Vitamin D Stimulates Serotonin Production via Induction of the Tryptophan Hydroxylase 2 Isoform in B14 Rat Medullary Neurons

Abstract

The active form of vitamin D3, 1,25‐dihydroxyvitamin D (1,25D), and serotonin (5‐HT) are postulated to play significant roles in abnormal social behavior associated with psychological conditions including autism spectrum disorders (ASDs) and depression. Moreover, we have observed that 1,25D regulates synthesis of two isoforms of tryptophan hydroxylase (TPH), the rate‐limiting enzyme in the 5‐HT biosynthetic pathway, including induction of the tryptophan hydroxylase 2 (TPH2) gene in the central nervous system (CNS) and suppression of tryptophan hydroxylase 1 (TPH1) expression in some peripheral tissues. Interestingly, major characteristics associated with autism may include low concentrations of serotonin in the CNS and elevated levels of serotonin in the periphery. Thus, in addition to assessing the effect of 1,25D on TPH gene expression, we also examined, for the first time, the ability of 1,25D to stimulate production of 5‐HT in neuronal cells. Rat serotonergic medullary cells (RN46A‐B14; B‐14) were cultured to confluency and plated in six‐well plates. After allowing cells to attach in the plates overnight, the cells were cultured in differentiation medium, followed by treatment of differentiated B‐14 cells with ethanol vehicle or 10−8 M 1,25D. At time zero, a 200 μL sample of media from each well was collected to serve as a baseline for 5‐HT concentration. The cells were then incubated over the next three days, and additional 200 μL samples were collected from each well at the 24‐, 48‐ and 72‐hour time points. A 5‐HT ELISA assay was then conducted using the collected samples. The results of the ELISA revealed a statistically significant increase (57%, p < 0.05) in 5‐HT production following treatment with 1,25D for 24 hours versus vehicle, with subsequently larger percent‐increases in 5‐HT synthesis observed at 48 and 72 hours (64% and 103%, respectively, p < 0.05). These results suggest that 1,25D stimulates the production of serotonin, likely through the induction of the neuronal TPH2 gene, and the time‐course of this effect appears to lag behind the induction of TPH mRNA which peaks at 24 hours. In summary, this study illuminates a novel coordinated biochemical and regulatory interaction between two neuromodulators, vitamin D and serotonin, thereby identifying a potential connection between serum vitamin D levels and the occurrence of psychiatric disorders commonly linked to an imbalance in CNS serotonin production, including autism and depression.Support or Funding InformationThis project was funded by the New College of Interdisciplinary Arts and Sciences at Arizona State University and the National Institutes of Health.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.