In vivo cartilage-formation potency of somatic stem cells is associated with responsiveness to TGFβ stimulation in vitro

Abstract Background: Somatic stem cell transplantation has been performed for cartilage injury, but the reparative mechanisms are still conflicting. The chondrogenic potential of stem cells are thought as promising features for cartilage therapy, however the correlation between their potential for chondrogenesis in vitro and in vivo remains undefined. The purpose of this study was to investigate the intrinsic chondrogenic condition depends on cell types and explore an indicator to select useful stem cells for cartilage regeneration.Methods: The chondrogenic potential of two different stem cell types derived from adipose tissue (ASCs) and synovium (SSCs) of mice and humans was assessed using bone morphogenic protein-2 (BMP2) and transforming growth factor-β1 (TGFβ1). Their reparative potential was also validated through transplantation into a mouse osteochondral defect model.Results: All cell types showed apparent chondrogenesis under the combination of BMP2 and TGFβ1 in vitro, as assessed by the formation of proteoglycan- and type 2 collagen (COL2)-rich tissues. However, our results vastly differed with those observed following single stimulation among species and cell types; apparent chondrogenesis of mouse ASCs, mouse SSCs, and human SSCs was observed with supplementation of BMP2, either BMP2 and TGFβ1, and BMP2, respectively. Human ASCs showed no chondrogenesis following single stimulation. Among human SSCs, two of six donors formed partially COL2-positive tissues in response to TGFβ1. However, unlike mouse cells, human cells showed fibrous components (COL1/3) with all treatments. Mouse SSCs formed hyaline-like cartilage (proteoglycan+/COL2+/COL1-/COL3-) in the transplanted site in vivo, but other cell types mainly formed COL1/3-positive fibrous tissues. Remarkably, only donors that showed chondrogenic response to TGFβ1 in vitro formed partially COL2-positive tissues in vivo. However, the area was mainly composed of COL1/3, indicating fibrous cartilage-like tissues.Conclusion: The chondrogenic response to TGFβ1 may represent the fate of stem cells when locally transplanted into cartilage defects.