Biophysical and chemical effects of fibrin on mesenchymal stromal cell gene expression

Mesenchymal stromal cells (MSCs) are multipotent cells that have high expansion yields and fibrin is a native extracellular matrix (ECM) material widely used for cell delivery and surgery. MSCs and fibrin have tremendous potential for tissue engineering applications, but the effect of fibrin on MSCs is not well characterized. The purpose of this study was to analyze the role of fibrin in modulating MSC phenotype by gene expression analysis. The results demonstrate that fibrin up-regulated MSC gene expression of vasculogenic (FLK1, ACTA2, VECAD, SM22 and CNN1), myogenic (MYF5 and MYH13), neurogenic (TH and GFAP) and chondrogenic (COL2A1) markers after 5 days incubation. These gene expression results were supported by induction of expression on the protein level for early lineage-specific markers such as ACTA2, FLK1 and MYF5. The ability of fibrin to modulate MSC gene expression was not affected by matrix pore size (80-110 microm diameter) or Young's modulus (5-25k Pa) and the differential expression of some phenotypic markers could be partially mimicked by other ECM proteins, such as fibronectin and collagen I. In some cases the inductive effect of fibrin on gene expression could be further augmented by the treatment with growth factors such as nerve growth factor. However, the effect of fibrin appeared to be limited, as MSCs did not differentiate into fully mature cells based on immunofluorescence staining after 12 days. This body of work provides a rational approach for studying the interactions of MSC with fibrin, which has important therapeutic implications for the delivery of stem cells.