Methylglyoxal induces platelet hyperaggregation and reduces thrombus stability by activating PKC and inhibiting PI3K/Akt pathway

Diabetes is characterized by a dysregulation of glucose homeostasis and platelets from patients with diabetes are known to be hyper-reactive and contribute to the accelerated development of vascular diseases. Since many of the deleterious effects of glucose have been attributed to its metabolite methylgyloxal (MG) rather than to hyperglycemia itself, the aim of the present study was to characterize the effects of MG on platelet function. Washed human platelets were pre-incubated for 15 min with MG and platelet aggregation, adhesion on matrix-coated slides and signaling (Western blot) were assessed ex vivo. In vivo, the effect of MG on thrombus formation was determined using the FeCl3-induced carotid artery injury model. MG potentiated thrombin-induced platelet aggregation and dense granule release, but inhibited platelet spreading on fibronectin and collagen. In vivo, MG accelerated thrombus formation but decreased thrombus stability. At the molecular level, MG increased intracellular Ca2+ and activated classical PKCs at the same time as inhibiting PI3K/Akt and the β3-integrin outside-in signaling. In conclusion, these findings indicate that the enhanced MG concentration measured in diabetic patients can directly contribute to the platelet dysfunction associated with diabetes characterized by hyperaggregability and reduced thrombus stability

Insulin Induces the Release of Vasodilator Compounds From Platelets by a Nitric Oxide–G Kinase–VAMP-3–dependent Pathway

Insulin-induced vasodilatation is sensitive to nitric oxide (NO) synthase (NOS) inhibitors. However, insulin is unable to relax isolated arteries or to activate endothelial NOS in endothelial cells. Since insulin can enhance platelet endothelial NOS activity, we determined whether insulin-induced vasodilatation can be attributed to a NO-dependent, platelet-mediated process

Cystathionine γ Lyase Sulfhydrates the RNA Binding Protein Human Antigen R to Preserve Endothelial Cell Function and Delay Atherogenesis

Hydrogen sulfide (H2S), generated by cystathionine γ lyase (CSE), is an important endogenous regulator of vascular function. The aim of the present study was to investigate the control and consequences of CSE activity in endothelial cells under physiological and proatherogenic conditions

Endothelial AMP-Activated Kinase α1 Phosphorylates eNOS on Thr495 and Decreases Endothelial NO Formation

AMP-activated protein kinase (AMPK) is frequently reported to phosphorylate Ser1177 of the endothelial nitric-oxide synthase (eNOS), and therefore, is linked with a relaxing effect. However, previous studies failed to consistently demonstrate a major role for AMPK on eNOS-dependent relaxation. As AMPK also phosphorylates eNOS on the inhibitory Thr495 site, this study aimed to determine the role of AMPKα1 and α2 subunits in the regulation of NO-mediated vascular relaxation. Vascular reactivity to phenylephrine and acetylcholine was assessed in aortic and carotid artery segments from mice with global (AMPKα−/−) or endothelial-specific deletion (AMPKαΔEC) of the AMPKα subunits. In control and AMPKα1-depleted human umbilical vein endothelial cells, eNOS phosphorylation on Ser1177 and Thr495 was assessed after AMPK activation with thiopental or ionomycin. Global deletion of the AMPKα1 or α2 subunit in mice did not affect vascular reactivity. The endothelial-specific deletion of the AMPKα1 subunit attenuated phenylephrine-mediated contraction in an eNOS- and endothelium-dependent manner. In in vitro studies, activation of AMPK did not alter the phosphorylation of eNOS on Ser1177, but increased its phosphorylation on Thr495. Depletion of AMPKα1 in cultured human endothelial cells decreased Thr495 phosphorylation without affecting Ser1177 phosphorylation. The results of this study indicate that AMPKα1 targets the inhibitory phosphorylation Thr495 site in the calmodulin-binding domain of eNOS to attenuate basal NO production and phenylephrine-induced vasoconstriction

Effect of MG on the phosphorylation of β3 integrin and Akt.

<p>(a) Effect of MG (MG, 1 mmol/L, 15 minutes) on fibronectin (Fn) and collagen (coll)-induced tyrosine phosphorylation of β3 integrin (Tyr747). (b) Effect of MG on thrombin -induced tyrosine phosphorylation (Tyr747) of β3 integrin in washed human platelets. (c) Effect of MG on fibronectin (Fn) and collagen (coll)-induced phosphorylation of Akt (Ser 473). (d) Effect of wortmannin (Wt, 20 nmol/L, 30 minutes) on fibronectin (Fn) and collagen (coll)-induced phosphorylation of β3 integrin (Tyr747) and Akt (Ser 473). The graphs summarise the data from 6 different experiments; *P<0.05, ***P<0.001 versus sol or CTL and ^# P<0.05, ^{# # #} P<0.001 versus agonists.</p

Effect of MG on platelet [Ca²⁺]_i and degranulation.

<p>(a) Increase in [Ca²⁺]_i measured in washed human platelets treated with either solvent (CTL) or methylglyoxal (MG, 1 mmol/L, 15 minutes) prior to the stimulation with thrombin. (b) Effect of MG pre-treatment on the thrombin (0.03U/ml)-induced release of ATP and (c) on the TRAP-induced surface expression of P-selectin. The graphs summarise the data from at least 6 different individuals; *P<0.05, **P<0.01 versus CTL.</p

Effect of MG on platelet adhesion, spreading and <i>in vivo</i> thrombus formation.

<p>(a) Representative pictures and (b) quantification of adherent and spread washed human platelets (to fibronectin (Fn)- or collagen (coll)-coated slides) pre-treated with either solvent (CTL) or methylglyoxal (MG, 1 mmol/L, 15 minutes). (c) Representative pictures (upper panel) and quantification (lower graphs) of the effect of <i>in </i><i>vivo</i> treatment of healthy mice with MG (1 mmol/L, 15 minutes) on thrombus size and time to peak after FeCl₃-induced injury of carotid artery. The graphs summarize data obtained in platelets from 12 subjects or 6 animals per group; *P<0.05, ***P<0.001, versus CTL.</p

Effect of MG on PKC activation.

<p>(a) Membrane translocation of PKCα and β in washed human platelets stimulated with either methylglyoxal (MG, 1 mmol/L, 15 minutes) or thrombin (0.03U/ml) alone or in combination. (b) Effect of methylglyoxal (MG, 1 mmol/L, 15 and 30 minutes) on the phosphorylation of MLC20 in the absence or in the presence of the PKC inhibitor Ro-318820 (Ro, 300 nM, 30 minutes). (c) Effect of MG on thrombin-induced phosphorylation of MLC20. (d) Effect of Ro-318220 on the thrombin-induced aggregation of washed human platelets treated or not with MG. The graphs summarise the data from 6-8 different experiments; *P<0.05, **P<0.01 versus CTL and ^# P<0.05, ^{# #} P<0.01 versus agonists.</p