Sabir Marya S, Haussler Mark R, Mallick Sanchita, Kaneko Ichiro, Lucas Daniel A, Haussler Carol A, Whitfield G Kerr, Jurutka Peter W
1School of Mathematical and Natural Sciences, Arizona State University, Phoenix, AZ USA.
2Department of Basic Medical Sciences, University of Arizona College of Medicine, Phoenix, AZ USA.
Genes Nutr. 2018 Jul 11;13:19. doi: 10.1186/s12263-018-0605-7. eCollection 2018.
Diminished brain levels of two neurohormones, 5-hydroxytryptamine (5-HT; serotonin) and 1,25-dihydroxyvitamin D (1,25D; active vitamin D metabolite), are proposed to play a role in the atypical social behaviors associated with psychological conditions including autism spectrum disorders and depression. We reported previously that 1,25D induces expression of tryptophan hydroxylase-2 (TPH2), the initial and rate-limiting enzyme in the biosynthetic pathway to 5-HT, in cultured rat serotonergic neuronal cells. However, other enzymes and transporters in the pathway of tryptophan metabolism had yet to be examined with respect to the actions of vitamin D. Herein, we probed the response of neuronal cells to 1,25D by quantifying mRNA expression of serotonin synthesis isozymes, TPH1 and TPH2, as well as expression of the serotonin reuptake transporter (SERT), and the enzyme responsible for serotonin catabolism, monoamine oxidase-A (MAO-A). We also assessed the direct production of serotonin in cell culture in response to 1,25D.
Employing quantitative real-time PCR, we demonstrate that mRNAs are 28- to 33-fold induced by 10 nM 1,25D treatment of cultured rat serotonergic neuronal cells (RN46A-B14), and the enhancement of mRNA by 1,25D is dependent on the degree of neuron-like character of the cells. In contrast, examination of , the gene product of which is a target for the SSRI-class of antidepressants, and , which encodes the predominant catabolic enzyme in the serotonin pathway, reveals that their mRNAs are 51-59% repressed by 10 nM 1,25D treatment of RN46A-B14 cells. Finally, serotonin concentrations are significantly enhanced (2.9-fold) by 10 nM 1,25D in this system.
These results are consistent with the concept that vitamin D maintains extracellular fluid serotonin concentrations in the brain, thereby offering an explanation for how vitamin D could influence the trajectory and development of neuropsychiatric disorders. Given the profile of gene regulation in cultured RN46A-B14 serotonergic neurons, we conclude that 1,25D acts not only to induce serotonin synthesis, but also functions at an indirect, molecular-genomic stage to mimic SSRIs and MAO inhibitors, likely elevating serotonin in the CNS. These data suggest that optimal vitamin D status may contribute to improving behavioral pathophysiologies resulting from dysregulation of serotonergic neurotransmission.
两种神经激素，5-羟色胺（5-HT；血清素）和1,25-二羟基维生素D（1,25D；活性维生素D代谢物）的脑内水平降低，被认为在与包括自闭症谱系障碍和抑郁症在内的心理状况相关的非典型社会行为中起作用。我们之前报道过，1,25D可诱导培养的大鼠血清素能神经元细胞中色氨酸羟化酶-2（TPH2）的表达，TPH2是血清素生物合成途径中的初始限速酶。然而，色氨酸代谢途径中的其他酶和转运体尚未就维生素D的作用进行研究。在此，我们通过定量血清素合成同工酶TPH1和TPH2的mRNA表达，以及血清素再摄取转运体（SERT）和负责血清素分解代谢的酶单胺氧化酶-A（MAO-A）的表达，来探究神经元细胞对1,25D的反应。我们还评估了细胞培养物中响应1,25D时血清素的直接产生情况。
采用定量实时PCR，我们证明，用10 nM 1,25D处理培养的大鼠血清素能神经元细胞（RN46A-B14）可使mRNA诱导28至33倍，且1,25D对mRNA的增强作用取决于细胞的神经元样特征程度。相比之下，对其基因产物是SSRI类抗抑郁药作用靶点的以及编码血清素途径中主要分解代谢酶的进行检测发现，用10 nM 1,25D处理RN46A-B14细胞可使它们的mRNA被抑制51 - 59%。最后，在该系统中，10 nM 1,25D可使血清素浓度显著升高（2.9倍）。
这些结果与维生素D维持脑内细胞外液血清素浓度的概念一致，从而为维生素D如何影响神经精神疾病的病程和发展提供了解释。鉴于培养的RN46A-B14血清素能神经元中的基因调控情况，我们得出结论，1,25D不仅作用于诱导血清素合成，还在间接的分子基因组阶段发挥作用，模拟SSRI和MAO抑制剂，可能提高中枢神经系统中的血清素水平。这些数据表明，最佳的维生素D状态可能有助于改善因血清素能神经传递失调导致的行为病理生理状况。
