α-synuclein is a small presynaptic neuronal protein, encoded by the SNCA gene, that is implicated genetically and neuropathologically in Parkinson’s disease (PD). A large body of evidence has established that PD pathogenesis is closely linked to increased levels of SNCA; however to date, the biochemical pathways and transcriptional elements that control SNCA expression are still obscure. Previous experiments in our laboratory in the PC12 cell line demonstrated that the transcription factor ZSCAN21 binds to the intron 1 region of the Snca gene and is strongly involved in its transcriptional regulation. Therefore, in the current experiments, we wished to characterize further the role of ZSCAN21 in Snca transcriptional regulation in primary cultures and in vivo. We find that in vivo ZSCAN21 is expressed in neurons and its levels are developmentally regulated in different brain regions where ASYN is also detected. Further, we confirmed through Chromatin Immunoprecipitation its presence in a binding complex in the intron 1 region of the Snca gene in rat cortical neuronal cultures. Importantly, lentiviral-mediated silencing of Zscan21 increased significantly the promoter activity of Snca as well as its mRNA and protein levels in such cultures. In contrast, Zscan21 mediated silencing in differentiated neurosphere cultures reduced Snca levels. Stereotaxic delivery of adeno-associated virus against Zscan21 in the postnatal and adult hippocampus, an area linked with the non-motor symptoms of PD, revealed no significant alterations in Snca levels, despite efficient Zscan21 knockdown. Interestingly, Zscan21 overexpression in cortical neurons with adenoviruses led to robust mRNA but negligible protein expression, suggesting that ZSCAN21 protein levels are tightly regulated post-transcriptionally and / or post-translationally. Therefore, overall, our study demonstrates that ZSCAN21, a transcription factor whose levels are under strict posttranscriptional / posttranslational control in neurons, is diversely implicated in the transcriptional regulation of Snca in respect to the developmental stage, at least in in vitro primary neuronal settings. In vivo, however, the unaltered Snca levels observed following Zscan21 downregulation, imply the presence of alternative or perhaps compensatory mechanisms that regulate Snca transcription in such settings. Furthermore, in a genetic case control study of the ZSCAN21 binding site in SNCA intron 1, we did not find polymorphisms between PD patients and controls, suggesting that genetic diversity within this region does not contribute to disease pathogenesis. Overall, given the diverse effects in cell culture, and the lack of discernible in vivo effects, and although further studies are needed, our work does not provide sufficient support for the idea of targeting ZSCAN21 in order to manipulate SNCA levels in synucleinopathy models
