Proceedings of The Physiological Society

Physiology 2016 (Dublin, Ireland) (2016) Proc Physiol Soc 37, PCA353

Poster Communications

Human monocytes adhere to vascular smooth muscle cells in a proinflammatory environment

S. M. Drysdale1, G. A. Gibson2, H. M. Wilson1, G. F. Nixon1

1. School of Medical Sciences, University of Aberdeen, Aberdeen, United Kingdom. 2. Cardiothoracic Surgery, Aberdeen Royal Infirmary, Aberdeen, United Kingdom.

Endothelial denudation following angioplasty in occluded blood vessels increases neointimal growth and leads to re-occlusion. Increased inflammation via the adhesion of circulating monocytes to exposed vascular smooth muscle cells (VSMCs) in denuded vessels may be involved. The aims of this study were to determine if human monocytes can adhere to human VSMCs and examine mediators which might regulate this process. VSMCs were cultured from saphenous veins obtained from patients undergoing coronary artery bypass surgery and monocytes were isolated from blood of healthy volunteers. A static adhesion assay was established using monocytes co-cultured for 1 hour with VSMCs. Firstly, monocytes and VSMCs were preincubated separately with 100ng/mL tumour necrosis factor (TNF)-α for 24 hours. Following co-culture, monocyte adhesion was significantly increased (3.9±0.9 fold increase compared to untreated, n=18, p<0.05). To determine which cell type was responsible for this adhesion, either VSMCs or monocytes were preincubated with TNF-α for 24 hours. In co-cultures where only monocytes were preincubated with TNF-α, there was no increase in adhesion (n=7). However, in co-cultures with only VSMCs preincubated with TNF-α, there was a significant increase in VSMC-monocyte adhesion (3.9±0.5 fold increase compared to untreated, n=7, p<0.05). To mimic the physiological environment, an adhesion assay under flow conditions was developed. Using this model, VSMCs preincubated with 100ng/mL TNF-α for 24 hours demonstrated significantly increased binding to untreated monocytes over 1 hour (5.3±1.4 fold increase compared to untreated, n=7, p<0.05). To examine the mechanisms involved, expression of adhesion molecules, intercellular adhesion molecule (ICAM)-1 and vascular cell adhesion molecule (VCAM)-1 in VSMCs was determined by immunoblotting. In TNF-α-treated human VSMCs, expression of both ICAM-1 and VCAM-1 were significantly increased compared to untreated VSMCs (n=4). To examine factors which, in addition to TNF-α, regulate monocyte-VSMC adhesion in cardiovascular disease, we incubated VSMCs with glycated albumin (an advanced glycation end-product linked with diabetes). Monocyte adhesion to VSMCs was increased 1.5±0.1 fold (n=7, p<0.05) under static conditions following incubation of VSMCs with 200µg/mL glycated albumin for 24 hours compared to normal albumin, and this was reflected under flow conditions. Glycated albumin also upregulated ICAM-1 and VCAM-1 expression in VSMCs (n=3). Values are mean ± S.E.M., compared by t test. In conclusion, human monocytes can adhere to human VSMCs in vitro under physiological conditions. This adhesion is upregulated by the cytokine TNF-α and advanced glycation end-products. These results indicate that increased monocyte adhesion to VSMCs can therefore play a role in initiating restenosis, especially in pro-inflammatory conditions and in diabetes.

Where applicable, experiments conform with Society ethical requirements