Chondrogenesis of human bone marrow-derived mesenchymal stem cells is modulated by complex mechanical stimulation and adenoviral-mediated overexpression of bone morphogenetic protein 2.

Abstract

Currently available methods to treat articular cartilage defects still fail to demonstrate satisfactory outcomes for many patients. Functional tissue engineering using human bone marrow-derived mesenchymal stem cells (hMSCs) is a promising alternative approach for the treatment of these defects. This study strived to investigate the combined effect of complex mechanical stimulation and adenoviral-mediated overexpression of bone morphogenetic protein 2 (BMP-2) on hMSC chondrogenesis. hMSCs were encapsulated in a fibrin hydrogel and seeded into biodegradable polyurethane (PU) scaffolds. A novel three-dimensional transduction protocol was used to transduce cells with an adenovirus encoding for BMP-2 (Ad.BMP-2). Control cells were left untransduced. Cells were cultured for 7 or 28 days in a chondropermessive medium, which lacks any exogenous growth factors. Thereby, the in vivo situation is mimicked more precisely. hMSCs in fibrin-PU composite scaffolds were either left as free-swelling controls or mechanically stimulated using a custom-built bioreactor system that is able to generate joint-like forces. Outcome parameters measured were BMP-2 concentration within the culture medium, and biochemical and gene expression analysis. Mechanical stimulation resulted in an upregulation of chondrogenic genes. Further, glycosaminoglycan (GAG)/DNA ratios were elevated in mechanically stimulated groups. Transduction with Ad.BMP-2 led to a pronounced upregulation of the gene aggrecan and an upregulation of Sox9 message after 7 days. Furthermore, a synergistic effect in combination with mechanical stimulation on collagen 2 message was detected after 7 days. This synergistic increase was more than 8-fold if compared to the additive effect of the application of each stimulus on its own. However, BMP-2 overexpression consistently resulted in a trend toward decreased GAG/DNA ratios in both mechanical stimulated and unloaded groups.