Cell Signaling by Tryptophan Catabolism

Area of Science:

• Biochemistry
• Immunology
• Neuroscience

Background:

• Tryptophan (Trp) metabolism branches into kynurenine (KP), serotonin, and indole (IP) pathways.
• These pathways produce metabolites regulating immune responses, neurotransmission, and metabolic homeostasis.
• Aryl hydrocarbon receptor (AhR) activation is a common theme, influenced by Trp metabolites.

Purpose of the Study:

• To review the physiological functions of Trp catabolism as a distributed signaling network.
• To highlight the role of Trp metabolites in immune regulation, cellular homeostasis, and disease.
• To present novel findings on kynurenine pathway metabolites and their signaling impact.

Main Methods:

• Literature review of Trp metabolism pathways and their signaling roles.
• Discussion of metabolite interactions with receptors like AhR, GPR35, and NMDA receptors.
• Integration of recent discoveries on kynurenine-carboxyketoalkene and cysteine-dependent pathways.

Main Results:

• Trp metabolites act as endogenous AhR ligands and modulate other signaling pathways.
• A novel redox-active mediator, kynurenine-carboxyketoalkene, links KP to cysteine-dependent pathways.
• KP flux connects inflammation and cellular energy metabolism; indole derivatives influence mucosal immunity.

Conclusions:

• Trp metabolism is a complex signaling network with critical roles in health and disease.
• Dysregulation of Trp metabolism is implicated in neurodegeneration, cancer, and inflammatory diseases.
• Understanding Trp metabolism offers insights into maintaining cellular homeostasis and immune control.