Abstract 16167: Homocysteine Induces Phosphorylation of Y731 on VE-cadherin by Activating a Metabotropic-to-Ionotropic Glutamate Receptor Cascade
Elevated plasma homocysteine (Hcy) induces multiple pathologic effects in vascular endothelium, but the mechanisms are poorly understood. Endothelial cell-cell (EC-EC) junctions are critical for maintaining the integrity of the endothelium. The adherens junction protein VE-cadherin is important in maintaining and regulating EC-EC junctions. Phosphorylation of VE-cadherin is a major signaling mechanism controlling EC-EC adherence. In neuronal tissue, Hcy activates both ionotropic (NMDAr) and metabotropic (mGluR5) glutamate receptors, which we have found to be expressed on cerebral endothelial cells. We tested the hypotheses that 1) Hcy induces phosphorylation of Y731 on VE-cadherin by activating mGluR5 and NMDAr and 2) this phosphorylation is dependent on activation of PKC. Using cerebral microvascular endothelial cells (bEnd.3), we found that Hcy increases phosphorylation (western blot and ELISA) of Y731 on VE-cadherin in a dose- and time-dependent manner (p<0.05). This response is attenuated with NMDAr and mGluR5 specific antagonists, memantine (100 μM) and MPEP (10 μM) respectively (p<0.05). Treating bEnd.3 with the NMDAr and mGluR5 specific agonists, NMDA (25 μM) and CHPG (25 μM), also increases Y731 phosphorylation on VE-cadherin (p<0.05). Activating the mGluR5 receptor with CHPG and simultaneously inhibiting the NMDAr receptor with memantine ameliorates the response of CHPG alone, while activating NMDAr and inhibiting mGluR5 does not (p<0.05). PKC inhibition with bisindolylmaleimide-I (1 μM) reduced Hcy, NMDA, and CHPG induced Y731 phosphorylation on VE-cadherin (p<0.05). All of the p-values expressed here represent n=10–32 where experiments were repeated 2–4 times. Our data show that Hcy induces phosphorylation of Y731 on VE-cadherin by activating mGluR5 receptors, which in turn drives an NMDAr-dependent response. PKC activation is required in this signaling cascade. These data demonstrate a fundamentally new mechanism for Hcy-mediated vascular dysfunction and present a new set of targets for testing therapeutic strategies in hyperhomocysteinemia.
- © 2010 by American Heart Association, Inc.