Induction and temporal changes of osteopontin mRNA and protein in the brain following systemic lipopolysaccharide injection.

We analyzed expression of osteopontin (OPN), a cytokine regulating tissue repair and inflammation, in astrocytes and microglia in response to systemic lipopolysaccharide (LPS) administration (250 microg/100 g). OPN mRNA expression appeared in subpial astrocytes as early as 6 h, and then spread over the brain parenchyma. The signal for OPN mRNA reached a peak at 24 h post-injection, and returned to basal levels after 48 h. Changes in OPN immunoreactivity in the LPS-injected rat mirrored OPN mRNA induction patterns. These results provide the first evidence of OPN induction in astrocytes and microglia following peripheral immune challenge, and suggest that OPN may play a key role in the pathogenesis of neuroinflammation.