TITLE:
Activation of Astrocytes in Vitro by Macrophages Polarized with Keratin Biomaterial Treatment
AUTHORS:
Bailey V. Fearing, Mark E. Van Dyke
KEYWORDS:
Keratin, Macrophage, Astrocyte, Glial Scar, Inflammation, Spinal Cord Injury, CSPGs
JOURNAL NAME:
Open Journal of Regenerative Medicine,
Vol.5 No.1,
March
4,
2016
ABSTRACT: 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.