Abstract
Genetic variation in nicotinic receptor alpha 5 (CHRNA5) has been associated with increased risk of addiction-associated phenotypes in humans yet little is known the underlying neural basis. Induced pluripotent stem cells (iPSCs) were derived from donors homozygous for either the major (D398) or the minor (N398) allele of the nonsynonymous single nucleotide polymorphism (SNP), rs16969968, in CHRNA5. To understand the impact of these nicotinic receptor variants in humans, we differentiated these iPSCs to dopamine (DA) or glutamatergic neurons and then tested their functional properties and response to nicotine. Results show that N398 variant human DA neurons differentially express genes associated with ligand receptor interaction and synaptic function. While both variants exhibited physiological properties consistent with mature neuronal function, the N398 neuronal population responded more actively with an increased excitatory postsynaptic current response upon the application of nicotine in both DA and glutamatergic neurons. Glutamatergic N398 neurons responded to lower nicotine doses (0.1 μM) with greater frequency and amplitude but they also exhibited rapid desensitization, consistent with previous analyses of N398-associated nicotinic receptor function. This study offers a proof-of-principle for utilizing human neurons to study gene variants contribution to addiction.
Highlights
Drug abuse and addiction are a major burden to society with the total cost of substance abuse in the U.S exceeding $600 billion annually (NIDA)
We considered whether the difference in response between N398 and D398 variant nicotinic acetylcholine receptor (nAChR) could be observed in cultures of purely excitatory neurons, which have been puromycin-selected to increase the uniformity of the cultures
We examined the effects of nicotine on spontaneous excitatory PSCs in both D398 and N398 human excitatory neurons
Summary
Drug abuse and addiction are a major burden to society with the total cost of substance abuse in the U.S exceeding $600 billion annually (NIDA). Given that variation in α5 expression alters nAChR expression and function[8], nonsynonymous variants within α5 are likely to affect neurophysiological functions, which potentially contribute to addictive behaviors[6]. How such nAChR gene variants in humans affect receptor activity along with neuronal function and lead to addiction behaviors is not known. Nicotine exhibited a transiently increased but desensitizing effect on synaptic transmission in excitatory iN cells These results provide important insights on how CHRNA5 gene variants may affect neuronal activity and offer a proof-of-principle for utilizing human neurons derived from somatic cells to study the contribution of gene variants to addiction behavior
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