Activin A improves retinal pigment epithelial cell survival on stiff but not soft substrates.

In several retinal degenerative disease pathologies, such as dry age-related macular degeneration (AMD), the retinal pigment epithelium (RPE) cell monolayer becomes dysfunctional. Promising tissue engineering treatment approaches implant RPE cells on scaffolds into the subretinal space. However, these approaches are not without challenges. Two major challenges that must be addressed are RPE dedifferentiation and the inflammatory response to cell/scaffold implantation. Design and optimization of scaffold cues for the purpose of RPE transplantation remain relatively unexplored, specifically the mechanical properties of the scaffolds. Prior work from our group indicated that by varying substrate moduli significant differences could be induced in cell cytoskeleton structure, cellular activity, and expression of inflammatory markers. We hypothesized that Activin A would provide rescue effects for cells demonstrating dedifferentiated characteristics. Results demonstrated that for cells on low modulus scaffolds, the mechanical environment was the dominating factor and Activin A was unable to rescue these cells. However, Activin A did demonstrate rescue effects for cells on high modulus scaffolds. This finding indicates that when cultured on scaffolds with an appropriate modulus, exogenous factors, such as Activin A, can improve RPE cell expression, morphology, and activity, while an inappropriate scaffold modulus can have devastating effects on RPE survival regardless of chemical stimulation. These findings have broad implications for the design and optimization of scaffolds for long-term successful RPE transplantation.