DNA methylation status of SOX10 correlates with its downregulation and oligodendrocyte dysfunction in schizophrenia

Abstract

Downregulation of oligodendrocyte-related genes, referred to as oligodendrocyte dysfunction, in schizophrenia has been revealed by DNA microarray studies. Because oligodendrocyte-specific transcription factors regulate the differentiation of oligodendrocytes, genes encoding them are prime candidates for oligodendrocyte dysfunction in schizophrenia. We found that the cytosine-guanine dinucleotide (CpG) island of sex-determining region Y-box containing gene 10 (SOX10), an oligodendrocyte-specific transcription factor, tended to be highly methylated in brains of patients with schizophrenia, correlated with reduced expression of SOX10. We also found that DNA methylation status of SOX10 also was associated with other oligodendrocyte gene expressions in schizophrenia. This may be specific to SOX10, because the CpG island of OLIG2, which encodes another oligodendrocyte-specific transcription factor, was rarely methylated in brains, and the methylation status of myelin-associated oligodendrocytic basic protein, which encodes structural protein in oligodendrocytes, did not account for their expressions or other oligodendrocyte gene expressions. Therefore, DNA methylation status of the SOX10 CpG island could be an epigenetic sign of oligodendrocyte dysfunction in schizophrenia.

Figure 1.

Expression and epigenetic analyses of SOX10. A, qRT-PCR of SOX10. p values were calculated by the Mann-Whitney U test. C, Control subjects (n = 14); SZ, schizophrenic patients (n = 13). The original data set (Torrey et al., 2000) was composed of 15 control subjects and 15 schizophrenic patients. One control subject was omitted from qRT-PCR data analysis, because we could not obtain appropriate amplification curves. Samples of two schizophrenic patients were omitted from DNA microarray analysis and qRT-PCR, because they showed poor quality, as revealed by denatured gel electrophoresis and the results of Test2chip (Affymetrix). B, Examples of DNA methylation status in a control subject (left) and a schizophrenic patient (right). Results of all subjects can be found in supplemental Figure 1 (available at www.jneurosci.org as supplemental material). Open circle, Nonmethylated CpG; closed circle, methylated CpG. C, Biallelic expression of SOX10. The arrow indicates an SNP at the 3′-untranslated region (reverse orientation of rs139883) in the postmortem brain cDNA sequence. Biallelic expression was also confirmed by cloning and sequence analysis of three independent subjects who had heterozygous alleles with regard to rs139883. D, Inverse correlation between methylation status and expression level of SOX10.

Figure 2.

DNA methylation status of oligodendrocyte genes. A, Genomic structure and CpG island of SOX10, OLIG2, and MOBP. Exons are denoted by boxes, with untranslated regions in white and translated regions in black. PCR-amplified regions for methylation analysis are underlined. B, DNA methylation status in postmortem brains. The percentage of methylated alleles is indicated in black. ND, Not determined. C, DNA methylation status in human cell lines. A2058, SHSY5Y, 1321N1, and TC42 are melanoma, neuroblastoma, astrocytoma, and lymphoblastoid cell lines, respectively. Expression levels of each oligodendrocyte gene were measured (+, detected; -, not detected). The relative expression levels in relation to GAPDH are as follows: 0.03363 (SOX10 in A2058), 0.00025 (OLIG2 in A2058), and 0.00005 (MOBP in SHSY5Y).