ATP7A and ATP7B copper transporters have distinct functions in the regulation of neuronal dopamine-β-hydroxylase

Abstract

Edited by Ruma Banerjee The copper (Cu) transporters ATPase copper-transporting alpha (ATP7A) and ATPase copper-transporting beta (ATP7B) are essential for the normal function of the mammalian central nervous system. Inactivation of ATP7A or ATP7B causes the severe neurological disorders, Menkes disease and Wilson disease, respectively. In both diseases, Cu imbalance is associated with abnormal levels of the catecholamine-type neurotransmitters dopamine and norepinephrine. Dopamine is converted to norepinephrine by dopamine-␤-hydroxylase (DBH), which acquires its essential Cu cofactor from ATP7A. However, the role of ATP7B in catecholamine homeostasis is unclear. Here, using immunostaining of mouse brain sections and cultured cells, we show that DBH-containing neurons express both ATP7A and ATP7B. The two transporters are located in distinct cellular compartments and oppositely regulate the export of soluble DBH from cultured neuronal cells under resting conditions. Down-regulation of ATP7A, overexpression of ATP7B, and pharmacological Cu depletion increased DBH retention in cells. In contrast, ATP7B inactivation elevated extracellular DBH. Proteolytic processing and the specific activity of exported DBH were not affected by changes in ATP7B levels. These results establish distinct regulatory roles for ATP7A and ATP7B in neuronal cells and explain, in part, the lack of functional compensation between these two transporters in human disorders of Cu imbalance. Copper (Cu) homeostasis is essential for the normal development and function of the mammalian brain (1-8). Either Cu deficiency or excess is highly detrimental. Two ATPdriven Cu transporters, ATP7A and ATP7B, play essential roles in balancing Cu levels in the brain. Inactivating mutations in either ATP7A or ATP7B are associated with severe neurologic disorders (Menkes disease and Wilson disease, respectively). In Menkes disease, one of the major biochemical hallmarks is an increased ratio of dopamine (DA) 2 to norepinephrine (NE), which is used as an early diagnostic marker of this disorder (9-12). In Wilson disease, catecholamine metabolism is also altered, as evidenced by a diminished secretion of DA and NE as well as an abnormal functioning of the dopaminergic system (13). Wilson disease patients present with parkinsonism, psychotic episodes, and schizophrenia, in addition to a spectrum of neurologic abnormalities. These clinical observations and similar findings in animal models of the Cu-related disorders suggest that both ATP7A and ATP7B contribute to catecholamine metabolism in the brain. However, our knowledge about specific roles of these transporters is very limited. Dopamine-␤-hydroxylase (DBH) is an important molecular link between the catecholamine metabolism and neuronal Cu homeostasis. This essential enzyme converts DA to NE in a reaction that requires a bound Cu cofactor (14, 15). DBH obtains Cu within the lumen of the secretory pathway during its biosynthetic maturation. Current evidence suggests that ATP7A, which transfers Cu from the cytoso...

Dopamine beta‐hydroxylase and its genetic variants in human health and disease

“…Recent reports have linked copper intracellular availability with intracellular trafficking and secretion of soluble DβH in the human neuroblastoma cell line SH‐SY5Y (Schmidt et al ). The authors used a genetic knockout of ATPase‐dependent copper transporters (ATP7A) or pharmacological intervention using copper chelators (bathocuproine disulfonate and tetrathiomolybdate).…”

“…The authors used a genetic knockout of ATPase‐dependent copper transporters (ATP7A) or pharmacological intervention using copper chelators (bathocuproine disulfonate and tetrathiomolybdate). Both methods resulted in diminished DβH soluble release and reduced intercellular DβH compartment size (Schmidt et al ). The authors also examined the effects of excess copper load by copper chloride (CuCl 2 ); interestingly, this did not alter soluble DβH level or compartment size.…”

General Aspects of Metal Ions as Signaling Agents in Health and Disease

“…In the CNS, copper signaling may influence synaptic transmission indirectly by modulating the synthesis of neurotransmitters, e.g., via the peptidylglycine α-amidating monooxygenase (PAM) [ 147 ] and dopamine β-hydroxylase (DBH) [ 148 ] pathways, or directly by being released into the synaptic cleft from the terminals of glutamatergic neurons [ 149 , 150 ]. However, the signal associated with copper ions has a different effect depending on the region where it is released; in the amygdala, copper acts towards enhancement of LTP [ 151 ], while in the hippocampus it shows a tendency to inhibit synaptic plasticity [ 145 ].…”

Dopamine β hydroxylase (DBH) polymorphisms do not contribute towards the clinical course of Wilson's disease in Indian patients

“…reported reduced expression and activity of DBH in ATP7B null mice. Again, immunohistochemistry of rat brain sections and cell culture studies by Schmidt et al . revealed that inactivation of ATP7B decreases DBH levels in neurons.…”