Single cell transcriptomic analyses reveal diverse and dynamic changes of distinct populations of lung interstitial macrophages in hypoxia-induced pulmonary hypertension

Abstract

IntroductionHypoxia is a common pathological driver contributing to various forms of pulmonary vascular diseases leading to pulmonary hypertension (PH). Pulmonary interstitial macrophages (IMs) play pivotal roles in immune and vascular dysfunction, leading to inflammation, abnormal remodeling, and fibrosis in PH. However, IMs’ response to hypoxia and their role in PH progression remain largely unknown. We utilized a murine model of hypoxia-induced PH to investigate the repertoire and functional profiles of IMs in response to acute and prolonged hypoxia, aiming to elucidate their contributions to PH development.MethodsWe conducted single-cell transcriptomic analyses to characterize the repertoire and functional profiles of murine pulmonary IMs following exposure to hypobaric hypoxia for varying durations (0, 1, 3, 7, and 21 days). Hallmark pathways from the mouse Molecular Signatures Database were utilized to characterize the molecular function of the IM subpopulation in response to hypoxia.ResultsOur analysis revealed an early acute inflammatory phase during acute hypoxia exposure (Days 1-3), which was resolved by Day 7, followed by a pro-remodeling phase during prolonged hypoxia (Days 7-21). These phases were marked by distinct subpopulations of IMs: MHCIIhiCCR2+EAR2+ cells characterized the acute inflammatory phase, while TLF+VCAM1hi cells dominated the pro-remodeling phase. The acute inflammatory phase exhibited enrichment in interferon-gamma, IL-2, and IL-6 pathways, while the pro-remodeling phase showed dysregulated chemokine production, hemoglobin clearance, and tissue repair profiles, along with activation of distinct complement pathways.DiscussionOur findings demonstrate the existence of distinct populations of pulmonary interstitial macrophages corresponding to acute and prolonged hypoxia exposure, pivotal in regulating the inflammatory and remodeling phases of PH pathogenesis. This understanding offers potential avenues for targeted interventions, tailored to specific populations and distinct phases of the disease. Moreover, further identification of triggers for pro-remodeling IMs holds promise in unveiling novel therapeutic strategies for pulmonary hypertension.

Interstitial macrophage phenotypes in Schistosoma-induced pulmonary hypertension

“…Despite these differences, both hypoxia and Schistosoma cause experimental and human PH. Work in the hypoxia PH system identified 4 IM subpopulations, characterized as MHCII hi CCR2 + EAR2 + , TLF + VCAM1 hi , MHCII hi CCR2 + EAR2 - , and TLF + VCAM1 lo ( 21 ). Comparing these 4 IM subpopulations in hypoxic-PH to the 3 populations in Schistosoma -PH identified that the Schistosoma -PH CCR2 + IMs were analogous to the hypoxia-PH MHCII hi CCR2 + EAR + IMs; the Schistosoma -PH MHCII hi IMs were analogous to the hypoxia-PH MHCII hi CCR2 + EAR - IMs; and the Schistosoma -PH FOLR2 + IMs were analogous to a combination of the TLF + VCAM hi and TLF + VCAM lo IMs in the hypoxia-PH model ( Supplementary Figure S19 ).…”

“…Pathologic mechanisms of monocyte recruitment and IMs are also present in hypoxia-induced PH ( 3 , 7 , 25 – 29 ). There is a high degree of similarity in the IM populations observed in both hypoxic- and Schistosoma-PH ( 21 ), although hypoxia induces a Type 1 inflammatory phenotype in IMs whereas Schistosoma induces a Type 2 inflammatory phenotype. scRNAseq analysis of the hypoxia-PH model revealed 2 IM subpopulations directly analogous to the CCR2+ and MHCII hi IM subpopulations in Schistosoma-PH ( 21 ).…”

“…There is a high degree of similarity in the IM populations observed in both hypoxic- and Schistosoma-PH ( 21 ), although hypoxia induces a Type 1 inflammatory phenotype in IMs whereas Schistosoma induces a Type 2 inflammatory phenotype. scRNAseq analysis of the hypoxia-PH model revealed 2 IM subpopulations directly analogous to the CCR2+ and MHCII hi IM subpopulations in Schistosoma-PH ( 21 ). Prolonged hypoxia up to 21 days drove the development of 2 TLF IM subpopulations ( 21 ), which are similar to the single Schistosoma -PH FOLR2+ population only studied up to 7 days.…”

“…scRNAseq analysis of the hypoxia-PH model revealed 2 IM subpopulations directly analogous to the CCR2+ and MHCII hi IM subpopulations in Schistosoma-PH ( 21 ). Prolonged hypoxia up to 21 days drove the development of 2 TLF IM subpopulations ( 21 ), which are similar to the single Schistosoma -PH FOLR2+ population only studied up to 7 days.…”

“…There are likely to be some differences due to mild hypoxia in cell physiology including IM phenotype with the 1500m elevation change, which is equivalent to a decrease in FiO2 from 21% to 19%. A comparison of scRNAseq data performed at sea level and Denver elevation reveals transcriptomic differences in oxidative phosphorylation and reactive oxygen species pathways ( 21 ).…”