Tryptophan Hydroxylase Mechanisms in Affective Disorders

Tryptophan hydroxylase (TPH) is the rate-limiting enzyme in the biosynthesis of serotonin, a neurotransmitter centrally implicated in mood regulation and affective disorders. Two isoforms, TPH1 and TPH2, mediate peripheral and central serotonin synthesis respectively. Alterations in TPH2 expression or activity—whether through genetic polymorphisms, post-translational modifications or epigenetic regulation—can shift serotonergic tone, affecting stress responsiveness, emotional resilience and susceptibility to depression and anxiety. Mechanistic research has uncovered links between histone acetylation, co-factor availability (notably tetrahydrobiopterin), enzyme stability and dimerisation in defining TPH2 catalytic efficiency. Emerging evidence also points to broader networks in which TPH2 interacts with neurotrophic factors, glucocorticoid signalling and metabolic sensors to shape synaptic plasticity and behavioural outcomes. Understanding these integrated pathways offers routes to novel diagnostics and targeted therapeutics for affective disorders.

Research from Nature Portfolio

Recent studies in a large animal model have explored how a common single-nucleotide polymorphism in the TPH2 gene influences behavioural and physiological responses to stress. Adult sheep carrying alternative alleles of this variant were assessed in open-field and isolation tests, with measurements of cortisol, prolactin, dehydroepiandrosterone, brain-derived neurotrophic factor and oxidative stress markers. While genotype affected behavioural scores—differentiating “calm” from “nervous” animals—it did not alter core endocrine or metabolic stress markers, suggesting adaptive neuroendocrine compensation. This work underscores the complexity of translating genotype into phenotype in serotonergic circuits and highlights the value of large-animal models for dissecting gene × environment interactions relevant to human mood disorders.

Tryptophan Hydroxylase Mechanisms in Affective Disorders publication trend

The graph below shows the total number of articles in tryptophan hydroxylase mechanisms in affective disorders across all publications each year (not limited to Nature Index journals).

Technical terms

Tryptophan hydroxylase 2 (TPH2): The central nervous system isoform of the enzyme that converts tryptophan to 5-hydroxytryptophan, the precursor of serotonin.

Histone acetylation: A reversible epigenetic modification of histone proteins that promotes chromatin relaxation and gene transcription, affecting TPH2 expression.

Brain-derived neurotrophic factor (BDNF): A growth factor that supports neuronal survival and synaptic plasticity, interacting with serotonergic signalling in mood regulation.

Single-nucleotide polymorphism (SNP): A single-base variation in the genome that can influence gene function or regulation, as exemplified by TPH2 variants affecting stress responses.

AMP-activated protein kinase (AMPK): A cellular energy sensor that regulates metabolic and transcriptional pathways, including ACSS2-mediated histone acetylation at the TPH2 locus.

References

1. D-mannose is a rapid inducer of ACSS2 to trigger rapid and long-lasting antidepressant responses through augmenting BDNF and TPH2 levels. Translational Psychiatry (2023).
2. Effects of the Combination of the C1473G Mutation in the Tph2 Gene and Lethal Yellow Mutations in the Raly-Agouti Locus on Behavior, Brain 5-HT and Melanocortin Systems in Mice. Biomolecules (2023).
3. Behavioural and physiological responses to stressors in sheep with temperament classified by genotype or phenotype. Scientific Reports (2024).
4. Stabilization of tryptophan hydroxylase 2 by l‐phenylalanine‐induced dimerization. FEBS Open Bio (2016).