β-Adrenoceptors Trigger Melatonin Synthesis in Phagocytes

Area of Science:

• Immunology
• Endocrinology
• Neuroscience

Background:

• Melatonin, the pineal hormone, signals darkness and is also synthesized by immune cells.
• Activated macrophages produce melatonin locally, promoting regulatory/tolerant phenotypes.
• Beta-adrenoceptor activation triggers pineal melatonin synthesis, and is linked to macrophage resolution (M2) and phagocytic activity, but its role in monocyte melatonin synthesis is unknown.

Purpose of the Study:

• To investigate if beta-adrenoceptor activation induces melatonin synthesis in monocytes and related immune cells.
• To elucidate the signaling pathways involved in catecholamine-stimulated melatonin synthesis in immune cells.

Main Methods:

• Stimulation of bone marrow-derived dendritic cells and RAW 264.7 macrophages with catecholamines.
• Analysis of melatonin synthesis pathways, including cyclic AMP/protein kinase A (PKA) and NF-κB activation.
• Investigation of beta-adrenoceptor involvement in melatonin production.

Main Results:

• Catecholamines were shown to stimulate melatonin synthesis in bone marrow-derived dendritic cells and RAW 264.7 macrophages.
• Beta-adrenoceptor activation was found to promote melatonin synthesis by activating the cyclic AMP/protein kinase A (PKA) pathway.
• Activation of the nuclear factor kappa B (NF-κB) pathway was observed, indicating its role in melatonin synthesis.

Conclusions:

• Extra-pineal melatonin synthesis is inducible in macrophages and dendritic cells by catecholamines via beta-adrenoceptor activation.
• The findings suggest that extra-pineal melatonin may act as an autocrine/paracrine signal in macrophages, maintaining low-grade inflammation and tolerant phenotypes.
• This highlights a novel mechanism for immune cell regulation and local inflammatory control.