Platelet Factor 4 Up-regulates the Expression of Matrix Metalloproteinase-9 in Macrophages via Toll-like Receptor 4

Aim To investigate whether platelet factor 4( PF4) modulates the matrix metalloproteinase-9( MMP-9) expression of macrophages. Methods THP-1 monocytes were differentiated into monocyte-derived macrophages by phorbol 12-myristate 13-acetate( PMA). After incubation with PF4( 0 ~ 200 μg /L),the MMP-9 expression of macrophages was determined by reverse-transcription polymerase chain reaction( RT-PCR) and Western blot. To determine the role of toll-like receptor 4( TLR4) in the regulation of MMP-9 expression,macrophages were pretreated with TLR4 blocker for 30 min,then incubated with PF4. Results Macrophages that were untreated showed a relatively low MMP-9 and TLR4 mRNA or protein levels; treatment of macrophages with PF4 increased MMP-9 and TLR4 expression. However,the high levels of MMP-9 and TLR4 expression induced by PF4 were significantly attenuated in the presence of TLR4 blocker.Conclusions PF4 may up-regulate MMP-9 expression in macrophages via TLR4.