ALTERED EXPRESSION OF LUNG EPITHELIAL ION AND FLUID TRANSPORTERS DURING PROGRESSION OF PULMONARY HYPERTENSION IN THE MONOCROTALINE MODEL

Abstract

Objective: Recent studies have evaluated a significant incidence of pleural effusions in patients with idiopathic and heritable pulmonary arterial hypertension (PAH) co-diagnosed with isolated right-sided heart failure (RHF). Coincidence of pleural effusions and RHF in these patients significantly increased mortality rate during follow-up. However, mechanism of pleural effusions formation has not been fully explained. Therefore, we examined expression of lung epithelial ion and fluid transporters responsible for alveolar fluid clearance (AFC), which may contribute to lung fluid accumulation under pathological conditions and potentially formation of pleural effusions. Design and method: 12-weeks old male Wistar rats were subcutaneously injected with monocrotaline (60 mg/kg, MCT) or vehicle (CON). The relative expression of AFC transporters: Na+/K+-ATPase alpha1, alpha2, beta1, beta3 subunits, epithelial sodium channel (ENaC) alpha, beta, gama subunits, cystic fibrosis transmembrane conductance regulator (CFTR) were determined by RT-qPCR 1, 2, 4 weeks after MCT application and also in end-stage disease (animals sacrificed after acute health deterioration, ∼ 4 weeks after MCT application) where pleural effusions were observed. Results: Increase in lung weight was observed from second week after MCT application and was more profound in end-stage disease (by 26 % compared to fourth week, p < 0.05). A downregulation of all three pore-forming subunits of ENaC was observed in end-stage disease, accompanied by downregulation of small beta3 subunit of Na+/K+-ATPase. Expression of catalytic alpha2 subunit of Na+/K+-ATPase gradually decreased with disease progression from first week after MCT (-80% in end-stage vs. CON, p < 0.05). On the other hand, we observed upregulation of CFTR (by 80%) and beta1 subunit of Na+/K+ATPase (by 79% vs. CON, p < 0.05) mainly in end-stage disease. Conclusions: Downregulation of lung epithelial ion and fluid transporters contributing to AFC is predominantly limited to higher stages of PH with a marked downregulation in end-stage. These expression alterations may contribute to overall lung weight increase observed in end-stage disease. However, observed early alpha2 subunit of Na+/K+-ATPase downregulation could participate on the pathogenesis of PH while upregulation of beta1 subunit and CFTR in end-stage disease could represent a compensatory mechanism.