Alpha-synuclein mRNA expression in oligodendrocytes in MSA

Abstract

Multiple system atrophy (MSA) is a progressive neurodegenerative disease presenting clinically with parkinsonian, cerebellar, and autonomic features. α-Synuclein (αsyn), encoded by the gene SNCA, is the main constituent of glial cytoplasmic inclusion (GCI) found in oligodendrocytes in MSA, but the methods of its accumulation have not been established. The aim of this study is to investigate alterations in regional and cellular SNCA mRNA expression in MSA as a possible substrate for GCI formation. Quantitative reverse transcription polymerase chain reaction (qPCR) was performed on postmortem brain samples from 15 MSA, 5 IPD, and 5 control cases to investigate regional expression in the frontal and occipital regions, dorsal putamen, pontine base, and cerebellum. For cellular expression analysis, neurons and oligodendrocytes were isolated by laser-capture microdissection from five MSA and five control cases. SNCA mRNA expression was not significantly different between the MSA, IPD and control cases in all regions (multilevel model, P = 0.14). After adjusting for group effect, the highest expression was found in the occipital cortex while the lowest was in the putamen (multilevel model, P < 0.0001). At the cellular level, MSA oligodendrocytes expressed more SNCA than control oligodendrocytes and expression in MSA neurons was slightly lower than that in controls, however, these results did not reach statistical significance. We have demonstrated regional variations in SNCA expression, which is higher in cortical than subcortical regions. This study is the first to demonstrate SNCA mRNA expression by oligodendrocytes in human postmortem tissue using qPCR and, although not statistically significant, could suggest that this may be increased in MSA compared to controls.

Keywords: glial cytoplasmic inclusions; laser-capture microdissection; multiple system atrophy; oligodendrocytes; α-synuclein.

Figure 1

SNCA mRNA regional expression (A) Expression between the different cases (adjusted for regions) shows no statistically significant differences between the groups although the lowest level of expression was found in MSA-SND and the highest in IPD cases (P = 0.14). (B) After adjusting for case type, a statistically significant difference in SNCA expression between regions was found (P < 0.0001), with the lowest expression in the dorsal putamen and the highest in the occipital cortex. Multilevel model test with significance level set at P = 0.05. The boxplot show median values as the line within the box, the box reflects the interquartile range and the whiskers the range of the values.PFR: posterior frontal region; OR: occipital region; Put-D: dorsal putamen; CBM: cerebellum; Ctx: cortex; WM: white matter; MSA: multiple system atrophy; SND: striatonigral degeneration; OPC: olivopontocerebellar; IPD: idiopathic Parkinson's disease; SNCA: α-synuclein.

Figure 2

SNCA mRNA cellular expression(A) SNCA is expressed in neurons and oligodendrocytes of both MSA and control cases. Expression in neurons is greater in controls as compared to MSA (P = 0.47), in contrast to oligodendrocytes where expression is greater in MSA (P = 0.18) but these results did not reach statistical significance. (B) Bar graph representing fold change of expression values between the different cases and cell types. No statistically significant differences were found although there was a trend toward increased expression in MSA oligodendrocytes when compared to control oligodendrocytes (P = 0.18), MSA neurons (P = 0.16) and control neurons (P = 0.18). In contrast, there was a slight decrease in αsyn expression in MSA neurons as compared to control neurons (P = 0.46). The greatest difference seems to be the increase in expression in MSA oligodendrocytes compared with MSA neurons. Mann–Whitney U test with significance level set at P = 0.05. The boxplot shows median values as the line within the box, the box reflects the interquartile range and the whiskers the range of the values. Oligo: oligodendrocytes; MSA: multiple system atrophy; SNCA: α-synuclein.