Abstract Body (Do not enter title and authors here): Background: Pulmonary hypertension (PH) is a lethal disease characterized in part by progressive pulmonary arteriole (PA) remodeling. Excessive PA fibrosis and macrophage infiltration are often present in PH, but potential association is obscure. We invesitgated the link between interstitial macrophage (iMΦ) infiltration and PA fibrosis in PH and idiopathic pulmonary arterial hypertension (IPAH).
Methods: Lung tissue samples from patients with IPAH (n=11) and experimental PH (sugen-5416 and hypoxia, hypoxia, or monocrotaline, n=5) animals (adult male and female SD rats) were obtained to analyze the extent of fibrosis in PA adventitia and media and their correlation to disease severity. Single-cell RNA sequencing, immunohistological analyses, iMΦs and PA smooth muscle cells (PASMCs) coculture, and transgenic animal experiments were used to investigate the cell heterogeneity and molecular mechanisms by which iMΦs promote PA medial fibrosis. Data in this study were analyzed with unpaired two-tailed t-tests with Welch’s correction, Kruskal-Wallis one-way ANOVA followed by Dunn’s test, RM ANOVA with Geisser-Greenhouse correction, or Pearson correlation test, and p < 0.05 was considered statistically significant.
Results: We found that increased collagen deposition and fibrosis in the PA media were correlated with PH severity, and iMΦ medial infiltration may be involved in these pathological processes. Single-cell transcriptomics suggested that ligand-receptor associations between MHCII^hiLYVE1^loCCR2^hi iMΦ and fibroblast-like vascular SMC subclusters contributed to PA medial fibrosis. Mechanistically, MHCII^hiLYVE1^loCCR2^hi iMΦs regulated PASMC phenotypic transition and collagen production through the wingless member 11 (WNT11)/planar cell polarity (PCP) pathway. Deletion of iMΦ-enriched Wnt11 in myeloid cells of PH rats (Itgam^CreERT2; Wnt11^fl/fl) normalized the fibrotic PASMC phenotype and decreased PA medial fibrosis, thereby protecting against PH. Moreover, myeloid-specific C-C motif chemokine receptor 2 (Ccr2) deficiency (Itgam^CreERT2; Ccr2^fl/fl) in PH-PAs inhibited MHCII^hiLYVE1^loCCR2^hi iMΦ infiltration.
Conclusions: PA medial fibrosis is a causative factor of PH, and the inhibition of MHCII^hiLYVE1^loCCR2^hi iMΦ pathogenicity or infiltration reverses PA medial fibrosis and thus alleviates PH.