Abstract Body (Do not enter title and authors here): Introduction: Pulmonary arterial hypertension (PAH) is a disaster disease characterized by obliterative vascular remodeling and persistent increase of vascular resistance, leading to right heart failure and premature death. Understanding the cellular and molecular mechanisms will help develop novel therapeutic approaches for PAH patients.

Hypothesis:We hypothesis that single-cell RNA sequencing analysis can help understand the cellular and molecular mechanisms that drive the disease initiation and progression.

Methods: 10 healthy donors, 10 idiopathic PAH, 10 drug and toxin induced PAH, 10 systemic and pulmonary shunting induced PAH patients from both male and female, and different ethical groups and races, and ages were obtained from PHBI. Lung tissue specimens were processed for fixed scRNA-seq. The cell proportion change, gene expression, and pathway analysis were evaluated between different disease subclasses, sex, age on different cell types.

Results: Our analysis reveals 317,414 cells, 33 clusters and 9 major cell types, including endothelial cells (ECs), alveolar cells, fibroblast, smooth muscle cells (SMCs), pericytes, myeloid cells, lymphocytes, airway epithelial cells, platelet. Cell proportion analysis demonstrated an increase in the proportions of venous ECs, adventitial fibroblasts and myofibroblasts, alveolar macrophages, B cells, plasma cells and a reduction in capillary ECs 2 and pericytes in PAH lungs. KEGG Pathway analysis showed that upregulated pathways related Herpes simplex virus 1 infection, ECM-receptor interaction, Complement and coagulation cascades, Hedgehog signaling, TGF-beta signaling pathway, and downregulated pathways related to IL-17 signaling, TNF signaling, MAPK signaling pathway were enriched in the PAH patients. Female PAH patients exhibit an increase of myofibroblasts and platelets proportion compared to male PAH patients. MsigDB Hallmark Pathway analysis showed that p53 pathway was upregulated, whereas Inflammatory Response, Hypoxia, Epithelial Mesenchymal Transition were downregulated in female PAH patients. PAH patients older than 21 years exhibit an increase in the cell proportion of Platelet, SMCs, Arterial ECs and Venous ECs, and alveolar macrophages and a reduction of B cells and plasma cells.

Conclusions: Our integrated analysis of human PAH lung atlas dataset provides a comprehensive understanding of lung cell populations and molecular signature in PAH patients with different sex, age and subclasses