The role of ERK signaling in protein hydrogel remodeling by vascular smooth muscle cells.

Collagen type I and fibrin hydrogels have been used for cell-based therapies and tissue engineering. These matrices can be broken down and remodeled by cells, but the effects that these proteins have on cell function are not completely understood. We examined activation of the extracellular signal-regulated kinase (ERK) signaling pathway by vascular smooth muscle cells (VSMC) in response to 2D and 3D matrices of type I collagen, fibrin, or a 1:1 composite mixture of these proteins. After 3 days of culture, ERK phosphorylation, osteopontin secretion, and MMP-2 activation were all markedly increased in 3D matrices, compared with 2D substrates. A strong positive correlation existed between these protein markers of the synthetic phenotype and phosphorylated ERK levels, and this relationship persisted across matrix geometries and compositions. Cell proliferation in 3D matrices was inversely correlated to ERK activation, while on 2D substrates a modest positive correlation was observed. Pharmacologic inhibition of ERK signaling confirmed that this pathway was involved in the observed phenotype shifts. This study suggests that contextual activation of the ERK pathway results in different effects on cell phenotype, depending on the geometry and composition of the ECM. These findings add to our understanding of cell function and remodeling in protein-based hydrogel biomaterials.