AbstractsBiology & Animal Science

Gene expression changes induced by mood stabilizer drugs in a serotonergic cell line

by Diana Balasubramanian

Institution: University of Otago
Year: 0
Keywords: Valproic acid; sepiapterin reductase; tetrahydrobiopterin; HDAC inhibition; mood stabilizer; epigenetics
Record ID: 1312984
Full text PDF: http://hdl.handle.net/10523/5480


Valproic acid (VPA) is widely used in the treatment and prophylaxis of bipolar disorder and epilepsy. Despite its extensive use, the mechanisms of action of this drug are still largely unclear. VPA is known to enhance GABA-mediated neurotransmission, and it modulates a variety of molecular signalling networks although no single mechanism has been implicated in its therapeutic action. Tetrahydrobiopterin (BH4) is an essential cofactor in the biosynthesis of neurotransmitters like serotonin, dopamine and noradrenalin, and the BH4 pathway may thus be important in mood biology. Prior work from this laboratory demonstrated that VPA caused a marked upregulation of Spr, the gene for sepiapterin reductase, which is a key enzyme in the BH4 synthesis pathway. This work therefore defined a potentially novel mechanism of action for VPA, operating through the BH4 pathway, which is further explored here in an in vitro cell culture setting. Using the rat serotonergic cell line RN46A, in which VPA induction of Spr was first observed, this effect was confirmed and further examined using real-time quantitative PCR (qPCR). About 8-fold induction of Spr was observed after 72 h exposure of RN46A cells to 0.5 mM VPA. The generality of this effect was then explored by treating three different rat neural cell lines (RN46A, C6 and H19-7) with various concentrations of VPA for 72 h and measuring Spr expression changes. With the aim of attaining greater understanding of this effect, a range of other drugs that are used as mood stabilizer drugs such as the anticonvulsants carbamazepine, lamotrigine and the classic mood stabilizer drug lithium were examined for Spr expression changes in RN46A cells. Of these, only lithium showed significant upregulation of Spr at therapeutically relevant doses. The action of both VPA and lithium on Spr expression suggested a potential mechanism of action shared by these two widely used mood stabilizer drugs. VPA has recently been recognized as an epigenetic drug, due to its ability to inhibit histone deacetylases and induce demethylation in specific genes. These effects offer new avenues for understanding the therapeutic actions of this drug. With the hypothesis that the HDAC inhibitory activity of VPA causes chromatin changes in the Spr promoter leading to upregulation of the gene, chromatin immunoprecipitation assays to analyse histone modifications at the Spr promoter were carried out. Histone acetylation at H3K9/K14ac histone marks near the Spr transcription start site in RN46A, after exposure to VPA, was found to be significantly increased. Correlation of increased histone acetylation with Spr upregulation suggests involvement of histone modifications in VPA action on this gene, thus defining one possible epigenetic mechanism of action for this mood stabilizer drug. The role of methylation changes at the Spr promoter in the upregulation of this gene in response to VPA exposure was also explored in this study. Bisulfite sequencing was carried out on DNA extracted from RN46A cells exposed to either VPA…