Enhanced Platelet Aggregation and Thrombogenic Tendency in Adiponectin-Deficient Mice.

Adiponectin is a 30 kDa protein secreted specifically from adipocytes and structurally composed of two distinct domains, C-terminal collagen-like domain and N-terminal complement C1q-like globular domain. Adiponectin is abundantly present in plasma at high concentration ranging from 2 to 30 μg/ml. The plasma levels of adiponectin decreased in patients with obesity and diabetes. Recently it has been demonstrated that adiponectin has an anti-atherogenic activity. Hypoadiponectinemia is an independent risk factor for coronary artery disease in men. However, the role of adiponectin in hemostasis and thrombosis still remains obscure. In this study, we examined its role in hemostasis and thrombosis using adiponectin-deficient (APN-KO) mice (Nat. Med. 2002 Maeda et al.). APN-KO mice were fed by normal chaw and studied at 8–12 weeks old. There were no differences in platelet counts, PT, APTT and plasma fibrinogen levels between APN-KO and Wild-Type mice. Neither Wild-Type nor APN-KO mice showed detectable atherosclerotic lesion in carotid artery as well as whole aorta. We examined tail-bleeding times as a measure of primary hemostasis. The tail bleeding time was 96.9 ± 34.9 seconds in APN-KO mice, which was shorter than that in wild type mice (130.9 ± 52.1 seconds, n=30, p<0.05). We next studied thrombus formation in mice carotid artery using He-Ne laser induced in vivo thrombus formation model. Thrombus formation was induced by the interaction of irradiated He-Ne laser with evans blue dye injected into blood flow. The thrombus volumes formed during 10 minutes were significantly larger in APN-KO mice (6.74 ± 2.87 x 10⁷ arbitrary units for wild-type v.s. 13.4 ± 4.25 x 10⁷ arbitrary units for APN-KO mice, n=10, p<0.01). Adenovirus-mediated supplement of adiponectin compensated for the thrombotic tendency in APN-KO mice. In order to clarify the effects of adiponectin on platelet functon, we performed ex vivo experiments. In platelet aggregation studies under stirring conditions using platelet-rich plasma, platelet aggregation induced by low concentrations of agonists (ADP 2.5μM, collagen 2.5μg/ml, PAR4 peptide 75μM) was enhanced in APN-KO mice. Again the adenovirus-mediated supplement of adiponectin compensated for the enhancement of platelet aggregation. We next studied the thrombus formation on collagen coated surface under flow conditions. The thrombus formation was enhanced in APN-KO mice under shear rate at 250s⁻¹. Our data provide a first evidence that adiponectin plays a role in hemostasis and thrombosis as a negative modulator of platelet function.