Integrative system 865
Disrupted daily light–dark cycles induce physical inactivity and enhance weight gain in mice depending on dietary fat intake Katsutaka Oishia,b,c and Sayaka Higo-Yamamotoa We evaluated associations between obesity induced by a high-fat diet (HFD) and the environmental light–dark (LD) cycle that entrains the master circadian clock located in the suprachiasmatic nucleus of mammals. Mice were fed normal diet or HFD for 6 weeks in individual cages with running wheels under a normal 12 h light–12 h dark cycle (LD 12 : 12) or an ultradian 3 h light–3 h dark cycle (LD 3 : 3) that might perturb the central clock. Circadian behavioral rhythms in mice fed both diets were disrupted by lightinduced direct suppression of the behavior (masking effect) under LD 3 : 3. The ultradian LD cycle reduced the total daily activity of wheel running and enhanced body weight gain in the mice fed the HFD. Secondary effects such as obesity are probably not associated with inactivity induced under these circumstances because wheel-running activity decreased markedly within a few days of transfer from LD 12 : 12 to LD 3 : 3. Food consumption was significantly suppressed under LD 3 : 3 in mice fed the HFD. These findings suggest that the aberrant LD cycle induced physical inactivity and enhanced
Introduction Endogenous oscillators control the behavioral and physiological circadian rhythms that regulate most mammalian functions such as feeding, sleep, body temperature, blood pressure, immune functions, hormonal secretion, and glucose and lipid metabolism. The central circadian clock in mammals is located in the suprachiasmatic nucleus (SCN) of the anterior hypothalamus [1,2]. Environmental light is the critical cue for daily resetting the SCN clock, and the phase and period of the pacemaker are entrained to environmental light–dark (LD) cycles [1,2]. Numerous studies at the molecular level have suggested that the circadian oscillator in the SCN is driven by self-sustained transcription/translation-based feedback loops consisting of periodically expressed clock genes [1,2]. Emerging evidence suggests that circadian regulation is closely linked to metabolic homeostasis and that dysregulated circadian rhythms can contribute toward metabolic diseases such as obesity and diabetes [3]. Shift work is implicated as a risk factor for chronic diseases such as cardiovascular disease, breast cancer, metabolic syndrome, and diabetes [4]. Misaligned endogenous circadian rhythms with unpredictable daily photoperiodic cycles facilitated by artificial lighting might contribute toward the development of metabolic 0959-4965 © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins
weight gain depending on dietary fat consumption. This might help to explain the higher incidence of obesity among shift workers. NeuroReport 25:865–869 © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins. NeuroReport 2014, 25:865–869 Keywords: circadian rhythm, high-fat diet, metabolic regulation, ultradian photoperiod, wheel running a Biological Clock Research Group, Biomedical Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki, b Department of Medical Genome Sciences, Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa and cDepartment of Applied Biological Science, Graduate School of Science and Technology, Tokyo University of Science, Noda, Chiba, Japan
Correspondence to Katsutaka Oishi, PhD, Biological Clock Research Group, Biomedical Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Central 6, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8566, Japan Tel/fax: + 81 29 861 6053; e-mail: [email protected] Received 9 April 2014 accepted 2 May 2014
disorders in 24-h societies [5]. However, whether unusual lighting stimuli directly or indirectly affect metabolic regulation through interaction with the endogenous circadian clock remains unknown. According to the discrete (nonparametric) entrainment model [6], the circadian rhythm becomes synchronized to LD cycles by daily phase resetting to adjust the endogenous (τ) to the Zeitgeber (T) period. The central circadian clock cannot entrain to environmental LD cycles when phase shifts caused by light pulses are smaller than the difference between τ and T. We previously examined the effects of ultradian 3 h light–3 h dark cycles (LD 3 : 3) on sedentary mice with obesity induced by a high-fat/ high-sucrose diet [7,8]. Circadian drinking behavior was disturbed under LD 3 : 3 because of light-induced direct suppression of the behavior (masking effect). Increased expression of hepatic gluconeogenic regulatory genes and hyperglycemia accompanied glucose intolerance under LD 3 : 3 in the sedentary mice. A sedentary lifestyle and being overweight because of an imbalance between physical activity and dietary energy intake are major public health, clinical, and economic issues in contemporary societies [9]. The running wheel has enabled widespread measurements of physical activity in laboratory rodents [10]. Wheel-running behavior reflects more than a tendency to be physically active, DOI: 10.1097/WNR.0000000000000202
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and various environmental conditions as well as genetic factors can influence circadian wheel-running activity [11]. Behavioral circadian rhythms are influenced by both environmental LD cycles [7,8] and food conditions [12 –14]. The present study assesses the effect of interaction between photoperiodic cycles and dietary fat on circadian wheel-running activity in mice.
Materials and methods Three-week-old male C57BL/6J mice (Japan SLC Inc., Hamamatsu, Japan) that were individually maintained in plastic cages containing animal paper bedding and running wheels (SW-15; Melquest, Toyama, Japan) were fed a normal diet (ND; CE-2; Clea Japan Inc., Tokyo, Japan) ad libitum for 3 weeks until daily wheel-running activity reached a plateau under a 12 h light–12 h dark cycle (LD 12 : 12; lights on, 0 : 00; lights off, 12 : 00), followed by the ND or a high-fat diet (HFD; high-fat diet 32; Clea Japan Inc.) under LD 12 : 12 or ultradian LD 3 : 3 cycles for 6 weeks. The light source was a white fluorescent lamp (500 lx at the cage level). Wheel-running activity was recorded continuously at 5-min intervals using the Chronobiology Kit (Stanford Software Systems, Stanford, California, USA) and activity data are displayed as actograms. The free-running period of individual mice was estimated using χ2 periodgrams. Animals were maintained and experiments proceeded under the approval of our institutional Animal Care and Use Committee (Permission #2012-020). All data are expressed as means ± SEM and were statistically evaluated by an analysis of variance and the Tukey–Kramer multiple comparison test using ExcelToukei 2010 software (Social Survey Research Information Co. Ltd, Tokyo, Japan). P less than 0.05 indicated a statistically significant difference.
Results and discussion Wheel-running rhythms became completely synchronized to LD 12 : 12 cycles in mice fed ND and with HFD (Fig. 1a and c). Free-running behavior was evident under ultradian LD 3 : 3 cycles in eight of 12 and in five of 11 mice fed the ND and HFD, respectively, in addition to light-induced direct suppression of the behavior, whereas the behavior was completely synchronized to LD 3 : 3 cycles in other mice (Fig. 1b and d). The periods of free running were longer than 24 h (25.0 ± 0.21 and 24.7 ± 0.22 h in mice fed the ND and HFD, respectively). These findings are similar to those found in wheelrunning activity under LD 3.5 : 3.5 [15] or LD 4 : 4 [16] and in the drinking behavior of sedentary mice under LD 3 : 3 [7,8]. Physical activity including wheel running typically decreased in rodents fed a HFD [11]. We compared the effect of aberrant LD cycles on spontaneous wheelrunning behavior between mice fed ND and HFD. The total daily activity was not affected by the ultradian
LD cycle in the mice fed the ND, although the activity gradually decreased over time with aging as described (Fig. 2) [11]. The total daily activity decreased by 40 and 60% under LD 12 : 12 and LD 3 : 3, respectively, in mice fed the HFD over the experimental period of 6 weeks, although the activity decreased by only 20% under ND feeding under both LD cycles. Notably, the total daily activity immediately decreased under ultradian LD cycles and remained throughout the experiment in mice fed the HFD. Ultradian LD cycles enhanced body weight (BW) gain throughout the study period in mice fed the HFD, but not the ND (Fig. 3a). Caloric intake was significantly lower in mice fed the HFD at the end of the experiment under both LD cycles (Fig. 3b). The caloric intake in mice fed the HFD was significantly reduced by the ultradian LD cycle at the end of the experiment, although BW was significantly increased. These findings suggested that physical inactivity was involved in the enhanced obesity of mice fed the HFD under LD 3 : 3, whereas hyperphagia was not. Caloric intake and BW gain were identical between LD 12 : 12 and LD 3 : 3 under ND feeding. Eight of 12 (ND) and five of 11 (HFD) mice showed free-running behavior under LD 3 : 3. However, the total daily activity and BW changes under LD 3 : 3 were identical between behaviorally synchronized and freerunning mice fed both ND and HFD. We found associations between dietary fat and physical inactivity under environmental photoperiodic disruption. Inactivity that develops under an aberrant photoperiod is probably not caused by secondary effects such as obesity because wheel-running activity decreased markedly within a few days of transfer from LD 12 : 12 to LD 3 : 3. Photoperiodic disruption did not affect wheel-running activity and BW gain under ND feeding. Chronic psychophysiological stress that causes depression-like behavior in rodents affects spontaneous wheel running [17–20]. LeGates et al. [15] recently suggested that an ultradian LD cycle (LD 3.5 : 3.5) induces depression-like behavior without affecting the circadian timing systems of sleep and body temperature, despite a longer circadian period. Here, ultradian LD 3 : 3 cycles decreased the daily total wheel-running activity in a manner that was dependent on the HFD. All of these findings together suggest that a high dietary fat intake reduces motivation to engage in wheel running by enhancing the depressionlike psychophysiological effects of environmental photoperiodic disruption. Hyperphagia and dysregulated food timing, energy metabolism, and insulin sensitivity are believed to be associated with unusual environmental illuminationinduced chronic circadian disturbances such as repeated phase-shifting and continuous light exposure that are associated with an increased incidence of obesity in
Copyright © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.
Chronodisruption enhances obesity Oishi and Higo-Yamamoto 867
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Circadian wheel-running activity of mice fed normal diet (ND) and high-fat diet (HFD) under light–dark (LD) 12 : 12 and LD 3 : 3 cycles. Mice were housed under LD 12 : 12 (lights on at 0 h) and then maintained under LD 12 : 12 (a, c) or transferred to ultradian LD 3 : 3 (b, d) cycles for 6 weeks. Left: representative double-plot actograms of wheel-running behavior. Dark phase duration is shaded in gray. Horizontal unfilled and solid bars indicate day and night, respectively. Right: χ2 periodgrams. Dotted lines, level of significance: 0.01.
experimental animals [7,8,21–23]. The present findings showed that a significant change in energy expenditure as well as physical inactivity might be associated with the aberrant LD cycle-induced obesity in mice fed a HFD.
Fonken et al. [23] showed a causal relationship between nighttime exposure to light and obesity despite equivalent caloric intake and total daily activity output. We showed previously that ultradian LD 3 : 3 cycles increase
Copyright © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.
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food intake, plasma levels of glycated proteins, hepatic gluconeogenic gene expression, and obesity with glucose intolerance under sedentary conditions [7,8]. The present findings showed that an aberrant photoperiod enhances obesity without hyperphagia, presumably by reducing wheel-running activity, in mice fed the HFD but not the ND. In addition to a direct effect on metabolic disorders, a HFD appears to be a risk factor for disrupted illumination-induced obesity by inducing inactivity in shift workers.
Acknowledgements This project was supported by a Grant-in-Aid for Scientific Research (C) KAKENHI (25350179) to Katsutaka Oishi from the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan.
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References Buhr ED, Takahashi JS. Molecular components of the mammalian circadian clock. Handb Exp Pharmacol 2013; 217:3–27. Dardente H, Cermakian N. Molecular circadian rhythms in central and peripheral clocks in mammals. Chronobiol Int 2007; 24:195–213.
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Changes in daily total wheel-running activity of mice fed normal diet (ND) and high-fat diet (HFD) under light–dark (LD) 12 : 12 and LD 3 : 3 cycles. (a) Daily total running distance. (b) Relative daily total activity of wheel running is expressed relative to the averaged activity of the pretreatment period for 5 days. Values are shown as means ± SEM (n = 11–12). Unfilled and filled circles represent mice fed ND under LD 12 : 12 and LD 3 : 3 cycles, respectively. Unfilled and filled triangles represent mice fed HFD under LD 12 : 12 and LD 3 : 3 cycles, respectively. #P < 0.05 between light conditions at each time point in mice fed ND. *P < 0.05 between light conditions at each time point in HFD-fed mice.
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Delezie J, Challet E. Interactions between metabolism and circadian clocks: reciprocal disturbances. Ann N Y Acad Sci 2011; 1243:30–46. Wang XS, Armstrong ME, Cairns BJ, Key TJ, Travis RC. Shift work and chronic disease: the epidemiological evidence. Occup Med (Lond) 2011; 61:78–89. Wyse CA, Selman C, Page MM, Coogan AN, Hazlerigg DG. Circadian desynchrony and metabolic dysfunction; did light pollution make us fat? Med Hypotheses 2011; 77:1139–1144. Pittendrigh CS, Daan S. A functional analysis of circadian pacemakers in nocturnal rodents: IV. Entrainment: Pacemaker as clock. J Comp Physiol 1976; 106:291–331. Oishi K. Disrupted light-dark cycle induces obesity with hyperglycemia in genetically intact animals. Neuro Endocrinol Lett 2009; 30:458–461. Oishi K, Itoh N. Disrupted daily light-dark cycle induces the expression of hepatic gluconeogenic regulatory genes and hyperglycemia with glucose intolerance in mice. Biochem Biophys Res Commun 2013; 432:111–115. Lakka TA, Bouchard C. Physical activity, obesity and cardiovascular diseases. Handb Exp Pharmacol 2005; 170:137–163. Sherwin CM. Voluntary wheel running: a review and novel interpretation. Anim Behav 1998; 56:11–27. Novak CM, Burghardt PR, Levine JA. The use of a running wheel to measure activity in rodents: relationship to energy balance, general activity, and reward. Neurosci Biobehav Rev 2012; 36:1001–1014. Bjursell M, Gerdin AK, Lelliott CJ, Egecioglu E, Elmgren A, Törnell J, et al. Acutely reduced locomotor activity is a major contributor to Western dietinduced obesity in mice. Am J Physiol Endocrinol Metab 2008; 294: E251–E260. Kohsaka A, Laposky AD, Ramsey KM, Estrada C, Joshu C, Kobayashi Y, et al. High-fat diet disrupts behavioral and molecular circadian rhythms in mice. Cell Metab 2007; 6:414–421.
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Oishi K, Uchida D, Ohkura N, Doi R, Ishida N, Kadota K, Horie S. Ketogenic diet disrupts the circadian clock and increases hypofibrinolytic risk by inducing expression of plasminogen activator inhibitor-1. Arterioscler Thromb Vasc Biol 2009; 29:1571–1577. 15 LeGates TA, Altimus CM, Wang H, Lee HK, Yang S, Zhao H, et al. Aberrant light directly impairs mood and learning through melanopsinexpressing neurons. Nature 2012; 491:594–598. 16 Park N, Cheon S, Son GH, Cho S, Kim K. Chronic circadian disturbance by a shortened light-dark cycle increases mortality. Neurobiol Aging 2012; 33:1122 e11–e22. 17 Gorka Z, Moryl E, Papp M. Effect of chronic mild stress on circadian rhythms in the locomotor activity in rats. Pharmacol Biochem Behav 1996; 54:229–234. 18 Meerlo P, Overkamp GJ, Daan S, Van Den Hoofdakker RH, Koolhaas JM. Changes in behaviour and body weight following a single or double social defeat in rats. Stress 1996; 1:21–32.
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Miyazaki K, Itoh N, Ohyama S, Kadota K, Oishi K. Continuous exposure to a novel stressor based on water aversion induces abnormal circadian locomotor rhythms and sleep-wake cycles in mice. PLoS One 2013; 8: e55452. Solberg LC, Horton TH, Turek FW. Circadian rhythms and depression: effects of exercise in an animal model. Am J Physiol 1999; 276: R152–R161. Barclay JL, Husse J, Bode B, Naujokat N, Meyer-Kovac J, Schmid SM, et al. Circadian desynchrony promotes metabolic disruption in a mouse model of shiftwork. PLoS One 2012; 7:e37150. Coomans CP, van den Berg SA, Houben T, van Klinken JB, van den Berg R, Pronk AC, et al. Detrimental effects of constant light exposure and high-fat diet on circadian energy metabolism and insulin sensitivity. FASEB J 2013; 27:1721–1732. Fonken LK, Workman JL, Walton JC, Weil ZM, Morris JS, Haim A, Nelson RJ. Light at night increases body mass by shifting the time of food intake. Proc Natl Acad Sci USA 2010; 107:18664–18669.
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Disrupted daily light–dark cycles induce physical inactivity and enhance weight gain in mice depending on dietary fat intake Katsutaka Oishia,b,c and Sayaka Higo-Yamamotoa We evaluated associations between obesity induced by a high-fat diet (HFD) and the environmental light–dark (LD) cycle that entrains the master circadian clock located in the suprachiasmatic nucleus of mammals. Mice were fed normal diet or HFD for 6 weeks in individual cages with running wheels under a normal 12 h light–12 h dark cycle (LD 12 : 12) or an ultradian 3 h light–3 h dark cycle (LD 3 : 3) that might perturb the central clock. Circadian behavioral rhythms in mice fed both diets were disrupted by lightinduced direct suppression of the behavior (masking effect) under LD 3 : 3. The ultradian LD cycle reduced the total daily activity of wheel running and enhanced body weight gain in the mice fed the HFD. Secondary effects such as obesity are probably not associated with inactivity induced under these circumstances because wheel-running activity decreased markedly within a few days of transfer from LD 12 : 12 to LD 3 : 3. Food consumption was significantly suppressed under LD 3 : 3 in mice fed the HFD. These findings suggest that the aberrant LD cycle induced physical inactivity and enhanced
Introduction Endogenous oscillators control the behavioral and physiological circadian rhythms that regulate most mammalian functions such as feeding, sleep, body temperature, blood pressure, immune functions, hormonal secretion, and glucose and lipid metabolism. The central circadian clock in mammals is located in the suprachiasmatic nucleus (SCN) of the anterior hypothalamus [1,2]. Environmental light is the critical cue for daily resetting the SCN clock, and the phase and period of the pacemaker are entrained to environmental light–dark (LD) cycles [1,2]. Numerous studies at the molecular level have suggested that the circadian oscillator in the SCN is driven by self-sustained transcription/translation-based feedback loops consisting of periodically expressed clock genes [1,2]. Emerging evidence suggests that circadian regulation is closely linked to metabolic homeostasis and that dysregulated circadian rhythms can contribute toward metabolic diseases such as obesity and diabetes [3]. Shift work is implicated as a risk factor for chronic diseases such as cardiovascular disease, breast cancer, metabolic syndrome, and diabetes [4]. Misaligned endogenous circadian rhythms with unpredictable daily photoperiodic cycles facilitated by artificial lighting might contribute toward the development of metabolic 0959-4965 © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins
weight gain depending on dietary fat consumption. This might help to explain the higher incidence of obesity among shift workers. NeuroReport 25:865–869 © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins. NeuroReport 2014, 25:865–869 Keywords: circadian rhythm, high-fat diet, metabolic regulation, ultradian photoperiod, wheel running a Biological Clock Research Group, Biomedical Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki, b Department of Medical Genome Sciences, Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa and cDepartment of Applied Biological Science, Graduate School of Science and Technology, Tokyo University of Science, Noda, Chiba, Japan
Correspondence to Katsutaka Oishi, PhD, Biological Clock Research Group, Biomedical Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Central 6, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8566, Japan Tel/fax: + 81 29 861 6053; e-mail: [email protected] Received 9 April 2014 accepted 2 May 2014
disorders in 24-h societies [5]. However, whether unusual lighting stimuli directly or indirectly affect metabolic regulation through interaction with the endogenous circadian clock remains unknown. According to the discrete (nonparametric) entrainment model [6], the circadian rhythm becomes synchronized to LD cycles by daily phase resetting to adjust the endogenous (τ) to the Zeitgeber (T) period. The central circadian clock cannot entrain to environmental LD cycles when phase shifts caused by light pulses are smaller than the difference between τ and T. We previously examined the effects of ultradian 3 h light–3 h dark cycles (LD 3 : 3) on sedentary mice with obesity induced by a high-fat/ high-sucrose diet [7,8]. Circadian drinking behavior was disturbed under LD 3 : 3 because of light-induced direct suppression of the behavior (masking effect). Increased expression of hepatic gluconeogenic regulatory genes and hyperglycemia accompanied glucose intolerance under LD 3 : 3 in the sedentary mice. A sedentary lifestyle and being overweight because of an imbalance between physical activity and dietary energy intake are major public health, clinical, and economic issues in contemporary societies [9]. The running wheel has enabled widespread measurements of physical activity in laboratory rodents [10]. Wheel-running behavior reflects more than a tendency to be physically active, DOI: 10.1097/WNR.0000000000000202
Copyright © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.
866
NeuroReport 2014, Vol 25 No 11
and various environmental conditions as well as genetic factors can influence circadian wheel-running activity [11]. Behavioral circadian rhythms are influenced by both environmental LD cycles [7,8] and food conditions [12 –14]. The present study assesses the effect of interaction between photoperiodic cycles and dietary fat on circadian wheel-running activity in mice.
Materials and methods Three-week-old male C57BL/6J mice (Japan SLC Inc., Hamamatsu, Japan) that were individually maintained in plastic cages containing animal paper bedding and running wheels (SW-15; Melquest, Toyama, Japan) were fed a normal diet (ND; CE-2; Clea Japan Inc., Tokyo, Japan) ad libitum for 3 weeks until daily wheel-running activity reached a plateau under a 12 h light–12 h dark cycle (LD 12 : 12; lights on, 0 : 00; lights off, 12 : 00), followed by the ND or a high-fat diet (HFD; high-fat diet 32; Clea Japan Inc.) under LD 12 : 12 or ultradian LD 3 : 3 cycles for 6 weeks. The light source was a white fluorescent lamp (500 lx at the cage level). Wheel-running activity was recorded continuously at 5-min intervals using the Chronobiology Kit (Stanford Software Systems, Stanford, California, USA) and activity data are displayed as actograms. The free-running period of individual mice was estimated using χ2 periodgrams. Animals were maintained and experiments proceeded under the approval of our institutional Animal Care and Use Committee (Permission #2012-020). All data are expressed as means ± SEM and were statistically evaluated by an analysis of variance and the Tukey–Kramer multiple comparison test using ExcelToukei 2010 software (Social Survey Research Information Co. Ltd, Tokyo, Japan). P less than 0.05 indicated a statistically significant difference.
Results and discussion Wheel-running rhythms became completely synchronized to LD 12 : 12 cycles in mice fed ND and with HFD (Fig. 1a and c). Free-running behavior was evident under ultradian LD 3 : 3 cycles in eight of 12 and in five of 11 mice fed the ND and HFD, respectively, in addition to light-induced direct suppression of the behavior, whereas the behavior was completely synchronized to LD 3 : 3 cycles in other mice (Fig. 1b and d). The periods of free running were longer than 24 h (25.0 ± 0.21 and 24.7 ± 0.22 h in mice fed the ND and HFD, respectively). These findings are similar to those found in wheelrunning activity under LD 3.5 : 3.5 [15] or LD 4 : 4 [16] and in the drinking behavior of sedentary mice under LD 3 : 3 [7,8]. Physical activity including wheel running typically decreased in rodents fed a HFD [11]. We compared the effect of aberrant LD cycles on spontaneous wheelrunning behavior between mice fed ND and HFD. The total daily activity was not affected by the ultradian
LD cycle in the mice fed the ND, although the activity gradually decreased over time with aging as described (Fig. 2) [11]. The total daily activity decreased by 40 and 60% under LD 12 : 12 and LD 3 : 3, respectively, in mice fed the HFD over the experimental period of 6 weeks, although the activity decreased by only 20% under ND feeding under both LD cycles. Notably, the total daily activity immediately decreased under ultradian LD cycles and remained throughout the experiment in mice fed the HFD. Ultradian LD cycles enhanced body weight (BW) gain throughout the study period in mice fed the HFD, but not the ND (Fig. 3a). Caloric intake was significantly lower in mice fed the HFD at the end of the experiment under both LD cycles (Fig. 3b). The caloric intake in mice fed the HFD was significantly reduced by the ultradian LD cycle at the end of the experiment, although BW was significantly increased. These findings suggested that physical inactivity was involved in the enhanced obesity of mice fed the HFD under LD 3 : 3, whereas hyperphagia was not. Caloric intake and BW gain were identical between LD 12 : 12 and LD 3 : 3 under ND feeding. Eight of 12 (ND) and five of 11 (HFD) mice showed free-running behavior under LD 3 : 3. However, the total daily activity and BW changes under LD 3 : 3 were identical between behaviorally synchronized and freerunning mice fed both ND and HFD. We found associations between dietary fat and physical inactivity under environmental photoperiodic disruption. Inactivity that develops under an aberrant photoperiod is probably not caused by secondary effects such as obesity because wheel-running activity decreased markedly within a few days of transfer from LD 12 : 12 to LD 3 : 3. Photoperiodic disruption did not affect wheel-running activity and BW gain under ND feeding. Chronic psychophysiological stress that causes depression-like behavior in rodents affects spontaneous wheel running [17–20]. LeGates et al. [15] recently suggested that an ultradian LD cycle (LD 3.5 : 3.5) induces depression-like behavior without affecting the circadian timing systems of sleep and body temperature, despite a longer circadian period. Here, ultradian LD 3 : 3 cycles decreased the daily total wheel-running activity in a manner that was dependent on the HFD. All of these findings together suggest that a high dietary fat intake reduces motivation to engage in wheel running by enhancing the depressionlike psychophysiological effects of environmental photoperiodic disruption. Hyperphagia and dysregulated food timing, energy metabolism, and insulin sensitivity are believed to be associated with unusual environmental illuminationinduced chronic circadian disturbances such as repeated phase-shifting and continuous light exposure that are associated with an increased incidence of obesity in
Copyright © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.
Chronodisruption enhances obesity Oishi and Higo-Yamamoto 867
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Circadian wheel-running activity of mice fed normal diet (ND) and high-fat diet (HFD) under light–dark (LD) 12 : 12 and LD 3 : 3 cycles. Mice were housed under LD 12 : 12 (lights on at 0 h) and then maintained under LD 12 : 12 (a, c) or transferred to ultradian LD 3 : 3 (b, d) cycles for 6 weeks. Left: representative double-plot actograms of wheel-running behavior. Dark phase duration is shaded in gray. Horizontal unfilled and solid bars indicate day and night, respectively. Right: χ2 periodgrams. Dotted lines, level of significance: 0.01.
experimental animals [7,8,21–23]. The present findings showed that a significant change in energy expenditure as well as physical inactivity might be associated with the aberrant LD cycle-induced obesity in mice fed a HFD.
Fonken et al. [23] showed a causal relationship between nighttime exposure to light and obesity despite equivalent caloric intake and total daily activity output. We showed previously that ultradian LD 3 : 3 cycles increase
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food intake, plasma levels of glycated proteins, hepatic gluconeogenic gene expression, and obesity with glucose intolerance under sedentary conditions [7,8]. The present findings showed that an aberrant photoperiod enhances obesity without hyperphagia, presumably by reducing wheel-running activity, in mice fed the HFD but not the ND. In addition to a direct effect on metabolic disorders, a HFD appears to be a risk factor for disrupted illumination-induced obesity by inducing inactivity in shift workers.
Acknowledgements This project was supported by a Grant-in-Aid for Scientific Research (C) KAKENHI (25350179) to Katsutaka Oishi from the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan.
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Body weight gain (a) and food intake (b) in mice fed normal diet (ND) and high-fat diet (HFD) under light–dark (LD) 12 : 12 and LD 3 : 3 cycles. Values are shown as means ± SEM (n = 11–12). Unfilled and filled circles represent LD 12 : 12 and LD 3 : 3, respectively. *P < 0.05 between light conditions at each time point in mice fed HFD.
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There are no conflicts of interest.
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Changes in daily total wheel-running activity of mice fed normal diet (ND) and high-fat diet (HFD) under light–dark (LD) 12 : 12 and LD 3 : 3 cycles. (a) Daily total running distance. (b) Relative daily total activity of wheel running is expressed relative to the averaged activity of the pretreatment period for 5 days. Values are shown as means ± SEM (n = 11–12). Unfilled and filled circles represent mice fed ND under LD 12 : 12 and LD 3 : 3 cycles, respectively. Unfilled and filled triangles represent mice fed HFD under LD 12 : 12 and LD 3 : 3 cycles, respectively. #P < 0.05 between light conditions at each time point in mice fed ND. *P < 0.05 between light conditions at each time point in HFD-fed mice.
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