High capacity of purified mesenchymal stem cells for cartilage regeneration

Abstract

Mesenchymal stem cells (MSCs) are a heterogeneous population of cells that proliferate and differentiate into bone, cartilage, and fat in vitro. Because of this multi-potency, the therapeutic applications of MSCs are under intensive exploration. The most common and redundant method for MSC cultivation requires prolonged culture on plastic dishes. The current study compared the differentiation/proliferative potency of purified mouse MSCs (CD45^-/ TER119^-/PDGFRα⁺/ Sca-1⁺ cells, or PαS cells) with whole bone marrow (WBM)-derived, plastic-adherent MSCs. After three passages, the surface expression levels of CD45, TER119, PDGFRα, and Sca-1 were evaluated in WBM and PαS cells. While PαS cells maintained high expression levels of both PDGFRα and Sca-1, WBM cells exhibited less expressed levels of these stem cell makers. Additionally, WBM cell cultures were frequently contaminated by CD45⁺ hematopoietic cells. Both cell migration and proliferation were significantly higher in PαS vs. WBM cells, indicating the enhanced differentiation potential of PαS cells for the mesenchymal lineage, and suggesting that WBM cell heterogeneity may regulate and limit the stemness of their MSC progeny. Consistent with this hypothesis, PαS cells transplanted locally at sites of cartilage defects displayed higher cartilage regeneration capacity than WBM cells in a rat osteochondral defect model. This is the first report to demonstrate its improved contribution to cartilage repair in vivo. Thus, the protocol employed for MSC isolation is crucial for the effective translation of MSC multi-potency into clinical therapeutics.