Chondrogenic Potential of CD90+ Progenitors Figure 5. Staining and TEM of Derived Tissue from Normal sfMPCs. The resultant tissue-like masses were stained with antibodies to Collagen 2 (A) and Aggrecan (C), nuclei were stained with TOTO3 (B, D). Cells were found in closer association to each other (E), with higher magnification showing production of collagen fibres (F). Cells were also found in proximity with the produced collagen ECM (E, F). Scale bars represent 200 mM. doi:10.1371/journal.pone.0043616.g005 Since OA leads to a progressive loss of cartilage and synovial progenitors cells have the potential to contribute to articular cartilage repair in vivo [34], the inability of OA sfMPCs to spontaneously differentiate into chondrocytes suggests that cell-to- cell aggregation and/or communication may be impaired in OA and somehow dampen the normal mechanism of chondrocyte PLOS ONE | www.plosone.org 7 August 2012 | Volume 7 | Issue 8 | e43616