Overexpression of Cancer- and Neurotransmitter-Associated Genes in the Nucleus Accumbens of Smokers

Abstract

The effects of smoking in the human brain were explored at the molecular level in the nucleus accumbens (NAcc), a key brain region involved in tobacco addiction. Gene expression data from post-mortem NAcc were analyzed according to smoking habits: Never smokers, Former smokers and Current smokers at the time of death. The effect of smoking was determined using an ANCOVA model, controlling for potential confounders (psychiatric diagnosis, gender, age, post-mortem interval, and brain pH) followed by pair-wise post-hoc comparisons. Q-values (false discovery rate adjusted p-values) < 0.05 were used in combination with afold change of > ±1.3 to identify the most relevant genes. The greatest number of differentially expressed genes (DEGs) were found in subjects with a recent history of smoking (Current smokers) compared to either Former or Never smokers. Only two genes were differentially expressed between Former and Never smokers, suggesting that the effects of smoking on gene expression in the brain may be transient. Ingenuity Pathway Analysis (IPA) of DEGs identified a significant over-representation of neurotransmitter system genes (glutamate, GABA) in Current smokers. IPA also revealed many genes associated with cancer in Current smokers compared to Former and Never smokers despite no known cancer in any subjects. Genes associated with neoplasms, glioblastoma, gliomas and tumor regulations are among the top 10 transcripts. Our findings show that active smokers have a significant increase in cancer-related genes and alterations in glutamate and GABA neurotransmitter systems in the NAcc. To our knowledge this is the first study to identify cancer-related genes in the NAcc in Current smokers who have no evidence of cancer.