Low-intensity pulsed ultrasound (LIPUS) can induce mesenchymal stem cell (MSC) differentiation, although the mechanism of its potential effects on chondrogenic differentiation is unknown. Since autophagy is known to regulate the differentiation of MSCs, the aim of our study was to determine whether LIPUS induced chondrogenesis via autophagy regulation. MSCs were isolated from the rat bone marrow, cultured in either standard or chondrogenic medium, and stimulated with 3 MHz of LIPUS given in 20% on–off cycles, with or without prior addition of an autophagy inhibitor or agonist. Chondrogenesis was evaluated on the basis of aggrecan (AGG) organization and the amount of type II collagen (COL2) and the mRNA expression of AGG, COL2, and SRY-related high mobility group-box gene 9 (SOX9) genes. LIPUS promoted the chondrogenic differentiation of MSCs, as shown by the changes in the extracellular matrix (ECM) proteins and upregulation of chondrogenic genes, and these effects were respectively augmented and inhibited by the autophagy inhibitor and agonist. Taken together, these results indicate that LIPUS promotes MSC chondrogenesis by inhibiting autophagy.

Aims: To evaluate the effect of ultrasound-targeted simvastatin-loaded microbubble destruction (UTMD_SV) for alleviation of the progression of osteoarthritis (OA) in rabbits through modulation of the peroxisome proliferator-activated receptor (PPARγ).Methods: In vitro, OA chondrocytes were treated with ultrasound (US), US-targeted microbubble destruction (UTMD), simvastatin (SV), and UTMD_SVon alternate days for four weeks. Chondrocytes were also treated with PPARγ inhibitor, PPARγ inhibitor+ UTMD_SV, and UTMD_SV. The cholesterol efflux rate and triglyceride levels were measured using an assay kit and oil red O staining, respectively. In vivo, the OA rabbits were treated with a single intra-articular injection of UTMD, SV, and UTMD_SVevery seven days for four weeks. Cartilage histopathology was assessed by safranin-O staining and the Mankin score. Total cholesterol (TC) and high-density lipoprotein-cholesterol (HDL-C) in rabbit knee synovial fluid were detected by enzyme-marker assay. Aggrecan, collagen II, and PPARγ expression levels were analyzed by Western blotting (WB).Results: In vitro, UTMD_SVsignificantly increased the cholesterol efflux rate and aggrecan, collagen II, and PPARγ levels in OA chondrocytes; these effects were blocked by the PPARγ inhibitor. In vivo, UTMD_SVsignificantly increased aggrecan, collagen II, PPARγ, and HDL-C levels, while TC levels and Mankin scores were decreased compared with the UTMD, SV, OA, and control groups.Conclusion: UTMD_SVpromotes cartilage extracellular matrix synthesis by modulating the PPARγ-mediated cholesterol efflux pathway in OA rabbits. Cite this article: Bone Joint Res 2021;10(10):693–703.

Objective: To evaluate ultrasound-targeted simvastatin-loaded microbubble destruction (UTMD_SV) attenuation of osteoarthritis (OA) progression in rabbits through modulation of the peroxisome proliferator-activated receptor (PPARγ)-mediated cholesterol efflux pathway.Methods: In vitro, chondrocytes were treated with ultrasound (US), US-targeted microbubble destruction (UTMD), simvastatin (SV) and UTMDsv on alternate days for 4 weeks. Chondrocytes were also treated with PPARγ inhibitor, PPARγ inhibitor+UTMDsv and UTMDsv. The cholesterol efflux rate and triglyceride were measured respectively by assay kit and oil red O staining. In vivo, the OA rabbits were treated with a single intra-articular injection of UTMD, SV and UTMD_SV every 7 days for 4 weeks. Cartilage histopathology was assessed by safranin-O staining and the Mankin score. Total cholesterol (TC) and high-density lipoprotein-cholesterol (HDL-C) in rabbit knee synovial fluid were detected by enzyme-marker assay. Aggrecan, collagen II and PPARγ expression levels were analyzed western blotting (WB).Results: OA models exhibited primarily by a loss of aggrecan and collagen II, changes to subchondral bone architecture and cartilage degradation. In vitro, UTMD_SV significantly increased the cholesterol efflux rate and aggrecan, collagen II and PPARγ levels in OA chondrocytes; these effects were blocked by the PPARγ inhibitor. In vivo, UTMD_SV significantly increased aggrecan, collagen II, PPARγ and HDL-C levels, while TC levels and Mankin scores were decreased compared with the UTMD, SV, OA and control groups (95% CI: 0.069 to 6.671).Conclusion: UTMD_SV promotes the expression of aggrecan and collagen II and relieve cartilage degradation by modulating the PPARγ-mediated cholesterol efflux pathway in rabbits.