ABSTRACT
MAP kinases (MAPKs) play a key role in photic entrainment signaling in the suprachiasmatic nuclei (SCN), the mammalian circadian clock. The control of MAPKs is a fine balance between specific kinases (MEKs) and phosphatases (MKPs), whose orchestration in the SCN is still unresolved. We have found MKP1/2 and MKP3 immunoreactive-cells in the hamster SCN, whose levels are rapidly increased in response to transient light stimulation in the subjective night (CT 18), when light is able to entrain the clock. Moreover, the expression level of MKP3 varies under light-dark cycles and constant darkness, peaking at noon, when MAPKs are in their activated state and begin their inactivation. These results show a different perspective on MAPKs in the SCN, which includes its regulation by a complex net of phosphatases.
Subject(s)
Circadian Rhythm/physiology , Dual Specificity Phosphatase 1/metabolism , Dual Specificity Phosphatase 6/metabolism , Photoperiod , Suprachiasmatic Nucleus/enzymology , Animals , Biological Clocks/physiology , Cricetinae , Light , Male , MesocricetusABSTRACT
Circadian entrainment involves photic stimulation of the suprachiasmatic molecular oscillator, including activation of the ERK/MAP kinase, which is phosphorylated endogenously during the day and in response to light during the night. We aimed to disrupt the diurnal cycle of ERK phosphorylation by in vivo transfection of a constitutively active form of MEK, a MAPK kinase. This procedure did not affect normal circadian parameters, but completely inhibited light-induced phase advances. Therefore, circadian regulation of the ERK pathway is not essential for the normal mechanism of the biological clock, but it is fundamental as an interface with environmental entrainment by light.
Subject(s)
Circadian Rhythm/physiology , Extracellular Signal-Regulated MAP Kinases/metabolism , Mesocricetus/physiology , Mitogen-Activated Protein Kinases/metabolism , Suprachiasmatic Nucleus/enzymology , Suprachiasmatic Nucleus/physiology , Animals , Cricetinae , Enzyme Activation , Green Fluorescent Proteins/metabolism , Male , Motor Activity/physiology , TransfectionABSTRACT
Circadian rhythms are entrained by light and by several neurochemical stimuli. In hamsters housed in constant darkness, i.c.v. administration of nerve growth factor (NGF) at various times in their circadian cycle produced phase shifts of locomotor activity rhythms that were similar in direction and circadian timing to those produced by brief pulses of light. Moreover, the effect of NGF and light were not additive, indicating signalling points in common. These points include the immediate-early gene c-fos and ERK1/2, a component of the mitogen-activated protein kinases (MAPK) family. NGF activates c-FOS and ERK1/2-MAPK in the suprachiasmatic nuclei, the site of a circadian clock in mammals, when administered during the subjective night but not during the day. The effect of NGF on ERK1/2 activation was not inhibited by the administration of MK-801, a glutamate/NMDA receptor antagonist. These results suggest that NGF, acting through MAPK activation, plays a role in photic entrainment of the mammalian circadian clock.
Subject(s)
Circadian Rhythm/drug effects , Mitogen-Activated Protein Kinases/metabolism , Nerve Growth Factor/pharmacology , Suprachiasmatic Nucleus/drug effects , Analysis of Variance , Animals , Behavior, Animal/drug effects , Blotting, Western/methods , Cell Count/methods , Cricetinae , Dizocilpine Maleate/pharmacology , Drug Interactions , Enzyme Activation/drug effects , Excitatory Amino Acid Antagonists/pharmacology , Gene Expression Regulation/drug effects , Gene Expression Regulation/physiology , Gene Expression Regulation/radiation effects , Immunohistochemistry/methods , Light , Male , Mitogen-Activated Protein Kinase 3/metabolism , Motor Activity/drug effects , Phosphorylation/drug effects , Proto-Oncogene Proteins c-fos/metabolism , Suprachiasmatic Nucleus/metabolism , Time FactorsABSTRACT
Circadian rhythms are entrained by light-activated signal transduction pathways in the biological clock. Among these, circadian and photic control of mouse suprachiasmatic ERK MAP kinase activation has been reported. In this paper we extend these results to hamsters and to the two other major members of the MAPK family: JNK and p38. The three kinases are rhythmically phosphorylated under light-dark and constant conditions, with maximal values during the day or subjective day. Light pulses during the subjective night induce rapid activation of the three enzymes, suggesting that the three MAP kinases might be implicated in mammalian photic entrainment.
Subject(s)
Circadian Rhythm/physiology , Light , Mitogen-Activated Protein Kinases/biosynthesis , Suprachiasmatic Nucleus/physiology , Animals , Blotting, Western , Cricetinae , Mesocricetus , Phosphorylation , Photic Stimulation , p38 Mitogen-Activated Protein KinasesABSTRACT
Mammalian circadian rhythms are generated by the hypothalamic suprachiasmatic nuclei and finely tuned to environmental periodicities by neurochemical responses to the light-dark cycle. Light reaches the clock through a direct retinohypothalamic tract, primarily through glutamatergic innervation, and its action is probably regulated by a variety of other neurotransmitters. A key second messenger in circadian photic entrainment is calcium, mobilized through membrane channels or intracellular reservoirs, which triggers the activation of several enzymes, including a calcium/calmodulin-dependent protein kinase and nitric oxide synthase. Other enzymes activated by light are mitogen-activated- and cGMP-dependent protein kinase; all of the above have been reported to be involved in the circadian responses to nocturnal light pulses. These mechanisms lead to expression of specific clock genes which eventually set the phase of the clock and of clock-controlled circadian rhythms.