Current approaches to treat osteoarthritis (OA) are insufficient. Autologous chondrocyte implantation (ACI) has been used for the past decade to treat patients with OA or focal cartilage defects. However, a number of complications have been reported post-ACI, including athrofibrosis and symptomatic hypertrophy. Thus, a long term ACI strategy should ideally incorporate methods to ‘prime’ autologous chondrocytes to form cartilage-specific matrix and
suppress hypertrophic mineralization. The objective of this study was to examine the effects of tyrosine rich amelogenin peptide (TRAP; an isoform of the develop mental protein amelogenin) on human articular cartilage cell (HAC) chondrogenic differentiation and hypertrophic
mineralization in vitro. Effects of chemically synthesized TRAP on HAC chondrogenic differentiation were determined by assessing: (i) sGAG production; (ii) Alcian blue staining for proteoglycans; (iii) Collagen type II immunostaining; and (iv) Expression of the chondrogenic genes SOX9, ACAN and COL2A1. Hypertrophic mineralization was assayed by: (i) ALP expression; (ii) Alizarin red staining for Ca+2 -rich bone nodules; (iii) OC immunostaining; and (iv) Expression of the Osteogenic/Hypertrophic genes Ihh and BSP. Chemically synthesized TRAP was found to suppress terminal osteogenic differentiation of HACs cultured in hype rtrophic mineralization-like conditions, an effect mediated via down regulation of the Ihh gene. Moreover, TRAP was found to augment chondrogenic differentiation of HACs via induction of SOX9 gene expression when cells were cultured in pro-chondrogenic media. The results obtained from this proof of concept study motivate further studies on the use of TRAP as part of a preconditioning regimen in autologous chondrocyte implantation procedures for OA patients and patients suffering from focal cartilage defects.