Endothelial surface N-glycans mediate monocyte adhesion and are targets for anti-inflammatory effects of peroxisome proliferator-activated receptor γ ligands.

Endothelial-monocyte interactions are regulated by adhesion molecules and key in the development of vascular inflammatory disease. Peroxisome proliferator-activated receptor (PPAR) γ activation in endothelial cells is recognized to mediate anti-inflammatory effects that inhibit monocyte rolling and adhesion. Herein, evidence is provided for a novel mechanism for the anti-inflammatory effects of PPARγ ligand action that involves inhibition of proinflammatory cytokine-dependent up-regulation of endothelial N-glycans. TNFα treatment of human umbilical vein endothelial cells increased surface expression of high mannose/hybrid N-glycans. A role for these sugars in mediating THP-1 or primary human monocyte rolling and adhesion was indicated by competition studies in which addition of α-methylmannose, but not α-methylglucose, inhibited monocyte rolling and adhesion during flow, but not under static conditions. This result supports the notion that adhesion molecules provide scaffolds for sugar epitopes to mediate adhesion with cognate receptors. A panel of structurally distinct PPARγ agonists all decreased TNFα-dependent expression of endothelial high mannose/hybrid N-glycans. Using rosiglitazone as a model PPARγ agonist, which decreased TNFα-induced high mannose N-glycan expression, we demonstrate a role for these carbohydrate residues in THP-1 rolling and adhesion that is independent of endothelial surface adhesion molecule expression (ICAM-1 and E-selectin). Data from N-glycan processing gene arrays identified α-mannosidases (MAN1A2 and MAN1C1) as targets for down-regulation by TNFα, which was reversed by rosiglitazone, a result consistent with altered high mannose/hybrid N-glycan epitopes. Taken together we propose a novel anti-inflammatory mechanism of endothelial PPARγ activation that involves targeting protein post-translational modification of adhesion molecules, specifically N-glycosylation.

Anti-inflammatory effects of isoflavones are dependent on flow and human endothelial cell PPARgamma.

The mechanisms by which isoflavones protect against inflammatory vascular disease remain unclear. Our previous observations suggest that one mechanism involves inhibition of monocyte-endothelial cell interactions in a process that is absolutely dependent on flow. The molecular mechanisms involved and the effects of structurally distinct isoflavones on this process are not known and are investigated herein. Using static and flow-dependent monocyte adhesion assays, our data show that exposure of endothelial cells to biologically relevant concentrations of isoflavones inhibits subsequent TNF-alpha induced monocyte adhesion only during flow. This inhibition involved activating endothelial PPARgamma by stimulating promoter sequences containing the PPARgamma response element by isoflavones and attenuating antiadhesive effects by siRNA targeting of PPARgamma. A comparison of structurally distinct isoflavones suggested a critical role for the A-ring. Using chlorinated derivatives of daidzein, a key structural requirement for PPARgamma agonist activity appears to be the presence of the 7-OH group and the lack of chlorine at the 6- or 8-positions in the A-ring. Collectively, these data support 1) a novel flow-dependent anti-inflammatory mechanism for PPARgamma ligands in vascular endothelial cells and 2) exemplify the current concepts of nutrients modulating disease via regulating specific cell signaling pathways.

Revealing anti-inflammatory mechanisms of soy isoflavones by flow: modulation of leukocyte-endothelial cell interactions.

The antiatherogenic effects of soy isoflavone consumption have been demonstrated in a variety of studies. However, the mechanisms involved remain poorly defined. Adhesion of monocytes to vascular endothelial cells is a key step within the inflammatory cascade that leads to atherogenesis. Many factors, including the physical forces associated with blood flow, regulate this process. Using an in vitro flow assay, we report that genistein, a principal component of most isoflavone preparations, inhibits monocyte adhesion to cytokine (TNF-alpha)-stimulated human vascular endothelial cells at physiologically relevant concentrations (0-1 microM). This effect is absolutely dependent on flow and is not observed under static conditions. Furthermore, this inhibition was dependent on activation of endothelial peroxisomal proliferator-activated receptor-gamma. No significant role for other reported properties of genistein, including antioxidant effects, inhibition of tyrosine kinases, or activation of estrogen receptors, was observed. Furthermore, the antiadhesive effects of genistein did not occur via modulation of the adhesion molecules E-selectin, ICAM-1, VCAM-1, or platelet-endothelial cell adhesion molecule-1. These data reveal a novel anti-inflammatory mechanism for isoflavones and identify the physical forces associated with blood flow and a critical mediator of this function.