A Murine Aortopulmonary-Shunt Model of Flow-Driven Pulmonary Hypertension

Abstract

BACKGROUND:

Chronic left-to-right shunting, as occurs with congenital heart disease or persistent ductus-like flow, exposes pulmonary circulation to sustained high-flow shear and pulsatile pressure and causes severe, flow-mediated arteriopathy. A scalable, minimally invasive mouse model that reproduces this hemodynamic trigger is needed to enable mechanistic dissection in a genetically tractable system.

METHODS:

An ultrasound-guided transcatheter aortopulmonary shunt (TAPS) procedure was developed to create ductus-like communication between the aortic arch and pulmonary artery. Shunt formation and patency were confirmed by B-mode echocardiography with color and pulsed-wave Doppler. Hemodynamics and right ventricle (RV) function were assessed by transthoracic echocardiography and closed-chest micromanometer catheterization at one month after surgery. A subset of animals was analyzed at 14 days for early endothelial plasticity. Bulk RNA sequencing of pulmonary arteries was performed to define transcriptional remodeling associated with shunt-driven disease.

RESULTS:

TAPS produced a sustained left-to-right overcirculation with Doppler-confirmed shunt flow which induced pulmonary artery hypertension (PAH) with elevated RV systolic pressure, increased pulmonary vascular load, and progressive RV dilation and dysfunction. Histological analyses demonstrated robust pulmonary arterial remodeling, including medial muscularization and thickening, adventitial expansion, and perivascular fibrosis, accompanied by RV cardiomyocyte hypertrophy and increased myocardial fibrosis. Transcriptomic profiling of pulmonary arteries revealed broad differential gene regulation consistent with PAH pathobiology, including inflammatory, proliferative, and profibrotic responses and increased mesenchymal/smooth muscle marker expression. Co-staining endothelial and mesenchymal markers supported endothelial phenotypic transition within the remodeled pulmonary arterial wall.

CONCLUSIONS:

TAPS establishes a minimally invasive, reproducible murine model of shunt-driven PAH triggered by flow-mediated arteriopathy. This platform provides a versatile tool to interrogate flow-sensing mechanisms and to evaluate therapies targeting both vasoreactivity and structural remodeling in PAH.

Graphical Abstract

Introduction:

Pulmonary arterial hypertension (PAH) is a devastating cardiopulmonary vasculopathy characterized by chronically elevated pulmonary arterial pressure, progressive pulmonary vascular remodeling, and eventual right ventricular (RV) failure¹. PAH continues to impose substantial morbidity and premature mortality despite major therapeutic advances². Hallmark pathogenic features include endothelial dysfunction and maladaptive vasoreactivity with impaired nitric oxide–prostacyclin signaling and heightened vasoconstrictor tone, coupled with proliferative and inflammatory remodeling of the pulmonary arterial wall³. This remodeling encompasses intimal thickening, smooth muscle cell (SMC) hypertrophy and hyperplasia, adventitial fibroblast activation, extracellular matrix accumulation, and occlusive vascular lesions in advanced disease that markedly elevate pulmonary vascular resistance (PVR)⁴. The consequent rise in RV afterload drives a characteristic transition from compensated RV hypertrophy to dilation, loss of contractile reserve, and ultimately RV failure, which remains the principal determinant of clinical outcomes in PAH⁵.

A mechanistically distinctive subset PAH is associated with congenital heart disease and defective heart development, where chronic left-to-right shunting provides a sustained hemodynamic insult rather than a primary hypoxic or toxic trigger⁶. In these patients, persistent high-flow overcirculation and increased pulsatile pressure expose the pulmonary vasculature to elevated shear stress, cyclic stretch, and altered pulsatility, accelerating the transition from an adaptive, compliant vascular bed to a maladaptive, obstructive arteriopathy^7–9. Over time, distal pulmonary arteries develop medial hypertrophy and muscularization, adventitial expansion and fibrosis, inflammatory infiltration, and progressive loss of vascular reserve, culminating in RV pressure overload, RV dysfunction, and heart failure^10–12. Although the clinical sequence is well recognized, the mechanistic bridge between chronic abnormal hemodynamics and irreversible structural remodeling remains incompletely defined. A central unresolved question is how flow-derived forces are sensed by the pulmonary endothelium and transduced into the multicompartment remodeling program that defines advanced shunt-associated PAH.

Experimental progress has been constrained by the limitations of widely used rodent PAH models. Chronic hypoxia and monocrotaline-based models have been invaluable for studying vasoconstriction, inflammation, and vascular remodeling, but they primarily reflect hypoxic stress or toxin-mediated endothelial injury and do not isolate the hemodynamic driver of flow-mediated arteriopathy¹³. As a result, these paradigms incompletely capture the initiating pathophysiology of shunt-associated PAH. This gap underscores the need for a complementary and reproducible model that recapitulates chronic left-to-right shunting and high-output pulmonary overcirculation.

In this study, we established a minimally invasive and ultrasound-guided Transcatheter Aortopulmonary Shunt (TAPS) model that creates ductus-like communication between aortic arch and pulmonary artery (PA) in adult mice. Rather than relying on open surgical anastomosis, TAPS leverages real-time echocardiographic guidance to localize the arch–PA interface and position a catheter/needle assembly for controlled shunt formation. This strategy was designed to minimize procedural trauma, reduce inter-operator variability, and allow rapid establishment of a consistent left-to-right shunt. Because echocardiography is integral to the procedure, shunt patency and directionality can be confirmed immediately by color Doppler, and peak shunt velocity can be quantified by pulsed-wave Doppler. This integration of procedural guidance and physiological validation is essential for linking the mechanical stimulus (flow and pressure loading) to downstream pulmonary vascular remodeling.

Methods:

The data that support the findings of this study are available from the corresponding author upon reasonable request. The raw RNA sequencing data are deposited to the NIH NCBI Sequence Read Archive (accession number PRJNA1406268).

Animal housing and TAPS surgery

All animal procedures were performed in accordance with institutional guidelines and an animal protocol approved by the Institutional Animal Care and Use Committee of the University of Missouri. Mice were housed under conventional conditions and randomly assigned to Sham or TAPS groups. Investigators performing hemodynamic measurements and image-based quantification were blinded to group allocation during analysis. For TAPS, 3-month-old male and female C56/BL/J mice (The Jackson Laboratories, strain #000664) were anesthetized with inhaled isoflurane. The left common carotid artery was exposed under a stereomicroscope and cannulated. A commercially available rodent tail-vein polyurethane catheter with stylet from SAI Infusion Technologies (MTV-01; outer radius ≈ 0.165 mm; 28 cm total length; 25G blunt access) was used as the shunt conduit. To enable controlled deployment of a short intravascular segment, the catheter wall was microscopically pre-cut with a surgical blade at four equidistant locations, each to approximately one-quarter of the wall depth, so that twisting could reliably fracture the catheter at the pre-cut region and leave a small segment (~2 mm) in place while allowing the remaining catheter to be withdrawn (Supplemental Figure S1). The catheter/needle assembly was advanced retrograde into the aortic arch under real-time ultrasound guidance; the inner metal needle was then used to create a controlled puncture to establish direct aortopulmonary communication, followed by advancement of the catheter to bridge the aortic arch and PA. Correct placement and shunt patency were confirmed immediately by B-mode imaging and Doppler. After deployment, the external catheter portion was withdrawn, and the carotid artery was secured. Sham animals underwent the same exposure/cannulation and catheter manipulation without creation/deployment of aortopulmonary communication.

Echocardiography and Doppler imaging (B-mode, color Doppler, and pulsed wave (PW) Doppler)

Transthoracic echocardiography was performed under isoflurane anesthesia using a high-frequency ultrasound system (Vevo F2 LT) one month after surgery. Color Doppler was used to confirm left-to-right shunt flow from the aortic arch into the PA, and PW Doppler was used to record the shunt jet and flow direction/velocity signatures consistent with a patent shunt. When physiologic substantiation of high-output shunting is required, the pulmonary-to-systemic flow ratio (Qp/Qs) was calculated from Doppler-derived stroke volume at the pulmonary and aortic outflow tracts using the standard continuity approach: $Q=CSA\times VTI\times HR$, where $CSA=\pi (D/2{)}^2,D$ is the outflow diameter measured in systole from 2D imaging, and $VTI$ is the velocity–time integral from PW Doppler at the same location. Heart rate was canceled out in the ratio so $Qp/Qs=(CS{A}_{PA}\times VT{I}_{PA})/(CS{A}_{Ao}\times VT{I}_{Ao})$. Measurements are averaged over multiple consecutive beats with stable heart rate.

RV short-axis imaging, RV area metrics, RV wall thickness at diastole (RVWTD), RV fractional area change (RVFAC), and PA acceleration time (AT) and ejection time (ET).

For RV structural and functional assessment, parasternal short-axis views were acquired one month after surgery with cine loops spanning at least 3–5 consecutive cardiac cycles. RV end-diastolic area (RVEDA) and RV end-systolic area (RVESA) were obtained by tracing the RV endocardial border at the frames corresponding to maximal and minimal RV cavity area, respectively. RVFAC was calculated as $(\mathit{\text{RVEDA}}-\mathit{\text{RVESA}})/\mathit{\text{RVEDA}}\times 100$. RVWTD was measured at the RV free wall in diastole using standardized landmarks within the short-axis plane. PA AT and ET were measured by PW Doppler with the sample volume positioned in the main PA (or proximal RV outflow tract immediately proximal to the PA valve, as appropriate for signal quality). AT was defined as the time from onset of systolic flow to peak velocity, and ET as the total duration of systolic flow. The PA AT/ET ratio was computed per animal from averaged beats acquired at consistent insonation angle and stable physiologic conditions.

Right ventricular systolic pressure (RVSP) measurement.

RVSP was measured by closed-chest catheterization under inhaled anesthesia using a high-fidelity micromanometer pressure catheter (SPR-671NR; Millar Instruments) one month after surgery. The catheter was introduced via the right jugular vein and advanced into the right heart under real-time pressure waveform guidance. After a brief equilibration period, RV pressure tracings were recorded under stable heart rate and respiratory conditions using a PowerLab data acquisition system with an appropriate bridge amplifier (ADInstruments). Peak RV systolic pressure was extracted from multiple consecutive beats and averaged to generate one value per mouse.

Immunostaining of lung tissue.

The tissue collection was conducted 14 days or one month after the Sham or TAPS surgery. The pulmonary circulation was cleared by perfusion with buffered saline, and lungs were inflation-fixed, processed, and sectioned. Paraffin sections were deparaffinized, rehydrated, subjected to heat-mediated antigen retrieval, and blocked prior to incubation with primary and fluorescent-labeled secondary antibodies followed by nuclear counterstaining with DAPI, as described previous¹⁴. Sections were imaged using standardized exposure settings on Keyence microscope across groups.

Elastic van Gieson (EVG) and Picrosirius Red staining of lung tissue.

EVG staining was used for vessel-wall morphometry and elastic lamina visualization, while Picrosirius Red staining was used to quantify collagen deposition/fibrosis. Quantification was performed on distal PAs meeting prespecified criteria (near-circular, transversely sectioned vessels with intact contours), stratified into predefined external diameter bins. For each mouse, multiple non-overlapping fields were acquired from comparable distal lung regions while avoiding large proximal vessels and bronchi-associated structures. All images were coded and analyzed by an investigator blinded to groups. Adventitial area was quantified on EVG-stained sections using a consistent region-of-interest definition across bins, and perivascular collagen/fibrosis was quantified on Picrosirius-stained sections as collagen-positive area within a standardized perivascular/adventitial region-of-interest.

Wheat germ agglutinin (WGA) staining of RV tissue.

For cardiomyocyte size assessment, hearts were collected, processed, and sectioned through the RV. Sections were stained with fluorescent WGA to delineate cardiomyocyte membranes and enable quantification of cardiomyocyte cross-sectional area from transversely sectioned myocytes with centrally located nuclei. For each mouse, cardiomyocytes were quantified across multiple non-overlapping fields using identical selection criteria, and images were coded and analyzed blinded to the group allocation.

Hematoxylin and Eosin and Masson’s trichrome staining of RV tissue.

Right-ventricular remodeling was assessed by Hematoxylin and Eosin staining for tissue architecture and Masson’s trichrome staining for collagen deposition. For trichrome analyses, fibrosis was quantified as the collagen-positive area within predefined myocardial regions-of-interest, excluding non-myocardial spaces, and averaged across multiple fields per animal with coded and blinded analysis.

RNA sequencing and bioinformatic analysis

Pulmonary arteries were isolated from Sham and TAPS mice (n=3 for each group) and immediately snap-frozen. Total RNA was extracted using a phenol/guanidinium-based method followed by column cleanup. RNA quantity and purity were assessed by spectrophotometry, and RNA integrity was evaluated by microfluidic electrophoresis. Only high-quality RNA (RIN ≥7.0) was advanced for library construction. Stranded mRNA-seq libraries were prepared by Novogene using poly(A) enrichment using an Illumina-compatible library preparation workflow. Libraries were sequenced at Novogene on an Illumina platform (NovaSeq 6000) to generate paired-end 150-bp reads. Raw FASTQ files were subjected to read-level quality control and adapter/low-quality trimming (fastp and Trimmomatic). Clean reads were aligned to the mouse reference genome (mm10) using a splice-aware aligner, and gene-level counts were generated against an annotated transcriptome using featureCounts. Differential gene expressions between TAPS and Sham PAs were performed in R using DESeq2 with a negative binomial generalized linear model and Wald testing. The differentially expressed genes were defined using the study’s prespecified thresholds (p≤0.05 and |log2FoldChange|≥1.0). For visualization, normalized expression values were transformed (variance-stabilizing or rlog transformation) for unsupervised hierarchical clustering/heatmaps, principal component analysis, and sample-level comparisons. The global expression distributions were displayed as log2(FPKM+1). Functional enrichment was assessed using Gene Ontology analysis (clusterProfiler) with multiple-testing correction performed by the Benjamini–Hochberg procedure and significance reported as adjusted P values where applicable.

Statistical analysis

All experiments were repeated at least three times. Data points represent independent biological replicates rather than technical replicates, and results are presented as mean ± SD unless otherwise specified. Prior to analysis, datasets were assessed for normality using the D’Agostino–Pearson omnibus normality test (α=0.05). For comparisons between two groups, an unpaired two-tailed Student’s t test was used for normally distributed data. Statistical analyses were performed using Prism 9.0 (GraphPad Software) or RStudio (Desktop 1.4.1717). Differences were considered statistically significant when nominal P<0.05, or adjusted P<0.05 when multiple testing correction was applied.

Two-Way ANOVA analysis for the association of RVSP with surgery (Sham vs. TAPS) or sex (Male vs. Female) revealed a significant or major effect of surgery (P<0.0001), but no the Sex (F_1,19=0.005, P=0.965), on the outcome of TAPS model. Since the hemodynamic load induced by TAPS is identical in males and females (see Major Resource table), data from male and female mice were pooled for statistical analyses.

Results:

TAPS procedure can be divided as perforation and shunt deployment steps (Figure 1A). B-mode echocardiography confirmed the proper placement (Figure 1A, upper panel). Color Doppler demonstrated the continuous shunt blood flow from AA to PA while PW Doppler quantified the peak velocity of blood flow through the shunt, confirming its hemodynamic impact (Figure 1A, lower panel). The mean Qp/Qs in TAPS mice was 2.6, consistent with a substantial left-to-right shunt and high-output pulmonary overcirculation. To determine whether TAPS promotes PAH comparable to human PAH, we measured the RVSP and found that RVSP was significantly elevated in TAPS mice (Figure 1B). Consistent with the sustained PAH, calponin immunostaining showed increased PA muscularization in TAPS mice (Figure 1B), with a significant shift toward fully muscularized arteries (F) compared to partially (P) and non-muscularized (N) arteries (Figure 1B, right panel). The PA also underwent extensive vascular remodeling as evidenced by medial thickening, perivascular fibrosis, and structural disorganization (Figure 1B, lower panel).

Figure 1. Hemodynamic, histological, and functional characterization of transcatheter aortopulmonary shunt (TAPS) mouse model.

A, Schematic of the two-stage TAPS (transcatheter aortopulmonary shunt) procedure and echocardiographic validation of shunt formation. B-mode imaging shows the presence of catheter and needle (C/N, red arrow) within the pulmonary artery (PA) during the procedure. After withdrawal, a remaining shunt (~2 mm) between the PA and aortic arch (AA) confirms successful patency (upper panel). B-mode and color Doppler imaging show continuous blood flow between the PA and the aortic arch. Pulse-wave (PW) Doppler reveals peak velocity of shunt flow, confirming hemodynamic impact (lower panel). B, Right ventricular systolic pressure (RVSP) was significantly elevated in TAPS mice, indicating pulmonary hypertension. Increased PA muscularization was shown by calponin-1 (CNN1) immunostaining (green). Scale bar=200 μm. Quantification categorizes arteries as non-muscularized (N), partially muscularized (P), or fully muscularized (F). Elastin Van Gieson (EVG) staining showed structural remodeling of the PAs; Picro-Sirius Red staining revealed increased vascular fibrosis (middle panel) in PAs with TAPS. Scale bar=50 μm. Wall thickness quantified with different-sized PAs. Unpaired t-test (two-tailed) performed for all quantifications, n=8. C, Representative echocardiographic images show right ventricular chamber enlargement in TAPS mice. LV: left ventricle, RV: right ventricle. RV dilation was observed in both End-systolic (ES) and end-diastolic (ED). Unpaired t-test (two-tailed), n=8. D, Quantification of RV function and morphology as well as the mouse survival rate. RV wall thickness at diastole (RVWTD) was significantly increased; RV fractional area change (RVFAC) was decreased, indicating reduced contractility; PA acceleration time to ejection time (PA AT/ET) ratio was reduced; and progressive mortality increased (Kaplan-Meier curve) in TAPS mice; Log-rank (Mantel-Cox) test, n=8 (upper panel). Wheat Germ Agglutinin (WGA) staining showing RV cross-sectional area and individual cardiomyocyte area increased in TAPS mice. Unpaired t-test (two-tailed), n=8 (lower panel). E, Co-immunostaining for endothelial marker Von Willebrand factor (vWF) and mesenchymal markers SMC α-actin (ACTA2) or Vimentin in PAs reveals endothelial-to-mesenchymal transition (EndoMT). vWF+ACTA2+ or vWF+Vimentin+ cells were observed in middle and outer vascular layers (arrows), indicating EndoMT with potential for proliferation and collagen deposition. Scale bar, 50 μm. Pulmonary endothelial cells undergoing EndoMT relative to total endothelial cells are quantified (lower panel). Unpaired t-test (two-tailed), n=8.

Chronic PAH often results in RV hypertrophy and dysfunction. Echocardiography revealed severe RV enlargement in TAPS mice, with a significantly increased RV chamber size at both end-systole and end-diastole (Figure 1C). TAPS mice also exhibited increased RVWTD, decreased RVFAC (indicative of impaired RV contractility), reduced PA AT/ET ratio, a hallmark of increased PA resistance, and progressive mortality (Figure 1D, upper panel). Histological analyses of the RV further corroborated pathological remodeling, revealing cardiomyocyte disorganization with increased cardiomyocyte size and significant myocardial interstitial fibrosis as shown by excessive collagen deposition in TAPS mice (Supplemental Figure S2). WGA staining further confirmed RV cardiomyocyte hypertrophy with significant increases in cross-sectional area of RV cardiomyocytes (Figure 1D, lower panel). These data indicate that TAPS-induced PAH results in pathological RV remodeling.

Given that endothelial-to-mesenchymal transition (EndoMT) is associated with PAH progression, we co-stained endothelial (Von Willebrand factor or vWF) and mesenchymal marker SMC α-actin (ACTA2) & Vimentin in PAs. vWF+ACTA2+ and vWF+Vimentin+ cells were detected in the inner and middle layers of TAPS mouse PAs, suggesting active EndoMT in the PA wall (Figure 1E). Consistent with mesenchymal activation and smooth muscle remodeling, ACTA2 and smooth muscle myosin heavy chain immunostaining demonstrated circumferential medial thickening in TAPS PAs with increased medial wall thickness compared with Sham (Supplemental Figure S3). In parallel, morphometric analyses of EVG- and Picrosirius Red–stained sections revealed the increased adventitial area and perivascular collagen deposition in TAPS mice across predefined vessel-size bins (Supplemental Figure S4), supporting layered remodeling of the PA wall. These EndoMT cells have the potential to proliferate and contribute to collagen deposition.

To determine whether the hemodynamic overload imposed by TAPS is accompanied by coordinated molecular reprogramming within the PA wall, we performed bulk RNA-seq on PAs harvested from Sham and TAPS mice. RNA-seq libraries demonstrated comparable sequencing performance and base composition across groups, as reflected by stable per-base quality/error profiles and balanced nucleotide contents along read positions (Supplemental Figure S5). Consistently, read preprocessing retained the vast majority of reads as clean reads with minimal losses attributable to adapters, low-quality bases, or ambiguous base calls, and global gene-expression distributions after normalization were highly similar across samples, indicating comparable library complexity and normalization performance (Supplemental Figure S6). Unsupervised hierarchical clustering of differentially expressed transcripts revealed clear segregation with TAPS PAs exhibiting a distinct expression signature compared with Sham controls (Figure 2A). The different molecular signatures were further supported by principal component analysis, which showed distinct gene clustering in PAs of Sham and TAPS mice (Supplemental Figure S7A).

Figure 2. RNA-seq profiling reveals broad transcriptional remodeling in pulmonary arteries (PAs) in TAPS mice.

A, Unsupervised hierarchical clustering heatmap of differentially expressed transcripts in PAs from TAPS and Sham mice. Rows represent transcripts, and relative expressions are displayed as scaled values (blue to red). Row annotations denote transcript length, biotype (e.g., protein-coding, lncRNA, pseudogene), and chromosome. B, Volcano plot of differential gene expression between TAPS and Sham PAs. Differentially expressed genes (TAPS vs Sham) were defined as p≤0.05 with |log2FoldChange|≥1.0; upregulated genes (1903 genes, red) and downregulated genes (1194 genes, green) are highlighted with non-significant genes shown in blue (23284 genes). Dashed lines indicate significance thresholds. C, Circular heatmap shows selected genes that are upregulated in TAPS PAs as compared to sham controls, including inflammatory cytokine/chemokine transcripts, proliferation marker genes, profibrotic/extracellular matrix-associated genes, as well as mesenchymal/SMC markers.

Consistent with the robust transcriptional response, differential expression analyses identified 3,097 significantly regulated genes using a threshold of p≤0.05 and |log2FoldChange|≥1.0, including 1,903 upregulated and 1,194 downregulated transcripts by the TAPS procedure, whereas 23,284 genes were not affected (Figure 2B). Examination of representative PAH-relevant pathways supported the activation of inflammatory and profibrotic programs and increased SMC marker genes. Specifically, TAPS PAs showed increased expression of inflammatory cytokine and chemokine genes, including interleukin 1 beta, tumor necrosis factor, interleukin 6, C-X-C motif chemokine ligand 1, and C-C motif chemokine ligand 2, together with induction of the proliferating cell nuclear antigen and extracellular matrix–associated profibrotic mediators connective tissue growth factor and collagen type I alpha 1 chain (Figure 2C). In parallel, TAPS pulmonary arteries exhibited increased expression of the mesenchymal and SMC marker genes (Figure 2C). In line with the changes of these transcripts, Gene Ontology analysis highlighted PAH-relevant functional categories, including cytokine activity, receptor–ligand signaling and signaling receptor regulator activity, and cell–cell adhesion mediator activity (Supplemental Figure S7B). Collectively, these transcriptomic data demonstrate broad remodeling of the PA gene program in TAPS mice, consistent with progressive PAH-associated vascular remodeling.

Discussion:

In the present study, we introduce a minimally invasive, ultrasound-guided TAPS approach that establishes ductus-like communication between the aortic arch and PA in adult mice, enabling immediate echocardiographic confirmation of the shunt patency and hemodynamic impact. By coupling real-time procedural guidance with Doppler-based physiologic validation and a standardized catheter modification strategy, TAPS reduces the variability and perioperative burden that limits surgical shunt paradigms in mice. The resulting phenotype, the sustained pulmonary hypertension with RV pressure overload, the distal PA muscularization, the layered arterial wall remodeling, and the progressive RV remodeling support the notion that chronic high-flow and pulsatile pressure loading are sufficient to drive a reproducible flow-mediated pulmonary arteriopathy in genetically tractable species.

A major value of TAPS is that it complements other established rodent PAH models by isolating a distinct initiating axis, i.e., persistent abnormal hemodynamics. Hypoxia-based protocols (with or without vascular endothelial growth factor pathway inhibition) and toxin-driven models (e.g., monocrotaline in rats) have provided important mechanistic insight into vasoconstriction, inflammation, and remodeling, but these approaches do not address mechanotransduction programs activated by long-term overcirculation and increased pulsatile load. Likewise, genetic models centered on heritable drivers (e.g., bone morphogenetic protein type II receptor perturbations) capture important components of disease susceptibility yet do not directly model the prolonged high-output physiology that typifies large left-to-right shunts. Therefore, TAPS offers a complementary and unique platform to dissect how sustained changes in shear stress and cyclic stretch are translated into multicompartment arterial wall remodeling as seen in persistent patent ductus arteriosus¹⁵.

Surgical systemic-to-pulmonary shunts have long served as cornerstone experimental platforms for studying flow-driven pulmonary vascular disease¹⁶. Interventional (catheter-based) approaches have also been demonstrated in large animals, including feasibility work creating transcatheter aortopulmonary connections in swine using specialized devices, supporting the concept that controlled shunt formation can be achieved without open thoracotomy when anatomy and equipment permit¹⁷. Although large animal aortopulmonary shunt models are highly valuable for translational physiology, they are not applicable for high throughput due to high cost. Additionally, mechanistic resolution is challenge with large animal models. Rodent flow models, often leveraging an aorto-caval shunt, have been standardized in rats to produce severe flow-induced PAH with staged medial hypertrophy followed by neointimal lesions and progressive small-vessel occlusion¹⁸. However, translating shunt-based PAH modeling to mice has been limited by microsurgical scale (vessel caliber/working space), bleeding susceptibility, and variability in shunt patency, all of which increase perioperative risk and experimental noise¹⁹. TAPS model overcomes these limitations by providing a simple and straightforward procedure. TAPS also enables interrogation of flow-mediated PAH mechanisms in a genetically tractable system. Specifically, these mice allow rapid and cell-type–specific genetic perturbation (by using endothelial-, smooth muscle–, fibroblast-, or immune lineage–restricted Cre drivers and inducible systems) and unbiased mechanistic discovery.

The biological plausibility of TAPS as a model of flow-mediated pulmonary vascular disease is reinforced by the layered remodeling and molecular programs observed in the PA wall. In addition to muscularization and medial thickening, TAPS lungs demonstrate adventitial expansion and perivascular collagen accumulation. Moreover, EndoMT is detectable within the PA wall, consistent with active endothelial plasticity in a remodeling milieu. At the transcriptomic level, pulmonary arteries from TAPS mice show broad reprogramming toward inflammatory, proliferative, and profibrotic states accompanied by increased expression of mesenchymal/SMC markers. Together, these findings support the notion that sustained overcirculation does not simply “stress” the pulmonary vasculature but also triggers coordinated shifts in vascular cell phenotype and extracellular matrix homeostasis that are core components of progressive PAH pathobiology.

TAPS has several limitations. First, although TAPS provides Doppler-verified shunt flow and clear evidence of pulmonary hypertension and remodeling, deeper hemodynamic phenotyping, such as formal shunt fraction, longitudinal cardiac output, and pulmonary vascular resistance estimation, would further substantiate the high-output physiology and facilitate direct comparison with clinical shunt-associated PAH trajectories. Second, because the stimulus is imposed in adult mice, TAPS models the hemodynamic consequences of a persistent large shunt rather than the developmental context of neonatal/infant pulmonary vascular adaptation; extending the approach to younger animals (or pairing TAPS with developmental time windows) could help address developmental plasticity that is central to congenital diseases. Third, catheter-based shunt creation introduces potential confounders that warrant continued attention in a long-term period, including potential shunt obstruction/thrombosis, variability in effective shunt caliber, or foreign-material effects. Material innovations (e.g., alternative polymers or bioresorbable segments) may further improve reproducibility and minimize off-target effects. Finally, as with all models, careful phenotypic boundary-setting will be important: the TAPS phenotype is expected to align most closely with flow-mediated PAH and may not recapitulate every hallmark of advanced idiopathic disease (e.g., complex plexiform lesions), which would guide how investigators select questions and endpoints.

In summary, TAPS establishes a practical and mechanistically focused murine platform in which sustained left-to-right, ductus-like overcirculation drives pulmonary vascular remodeling and RV dysfunction in a manner aligned with shunt-associated PAH pathophysiology. By enabling rigorous genetic perturbation in the setting of a defined hemodynamic stimulus, TAPS can accelerate discovery around flow-sensing and mechanotransduction pathways, clarify how endothelial plasticity and multicompartment remodeling are coordinated, and provide an efficient preclinical testbed for both vasodilatory and anti-remodeling strategies in PAH.

Supplementary Material

Supplemental Figures S1–S7

Major Resources Table

Clinical Implications:

The aortopulmonary shunt (TAPS) model is a novel and minimally invasive murine platform reproducing the hemodynamics of congenital heart disease-associated pulmonary arterial hypertension (PAH). Unlike existing hypoxia or toxin-based models, TAPS isolates chronic high-flow overcirculation as the primary driver of the disease, recapitulating key pathological features seen in humans, including pulmonary vascular remodeling, endothelial-to-mesenchymal transition, and right ventricular dysfunction. Clinically, this model bridges a critical translational gap by providing a reproducible, genetically tractable system to investigate how hemodynamic forces (shear stress and pulsatile load) trigger maladaptive arteriopathy. By elucidating the specific mechanotransduction pathways involved in shunt-driven PAH, TAPS enables the identification of novel therapeutic targets distinct from those addressed by current vasodilators. Ultimately, this model could be used as a versatile testbed for evaluating new interventions aimed at reversing structural remodeling or preventing right heart failure in patients with flow-mediated pulmonary hypertension.

NONSTANDARD ABBREVIATIONS AND ACRONYMS:

PAH

Pulmonary arterial hypertension

RV

Right ventricle

SMC

Smooth muscle cell

PVR

Pulmonary vascular resistance

TAPS

Transcatheter aortopulmonary shunt

PA

Pulmonary artery

PW

Pulsed wave

RVWTD

RV wall thickness at diastole

RVFAC

RV fractional area change

AT

Acceleration time

ET

Ejection time

RVEDA

RV end-diastolic area

RVESA

RV end-systolic area

RVSP

Right ventricular systolic pressure

EVG

Elastic van Gieson

WGA

Wheat germ agglutinin

EndoMT

Endothelial-to-mesenchymal transition

vWF

Von Willebrand factor

ACTA2

SMC α-actin