Upregulation of serotonin transporter by alcohol in human dendritic cells: possible implication in neuroimmune deregulation.
BACKGROUND
Alcohol is the most widely abused substance and its chronic consumption causes neurobehavioral disorders. It has been shown that alcohol affects the function of immune cells. Dendritic cells (DC) serve as the first line of defense against infections and are known to accumulate neurotransmitters such as 5-hydroxytryptamine (5-HT). The enzyme monoamine oxidase-A (MAO-A) degrades 5-HT that is associated with clinical depression and other neurological disorders. 5-HT is selectively transported into neurons through the serotonin transporter (SERT), which is a member of the sodium- and chloride-dependent neurotransmitter transporter (SLC6) family. SERT also serves as a receptor for psychostimulant recreational drugs. It has been demonstrated that several drugs of abuse such as amphetamine and cocaine inhibit the SERT expression; however, the role of alcohol is yet to be elucidated. We hypothesize that alcohol can modulate SERT and MAO-A expression in DC, leading to reciprocal downregulation of 5-HT in extracellular medium.


METHODS
Dendritic cells were treated with different concentrations (0.05% to 0.2%v/v) of alcohol for 24-72 hours and processed for SERT and MAO-A expression using Q-PCR and Western blots analysis. In addition, SERT function in DC treated with alcohol both in the presence and absence of imipramine, a SERT inhibitor was measured using 4-[4-(dimethylamino)styryl]-1-methylpyridinium iodide uptake assay. 5-HT levels in culture supernatant and intracellular 5-hydroxy indole acetic acid (5-HIAA) and cyclic AMP were also quantitated using ELISA.


RESULTS
Dendritic cells treated with 0.1% alcohol for 24 hours showed significant upregulation of SERT and MAO-A expression compared with untreated DC. We also observed that 0.1% alcohol enhanced the function of SERT and decreased extracellular 5-HT levels compared with untreated DC cultures, and this was associated with the elevation of intracellular 5-HIAA and cyclic AMP levels.


CONCLUSIONS
Our study suggests that alcohol upregulates SERT and MAO-A by elevating cyclic AMP, which may lead to decreased concentration of 5-HT in the extracellular medium. As 5-HT is a major neurotransmitter and an inflammatory mediator, its alcohol-mediated depletion may cause both neurological and immunological deregulation.
Babu
Dakshayani Kadiyala
DK
Department of Immunology, College of Medicine, Institute of NeuroImmune Pharmacology, Florida International University, Miami, Florida 33199, USA.
Diaz
Alain
A
Samikkannu
Thangavel
T
Rao
Kurapati V K
KV
Saiyed
Zainulabedin M
ZM
Rodriguez
Jose W
JW
Nair
Madhavan P N
MP
D015153:Blotting, Western; D002492:Central Nervous System Depressants / Q000494:pharmacology*; D000242:Cyclic AMP / Q000378:metabolism; D003713:Dendritic Cells / Q000187:drug effects / Q000276:immunology* / Q000378:metabolism*; D004797:Enzyme-Linked Immunosorbent Assay; D000431:Ethanol / Q000494:pharmacology*; D005110:Extracellular Space / Q000187:drug effects / Q000378:metabolism; D005434:Flow Cytometry; D006801:Humans; D006897:Hydroxyindoleacetic Acid / Q000378:metabolism; D008995:Monoamine Oxidase / Q000378:metabolism; D009000:Monocytes / Q000187:drug effects; D009420:Nervous System / Q000187:drug effects / Q000276:immunology*; D012313:RNA / Q000096:biosynthesis / Q000302:isolation & purification; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012701:Serotonin / Q000378:metabolism; D050486:Serotonin Plasma Membrane Transport Proteins / Q000096:biosynthesis* / Q000235:genetics; D015854:Up-Regulation / Q000187:drug effects
D002492:Central Nervous System Depressants; D050486:Serotonin Plasma Membrane Transport Proteins; D012701:Serotonin; D000431:Ethanol; D006897:Hydroxyindoleacetic Acid; D012313:RNA; D000242:Cyclic AMP; D008995:Monoamine Oxidase