Mesenchymal stem cells (MSCs) have been widely used for tissue repair and regeneration. However, the inherent drawbacks, including limited cell survival after cell transplantation, have hindered direct MSC transplantation for tissue repair and regeneration. The aim of this study was to investigate if exosomes isolated from MSCs can promote the proliferation and differentiation of human primary osteoblastic cells (HOBs) and be potentially used for bone tissue regeneration. We showed that adipose tissue-derived MSC (ASC)-derived exosomes (ASC-EXO) were able to promote the proliferation and osteogenic differentiation in HOBs; and the trophic effects of ASC-EXO on HOBs were further harnessed when ASCs were preconditioned with tumor necrosis factor-alpha (TNF-α) for 3 days, which mimics the acute inflammatory phase upon bone injury. In addition, we showed that Wnt-3a content was elevated in ASC-EXO when ASCs were preconditioned by TNF-α, and inhibiting Wnt signaling decreased the osteogenic gene expression levels in HOBs which were cultured in TNF-α preconditioned ASCs conditioned medium. In conclusion, it was demonstrated that ASC-EXO, especially primed by TNF-α preconditioning on ASCs, offer a promising approach to replace direct stem cell transplantation for bone repair and regeneration.

Ideally, biomaterials have inductive properties, favoring specific lineage differentiation. For chondrogenic induction, these properties have been attributed to collagen type II. However, the underlying mechanisms are largely unknown. This study aimed to investigate whether collagen type II favors chondrogenic induction by affecting cell shape through β1 integrins and Rho A/Rock signaling. For this purpose, adipose tissue–derived stem cells (ASCs) were encapsulated in collagen type I or II gels and cultured in plain and chondrogenic medium. It was demonstrated that (i) ASCs showed more efficient chondrogenic induction (higher collagen X, aggrecan, sox6, sox9, and collagen II gene expression) in both plain and chondrogenic media in collagen type II versus collagen type I gels; (ii) ASCs showed lower Rock 2 gene expression and a more rounded cell shape in collagen type II versus type I gels when grown in plain medium; (iii) Rock inhibitor (Y27632) more effectively enhanced chondrogenic gene expression of ASCs in collagen type I than in collagen type II gels, and diminished differences in chondrogenic gene expression and cell shape of ASCs between the two gel types; and (iv) β1 integrins blocking not only reduced the differences of chondrogenic gene expression but also eliminated the differences of Rock 1 and Rock 2 gene expressions and cell shape when comparing ASCs embedded in collagen type I and II gels. We conclude that collagen type II provides the inductive signaling for chondrogenic differentiation in ASCs by evoking a round cell shape through β1 integrin–mediated Rho A/Rock signaling pathway.