Is DNA methylation responsible for immune system dysfunction in schizophrenia?

Aberrant DNA methylation of blood in schizophrenia by adjusting for estimated cellular proportions

DNA methylation, which is the transference of a methyl group to the 5'-carbon position of the cytosine in a CpG dinucleotide, is one of the major mechanisms of epigenetic modifications. A number of studies have demonstrated altered DNA methylation of peripheral blood cells in schizophrenia (SCZ) in previous studies. However, most of these studies have been limited to the analysis of the CpG sites in CpG islands in gene promoter regions, and cell-type proportions of peripheral leukocytes, which may be one of the potential confounding factors for DNA methylation, have not been adjusted in these studies. In this study, we performed a genome-wide DNA methylation profiling of the peripheral leukocytes from patients with SCZ and from non-psychiatric controls (N = 105; 63 SCZ and 42 control subjects) using a quantitative high-resolution DNA methylation microarray which covered across the whole gene region (485,764 CpG dinucleotides). In the DNA methylation data analysis, we first estimated the cell-type proportions of each sample with a published algorithm. Next, we performed a surrogate variable analysis to identify potential confounding factors in our microarray data. Finally, we conducted a multiple linear regression analysis in consideration of these factors, including estimated cell-type proportions, and identified aberrant DNA methylation in SCZ at 2,552 CpG loci at a 5% false discovery rate correction. Our results suggest that altered DNA methylation may be involved in the pathophysiology of SCZ, and cell heterogeneity adjustments may be necessary for DNA methylation analysis.

Is T-helper type 2 shift schizophrenia-specific? Primary results from a comparison of related psychiatric disorders and healthy controls

AIM

An imbalance between T-helper type 1 (Th1) and type 2 (Th2) cytokines has been implicated in schizophrenia, although empirical evidence is rare. The aim of this study was to examine if a Th1/Th2 imbalance occurs in schizophrenia and schizophrenia-related disorder.

METHODS

Twenty-six subjects with schizophrenia, 26 subjects with schizophrenia-related disorders, and 26 healthy controls were recruited. The Human Th1/Th2 Cytokine Cytometric Bead Array Kit-II was utilized to assess serum Th1/Th2 cytokines and ratios simultaneously. MANOVA was used to detect differences among the three diagnostic groups in distinct Th1/Th2 cytokines/ratios. Pearson/Spearman correlations were used to examine the relationships between distinct Th1/Th2 cytokines/ratios and clinical/psychopathological data in schizophrenia.

RESULTS

Interferon (IFN)-γ/interleukin (IL)-4, IFN-γ/IL-10, IL-2/IL-4, and tumor necrosis factor (TNF)-α/IL-4 ratios were significantly decreased in schizophrenia, but not in schizophrenia-related disorders compared to healthy controls. IFN-γ/IL-4 and IFN-γ/IL-10 in schizophrenia subjects positively correlated with age, but not in schizophrenia-related disorder subjects or in healthy controls.

CONCLUSION

A clear Th2 shift was observed in schizophrenia, but not in schizophrenia-related disorders. The Th2 shift in schizophrenia appeared to be an aberrant developmental phenomenon.