Manipulation of macrophage polarization to facilitate repair in injured spinal cord

Abstract

Following spinal cord injury, the majority of macrophages inthe microenvironment are polarized to the M1 (pro-inflammatory)phenotype within the first week, and few to the M2 (anti-inflammatory) phenotype. Recent works that revealed positiveeffects of chondroitinase ABC (ChABC) on axonal growth in rat mod-els of spinal cord injury however indicated shift in macrophagepolarization towards M2. We hypothesize that cytokines normallysequestered by chondroitin sulphate (CS) moieties in the cord envi-ronment become mobilized with ChABC activity to mediate theshift in macrophage polarization. In this study, we used naïve (M0)macrophages derived from adult rat bone marrow as a model.Lipopolysaccharide (LPS) was added to the cultures to induce polar-ization of M0 macrophages to the M1 phenotype. Treatment of thecultures with ChABC led to lowered expression of M1 markers andelevated expression of M2 markers, compared to vehicle control.We further tested our hypothesis by live cell-labeling of proteinsassociated with the pericellular CS moieties with use of biotin, andanalyzing them using streptavidin-assisted pulldown assays fol-lowed by Western blot. The screening revealed the presence of IL10and IL4 among the tagged proteins, suggesting that the pericellularCS of M1 macrophages serve as a reservoir for M2 inducers. Under-standing the mechanisms of macrophage polarization would allowus to develop novel treatment strategies involving manipulation ofM2 polarization to enhance recovery from spinal cord injuries