-Gal Nanoparticles in CNS Trauma: I. In Vitro Activation of Microglia Towards a Pro-Healing State

Background:Macrophages and microglia play critical roles after spinal cord injury (SCI), with the pro-healing, anti-inflammatory (M2) subtype being implicated in tissue repair. We hypothesize that promoting this phenotype within the post-injured cord microenvironment may provide beneficial effects for mitigating tissue damage. As a proof of concept, we propose the use of nanoparticles incorporating the carbohydrate antigen, galactose-alpha-1,3-galactose (alpha-gal epitope) as an immunomodulator to transition human microglia (HMC3) cells toward a pro-healing state.Methods:Quiescent HMC3 cells were acutely exposed to alpha-gal nanoparticles in the presence of human serum and subsequently characterized for changes in cell shape, expression of anti or pro-inflammatory markers, and secretion of phenotype-specific cytokines.Results:HMC3 cells treated with serum activated alpha-gal nanoparticles exhibited rapid enlargement and shape change in addition to expressing CD68. Moreover, these activated cells showed increased expression of anti-inflammatory markers like Arginase-1 and CD206 without increasing production of pro-inflammatory cytokines TNF-alpha or IL-6.Conclusion:This study is the first to show that resting human microglia exposed to a complex of alpha-gal nanoparticles and anti-Gal (from human serum) can be activated and polarized toward a putative M2 state. The data suggests that alpha-gal nanoparticles may have therapeutic relevance to the CNS microenvironment, in both recruiting and polarizing macrophages/microglia at the application site. The immunomodulatory activity of these alpha-gal nanoparticles post-SCI is further described in the companion work (Part II).Graphical abstractResting microglia subjected to alpha-gal nanoparticle treatment in the presence of anti-Gal (found in serum) become activated and exhibit pro-healing phenotypic markers (Arginase-1, CD206) and secrete VEGF. Expression of pro-inflammatory markers (IL-6, TNF-alpha) was concomitantly reduced.