Fig. 4

Aged-bone marrow mesenchymal stem cell (BMSC) exosomes target osteoclasts in vitro. a Colocalization of labelled BMSC-exosomes and bone marrow monocyte (BMM) nuclei. b, c Schematic illustration of the Transwell assay. The bottom membrane was stained with crystal violet after 24-h culture in vitro. d, e Representative images of TRAP-stained multinucleated osteoclasts treated with aged exosomes without zinc (A-EXOs) or aged exosomes with zinc addition (AZ-EXOs) and the area and number of TRAP‐positive cells. f Podosomal actin belts in osteoclasts treated with A-EXOs or AZ-EXOs; nuclei were counterstained with 4′,6-diamidino-2-phenylindole. g Semi-quantitative statistical analysis of osteoclastogenesis-related expression (TRAP and CTR). h, i Representative scanning electron microscopy images of bone resorption pits on different bovine bone slices and their resorption area. j Confocal microscopy observation of 3D reconstruction on different bovine bone slices (n = 3, *p < 0.05, **p < 0.01)