Endothelial cells in chronic thromboembolic pulmonary hypertension exhibit cytoskeletal alteration
Authors: Peracaula M , Martinez-Blanco A , Gavara N , Gratacos M , I Peinado V , Blanco I , Barbera J A , Tura-Ceide O 
Published: May 2024

Abstract

Funding Acknowledgements
Type of funding sources: Public grant(s) – EU funding. Main funding source(s): Health Research Fund (Fondo de Investigación Sanitaria [FIS]) from the Instituto de Salud Carlos III

Introduction
Endothelial dysfunction (ED) is pivotal in Chronic Thromboembolic Pulmonary Hypertension (CTEPH) due to structural and functional alterations in endothelial. Previous studies have shown the critical function of cytoskeletal elements, particularly actin microfilaments and microtubules, along with associated cell adhesion complexes, in the endothelial integrity. Nevertheless, precise alterations in the cytoskeletal elements of endothelial cells (ECs) in CTEPH patients remain unclear.

Purpose
This study aims to investigate the cytoskeleton changes in CTEPH-ECs compared to healthy ECs, characterizing morphological and structural differences. Objectives involve assessing microtubules and microfilaments expression, and their influence on ECs migratory capacity. Finally, our study aims to gain novel insights into the spatial organization of cytoskeleton components in CTEPH patients.

Methods
CTEPH-ECs were isolated from freshly resected pulmonary endarterectomy specimens of CTEPH patients, while human pulmonary artery ECs (HPAE) were used as healthy controls. Fluorescence immunocytochemistry assessed phenotypic and compositional characteristics of the cytoskeleton. Morphometric analysis described morphology and filament organization of cytoskeletal proteins using a custom-built pipeline. X-ray microscopy examined the phenotype and cytoskeletal components distribution. The migration assay evaluated how these structural differences affected ECs migratory capacity and the cytoskeletal elements expression.

Results
CTEPH-ECs exhibited larger surface area (1352 vs 662µm2, p&lt;0.01) and a more stellate morphology (0.365 vs 0.289, p&lt;0.01) than HPAE-ECs. Immunostaining indicated altered cytoskeletal composition in CTEPH-ECs with significantly higher tubulin expression, expressed in microtubules, (3327 vs 2238AU, p&lt;0.01) and F-actin microfilaments (2068 vs 1300AU, p&lt;0.01) compared to HPAE. Similarly, CTEPH-ECs showed reduced G-actin expression (3002 vs 7461AU, p&lt;0.01).
Morphometric analysis demonstrated that microfilaments were thinner (0.623 vs 0.831AU, p&lt;0.01), more straight (0.135 vs. 0.172, p&lt;0.01) and more aligned (0.132 vs. 0.156, p&lt;0.01) in CTEPH-ECs. Microtubule thickness decreased compared to HPAE-ECs (0.341 vs 1.371AU, p&lt;0.01). CTEPH-ECs showed impaired wound healing (60 vs 89% closure, p&lt;0.05). CTEPH group showed an increase in microtubules and microfilaments expression during wound healing, but with irregular patterns, unlike the constant levels in HPAE. TXM-technology revealed spatial organization differences, especially expansive microtubules distribution in CTEPH-ECs (4.2*10^7 vs. 8.7*10^6 nm³, p&lt;0.05).

Conclusion
These preliminary findings highlight significant structural and compositional differences in CTEPH-ECs, along with altered wound healing capacity, suggesting dynamic cytoskeletal and cellular changes in CTEPH. Understanding these alterations is crucial for advancing CTEPH knowledge and identifying potential therapeutic targets.