Upregulation of TET1 and downregulation of APOBEC3A and APOBEC3C in the parietal cortex of psychotic patients

Abstract

Increasing evidence suggests that epigenetic dysfunction may account for the alteration of gene transcription present in neuropsychiatric disorders such as schizophrenia (SZ), bipolar disorder (BP) and autism. Here, we studied the expression of the ten-eleven translocation (TET) gene family and activation-induced deaminase/apolipoprotein B mRNA-editing enzymes (AID/APOBEC) in the inferior parietal lobule (IPL) (BA39-40) and the cerebellum of psychotic (PSY) patients, depressed (DEP) patients and nonpsychiatric (CTR) subjects obtained from the Stanley Foundation Neuropathology Consortium Medical Research Institute. These two sets of enzymes have a critical role in the active DNA demethylation pathway. The results show that TET1, but not TET2 and TET3, mRNA and protein expression was increased (two- to threefold) in the IPL of the PSY patients compared with the CTR subjects. TET1 mRNA showed no change in the cerebellum. Consistent with the increase of TET1, the level of 5-hydroxymethylcytosine (5hmC) was elevated in the IPL of PSY patients but not in the other groups. Moreover, higher 5hmC levels were detected at the glutamic acid decarboxylase67 (GAD67) promoter only in the PSY group. This increase was inversely related to the decrease of GAD67 mRNA expression. Of 11 DNA deaminases measured, APOBEC3A mRNA was significantly decreased in the PSY and DEP patients, while APOBEC3C was decreased only in PSY patients. The other APOBEC mRNA studied failed to change. Increased TET1 and decreased APOBEC3A and APOBEC3C found in this study highlight the possible role of altered DNA demethylation mechanisms in the pathophysiology of psychosis.

Figure 1

Schematic representation of putative DNA methylation/demethylation pathways. AID/APOBEC, activation-induced deaminase/apolipoprotein B RNA-editing catalytic component; BER, base excision repair; C, cytosine; DNMT, DNA methyltransferase; 5hmC, 5-hydroxylmethylcytosine; 5hmU, 5-hydroxylmethyluracil; 5mC, 5-methylcytosine; TDG, thymine DNA glycosylase; TET, ten-eleven translocation protein.

Figure 2

(a) Ten-eleven translocation (TET)1 protein expression in the nonpsychiatric (CTR), depressed (DEP) and psychotic (PSY) group. In the inset is the representative gel image of western blot of TET1 and β-actin. The TET1 protein expression was increased in the PSY group compared with the CTR group: *P<0.01 (one-way analysis of variance (ANOVA)). Each value represents mean±s.e.m. of the optical density (OD) ratio of TET1 protein vs β-actin. (b) Levels of 5-methylcytosine (5mC) and 5-hydroxylmethylcytosine (5hmC) expression in total DNA isolated from the CTR, DEP and PSY groups. Each value represents the OD ratios of 5mC and 5hmC immunostaining (calculated from their corresponding standard curves) and the DNA loaded on the membrane (calculated from standard curve). The 5hmC level was increased in the PSY group compared with the CTR group (*P<0.01), while 5mC levels failed to change. The data represent the mean±s.e.m.

Figure 3

Pearson's correlation analysis between relative ten-eleven translocation (TET)1mRNA expression and 5-hydroxylmethylcytosine (5hmC) (a) or 5-methylcytosine (5mC) (b) levels of all groups. (c) Plots of TET1 mRNA and 5hmC levels from nonpsychiatric (CTR) subjects and psychotic (PSY) patients. The line represents median value. BP, bipolar disorder; DEP, depressed; SZ, schizophrenia.

Figure 4

Increased 5-hydroxymethylcytosine (5hmC) at the glutamic acid decarboxylase 67 (GAD67) promoter in psychotic (PSY) patients. Binding of 5-methylcytosine (5mC) (a) and 5hmC (b) to GAD67 promoter was measured by immunoprecipitation using specific 5hmC and 5mC antibodies with previously published procedures. We find significantly increased 5hmC, but not 5mC, in PSY patients () compared with nonpsychiatric (CTR) subjects (□) at both regions of the GAD67 promoter examined. *P<0.05 vs CTR; **P<0.01 vs CTR.