Overexpression of the human VPAC ₂ receptor in the suprachiasmatic nucleus alters the circadian phenotype of mice

Abstract

The neuropeptides vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) belong to a superfamily of structurally related peptide hormones that includes glucagon, glucagon-like peptides, secretin, and growth hormonereleasing hormone. Microinjection of VIP or PACAP into the rodent suprachiasmatic nucleus (SCN) phase shifts the circadian pacemaker and VIP antagonists, and antisense oligodeoxynucleotides have been shown to disrupt circadian function. VIP and PACAP have equal potency as agonists of the VPAC 2 receptor (VPAC2R), which is expressed abundantly in the SCN, in a circadian manner. To determine whether manipulating the level of expression of the VPAC 2R can influence the control of the circadian clock, we have created transgenic mice overexpressing the human VPAC 2R gene from a yeast artificial chromosome (YAC) construct. The YAC was modified by a strategy using homologous recombination to introduce (i) the HA epitope tag sequence (from influenza virus hemagglutinin) at the carboxyl terminus of the VPAC 2R protein, (ii) the lacZ reporter gene, and (iii) a conditional centromere, enabling YAC DNA to be amplified in culture in the presence of galactose. High levels of lacZ expression were detected in the SCN, habenula, pancreas, and testis of the transgenic mice, with lower levels in the olfactory bulb and various hypothalamic areas. Transgenic mice resynchronized more quickly than wild-type controls to an advance of 8 h in the light-dark (LD) cycle and exhibited a significantly shorter circadian period in constant darkness (DD). These data suggest that the VPAC 2R can influence the rhythmicity and photic entrainment of the circadian clock. E vidence is accumulating to suggest that the neuropeptides vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) may play important roles in the control of the circadian clock in the suprachiasmatic nucleus (SCN). VIP is synthesized in cells of the retinorecipient region of the rodent SCN (1, 2), at least some of which may have a direct retinal input (3). These cells form synapses with vasopressin-containing cells in the dorsomedial SCN as well as contacts with other VIP cells (4). There is diurnal variation of VIP immunoreactivity (5) and prepro VIP mRNA (6, 7) in the SCN. Exogenous VIP can mimic the phase-advancing and -delaying effects of light pulses (8, 9). VIP antagonists (10) and VIP antisense oligodeoxynucleotides (11) have been shown to disrupt circadian function. Elevated SCN levels of VIP mRNA have been found in two mutant rodent strains [the tau mutant hamster (12) and the spontaneously hypertensive (SHR) rat (13)] that exhibit a significantly shorter free-running period in constant darkness (DD), consistent with an involvement of VIP in establishing the free-running period of the circadian clock.In the SCN, PACAP originates almost exclusively from a subpopulation of glutamate-containing retinal ganglion cells (14, 15) that terminate in the retinorecipient region of the SC...

Structural and functional identification of the pituitary adenylate cyclase-activating polypeptide receptor VPAC2 from the frog Rana tigrina rugulosa

“…It was proposed that these receptors in the cerebral cortex are involved in the regulation of energy metabolism. In the hypothalamus, VPAC 1 R is not expressed while VPAC 2 R is present at high levels in the suprachiasmatic nucleus and there was evidence suggesting the involvement of this receptor in regulating circadian rhythm (Piggins et al 1995, Shen et al 2000. In summary, our results are consistent with previous reports; the fVPAC 2 R homologue is widely distributed in both peripheral tissues and various regions of the brain.…”

“…VPAC 1 R is expressed almost exclusively in the cerebral cortex and hippocampus (Ishihara et al 1992) while VPAC 2 R has a wider distribution and is expressed in the olfactory bulb, hypothalamus, hippocampus, brainstem, pituitary and cerebellum (Lutz et al 1993, Usdin et al 1994, Sheward et al 1995. Interestingly, high levels of VPAC 2 R were detected in the suprachiasmatic nucleus and it is possible that this receptor is involved in the control of circadian rhythm (Piggins et al 1995, Shen et al 2000. Recently, a frog PACAP/VIP receptor (fPVR) (Alexandre et al 1999) which is structurally more related to the mammalian VPAC 1 Rs was isolated.…”

The roles of vasoactive intestinal polypeptide in the mammalian circadian clock

“…In comparison with control wild-types, these mutant mice show a shortened circadian period when maintained in constant dim red light and an increased rate of re-entrainment when the light-dark cycle is reset (Shen et al 2000). Moreover, Watanabe et al (2000) demonstrated that exogenous VIP reset the secretion of AVP from organotypic SCN cultures with a temporal pattern of sensitivity resembling that of a photic phase-response curve.…”

Maternity-related plasticity in circadian rhythms of bumble-bee queens

“…Similar dim red light illumination is commonly used for monitoring locomotor activity in circadian studies (e.g. [4,5,7,[24][25][26]). We monitored locomotor activity and analysed circadian rhythms with the CLOCKLAB data acquisition and analysis system (Actimetrics Co., Wilmette, IL, USA).…”