Introduction:
Neovascularization in response to ischemia depends on inflammation, angiogenesis and reactive oxygen species (ROS). Copper (Cu) is implicated in inflammation and angiogenesis. We reported that cytosolic Cu chaperone Atox1 activates secretory Cu enzymes lysyl oxidase (LOX), while nuclear Atox1 functions as a Cu-dependent transcription factor to promote ROS/NFkB-dependent inflammation in endothelial cells (ECs). However, mechanism of Atox1 nuclear translocation as well as role of endothelial Atox1 in inflammatory angiogenesis in vivo remain unknown. SUMOylation and its deSUMOylation by SENPs regulates transcription factor function. Silica analysis identified a conserved putative SUMOylation motif at Lys(K3) of Atox1.
Results:
Atox1 expression was dramatically increased in angiogenic ECs in mice hindlimb ischemia model. EC-specific Atox1-deficient mice significantly reduced angiogenesis (CD31+, 67%) and Mac+ inflammatory cells in ischemic tissues. In cultured ECs, inflammatory cytokine TNFα or hypoxia promoted Atox1 nuclear translocation and Atox1 SUMOylation (3.6-fold), which were inhibited by antioxidant NAC or overexpression of “SUMO-dead” Atox1K3R. Mechanistically, TNFα induced Cys603 oxidation/inactivation of SENP1 in cytosol, which in turn increased Atox1 SUMOylation and nuclear translocation. Functionally, siAtox1or Atox1K3R inhibited TNFα-induced inflammatory/angiogenic genes VCAM/ICAM, IL-15 and RANTES. In nucleus with reduced state, ChIP assay using SUMO-Atox1 revealed that Atox1 deSUMOylation by nuclear SENP1 increases Atox1 transcriptional activity for inflammatory genes. In parallel, Atox1K3R which maintains Cu chaperone function inhibited TNFα-induced EC permeability by activating LOX. In vivo, Atox1 SUMOylation was increased after hindlimb ischemia while CRISPR/Cas9-generated SUMO-dead Atox1K3R knock-in mice showed impaired angiogenesis in hindlimb ischemia model.
Conclusion:
Atox1 SUMOylation via oxidative/inactivation of SENP1 in cytosol promotes: 1) its translocation to nucleus where deSUMOylated Atox1 can function as Cu-dependent transcription factor to drive inflammatory angiogenesis and 2) EC barrier dysfunction in inflamed/hypoxic ECs after ischemic injury.
Induction of inflammatory angiogenesis by monocyte chemoattractant protein-1
