Pulmonary arterial hypertension (PAH) is a fatal disease characterized by vascular remodeling which leads to the rise the pulmonary arterial pressure (PAP) and ultimately right heart (RV) failure. Gene–based therapy is a potential new approach to treat PAH since it addresses root cause disease mechanisms of apoptosis and vascular smooth muscle proliferation in the lung vasculature. In this study, we evaluated SERCA2a gene therapy in severe pneumonectomy plus MCT (PNT-MCT) model of PAH with advanced MRI characterization of the left and RV.
Following baseline MRI, Contralateral PNT was performed in male Sprague Dawley rats. One week later, the animals received an injection of MCT. At 3 weeks, the severity of PAH disease was confirmed hemodynamically with MRI, then 2 groups of PNT-MCT rats received either intratracheal delivery of gene construct with adeno-associated virus/SERCA2a (AAV1/SERCA2a) or null vector. Hemodynamic parameters were determined by MRI and RV catheterization at 6 weeks post baseline.
Four weeks after gene delivery, the global RV function was improved in AAV1.SERCA2a treated-animals with an increase of stroke volume and ejection fraction compared to saline group (275 ± 22 ± vs. 192 ± 22 uL and 56 ± 3 ±vs. 44 ± 3 %, p<0.05), while RV end systolic volume was decreased (199 ± 16 ±vs. 283 ± 24 uL, p<0.05). Hemodynamic parameters including mean pulmonary pressure were improved in AAV1.SERCA2a group (26 ± 3 mmHg vs. 61 ± 6 mmHg and 21 ± 3 mmHg vs. 41 ± 3 mmHg respectively, p<0.01) compared to control. At 6 weeks, the SERCA2a gene therapy group measured 4.4 ±0.1mm vs. 5.3 ± 0.1 mm in controls, p<0.01 as compared to a baseline of 4mm confirming the reversal of dilation. The right ventricular lengths measured from the tricuspid valve to apex were affected: Control at 6 weeks 12.0 ±0.2 mm vs. SERCA2a at 6 weeks 15.6 ±1.1 mm as compared with baseline 15.1 ± 0.3mm. These data taken together demonstrate the value in tracking RV length and width dimensions which positively correlate with ejection fraction. Additionally, TAPSE long axis plane calculations confirmed SERCA2a rescued function with a displacement of 4.1±0.6 mm vs. 6 weeks control of 2.7±0.4mm against a baseline reference 5.2±0.2 mm, p<0.05. Histologically, the animals after gene therapy showed a significant regression of plexiform lesions from grade 4 to grade 1-2.
In conclusion, intratracheal administration of AAV1/SERCA2a gene can reverse the severe PAH phenotype and may be considered as a potential treatment. MRI is a powerful tool to quantify the degree of PAH rescue over time and represents a major achievement to improve the execution of translational studies.