Bone marrow mesenchymal stem cell-derived exosomal lactate dehydrogenase A promotes tendon-bone healing via histone lactylation-mediated cartilage regeneration

Figure 1 Exosomes derived from bone marrow mesenchymal stem cells highly expresses lactate dehydrogenase A. A and B: Representative transmission electron microscopy images and particle size distribution curves of exosomes derived from bone marrow mesenchymal stem cells; C: Images of chondrocyte stem cells uptake of PKH26-labeled exosomes derived from bone marrow mesenchymal stem cells; D: Protein expression analysis of lactate dehydrogenase A. LDHA: Lactate dehydrogenase A.

Figure 2 Exosomes derived from bone marrow mesenchymal stem cells promotes anterior cruciate ligament reconstruction tendon bone healing. A: Lactate dehydrogenase A protein expression in bone tissues of anterior cruciate ligament reconstruction rats; B: Representative micro-computed tomography images of the humeral head in each group at week 8 postoperatively; C: Representative images of hematoxylin and eosin staining in different treatment groups with quantification of histological scores; D: Safranin O-Fast green staining of the tendon-bone interface and quantification of fibrocartilage in the interface region. LDHA: Lactate dehydrogenase A; ACLR: Anterior cruciate ligament reconstruction; Exo: Exosomes; HE: Hematoxylin and eosin; SOFG: Safranin O-Fast green.

Figure 3 Exosomes derived from bone marrow mesenchymal stem cells promotes the proliferation and differentiation of chondrocyte stem cells. A: Western blotting showed the presence of exosomes derived from bone marrow mesenchymal stem cells (BMSC-Exos) lactate dehydrogenase A; B: Extracellular lactate content analysis; C: Cell counting kit 8 analysis of the effect of BMSC-Exos on chondrocyte stem cells proliferation; D: Expression of collagen II, SOX9 and aggrecan proteins and genes in chondrocyte stem cells after co-incubation with BMSC-Exos. ^aP < 0.05 vs control, ^bP < 0.01 vs control. LDHA: Lactate dehydrogenase A; BMSC-Exo: Exosomes derived from bone marrow mesenchymal stem cell.

Figure 4 Lactate dehydrogenase A regulates H3K18 Lactylation and bone morphogenetic protein 7 expression in chondrocyte stem cells. A: Level of H3K18 Lactylation in chondrocyte stem cells from control, bone marrow mesenchymal stem cells and bone marrow mesenchymal stem cells + short hairpin RNA lactate dehydrogenase A groups; B: Enrichment of H3K18 Lactylation at the bone morphogenetic protein 7 (BMP7) promoter was measured by a chromatin immunoprecipitation-quantitative polymerase chain reaction assay; C: Promoter activity of BMP7 was analyzed by luciferase reporter gene assay; D and E: The RNA and protein level of BMP7 was analyzed by quantitative polymerase chain reaction and western blotting assay. ^aP < 0.05 vs control, ^bP < 0.01 vs control. LDHA: Lactate dehydrogenase A; BMSC-Exo: Exosomes derived from bone marrow mesenchymal stem cell; BMP: Bone morphogenetic protein 7.

Figure 5 Exosomes derived from bone marrow mesenchymal stem cells lactate dehydrogenase A promotes chondrocyte stem cells proliferation by upregulating bone morphogenetic protein 7. A: Protein expression levels of lactate dehydrogenase A and bone morphogenetic protein 7 in chondrocyte stem cells (CSPCs) after different treatments; B: Lactate content secreted by CSPCs; C: Cell viability measured by cell counting kit 8; D: Protein levels of type II collagen, SOX9 and aggrecan in CSPCs. ^bP < 0.01 vs control. LDHA: Lactate dehydrogenase A; BMSC-Exo: Exosomes derived from bone marrow mesenchymal stem cell; BMP: Bone morphogenetic protein 7.