TAK1: a potential therapeutic target for retinal neovascularization

Retinal neovascularization, or pathological angiogenesis in the retina, is a leading cause of blindness in developed countries. Pathological angiogenesis occurs through the complex activation of pro-inflammatory and pro-angiogenic pathways. Transforming growth factor-β-activated kinase 1 (TAK1) is a mitogen-activated protein kinase kinase kinase (MAPKKK) activated by TGF-β1 and other pro-inflammatory cytokines such as tumor necrosis factor α (TNFα) and interleukin-1 (IL-1). TAK1 is a key mediator of inflammation, innate immune responses, apoptosis and tissue homeostasis and plays an important role in physiological angiogenesis. Its role in pathological angiogenesis, particularly in retinal neovascularization, remains unclear. We investigated the regulatory role of TAK1 in pathological angiogenesis in the retina. Transcriptome analysis of human retina featuring retinal neovascularization revealed enrichment of known TAK1-mediated signaling pathways. Genetic or pharmacological inhibition of TAK1 activation in human endothelial cells induced by TNFα or IL-1 stimulation led to inhibition of phosphorylation of major kinases, including nuclear factor kappa B (NFκB) and mitogen-activated protein kinase (MAPK) signaling pathways. Suppression of this signaling, in turn, decreased expression of downstream genes associated with inflammation and angiogenesis, suggesting that TAK1 is required for these pathological processes. Transcriptome analysis of endothelial cells revealed that TAK1 knockout prevented inflammatory and immune responses induced by TNFα stimulation, mainly via cytokine and chemokine activity. Selective inhibition of TAK1 by 5Z-7-oxozeaenol in vitro ameliorated pro-angiogenic activity, including endothelial cell proliferation, migration and tube formation. Moreover, 5Z-7-oxozeaenol attenuated aberrant retinal angiogenesis in rats following oxygen-induced retinopathy. Our finding shows that TAK1 plays a key role in pathological angiogenesis in the retina. Selective inhibition of TAK1 prevents pathological angiogenesis, suggesting that TAK1 could be a potential therapeutic target for retinal neovascularization. GRAPHICAL ABSTRACT