Critical role of fractalkine (CX3CL1) in cigarette smoke-induced mononuclear cell adhesion to the arterial endothelium

Background Cigarette smoking is an important risk factor for the development of cardiovascular disease, yet the pathways through which this may operate are poorly understood. Therefore, the mechanism underlying cigarette smoke (CS)-induced arterial endothelial dysfunction and the potential link with fractalkine/CX(3)CL1 upregulation were investigated. Methods and results Stimulation of human arterial umbilical endothelial cells (HUAECs) with pathophysiological concentrations of CS extract (1% CSE) increased CX(3)CL1 expression. Neutralisation of CX(3)CL1 activity under dynamic flow conditions significantly inhibited CSE-induced mononuclear cell adhesion to HUAECs (67%). The use of small interfering RNA (siRNA) revealed that nicotinamide adenine dinucleotide phosphate (NADPH) oxidase 5 (Nox5) but not Nox2 or Nox4 is the main NADPH isoform involved in CSE-induced CX(3)CL1 upregulation and mononuclear cell arrest. Knock down of HUAEC tumour necrosis factor alpha expression with siRNA or pharmacological inhibition of p38 mitogen-activated protein kinase and nuclear factor kappa B also abolished these responses. Interestingly, circulating monocytes and lymphocytes from patients with chronic obstructive pulmonary disease (COPD) (n=29) versus age-matched controls (n=23) showed CX(3)CR1overexpression. Furthermore, CX(3)CL1 neutralisation dramatically diminished their enhanced adhesiveness to CSE-stimulated HUAECs. Finally, when animals were exposed for 3 days to CS, a mild inflammatory response in the lung was observed which was accompanied by enhanced CX(3)CL1 expression in the cremasteric arterioles, an organ distant from the lung. CS exposure resulted in increased leukocyte-arteriolar endothelial cell adhesion which was significantly reduced (51%) in animals lacking CX(3)CL1 receptor (CX(3)CR1). Conclusions These results suggest that CS induces functional CX(3)CL1 expression in arterial endothelium and leukocytes from patients with COPD show increased CX(3)CL1-dependent adhesiveness. Therefore, targeting the CX(3)CL1/CX(3)CR1 axis might prevent COPD-associated cardiovascular disorders.