m 6 A mRNA methylation in human brain is disrupted in Lewy body disorders.

N6-methyladenosine modification of RNA (m 6 A) regulates translational control which may influence neuronal dysfunction underlying neurodegenerative diseases. Using microscopy and a machine learning approach, we performed cellular profiling of m 6 A-RNA abundance and YTHDF1/YTHDF3 m 6 A reader expression within four regions of the human brain from non-affected individuals and individuals with Parkinson's disease, Dementia with Lewy bodies (DLB) or Mild Cognitive Impairment (MCI). In non-diseased tissue, we found m 6 A-modified RNAs showed cell-type and sub-compartment-specific variation. YTHDF1 and YTHDF3 showed opposing expression patterns in the cerebellum, and frontal and cingulate cortices. Machine learning quantitative image analysis revealed that m 6 A-modified transcripts were significantly altered in localisation and abundance in disease tissue with significant decreases in m 6 A-RNAs in Parkinson's disease, and significant increases in m 6 A-RNA abundance in Dementia with Lewy bodies. MCI tissue showed variability across regions but similar to DLB, in brain areas with an overall significant increase in m 6 A-RNAs, modified RNAs within dendritic processes were reduced. Using mass spectrometry proteomic datasets to corroborate our findings, we found significant changes in YTHDF3 and m 6 A anti-reader protein abundance in Alzheimer's disease (AD) and asymptomatic AD/MCI tissue and correlation with cognitive resilience. These results provide evidence for disrupted m 6 A regulation in Lewy body diseases and a plausible mechanism through which RNA processing could contribute to the formation of Lewy bodies and other dementia-associated pathological aggregates. The findings suggest that manipulation of epitranscriptomic processes influencing translational control may lead to new therapeutic approaches for neurodegenerative diseases.