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Michael H Hastings

Publications and source records attributed to Michael H Hastings.

At least 19 recordsLinked to original sources
PubMed2007

Prokineticin receptor 2 (Prokr2) is essential for the regulation of circadian behavior by the suprachiasmatic nuclei.

The suprachiasmatic nucleus (SCN), the brain's principal circadian pacemaker, coordinates adaptive daily cycles of behavior and physiology, including the rhythm of sleep and wakefulness. The cellular mechanism sustaining SCN circadian timing is well characterized, but the neurochemical pathways by which SCN neurons coordinate circadian behaviors remain unknown. SCN transplant studies suggest a role for (unidentified) secreted factors, and one potential candidate is the SCN neuropeptide prokineticin 2 (Prok2). Prok2 and its cognate prokineticin receptor 2 (Prokr2/Gpcr73l1) are widely expressed in both the SCN and its neural targets, and Prok2 is light-regulated. Hence, they may contribute to cellular timing within the SCN, entrainment of the clock, and/or they may mediate circadian output. We show that a targeted null mutation of Prokr2 disrupts circadian coordination of the activity cycle and thermoregulation. Specifically, mice lacking Prokr2 lost precision in timing the onset of nocturnal locomotor activity; and under both a light/dark cycle and continuous darkness, there was a pronounced temporal redistribution of activity away from early to late circadian night. Moreover, the coherence of circadian behavior was significantly reduced, and nocturnal body temperature was depressed. Entrainment by light is not, however, dependent on Prokr2, and bioluminescence real-time imaging of organotypical SCN slices showed that the mutant SCN is fully competent as a circadian oscillator. We conclude that Prokr2 is not necessary for SCN cellular timekeeping or entrainment, but it is an essential link for coordination of circadian behavior and physiology by the SCN, especially in defining the onset and maintenance of circadian night.

Animals↗
PubMed2006

Circadian orchestration of the hepatic proteome.

Circadian rhythms are essential to health. Their disruption is associated with metabolic diseases in experimental animals and man. Local metabolic rhythms represent an output of tissue-based circadian clocks. Attempts to define how local metabolism is temporally coordinated have focused on gene expression by defining extensive and divergent "circadian transcriptomes" involving 5%-10% of genes assayed. These analyses are inevitably incomplete, not least because metabolic coordination depends ultimately upon temporal regulation of proteins. We therefore conducted a systematic analysis of a mammalian "circadian proteome." Our analysis revealed that up to 20% of soluble proteins assayed in mouse liver are subject to circadian control. Many of these circadian proteins are novel and cluster into discrete phase groups so that the liver's enzymatic profile contrasts dramatically between day and night. Unexpectedly, almost half of the cycling proteins lack a corresponding cycling transcript, as determined by quantitative PCR, microarray, or both and revealing for the first time the extent of posttranscriptional mechanisms as circadian control points. The circadian proteome includes rate-limiting factors in vital pathways, including urea formation and sugar metabolism. These findings provide a new perspective on the extensive contribution of circadian programming to hepatic physiology.

Animals↗
PubMed2006

Hibernation proteins: preparing for life in the freezer.

Hibernation is an extreme response to a seasonal environment, yet we know almost nothing about how it is timed or how vital cellular functions are sustained in the face of plummeting body temperature. In this issue of Cell, kondo et al. (2006) identify a liver-derived protein complex as an essential coordinator of this adaptation to the depredations of winter.

Animals↗
PubMed2006

Metabolic regulation: fasting in the dark.

It is natural to starve. Learning how animals cope by juggling their scarce metabolic resources should therefore allow us to pinpoint physiological switches relevant to diabetes and cardiovascular disease. One known environmental trigger to metabolic adaptation is darkness; new studies suggest its endocrine mediator is 5' AMP.

Adenosine Monophosphate↗
PubMed2006

Synchronization and maintenance of timekeeping in suprachiasmatic circadian clock cells by neuropeptidergic signaling.

Circadian timekeeping in mammals is driven by transcriptional/posttranslational feedback loops that are active within both peripheral tissues and the circadian pacemaker of the suprachiasmatic nuclei (SCN). Spontaneous synchronization of these molecular loops between SCN neurons is a primary requirement of its pacemaker role and distinguishes it from peripheral tissues, which require extrinsic, SCN-dependent cues to impose cellular synchrony. Vasoactive intestinal polypeptide (VIP) is an intrinsic SCN factor implicated in acute activation and electrical synchronization of SCN neurons and coordination of behavioral rhythms. Using real-time imaging of cellular circadian gene expression across entire SCN slice cultures, we show for the first time that the Vipr2 gene encoding the VPAC2 receptor for VIP is necessary both to maintain molecular timekeeping within individual SCN neurons and to synchronize molecular timekeeping between SCN neurons embedded within intact, organotypical circuits. Moreover, we demonstrate that both depolarization and a second SCN neuropeptide, gastrin-releasing peptide (GRP), can acutely enhance and synchronize molecular timekeeping in Vipr2-/- SCN neurons. Nevertheless, transiently activated and synchronized Vipr2-/- cells cannot sustain synchrony in the absence of VIP-ergic signaling. Hence, neuropeptidergic interneuronal signaling confers a canonical property upon the SCN: spontaneous synchronization of the intracellular molecular clockworks of individual neurons.

Animals↗
PubMed2006

Circadian timing in health and disease.

Metabolic status varies predictably on a daily and seasonal basis in order to adapt to the cyclical environment. The hypothalamic circadian pacemaker of the suprachiasmatic nuclei (SCN) co-ordinates these metabolic cycles. Circadian timing is based upon a transcriptional/post-translational negative feedback loop involving a series of core clock genes and their products. Local molecular clocks in peripheral tissues are synchronised by a variety of autonomic, paracrine and endocrine cues reflective of SCN time, thereby ensuring internal temporal co-ordination and optimal metabolic function. Disturbances of this co-ordination, as occur in long-term shift work, have a major impact on health.

Animals↗
PubMed2005

Circadian clocks: neural and peripheral pacemakers that impact upon the cell division cycle.

Circadian clocks are pervasive entities that allow organisms to maintain rhythms of approximately 24h, independently of external cues, thereby adapting them to the solar cycle. Recent studies have shown that molecular circadian clocks are important for the proper orchestration of the cell division cycle. For the first time, this provides a framework to understand the interactions between these two evolutionarily linked timers. Here we review the current model of the circadian clock and the molecular methods that can be used to investigate its function. We then map out links to the cell cycle at the cellular level. Furthermore, we review recent progress that has linked dysfunction of the clockwork with the pathogenesis of cancer. Disruption of circadian timing (as occurs in jet-lag, shift work and dementia) thus has far reaching consequences for normal regulation of cell division. The implications of this for the health of a "24-h society" are apparent.

Animals↗
PubMed2005

Circadian biology: fibroblast clocks keep ticking.

Real-time cellular imaging of gene expression has revealed that fibroblasts contain a robust, self-sustained and cell-autonomous circadian oscillator, with a range of properties that both overlap and contrast with those of the neural clock of the suprachiasmatic nuclei.

Animals↗
PubMed2005

Disintegration of the sleep-wake cycle and circadian timing in Huntington's disease.

Sleep disturbances in neurological disorders have a devastating impact on patient and carer alike. However, their pathological origin is unknown. Here we show that patients with Huntington's disease (HD) have disrupted night-day activity patterns. This disruption was mirrored in a transgenic model of HD (R6/2 mice) in which daytime activity increased and nocturnal activity fell, eventually leading to the complete disintegration of circadian behavior. The behavioral disturbance was accompanied by marked disruption of expression of the circadian clock genes mPer2 and mBmal1 in the suprachiasmatic nuclei (SCN), the principal circadian pacemaker in the brain. The circadian peak of expression of mPer2 was prematurely truncated, and the mRNA levels of mBmal1 were attenuated and failed to exhibit a significant circadian oscillation. Circadian cycles of gene expression in the motor cortex and striatum, markers of behavioral activation in wild-type mice, were also suppressed in the R6/2 mice, providing a neural correlate of the disturbed activity cycles. Increased daytime activity was also associated with reduced SCN expression of prokineticin 2, a transcriptional target of mBmal1 encoding a neuropeptide that normally suppresses daytime activity in nocturnal mammals. Together, these molecular abnormalities could explain the pathophysiological changes in circadian behavior. We propose that circadian sleep disturbances are an important pathological feature of HD, that they arise from pathology within the SCN molecular oscillation, and that their treatment will bring appreciable benefits to HD patients.

Adult↗
PubMed2005

Analysis of circadian mechanisms in the suprachiasmatic nucleus by transgenesis and biolistic transfection.

Analysis of the cellular and molecular mechanisms that underlie the circadian pacemaker of the suprachiasmatic nuclei (SCN) requires in vitro preparations amenable to genetic manipulation that can provide dynamic measures of circadian activity in real time over multiple circadian cycles. This article focuses on the value of the SCN organotypic slice for such studies. Specifically, it describes the use of tissues from genetically modified mice in which the circadian promoter of the mPer1 gene is used to drive the expression of either firefly luciferase or destabilized green fluorescent protein optical reporters. Furthermore, we describe a procedure for biolistic (particle-mediated) transfection of SCN organotypic slices with fluorescent reporters that can be used to explore the cis-acting elements and trans-acting factors that control circadian patterning, and also the interactions between subpopulations of neuronal oscillators within the SCN assemblage.

Animals↗
PubMed2004

Effects of chronic jet lag on tumor progression in mice.

Frequent transmeridian flights or predominant work at night can increase cancer risk. Altered circadian rhythms also predict for poor survival in cancer patients, whereas physical destruction of the suprachiasmatic nuclei (SCN), the hypothalamic circadian pacemaker, accelerates tumor growth in mice. Here we tested the effect of functional disruption of circadian system on tumor progression in a novel experimental model of chronic jet lag. B6D2F(1) mice were synchronized with 12 hours of light and 12 hours of darkness or underwent repeat 8-hour advances of the light/dark cycle every 2 days before inoculation of Glasgow osteosarcoma. The 24-hour changes were assessed for plasma corticosterone, clock protein mPER1 expression in the SCN, and mRNA expression of clock genes mPer2 and mRev-erbalpha in liver and tumor. Time series were analyzed by spectral analysis and/or Cosinor. Differences were compared with analysis of variance (ANOVA). The 24-hour rest/activity cycle was ablated, and the rhythms of body temperature, serum corticosterone, and mPER1 protein expression in the SCN were markedly altered in jet-lagged mice as compared with controls (ANOVA, P < 0.001 for corticosterone and P = 0.01 for mPER1). Tumor grew faster in the jet-lagged animals as compared with controls (ANOVA, P < 0.001), whereas exposure to constant light or darkness had no effect (ANOVA, P = 0.66 and P = 0.8, respectively). The expression of mPer2 and mRev-erbalpha mRNAs in controls showed significant circadian rhythms in the liver (P = 0.006 and P = 0.003, respectively, Cosinor) and in the tumor (P = 0.04 and P < 0.001). Both rhythms were suppressed in the liver (P = 0.2 and P = 0.1, respectively, Cosinor) and in the tumor (P = 0.5) of jet-lagged mice. Altered environmental conditions can disrupt circadian clock molecular coordination in peripheral organs including tumors and play a significant role in malignant progression.

Animals↗
PubMed2004

Feeding and behavioural effects of central administration of the melanocortin 3/4-R antagonist SHU9119 in obese and lean Siberian hamsters.

Siberian hamsters accumulate fat reserves in long photoperiods, but show a long-term decrease in food intake and body weight when exposed to a short winter photoperiod. The aim of this study was to determine the role of central melanocortin 3/4 receptors (MC3/4-R) in generating this chronic catabolic state by investigating the effects of SHU9119, a MC3/4-R antagonist, on food intake and associated behaviours. In adult male hamsters, intra-cerebroventricular infusions of SHU9119 significantly increased food intake in a dose-dependent manner. The time course of action was slow, food intake being increased between 4 and 24 h after intra-cerebroventricular administration. A similar degree of increase in food intake occurred in fat hamsters in long days and in lean hamsters chronically exposed to short days. Intra-cerebroventricular treatment with MTII (a MC3/4-R agonist) significantly decreased food intake for up to 24 h after treatment, and SHU9119 reversed these suppressive effects between 4 and 24 h after treatment, a similar time course to that observed when SHU9119 was administered alone. We conclude that endogenous melanocortin peptides acting via MC3/4-R are involved in the regulation of food intake in hamsters in both anabolic and catabolic states, but these acute studies do not provide evidence that increased activity of this hypothalamic system underlies the seasonal decrease in food intake that contributes to the long-term catabolic state in short days.

Analysis of Variance↗
PubMed2004

Persistent twenty-four hour changes in liver and bone marrow despite suprachiasmatic nuclei ablation in mice.

Rest-activity or cortisol rhythms can be altered in cancer patients, a condition that may impair the benefits from a timed delivery of anticancer treatments. In rodents, the circadian pattern in rest-activity is suppressed by the destruction of the suprachiasmatic nuclei (SCN) in the hypothalamus. We sought whether such ablation would result in a similar alteration of cellular rhythms known to be relevant for anticancer drug chronopharmacology. The SCN of 77 B6D2F(1) mice synchronized with 12 h of light and 12 h of darkness were destroyed by electrocoagulation [SCN(-)], while 34 animals were sham operated. Activity and body temperature were recorded by telemetry. Blood and organs were sampled at one of six circadian times for determinations of serum corticosterone concentration, blood leukocyte count, reduced glutathione (GSH), and dihydropyrimidine dehydrogenase (DPD) mRNA expression in liver and cell cycle phase distribution of bone marrow cells. Sham-operated mice displayed significant 24-h rhythms in rest-activity and body temperature, whereas such rhythms were found in none and in 15% of the SCN(-) mice, respectively. SCN lesions markedly altered the rhythmic patterns in serum corticosterone and liver GSH, which became nonsinusoidal. Liver DPD mRNA expression and bone marrow cell cycle phase distribution displayed similar 24-h sinusoidal patterns in sham-operated and SCN(-) mice. These results support the existence of another light-dark entrainable pacemaker that can coordinate cellular functions in peripheral organs. They suggest that the delivery of anticancer treatments at an optimal time of day may still be beneficial, despite suppressed rest-activity or cortisol rhythms.

Anesthesia↗
PubMed2004

Neurotrophic effects of BDNF on embryonic gonadotropin-releasing hormone (GnRH) neurons.

Secretion of gonadotropin-releasing hormone (GnRH) at the median eminence is the essential activator of the reproductive axis. The mechanisms by which embryonic GnRH neurons migrate from the olfactory placode to the preoptic area and then elaborate neurites that course through the hypothalamus to terminate at the median eminence are largely unknown. We investigated the hypothesis that GnRH neurite outgrowth is promoted by brain-derived neurotrophic factor (BDNF) because GnRH neurites course through BDNF-rich areas of the forebrain during their development. Confocal microscopy revealed that most (86%) cultured embryonic GnRH cells tagged with a green fluorescent protein reporter were immunoreactive for TrkB. In primary cultures of E12.5 olfactory tissue, treatment with BDNF induced a dose-dependent increase in neurite outgrowth, but had no discernible effect on branching. BDNF induced phosphorylation of Ca(2+)/cAMP response element-binding protein (pCREB) in both GnRH and non-GnRH cells in these cultures. This was not associated with phosphorylation of ERK in GnRH-immunoreactive cells, though BDNF treatment did stimulate pERK in neighbouring non-GnRH cells. Promotion of neurite outgrowth is unlikely therefore to result from activation of the Ras-MAPK/ERK pathway. We conclude that the developing GnRH secretory system is directly sensitive to BDNF and that this polypeptide functions as a neurotrophic factor for GnRH neurons.

Animals↗
PubMed2004

Clock genes, oscillators, and cellular networks in the suprachiasmatic nuclei.

The mammalian SCN contains a biological clock that drives remarkably precise circadian rhythms in vivo and in vitro. Recent advances have revealed molecular and cellular mechanisms required for the generation of these daily rhythms and their synchronization between SCN neurons and to the environmental light cycle. This review of the evidence for a cell-autonomous circadian pacemaker within specialized neurons of the SCN focuses on 6 genes implicated within the pace making mechanism, an additional 4 genes implicated in pathways from the pacemaker, and the intercellular and intracellular mechanisms that synchronize SCN neurons to each other and to solar time.

Animals↗
PubMed2003

Circadian clocks: self-assembling oscillators?

Circadian clocks are auto-regulatory loops in which 'clock' gene products feedback to regulate their own expression. This explains how they keep oscillating, but how do they first get going? It appears that the transcription factor dClock not only drives the oscillation within the fruit fly's clock, but also plays a pivotal role in pre-assembling the clockwork.

Animals↗
PubMed2003

Disruption of circadian coordination accelerates malignant growth in mice.

An animal model (mice B6D2F1) was developed to study the consequence of suprachiasmatic nuclei (SCN) destruction on tumor growth. SCN destruction abolished the rest-activity and body temperature rhythms and markedly altered the rhythms in serum corticosterone concentration and lymphocyte count. Tumor growth was faster in mice with lesioned SCN than in controls for both tumor models studied, Glasgow osteosarcoma (GOS) and pancreatic adenocarcinoma (P03). This shows that disruption of circadian coordination accelerates malignant growth in mice, suggesting that the host circadian clock controls tumor progression.

Adenocarcinoma↗