Biology subjects

Newman, A. H.

Publications and source records attributed to Newman, A. H..

8 recordsLinked to original sources

bioRxiv2024

A subtle modification of modafinil-based DAT inhibitors changes conformational preference

Modafinil analogs with either a sulfoxide or sulfide moiety have improved binding affinities at the human dopamine transporter (hDAT) compared to modafinil, with lead sulfoxide-substituted analogs showing characteristics of atypical inhibition (e.g., JJC8-091). Interestingly, the only distinction between sulfoxide and sulfide substitution is the presence of one additional oxygen atom. To elucidate why such a subtle difference in ligand structure can result in different typical or atypical profiles, we investigated two pairs of analogs. Our quantum mechanical calculations revealed a more negatively charged distribution of electrostatic potential surface of the sulfoxide substitution. Using molecular dynamics simulations, we demonstrated that sulfoxide-substituted modafinil analogs have a propensity to attract more water into the binding pocket. They also exhibited a tendency to dissociate from Asp79 and form a new interaction with Asp421, consequently promoting an inward-facing conformation of DAT. In contrast, sulfide-substituted analogs did not display these effects. These findings deepen our understanding of the functionally relevant conformational spectrum of DAT.

biophysics↗

bioRxiv2024

Linkers in bitopic agonists shape bias profile among transducers for the dopamine D2 and D3 receptors

Bitopic ligands bind both orthosteric and allosteric or secondary binding sites within the same receptor, often resulting in improvement of receptor selectivity, potency, and efficacy. In particular, for both agonists and antagonists of the dopamine D2 and D3 receptors (D2R and D3R), the primary therapeutic targets for several neurological and neuropsychiatric disorders, bitopic ligand design has proved advantageous in achieving better pharmacological profiles in vitro. Although the two pharmacophores within a bitopic ligand are typically considered the main drivers of conformational change for a receptor, the role of the linker that connects the two has not yet been systematically studied for its relevance in receptor activity profiles. Here, we present a comprehensive analysis of sumanirole and PF592,379-based indole-containing bitopic compounds in agonist activity at D2R and D3R, with a focus on linker chemical space and stereochemistry achieved through testing seven distinct chirally resolved linkers. The current study examines the structure activity relationships (SAR) of these linkers extensively, beyond the conventional level, by characterizing activation of all putative transducers over a 44 min time course. Our multiparametric analysis provides previously unappreciated clarity of linker-dependent effects, highlighting the utility of this applied comprehensive approach and the significance of linker type in the shaping of transducer bias profiles.

pharmacology and toxicology↗

bioRxiv2022

Fast-synaptic axo-axonal transmission from striatal cholinergic interneurons onto dopamine fibers.

Transmission from striatal cholinergic interneurons (CINs) controls dopamine release through nicotinic acetylcholine receptors (nAChRs) on dopaminergic axons. Anatomical studies suggest that cholinergic terminals signal predominantly through non-synaptic volume transmission. However, the influence of cholinergic transmission on electrical signaling in axons remains unclear. We examined axo-axonal transmission from CINs onto dopaminergic axons using perforated-patch recordings which revealed rapid spontaneous EPSPs with properties characteristic of fast synapses. Pharmacology showed that axonal EPSPs (axEPSPs) were mediated primarily by high-affinity 6-containing receptors. Remarkably, axEPSPs triggered spontaneous action potentials locally in dopaminergic axons, suggesting these axons perform integration to convert synaptic input into spiking, a function associated with somatodendritic compartments. We investigated cross-species validity of cholinergic axo-axonal transmission by recording dopaminergic axons in macaque putamen and found similar axEPSPs. Thus, we reveal that fast synaptic-like neurotransmission underlies cholinergic signaling onto dopaminergic axons, providing insight into how nicotinic receptors shape electrical signaling directly in axon terminals.

neuroscience↗

bioRxiv2021

Nanoscopic dopamine transporter distribution and conformation are inversely regulated by excitatory drive and D2-autoreceptor activity

The nanoscopic organization and regulation of individual molecular components in presynaptic varicosities of neurons releasing modulatory volume neurotransmitters like dopamine (DA) remain largely elusive. Here we show by application of several super-resolution microscopy techniques to cultured neurons and mouse striatal slices, that the dopamine transporter (DAT), a key protein in varicosities of dopaminergic neurons, exists in the membrane in dynamic equilibrium between an inward-facing nanodomain-localized and outward-facing unclustered configuration. The balance between these configurations is inversely regulated by excitatory drive and by DA D2-autoreceptor activation in manner dependent on Ca2+-influx via N-type voltage-gated Ca2+-channels. The DAT nanodomains contain tens of transporters molecules and overlap with nanodomains of PIP2 (phosphatidylinositol-4,5-bisphosphate) but show little overlap with D2-autoreceptor, syntaxin-1 and clathrin nanodomains. Summarized, the data reveal a mechanism for rapid alterations in nanoscopic DAT distribution and show a striking link of this to the conformational state of the transporter.

neuroscience↗

bioRxiv2020

A dominant-negative variant in the dopamine transporter PDZ-binding motif is linked to parkinsonism and neuropsychiatric disease

Dopaminergic dysfunction is central to movement disorders and mental diseases. The dopamine transporter (DAT) is essential for the regulation of extracellular dopamine but the genetic and mechanistic link between DAT function and dopamine-related pathologies remains elusive. Particularly, the pathophysiological significance of monoallelic missense mutations in DAT is unknown. Here we identify a novel coding DAT variant, DAT-K619N, in a patient with early-onset parkinsonism and comorbid neuropsychiatric disease and in 22 individuals from exome-sequenced samples of neuropsychiatric patients. The variant localizes to the critical C-terminal PDZ-binding motif of DAT and causes reduced uptake capacity, decreased surface expression, and accelerated turnover of DAT in vitro. In vivo, we demonstrate that expression of DAT-K619N in mice and dropsophila imposes impairments in dopamine transmission with accompanying changes in dopamine-directed behaviors. Importantly, both cellular studies and viral overexpression of DAT-K619N in mice show that DAT-K619N has a dominant-negative effect which collectively implies that a single dominant-negative genetic DAT variant can confer risk for neuropsychiatric disease and neurodegenerative early-onset parkinsonism.

neuroscience↗

bioRxiv2020

A tropane-based ibogaine analog rescues folding-deficient SERT and DAT

Missense mutations that give rise to protein misfolding are rare, but collectively, defective protein folding diseases are consequential. Folding deficiencies are amenable to pharmacological correction (pharmacochaperoning), but the underlying mechanisms remain enigmatic. Ibogaine and its active metabolite noribogaine correct folding defects in the dopamine transporter (DAT), but they rescue only a very limited number of folding-deficient DAT mutants, which give rise to infantile Parkinsonism and dystonia. Herein, a series of analogs was generated by reconfiguring the complex ibogaine ring system and exploring the structural requirements for binding to wild type transporters, and for rescuing two equivalent synthetic folding-deficient mutants, SERT-PG601,602AA and DAT-PG584,585AA. The most active tropane-based analog (9b) was also an effective pharmacochaperone in vivo, in Drosophila harboring DAT-PG584,585AA and rescued six out of 13 disease-associated human DAT mutants in vitro. Hence, a novel lead pharmacochaperone has been identified that demonstrates medication development potential for patients harboring DAT mutants.

pharmacology and toxicology↗

bioRxiv2020

Effects of Selective Dopamine D2 or D3 Receptor Antagonism on Morphine-Induced Locomotion in Mice

Recent preclinical studies have reported that pretreatment with the novel and highly-selective dopamine D3 receptor (D3R) antagonists R-VK4-40 or VK4-116 attenuates the abuse-related behavioral effects of oxycodone while enhancing its analgesic properties. However, whether these observed effects are generalizable to the broad class of D3R antagonists and/or extend to opioids other than oxycodone has not been extensively explored. The present study sought to assess the impact of pretreatment with another selective D3R antagonist, PG01037, on several behavioral effects of morphine in mice. C57Bl/6J mice were pretreated with PG01037 (0 - 10 mg/kg) and tested for 1) hyperlocomotion induced by acute morphine (5.6 - 56 mg/kg), 2) locomotor sensitization following repeated morphine (56 mg/kg), 3) antinociception following acute morphine (18 mg/kg), and 4) catalepsy following administration of PG01037 alone or in combination with morphine (56 mg/kg). PG01037 dose-dependently attenuated morphine-induced hyperlocomotion and morphine-induced antinociception at doses that did not alter basal locomotion or nociception alone, but did not prevent the induction of locomotor sensitization following repeated morphine administration. Moreover, PG01037 did not induce catalepsy either alone or in combination with morphine. These results suggest that attenuation of acute opioid-induced hyperlocomotion may be a behavioral effect shared among D3R-selective antagonists, thus supporting continued investigations into their use as potential treatments for opioid use disorder. However, PG01037 is unlike newer, highly-selective D3R antagonists in its capacity to reduce opioid-induced antinociception, indicating that modulation of opioid analgesia may vary across different D3R antagonists.

neuroscience↗

bioRxiv2018

Selective D2 and D3 receptor antagonists oppositely modulate cocaine responses in mice via distinct postsynaptic mechanisms in nucleus accumbens

BackgroundThe D3 receptor (D3R) has emerged as a promising pharmacotherapeutic target for the treatment of several diseases including schizophrenia, Parkinsons disease, and substance use disorders. However, studies investigating the modulatory impact of D3R antagonism on dopamine neurotransmission or the effects drugs of abuse have produced mixed results, in part because D3R-targeted compounds often also interact with D2 receptors (D2R). The purpose of this study was to compare the consequences of selective D2R or D3R antagonism on the behavioral effects of cocaine in mice, and to identify the neurobiological mechanisms underlying their modulatory effects.\n\nMethodsWe characterized the effects of selective D2R or D3R antagonism in mice on 1) basal and cocaine-induced locomotor activity, 2) presynaptic dopamine release and clearance in the nucleus accumbens using ex vivo fast scan cyclic voltammetry, and 3) dopamine-mediated signaling in D1-expressing and D2-expressing medium spiny neurons using ex vivo electrophysiology.\n\nResultsPretreatment with the selective D2R antagonist L-741,626 attenuated, while pretreatment with the selective D3R antagonist PG01037 enhanced, the locomotor-activating effects of acute and repeated cocaine administration. While both antagonists potentiated cocaine-induced increases in presynaptic DA release, D3R blockade uniquely facilitated DA-mediated excitation of D1-expressing medium spiny neurons in the nucleus accumbens.\n\nConclusionsSelective D3R antagonism potentiates the behavioral-stimulant effects of cocaine in mice, an effect that is in direct opposition to that produced by selective D2R antagonism or nonselective D2-like receptor antagonists, likely by facilitating D1-mediated excitation in the nucleus accumbens. These findings provide important insights into the neuropharmacological actions of D3R antagonists on mesolimbic dopamine neurotransmission.

neuroscience↗