Rhythmic expression of the melatonergic biosynthetic pathway and its differential modulation in vitro by LPS and IL10 in bone marrow and spleen

Abstract

Daily oscillation of the immune system follows the central biological clock outputs control such as melatonin produced by the pineal gland. Despite the literature showing that melatonin is also synthesized by macrophages and t lymphocytes, no information is available regarding the temporal profile of the melatonergic system of immune cells and organs in steady-state. Here, the expression of the enzymes arylalkylamine-n-acetyltransferase (AA-nAt), its phosphorylated form (p-AA-nAt) and acetylserotonin-O-methyltransferase (ASMT) were evaluated in phagocytes and T cells of the bone marrow (BM) and spleen. We also determined how the melatonergic system of these cells is modulated by LPS and the cytokine IL-10. The expression of the melatonergic enzymes showed daily rhythms in BM and spleen cells. Melatonin rhythm in the BM, but not in the spleen, follows P-AA-NAT daily variation. In BM cells, LPS and IL10 induced an increase in melatonin levels associated with the increased expressions of P-AA-NAT and ASMT. In spleen cells, LPS induced an increase in the expression of P-AA-NAT but not of melatonin. Conversely, IL10 induced a significant increase in melatonin production associated with increased AA-NAT/P-AA-NAT expressions. In conclusion, BM and spleen cells present different profiles of circadian production of local melatonin and responses to immune signals.Organs and cells of the immune system present daily variations regulated by oscillators present in each cell 1-6 . The intrinsic circadian clock of most of the immune cells imposes circadian expression of downstream genes and functions 4 . This is the case for the expression of pattern-recognition receptors and cytokines, the recruitment to tissues and the phagocytic activity of monocytes, macrophages and microglia 7-10 . Clock genes are also circadian expressed in mouse lymph nodes 10,11 and in B splenic cells 12 , where they control the activity of the cells 4,11 . Besides the intrinsic rhythmicity of cells and organs, there is a central synchronization that relies on neural and hormonal signaling controlled by the central clock in the suprachiasmatic nuclei 13,14 . After a sympathetic input, the darkness hormone melatonin, prolactin and glucocorticoids impose, for example, a daily rhythm in the migration of leukocytes to peripheral tissues 6 .In vertebrates, melatonin is known to be produced in a rhythmic manner by the pineal gland and retina, constitutively by the gastrointestinal tract and on demand by some immunocompetent cells 15,16 . Activated monocytes/macrophages/microglia and T lymphocytes expressed the enzymes arylalkylamine-N-acetyltransferase (AA-NAT), its active phosphorylated form (P-AA-NAT) and acetylserotonin-O-methyltransferase (ASMT) and melatonin 17-21 . In the spleen and in the bone marrow (BM), some works have shown the expression and activity of the melatonergic enzymes 22-24 , however, whether the immune cells of these organs also present www.nature.com/scientificreports www.nature.com/scientificreports/ circadian variations of the melaton...

Melatonin and Cancer: A Polyhedral Network Where the Source Matters

“…In bone marrow, locally produced melatonin [ 68 ] likely exerts on-site protection against oxidative stress in these vulnerable hematopoietic cells, probably by enhancing the immune capacity of derived immune cells such as lymphocytes [ 69 ]. The rhythmic expression of melatonergic enzymes has been recently described in this tissue, with a peak during the night, which correlates with the intracellular concentration of melatonin [ 70 ]. These authors also support the idea that the bone marrow could rhythmically produce its own melatonin, complementing the one from the pineal gland, thus not discarding the possibility of circulating uptake.…”

“…In addition, melatonin may play an important role in surveillance against the infection, inflammation, and recovery phases of acute defence response [ 75 , 76 ]. Regarding the variation in the melatonergic biosynthetic machinery, it has been recently described to present higher levels of expression during the diurnal phase, with the melatonin peak occurring in the dark phase and thus with no correlation between melatonin levels and the expression of its enzymes [ 70 ]. These authors suggest the possibility that nocturnal melatonin in the spleen is derived from the pineal gland, although the endogenous production of melatonin in the spleen has been also previously demonstrated [ 64 ].…”

“…Similar conclusions have been derived from the increase in melatonin content in the rat liver and brain after pinealectomy [ 111 ]. In the spleen, although the melatonergic biosynthetic pathway shows a greater expression during the diurnal phase, a melatonin peak occurs in the dark phase [ 70 ]. This suggests that, although enzymatic machinery for melatonin production is expressed in the spleen, its nocturnal melatonin content might be derived from the pineal gland.…”

Research progress of melatonin (MT) in improving ovarian function: a review of the current status

“…MT can also be secreted in the retina, digestive tract, and ovary [ 7 – 9 ]. The pineal gland cells use tryptophan in the blood as raw materials to produce serotonin (5-HT) through the hydroxylation and decarboxylation of tryptophan hydroxylase (THP) and aromatic amino acid decarboxylase (AADC), and further synthesize MT through the acetylation and methylation of N-acetyltransferase (NAT) and oxindole-oxy-methyltransferase (HIOMT) ( Figure 1 ) [ 10 ].…”

“… Synthesis of melatonin (MT) in human whole body [ 10 ]. Abbreviations: NAT, serotonin-N-acetyl transferase; and HOMT, hydroxyindole-O-methyltransferase.…”