Characterization of murine polyspecific monoamine transporters

Abstract

The dysregulation of monoamine clearance in the central nervous system occurs in various neuropsychiatric disorders, and the role of polyspecific monoamine transporters in monoamine clearance is increasingly highlighted in recent studies. However, no study to date has properly characterized polyspecific monoamine transporters in the mouse brain. In the present study, we examined the kinetic properties of three mouse polyspecific monoamine transporters [organic cation transporter 2 (Oct2), Oct3, and plasma membrane monoamine transporter (Pmat)] and compared the absolute mRNA expression levels of these transporters in various brain areas. First, we evaluated the affinities of each transporter for noradrenaline, dopamine, serotonin, and histamine, and found that mouse ortholog substrate affinities were similar to those of human orthologs. Next, we performed drug inhibition assays and identified interspecies differences in the pharmacological properties of polyspecific monoamine transporters; in particular, corticosterone and decynium‐22, which are widely recognized as typical inhibitors of human OCT3, enhanced the transport activity of mouse Oct3. Finally, we quantified absolute mRNA expression levels of each transporter in various regions of the mouse brain and found that while all three transporters were ubiquitously expressed, Pmat was the most highly expressed transporter. These results provide an important foundation for future translational research investigating the roles of polyspecific monoamine transporters in neurological and neuropsychiatric disease.

Comparative analysis of novel decynium-22 analogs to inhibit transport by the low-affinity, high-capacity monoamine transporters, organic cation transporters 2 and 3, and plasma membrane monoamine transporter

“…5C) are similar to prior studies (Hayer-Zillgen et al, 2002), where corticosterone preferentially bound to hOCT3 (IC 50 = 0.6 μM) relative to hOCT2 (IC 50 ≈ 80 μM). Corticosterone is also a poor blocker of hPMAT-driven transport (Engel, Zhou, & Wang, 2004; Russ, H. et al, 1993), as supported by its observed IC 50 ≈ 1 mM in our experiments, and in the literature (Engel et al, 2004; Miura et al, 2017). The consistency of our results with the literature establishes an important platform on which to perform comparative analyses of D22 analogs in human transporter expressing cell lines.…”

“…Mouse models are an essential preclinical resource to study the action of low-affinity transporters. Functional similarities have been observed between the uptake kinetics of substrates like dopamine, MPP + , and serotonin by human and mouse PMAT (Miura et al, 2017; Shirasaka et al, 2016). On the other hand, hOCT3 and mOCT3 were found to share similar affinities for MPP + , but not serotonin (Massmann et al, 2014).…”

Extreme enhancement or depletion of serotonin transporter function and serotonin availability in autism spectrum disorder

“…These studies suggest that "uptake 2" mechanisms, putatively OCT3, may play a significant role in 5-HT signaling and homeostasis, particularly when SERT function is reduced [147,152,153]. Further, uptake by OCT2 [154,155] and OCT3 is inhibited by corticosterone [148,156,157]. Therefore, hormonal interference of "uptake 2" clearance in later life could contribute to stressexacerbated symptoms of autism, especially during perceived stressful social situations in cases where these secondary transporters may have been permanently upregulated to compensate for impaired SERT function.…”

Constitutive plasma membrane monoamine transporter (PMAT, Slc29a4) deficiency subtly affects anxiety‐like and coping behaviours

“…Expression of PMAT is greater in brain than in other organs, and PMAT is more highly expressed in brain than other uptake 2 transporters (Dahlin, Xia, Kong, Hevner, & Wang, 2007;Duan & Wang, 2010;Engel, Zhou, & Wang, 2004;Miura et al, 2017). Therefore, loss of PMAT function might have more pronounced behavioural effects than those observed in mice lacking an OCT.…”

“…Moreover, the polyspecific uptake 2 transporters exhibit differential affinities for monoamine neurotransmitters. PMAT preferentially transports serotonin and dopamine, whereas OCTs display higher affinities for histamine, epinephrine and norepinephrine (Duan & Wang, ; Miura et al., ). Thus, serotonergic and dopaminergic signalling in brains of PMAT‐deficient mice might be prolonged, although this has not yet been directly investigated.…”