Production of macrophage inflammatory protein-a following hypoxia/reoxygenation in glial cells

Polymorphonuclear neutrophils (PMNs) are known to mediate brain inflammatio n following hypoxia/reoxygenation (H/R), but the precise mechanisms leading to PMN recruitment are undefined. The alpha -chemokine macrophage inflamma tory protein-2 (MIP-S) has specificity for the recruitment of PMNs. In this study, we found that 8 or 12 h of hypoxia followed by 24-h reoxygenation ( H8/R24 or H12/R24) induced MIP-S secretion in cultures of enriched microgli a or mixed glia, respectively. Microglia, however, could not survive longer duration (>12 h) of hypoxia. Astrocytes did not produce any significant am ount of MIP-8 even though astrocytes maintained 98-99% viability following H12/R24. We also found that microglia survived the H/R treatment better (fo llowing H24) in the presence of astrocytes (mixed glial culture) than in mi croglia-enriched culture. Reoxygenation for prolonged periods (3 and 5 days ) following H24 resulted in progressively larger increases in MIP-8 product ion (20- and 60-fold, respectively) in mixed glial cultures. Immunocytochem ical staining revealed that the cells expressing MIP-8 in response to H/R w ere microglia rather than astrocytes in mixed glial cultures. Examination o f MIP-2 mRNA expression showed that WR upregulated MIP-S gene expression. T aken together, our data suggest that microglial cells are an important sour ce of MIP-8 production and suggest a potential injury mechanism involving b rain-derived production of MIP-8 in H/R. (C) 2000 Wiley-Liss, Inc.