Effects of PACAP on the Circadian Changes of Signaling Pathways in Chicken Pinealocytes

Abstract

Pituitary adenylate cyclase-activating polypeptide (PACAP) is involved in the regulation of circadian rhythms. In mammals, the brain's biological clock is the suprachiasmatic nucleus, receiving photic information from the retina through the retinohypothalamic pathway, where PACAP is the main cotransmitter of glutamate. The primary conductor of circadian rhythms of birds is the pineal gland. The presence of PACAP has been demonstrated both in the rat and avian pineal gland, where PACAP stimulates melatonin synthesis. The signaling mechanism, by which PACAP modulates melatonin synthesis and circadian rhythmic functions of the pineal gland, is only partially known. The aim of the present study was to investigate the effects of PACAP on the changes of p38 mitogen-activated protein kinase (MAPK) and 14-3-3 protein in chick pineal cell culture both of which have been shown to participate in the regulation of rhythmic functions. Pineal cells were treated with 1, 10, or 100 nM PACAP38 every 4 h during a 24-h period. The phosphorylation of p38 MAPK showed obvious changes during the observed 24 h, while the level of 14-3-3 protein did not. We found that the lowest used dose of PACAP did not cause any phase alteration in p38 MAPK phosphorylation. Ten nM PACAP induced a 4-h-long delay and 100 nM abolished the circadian changes of p38 MAPK phosphorylation. PACAP was not effective on the level of 14-3-3 protein in the early morning hours, and only the highest tested dose (100 nM) could evoke a change in the appearance of 14-3-3 between midday and midnight hours. In summary, PACAP modulated the phosphorylation of p38 MAPK and the appearance of 14-3-3 protein in the chicken pineal cells, but these effects were dose dependent and also depended on the time of day.

Identification of a gene associated with avian migratory behaviour

“…For example, exposure of the chicken pineal gland to PACAP induces a transitory increase in melatonin secretion, but does not cause phase shift of the melatonin rhythm [64–66]. PACAP has also been shown to directly influence clock gene expression [67] and affect signalling pathways that integrate the molecular clock in the functionality of circadian rhythms in a dose- and phase-dependent manner [68]. Further studies are needed to determine whether the ADCYAP1 polymorphism exerts its effect on nocturnal migratory restlessness via a phase-shift of the endogenous oscillator(s) or via a modulation of the downstream processes of the molecular clock.…”

Pituitary Adenylate Cyclase-Activating Polypeptide and Its Receptors: 20 Years after the Discovery

“…It has been suggested that the effect PACAP could involve the phosphorylation of the p38 MAPK (Racz et al, 2008).…”

Pituitary Adenylate Cyclase Activating Polypeptide (PACAP) Signalling Exerts Chondrogenesis Promoting and Protecting Effects: Implication of Calcineurin as a Downstream Target

“…In spite of the large variety of tissues containing or releasing PACAP, there are only sporadic data about its function in skeletal elements such as bone [7]–[9]; in particular, its presence in hyaline cartilage has not been reported. PACAP is a multifunctional peptide that can regulate diverse physiological processes such as testicular ageing [10], circadian rhythm [11], brain development [12] or cell migration [13]. PACAP is also regarded as a neurotrophic [14], [15] and anti-inflammatory substance in the CNS [16] and is reported to prevent harmful effects of oxidative stress in various tissues [17]–[19].…”