Differential regulation of alpha7 nicotinic receptor gene (CHRNA7) expression in schizophrenic smokers

Abstract

The alpha7 neuronal nicotinic receptor gene (CHRNA7) has been implicated in the pathophysiology of schizophrenia by genetic and pharmacological studies. Expression of the alpha7* receptor, as measured by [(125)I]alpha-bungarotoxin autoradiography, is decreased in postmortem brain of schizophrenic subjects compared to non-mentally ill controls. Most schizophrenic patients are heavy smokers, with high levels of serum cotinine. Smoking changes the expression of multiple genes and differentially regulates gene expression in schizophrenic hippocampus. We examined the effects of smoking on CHRNA7 expression in the same tissue and find that smoking differentially regulates expression of both mRNA and protein for this gene. CHRNA7 mRNA and protein levels are significantly lower in schizophrenic nonsmokers compared to control nonsmokers and are brought to control levels in schizophrenic smokers. Sufficient protein but low surface expression of the alpha7* receptor, seen in the autoradiographic studies, suggests aberrant assembly or trafficking of the receptor.

Figure 1

CHRNA7 signal intensity is significantly reduced in schizophrenic nonsmokers compared to schizophrenic smokers. The probe set for CHRNA7 on the oligonucleotide array detected significantly reduced signal intensity in schizophrenic nonsmokers compared to patient smokers. *p<0.05

Figure 2

CHRNA7 displays reduced mRNA and protein levels in schizophrenic nonsmokers. a The microarray probe set for CHRNA7, shown in red, was designed to detect expression from both the full-length CHRNA7 and the duplicated fusion gene, CHRFAM7A. b Reduced α7 nAChR mRNA expression was observed in schizophrenic nonsmokers relative to smokers by RT-PCR and western blot analyses. QRT-PCR primers, shown in blue (a), were designed to specifically amplify either CHRFAM7A or CHRNA7. Schizophrenic nonsmokers displayed significantly reduced mRNA and protein expression relative to patient smokers. Patient nonsmokers also had lower expression compared to control nonsmokers, but this difference was statistically significant only at the mRNA level. Representative protein bands from western blots, below the graph, show the quantified protein amounts. QRT-PCR and western blot assays overlapped by 14 subjects (three control nonsmokers, three control smokers, four schizophrenic non-smokers, and four schizophrenic smokers). Mean relative mRNA amounts (± SEM) for each subject group are shown. *p<0.05, **p<0.01