Hypoxia-Induced Epas1-Myl9/12 Axis Shapes the Pathology of Pulmonary Hypertension

Pulmonary hypertension (PH) is a progressive cardiopulmonary disorder characterized by vascular remodeling, abnormal vasoconstriction of small lung arteries, and right heart failure. Hypoxia causes vascular damage, leading to vessel stenosis or occlusion by aberrant endothelial cells, hypertrophy of the tunica media, and thrombus formation. But the precise molecular mechanisms underlying the pathology of PH have been uncertain.

To investigate the pathogenic role of Myl (myosin light chain) 9/12 in PH, we utilized the Sugen/hypoxia mouse model, generated by administration of the VEGF (vascular endothelial growth factor) receptor inhibitor SU5416 under hypoxic conditions (10% O₂). Lung tissues of patients with PH and human lung microvascular endothelial cells were used to examine their endothelial changes. Platelet-specific Myl9-deficient mice were generated to determine the contribution of platelet-derived Myl9 to the development of PH. The therapeutic efficacy of the anti-Myl9/12 antibody was evaluated by hemodynamics, histological analyses, and single-cell RNA sequencing. Furthermore, serum MYL9, MYL12A, and MYL12B levels were measured in patients with PH and analyzed for clinical correlation.

We identified microthrombi containing Myl9/12 in both patients with PH and the PH mouse model. Platelet-derived Myl9 partially contributed to PH development by promoting cellular infiltration. Furthermore, hypoxia upregulated the expression of Myl9/12 through EPAS1 (endothelial PAS domain protein 1) in proliferated lung vascular endothelial cells and induced the release of Myl9/12 into the extracellular space. Anti-Myl9/12 antibody treatment attenuated PH in the mouse model by reducing microthrombus formation, inflammatory cell infiltration, tissue hypoxia, and vascular remodeling. The established PH in Sugen/hypoxia mice was also attenuated by the treatment with anti-Myl9/12 antibody. Moreover, serum levels of Myl9 but not MYL12A or MYL12B levels reflected the severity of PH in patients.

These findings reveal that Myl9/12 play a pathogenic role in developing vascular lesions of PH and could be a new therapeutic target for PH.