Monocytes and interstitial macrophages contribute to hypoxic pulmonary hypertension
Rahul Kumar, … , Qadar Pasha, Brian B. Graham
Rahul Kumar, … , Qadar Pasha, Brian B. Graham
Published January 30, 2025
Citation Information: J Clin Invest. 2025;135(6):e176865. https://doi.org/10.1172/JCI176865.
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Research Article Inflammation Vascular biology

Monocytes and interstitial macrophages contribute to hypoxic pulmonary hypertension

Abstract

Hypoxia is a major cause of pulmonary hypertension (PH) worldwide, and it is likely that interstitial pulmonary macrophages contribute to this vascular pathology. We observed in hypoxia-exposed mice an increase in resident interstitial macrophages, which expanded through proliferation and expressed the monocyte recruitment ligand CCL2. We also observed an increase in CCR2+ macrophages through recruitment, which express the protein thrombospondin-1, which functionally activates TGF-β to cause vascular disease. Blockade of monocyte recruitment with either CCL2-neutralizing antibody treatment or CCR2 deficiency in the bone marrow compartment suppressed hypoxic PH. These data were supported by analysis of plasma samples from humans who traveled from low (225 m) to high (3500 m) elevation, revealing an increase in thrombospondin-1 and TGF-β expression following ascent, which was blocked by dexamethasone prophylaxis. In the hypoxic mouse model, dexamethasone prophylaxis recapitulated these findings by mechanistically suppressing CCL2 expression and CCR2+ monocyte recruitment. These data suggest a pathologic cross talk between 2 discrete interstitial macrophage populations, which can be therapeutically targeted.

Authors

Rahul Kumar, Kevin Nolan, Biruk Kassa, Neha Chanana, Tsering Palmo, Kavita Sharma, Kanika Singh, Claudia Mickael, Dara Fonseca Balladares, Julia Nilsson, Amit Prabhakar, Aastha Mishra, Michael H. Lee, Linda Sanders, Sushil Kumar, Ari B. Molofsky, Kurt R. Stenmark, Dean Sheppard, Rubin M. Tuder, Mohit D. Gupta, Tashi Thinlas, Qadar Pasha, Brian B. Graham

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Figure 2

Classical monocytes serve as a precursor of inflammatory IMs following hypoxia exposure.

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Classical monocytes serve as a precursor of inflammatory IMs following h...
Time course–based flow cytometry analysis showed increased numbers of (A) classical and (B) nonclassical monocytes in circulation and (C) recruitment of IMs with (D) higher proliferation after 3 days of hypoxia in lungs (n = 6/group; all female mice). (E) Double reporter (Ccr2RFPCx3cr1GFP) mice flow cytometry revealed extravascular IMs subsets: RFP+ (recent recruitment from the circulatory CCR2+ monocytes) and another RFP– GFP+ resident (FOLR2+) IMs (representative image of n = 12–13/group). (F) Quantitative analysis showed significant increases in CCR2+ IMs and FOLR2+ resident IMs following hypoxia exposure (n = 13 in Nx; 8 female, 5 male; n = 12 in Hx, 8 female, 4 male). (G) WT mice flow cytometry showed elevated total IMs after hypoxia (n = 7/group; all female mice). (H) Both CCR2+ IMs and FOLR2+ resident IMs increased significantly following hypoxia exposure (n = 7/group; all female mice). (I) FOLR2+ IMs were highly positive for the proliferation marker Ki-67 after hypoxia exposure (n = 7/group; all female mice). (J) Ccr2ERT2–Cre x R26Stop(fl/fl)tdTomato lineage tracing system efficiently labeled CCR2+ IMs with tdT in hypoxia compared with FOLR2+ IMs following tamoxifen injection (n = 4/group; 2 male, 2 female in Nx; 2 male, 2 female in Hx group). (K) Cx3cr1ERT2–Cre x R26Stop(fl/fl)tdTomato lineage tracing system efficiently marks resident FOLR2+ IMs with tdTomato (tdT); circulatory CCR2+ monocytes also showed slightly higher tdT+ labeled in hypoxia compared with normoxia (n = 4–5/group; 2 male, 2 female in Nx; 2 male and 3 female in Hx group). ANOVA followed by Tukey’s post hoc test was conducted for Panels A, B, F, J, and K. Kruskal-Wallis ANOVA followed by Dunn’s post hoc test was used for panels C, D, and G–I. mean ± SD plotted. #P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001. n, number of animals; NC, nonclassical; Nos., number; IMs, interstitial macrophages.