Abstract
Endothelial cells lining the blood vessels are principal players in vascular inflammatory responses. Dysregulation of endothelial cell function caused by hyperglycemia, dyslipidemia, and hyperinsulinemia often result in impaired vasoregulation, oxidative stress, inflammation, and altered barrier function. Various stressors including high glucose stimulate the release of nucleotides thus initiating signaling via purinergic receptors. However, purinergic modulation of inflammatory responses in endothelial cells caused by high glucose and palmitate remains unclear. In the present study, we investigated whether the effect of high glucose and palmitate is mediated by P2X7 and P2X4 and if they play a role in endothelial cell dysfunction. Transcript and protein levels of inflammatory genes as well as reactive oxygen species production, endothelial-leukocyte adhesion, and cell permeability were investigated in human umbilical vein endothelial cells exposed to high glucose and palmitate. We report high glucose and palmitate to increase levels of extracellular ATP, expression of P2X7 and P2X4, and inflammatory markers. Both P2X7 and P2X4 antagonists inhibited high glucose and palmitate-induced interleukin-6 levels with the former having a significant effect on interleukin-8 and cyclooxygenase-2. The effect of the antagonists was confirmed with siRNA knockdown of the receptors. In addition, P2X7 mediated both high glucose and palmitate-induced increase in reactive oxygen species levels and decrease in endothelial nitric oxide synthase. Blocking P2X7 inhibited high glucose and palmitate-induced expression of intercellular adhesion molecule-1 and vascular cell adhesion molecule-1 as well as leukocyte-endothelial cell adhesion. Interestingly, high glucose and palmitate enhanced endothelial cell permeability that was dependent on both P2X7 and P2X4. Furthermore, antagonizing the P2X7 inhibited high glucose and palmitate-mediated activation of p38-mitogen activated protein kinase. These findings support a novel role for P2X7 and P2X4 coupled to induction of inflammatory molecules in modulating high glucose and palmitate-induced endothelial cell activation and dysfunction.
Highlights
The metabolic syndrome is a condition that is defined by increased insulin resistance, type 2 diabetes (T2D), obesity, and hypertension
Glucose and palmitate could affect levels of extracellular adenosine 5’-triphosphate (eATP) in the human umbilical vein endothelial cells (HUVECs) and we observed a significant increase in the relative luminescence, which is proportional to the amount of ATP
Dietary factors contribute to the etiology and pathophysiology of the dysfunctional endothelium characterized by endothelial cell activation, augmented pro-inflammatory events, and attenuated barrier function increasing the risk of atherosclerosis
Summary
The metabolic syndrome is a condition that is defined by increased insulin resistance, type 2 diabetes (T2D), obesity, and hypertension. The vascular endothelium is a source of autocrine and paracrine mediators that modulate vascular tone, cell adhesion, permeability, and vessel wall inflammation wherein stimuli such as extracellular adenosine 5’-triphosphate (eATP), glucose, and palmitate are known triggers for inflammatory responses or activation of the inflammasome in various cell types [6,7,8,9]. High glucose is known to release eATP, which can orchestrate a cascade of events that lead to activation of the purinergic-signaling axis [13,14]. Increasing evidence points to the role of P2X7 and P2X4 in modulating inflammatory responses in both immune and non-immune cells as well as in the retinal and renal microvasculature [15,16,17,18,19,20]. Alterations in P2X7 expression and receptor-dependent responses are reported in T2D patient fibroblasts, β cells, and peripheral blood mononuclear cells (PBMCs) implicating this receptor in T2D pathogenesis [21,22,23]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
