Deletion of repressor activator protein 1 impairs acetylcholine-induced relaxation due to production of reactive oxygen species

Abstract

INTRODUCTION: Repressor activator protein 1 (Rap1) is a telomeric protein which resides within the shelterin complex docked at chromosomal ends. Besides regulating chromosome integrity, it also takes part in metabolic regulation and body-weight homeostasis. Its role, if any, in vascular responsiveness is unknown. PURPOSE: The present study investigated if Rap1 deletion affects vascular responsiveness in mice. METHODS: Rap1 knockout and wild-type littermates on a C57BL/6N background [aged between 12-16 weeks and fed standard chow] were used. Thoracic aortae were harvested and rings (with or without endothelium) were suspended in wire myographs to determine contractions and relaxations (during contractions to 10-6 mol/L phenylephrine). Contractions were expressed as percentage to the reference response obtained with 60mmol/L potassium solution at the beginning of the experiment, while relaxations were expressed as percentage of the contraction to phenylephrine. RESULTS: Relaxations to acetylcholine in aortic rings with endothelium were abolished by NG-nitro-L-arginine methyl ester (L-NAME; 10-4 M; nitric oxide synthase inhibitor) and diminished significantly in Rap1 knockout compared to wild type preparations. Relaxations to other endothelium-dependent vasodilators [insulin, UK14304 (α2 adrenergic agonist), A23187 (calcium ionophore)] were not significantly different between aortae of Rap1 knockout compared to wild type mice. Likewise, relaxations to exogenous nitric oxide donors were similar in aortae without endothelium of both groups. In Rap1 knockout aortae, treatment with reactive oxygen species scavengers could significantly restore acetylcholine-induced relaxations. CONCLUSION: Deletion of Rap1 results in impaired acetylcholine-induced endothelium-dependent relaxations. This impairment can be attributed to the increased production of reactive oxygen species reducing the bioavailability of nitric oxide, without changes in the responsiveness of vascular smooth muscle to the endothelium-derived mediator.