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 O2-sensitive, voltage-gated potassium channels (Kv) in pulmonary artery smooth muscle cells (PASMCs). CH decreases Kv channel current/expression and depolarizes and causes Ca2+ 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 O2-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 O2-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.