PHF23 negatively regulates the autophagy of chondrocytes in osteoarthritis.

AIM: Osteoarthritis (OA) is the main cause of disability and joint replacement surgery in the elderly. As a crucial cell survival mechanism, autophagy has been reported to decrease in OA. PHF23 is a new autophagy inhibitor which was first reported by us previously. This study aimed to explore the anti-autophagic mechanism of PHF23 to make it a possible therapeutic target of OA. MAIN METHOD: Lentiviral vectors specific to PHF23 were used on chondrocytes (C28/I2) to establish PHF23 overexpressed or knockdown stable cell strains. Interleukin (IL)-1ß (10 ng/mL) and chloroquine (CQ, 25 uM) were used as an inducer of OA and inhibitor of lysosome, respectively. Autophagy was evaluated by autophagosome formation using transmission electron microscopy (TEM) and western blot analysis of P62 and LC3B on different groups of cells. Effects of PHF23 on OA were evaluated by collagen II immunofluorescent staining and western blot analysis of OA-associated proteins MMP13 and ADAMTS5. Effects of PHF23 on AMPK and mTOR/S6K pathways and mitophagy were determined by western blot analysis. KEY FINDINGS: Knockdown of PHF23 enhanced IL-1ß-induced autophagy, while overexpression of PHF23 exerted the opposite effect. Knockdown of PHF23 protected chondrocytes against IL-1ß-induced OA by decreasing the levels of OA-associated proteins and increasing expression of Collagen II. Knockdown of PHF23 also increased mitophagy level and altered the phosphorylation levels of AMPK, mTOR, and S6K. SIGNIFICANCE: PHF23 downregulates autophagy, mitophagy in IL-1ß-induced OA-like chondrocytes and alters the activities of AMPK and mTOR/S6K, which suggests that PHF23 may be a possible therapeutic target for OA.

Intraarticular Injection of Allogenic Mesenchymal Stem Cells has a Protective Role for the Osteoarthritis.

BACKGROUND: Researchers initially proposed the substitution of apoptotic chondrocytes in the superficial cartilage by injecting mesenchymal stem cells (MSCs) intraarticularly. This effect was termed as bio-resurfacing. Little evidence supporting the treatment of osteoarthritis (OA) by the delivery of a MSC suspension exists. The aim of this study was to investigate the effects of injecting allogenic MSCs intraarticularly in a rat OA model and to evaluate the influence of immobility on the effects of this treatment. METHODS: We established a rat knee OA model after 4 and 6 weeks and cultured primary bone marrow MSCs. A MSC suspension was injected into the articular space once per week for 3 weeks. A subgroup of knee joints was immobilized for 3 days after each injection, while the remaining joints were nonimmobilized. We used toluidine blue staining, Mankin scores, and TdT-mediated dUTP-biotin nick end labeling staining to evaluate the therapeutic effect of the injections. Comparisons between the therapy side and the control side of the knee joint were made using paired t-test, and comparisons between the immobilized and nonimmobilized subgroups were made using the unpaired t-test. A P value < 0.05 was considered significant. RESULTS: The three investigative approaches revealed less degeneration on the therapy sides of the knee joints than the control sides in both the 4- and 6-week groups (P < 0.05), regardless of immobilization. No significant differences were observed between the immobilized and nonimmobilized subgroups (P > 0.05). CONCLUSIONS: Therapy involving the intraarticular injection of allogenic MSCs promoted cartilage repair in a rat arthritis model, and 3-day immobility after injection had little effect on this therapy.

[Effect of mitochondrial dysfunction of chondrocyte on cartilage degeneration].

OBJECTIVE: To evaluate the effect of chondrocyte mitochondrial dysfunction on the development of cartilage degeneration. METHODS: In the study, 10 cartilage samples of the knee joint were collected during total knee arthroplasty surgery because of OA from April to October of 2012 in Peking University First Hospital. All the tissues were taken from transmission electron microscope (TEM) observation grouped by Outerbridge classification. Then, TEM observation, quantitative detection of mitochondrial respiratory chain enzyme complex 1,2,2+3,4 and ATPase activity, detection of the mitochondrial membrane potential by JC-1 method were taken with cultured normal and OA chondrocytes. Healthy chondrocytes from 10 normal cartilage samples were divided into 2 groups: the normal control group and rotenone group. The ultrastuctrure alterations of mitochondria, mitochondrial membrane potential, apoptosis rate and collagen II content were compared. RESULTS: With the aggravation of cartilage degeneration, mitochondria swelling, outer membrane rupture, cristae destruction and disappearance were observed in both the tissue and cell TEM examinations. JC-1 staining showed a decreased membrane potential in OA chondrocytes which had a lower red/green fluorescence ratio of 1.50 than that of the normal chondrocytes of 2.58. mitochondrial respiratory chain (MRC) enzyme complex 1,2,2+3,4 and ATPase activity of the OA chondrocytes also represented a decreased tendency compared with the normal chondrocytes although the difference was not significant (P=0.109,0.197,0.098,0.169,0.145). The mitochondria in the Ro group cells showed OA-like changes morphologically by TEM detection. JC-1 staining showed a decreased mitochondrial membrane potential in the Ro group chondrocytes which had a lower red/green fluorescence ratio of 1.78 than that of the normal ones of 2.58. Apoptosis examination represented a higher apoptosis rate of 7.53% in the Ro group chondrocytes than that of the normal ones of 4.38%. Collagen II content of the chondrocytes in the Ro group was (44.63 ± 7.11) µg/L , significantly lower than (72.88 ± 24.3) µg/L in the control group (P=0.044). CONCLUSION: Mitochondrial function is impaired in OA chondrocyte. Mitochondrial function destruction results in an increased chondrocyte apoptosis rate and a decreased collagen II secretion.