ABSTRACT
The importance of identifying VEGF-independent pathways in pathological angiogenesis is increasingly recognized as a result of the emerging drug resistance to anti-VEGF therapies. PDGF-CC is the third member of the PDGF family discovered after more than two decades of studies on PDGF-AA and PDGF-BB. The biological function of PDGF-CC and the underlying cellular and molecular mechanisms remain largely unexplored. Here, using different animal models, we report that PDGF-CC inhibition by neutralizing antibody, shRNA, or genetic deletion suppressed both choroidal and retinal neovascularization. Importantly, we revealed that PDGF-CC targeting acted not only on multiple cell types important for pathological angiogenesis, such as vascular mural and endothelial cells, macrophages, choroidal fibroblasts and retinal pigment epithelial cells, but also on the expression of other important angiogenic genes, such as PDGF-BB and PDGF receptors. At a molecular level, we found that PDGF-CC regulated glycogen synthase kinase (GSK)-3beta phosphorylation and expression both in vitro and in vivo. Activation of GSK3beta impaired PDGF-CC-induced angiogenesis, and inhibition of GSK3beta abolished the antiangiogenic effect of PDGF-CC blockade. Thus, we identified PDGF-CC as an important candidate target gene for antiangiogenic therapy, and PDGF-CC inhibition may be of therapeutic value in treating neovascular diseases.
Subject(s)
Lymphokines/genetics , Neovascularization, Pathologic/genetics , Platelet-Derived Growth Factor/genetics , RNA Interference , Animals , Antibodies, Neutralizing/pharmacology , Becaplermin , Blotting, Western , Cells, Cultured , Chick Embryo , Choroidal Neovascularization/genetics , Choroidal Neovascularization/metabolism , Choroidal Neovascularization/prevention & control , Female , Fluorescent Antibody Technique , Gene Expression Regulation , Glycogen Synthase Kinase 3/metabolism , Glycogen Synthase Kinase 3 beta , Humans , Lymphokines/immunology , Lymphokines/metabolism , Macrophages/cytology , Macrophages/drug effects , Macrophages/metabolism , Male , Mice , Mice, Inbred C57BL , Mice, Knockout , Neovascularization, Pathologic/metabolism , Neovascularization, Pathologic/prevention & control , Phosphorylation , Platelet-Derived Growth Factor/immunology , Platelet-Derived Growth Factor/metabolism , Proto-Oncogene Proteins c-sis , Receptors, Platelet-Derived Growth Factor/genetics , Receptors, Platelet-Derived Growth Factor/metabolism , Reverse Transcriptase Polymerase Chain ReactionABSTRACT
Platelet-derived growth factor CC (PDGF-CC) is the third member of the PDGF family discovered after more than two decades of studies on the original members of the family, PDGF-AA and PDGF-BB. The biological function of PDGF-CC remains largely to be explored. We report a novel finding that PDGF-CC is a potent neuroprotective factor that acts by modulating glycogen synthase kinase 3beta (GSK3beta) activity. In several different animal models of neuronal injury, such as axotomy-induced neuronal death, neurotoxin-induced neuronal injury, 6-hydroxydopamine-induced Parkinson's dopaminergic neuronal death, and ischemia-induced stroke, PDGF-CC protein or gene delivery protected different types of neurons from apoptosis in both the retina and brain. On the other hand, loss-of-function assays using PDGF-C null mice, neutralizing antibody, or short hairpin RNA showed that PDGF-CC deficiency/inhibition exacerbated neuronal death in different neuronal tissues in vivo. Mechanistically, we revealed that the neuroprotective effect of PDGF-CC was achieved by regulating GSK3beta phosphorylation and expression. Our data demonstrate that PDGF-CC is critically required for neuronal survival and may potentially be used to treat neurodegenerative diseases. Inhibition of the PDGF-CC-PDGF receptor pathway for different clinical purposes should be conducted with caution to preserve normal neuronal functions.
