Osteopontin directly modulates cytokine expression of primary microglia and increases their survival.

Osteopontin (OPN) is constitutively expressed in the brain and upregulated during neuroinflammation, e.g., focal cerebral ischemia. In OPN-deficient mice, microglia are deregulated after ischemia, but specific OPN-effects on microglia remain elusive. Primary microglia were cultured in the presence or absence of OPN. The survival of microglia under stress conditions was dose-dependently increased by OPN. Lipopolysaccharides (LPS)-induced release of nitric oxide (NO), TNF-α, and IL-6, as well as expression of inducible Nitric Oxide Synthase (iNOS), were attenuated by OPN. Data suggest that OPN modulates microglia function by shifting their inflammatory profile towards a neutral anti-inflammatory phenotype.