Insulin inhibits tissue factor expression in monocytes

Objectives: Platelets from healthy subjects are inhibited by insulin but type 2 diabetes mellitus (T2DM) platelets have become insulin-resistant, which might explain their hyperactivity. In the present study we investigated whether monocytes are responsive to insulin. Methods and results: LPS-induced tissue factor (TF) upregulation was measured in human monocytes and monocytic THP-1 cells in a factor Xa generation assay. Insulin (0.1-100 nmol L-1) induced a dose-dependent inhibition in both cell types and in monocytes 100 nmol L-1 insulin inhibited cytosolic, membrane-bound and microparticle TF by 32 +/- 2, 27 +/- 3 and 52 +/- 4% (n = 3). Insulin induced Tyr phosphorylation of the insulin receptor (INS-R) and formation of an INS-R - G(i)alpha(2) complex, suggesting interference with LPS-induced cAMP control. Indeed, insulin interfered with LPS-induced cAMP decrease and TF upregulation in a manner similar to an inhibitor of G(i) (pertussis toxin) and agents that raise cAMP (iloprost, forskolin, IBMX) reduced TF upregulation. Although LPS failed to raise cytosolic Ca2+, quenching of Ca2+ increases (BAPTA-AM) reduced and induction of Ca2+ entry (ionophore, P2X7 activation) enhanced upregulation of TF mRNA and procoagulant activity. Insulin interfered with MCP-1-induced Ca2+ mobilization but not with ATP-induced Ca2+ rises. Conclusions: Insulin inhibits TF expression in monocytes and monocyte-derived microparticles through interference with G(i)alpha(2)-mediated cAMP suppression, which attenuates Ca2+-mediated TF synthesis.