Cyclopamine Attenuates Pulmonary Arterial Hypertension Development: Implications of Hedgehog Signaling Involvement for the Pathophysiology

Pulmonary arterial hypertension (PAH) is one of the most severe pulmonary diseases. Although combination therapies of the key drugs have improved survival rates, unmet needs remain in its management. We examined the effects of cyclopamine, a Hedgehog (HH) signaling inhibitor, as a potential novel therapeutic approach for PAH. C57BL/6J male mice were exposed to 10% oxygen for 3 weeks to induce pulmonary hypertension. One week after hypoxia exposure, these mice were treated with cyclopamine or vehicle. Cyclopamine significantly attenuated right ventricular (RV) systolic pressure (H + C: 31 mmHg vs. H: 38 mmHg, p < 0.01) and RV hypertrophy (H + C: 0.28 vs. H: 0.37, p < 0.01). The fully muscularized small pulmonary arteries significantly decreased with cyclopamine (H + C: 30% vs. H: 80%, p < 0.01), suggesting a mediation by vascular remodeling inhibition. In vitro, human pulmonary arterial smooth muscle cells (HPASMC) exposed to hypoxia revealed that the inhibitory action of cyclopamine was limited to hypoxia-promoted cell proliferation. In single-cell RNA sequencing analysis of mice lungs treated with cyclopamine, the signaling pathways of vascular smooth muscle contraction and cGMP-PKG, that is, key regulators in PAH development through vascular remodeling, were suppressed in cells with the characteristics of vascular endothelial and smooth muscle cells. RNA sequencing analysis of hypoxia-exposed hPASMCs revealed that the pathways related to extracellular matrix regulation were particularly recovered. Our animal model-based data revealed that HH signaling inhibition would improve PAH development by suppressing pulmonary vascular remodeling.