Background and aims:
Chronic thromboembolic pulmonary hypertension (CTEPH) is defined as a subtype of pulmonary hypertension (PH). CTEPH is the only form of PH that differs from others concerning its treatment and pathophysiology. It is characterized by fibrotic obstructions in the pulmonary arteries that lead to increased pulmonary vascular resistance. The resulting pulmonary hypertension causes right ventricular (RV) remodeling and hypertrophy and finally leads to progressive right heart failure and death. Unlike other forms of PH, CTEPH is curable by pulmonary endarterectomy (PEA) surgery, which removes residual thrombus material from the vessel wall and causes improvements in pulmonary hemodynamics and RV function and the amelioration of symptoms.

The aim of this study is to use RNA-sequencing (RNA-seq) data from human RV tissue to delineate the gene expression signatures and signalling pathways in the RV of CTEPH patients before and after PEA surgery in order to identify potential biomarkers of RV remodeling.

Methods:
RNA-seq followed by bioinformatics analysis was performed on the RV biopsies (n=14) obtained from CTEPH patients before PEA (pre-PEA) surgery and data were compared with that of the RV biopsies obtained after PEA (post-PEA) surgery, during the 12 months follow up evaluation. DESeq was used to identify the log₂ fold differences of differentially expressed genes (DEGs), adjusted p≤ 0.05, and ingenuity for gene ontologies.

Results:
RNA-seq analysis of RV of CTEPH patients (n=14) identified 2799 genes with log₂ fold change ≥0.585 and a false discovery rate (FDR) ≤0.05 that were considered differentially regulated between samples from patients Pre and Post PEA surgery. Using this multi analytic approach, the abundant number of DEGs identified a major shift in the transcriptional landscape of the RV in CTEPH patients. To identify potential biomarkers from these DEGs, large-scale bioinformatic analysis of different datasets shortlisted 250 DEGs that were associated with the development of cardiovascular disease. Comprehensive transcriptional profiling of RV revealed a major shift due to PEA surgery. Pathway analysis and gene ontology enrichment confirmed altered regulation of Janus kinase/ signal transducers and activators of transcription (Jak-STATs) signalling pathway, activation of the hypoxia response via hypoxia-inducible factor 1 (HIF-1) signalling, advanced glycation end products and their receptors (AGE-RAGE), hippo and calcium signalling pathways, mitogen-activated protein kinase (MAPK) cascades, cyclic adenosine monophosphate (cAMP) signaling, platelet-derived growth factor (PDGF) pathways, human T-cell leukemia virus type 1 (HTLV-1) infection pathway, activation of various cancer and type II diabetes mellitus pathways in post-PEA compared with pre-PEA samples.

Conclusion:
Extensive and unbiased transcriptomic profiling of RV biopsies from CTEPH patients by RNA-seq data shows substantial changes in the transcriptional landscape of the patients pre- vs post-PEA.