GLI1+ Cells Contribute to Vascular Remodeling in Pulmonary Hypertension

Abstract

BACKGROUND: The precise origin of newly formed ACTA2+ (alpha smooth muscle actin-positive) cells appearing in nonmuscularized vessels in the context of pulmonary hypertension is still debatable although it is believed that they predominantly derive from preexisting vascular smooth muscle cells (VSMCs). METHODS: Gli1 Cre-ERT2 ; tdTomato flox mice were used to lineage trace GLI1+ (glioma-associated oncogene homolog 1-positive) cells in the context of pulmonary hypertension using 2 independent models of vascular remodeling and reverse remodeling: hypoxia and cigarette smoke exposure. Hemodynamic measurements, right ventricular hypertrophy assessment, flow cytometry, and histological analysis of thick lung sections followed by state-of-the-art 3-dimensional reconstruction and quantification using Imaris software were used to investigate the contribution of GLI1+ cells to neomuscularization of the pulmonary vasculature. RESULTS: The data show that GLI1+ cells are abundant around distal, nonmuscularized vessels during steady state, and this lineage contributes to around 50% of newly formed ACTA2+ cells around these normally nonmuscularized vessels. During reverse remodeling, cells derived from the GLI1+ lineage are largely cleared in parallel to the reversal of muscularization. Partial ablation of GLI1+ cells greatly prevented vascular remodeling in response to hypoxia and attenuated the increase in right ventricular systolic pressure and right heart hypertrophy. Single-cell RNA sequencing on sorted lineage-labeled GLI1+ cells revealed an Acta2 high fraction of cells with pathways in cancer and MAPK signaling as potential players in reprogramming these cells during vascular remodeling. Analysis of human lung-derived material suggests that GLI1 signaling is overactivated in both group 1 and group 3 pulmonary hypertension and can promote proliferation and myogenic differentiation. CONCLUSIONS: Our data highlight GLI1+ cells as an alternative cellular source of VSMCs in pulmonary hypertension and suggest that these cells and the associated signaling pathways represent an important therapeutic target for further studies.

New Kid on the Block: GLI1+ Cells and Pulmonary Arterioles Neomuscularization

“…Indeed, the authors discovered a subpopulation of GLI1+ mesenchymal stromal celllike cells that already express ACTA2 in non-PH conditions and could be responsible for producing GLI1+ SMC during PH. Furthermore, PDGFR-β and KLF4, known drivers of ACTA2-positive progenitor SMC dedifferentiation, 6 appeared to be also upregulated in GLI1+ lung cells from mice with hypoxia-induced PH, 8 supporting possible shared origins or at least similarities in lineage. Nevertheless, further research is needed to delineate the specific and overlapping roles of these two cell populations in PH-related distal neomuscularization.…”

“…7 Combining lineage-tracing with flow cytometry, singlecell RNA sequencing, immunofluorescence analysis, and 3-dimensional reconstruction, the authors found that, in the settings of hypoxia-and smoke exposure-induced PH in mice, lung GLI+ cells acquire ACTA2 and participate in the remodeling of muscularized PAs and neomuscularization of pulmonary arterioles. 8 Intriguingly, the authors' findings suggested that neomuscularization in PH is likely a combination of 2 processes: proximal-todistal muscularization by preexisting SMC progenitors and distal muscularization by GLI1+ cells with newly established SMC identity (Figure).…”

“…Moreover, partial ablation of GLI1+ cells in mice slowed hypoxia-induced pulmonary vascular remodeling and slightly reduced right ventricular pressures. 8 These findings suggest GLI1 as a potential therapeutic target and call for comprehensive preclinical studies to determine its potential attractiveness to reverse established pulmonary vascular remodeling and experimental PH. Furthermore, given that neomuscularization of pulmonary arterioles contributes to reduced PA compliance, a predictor of increased mortality in patients with PH, targeting GLI1+ cells could emerge as an attractive strategy to attenuate or even reverse neomuscularization in PH.…”