1,25-Dihydroxyvitamin D regulates expression of the tryptophan hydroxylase 2 and leptin genes: implication for behavioral influences of vitamin D.
Level 5 - mechanism / opinion, no new human data
In vitro laboratory/bench study evaluating transcriptional mechanisms in cell cultures
PubMed 26071405 · doi:10.1096/fj.14-269811
What was done
The researchers evaluated the transcriptional regulation of human tryptophan hydroxylase 2 (TPH2) and leptin (Lep) by 1,25-dihydroxyvitamin D3 (1,25D). They probed candidate vitamin D responsive elements (VDREs) at -7/-10 kb in human TPH2 using binding assays with the vitamin D receptor (VDR)-retinoid X receptor (RXR) complex and reporter gene assays. They measured TPH2 mRNA expression after treatment with 10 nM 1,25D in human U87 glioblastoma cells and rat serotonergic RN46A-B14 cells. They also quantified leptin mRNA levels following 1,25D exposure in mouse adipocytes and human glioblastoma cells, and performed chromatin immunoprecipitation sequencing (ChIP-seq) on the mouse Lep gene.
What was found
Both TPH2 VDREs bound the VDR-RXR complex and drove reporter transcription in response to 1,25D. Treatment with 10 nM 1,25D increased TPH2 mRNA by 2.2-fold in human U87 glioblastoma cells and by 47.8-fold in rat serotonergic RN46A-B14 cells. In mouse adipocytes, 1,25D repressed leptin mRNA by at least 84%, whereas in human glioblastoma cells, it increased leptin mRNA by 15.1-fold. ChIP-seq identified a regulatory module at -28 kb in the mouse Lep gene harboring 3 VDREs that recruited VDR, RXR, C/EBPβ, and RUNX2 upon 1,25D stimulation.
Why it matters
This study provides a molecular mechanism showing that active vitamin D directly regulates the expression of TPH2 (the rate-limiting enzyme for brain serotonin synthesis) and leptin via specific responsive elements. This offers a biological rationale for how vitamin D status could influence brain serotonin pathways and metabolic signaling.
Limits
The findings are derived entirely from in vitro cell line models (human glioblastoma, rat serotonergic cells, and mouse adipocytes). The study did not assess functional serotonin production, metabolic endpoints, or behavioral outcomes in live animal models or humans.
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