Pak1 plays an important role in several cellular processes including cell migration, but its role in pathological angiogenesis is not known. Here we have determined its role in pathological retinal angiogenesis using Oxygen Induced Retinopathy (OIR) model. VEGFA induced Pak1 and its effector cofilin phosphorylation in time-dependent as well as p38β-dependent manner in HRMVECs. Depletion of the levels of any of these molecules inhibited VEGFA-induced HRMVECs F-actin stress fiber formation, migration, proliferation, sprouting, and tube formation. In accordance with these observations, hypoxia induced Pak1 and Cofilin phosphorylation with p38β being downstream to Pak1 and upstream to cofilin. Furthermore, Pak1 deficiency abolished hypoxia-induced p38β and cofilin phosphorylation and abrogated retinal endothelial cell proliferation, tip cell formation and neovascularization. In addition, siRNA-mediated downregulation of p38β or cofilin levels in WT mouse retina also diminished endothelial cell proliferation, tip cell formation and neovascularization. Together, these observations suggest that, while p38β-Pak1-cofilin axis is required for HRMVECs migration, proliferation, sprouting and tubulogenesis, Pak1-p38β-cofilin signaling is essential for hypoxia-induced retinal endothelial cell proliferation, tip cell formation and neovascularization.
Matrix stiffness modulates tip cell formation through the p-PXN-Rac1-YAP signaling axis
