REELIN GENE EXPRESSION AND EPIGENETIC STATUS IN TEMPORAL CORTEX OF AUTISTIC BRAINS

Background: Reelin plays a pivotal role in neurodevelopment and has been implicated in autism pathogenesis. The methylation status of the reelin gene (RELN) promoter regulates gene expression and RELN promoter hypermethylation has been found in post-mortem brains of schizophrenic and bipolar patients.

Objectives: to correlate RELN gene expression with promoter methylation status in the same post-mortem termporocortical tissue samples (BA41/42 or 22) of 9 patient-control pairs (M:F=7:2, pre:post-puberal=3:6).

Methods: gene expression was assessed by oligonucleotide DNA microarray analysis followed by real-time qPCR. RELN promoter methylation status was verified by bisulphite treatment, amplification by nested PCR and DNA sequencing of 17-22 clones/subject.

Results: RELN gene expression was reduced on average by 47% using oligonucleotide DNA microarray analysis. Compared to controls, RELN mRNA was significantly reduced in postpuberal (N=6 pairs, P<0.05 ), but not in prepuberal patients (N=3 pairs, P=0.51). Postpuberal patients and controls did not differ in mean total number of methylated clones, but patients displayed much heavier methylation at the 5’ promoter end compared to controls (P<0.000001). Conversely, postpuberal controls displayed heavier methylation at the 3’ promoter end (P<0.000001). No significant correlation was found between RELN mRNA levels and RELN promoter methylation, regardless of status, promoter region and age.

Conclusions: sex hormones seemingly trigger RELN promoter methylation both in normal individuals and in autistic patients; there is a highly significant difference in methyl CpG distributions between autistic and control brains. The lack of correlation between RELN mRNA levels and RELN promoter methylation could be due to higher level epigenetic mechanisms, such as histone acetylation. This hypothesis is currently being explored.