In Vivo Gene Transfer of the O 2 -Sensitive Potassium Channel Kv1.5 Reduces Pulmonary Hypertension and Restores Hypoxic Pulmonary Vasoconstriction in Chronically Hypoxic Rats

Abstract

Background— Alveolar hypoxia acutely elicits pulmonary vasoconstriction (HPV). Chronic hypoxia (CH), despite attenuating HPV, causes pulmonary hypertension (CH-PHT). HPV results, in part, from inhibition of O 2 -sensitive, voltage-gated potassium channels (Kv) in pulmonary artery smooth muscle cells (PASMCs). CH decreases Kv channel current/expression and depolarizes and causes Ca 2+ overload in PASMCs. We hypothesize that Kv gene transfer would normalize the pulmonary circulation (restore HPV and reduce CH-PHT), despite ongoing hypoxia. Methods and Results— Adult male Sprague-Dawley rats were exposed to normoxia or CH for 3 to 4 weeks and then nebulized orotracheally with saline or adenovirus (Ad5) carrying genes for the reporter, green fluorescent protein reporter±human Kv1.5 (cloned from normal PA). HPV was assessed in isolated lungs. Hemodynamics, including Fick and thermodilution cardiac output, were measured in vivo 3 and 14 days after gene therapy by use of micromanometer-tipped catheters. Transgene expression, measured by quantitative RT-PCR, was confined to the lung, persisted for 2 to 3 weeks, and did not alter endogenous Kv1.5 levels. Ad5-Kv1.5 caused no mortality or morbidity, except for sporadic, mild elevation of liver transaminases. Ad5-Kv1.5 restored the O 2 -sensitive K + current of PASMCs, normalized HPV, and reduced pulmonary vascular resistance. Pulmonary vascular resistance decreased at day 2 because of increased cardiac output, and remained reduced at day 14, at which time there was concomitant regression of right ventricular hypertrophy and PA medial hypertrophy. Conclusions— Kv1.5 is an important O 2 -sensitive channel and potential therapeutic target in PHT. Kv1.5 gene therapy restores HPV and improves PHT. This is, to the best of our knowledge, the first example of K + channel gene therapy for a vascular disease.