Exploring the Impact of Endothelial Bone Morphogenetic Protein Receptor 2 Loss on Phosphoinositide and Cytoskeletal Assembly Dynamics and the Pathobiology of Pulmonary Arterial Hypertension
Pulmonary Arterial Hypertension , Intracellular Trafficking , Endothelial Cells , Bone Morphogenetic Protein Receptor II
Background: The regulation of intracellular trafficking between the trans-Golgi network (TGN) and plasma membrane (PM) is vital for protein secretion and growth factor signaling, which involves recycling and PM localization of cell surface receptors. These processes depend on the cytoskeleton and the presence of phosphoinositide (PI) species in specific intracellular compartments. Pulmonary arterial hypertension (PAH) is a disease characterized by lung vascular obstruction, endothelial dysfunction, and heterozygous germline mutations in BMPR2, which encodes the bone morphogenetic protein (BMP) type II receptor. Previous research has shown that silencing of endothelial BMPR2 transcripts impairs cell surface receptor trafficking through the TGN. However, the role of BMPR-II in actin assembly, PI dynamics, their functional impact on angiogenesis, and the contribution of alternative BMPR2-derived circular RNAs (circRNA) to these processes remain unexplored. This study explored the hypothesis that endothelial BMPR2 loss alters the structures of organelles central to trafficking and cytoskeletal assembly dynamics, resulting in impaired intracellular trafficking and an associated hyperproliferative phenotype. Results: Human pulmonary arterial endothelial cells (HPAECs) treated with siRNA targeting linear BMPR2 transcripts (siLn), BMPR2-derived circ5078 (siCIRC), or both (siBMPR2) demonstrated abnormalities in TGN structures, enlarged early endosomes, and an altered cytoskeleton compared to controls. Additionally, siBMPR2 cells exhibited accelerated ERK phosphorylation kinetics upon VEGF stimulation, similar to siCIRC and siLn HPAECs. Further, siBMPR2 HPAECs demonstrated an imbalance in the levels of the PI species PI4P and PI(4,5)P2. Conclusion: This study revealed abnormalities in intracellular organelles and the cytoskeleton, altered ERK phosphorylation kinetics in response to VEGF stimulation, and differential abundance of PI4P and PI(4,5)P2 in BMPR2-silenced HPAECs.