Multiple system atrophy (MSA) is a sporadic and ultimately fatal neurodegenerative disease that develops on the progressive loss of neurons in several brain regions. MSA shows both Parkinson-like symptoms and a range of other disorders resulting from disturbances to central motor pathways (in the brain and spinal cord) the cerebellum and the autonomic nervous system. There is currently no curative treatment. What causes MSA and the molecular processes driving its development remain mysterious.

In a study headed by the Epigenetic and Environment Laboratory (LEE/CNRGH), in partnership with the Bispebjerg-Frederiksberg University Hospital's Research Laboratory for Stereology and Neuroscience (RLSN; Copenhagen, Denmark), a team of researchers compared the DNA methylation profiles of MSA and normal brain tissue samples.

In their work published in Acta Neuropathologica Communications, the team performed an epigenome-wide association study (EWAS) in the prefrontal cortex, focusing on two epigenetic markers, 5-methylcytosine (5mC) and 5-hydroxymethylcytosine (5hmC), both known to play roles in a wide array of biological functions.

DNA methylation is an epigenetic¹ process involving a post-replication chemical modification of cytosine residues in palindromic, 5'-CG-3' sequences called CpG sites. In mammals, the methyl group is transferred to the 5-position of the cytosine pyrimidine ring, thus creating the modified nucleobase 5-methylcytosine (5mC). Oxidation of the 5-methyl group of 5mC results in 5-hydroxymethylcytosine (5hmC).

These modified nucleobases are epigenetic markers and present in various regions of the genome (e.g., promoter regions), where they play important roles in gene expression. Studies have shown 5hmC to be widely present in the brain and associated with the development of certain neurological diseases. More recently, researchers identified differences in the expression rates of 5mC and 5hmC in particular areas of the brains of patients with MSA, but did not go so far as to identify correlations between methylation and biological functions and/or phenotypes.

It is in this setting that the LEE/RLSN team carried out their EWAS to quantify and compare DNA methylation and hydroxymethylation profiles in brain tissue samples taken from 41 patients with MSA and 37 healthy controls. They deployed 5mC and 5hmC-specific probes to analyze more than 850,000 CpG methylation sites at the nucleotide level.

Five 5mC probes were identified, including one mapped to the AREL1 gene, which codes for a protein involved in ubiquitination and antigen presentation. For that location, and in the MSA samples, the group measured a reduction in 5mC and an increase in 5hmC.

Also, a transcriptome analysis showed increases in both AREL1 and HLA expression in MSA, suggesting modulation of the immune system in MSA patients. Functional DNA methylation modules associated with inflammatory processes were also identified.

The results published by the LEE/RLSN team support the hypothesis of an active neuro-immune response in patients with MSA. Because epigenetic modifications are reversible, this knowledge gained on their regulatory mechanisms may shine a light on pathways to novel therapeutic strategies.

The LEE researchers will continue this study as part of a European project on rare diseases financed by ERANET.

1: Epigenetics describes heritable mechanisms able to change gene expression without modifying the DNA sequence. Epigenetic changes remain present through cell divisions and can thus direct the destiny of the cell.