Abstract
PurposeMultipotent stromal cell (MSC)-based regenerative strategy has shown promise for the repair of cartilage, an avascular tissue in which cells experience hypoxia. Hypoxia is known to promote the early chondrogenic differentiation of MSC. The aim of our study was therefore to determine whether low oxygen tension could be used to enhance the regenerative potential of MSC for cartilage repair.MethodsMSC from rabbit or human adipose stromal cells (ASC) were preconditioned in vitro in control or chondrogenic (ITS and TGF-β) medium and in 21 or 5% O2. Chondrogenic commitment was monitored by measuring COL2A1 and ACAN expression (real-time PCR). Preconditioned rabbit and human ASC were then incorporated into an Si-HPMC hydrogel and injected (i) into rabbit articular cartilage defects for 18 weeks or (ii) subcutaneously into nude mice for five weeks. The newly formed tissue was qualitatively and quantitatively evaluated by cartilage-specific immunohistological staining and scoring. The phenotype of ASC cultured in a monolayer or within Si-HPMC in control or chondrogenic medium and in 21 or 5% O2 was finally evaluated using real-time PCR.Results/Conclusions5% O2 increased the in vitro expression of chondrogenic markers in ASC cultured in induction medium. Cells implanted within Si-HPMC hydrogel and preconditioned in chondrogenic medium formed a cartilaginous tissue, regardless of the level of oxygen. In addition, the 3D in vitro culture of ASC within Si-HPMC hydrogel was found to reinforce the pro-chondrogenic effects of the induction medium and 5% O2. These data together indicate that although 5% O2 enhances the in vitro chondrogenic differentiation of ASC, it does not enhance their in vivo chondrogenesis. These results also highlight the in vivo chondrogenic potential of ASC and their potential value in cartilage repair.
Highlights
Articular cartilage is an avascular and poorly cellularized tissue that has a limited capacity for self-repair after injury
The rASC were cultured in a monolayer under NCT, NCH, or HCH conditions (Fig. 1A)
The expression of col2a1 and acan became detectable in the NCH condition and substantially increased in rASC cultured in HCH conditions with significant 4.5- and 1.6-fold increases, respectively, compared with the NCH condition (Fig. 2A)
Summary
Articular cartilage is an avascular and poorly cellularized tissue that has a limited capacity for self-repair after injury. Only full-thickness defects, which affect both the subchondral bone and cartilage exhibit a repair process that leads to the formation of fibrocartilage. This fibrocartilage does not display the mechanical properties of native articular cartilage [1] and degrades rapidly. For the treatment of cartilage defects, none of these techniques results in a complete regeneration of cartilage tissue [4] To address this clinical issue, autologous chondrocyte transplantation (ACT) initially developed by Brittberg et al has been introduced into clinical use to treat focal lesions of the knee joint [5,6,7]. Among the various tissues from which MSC can PLOS ONE | www.plosone.org
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