Activation of Astrocytes in Vitro by Macrophages Polarized with Keratin Biomaterial Treatment

Reactive astrocytes contribute to glial scarring by rapid proliferation and up-regulation of glial fibrillary acidic protein (GFAP) expression and production of chondroitin sulfate proteoglycans (CSPGs). CSPGs play a crucial role in formation of the glial scar, which takes over the lesion site following spinal cord injury (SCI). This process corresponds to the inflammatory response of macrophages, which polarize toward a dominant pro-inflammatory M1 phenotype following SCI. The M1 phenotype is known to release various cytotoxic compounds that exacerbate the glial scar, which in turn impedes tissue regeneration. Recent studies have shown that anti-inflammatory M2 macrophages play a role in allowing neurite extensions to occur, even across inhibitory substrates, and can lessen the degree of secondary damage. Based on earlier results demonstrating that keratin biomaterials may polarize macrophages toward an anti-inflammatory M2 phenotype, we test the hypothesis that these polarized macrophages will have the potential to indirectly effect astrogliosis. Using an in vitro model of reactive astrogliosis, macrophage-conditioned media from cells that have been cultured with soluble keratin for 24 hours or 7 days appears to decrease reactivity and associates CSPG production. These results are statistically similar to the control M2 macrophage conditioned media. A comparable collagen-conditioned macrophage media does not resolve astrocyte reactivity, while control M1 macrophage conditioned media results in an increase in GFAP expression. These data suggest keratin-derived macrophages are more functionally similar to M2 macrophages and that keratin treatment may aid in limiting secondary inflammatory-mediated damage.