Expression of Dopamine D1-4 and Serotonin 5-HT1A-3A Receptors in Blood Mononuclear Cells in Schizophrenia

Abstract

Introduction: The aim of this study was to determine the mRNA expression profile of dopamine D₁, D₂, D₃, D₄ and serotonin 5-HT_1A, 5-HT_2A, and 5-HT_3A receptors in peripheral blood mononuclear cells (PBMCs) in schizophrenia and the in vitro effect of antipsychotics on the expression of these receptors in PBMCs of healthy subjects. Materials and Methods: Twenty-seven patients with schizophrenia and 29 healthy controls were recruited for the study. All study subjects underwent thorough clinical assessment, including anthropometric and body composition measurements. The expression of mRNA for dopamine D_1-4 and serotonin 5-HT_1A-3A receptors was measured using quantitative RT-PCR in peripheral blood mononuclear cells. In vitro mRNA and protein expression of these receptors was measured using quantitative RT-PCR and Western Blotting in PBMCs cultured with quetiapine, haloperidol, aripiprazole, risperidone, olanzapine or clozapine at IC₅₀, half of IC₅₀, and one-quarter of IC₅₀ concentrations. Results: The key finding was that the schizophrenia group demonstrated significantly higher mRNA expression of D₁, D₂ and D₄ receptors (p < 0.001), and significantly lower mRNA expression of 5-HT_3A receptors (p < 0.01). After adjusting for smoking, the mRNA expression of D₁ lost its significance, while that of D₃, 5-HT_1A, 5-HT_2A became significant (all three were lower in the schizophrenia group). These receptors also demonstrated different ratios of mRNA expression in the schizophrenia group. The in vitro experiments showed that high concentrations of antipsychotics influenced the mRNA and protein expression of all studied receptors. Conclusion: Schizophrenia patients display a distinctive pattern of dopamine and serotonin receptor mRNA expression in blood mononuclear cells. This expression is little affected by antipsychotic treatment and it may therefore serve as a useful diagnostic biomarker for schizophrenia.

Keywords: PBMCs; Schizophrenia; biomarkers; dopamine receptors; serotonin receptors.

Figure 1

mRNA expression of dopamine D₁₋₄ and serotonin 5-HT_1A−3A in PBMCs of study subjects (unadjusted for smoking). Middle horizontal line indicate mean, outer horizontal bars represent standard deviation.

Figure 2

Ratios of mRNA expression of dopamine D₁₋₄ and serotonin 5-HT_1A−3A receptors in PBMCs of study subjects (unadjusted for smoking). Horizontal bar represent mean and standard deviation. *** p < 0.001; NS, non-significant; X axes are log₁₀ scaled.

Figure 3

IC₅₀ profiles of the PBMCs after treatment with antipsychotics. Graphs representing the proliferation of PMBCs treated with different concentrations of quetiapine, haloperidol, aripiprazole, risperidone, olanzapine, or clozapine. Above the graph, the IC50 value for each drug is presented.

Figure 4

The effect of antipsychotic treatment on dopamine D₁₋₄ and serotonin 5-HT_1A−3A receptors mRNA expression in PBMCs. Graphs represent the relative gene expression of dopamine (D₁₋₄) and serotonin (5-HT_1A−3A) receptors in PBMCs treated in vitro with antipsychotics (APs): quetiapine (Q), haloperidol (H), aripiprazole (A), risperidone (R), olanzapine (O), or clozapine (C) in dose corresponding to IC₅₀, half of the IC₅₀ and a quarter of IC₅₀. Constitutive receptor expression served as the control. All results were normalized to ACTB. Bars represent mean and standard deviation. *p < 0.05; ***p < 0.001.

Figure 5

The effect of antipsychotic treatment on dopamine D₁₋₄ and serotonin 5-HT_1A−3A receptors protein expression in PBMCs. Graphs show the relative protein level of dopamine (D₁₋₄) and serotonin (5-HT_1A−3A) receptors in PCMBs treated in vitro with antipsychotics (APs): quetiapine (Q), haloperidol (H), aripiprazole (A), risperidone (R), olanzapine (O), or clozapine (C) in doses corresponding to IC₅₀ and one of a quarter of IC₅₀. Constitutive receptor expression served as the control. All results were normalized to GAPDH (loading control). One representative blot of the three independent experiments is shown. Bars represent mean and standard deviation. *p < 0.05; **p < 0.01; ***p < 0.001.