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Background. Previous studies have reported that mitochondrial dysfunction participates in the pathological process of osteoarthritis (OA). However, studies that improve mitochondrial function are rare in OA. Mitochondrial transfer from mesenchymal stem cells (MSCs) to OA chondrocytes might be a cell-based therapy for the improvement of mitochondrial function to prevent cartilage degeneration. This study aimed to determine whether MSCs can donate mitochondria and protect the mitochondrial function and therefore reduce cartilage degeneration. Methods. Bone-marrow-derived mesenchymal stromal cells (BM-MSCs) were harvested from the marrow cavities of femurs and tibia in young rats. OA chondrocytes were gathered from the femoral and tibial plateau in old OA model rats. BM-MSCs and OA chondrocytes were co-cultured and mitochondrial transfer from BM-MSCs to chondrocytes was identified. Chondrocytes with mitochondria transferred from BM-MSCs were selected by fluorescence-activated cell sorting. Mitochondrial function of these cells, including mitochondrial membrane potential (Δψm), the activity of mitochondrial respiratory chain (MRC) enzymes, and adenosine triphosphate (ATP) content were quantified and compared to OA chondrocytes without mitochondrial transfer. Chondrocytes proliferation, apoptosis, and secretion ability were also analyzed between the two groups. Results. Mitochondrial transfer was found from BM-MSCs to OA chondrocytes. Chondrocytes with mitochondrial from MSCs (MSCs + OA group) showed increased mitochondrial membrane potential compared with OA chondrocytes without mitochondria transfer (OA group) (1.79 ± 0.19 vs. 0.71 ± 0.12, t = 10.42, P < 0.0001). The activity of MRC enzymes, including MRC complex I, II, III, and citrate synthase was also improved (P < 0.05). The content of ATP in MSCs + OA group was significantly higher than that in OA group (161.90 ± 13.49 vs. 87.62 ± 11.07 nmol/mg, t = 8.515, P < 0.0001). Meanwhile, we observed decreased cell apoptosis (7.09% ± 0.68% vs.15.89% ± 1.30%, t = 13.39, P < 0.0001) and increased relative secretion of type II collagen (2.01 ± 0.14 vs.1.06 ± 0.11, t = 9.141, P = 0.0008) and proteoglycan protein (2.08 ± 0.20 vs. 0.97 ± 0.12, t = 8.227, P = 0.0012) in MSCs + OA group, contrasted with OA group. Conclusions. Mitochondrial transfer from BM-MSCs provided protection for OA chondrocytes against mitochondrial dysfunction and degeneration through improving mitochondrial function, cell proliferation, and inhibiting apoptosis in chondrocytes. This finding may offer a new therapeutic direction for OA.

Objectives. Carbon-based nanomaterials have gained attention in the field of biomedicine in recent years, especially for the treatment of complicated diseases such as cancer. Here, we report a novel carbon-based nanomaterial, named carbon quantum dots (CQDs), which has potential for cancer therapy. We performed a systematic study on the effects of CQDs on the osteosarcoma 143B cell line in vitro and in vivo. Methods. Cell counting assay, the neutral red assay, lactic dehydrogenase assay, and fluorescein isothiocyanate (FITC) Annexin V/Propidium iodide (PI) were used to detect the cytotoxicity and apoptosis of CQDs on the 143B cell line. Intracellular reactive oxygen species (ROS) were detected by the oxidation-sensitive fluorescent probe 2′,7′-dichlorofluorescein diacetate. The JC-10 assay was used to detect the mitochondrial membrane potential (MMP) of 143B cells incubated with CQDs. The effects of CQDs on the 143B cell line were evaluated by Western blot and immunofluorescence analysis of apoptosis-related proteins Bax, Bcl-2, cytochrome-C, caspase-3, cleaved-caspase-3, PARP1, and cleaved-PARP1. Male tumor-bearing BALB/c nude mice were used to investigate the antitumor effects of CQDs, and the biosafety of CQDs in vivo was tested in male BALB/c mice by measuring weight changes, hematology tests, and histological analyses of major organs. Results. CQDs exhibited a high cytotoxicity and induced apoptosis toward the 143B cell line. CQDs can also significantly increase the intracellular level of ROS and lower the mitochondrial membrane potential levels of 143B cells. CQDs increase apoptotic protein expression to induce apoptosis of 143B cells by triggering the mitochondrial apoptotic signaling pathway. The tumor volume in the CQD-treated mice was smaller than that in the control group, the tumor volume inhibition rate was 38.9%, and the inhibitory rate by tumor weight was 30.1%. All biosafety test indexes were within reference ranges, and neither necrosis nor inflammation was observed in major organs. Conclusions. CQDs induced cytotoxicity in the 143B cell line through the mitochondrial apoptotic signaling pathway. CQDs not only showed an antitumor effect but also high biocompatibility in vivo. As a new carbon-based nanomaterial, CQDs usage is a promising method for novel cancer treatments.

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)-1β (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-1β-induced autophagy, while overexpression of PHF23 exerted the opposite effect. Knockdown of PHF23 protected chondrocytes against IL-1β-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-1β-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.