von Willebrand factor antagonizes nitric oxide synthase to promote insulin resistance during hypoxia

Hypoxic respiratory diseases or hypoxia exposures are frequently accompanied by glucose intolerance and impaired nitric oxide (NO) availability. However, the molecular mechanism responsible for impaired NO production and insulin resistance (IR) during hypoxia remains obscure. In this study, we investigated the possible mechanism of impaired NO production and IR during hypoxia in a mouse model. Mice were exposed to hypoxia for different periods of time (0-24 h), and parameters of IR and endothelial dysfunctions were analyzed. Exposure to hypoxia resulted in a time-dependent increase in IR as well as multimeric forms of von Willebrand factor (vWF) and subsequently a decrease in eNOS activity. Preincubation with plasma of hypoxia-exposed animals (different time points) or human vWF inhibited insulin-induced NO production in a dose-dependent manner; larger doses of insulin reversed the effect. In contrast, preincubation of vWF-immunodepleted plasma failed to inhibit insulin-induced NO production, whereas vWF immunoneutralization abolished the effect of hypoxia-induced IR and D-[U-(14)C]glucose uptake. Furthermore, the interactions between vWF and eNOS were studied by far-Western blotting, co-immunoprecipitation, and surface plasma resonance spectroscopy. Kinetic analyses showed that the dissociation constant (KD), inhibitory constant (Ki), and half-maximal inhibitory concentration (IC50) were 1.79 × 10(-8) M, 250 pM, and 18.31 pM, respectively, suggesting that vWF binds to eNOS with a high affinity and greater efficacy for activator (insulin) inhibition. These results indicated that vWF, an antagonist of eNOS, inhibits insulin-induced NO production and causes IR.