Making cartilage from fat-based stem cells would be so much more attractive if we didn’t have to use exogenous sources of growth factors. Nevertheless, fat-based stem cells remain quite attractive as a source of cartilage since these cells can be grown in culture to large numbers and can also be readily differentiated into chondrocytes if they are stimulated with the growth factor transforming growth factor-β1 (TGF-β1). Using exogenous TGF-β1, however, has side undesirable effects. Is there another way?
Maybe. A new study by Loran Solorio and Eben Alsberg at Case Western Reserve University has used a culture medium containing TGF-β1-loaded microspheres to make cartilage from fat-based stem cells in culture. This technique can make cartilage without any exogenous growth factors, since all growth factors required for cartilage production are found within the culture system.
In this study, Solorio and Alsberg used exogenous TGF-β1 to induce cartilage formation in fat-based stem cells that were grown in sheets. These sheets of cells made cartilage after 3 weeks. Once it was clear that their experimental system worked well, they used TGF-β1-loaded gelatin microspheres to deliver the growth factor. By tweaking the quantity of microspheres and the concentration of TGF-β1 required for this to work, Solorio and Alsberg showed that the use of TGF-β1-loaded microspheres could induce cartilage formation as well as exogenous TGF-β1. Staining for cartilage-specific molecules and detailed microscopic observation of the cartilage showed that it was indeed, good, solid cartilage.
This publication is the first demonstration of the self-assembly of fat-derived stem cells into high-density cell sheets capable of forming cartilage in the presence of TGF-β1-releasing microspheres. The incorporation of these microspheres might bypass the need for extended culture of the stem cells, potentially allowing stem cells sheets to be implanted more rapidly into defects to regenerate cartilage in a living organism.