Engineering a 3D cartilage model from human stem cells


Osteoarthritis (OA) is the most prevalent form of joint disease, affecting 10 million people in the UK alone1. OA is characterized by a progressive degeneration of joint cartilage and results in pain and impaired function of the affected joints; negatively affecting quality of life of patients.
There is an urgent clinical need to better understand the mechanisms underlying disease development and progression, and to develop diagnostic assays for early identification of patients at risk of developing OA.2,3 Progress in these areas requires realistic experimental models. However existing animal models do not accurately replicate the human condition4,5, and human tissue (whilst more relevant) is typically from arthroplasty of patients with advanced OA, so is not informative.

We have designed a method to produce tissue closely resembling articular cartilage from human stem cells. Human chondrocyte progenitor cells were isolated from the joints of healthy donors, and cultured for 35days to generate three dimensional cartilage constructs (6mm diameter, 1mm height). These constructs showed similar biochemical, histological and mechanical properties to native human articular cartilage (stratification into zones, matrix organisation and biomechanical integrity). Exposure of constructs to cyclical loading or to inflammatory cytokines induced mechanoresponse genes and MMP-13/ADAMTS-4 mediated cartilage breakdown, respectively
To investigate changes in expression of glycosylation-related genes, treated and untreated constructs were analyzed using microarrays. Analysis identified several candidate markers of OA-initiation, and changes to protein expression and distribution following OA-induction was confirmed by immunohistochemistry and Western blotting, confirmed in human cartilage biopsies obtained during joint replacement for OA.

This therefore provides a new tool for analyzing cartilage responses to external stimuli (loading, inflammation, drugs) and modeling disease states. We successfully used this model to identify qualitative changes in protein glycosylation during development of human OA. The potential use of these epitopes as diagnostic biomarkers for OA is now under investigation.