title: Targeting the IRE1α/XBP1 and ATF6 arms of the unfolded protein response enhances VEGF blockade to prevent retinal and choroidal neovascularization.
abstract: Although anti-vascular endothelial growth factor (VEGF) treatments reduce pathological neovascularization in the eye and in tumors, the regression is often not sustainable or is incomplete. We investigated whether vascular endothelial cells circumvent anti-VEGF therapies by activating the unfolded protein response (UPR) to override the classic extracellular VEGF pathway. Exposure of endothelial cells to VEGF, high glucose, or H2O2 up-regulated the X-box binding protein-1/inositol-requiring protein-1 (IRE1) α and activating transcription factor 6 (ATF6) arms of the UPR compared with untreated cells. This was associated with increased expression in α-basic crystallin (CRYAB), which has previously bound VEGF. siRNA knockdown or pharmacological blockade of IRE1α, ATF6, or CRYAB increased intracellular VEGF degradation and decreased full-length intracellular VEGF. Inhibition of IRE1α, ATF6, or CRYAB resulted in an approximately 40% reduction of in vitro angiogenesis, which was further reduced in combination with a neutralizing antibody against extracellular VEGF. Blockade of IRE1α or ATF6 in the oxygen-induced retinopathy or choroidal neovascularization mouse models caused an approximately 35% reduction in angiogenesis. However, combination therapy of VEGF neutralizing antibody with UPR inhibitors or siRNAs reduced retinal/choroidal neovascularization by a further 25% to 40%, and this inhibition was significantly greater than either treatment alone. In conclusion, activation of the UPR sustains angiogenesis by preventing degradation of intracellular VEGF. The IRE1α/ATF6 arms of the UPR offer a potential therapeutic target in the treatment of pathological angiogenesis.
authors: Department of Pharmacology and Therapeutics, University of Florida, Gainesville, Florida 32610, USA.
authors: Li
authors: L
authors: Liu
authors: Xiaoping
authors: X
authors: Qi
authors: Zhijuan
authors: Z
authors: Chen
authors: Lynn
authors: L
authors: Shaw
authors: Jun
authors: J
authors: Cai
authors: Layton H
authors: LH
authors: Smith
authors: Maria B
authors: MB
authors: Grant
authors: Michael E
authors: ME
authors: Boulton
mesh_terms: D051702:Activating Transcription Factor 6 / Q000378:metabolism*; D000818:Animals; D002417:Cattle; D020256:Choroidal Neovascularization / Q000473:pathology / Q000517:prevention & control*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004195:Disease Models, Animal; D059865:Endoplasmic Reticulum Stress / Q000187:drug effects; D042783:Endothelial Cells / Q000187:drug effects / Q000378:metabolism; D005110:Extracellular Space / Q000187:drug effects / Q000378:metabolism; D055785:Gene Knockdown Techniques; D042541:Intracellular Space / Q000187:drug effects / Q000378:metabolism; D007834:Lasers; D007928:Lethal Dose 50; D051379:Mice; D008810:Mice, Inbred C57BL; D055806:Microvessels / Q000473:pathology; D059748:Proteolysis / Q000187:drug effects; D034741:RNA, Small Interfering / Q000378:metabolism; D000071701:Regulatory Factor X Transcription Factors; D012160:Retina / Q000473:pathology; D015861:Retinal Neovascularization / Q000473:pathology / Q000517:prevention & control*; D015398:Signal Transduction / Q000187:drug effects; D014157:Transcription Factors / Q000378:metabolism*; D056811:Unfolded Protein Response / Q000187:drug effects; D015854:Up-Regulation / Q000187:drug effects; D042461:Vascular Endothelial Growth Factor A / Q000037:antagonists & inhibitors* / Q000378:metabolism / Q000494:pharmacology; D000071717:X-Box Binding Protein 1; D038203:alpha-Crystallin B Chain / Q000378:metabolism
chemical_list: D051702:Activating Transcription Factor 6; D004268:DNA-Binding Proteins; D034741:RNA, Small Interfering; D000071701:Regulatory Factor X Transcription Factors; D014157:Transcription Factors; D042461:Vascular Endothelial Growth Factor A; D000071717:X-Box Binding Protein 1; C000605544:Xbp1 protein, mouse; D038203:alpha-Crystallin B Chain
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