Endothelial dysfunction and vascular remodelling are major mechanisms contributing to the development and progression of pulmonary arterial hypertension (PAH). Pulmonary vascular cells in PAH exhibit a mitochondrial-metabolic phenotype similar to that seen in cancer, indicating that the knowledge gained from cancer research may help in the treatment of PH. Recently, adenylate kinase isoenzyme 4 (AK4) was demonstrated as a potent marker of poor clinical outcomes that promotes metabolic reprograming and metastasis of lung cancer. However, the role of AK4 in the development of PH is completely unknown. The aim of our study was to investigate the impact of AK4 on hypoxia-driven responses of pulmonary artery smooth muscle cells (PASMC) and pulmonary microvascular endothelial cells (PMVEC) in order to evaluate this protein as a new possible target in PH. We found that AK4 is upregulated in both PASMC and PMVEC exposed to hypoxia in HIF-1α-dependent manner as well as in chronic hypoxia mouse model representing group III of PH classification.
Furthermore, immunohistochemical staining of human lungs showed a significant increase in AK4 level in the pulmonary vasculature of IPAH patients as compared to donors. Using siRNA-mediated gene silencing technique, we found that AK4 downregulation in PASMC slightly increases cell proliferation but markedly improves the mitochondrial respiratory function reflected as the oxygen consumption rate measured with Seahorse approach. Whereas AK4 silencing in PMVEC leads to decrease in apoptosis through the inhibition of ERK1/2 phosphorylation and caspase 3/7 activity. Our findings indicate that AK4 might play a distinct role in different types of pulmonary cells, and AK4 targeting might be a novel approach to modulate hypoxia-driven responses in the pulmonary vasculature.
We acknowledge the support of the European Respiratory Society, and the Deutsches Zentrums für Lungenforschung (Fellowship LTRF 2018).