Blockade of JAK2 protects mice against hypoxia-induced pulmonary arterial hypertension by repressing pulmonary arterial smooth muscle cell proliferation

Objectives: Hypoxia is an important risk factor for pulmonary arterial remodelling in pulmonary arterial hypertension (PAH), and the Janus kinase 2 (JAK2) is believed to be involved in this process. In the present report, we aimed to investigate the role of JAK2 in vascular smooth muscle cells during the course of PAH. Methods: Smooth muscle cell (SMC)-specific Jak2 deficient mice and their littermate controls were subjected to normobaric normoxic or hypoxic (10% O₂) challenges for 28 days to monitor the development of PAH, respectively. To further elucidate the potential mechanisms whereby JAK2 influences pulmonary vascular remodelling, a selective JAK2 inhibitor was applied to pre-treat human pulmonary arterial smooth muscle cells (HPASMCs) for 1 hour followed by 24-hour hypoxic exposure. Results: Mice with hypoxia-induced PAH were characterized by the altered JAK2/STAT3 activity in pulmonary artery smooth muscle cells. Therefore, induction of Jak2 deficiency in SMCs protected mice from hypoxia-induced increase of right ventricular systolic pressure (RVSP), right ventricular hypertrophy and pulmonary vascular remodelling. Particularly, loss of Jak2 significantly attenuated chronic hypoxia-induced PASMC proliferation in the lungs. Similarly, blockade of JAK2 by its inhibitor, TG-101348, suppressed hypoxia-induced human PASMC proliferation. Upon hypoxia-induced activation, JAK2 phosphorylated signal transducer and activator of transcription 3 (STAT3), which then bound to the CCNA2 promoter to transcribe cyclin A2 expression, thereby promoting PASMC proliferation. Conclusions: Our studies support that JAK2 could be a culprit contributing to the pulmonary vascular remodelling, and therefore, it could be a viable target for prevention and treatment of PAH in clinical settings.