Gene expression effects of lithium and valproic acid in a serotonergic cell line.

Valproic acid (VPA) and lithium are widely used in the treatment of bipolar disorder. However, the underlying mechanism of action of these drugs is not clearly understood. We used RNA-Seq analysis to examine the global profile of gene expression in a rat serotonergic cell line (RN46A) after exposure to these two mood stabilizer drugs. Numerous genes were differentially regulated in response to VPA (log2 fold change ≥ 1.0; i.e., odds ratio of ≥2, at false discovery rate <5%), but only two genes ( Dynlrb2 and Cdyl2) showed significant differential regulation after exposure of the cells to lithium, with the same analysis criteria. Both of these genes were also regulated by VPA. Many of the differentially expressed genes had functions of potential relevance to mood disorders or their treatment, such as several serpin family genes (including neuroserpin), Nts (neurotensin), Maob (monoamine oxidase B), and Ap2b1, which is important for synaptic vesicle function. Pathway analysis revealed significant enrichment of Gene Ontology terms such as extracellular matrix remodeling, cell adhesion, and chemotaxis. This study in a cell line derived from the raphe nucleus has identified a range of genes and pathways that provide novel insights into potential therapeutic actions of the commonly used mood stabilizer drugs.

Valproic acid exposure leads to upregulation and increased promoter histone acetylation of sepiapterin reductase in a serotonergic cell line.

Valproic acid (VPA) is a widely used antiepileptic drug and first-line treatment in bipolar disorder, although the mechanisms underlying its therapeutic effects are largely unknown. Recently, the recognition of VPA as an epigenetic drug offers new opportunities for understanding its therapeutic actions. In a rat serotonergic cell line (RN46A) we observed that VPA exposure has a strong upregulatory effect on the gene for sepiapterin reductase (SPR), a key enzyme involved in the tetrahydrobiopterin (BH4) synthetic pathway. 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. Using real-time quantitative PCR we show that VPA, at therapeutically relevant doses, increases the expression of the Spr gene by about 8-fold in RN46A cells. In addition, Spr protein levels in VPA-exposed cells were elevated, as were the intracellular BH4 levels. HDAC inhibitors (HDACI) trichostatin A and sodium butyrate also upregulated Spr, but this was not observed using the VPA-analogue valpromide, which lacks HDAC inhibitory activity. Further examination of this effect revealed that exposure to VPA increased the acetylated histone mark H3K9/K14ac at the Spr promoter. The DNMT inhibitor 5'aza-dC also upregulated Spr by over 8-fold. However, DNA methylation status across the Spr promoter did not change in response to VPA. The BH4 pathway is fundamental to the regulation of neurotransmitters relevant to mood disorders, and this epigenetic effect of VPA at the Spr promoter may represent a novel mechanism through which VPA achieves its therapeutic action.