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Timothy Klouda, DO





Boston Children Hospital Department of Pediatrics


Division of Pulmonary Medicine


Timothy Klouda DO, Savas Tsikis MD, Tiffany Liu BS , Yunhye Kim PhD Gary Visner DO, Mark Puder MD PhD, Benjamin Raby MD, Ke Yuan PhD

Principal Investigator

Ke Yuan


The role of vascular mural cells in a novel flow-induced pulmonary hypertension model


Intro: Patients with congenital heart disease (CHD) are exposed to increased blood flow and periods of hypoxia (Hx) putting them at risk for pulmonary arterial hypertension (PAH). The mechanism which increased blood flow results in vascular remodeling is unclear. We created a “two-hit” murine model of pulmonary hypertension (PH) by combining Hx and shear stress via left pneumonectomy (LP) to study vascular remodeling in PAH-CHD patients.

Methods: LP was performed in mice followed by assessments for PH including right ventricle systolic pressure (RVSP), Fulton index (a measurement of right ventricle hypertrophy) and echocardiogram. Pulmonary smooth muscle cells (SMCs) were isolated with Cd146 Dynabeads and Cxcl12/Cxcr4 signaling measured with qPCR. LP mice were exposed to 3 weeks of hypoxia and similar measurements performed. Patient tissues was stained for CXCL12 and SMCs.

Results: LP mice developed moderate PH demonstrated by elevated RVSP (28mm Hg vs control 24mm Hg) and Fulton index (31.1% vs control 21.9%) at post-operative day 14. Using a lineage tracing reporter mouse line we observed an increase in SMA+ cells on arterioles (<50µm) compared to controls, suggesting SMCs contribute to muscularization. Cd146+ SMCs were isolated from LP lungs and identified a 4-fold increase in Cxcl12 and Cxcr4 expression by qPCR. LP mice subjected to 3 weeks of Hx demonstrated severe PH (RVSP: 41mm Hg), right ventricle hypertrophy (Fulton index: 40%) and RV dysfunction measured by echocardiogram. Immunoflourescent staining revealed excessive vascular remodeling of distal arterioles in LP/Hx mice compared to controls. CXCL12 was upregulated in the SMC layer of PAH patient tissues.

Conclusion: We identified that the upregulation of the Cxcl12/Cxcr4 pathway in SMCs contributes to flow-induced vascular remodeling and the development of PH. We also introduce a novel murine model of PH (LP/Hx) that will allow future investigation to better understand flow-induced vascular remodeling and study PAH-CHD.

Clinical Implications

Increased blood flow has been suspected to contribute to vascular remodeling in pulmonary hypertension (PH), however the mechanism is unclear. After major lung resection, 37% of patients will develop moderate PH within a year of surgery. Patients with congenital heart disease (CHD) are at risk for the development of PH. Despite recent advances in the care of patients with CHD, the incidence of pulmonary arterial hypertension (PAH) is 10%, leading to morbidity and mortality. We identify SMCs contribute to flow-induced vascular remodeling through the Cxcl12/Cxcr4 pathway, providing novel insight into the pathogenesis of flow-induced PH which will lead to better therapeutic options. In addition, by combining hypoxia and increased blood flow with the left pneumonectomy procedure, we established a novel “two hit” murine model of PH which will allow for the integration of fate mapping and gene knock out mice with advanced bioinformatics to study flow induced vascular remodeling.