Objective To conduct postmortem human brain research into the neuropathological basis of schizophrenia, it is critical to establish cohorts that are well-characterised and well-matched. Our objective was to determine if specimen characteristics, including: diagnosis, age, postmortem interval (PMI), brain acidity (pH), and/or the agonal state of the subject at death related to RNA quality, and to determine the most appropriate reference gene mRNAs. Methods We selected a matched cohort of 74 cases (37 schizophrenia / schizoaffective disorder cases and 37 controls cases). Middle frontal gyrus tissue was pulverised, tissue pH was measured, RNA isolated for cDNA from each case, and RNA integrity number (RIN) measurements were assessed. Using RT-PCR, we measured nine housekeeper genes and calculated a geomean in each diagnostic group. Results We found that the RINs were very good (mean 7.3) and all nine housekeeper control genes were significantly correlated with RIN. Seven of nine housekeeper genes were also correlated with pH, and two clinical variables, agonal state and duration of illness did have an effect on some control mRNAs. No major impact of PMI or freezer time on housekeeper mRNAs was detected. Our results show that people with schizophrenia had significantly less PPIA, and SDHA and tended to have less GUSB and B2M mRNA suggesting that these control genes may not be good candidates for normalisation. Conclusions In our cohort, less than 10% variability in RIN values was detected and the diagnostic groups were well matched overall. Our cohort was adequately powered (0.80–0.90) to detect mRNA differences (25%) due to disease. Our study suggests that multiple factors should be considered in mRNA expression studies of human brain tissues. When schizophrenia cases are adequately matched to control cases subtle differences in gene expression can be reliably detected.

Stress has been implicated in the onset and illness course of schizophrenia and bipolar disorder. The effects of stress in these disorders may be mediated by abnormalities of the hypothalamic-pituitary-adrenal axis, and its corticosteroid receptors. We investigated mRNA expression of the glucocorticoid receptor (GR) and mineralocorticoid receptor (MR), and protein expression of multiple GRα isoforms, in the prefrontal cortex of 37 schizophrenia cases and 37 matched controls. Quantitative real-time PCR, western blotting, and luciferase assays were employed. In multiple regression analysis, schizophrenia diagnosis was a significant predictor of total GR mRNA expression (p<0.05), which was decreased (11.4%) in schizophrenia cases relative to controls. No significant effect of diagnosis on MR mRNA was detected. At the protein level, no significant predictors of total GRα protein or the full-length GRα isoform were identified. However, schizophrenia diagnosis was a strong predictor (p<0.0005) of the abundance of a truncated ≈ 50 kDa GRα protein isoform, putative GRα-D1, which was increased in schizophrenia cases (80.4%) relative to controls. This finding was replicated in a second cohort of 35 schizophrenia cases, 34 bipolar disorder cases, and 35 controls, in which both schizophrenia and bipolar disorder diagnoses were significant predictors of putative GRα-D1 abundance (p<0.05 and p=0.005, respectively). Full-length GRα was increased in bipolar disorder relative to schizophrenia cases. Luciferase assays demonstrated that the GRα-D1 isoform can activate transcription at glucocorticoid response elements. These findings confirm total GR mRNA reductions in schizophrenia and provide the first evidence of GR protein isoform abnormalities in schizophrenia and bipolar disorder.