The siRNA-mediated knockdown of AP-1 restores the function of the pulmonary artery and the right ventricle by reducing perivascular and interstitial fibrosis and key molecular players in cardiopulmonary disease.

Background: Pulmonary hypertension (PH) is a complex multifactorial vascular pathology characterized by an increased pulmonary arterial pressure, vasoconstriction, remodelling of the pulmonary vasculature, thrombosis in situ and inflammation associated with right-side heart failure. Herein, we explored the potential beneficial effects of treatment with siRNA AP-1 on pulmonary arterial hypertension (PAH), right ventricular dysfunction along with perivascular and interstitial fibrosis in pulmonary artery-PA, right ventricle-RV and lung in an experimental animal model of monocrotaline (MCT)-induced PAH.

Methods: Golden Syrian hamsters were divided into: (1) C group-healthy animals taken as control; (2) MCT group obtained by a single subcutaneous injection of 60 mg/kg MCT at the beginning of the experiment; (3) MCT-siRNA AP-1 group received a one-time subcutaneous dose of MCT and subcutaneous injections containing 100 nM siRNA AP-1, every two weeks. All animal groups received water and standard chow ad libitum for 12 weeks.

Results: In comparison with the MCT group, siRNA AP-1 treatment had significant beneficial effects on investigated tissues contributing to: (1) a reduction in TGF-β1/ET-1/IL-1β/TNF-α plasma concentrations; (2) a reduced level of cytosolic ROS production in PA, RV and lung and notable improvements regarding the ultrastructure of these tissues; a decrease of inflammatory and fibrotic marker expressions in PA (COL1A/Fibronectin/Vimentin/α-SMA/CTGF/Calponin/MMP-9), RV and lung (COL1A/CTGF/Fibronectin/α-SMA/F-actin/OB-cadherin) and an increase of endothelial marker expressions (CD31/VE-cadherin) in PA; (4) structural and functional recoveries of the PA [reduced Vel, restored vascular reactivity (NA contraction, ACh relaxation)] and RV (enlarged internal cavity diameter in diastole, increased TAPSE and PRVOFs) associated with a decrease in systolic and diastolic blood pressure, and heart rate; (5) a reduced protein expression profile of AP-1S3/ pFAK/FAK/pERK/ERK and a significant decrease in the expression levels of miRNA-145, miRNA-210, miRNA-21, and miRNA-214 along with an increase of miRNA-124 and miRNA-204.

Conclusions: The siRNA AP-1-based therapy led to an improvement of pulmonary arterial and right ventricular function accompanied by a regression of perivascular and interstitial fibrosis in PA, RV and lung and a down-regulation of key inflammatory and fibrotic markers in MCT-treated hamsters.