Abstract 13141: Accumulation of Aggrecan at Sites of Increased Pulmonary Arterial Pressure in Idiopathic Pulmonary Arterial Hypertension

Introduction: Pulmonary arterial hypertension (PAH) is a lethal condition lacking curative pharmacotherapy. Expansion of the extracellular matrix occurs in early stages of pulmonary angiopathy, but the presence of individual matrix components warrants further investigation. Accumulation of the osmotically active matrix proteoglycan aggrecan has been associated with swelling and disruption of vessel wall integrity in systemic arteries. Whether aggrecan is present to any significant extent in PAH tissue, and what potential role it may have, is not known. Methods: Paraffin-embedded lung tissue from 11 patients with idiopathic PAH was imaged using synchrotron-based phase contrast micro-CT at the TOMCAT beamline, Swiss Light Source. Image analysis was performed in Fiji and Amira. Imaged blocks were subsequently sectioned for histology, immunohistochemistry with an aggrecan core protein antibody and RNAscope in situ hybridization. qPCR was performed to investigate gene expression. Failed donor lungs were used as controls. Results: Aggrecan core protein was identified in vascular lesions of all 11 patients with idiopathic PAH, localized to cellular rather than fibrotic or collagenous lesions. RNAscope in situ hybridization confirmed local production of ACAN mRNA in diseased vessels. Quantification of repeated immunohistochemistry demonstrated significantly increased accumulation of aggrecan in patients with idiopathic PAH compared to failed donor lung controls. ACAN and ADAMTS15 mRNA were also found to be up-regulated in pulmonary arteries from patients with IPAH, indicating ongoing proteolytic turnover. Image analysis and three-dimensional renderings of pulmonary arteries identified aggrecan in lumen-reducing lesions containing cellular connective tissue, at sites of intrapulmonary bronchopulmonary shunting and at sites of elevated pulmonary blood pressure. Conclusions: Our findings indicate local production and accumulation of aggrecan in pressure-related lesions of idiopathic PAH. This work strengthens the hypothesis that aggrecan plays a role in arterial adaptations to altered hemodynamics and is the first to suggest a role for aggrecan in pulmonary arterial homeostasis and idiopathic PAH.