Role of Copper Transport Protein Antioxidant 1 in Angiotensin II–Induced Hypertension

Abstract

Extracellular superoxide dismutase (SOD3) is a secretory copper enzyme involved in protecting angiotensin II (Ang II)-induced hypertension. We previously found that Ang II upregulates SOD3 expression and activity as a counter-regulatory mechanism; however, underlying mechanisms are unclear. Antioxidant-1 (Atox1) is shown to act as a copper-dependent transcription factor as well as copper chaperone for SOD3 in vitro, but its role in Ang II-induced hypertension in vivo is unknown. Here we show that Ang II infusion increases Atox1 expression as well as SOD3 expression and activity in aortas of wild-type mice, which are inhibited in mice lacking Atox1. Accordingly, Ang II increases vascular O2•− production, reduces endothelium-dependent vasodilation and increases vasoconstriction in mesenteric arterioles to a greater extent in Atox1−/− than in wild-type mice. This contributes to augmented hypertensive response to Ang II in Atox1−/− mice. In cultured vascular smooth muscle cells, Ang II promotes translocation of Atox1 to the nucleus, thereby increasing SOD3 transcription by binding to Atox1 responsive element in the SOD3 promoter. Furthermore, Ang II increases Atox1 binding to the copper exporter ATP7A which obtains copper from Atox1 as well as translocation of ATP7A to plasma membranes where it colocalizes with SOD3. As its consequence, Ang II decreases vascular copper levels, which is inhibited in Atox1−/− mice. In summary, Atox1 functions to prevent Ang II-induced endothelial dysfunction and hyper-contraction in resistant vessels as well as hypertension in vivo by reducing extracellular O2•− levels via increasing vascular SOD3 expression and activity.

An Expanding Range of Functions for the Copper Chaperone/Antioxidant Protein Atox1

“…These pioneering studies were subsequently replicated in a mammalian system, where genetic inactivation of a mouse Atx1 ortholog (Atox1) was found to greatly impair copper delivery from placenta to fetus resulting in copper deficiency and high mortality of newborn pups (29). More recent studies using Atox1 -/ -mice with a different genetic background found less copper deficiency and mortality compared to the earlier report (72). However, this latter study revealed a significant inhibitory effect of Atox1 inactivation on copper delivery (via Cu-ATPase ATP7A) to SOD3, an important antioxidant molecule at the cell surface.…”

“…However, this latter study revealed a significant inhibitory effect of Atox1 inactivation on copper delivery (via Cu-ATPase ATP7A) to SOD3, an important antioxidant molecule at the cell surface. In addition, downregulation of SOD3 mRNA and protein in response to Atox1 inactivation was observed, making connection between copper metabolism and anti-oxidant defense even more intertwined (72 These findings opened an avenue for intensive investigations of biochemical properties of Atox1 and the mechanism of Atox1-mediated copper delivery to the secretory pathway. Over the years, great progress has been made in these areas Copper enters the cell through the high-affinity copper transporter Ctr1 and binds to cytosolic copper chaperones (Atox1 and CCS) and/or small thiol molecules such as glutathione for further intracellular distribution (''Labile'' Cu pool).…”

“…Data obtained in several different organisms indicate that, although important, Atox1 is not obligatory for the activity of the copper-exporting systems, and may only be required for copper export via secretory pathway when copper is limiting. Mice and flies with the genetically deleted Atox1 are born and develop into adulthood, whereas this does not happen if they lack active copper transporters (34,72). New data have emerged showing a protective effect of Atox1 on cells' growth in low GSH (30) along with the studies illustrating the dual role of Atox1 in maintaining the mRNA levels for the secreted Cu/Zndependent superoxide dismutase 3, SOD3 along with transferring copper to SOD3 during biosynthesis (42).…”

Behind the Link between Copper and Angiogenesis: Established Mechanisms and an Overview on the Role of Vascular Copper Transport Systems

“…The physical association between ATP7A and SOD3 in angiotensin II-treated mutant mice attests to the attempt to rescue the increase of vascular superoxide through an enhanced loading of the antioxidant cuproenzyme with copper [141]. Ozumi et al [142] pointed out the role of the cytosolic copper transport protein ATOX1, from which ATP7A pumps obtain copper ions, in the vascular response to angiotensin II. The importance of ATOX1 in such a context is emphasized by the restricted intracellular copper content (10 -18 M ) [76].…”

“…The importance of ATOX1 in such a context is emphasized by the restricted intracellular copper content (10 -18 M ) [76]. An enhanced copper egress from endothelia has been detected in response to angiotensin II, associated with active SOD3 biosynthesis and release [142]. Interestingly, a recent study on vascular complications in diabetes mellitus induced in mice evidenced a reduced expression of ATP7A in blood vessels, associated with an impairment of SOD3 activity [143].…”