Abstract
Dopamine (DA) is a neurotransmitter that plays roles in movement, cognition, attention, and reward responses, and deficient DA signaling is associated with the progression of a number of neurological diseases, such as Parkinson's disease. Due to its critical functions, DA expression levels in the brain are tightly controlled, with one important and rate-limiting step in its biosynthetic pathway being catalyzed by tyrosine hydroxylase (TH), an enzyme that uses iron ion (Fe2+) as a cofactor. A role for metal ions has additionally been associated with the etiology of Parkinson's disease. However, the way dopamine synthesis is regulated in vivo or whether regulation of metal ion levels is a component of DA synthesis is not fully understood. Here, we analyze the role of Catsup, the Drosophila ortholog of the mammalian zinc transporter SLC39A7 (ZIP7), in regulating dopamine levels. We found that Catsup is a functional zinc transporter that regulates intracellular zinc distribution between the ER/Golgi and the cytosol. Loss-of-function of Catsup leads to increased DA levels, and we showed that the increased dopamine production is due to a reduction in zinc levels in the cytosol. Zinc ion (Zn2+) negatively regulates dopamine synthesis through direct inhibition of TH activity, by antagonizing Fe2+ binding to TH, thus rendering the enzyme ineffective or non-functional. Our findings uncovered a previously unknown mechanism underlying the control of cellular dopamine expression, with normal levels of dopamine synthesis being maintained through a balance between Fe2+ and Zn2+ ions. The findings also provide support for metal modulation as a possible therapeutic strategy in the treatment of Parkinson's disease and other dopamine-related diseases.
