Glycated LDL increase VCAM-1 expression and secretion in endothelial cells and promote monocyte adhesion through mechanisms involving endoplasmic reticulum stress

Abstract

Type 2 Diabetes Mellitus is a worldwide epidemic, and its atherosclerotic complications produce morbidity and mortality in affected patients. It is known that the vascular cell adhesion molecule-1 (VCAM-1) levels are increased in the sera of diabetic patients. Our aim was to investigate the impact of the endoplasmic reticulum stress (ERS) in VCAM-1 expression and secretion in human endothelial cells (HEC) exposed to glycated low-density lipoproteins (gLDL). The results showed that 24 h incubation of HEC with gLDL induces (i) stimulation of VCAM-1 expression and secretion, determining increased monocyte adhesion to HEC; (ii) RAGE up-regulation and free cholesterol loading; (iii) ERS activation (increased eIF2α phosphorylation and CHOP mRNA levels, and decreased GRP78 protein expression); and (iv) oxidative stress [increased levels of reactive oxygen species (ROS) and glutamate cysteine ligase catalytic unit gene expression]. Treatment of gLDL-exposed HEC with ERS inhibitors, salubrinal (Sal) and sodium phenylbutyrate (PBA), decreased intracellular ROS. Incubation of gLDL-exposed cells with the anti-oxidant N-acetyl-cysteine (NAC) reduced ERS, revealed by decreased eIF2α phosphorylation and CHOP gene expression and increased GRP78 expression, thus validating the interconnection between ERS and oxidative stress. Sal, PBA, NAC and inhibitors of p38 MAP kinase and NF-kB induced the decrease of VCAM-1 expression and of the ensuing monocyte adhesion induced by gLDL. In conclusion, in HEC, gLDL stimulate the expression of cellular VCAM-1, the secretion of soluble VCAM-1, and the adhesion of monocytes through mechanisms involving p38 MAP kinase and NF-kB signalling pathways activated by RAGE, ERS and oxidative stress, thus contributing to diabetic atherosclerosis.

Caffeic acid attenuates the inflammatory stress induced by glycated LDL in human endothelial cells by mechanisms involving inhibition of AGE‐receptor, oxidative, and endoplasmic reticulum stress

“…It is well known that the inflammatory stress is directly linked to the oxidative stress, well known for its contribution to the diabetic complications . Using NAC, a wide spectrum antioxidant, we have previously shown and now confirm that inhibition of the oxidative stress diminishes VCAM‐1 secretion from gLDL‐ exposed HEC . In addition, we now show that CRP secretion in gLDL‐exposed HEC is also inhibited by NAC, in good agreement with a previous published study in HEC incubated with electronegative LDL .…”

“…Moreover, CAF decreases the secretion of VCAM‐1 and MCP‐1 induced by gLDL in HEC, the results confirming previous data showing that CAF decreases inflammation in HEC incubated with resistin or high glucose or in a hyperhomocysteinemia in vivo model by attenuating NF‐kB signaling . We have previously shown that the secretion of VCAM‐1 and MCP‐1 is stimulated in gLDL‐exposed HEC by activation of NF‐kB . The addition of CAF in the culture medium of gLDL‐exposed HEC decreased the phosphorylation of p65 subunit of NF‐kB (data not shown), confirming the latter as an important molecular mechanism for the observed anti‐inflammatory properties of CAF.…”

“…Our results are in good agreement with previously reported data showing that CAF decrease NOX4 in the liver of fluoride-treated rats [34]. Our previous results show that the oxidative stress induced by gLDL in HEC is directly connected with ERS, and that VCAM-1 secretion is ERS-dependent [11]. Using SAL, an ERS inhibitor, we show for the first time that CRP expression in gLDLexposed HEC is diminished by ERS alleviation.…”

“…Interestingly, it was shown that the interaction of RAGE with HMGB1 determines an inflammatory response in EC, by the activation of ERS . We and others have previously shown and now confirm that gLDL stimulate RAGE expression in HEC . Furthermore, we now demonstrate that inhibition of gLDL–RAGE interaction induces the decrease of VCAM‐1 and MCP‐1 secretion in HEC culture medium.…”

“…activation of NF-kB [9,11]. The addition of CAF in the culture medium of gLDL-exposed HEC decreased the phosphorylation of p65 subunit of NF-kB (data not shown), confirming the latter as an important molecular mechanism for the observed anti-inflammatory properties of CAF.…”