Effect of deuterium on the circadian period and metabolism in wild-type and tau mutant Syrian hamsters

Homozygous tau mutant Syrian hamsters (tau-/-) have a free-running circadian period (τ) around 20 h and a proportionally higher metabolic rate compared with wild-type hamsters (tau+/+) with a period of circa 24 h. In this study, we applied deuterium oxide (D2O) to hamsters to test whether deuteration affects the circadian period of locomotor activity and metabolic rate in both genotypes. Running wheel activity and the metabolic rate were measured in constant illumination before, during, and after administration of 25% deuterium in drinking water. Wild-type hamsters lengthened their circadian period by 1.19 h (SD = 0.29 h) due to D2O application and tau-/- hamsters by 1.20 h (SD = 0.39 h). Deuteration changed neither the amount of activity nor the duration of activity phase (α) in either genotype. The mass specific average metabolic rate (AMR, the oxygen consumption over 24 h) and the mass specific resting metabolic rate (RMR) did not differ during deuteration compared with non-deuteration conditions for either genotype. Both with and without D2O, tau-/- hamsters had higher metabolic rates than tau+/+ hamsters. There was no correlation between changes in the circadian period of locomotor activity and metabolic rates caused by D2O.

Critical cholangiocarcinogenesis control by cryptochrome clock genes

A coordinated network of molecular circadian clocks in individual cells generates 24-hour rhythms in liver metabolism and proliferation. Circadian disruption through chronic jet lag or Per2 clock gene mutation was shown to accelerate hepatocarcinoma development in mice. Since divergent effects were reported for clock genes Per and Cry regarding xenobiotic toxicity, we questioned the role of Cry1 and Cry2 in liver carcinogenesis. Male WT and Cry1-/-Cry2-/- mice (C57Bl/6 background) were chronically exposed to diethylnitrosamine (DEN) at ZT11. Rest-activity and body temperature rhythms were monitored using an implanted radiotransmitter. Serum aspartate and alanine aminotransferases (AST, ALT) were determined on four occasions during the progression stage. After 7 months, serum alkaline phosphatases (ALP) were determined, and livers were sampled for microscopic tumor nodule counting and histopathology. Five months after initiation of DEN treatment, we found that Cry1-/-Cry2-/- mice developed severe liver dysplasia, as evident from the increased AST, ALT and ALP levels, as compared to WT mice. DEN exposure induced primary liver cancers in nearly fivefold as many Cry1-/-Cry2-/- mice as compared to WT mice (p= 0.01). Microscopic study revealed no difference in the average number of hepatocarcinomas and a nearly 8-fold increase in the average number of cholangiocarcinomas in Cry1-/-Cry2-/- mice, as compared to WT mice. The study validated the hypothesis that molecular circadian clock disruption dramatically increased chemically-induced liver carcinogenesis. In addition, the pronounced shift towards cholangiocarcinoma in DEN exposed Cry1-/-Cry2-/- mice revealed a critical role of the Cry clock genes in bile duct carcinogenesis. This article is protected by copyright. All rights reserved

Phase resetting of the mammalian circadian clock by DNA damage

SummaryTo anticipate the momentum of the day, most organisms have developed an internal clock that drives circadian rhythms in metabolism, physiology, and behavior [1]. Recent studies indicate that cell-cycle progression and DNA-damage-response pathways are under circadian control [2–4]. Because circadian output processes can feed back into the clock, we investigated whether DNA damage affects the mammalian circadian clock. By using Rat-1 fibroblasts expressing an mPer2 promoter-driven luciferase reporter, we show that ionizing radiation exclusively phase advances circadian rhythms in a dose- and time-dependent manner. Notably, this in vitro finding translates to the living animal, because ionizing radiation also phase advanced behavioral rhythms in mice. The underlying mechanism involves ATM-mediated damage signaling as radiation-induced phase shifting was suppressed in fibroblasts from cancer-predisposed ataxia telangiectasia and Nijmegen breakage syndrome patients. Ionizing radiation-induced phase shifting depends on neither upregulation or downregulation of clock gene expression nor on de novo protein synthesis and, thus, differs mechanistically from dexamethasone- and forskolin-provoked clock resetting [5]. Interestingly, ultraviolet light and tert-butyl hydroperoxide also elicited a phase-advancing effect. Taken together, our data provide evidence that the mammalian circadian clock, like that of the lower eukaryote Neurospora [6], responds to DNA damage and suggest that clock resetting is a universal property of DNA damage

The rate of living in tau mutant Syrian hamsters : studies on the impact of a circadian allele on temporal organisation

De temporele organisatie van gedrag en fysiologie in de meeste organismen is gebaseerd op een inwendig gegenereerd 24 uurs patroon. Deze "circadiane" ritmiciteit is in de evolutie ontstaan als aanpassing aan de aardrotatie. Naast de circadiane oscillatie treden er biologische cvcli op op allerlei andere tijdschalen. ... Zie: Samenvatting.

Enhanced Longevity in Tau Mutant Syrian Hamsters, Mesocricetus auratus

The single-gene mutation tau in the Syrian hamster shortens the circadian period by about 20% in the homozygous mutant and simultaneously increases the mass-specific metabolic rate by about 20%. Both effects might be expected to lead to a change in longevity. To test such expectations, the life span of male and female hamsters from three genotypes (wild-type, heterozygous, and homozygous tau mutants, all derived from heterozygote crosses to randomize the genetic background) was recorded in constant darkness. Male hamsters lived significantly longer than females: the overall average life span was 96.9 weeks (SE = 2.5, n = 118) for males and 82.0 weeks (SE = 2.1, n = 99) for females. To our surprise, male and female homozygous mutant hamsters lived significantly longer rather than shorter compared to wild-types. For males, the difference between the two genotypes was on average 14%; for females, the difference was 16%. The mortality rate of wild-type males was significantly different from that of homozygous tau males but not different from that of heterozygotes. Overall, survival of wild-type females was statistically distinguishable from both heterozygous and homozygous mutant females. Male and female wild-type hamsters were heavier than homozygote mutants throughout the entire life span, and heterozygous mutants had intermediate weights. There was no correlation between body mass and life span, and the causes of the extended life span in tau mutant hamsters remain unresolved.

Maternal and pup genotype contribution to growth in wild-type and tau mutant Syrian hamsters

The single gene mutation tau in the Syrian hamster-apart from its effect on the circadian organization of locomotor activity-has a pronounced influence on body weight. In this study we investigate the impact of maternal and pup genotypes at the tau-locus on the growth rate of pups. Homozygous tau mutant hamsters (circadian period of 20 hours) had lower growth rates and adult body weights than wild-type hamsters, whereas heterozygous tau mutants (circadian period of 22 hours) were intermediate. In addition, heterozygous pups from heterozygous dams grew heavier than those from wild-type and homozygous dams. The effect of maternal genotype was further evaluated in a cross-foster design, where wild-type and homozygous mutant pups were fostered at birth to either wild-type or homozygous mutant dams. At all ages, the maternal tau genotype had a negative effect on body weight, whereas the pup tau genotype had a positive effect during the preweaning period and a negative effect afterward

Photic sensitivity ranges of hamster pupillary and circadian phase responses do not overlap

Mammalian retinal photoreceptors form an irradiance detection system that drives many nonvisual responses to light such as pupil reflex and resetting of the circadian clock. To understand the role of pupil size in circadian light responses, pupil diameter was pharmacologically manipulated and the effect on behavioral phase shifts at different irradiance levels was studied in the Syrian hamster. Dose-response curves for steady-state pupil size and for behavioral phase shifts were constructed for 3 pupil conditions (dilated, constricted, and control). Retinal irradiance was calculated from corneal irradiance, pupil size, retinal surface area, and absorption of ocular media. The sensitivity of photic responses to retinal irradiance is approximately 1.5 log units higher than to corneal irradiance. When plotted against corneal irradiance, pharmacological pupil constriction reduces the light sensitivity of the circadian system, but pupil dilation has no effect. As expected, when plotted against retinal irradiance all dose-response curves superimposed, confirming that the circadian system responds to photon flux on the retina. Pupil dilation does not increase the circadian response to increasing irradiance, since the response of the circadian system attains saturation at irradiance levels lower than those required to induce pupil constriction. The main finding shows that due to the different response sensitivities, the effect of pupil constriction on the light sensitivity of the circadian system in the hamster under natural conditions is virtually negligible. We further suggest the existence of distinct modulating mechanisms for the differential retinal irradiance sensitivity of the pupil system and the circadian system, which enables the different responses to be tuned to their specific tasks while using similar photoreceptive input

Temporal Organization of Feeding in Syrian Hamsters with a Genetically Altered Circadian Period

The variation in spontaneous meal patterning was studied in three genotypes (tau +/+, tau +/− and tau −/−) of the Syrian hamster with an altered circadian period. Feeding activity was monitored continuously in 13 individuals from each genotype in constant dim light conditions. All three genotypes had on average six feeding episodes during the circadian cycle (about 20h in homozygous tau mutants and 22h in heterozygotes compared with 24h in wild-type hamsters). Thus, homozygous tau mutant hamsters had significantly more feeding episodes per 24h than wild types, and heterozygotes were intermediate. The average duration of feeding bouts (FBs) was indistinguishable (around 30 minutes) among the three genotypes, whereas the intermeal (IM) intervals were significantly shorter for homozygote tau mutant hamsters (99 minutes), intermediate for heterozygotes (116 minutes), and the longest for wild-type hamsters (148 minutes). Thus, the meal-to-meal duration was on average 25% shorter in homozygous tau mutants (16% in heterozygous) than in wild-type hamsters. The reduction of the circadian period has a pronounced effect on short-term feeding rhythms and meal frequency in hamsters carrying the tau mutation.