Ovine Models of Congenital Heart Disease and the Consequences of Hemodynamic Alterations for Pulmonary Artery Remodeling

The natural history of pulmonary vascular disease associated with congenital heart disease (CHD) depends on associated hemodynamics. Patients exposed to increased pulmonary blood flow (PBF) and pulmonary arterial pressure (PAP) develop pulmonary vascular disease more commonly than patients exposed to increased PBF alone. To investigate the effects of these differing mechanical forces on physiologic and molecular responses, we developed two models of CHD using fetal surgical techniques: 1) left pulmonary artery (LPA) ligation primarily resulting in increased PBF and 2) aortopulmonary shunt placement resulting in increased PBF and PAP. Hemodynamic, histologic, and molecular studies were performed on control, LPA, and shunt lambs as well as pulmonary artery endothelial cells (PAECs) derived from each. Physiologically, LPA, and to a greater extent shunt, lambs demonstrated an exaggerated increase in PAP in response to vasoconstricting stimuli compared with controls. These physiologic findings correlated with a pathologic increase in medial thickening in pulmonary arteries in shunt lambs but not in control or LPA lambs. Furthermore, in the setting of acutely increased afterload, the right ventricle of control and LPA but not shunt lambs demonstrates ventricular-vascular uncoupling and adverse ventricular-ventricular interactions. RNA sequencing revealed excellent separation between groups via both principal components analysis and unsupervised hierarchical clustering. In addition, we found hyperproliferation of PAECs from LPA lambs, and to a greater extent shunt lambs, with associated increased angiogenesis and decreased apoptosis in PAECs derived from shunt lambs. A further understanding of mechanical force-specific drivers of pulmonary artery pathology will enable development of precision therapeutics for pulmonary hypertension associated with CHD.

Analysis of the microRNA signature driving adaptive right ventricular hypertrophy in an ovine model of congenital heart disease

The right ventricular (RV) response to pulmonary arterial hypertension (PAH) is heterogeneous. Most patients have maladaptive changes with RV dilation and RV failure, whereas some, especially patients with PAH secondary to congenital heart disease, have an adaptive response with hypertrophy and preserved systolic function. Mechanisms for RV adaptation to PAH are unknown, despite RV function being a primary determinant of mortality. In our congenital heart disease ovine model with fetally implanted aortopulmonary shunt (shunt lambs), we previously demonstrated an adaptive physiological RV response to increased afterload with hypertrophy. In the present study, we examined small noncoding microRNA (miRNA) expression in shunt RV and characterized downstream effects of a key miRNA. RV tissue was harvested from 4-wk-old shunt and control lambs ( n = 5), and miRNA, mRNA, and protein were quantitated. We found differential expression of 40 cardiovascular-specific miRNAs in shunt RV. Interestingly, this miRNA signature is distinct from models of RV failure, suggesting that miRNAs might contribute to adaptive RV hypertrophy. Among RV miRNAs, miR-199b was decreased in the RV with eventual downregulation of nuclear factor of activated T cells/calcineurin signaling. Furthermore, antifibrotic miR-29a was increased in the shunt RV with a reduction of the miR-29 targets collagen type A1 and type 3A1 and decreased fibrosis. Thus, we conclude that the miRNA signature specific to shunt lambs is distinct from RV failure and drives gene expression required for adaptive RV hypertrophy. We propose that the adaptive RV miRNA signature may serve as a prognostic and therapeutic tool in patients with PAH to attenuate or prevent progression of RV failure and premature death. NEW & NOTEWORTHY This study describes a novel microRNA signature of adaptive right ventricular hypertrophy, with particular attention to miR-199b and miR-29a.

Pushing the envelope: a treat and repair strategy for patients with advanced pulmonary hypertension associated with congenital heart disease

Pulmonary arterial hypertension (PAH) is a frequent complication of congenital heart disease as a consequence of altered pulmonary hemodynamics with increased pulmonary blood flow and pressure. The development of pulmonary vascular disease (PVD) in this patient population is an important concern in determining operative strategy. Early, definitive surgical repair, when possible, is the best therapy to prevent and treat PVD. However, this is not possible in some patients because they either presented late, after the development of PVD, or they have complex lesions not amenable to one-step surgical correction, including patients with single ventricle physiology, who have a continuing risk of developing PVD. These patients represent an important, high-risk subgroup and many have been considered inoperable. We present a case series of two patients with complex congenital heart disease and advanced PVD who successfully underwent a treat and repair strategy with aggressive PAH therapies before surgical correction. Both patients had normalization of pulmonary vascular resistance prior to surgical correction. Caution is warranted in applying this strategy broadly and long-term follow-up for these patients is crucial. However, this treat and repair strategy may allow for favorable outcomes among some patients who previously had no therapeutic options.

Pulmonary artery smooth muscle cell hyperproliferation and metabolic shift triggered by pulmonary overcirculation

Vascular cell hyperproliferation and metabolic reprogramming contribute to the pathophysiology of pulmonary arterial hypertension (PAH). An important cause of PAH in children with congenital heart disease (CHD) is increased pulmonary blood flow (PBF). To better characterize this disease course we studied early changes in pulmonary artery smooth muscle cell (PASMC) proliferation and metabolism using a unique ovine model of pulmonary overcirculation. Consistent with PAH in adults, PASMCs derived from 4-wk-old lambs exposed to increased PBF (shunt) exhibited increased rates of proliferation. While shunt PASMCs also exhibited significant decreases in mitochondrial oxygen consumption, membrane potential, and tricarboxylic acid (TCA) cycle function, suggesting a switch to Warburg metabolism as observed in advanced PAH in adults, they unexpectedly demonstrated decreased glycolytic lactate production, likely due to enhanced flux through the pentose phosphate pathway (PPP). This may be a response to the marked increase in NADPH oxidase (Nox) activity and decreased NADPH/NADP+ ratios observed in shunt PASMCs. Consistent with these findings, pharmacological inhibition of Nox activity preferentially slowed the growth of shunt PASMCs in vitro. Our results therefore indicate that PASMC hyperproliferation is observed early in the setting of pulmonary overcirculation and is accompanied by a unique metabolic profile that is independent of HIF-1α, PDHK1, or increased glycolytic flux. Our results also suggest that Nox inhibition may help prevent pulmonary overcirculation-induced PAH in children born with CHD.

Right ventricular nitric oxide signaling in an ovine model of congenital heart disease: a preserved fetal phenotype

We recently reported superior right ventricle (RV) performance in response to acute afterload challenge in lambs with a model of congenital heart disease with chronic left-to-right cardiac shunts. Compared with control animals, shunt lambs demonstrated increased contractility because of an enhanced Anrep effect (the slow increase in contractility following myocyte stretch). This advantageous physiological response may reflect preservation of a fetal phenotype, since the RV of shunt lambs remains exposed to increased pressure postnatally. Nitric oxide (NO) production by NO synthase (NOS) is activated by myocyte stretch and is a necessary intermediary of the Anrep response. The purpose of this study was to test the hypothesis that NO signaling is increased in the RV of fetal lambs compared with controls and shunt lambs have persistence of this fetal pattern. An 8-mm graft was placed between the pulmonary artery and aorta in fetal lambs (shunt). NOS isoform expression, activity, and association with activating cofactors were determined in fetal tissue obtained during late-gestation and in 4-wk-old juvenile shunt and control lambs. We demonstrated increased RNA and protein expression of NOS isoforms and increased total NOS activity in the RV of both shunt and fetal lambs compared with control. We also found increased NOS activation and association with cofactors in shunt and fetal RV compared with control. These data demonstrate preserved fetal NOS phenotype and NO signaling in shunt RV, which may partially explain the mechanism underlying the adaptive response to increased afterload seen in the RV of shunt lambs.