GLI1+ cells contribute to vascular remodeling in hypoxia- and cigarette smoke-induced pulmonary hypertension

The precise origin of newly formed alpha smooth muscle actin-positive (ACTA2+) cells appearing in non-muscularized vessels in the context of pulmonary hypertension (PH) is still debatable, although it is believed that they predominantly derive from pre-existing vascular smooth muscle cells (VSMCs). Here, Gli1Cre-ERT2; tdTomatoflox mice were used to lineage-trace GLI1+ cells in the context of PH using two independent models of vascular remodeling (VR) and reverse remodeling (RR): hypoxia and cigarette-smoke exposure (SE). Hemodynamic measurements, right ventricular hypertrophy assessment, flow cytometry, and histological analysis of thick lung sections followed by state-of-the-art 3D reconstruction and quantification using Imaris software were used to investigate the contribution of GLI1+ cells to neo-muscularization of the pulmonary vasculature. The data show that GLI1+ cells are abundant around distal, non-muscularized, vessels during steady state, and that this lineage contributes to around 50% of newly formed ACTA2+ cell around these normally non-muscularized vessels. During RR, cells derived from the GLI1+ lineage are largely cleared in parallel to the reversal of muscularization. Partial ablation of GLI1+ cells greatly prevented VR in response to hypoxia and attenuated the increase in RVSP and right heart hypertrophy. Single-cell RNA sequencing (scRNA-seq) on sorted lineage-labeled GLI1+ cells revealed an Acta2high fraction of cells with pathways in cancer and MAPK signaling as potential players in reprogramming these cells during VR. Analysis of human lung-derived material suggests that GLI1 signaling is overactivated in both Group 1 and Group 3 PH and can promote proliferation and myogenic differentiation. Our data highlight GLI1+ cells as an alternative cellular source of VSMCs in PH and suggest that these cells and the associated signaling pathways represent an important therapeutic target for further studies. Overall design: Fresh flow cytometry sorted GLI1+ cells from Gli1CreERT2; tdTomatoflox mouse lung tissue from hypoxia conditions were then processed to scRNA-seq