Osteopontin-deficient bone cells are defective in their ability to produceNO in response to pulsatile fluid flow

Osteopontin (OPN) is a noncollagenous component of bone matrix. It mediates cell attachment and activates signal transduction pathways. In this work, bone cells, cultured from fragments of long bones derived from wild-type an d OPN-/- ("knock-out") mice, were exposed to pulsatile fluid flow (PFF) ove r a 60-min period. The medium was assayed periodically for nitric oxide (NO ) and prostaglandin E-2 (PGE(2)) release. OPN+/+ cells exhibited a peak of NO production 5-10 min after the onset of PFF, decreasing to a stable plate au at 15 min; much less NO was produced by the OPN-/- cells. PFF resulted i n reduced PGE2 release by both cell types, although the reduction was less for the OPN-/- cells in the 15-30 min window. Both cell types exhibited a s imilar enhancement of cyclooxygenase2 mRNA levels 60 min after initiation o f PFF. These results suggest that bone cells require OPN to respond fully t o PFF as assessed by increased NO and reduced PGE synthesis. (C) 2001 Acade mic Press.