# Human Retinal Progenitor Cell (hRPC) Migration in Three-Dimensional (3D) Environments of Varying Stiffness and Composition

## TL;DR

This study explores how human retinal progenitor cells migrate in 3D environments with different stiffness and composition to improve retinal cell implantation success.

## Contribution

The study identifies how material stiffness and soluble factors like SDF and HGF influence hRPC migration in 3D gels.

## Key findings

- hRPCs migrated more in nonphoto crosslinked collagen gels with higher stiffness and gel component concentrations.
- Soluble factors SDF and HGF increased hRPC migration compared to media alone.
- Akt and MAPK signaling pathways were found to correlate with hRPC migration.

## Abstract

Retinal degeneration is the leading cause of blindness worldwide. Subretinal implantation of human retinal progenitor cells (hRPCs) has shown great promise in models of retinal degeneration for restoration of vision but is limited by extremely low (< 2%) integration into the retina. Successful integration of implanted cells requires their migration from the site of implantation into the degenerating retina. Little is known about what cues promote RPC migration in the context of the postimplantation microenvironment, such as cues presented by a biomaterial carrier. We utilized a high-throughput assay to study the migration of hRPCs in three-dimensional hydrogel matrices of varying chemical composition and stiffness and, with exposure to different soluble factors, to identify cues important for hRPC migration and associated cell signaling events driving migration. Collagen type I, collagen type I methacrylate, and hyaluronic acid glycidyl methacrylate gels were developed with variable stiffness. The impact of key growth factors in neural development, regeneration, and cell migration such as epidermal growth factor (EGF), fibroblast growth factor (FGF), stromal cell–derived factor (SDF), and hepatocyte growth factor (HGF) was studied using hRPCs in 2 mg/mL collagen type I gels. Migration of the hRPCs varied significantly in gels of different composition and stiffness, with higher levels of mean migration distance after 48 h in nonphoto crosslinked collagen-based gels with higher concentrations of gel components and associated compressive moduli. In addition, the presence of SDF and HGF in collagen gels increased hRPC migration compared to media alone. Key signaling nodes correlating with hRPC migration were identified in Akt and MAPK signaltransduction pathways using bead-based multiplex ELISA and partial least-squares regression (PLSR) modeling. These results motivate the further exploration of material stiffness and co-delivery of soluble factors as important design parameters in cell delivery vehicles to promote transplanted hRPC migration and successful integration into degenerating retina.