T reg Cells Attenuate Pulmonary Venous Remodeling in PH-LHD via NLRC3 Signaling

BACKGROUND: Pulmonary venous remodeling is a key pathological feature of pulmonary hypertension associated with left heart disease (PH-LHD). This study aims to investigate the role of regulatory T (T reg ) cells in this process. METHODS: We used mouse models with transverse aortic constriction and cell depletion of Foxp3-DTR/tdTomato mice to examine T reg cells’ function around pulmonary veins in PH-LHD in vivo. To confirm the effect of Nlrc3 −/− T reg cells on PH-LHD, we utilized 3 mouse models: Nlrc3 knockout mice, athymic mice, and endothelial cell lineage tracing Cdh5CreERT2 +/ − -mT/mG +/ − mice. The interaction proteins and signaling pathways of T reg cells during endothelial-to-mesenchymal transition were elucidated by protein docking prediction, coimmunoprecipitation and cocultivation of T reg cells with venous endothelial cells. RESULTS: T reg cells were abundant around pulmonary veins of transverse aortic constriction–induced PH-LHD and were essential for promoting inflammation resolution and inhibiting pulmonary venous remodeling. Nlrc3 expression was reduced in mice and patients with PH-LHD. NLRC3 (nucleotide-oligomerization domain-like receptor family CARD domain containing 3) deficiency inhibited T reg cell proliferation and impaired their immunosuppressive and endothelial-to-mesenchymal transition–protective effects. Mechanistically, NLRC3 interacted with TRAM (TRIF-related adaptor molecule) and regulated IRF3/NF-κB (nuclear factor-κB) p65 signaling in CD4 + T cells. NLRC3-deficient T reg cells promoted IL (interleukin)-18 expression through IRF3/NF-κB p65 signaling, and thus IL-18 secretion activated endothelial RTK (receptor tyrosine kinase) signaling, favoring endothelial-to-mesenchymal transition progression in pulmonary veins and PH-LHD progress. This process was reversible with IL-18 binding protein in vivo. CONCLUSIONS: NLRC3 is crucial for T reg cells to prevent pulmonary venous remodeling in PH-LHD, primarily by modulating IL-18 secretion, which inhibits endothelial-to-mesenchymal transition and thereby improves disease progression and prognosis.