toxin under a selenium-deficient nutritional status induces chondrocyte death, which emphasizes the role of chondrocyte apoptosis in cartilage damage and progression of KBD.

Dietary fat-associated osteoarthritic chondrocytes gain resistance to lipotoxicity through PKCK2/STAMP2/FSP27

Free fatty acids(FFAs), which are elevated with metabolic syndrome, are considered the principal offender exerting lipotoxicity. Few previous studies have reported a causal relationship between FFAs and osteoarthritis pathogenesis. However, the molecular mechanism by which FFAs exert lipotoxicity and induce osteoarthritis remains largely unknown. We here observed that oleate at the usual clinical range does not exert lipotoxicity while oleate at high pathological ranges exerted lipotoxicity through apoptosis in articular chondrocytes. By investigating the differential effect of oleate at toxic and nontoxic concentrations, we revealed that lipid droplet(LD) accumulation confers articular chondrocytes, the resistance to lipotoxicity. Using high fat diet-induced osteoarthritis models and articular chondrocytes treated with oleate alone or oleate plus palmitate, we demonstrated that articular chondrocytes gain resistance to lipotoxicity through protein kinase casein kinase 2(PKCK2)—six-transmembrane protein of prostate 2(STAMP2)—and fat-specific protein 27(FSP27)-mediated LD accumulation. We further observed that the exertion of FFAs-induced lipotoxicity was correlated with the increased concentration of cellular FFAs freed from LDs, whether FFAs are saturated or not. In conclusion, PKCK2/STAMP2/FSP27-mediated sequestration of FFAs in LD rescues osteoarthritic chondrocytes. PKCK2/STAMP2/FSP27 should be considered for interventions against metabolic OA.

STUDY ON THE EFFECT OF T-2 TOXIN AND SELENIUM ON CD44 EXPRESSION IN THE CULTURED HUMAN FETAL CHONDROCYTES IN VITRO

Objective To investigate the effect on the structure of reestablished cartilage in vitro and CD44 expression on chondrocytes and compare the inducing effect on the reestablished cartilage in vitro between cortical bone matrix gelatin and cancellous bone matrix gelatin. Methods To plant human fetal chondrocytes on the BMG, the damage of the cultured chondrocytes was observed by the optical microscope (HE staining). The immunohistochemistry of CD44 was quantitative analysis by the image collection and analysis system. Results With the increasing concentration of T 2 toxin, the damage of chondroytes was more and more evident and CD44 expression was lowered. After adding selenium, the damage was relieved and CD44 expression increased. The density of chondrocytes on the cortical bone matrix gelatin was much higher than that on the cancellous bone matrix gelatin. Conclusion T 2 toxin can lower the CD44 expression on the chondrocytes and adding selenium can relieve the damage caused by T 2toxin and increased CD44 expression. The inducing effect on reestablished cartilage in vitro of cortical bone matrix gelatin was much higher than that of cancellous bone matrix gelatin.

Effects of Cryoprotective Agents on the Bovine Articular Chondrocyte Viability

Cryopreservation is the process of choice for long term preservation of cells and tissues. In this study, the effects of cryoprotective agents, dimethyl sulfoxide(DMSO), glycerol and 1,2 propanediol on the bovine articular chondrocyte viability were examined experimentally. The CPA was added at the concentrations of 0 6, 0 9, 1 2 and 1 5 mol/L and at 4 ℃ and 37 ℃ and removed at 37 ℃ in one step. CPA stepwise addition and removal at 0 6 and 1 2 mol/L and at 37 ℃ was also tested as an alternative protocol. Cell volume excursion during DMSO addition and removal was estimated and correlated well with cell survival rates. Solution makeup affects cell survival rate and a stepwise protocol can improve the cell survival rates significantly.

A high-resolution route map reveals distinct stages of chondrocyte dedifferentiation for cartilage regeneration

Articular cartilage damage is a universal health problem.Despite recent progress,chondrocyte dedifferentiation has severely compromised the clinical outcomes of cell-based cartilage regeneration.Loss-of-function changes are frequently observed in chondrocyte expansion and other pathological conditions,but the characteristics and intermediate molecular mechanisms remain unclear.In this study,we demonstrate a time-lapse atlas of chondrocyte dedifferentiation to provide molecular details and informative biomarkers associated with clinical chondrocyte evaluation.We performed various assays,such as single-cell RNA sequencing(scRNA-seq),live-cell metabolic assays,and assays for transposase-accessible chromatin with high-throughput sequencing(ATAC-seq),to develop a biphasic dedifferentiation model consisting of early and late dedifferentiation stages.Early-stage chondrocytes exhibited a glycolytic phenotype with increased expression of genes involved in metabolism and antioxidation,whereas late-stage chondrocytes exhibited ultrastructural changes involving mitochondrial damage and stress-associated chromatin remodeling.Using the chemical inhibitor BTB06584,we revealed that early and late dedifferentiated chondrocytes possessed distinct recovery potentials from functional phenotype loss.Notably,this two-stage transition was also validated in human chondrocytes.An image-based approach was established for clinical use to efficiently predict chondrocyte plasticity using stage-specific biomarkers.Overall,this study lays a foundation to improve the quality of chondrocytes in clinical use and provides deep insights into chondrocyte dedifferentiation.

Protective role of FoxO transcription factors against oxidative stress-induced chondrocyte dysfunction:a new therapeutic target for osteoarthritis

Chondrocyte dysfunction has been demonstrated to be a major inducer of osteoarthritis(OA).The pathological mechanism of chondrocyte dysfunction is definitely multifactoral,but oxidative stressis regarded as one of the leading causes of apoptosis,autophagy,senescence,and mitochondrial dysfunctionin chondrocytes.Strategies for arresting oxidative stress-induced chondrocyte dysfunction have been considered as potential therapeutic targets for OA.Recently,fork head box O(Fox O)transcription factors have been determined to play a protective role in chondrocytes through the regulation of autophagy and defense against oxidative stress;they also regulate growth,maturation,and matrix synthesis.To explore Fox O′s potential role in the treatment of OA,we first discussed the recent advances in the field of oxidative stress-induced chondrocyte dysfunction and then emphasized the protective role of fox otranscription factors as a potential molecular target for the treatment of OA.Understanding the function of fox otranscription factors will be important in designing next-generation therapies to prevent or reverse the development of OA.