NeuronalSNCAtranscription during Lewy body formation

Abstract

Background: Misfolded alpha-synuclein (a-syn) is believed to contribute to neurodegeneration in Lewy body disease (LBD) based on considerable evidence including a gene-dosage effect observed in relation to point mutations and multiplication of SNCA in familial Parkinson disease. A contradictory concept proposes early loss of the physiological a-syn as the major driver of neurodegeneration. There is a paucity of data on SNCA transcripts in various a-syn immunoreactive cytopathologies. Methods: SNCA transcripts in neurons without and with various a-syn immunoreactive cytopathologies in the substantia nigra and amygdala in LBD (n = 5) were evaluated using RNAscope combined with immunofluorescence for disease-associated a-syn. Single-nucleus RNA sequencing was performed to elucidate cell-type specific SNCA expression in non-diseased frontal cortex (n = 3). Results: SNCA transcripts in neurons with punctate a-syn immunoreactivity were preserved both in the substantia nigra and amygdala but were reduced in neurons with compact a-syn inclusions. Only single SNCA transcripts were detected in astrocytes with or without a-syn immunoreactivity in the amygdala. Single-nucleus RNA sequencing revealed that excitatory and inhibitory neurons, oligodendrocyte progenitor cells, oligodendrocytes, and homeostatic microglia expressed SNCA transcripts, while expression was largely absent in astrocytes and microglia. Conclusions: The preserved cellular SNCA expression in the more abundant non-Lewy body type a-syn cytopathologies provides a pool for local protein production that can aggregate and serve as a seed for misfolded a-syn. Successful segregation of disease-associated a-syn is associated with the exhaustion of SNCA production in the terminal cytopathology, the Lewy body. Our observations support a therapeutic strategy incorporating a finely tuned dual approach targeting the elimination of misfolded a-syn along with the reduction of the SNCA transcription to avoid feeding of pathological a-syn seeding.