The Secretory Profiles of Cultured Human Articular Chondrocytes and Mesenchymal Stem Cells: Implications for Autologous Cell Transplantation Strategies

This study was undertaken to compare the phenotype of human articular chondrocytes (ACs) and bone marrow-derived mesenchymal stem cells (MSCs) after cell expansion by studying the spectrum of proteins secreted by cells into the culture medium. ACs and MSCs were expanded in monolayer cultures for some weeks, as done in standard cell transplantation procedures. Initially, the expression of cartilage signature genes was compared by real-time PCR. Metabolic labeling of proteins (SILAC) in combination with mass spectrometry (LC/MS-MS) was applied to investigate differences in released proteins. In addition, multiplex assays were carried out to quantify the amounts of several matrix metalloproteases (MMPs) and their natural inhibitors (TIMPs). Expanded chondrocytes showed a slightly higher expression of cartilage-specific genes than MSCs, whereas the overall spectra of released proteins were very similar for the two cell types. In qualitative terms MSCs seemed to secrete similar number of extracellular matrix proteins (43% vs. 45% of total proteins found) and catabolic agents (9% vs. 10%), and higher number of anabolic agents (12 % vs. 7%) compared to ACs. Some matrix-regulatory agents such as serpins, BMP-1, and galectins were detected only in MSC supernatants. Quantitative analyses of MMPs and TIMPs revealed significantly higher levels of MMP-1, MMP-2, MMP-3, and MMP-7 in the medium of ACs. Our data show that after the expansion phase, both ACs and MSCs express a dedifferentiated phenotype, resembling each other. ACs hold a phenotype closer to native cartilage at the gene expression level, whereas MSCs show a more anabolic profile by looking at the released proteins pattern. Our data together with the inherent capability of MSCs to maintain their differentiation potential for longer cultivation periods would favor the use of these cells for cartilage reconstruction.