G protein-coupled receptor 55 activated by palmitoylethanolamide is associated with the development of nocturia associated with circadian rhythm disorders

Aims: Bladder function is regulated by clock genes and dysregulation of circadian bladder function can cause nocturia. The blood concentration of palmitoylethanolamide (PEA), a fatty acid metabolite, changes with circadian rhythm. Clock gene abnormalities demonstrate the highest PEA levels during the sleep phase. PEA is a GPR55 agonist that influences urination; therefore, increased PEA during the sleep phase may cause nocturia. Herein, we investigated the function of GPR55 to evaluate the relationship between GPR55 and nocturia that evoked higher PEA during the sleep phase in patients with circadian rhythm disorders. Main methods: Male C57BL/6 mice were used. GPR55 localization was evaluated by immunofluorescence staining, qRT-PCR, and western blotting. Variations in PEA-induced intracellular Ca2+ concentrations were measured in primary cultured mouse urothelial cells (UCs) using Ca2+ imaging. PEA-induced NGF and PGI2 release in UCs was measured by ELISA. The micturition reflex pathway after PEA administration was evaluated using immunofluorescence staining. Key findings: GPR55 was predominant in the UC layer. PEA induced release of Ca2+ from the endoplasmic re-ticulum into the UC cytoplasm. ELISA and immunofluorescence staining revealed that NGF and PGI2 were released from bladder UCs, stimulated the pontine micturition center in mice, and induced nocturia. Significance: The loss of regular circadian metabolizing rhythm in fatty acids causes higher blood PEA levels during the sleep phase. Binding of PEA to GPR55 in UC may activate the downstream processes of the micturition reflex, leading to nocturia. These findings suggest a new mechanism for nocturia and its potential as a therapeutic target.