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General Comment |
The dopamine transporter (DAT1) that acts to take released dopamine back up into presynaptic terminals has been
implicated in human disorders such as parkinsonism, Tourette syndrome, and substance abuse.
NCBI Summary:
This gene encodes a dopamine transporter which is a member of the sodium- and chloride-dependent neurotransmitter transporter family. The 3' UTR of this gene contains a 40 bp tandem repeat, referred to as a variable number tandem repeat or VNTR, which can be present in 3 to 11 copies. Variation in the number of repeats is associated with idiopathic epilepsy, attention-deficit hyperactivity disorder, dependence on alcohol and cocaine, susceptibility to Parkinson disease and protection against nicotine dependence.[provided by RefSeq, Nov 2009]
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Comment |
Dopamine in human follicular fluid is associated with cellular uptake and metabolism-dependent generation of reactive oxygen species in granulosa cells: implications for physiology and pathology. Saller S 2013 et al.
STUDY QUESTION
Is the neurotransmitter dopamine (DA) in the human ovary involved in the generation of reactive oxygen species (ROS)?
SUMMARY ANSWER
Human ovarian follicular fluid contains DA, which causes the generation of ROS in cultured human granulosa cells (GCs), and alterations of DA levels in follicular fluid and DA uptake/metabolism in GCs in patients with polycystic ovary syndrome (PCOS) are linked to increased levels of ROS.
WHAT IS KNOWN ALREADY
DA is an important neurotransmitter in the brain, and the metabolism of DA results in the generation of ROS. DA was detected in human ovarian homogenates, but whether it is present in follicular fluid and plays a role in the follicle is not known.
STUDY DESIGN, SIZE AND DURATION
We used human follicular fluid from patients undergoing in vitro fertilization (IVF), GCs from patients with or without PCOS and also employed mathematical modeling to investigate the presence of DA and its effects on ROS.
PARTICIPANTS/MATERIALS, SETTING AND METHODS
DA in follicular fluid and GCs was determined by enzyme-linked immunosorbent assay. GC viability, apoptosis and generation of ROS were monitored in GCs upon addition of DA. Inhibitors of DA uptake and metabolism, an antioxidant and DA receptor agonists, were used to study cellular uptake and the mechanism of DA-induced ROS generation. Human GCs were examined for the presence and abundance of transcripts of the DA transporter (DAT; SLC6A3), the DA-metabolizing enzymes monoamine oxidases A/B (MAO-A/B) and catechol-O-methyltransferase and the vesicular monoamine transporter. A computational model was developed to describe and predict DA-induced ROS generation in human GCs.
MAIN RESULTS AND ROLE OF CHANCE
We found DA in follicular fluid of ovulatory follicles of the human ovary and in GCs. DAT and MAO-A/B, which are expressed by GCs, are prerequisites for a DA receptor-independent generation of ROS in GCs. Blockers of DAT and MAO-A/B, as well as an antioxidant, prevented the generation of ROS (P < 0.05). Agonists of DA receptors (D1 and D2) did not induce ROS. DA, in the concentration range found in follicular fluid, did not induce apoptosis of cultured GCs. Computational modeling suggested, however, that ROS levels in GCs depend on the concentrations of DA and on the cellular uptake and metabolism. In PCOS-derived follicular fluid, the levels of DA were higher (P < 0.05) in GCs, the transcript levels of DAT and MAO-A/B in GCs were 2-fold higher (P < 0.05) and the DA-induced ROS levels were found to be more than 4-fold increased (P < 0.05) compared with non-PCOS cells. Furthermore, DA at a high concentration induced apoptosis in PCOS-derived GCs.
LIMITATIONS, REASONS FOR CAUTION
While the results in IVF-derived follicular fluid and in GCs reveal for the first time the presence of DA in the human follicular compartment, functions of DA could only be studied in IVF-derived GCs, which can be viewed as a cellular model for the periovulatory follicular phase. The full functional importance of DA-induced ROS in small follicles and other compartments of the ovary, especially in PCOS samples, remains to be shown.
WIDER IMPLICATIONS OF THE FINDINGS
The results identify DA as a factor in the human ovary, which, via ROS generation, could play a role in ovarian physiology and pathology. The results obtained in samples from women with PCOS suggest the involvement of DA, acting via ROS, in this condition.
STUDY FUNDING/COMPETING INTERESTS
This work was supported by a grant from DFG MA1080/17-3 and in part MA1080/19-1. There are no competing interests.
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Comment |
Mayerhofer A, reported that intraovarian neurons contain tyrosine hydroxylase (TH), the
rate-limiting enzyme in catecholamine biosynthesis. They showed that the primate ovary expresses both the
genes encoding TH and dopamine beta-hydroxylase (DBH), the key enzymes in
norepinephrine (NE) biosynthesis.
Oocytes contain neither TH mRNA nor protein,
indicating that they are unable to synthesize dopamine (DA). They did, however,
express a DA transporter gene identical to that found in human brain. The
physiological relevance of this transporter system and DBH in oocytes was
indicated by the ability of isolated oocytes to metabolize exogenous DA into NE.
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