Melatonin signaling in mouse cerebellar granule cells with variable native MT1 and MT2 melatonin receptors

Abstract

Although G protein-coupled MT1 and MT2 melatonin receptors are expressed in neurons of the mammalian brain including in humans, relatively little is known about the influence of native MT1 and MT2 melatonin receptors on neuronal melatonin signaling. Whereas human cerebellar granule cells (CGC) express only MT1 receptors, mouse CGC express both MT1 and MT2. To study the effects of altered neuronal MT1/MT2 receptors, we used CGC cultures prepared from immature cerebella of wild-type mice (MT1/MT2 CGC) and MT1-and MT2-knockout mice (MT2 and MT1 CGC, respectively). Here we report that in MT1/MT2 cultures, physiological (low nanomolar) concentrations of melatonin decrease the activity (phosphorylation) of extracellular-signal-regulated kinase (ERK) whereas a micromolar concentration was ineffective. Both MT1 and MT2 deficiencies transformed the melatonin inhibition of ERK into melatonin-induced ERK activation. In MT1/MT2 CGC, 1 nM melatonin inhibited serine/threonine kinase Akt, whereas in MT1 and MT2 CGC, this concentration was ineffective. Under these conditions, both MT1 and MT2 deficiencies prevented melatonin from inhibiting forskolin-stimulated cAMP levels and cFos immunoreactivity. We demonstrated that selective removal of native neuronal MT1 and MT2 receptors has profound effect on the intracellular actions of low/physiological concentrations of melatonin. Since the expression of MT1 and MT2 receptors is cell-type-specific and species-dependent, we postulate that the pattern of expression of neuronal melatonin receptor types in different brain areas and cells could determine the capabilities of endogenous melatonin in regulating neuronal functioning.

Melatonin protects rat cerebellar granule cells against electromagnetic field‐induced increases in Na+ currents through intracellular Ca2+ release

“…Transfection experiments have demonstrated that when expressed in the same cell type, MT 1 and MT 2 receptors may couple to different signalling pathways . Both our work and that of Marta indicate that the presence of native MT 1 /MT 2 receptors in mouse and rat cerebellar GCs mediates the effects of MT on intracellular signalling pathways . Thus, it is possible that 1–5 μM MT may activate both MT 1 and MT 2 receptors simultaneously, thereby inducing a coordinated and integrated effect on PKA.…”

Distribution of MT1 Melatonin Receptor Promoter-Driven RFP Expression in the Brains of BAC C3H/HeN Transgenic Mice

“…A previous study using 2-[ 125 I]-iodomelatonin binding assay showed that melatonin receptors were expressed in the cerebellum of rats, but the binding localization was restricted to the Purkinje cell and molecular layers (Laudon et al 1988). Although signaling of the MT 1 and MT 2 melatonin receptors has been studied in some of the cells of the cerebellum (Imbesi et al 2008a), their role in the function of the cerebellum remain to be elucidated. In our study, RFP-MT 1 expression localized to the granular layer of the cerebellum, which is supported by previous studies using the 2-[ 125 I]iodomelatonin binding assay and in situ hybridization/RT-PCR for MT 1 mRNA in human and mouse cerebellar tissue Imbesi et al 2008a;Imbesi et al 2008b;Imbesi et al 2008c;Mazzucchelli et al 1996;Poirel et al 2003).…”

Melatonin modulation of intracellular signaling pathways in hepatocarcinoma HepG2 cell line: role of the MT1 receptor

“…It has been shown that melatonin inhibits activity of adenylyl cyclase in a dose‐dependent manner [44]. Previous studies have indicated that the coupling of both MT1 and MT2 receptors seem to be necessary to inhibit adenyl cyclase when melatonin is administered at low doses [45]. This could help to explain our results, and the fact that melatonin at 1000 μ m melatonin did not significantly change cAMP levels in HepG2, in which MT2 is not present and only MT1 is expressed.…”