Reelin promoter hypermethylation in schizophrenia

Reelin mRNA and protein levels are reduced by approximately 50% in various cortical structures of postmortem brain from patients diagnosed with schizophrenia or bipolar illness with psychosis. In addition, the mRNA encoding the methylating enzyme, DNA methyltransferase 1, is up-regulated in the same neurons that coexpress reelin and glutamic acid decarboxylase 67. We have analyzed the extent and pattern of methylation within the CpG island of the reelin promoter in genomic DNA isolated from cortices of schizophrenia patients and nonpsychiatric subjects. Ten (The Stanley Foundation Neuropathology Consortium) and five (Harvard Brain Collection) schizophrenia patients and an equal number of nonpsychiatric subjects were selected from each brain collection. Genomic DNA was isolated, amplified (from base pair -527 to base pair +322) after bisulphite treatment, and sequenced. The results show that within the promoter region there were interesting regional variations. There was increased methylation at positions -134 and 139, which is particularly important for regulation, because this portion of the promoter is functionally competent based on transient transfection assays. This promoter region binds a protein present in neuronal precursor nuclear extracts that express very low levels of reelin mRNA; i.e., an oligonucleotide corresponding to this region and that contains methylated cytosines binds more tightly to extracts from nonexpressing cells than the nonmethylated counterpart. Collectively, the data show that this promoter region has positive and negative properties and that the function of this complex cis element relates to its methylation status.