Complex Effects of the ZSCAN21 Transcription Factor on Transcriptional Regulation of α-Synuclein in Primary Neuronal Cultures and in Vivo

Abstract

␣-Synuclein, a presynaptic neuronal protein encoded by the SNCA gene, is strongly implicated in Parkinson disease (PD). PD pathogenesis is linked to increased SNCA levels; however, the transcriptional elements that control SNCA expression are still elusive. Previous experiments in PC12 cells demonstrated that the transcription factor zinc finger and SCAN domain containing 21 (ZSCAN21) plays an important regulatory role in SNCA transcription. Currently, we characterized the role of ZSCAN21 in SNCA transcription in primary neuronal cultures and in vivo. We found that ZSCAN21 is developmentally expressed in neurons in different rat brain regions. We confirmed its binding in the intron 1 region of SNCA in rat cortical cultures. Lentivirusmediated silencing of ZSCAN21 increased significantly SNCA promoter activity, mRNA, and protein levels in such cultures. In contrast, ZSCAN21 silencing reduced SNCA in neurosphere cultures. Interestingly, ZSCAN21 overexpression in cortical neurons led to robust mRNA but negligible protein expression, suggesting that ZSCAN21 protein levels are tightly regulated post-transcriptionally and/or post-translationally in primary neurons. Efficient adeno-associated virus-mediated knockdown of ZSCAN21 in the postnatal and adult hippocampus, an area linked with non-motor PD symptoms, revealed no significant alterations in SNCA levels. Overall, our study demonstrates that ZSCAN21 is involved in the transcriptional regulation of SNCA in primary neuronal cultures, but the direction of the effect is variable, likely depending on neuronal maturation. However, the unaltered SNCA levels observed following ZSCAN21 downregulation in the rat brain, possibly due to compensatory mechanisms, imply that ZSCAN21 is not a master regulator of SNCA in vivo.Genetic alterations in SNCA are closely linked to familial and sporadic PD.2 Several lines of evidence have directly linked increased levels of wild type SNCA with dysfunctional and abnormal SNCA deposition and neurodegeneration in animal models and in humans, whereas polymorphisms within and around the SNCA gene locus are correlated to increased risk of PD (1). Importantly, large unbiased genome-wide association studies established single nucleotide polymorphisms in the SNCA region as one of the most common risk factors for sporadic PD (2-6). Collectively, these studies support the overarching idea that dysregulation of SNCA levels, leading to its excess accumulation and aggregation, is a major factor in PD pathogenesis. Nonetheless, to date not much is known about the regulation of SNCA levels in general, let alone its transcriptional regulation. From previous studies it is well established that under physiological conditions SNCA mRNA levels are developmentally induced in the rat brain (7). The mechanisms involved in the developmental transcriptional regulation of SNCA remain elusive. Conversely, under pathological conditions in PD there has been controversy regarding the expression levels of SNCA mRNA in the brains of sporadic PD patients, with studies re...

The Histone Variant MacroH2A Blocks Cellular Reprogramming by Inhibiting Mesenchymal-to-Epithelial Transition

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Advancing Stem Cell Models of Alpha-Synuclein Gene Regulation in Neurodegenerative Disease

“…Transcription factor zinc finger and SCAN domain containing 21 (ZSCAN21) which is expressed in different brain areas, regulates alpha-synuclein expression (Dermentzaki et al, 2016 ). Depending on the cell type and maturation level, ZSCAN21 can have antagonistic effects on transcription of alpha-synuclein.…”

“…On the contrary, when ZSCAN 21 is knocked down in neurosphere stem cell cultures, alpha-synuclein expression is reduced, but no alterations are observed in postnatal and adult hippocampus. When ZSCAN21 is overexpressed in cortical neurons only SNCA mRNA is increased, but not alpha-synuclein protein expression which suggests that ZSCAN21 is not a master regulator and additional regulatory mechanisms are involved (Dermentzaki et al, 2016 ).…”

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“…Expression of α-synuclein is regulated by various transcription factors, such as zinc finger and SCAN domain containing 21 (ZSCAN21) (Clough et al 2009 ; Dermentzaki et al 2016 ), GATA-1 and GATA-2 (Scherzer et al 2008 ), Nurr1 (Yang and Latchman 2008 ), TRIM32 (Pavlou et al 2017 ), and p27 Kip1 (Gallastegui et al 2018 ). These transcription factors interact directly with the promotor region of α-synuclein, and this critical link between these transcription factors and α-synuclein may enable the design of therapies to lower production of α-synuclein.…”