Regulation of neuronal circHomer1 biogenesis by PKA/CREB/ERK-mediated pathways and effects of glutamate and dopamine receptor blockade.

Abstract

There are currently only very few efficacious drug treatments for SCZ and BD, none of which can significantly ameliorate cognitive symptoms. Thus, further research is needed in elucidating molecular pathways linked to cognitive function and antipsychotic treatment. Circular RNAs (circRNAs) are stable brain-enriched non-coding RNAs, derived from the covalent back-splicing of precursor mRNA molecules. CircHomer1 is a neuronal-enriched, activity-dependent circRNA, derived from the precursor of the long HOMER1B mRNA isoform, which is significantly downregulated in the prefrontal cortex of subjects with psychosis and is able to regulate cognitive function. Even though its relevance to psychiatric disorders and its role in brain function and synaptic plasticity have been well established, little is known about the molecular mechanisms that underlie circHomer1 biogenesis in response to neuronal activity and psychiatric drug treatment. Here we suggest that the RNA-binding protein (RBP) FUS positively regulates neuronal circHomer1 expression. Furthermore, we show that the MEK/ERK and PKA/CREB pathways positively regulate neuronal circHomer1 expression, as well as promote the transcription of Fus and Eif4a3, another RBP previously shown to activate circHomer1 biogenesis. We then demonstrate via both in vitro and in vivo studies that NMDA and mGluR5 receptors are upstream modulators of circHomer1 expression. Lastly, we report that in vivo D2R antagonism increases circHomer1 expression, whereas 5HT2AR blockade reduces circHomer1 levels in multiple brain regions. Taken together, this study allows us to gain novel insights into the molecular circuits that underlie the biogenesis of a psychiatric disease-associated circRNA.

The noncoding circular RNAcircHomer1regulates developmental experience-dependent plasticity in mouse visual cortex

“…7A). Such regulation could be facilitated by recently described molecular pathways underlying circHomer1 biogenesis (44) or by changes in other Homer1 mRNA products not measured in our experiments (for instance, Homer1b (42)). Future work is needed to determine if Homer1a can indeed give rise to circHomer1, whether circularization meaningfully decreases linear mRNA availability, and if circular RNA decay rate is static or itself regulated by activity.…”

“…Circular RNA species decay more slowly than their linear counterparts (45) and changes in transcription thus tend to result in larger, longer relative increases in circRNA levels (46), but this seems insufficient to explain this discrepancy. More plausible, perhaps, is that the rate of Homer1 circularization is itself regulated by activity (44). Thus, we asked whether a constant circularization rate of Homer1b and Homer1a, a variable circularization rate of Homer1b, or a variable circularization rate of Homer1b and Homer1a best fit our observed data (Supplementary Fig.…”

“…It remains unclear how neuronal activity regulates circHomer1 expression, as the only demonstrated precursor of circHomer1 is non-activity dependent Homer1b mRNA (44). Given that Homer1a contains the relevant regions to form circHomer1, including a section of intron 5 (44), it is plausible that circHomer1 could derive from Homer1a, allowing its expression to change in tandem with Homer1a transcription. However, during MD and development in vivo and bicuculline treatment in vitro, we observed timepoints where changes in circHomer1 expression appear decoupled from or even opposing changes in Homer1a.…”

“…It remains unclear how neuronal activity regulates circHomer1 expression, as the only demonstrated precursor of circHomer1 is non-activity dependent Homer1b mRNA (44). Given that Homer1a contains the relevant regions to form circHomer1, including a section of intron 5 (44), it is plausible that circHomer1 could derive from Homer1a, allowing its expression to change in tandem with Homer1a transcription.…”

“…As it is unclear what stages in the biogenesis of circHomer1 confer its activitydependence, we compared three nested dynamical system models(69) of circHomer1 expression with the same basic architecture to assess which best fit our data. We We hypothesized (42,44) that the activity-dependence of circHomer1 expression was most likely to arise from circularization of an activity-dependent mRNA (Homer1a) and/or activity dependent circularization of a constitutively expressed mRNA (Homer1b).…”