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Epigenetic Dysregulation in the Developing Down Syndrome Brain

ABSTRACT: Using Illumina 450K arrays, 1.85% of analyzed CpG sites were hypermethylated and 0.31% hypomethylated in fetal Down syndrome (DS) cortex throughout the genome. The vast majority of differentially methylated promoters and genes was hypermethylated in DS and located outside chromosome 21, including the γ-protocadherin (PCDHG) cluster on chromosome 5q31, which is crucial for neural circuit formation in the developing brain. Bisulfite pyrosequencing and targeted RNA sequencing showed that several genes of PCDHG subfamilies A and B are hypermethylated and transcriptionally downregulated in fetal DS cortex. Decreased PCDHG expression is expected to reduce dendrite arborization and growth in cortical neurons. Dysregulation of CPT1B and NOX5 may be associated with mitochondrial dysfunction and increased cell damage in the developing DS brain. Since constitutive hypermethylation of PCDHG and other genes affects multiple tissues, including blood, it may provide useful biomarkers for DS brain development and pharmacologic targets for therapeutic interventions.

ORGANISM(S): Homo sapiens

PROVIDER: GSE73747 | GEO | 2016/08/03

SECONDARY ACCESSION(S): PRJNA297812

REPOSITORIES: GEO

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Project description:Background: Trisomy 21 causes Down syndrome (DS), but the mechanisms by which the extra chromosome leads to deficient intellectual and immune function are not well understood. Results: Here, we profile CpG methylation in DS and control cerebral and cerebellar cortex of adults and cerebrum of fetuses. We purify neuronal and non-neuronal nuclei and T-lymphocytes and find biologically relevant genes with DS-specific methylation (DS-DM) in brain cells. Some genes show brain-specific DS-DM, while others show stronger DS-DM in T cells. Both 5-methyl-cytosine and 5-hydroxy-methyl-cytosine contribute to the DS-DM. Thirty percent of genes with DS-DM in adult brain cells also show DS-DM in fetal brains, indicating early onset of these epigenetic changes, and we find early maturation of methylation patterns in DS brain and lymphocytes. Some, but not all, of the DS-DM genes show differential expression. DS-DM preferentially affected CpGs in or near specific transcription factor binding sites, implicating a mechanism involving altered transcription factor binding. Methyl-seq of brain DNA from mouse models with sub-chromosomal duplications mimicking DS reveals partial but significant overlaps with human DS-DM and shows that multiple chromosome 21 genes contribute to the downstream epigenetic effects. Conclusions: These data point to novel biological mechanisms in DS and have general implications for trans effects of chromosomal duplications and aneuploidies on epigenetic patterning. Bisulfite converted DNA from 119 samples from Down syndrome patients and controls were hybridised to the Illumina Infinium 450k Human Methylation Beadchip. In addition, we re-analyzed 6 Down syndrome and 6 control cerebellum DNA samples on the 450K BeadChips using an adaptation of the Illumina probe preparation protocol (TrueMethyl kit; Cambridge Epigenetics, CEGX), in which parallel analyses of bisulfite and oxidative bisulfite DNA for each sample allows assessment of the relative contributions of 5mC and 5hmC to net methylation.

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Epigenetic Dysregulation in the Developing Down Syndrome Brain

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