Choline promotes nicotinic receptor alpha4 + beta2 up-regulation

Area of Science:

• Neuroscience
• Pharmacology
• Cell Biology

Background:

• Neuronal nicotinic acetylcholine receptors (nAChRs), particularly those composed of alpha4 and beta2 subunits, are crucial for nicotine binding in the brain.
• Chronic nicotine exposure leads to the up-regulation of these alpha4 + beta2 nAChRs, but the endogenous mediators are not fully understood.

Purpose of the Study:

• To investigate the role of choline as an endogenous mediator in the up-regulation of alpha4 + beta2 nAChRs.
• To elucidate the mechanisms underlying choline-mediated nAChR up-regulation, including its interaction with inflammatory pathways.

Main Methods:

• Utilized HEK293 cells stably expressing alpha4 + beta2 nAChRs.
• Measured receptor up-regulation via [(3)H]epibatidine density and beta2 subunit protein expression.
• Employed the choline kinase inhibitor hemicholinium-3 (HC3) and the p38 MAPK inhibitor SB202190.
• Investigated interactions with nicotine and tumor necrosis factor alpha (TNF-α).

Main Results:

• Choline dose-dependently up-regulates alpha4 + beta2 nAChRs, increasing beta2 subunit protein expression.
• Hemicholinium-3 (HC3) inhibited choline-mediated up-regulation by approximately 60%, indicating both HC3-dependent and -independent pathways.
• Choline's up-regulation effect was not additive with nicotine but was additive with weaker promoters.
• Co-application with tumor necrosis factor alpha (TNF-α) further enhanced choline-mediated up-regulation, involving increased alpha4 and beta2 protein expression, inhibited by SB202190.

Conclusions:

• Choline acts as an endogenous mediator that up-regulates alpha4 + beta2 nAChRs.
• The up-regulation involves both HC3-sensitive and insensitive mechanisms and is modulated by inflammatory cytokines like TNF-α via p38 MAPK.
• These findings suggest that alpha4 + beta2 nAChR up-regulation is a physiological response to metabolic and inflammatory changes.