Chemical changes drive rapid copper transport in developing neurons
Researchers at Johns Hopkins University report that developing neurons shift how they use copper much more rapidly than mature neurons. Using a precision fluorescent sensor in chicken embryos, the team detected dramatic changes in copper allocation as neurons mature—shifting the metal’s role from mitochondrial energy production and antioxidant defense toward activation of copper-dependent enzymes in the secretory pathway that support neuronal signaling and differentiation.
In a study published in Nature Communications, the investigators describe how small redox changes in cells lead to a coordinated increase in copper flow into the secretory pathway during neuronal differentiation. These results clarify how neurons rapidly reassign copper to meet changing biochemical needs during development.
“Biochemical studies had shown that many proteins involved in neural differentiation require copper, and we also knew there is a big spike in the brain’s copper levels at a certain stage of development,” says Svetlana Lutsenko, Ph.D., professor of physiology at the Johns Hopkins University School of Medicine. “With these new results, we now know much more about how developing neurons repurpose copper for their evolving functions.”
Postdoctoral fellow Yuta Hatori, Ph.D., used a genetically encoded protein sensor that changes its fluorescence depending on the cellular redox state—the balance between reduction and oxidation that governs many biochemical reactions. Cells manage their internal redox environment largely through the glutathione system: the ratio between reduced glutathione (GSH) and its oxidized form, glutathione disulfide (GSSG). Working with colleagues in the Department of Neuroscience and under the leadership of Shanthini Sockanathan, D.Phil., the team introduced the sensor gene into chicken embryos at different developmental stages and tracked how the redox state of motor neurons changes as they differentiate.
Further experiments revealed a mechanistic link between redox changes and copper transport. As neurons differentiate, the cytosolic environment becomes more uniformly reducing, which facilitates reduction of the copper chaperone Atox1. Reduction of Atox1 exposes its copper-binding site and frees the protein to shuttle copper. At the same time, differentiating neurons increase expression of Atox1 and the copper transporter ATP7A. Together these changes boost copper flux into the secretory pathway, delivering the metal to copper-dependent enzymes whose expression rises in mature neurons and which are essential for neuronal signaling.
The study highlights why precise intracellular copper routing is critical for normal brain function. Lutsenko notes that the same redox-sensitive mechanisms could be vulnerable in aging or disease. Age-related decline in redox control might alter copper handling in the secretory pathway, with potential consequences for neuronal maintenance and signaling.
With this improved understanding of normal copper dynamics during neuronal differentiation, the Johns Hopkins team plans to investigate what happens when copper processing fails. Their next studies will examine cells from patients with Wilson disease, a genetic disorder that disrupts copper metabolism, to determine whether the redox-regulated copper routing described here is impaired in disease states.
Other contributors to the paper include Ye Yan, Katharina Schmidt, Eri Furukawa, Nesrin M. Hasan, Nan Yang and Chin-Nung Liu, all affiliated with the Johns Hopkins University School of Medicine.
Funding: This research was supported by the National Institute of General Medical Sciences (R01 GM101502), the National Institute of Diabetes and Digestive and Kidney Diseases (DK071865), and the National Institute of Neurological Disorders and Stroke (NS046336).
Source: Shawna Williams — Johns Hopkins Medicine
Image credit: The image is in the public domain.
Original research: Full open-access article “Neuronal differentiation is associated with a redox-regulated increase of copper flow to the secretory pathway” by Yuta Hatori, Ye Yan, Katharina Schmidt, Eri Furukawa, Nesrin M. Hasan, Nan Yang, Chin-Nung Liu, Shanthini Sockanathan and Svetlana Lutsenko, Nature Communications. Published online February 16, 2016. doi:10.1038/ncomms10640
Abstract
Neuronal differentiation is associated with a redox-regulated increase of copper flow to the secretory pathway
Brain development depends on tightly regulated copper homeostasis: both deficiency and excess of copper cause severe neurological problems. The authors demonstrate that neuronal differentiation raises cellular demand for copper, particularly within the secretory pathway. Copper delivery to this compartment is controlled by coordinated transcriptional and metabolic changes. Quantitative real-time imaging revealed a gradual shift in the oxidation state of cytosolic glutathione during differentiation, moving from a range of redox states to a uniformly reducing cytosol. This change promotes reduction of the copper chaperone Atox1, exposing its metal-binding site and enabling copper transfer. Concurrently, expression of Atox1 and the copper transporter ATP7A increases, producing enhanced copper flux through the secretory pathway. The resulting redistribution balances cytosolic copper and supplies cofactors to copper-dependent enzymes, whose expression rises in differentiated neurons. The direct link between glutathione-driven redox changes and copper compartmentalization enables rapid metabolic adjustments essential for normal neuronal function.
“Neuronal differentiation is associated with a redox-regulated increase of copper flow to the secretory pathway” by Yuta Hatori et al., Nature Communications. Published online February 16, 2016. doi:10.1038/ncomms10640