Sex and diet-dependent gene alterations in human and rat brains with a history of nicotine exposure.

INTRODUCTION

Chronic nicotine exposure induces changes in the expression of key regulatory genes associated with metabolic function and neuronal alterations in the brain. Many bioregulatory genes have been associated with exposure to nicotine, but the modulating effects of sex and diet on gene expression in nicotine-exposed brains have been largely unexplored. Both humans and rodents display motivation for nicotine use and the emergence of withdrawal symptoms during abstinence. Research comparing pre-clinical models with human subjects provides an important opportunity to understand common biomarkers of the harmful effects of nicotine as well as information that may help guide the development of more effective interventions for nicotine cessation.

METHODS

Human postmortem dorsolateral prefrontal cortex (dLPFC) tissue BA9 was collected from female and male subjects, smokers and non-smokers ( = 12 per group). Rat frontal lobes were collected from female and male rats that received a regular diet (RD) or a high-fat diet (HFD) ( = 12 per group) for 14 days following implantation of a osmotic mini-pump (Alzet) that delivered nicotine continuously. Controls (control-s) received a sham surgical procedure. RNA was extracted from tissue from human and rat samples and reversed-transcribed to cDNA. Gene expression of (Cholinergic receptor nicotinic alpha 10), (Ceramide Kinase-Like), (SET and MYD Domin Containing 1), and (Fatty Acid 2-Hydrolase) in humans was compared to rats in each subset of groups and quantified by qPCR methods. Additionally, protein expression of FA2H was analyzed by immunohistochemistry (IHC) in human dLPFC.

RESULTS

Humans with a history of smoking displayed decreased ( = 0.0005), ( ≤ 0.0001), and ( = 0.0005) expression and increased ( = 0.0097) expression compared to non-smokers ( < 0.05). Similar patterns of results were observed in nicotine exposed vs. control rats. Interestingly, sex-related differences in gene expression for and were observed. In addition, ANCOVA analysis showed a significant effect of nicotine in a sex-different manner, including an increase in in male and female rats with RD or HFD. In rats exposed to an HFD, gene expression was lower in nicotine-treated rats compared to RD rats treated with nicotine. Protein expression of ( = 0.001) by IHC was significantly higher in smokers compared to non-smokers.

CONCLUSION

These results suggest that a history of long-term nicotine exposure in humans alters the expression of sphingolipid metabolism-related (, , and ) and neuronal () marker genes similarly as compared to rats. Sex- and diet-dependent differences appear in nicotine-exposed rats, critical in regulating sphingolipid metabolism and nicotinic acetylcholine receptors. This research enhances the construct validity of rat models of nicotine usage by showing a similar pattern of changes in gene expression in human subjects with a smoking history.