Abstract
BackgroundExcessive levels of methylglyoxal (MG) encountered in diabetes foster enhanced leukocyte-endothelial cell interactions, mechanisms of which are incompletely understood. MG genomically upregulates endothelial serum- and glucocorticoid-inducible kinase 1 (SGK1) which orchestrates leukocyte recruitment by regulating the activation and expression of transcription factors and adhesion molecules. SGK1 regulates a myriad of ion channels and carriers including the Na+/H+ exchanger NHE1. Here, we explored the effect of MG on SGK1-dependent NHE1 activation and the putative role of NHE1 activation in MG-induced leukocyte recruitment and microvascular hyperpermeability.MethodsUsing RT-PCR and immunoblotting, we analyzed NHE1 mRNA and protein levels in murine microvascular SVEC4-10EE2 endothelial cells (EE2 ECs). NHE1 phosphorylation was detected using a specific antibody against the 14-3-3 binding motif at phospho-Ser703. SGK in EE2 ECs was silenced using targeted siRNA. ROS production was determined using DCF-dependent fluorescence. Leukocyte recruitment and microvascular permeability in murine cremasteric microvasculature were measured using intravital microscopy. The expression of endothelial adhesion molecules was determined by immunoblotting and confocal imaging analysis.ResultsMG treatment significantly upregulated NHE1 mRNA and dose-dependently increased total- and phospho-NHE1. Treatment with SGK1 inhibitor GSK650394, antioxidant Tempol and silencing SGK all blunted MG-triggered phospho-NHE1 upregulation in EE2 ECs. NHE1 inhibitor cariporide attenuated MG-triggered ROS production, leukocyte adhesion and emigration and microvascular hyperpermeability, without affecting leukocyte rolling. Cariporide treatment did not alter MG-triggered upregulation of P- and E-selectins, but reduced endothelial ICAM-1 expression.ConclusionMG elicits SGK1-dependent activation of endothelial Na+/H+ exchanger NHE1 which participates in MG-induced ROS production, upregulation of endothelial ICAM-1, leukocyte recruitment and microvascular hyperpermeability. Pharmacological inhibition of NHE1 attenuates the proinflammatory effects of excessive MG and may, thus, be beneficial in diabetes-associated inflammation.
Highlights
Increased interaction of leukocytes with activated vascular endothelium participates in the inflammatory sequelae of diabetes [1,2,3]
We found that treatment of EE2 SVEC4-10EE2 endothelial cells (ECs) with MG significantly enhanced Na+/H+ exchanger 1 (NHE1) and phospho-NHE1 in a dose-dependent manner, an effect reaching statistical significance at 100 μM MG (NHE1) and 50 μM respectively (Figure 1A)
To corroborate our in vitro observations, we demonstrate that an intrascrotal injection of MG for 4 h significantly upregulated total- and phospho-NHE1 levels in cremaster muscle (Figure 1C)
Summary
Increased interaction of leukocytes with activated vascular endothelium participates in the inflammatory sequelae of diabetes [1,2,3]. MG was shown to temporally activate glycogen synthase kinase 3 (GSK3) and serum- and glucocorticoidinducible kinase 1 (SGK1) which, in turn, stimulate endothelial nuclear factor-κB (NF-κB) and cyclic AMP response element-binding protein (CREB), two transcription factors that are important in mediating inflammatory responses [22]. SGK1 regulates a wide array of ion channels and carriers including the Na+/H+ exchangers NHE1 and NHE3 [24,25,26,27,28,29]. Excessive levels of methylglyoxal (MG) encountered in diabetes foster enhanced leukocyte-endothelial cell interactions, mechanisms of which are incompletely understood. MG genomically upregulates endothelial serum- and glucocorticoid-inducible kinase 1 (SGK1) which orchestrates leukocyte recruitment by regulating the activation and expression of transcription factors and adhesion molecules. We explored the effect of MG on SGK1-dependent NHE1 activation and the putative role of NHE1 activation in MG-induced leukocyte recruitment and microvascular hyperpermeability
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