Gin-Fu Chen

Unexpected role of the copper transporter ATP7A in PDGF-induced vascular smooth

Rationale: Copper, an essential nutrient, has been implicated in vascular remodeling and atherosclerosis with unknown mechanism. Bioavailability of intracellular copper is regulated not only by the copper importer CTR1 (copper transporter 1) but also by the copper exporter ATP7A (Menkes ATPase), whose function is achieved through copper-dependent translocation from trans-Golgi network (TGN). Platelet-derived growth factor (PDGF) promotes vascular smooth muscle cell (VSMC) migration, a key component of neointimal formation. Objective: To determine the role of copper transporter ATP7A in PDGF-induced VSMC migration. Methods and Results: Depletion of ATP7A inhibited VSMC migration in response to PDGF or wound scratch in a CTR1/copper-dependent manner. PDGF stimulation promoted ATP7A translocation from the TGN to lipid rafts, which localized at the leading edge, where it colocalized with PDGF receptor and Rac1, in migrating VSMCs. Mechanistically, ATP7A small interfering RNA or CTR small interfering RNA prevented PDGF-induced Rac1 translocation to the leading edge, thereby inhibiting lamellipodia formation. In addition, ATP7A depletion prevented a PDGF-induced decrease in copper level and secretory copper enzyme precursor prolysyl oxidase (Pro-LOX) in lipid raft fraction, as well as PDGF-induced increase in LOX activity. In vivo, ATP7A expression was markedly increased and copper accumulation was observed by synchrotron-based x-ray fluorescence microscopy at neointimal VSMCs in wire injury model. Conclusions: These findings suggest that ATP7A plays an important role in copper-dependent PDGF-stimulated VSMC migration via recruiting Rac1 to lipid rafts at the leading edge, as well as regulating LOX activity. This may contribute to neointimal formation after vascular injury. Our findings provide insight into ATP7A as a novel therapeutic target for vascular remodeling and atherosclerosis.

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

Extracellular superoxide dismutase (SOD3) is a secretory copper enzyme involved in protecting angiotensin II (Ang II)–induced hypertension. We found previously that Ang II upregulates SOD3 expression and activity as a counterregulatory mechanism; however, underlying mechanisms are unclear. Antioxidant 1 (Atox1) is shown to act as a copper-dependent transcription factor, as well as a 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 superoxide production, reduces endothelium-dependent vasodilation, and increases vasoconstriction in mesenteric arteries 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 hypercontraction in resistant vessels, as well as hypertension, in vivo by reducing extracellular superoxide levels via increasing vascular SOD3 expression and activity.

Role of copper transport protein Antioxidant-1 in Angiotensin II-induced hypertension: A key regulator of Extracellular SOD

Extracellular superoxide dismutase (SOD3) is a secretory copper enzyme involved in protecting angiotensin II (Ang II)–induced hypertension. We found previously that Ang II upregulates SOD3 expression and activity as a counterregulatory mechanism; however, underlying mechanisms are unclear. Antioxidant 1 (Atox1) is shown to act as a copper-dependent transcription factor, as well as a 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 superoxide production, reduces endothelium-dependent vasodilation, and increases vasoconstriction in mesenteric arteries 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 hypercontraction in resistant vessels, as well as hypertension, in vivo by reducing extracellular superoxide levels via increasing vascular SOD3 expression and activity.