OBJECTIVEThe expression of tissue factor (TF) in vascular smooth muscle cells (VSMCs) plays an important role in the pathogenesis of artherosclerosis (AS) and thrombosis. Hyperhomocysteinemia is a risk factor for AS. Annexin A5, a calcium-dependent anionic-phospholipid-binding protein has anticoagulant effect mediated by its interaction with phosphatidylserine. We investigated the effects of Annexin A5 on homocysteine (Hcy)-induced TF expression and activity in VSMCs.

METHODSHuman umbilical artery VSMCs were cultured by tissue explanting method, incubated with Hcy at various concentrations in the absence and presence of Annexin A5 (50 microg/ml)/mono-TFAb (10 microg/ml). Flow Cytometry (FCM) was used to detect the expression of TF on the surface of VSMCs. Protein expression of TF was detected by Western blot. Determination of TF activity by factor Xa generation.

RESULTSThe expression level of TF protein on the surface of the resting VSMCs was low [the positive rate was (4.01 +/- 2.11)%] and could be upregulated by Hcy [peaked at 1000 micromol/L, the positive rate was (37.67 +/- 4.96)%]. Annexin A5, as well as mono-TFAb could significantly inhibit Hey-induced TF membrane expression, release activity and protein expression.

CONCLUSIONSThese results suggest that Annexin A5 could inhibit Hcy-induced expression and activity of TF in VSMCs as well as TF release of VSMCs. Annexin A5 might play an active role on attenuating AS and reducing coronary thrombosis by inhibiting TF pathway.