Interstitial Macrophage-Derived Thrombospondin-1 Contributes to Hypoxia-Induced Pulmonary Hypertension

Author(s): Kumar, Rahul; Mickael, Claudia; Kassa, Biruk; Sanders, Linda; Hernandez-Saavedra, Daniel; Koyanagi, Daniel E; Kumar, Sushil; Pugliese, Steve C; Thomas, Stacey; McClendon, Jazalle; Maloney, James P; Janssen, William J; Stenmark, Kurt R; Tuder, Rubin M; Graham, Brian B | Abstract: TGF-β signaling is required for chronic hypoxia-induced pulmonary hypertension (PH). The activation of TGF-β by thrombospondin-1 (TSP-1) contributes to the pathogenesis of hypoxia-induced PH. However, neither the cellular source of pathologic TSP-1 nor the downstream signaling pathway that link activated TGF-β to PH have been determined. In this study, we hypothesized that circulating monocytes, which are recruited to become interstitial macrophages, are the major source of TSP-1 in hypoxia-exposed mice, and TSP-1 activates TGF-β with increased Rho kinase signaling, causing vasoconstriction. Flow cytometry revealed that a specific subset of interstitial macrophages is the major source of pathologic TSP-1 in hypoxia. Intravenous depletion and parabiosis experiments demonstrated that these cells are circulating prior to recruitment into the interstitium. Rho kinase mediated vasoconstriction was a major downstream target of active TGF-β. Thbs1 deficient bone marrow protected against hypoxic-PH by blocking TGF-β activation and Rho kinase-mediated vasoconstriction. In hypoxia-challenged mice, bone marrow derived and circulating monocytes are recruited to become interstitial macrophages which express TSP-1, resulting in TGF-β activation and Rho kinase-mediated vasoconstriction. Inflammation contributes to the pathogenesis of many forms of pulmonary hypertension, but blocking inflammation has not been a successful therapeutic strategy to date. Here we found that mice with experimental hypoxia-induced pulmonary hypertension have recruitment of circulating, classical monocytes into the lungs, and that these cells express the protein thrombospondin-1 that causes activation of TGF-β and results in Rho-kinase mediated vasoconstriction. These data suggest that more precise targeting of inflammation, such as blocking specific cells like monocytes or cytokines like TGF-β, would be a more effective future therapeutic approach for pulmonary hypertension etiologies where these pathways underlie disease pathogenesis.