Purpose

A major drawback of current cartilage and intervertebral disc (IVD) tissue engineering is that human mesenchymal stem cells (MSCs) from osteoarthritic (OA) patients express high levels of type X collagen. Type X collagen is a marker of late stage chondrocyte hypertrophy, linked with endochondral ossification, which precedes bone formation. However, it has been shown that a novel plasma-polymer, called nitrogen-rich plasma-polymerized ethylene (PPE:N), is able to inhibit type X collagen expression in committed MSCs. The aim of this study was to determine if the decreased expression of type X collagen, induced by the PPE:N surfaces is maintained when MSCs are removed from the surface and transferred to pellet cultures in the presence of serum and growth factor free chondrogenic media.

Purpose: Several studies have been directed toward using mesenchymal stem cells (MSCs) from osteoarthritic (OA) patients for cartilage or disc repair because these patients are the ones that will require a source of autologous stem cells if biological repair of tissue lesions is to be a therapeutic option. A major drawback of current cartilage and intervertebral disc tissue engineering repair is that these cells rapidly express type X collagen, a marker of late stage chondrocyte hyperthrophy implicated in endochondral ossification. However, a novel plasma-polymerized thin film material, named nitrogen-rich plasma-polymerized ethylene (PPE:N), is able to inhibit type X collagen expression in committed MSCs. The specific aim of this study was to determine if the suppression of type X collagen by PPE:N is maintained when MSCs are transferred to pellet cultures in chondrogenic defined media.

Method: MSCs were obtained from aspirates from the intramedullary canal of donors undergoing total hip replacement for OA using a protocol approved by the Research Ethics Committee of our institution. Cells were then expanded for 2–3 passages in DMEM high glucose supplemented with 10% fetal bovine serum, 100 U/ml penicillin, and 100 μg/ml streptomycin, and finally cultured on polystyrene (PS) cell culture dishes or PPE: N surfaces for 3 and 7 days. Cells were transferred for 3 additional days in a chondrogenic serum free media (DMEM high glucose supplemented with 2 mM L-glutamine, 20 mM HEPES, 45 mM NaHCO3, 100 U/ml penicillin, 100 μg/ml streptomycin, 1 mg/ml bovine serum albumin, 5 μg/ml insulin, 50 μg/ml ascorbic acid, 5 ng/ ml sodium selenite, 5 μg/ml transferrin) in pellet culture or on PS cell culture dishes. Cells were then lysed and proteins were separated on 4–20% acrylamide gels and transferred to nitrocellulose membranes. Type X collagen was detected by Western blot; GAPDH expression was used as an internal control for protein loading.

Results: Results showed that type X collagen protein was expressed in MSCs from OA patients cultured on polystyrene but was suppressed when cultured on PPE: N. Since defined chondrogenic medium are commonly used in pellet culture to promote in vitro chondrogenesis, we then investigated the effect of transferring cells pre-cultured on PPE:N into pellet culture on type X collagen expression. However, the decreased type X collagen expression was not maintained in these conditions and that the expression returned to control values. The decreased type X collagen expression was maintained when the cells were cultured on PS cell culture dishes.

Conclusion: The use of MSCs is promising for tissue engineering of cartilage and intervertebral disc. The present study confirmed the potential of PPE:N surfaces in suppressing type X collagen expression in MSCs from OA patients. However, when MSCs stem cells are transferred to pellet cultures, type X collagen is rapidly re-expressed suggesting that pellet cultures may not be suitable for chondrogenesis of MSCs from OA patients.