Role of AP-2α Transcription Factor in the Regulation of Synapsin II Gene Expression by Dopamine D1 and D2 Receptors

Abstract

Synapsins are a family of neuron-specific phosphoproteins involved in synaptic vesicle docking, synaptogenesis, and synaptic plasticity. Previous studies have reported an increase in synapsin II protein by dopaminergic agents in the striatum, medial prefrontal cortex, and nucleus accumbens. This study investigated the mechanistic pathway involved in synapsin II regulation by dopaminergic drugs using primary midbrain neurons to determine which of several transcription factors regulates synapsin II expression. Protein kinase A (PKA) participation in the signaling pathway was examined using selective PKA inhibitors, which reduced synapsin II expression in cell cultures while dopaminergic agents were unable to increase synapsin II in the presence of the PKA inhibitor. Transcription factor involvement was further investigated using separate cultures treated with antisense deoxyoligonucleotides (ADONs) against the following transcription factors: activating protein 2 alpha (AP-2alpha), early growth response factor 1 (EGR-1), or polyoma enhancer activator-3 (PEA-3). Selective knockdown of AP-2alpha by ADONs reduced synapsin II levels, whereas treatment with EGR-1 and PEA-3 ADONs did not affect synapsin II expression. Furthermore, dopaminergic agents were no longer able to influence synapsin II concentrations following AP-2alpha knockdown. Collectively, these results indicate that a cyclic adenosine-3',5'-monophosphate/PKA-dependent mechanism involving the AP-2alpha transcription factor is likely responsible for the increase in neuronal synapsin II following dopamine D1 receptor stimulation or dopamine D2 receptor inhibition.

Change in expression of vesicular protein synapsin II by chronic treatment with D2 allosteric modulator PAOPA

“…The presynaptic protein synapsin II has shown significant involvement in the etiology of schizophrenia, and previous studies from our lab have linked modulation of this protein to activation of dopamine receptors [10,41]. The current study shows that a significant increase in synapsin IIa expression occurs in dopaminergic regions strongly implicated in schizophrenia, including the striatum, mPFC, and NAc, following chronic administration of PAOPA.…”

“…Regulation of synapsin II expression has previously been shown to occur by modulation of the dopamine D1 and D2 receptors [10,41]. In this current study, increases in synapsin IIa were observed in dopamine rich regions, including the striatum, NAc and mPFC.…”

“…Similarly, results from our lab showed decreased levels of the synapsin II transcript in the dorsolateral prefrontal cortex of patients affected with schizophrenia [47]. The lifetime antipsychotic drug use in these studies has been shown to positively correlate with synapsin II expression, particular the synapsin IIa isoform, via interaction with dopamine D1 and D2 receptors (D2R) [10,26,41,47]. Finally, previous studies from our lab have also shown that knockdown of synapsin II globally [17,18] as well as specifically within the medial prefrontal cortical regions of animal models [16,19], induces schizophrenia-like behavioral abnormalities.…”

“…Stimulation of D1 receptor activity by agonists, or attenuation of D2 activity by antagonists, results in increased synapsin II levels [11,41]. The use of PAOPA, has previously been shown to promote internalization of the D2R, thereby decreasing overall availability of this receptor, similar to an antagonist, but with a more fine-tuned and subtle technique [1].…”

“…Synapsin expression is regulated by dopaminergic pathways which can be affected by long-term ligand modulation [10,41]. In this study, PAOPA was observed to have significant effects in modulating synapsin IIa expression within all three brain regions of treated animals, leading to an increase in levels of synapsin IIa by 48% in the striatum (*p = 0.0126), 119% in the nucleus accumbens (*p = 0.0103) and 30% in the mPFC (*p = 0.0296; Fig.…”