In a recent study, we demonstrated that mesenchymal stem cells (MSCs) derived from the synovial membranes of bovine shoulder joints could differentiate into chondrocytes when cultured in alginate. The purpose of the present study was to establish the conditions under which synovial MSCs derived from aging human donors can be induced to undergo chondrogenic differentiation using the same alginate system.
MSCs were obtained by digesting the knee-joint synovial membranes of osteoarthritic human donors (aged 59-76 years), and expanded in monolayer cultures. The cells were then seeded at a numerical density of 4x10(6)/ml within discs of 2% alginate, which were cultured in serum-containing or serum-free medium (the latter being supplemented with 1% insulin, transferrin, selenium (ITS). The chondrogenic differentiation capacity of the cells was tested by exposing them to the morphogens transforming growth factor-beta1 (TGF-beta1), TGF-beta2, TGF-beta3, insulin-like growth factor-1 (IGF-1), bone morphogenetic protein-2 (BMP-2) and BMP-7, as well as to the synthetic glucocorticoid dexamethasone. The relative mRNA levels of collagen types I and II, of aggrecan and of Sox9 were determined quantitatively by the real-time polymerase chain reaction (PCR). The extracellular deposition of proteoglycans was evaluated histologically after staining with Toluidine Blue, and that of type-II collagen by immunohistochemistry.
BMP-2 induced the chondrogenic differentiation of human synovial MSCs in a dose-dependent manner. The response elicited by BMP-7 was comparable. Both of these agents were more potent than TGF-beta1. A higher level of BMP-2-induced chondrogenic differentiation was achieved in the absence than in the presence of serum. In the presence of dexamethasone, the BMP-2-induced expression of mRNAs for aggrecan and type-II collagen was suppressed; the weaker TGF-beta1-induced expression of these chondrogenic markers was not obviously affected.
We have demonstrated that synovial MSCs derived from the knee joints of aging human donors possess chondrogenic potential. Under serum-free culturing conditions and in the absence of dexamethasone, BMP-2 and BMP-7 were the most potent inducers of this transformation process.