- Email: [email protected]
Circadian Rhythm and the Gut Microbiome
CHAPTER NINE
Circadian Rhythm and the Gut Microbiome R.M. Voigt*, C.B. Forsyth*, S.J. Green†, P.A. Engen*, A. Keshavarzian*,{,1 *Rush University Medical Center, Chicago, IL, United States † DNA Services Facility, Research Resources Center, University of Illinois at Chicago, Chicago, IL, United States { Utrecht Institute for Pharmaceutical Sciences, Utrecht University, Utrecht, The Netherlands 1 Corresponding author: e-mail address: [email protected]
Contents 1. Circadian Rhythms in Health 1.1 What Are Circadian Rhythms? 1.2 Central vs Peripheral Circadian Clocks 2. Circadian Rhythms in Disease 2.1 What Factors Disrupt Circadian Rhythms? 2.2 Consequences of Circadian Rhythm Disruption 3. Circadian Rhythms and the Intestinal Microbiota 3.1 How Do Bacterial Circadian Rhythms Impact Host Metabolism? 4. Conclusion References
194 194 196 197 197 198 199 201 202 203
Abstract Circadian rhythms are 24-h patterns regulating behavior, organs, and cells in living organisms. These rhythms align biological functions with regular and predictable environmental patterns to optimize function and health. Disruption of these rhythms can be detrimental resulting in metabolic syndrome, cancer, or cardiovascular disease, just to name a few. It is now becoming clear that the intestinal microbiome is also regulated by circadian rhythms via intrinsic circadian clocks as well as via the host organism. Microbiota rhythms are regulated by diet and time of feeding which can alter both microbial community structure and metabolic activity which can significantly impact host immune and metabolic function. In this review, we will cover how host circadian rhythms are generated and maintained, how host circadian rhythms can be disrupted, as well as the consequences of circadian rhythm disruption. We will further highlight the newly emerging literature indicating the importance of circadian rhythms of the intestinal microbiota.
International Review of Neurobiology, Volume 131 ISSN 0074-7742 http://dx.doi.org/10.1016/bs.irn.2016.07.002
#
2016 Elsevier Inc. All rights reserved.
193
194
R.M. Voigt et al.
1. CIRCADIAN RHYTHMS IN HEALTH 1.1 What Are Circadian Rhythms? Circadian rhythms are rhythmic patterns of approximately 24 h that are exhibited by most organisms including bacteria, fungi, plants, and animals (Hastings, Reddy, et al., 2003). The circadian clock regulates and optimizes the function of cells, organs, systems, and behavior based on the 24-h day (Mohawk, Green, et al., 2012). Activity–rest cycles and feast–famine cycles that are features of our 24-h day drive physiological and cellular adaptations in a wide variety of processes including gastrointestinal function, metabolic processes, and cellular transcription and translation, just to name a few (Reddy & O’Neill, 2010). However, the ability to respond and adapt to changes in the environment is vital for survival; thus, physiological patterns controlled by circadian rhythms also can be influenced by external cues. Circadian rhythms are endogenous which means that they are observed independent of external cues and this rhythmicity is based on the function of the molecular circadian clock (Reppert & Weaver, 2002). The molecular clock is a transcriptional–translational autoregulatory feedback loop that takes approximately 24 h to complete, and while the specifics of the molecular clock differ amongst various organisms, they all exhibit an endogenous 24 h pattern. The mammalian core circadian clock is comprised of the transcription factors “Clock” (circadian locomotor output cycles kaput) and “Bmal1” (brain and muscle aryl hydrocarbon receptor nuclear translocatorprotein 1) which bind to the E-box promoter initiating transcription and subsequent translation of so-called clock-controlled genes (Bunger, Wilsbacher, et al., 2000; Mohawk et al., 2012; Schibler, 2005) (Fig. 1). Two clock-controlled genes are period (Per) and cryptochrome (Cry), and the accumulation and dimerization of PER and CRY proteins result in feedback inhibition whereby further CLOCK and BMAL1-mediated transcription is inhibited (van der Horst, Muijtjens, et al., 1999). Degradation of PER and CRY releases the feedback inhibition and the cycle begins anew. In addition to this core clock, there are other mechanisms of regulation including posttranscriptional and posttranslational modifications that result in “fine-tuning” of the clock, including nuclear receptors retinoic acid-related orphan receptor alpha (Rora), reverse erythroblastosis virus alpha (Rev-erba), and sirtuin 1 (Sirt1) (Bass & Takahashi, 2011; Grimaldi, Nakahata, et al., 2009).
195
Circadian Rhythm and the Gut Microbiome
PER1/2 CRY1/2
CLOCK
BMAL1
E-Box
Per1/Per2 Cry1/Cry2 CCG
PER1/2 CRY1/2
Fig. 1 The molecular circadian clock. The mammalian core circadian clock is comprised of the transcription factors “CLOCK” (circadian locomotor output cycles kaput) and “BMAL1” (brain and muscle aryl hydrocarbon receptor nuclear translocator-protein 1) which bind to the E-box promoter initiating transcription and subsequent translation of so-called clock-controlled genes (CCG). Two clock-controlled genes are period (Per1/Per2) and cryptochrome (Cry1/Cry2), and the accumulation and dimerization of PER and CRY proteins result in feedback inhibition whereby further CLOCK and BMAL1-mediated transcription is inhibited. Degradation of PER and CRY releases the feedback inhibition and the cycle begins anew.
Microorganisms colonize every accessible surface of the host organism. Thus, microorganisms are found on our skin, in our nasal passages, and in our gastrointestinal tract. Not surprisingly, given the importance and ubiquitous nature of circadian rhythms across the kingdoms, some bacteria also exhibit circadian rhythms. The bacterial clock has primarily been studied in Cyanobacteria (i.e., a bacterial phylum of photosynthetic microorganisms) which contain a molecular clock that is comprised of only three proteins KaiA, KaiB, and KaiC. These proteins function in a transcriptional feedback loop similar to that in mammals (Cohen & Golden, 2015). Also, one species of bacteria that is found in the human intestine, Enterobacter aerogenes, was recently shown to be responsive to the circadian hormone melatonin and exhibits an endogenous daily rhythm (Paulose, Wright, et al., 2016). Circadian rhythms can be entrained or adjusted by cues in the environment in order to synchronize the organism with external cues which are known as zeitgebers (i.e., time givers) (Fig. 2). Light–dark cycles strongly regulate the mammalian central clock via inputs from the eye into the master circadian pacemaker located in the suprachiasmatic nucleus (SCN) of the hypothalamus. The ability of circadian rhythms to entrain to the environment is important for several reasons: (1) the ability to adapt to changes
196
R.M. Voigt et al.
Central circadian rhythms Regulated by: Light–dark cycles Disrupted by: Shift work Rotating work schedules Social jet lag Light at night
Intestinal circadian rhythms Regulated by: Time of eating Disrupted by: Irregular eating schedules Late night eating
Fig. 2 Central and peripheral circadian clocks. Circadian rhythms and the molecular circadian clock are found in nearly every mammalian cell, with different molecular clocks regulated by different environmental cues. Light–dark cycles regulate the mammalian central circadian clock located in the suprachiasmatic nucleus (SCN) located in the hypothalamus. The SCN integrates inputs from the eye synchronizing circadian rhythms in the periphery via sympathetic and parasympathetic signals. Time of meal consumption (i.e., timing of nutrient availability) strongly regulates circadian clocks in the intestine and liver. Alterations in light:dark cycles or time of eating can disrupt central and peripheral rhythms, respectively, which can have detrimental health outcomes.
in the environment is critical for survival (e.g., seasonal changes in light–dark cycles and food availability) and (2) the molecular circadian clock is not exactly 24 h in duration and must constantly be readjusted to align with the environment. Human circadian rhythms average 24.2 h per day; however, variations among humans are observed, and this accounts for different chronotypes: night owls vs morning larks (Ehret, 1974). Without the ability of circadian rhythms to be adjusted by environmental cues, rhythms would gradually become desynchronized from the environment, with a resulting loss in the ability of the circadian rhythms to optimize biological functions.
1.2 Central vs Peripheral Circadian Clocks Circadian rhythms and the molecular circadian clock are found in nearly every mammalian cell, with different molecular clocks regulated by different environmental cues (Yoo, Yamazaki, et al., 2004) (Fig. 2). Light–dark cycles
Circadian Rhythm and the Gut Microbiome
197
are important regulators of the mammalian central circadian clock located in the SCN. The SCN has two essential functions: integrating inputs from the optic nerve and synchronizing circadian rhythms in the periphery through sympathetic and parasympathetic signals (Welsh, Takahashi, et al., 2010; West & Bechtold, 2015). For some time, it was believed that the ablation of the SCN would abolish circadian rhythms in the periphery. However, subsequent studies have shown that destruction or inactivation of the SCN does not prevent circadian rhythms from being observed in the periphery, but rather the rhythms become gradually desynchronized from one another without input from the SCN (Guo, Brewer, et al., 2006; Yoo et al., 2004). This observation is consistent with the idea that circadian rhythms are endogenous, but that cues from the environment help entrain the rhythms to synchronize them with the external environment. While light is a regulator of the central circadian clock, it is important to note that other external cues can regulate molecular clocks in peripheral tissues. For example, time of meal consumption (i.e., timing of nutrient availability) strongly regulates circadian clocks in the intestine and liver and these clocks are also impacted by diet composition (e.g., high-fat or high-sugar diets) (Mattson, Allison, et al., 2014; Mendoza, 2007). Exercise also can regulate circadian rhythms in muscle and lung tissue (Youngstedt, Kline, et al., 2016). Thus, regular and predictable patterns of eating or exercise will allow an organism to best adapt to and respond to stresses induced by these activities (e.g., oxidative stress).
2. CIRCADIAN RHYTHMS IN DISEASE 2.1 What Factors Disrupt Circadian Rhythms? Disruption of circadian rhythms in humans can be the consequence of numerous lifestyle factors, with shift work and traveling between time zones being some of the most obvious causes. However, other factors contribute to disrupted circadian homeostasis. These include (but are not limited to): (1) light exposure at night (e.g., use of light emitting electronic devices), which can alter rhythmicity via inputs from the eye directly to the SCN (Burgess & Molina, 2014; Fonken, Weil, et al., 2013; Fonken, Workman, et al., 2010); (2) time of eating close to or during the rest period (i.e., typically within 2 h of the normal rest time) can effectively uncouple central circadian rhythms from those in the intestine and liver (Asher & Sassone-Corsi, 2015; Mattson et al., 2014); (3) social jet lag, wherein daily schedules are altered on work-free days compared to work days a leading to disruptions in central and
198
R.M. Voigt et al.
peripheral circadian rhythmicity (Roenneberg, Allebrandt, et al., 2012; Wittmann, Dinich, et al., 2006); and (4) diet composition. For example, alcohol consumption disrupts central circadian rhythms (Forsyth, Voigt, et al., 2015; Swanson, Gorenz, et al., 2015) and diets high in fat can disrupt circadian rhythms in the intestine (Leone, Gibbons, et al., 2015; Zarrinpar, Chaix, et al., 2014).
2.2 Consequences of Circadian Rhythm Disruption A number of studies have demonstrated higher rates of cancer (breast and prostate), cardiovascular disease, obesity, psychiatric, and neurodegenerative diseases in shift workers (Bechtold, Gibbs, et al., 2010; Golombek, Casiraghi, et al., 2013; Zelinski, Deibel, et al., 2014). Individuals with a late chronotype (i.e., night owl) are at a higher risk for developing poor health outcomes than individuals with an early chronotype, possibly because these individuals tend to eat close to the rest period, thereby uncoupling rhythms in the liver/intestine from the central pacemaker (Foster, Peirson, et al., 2013; Golombek et al., 2013; Roenneberg et al., 2012; Zelinski et al., 2014). But why do these detrimental consequences occur? One common feature among the diseases associated with circadian rhythm disruption is that they appear to be triggered or promoted by inflammatory processes. One source of “sterile inflammation” is the intestine which is in constant contact with bacteria, fungi, and viruses in the intestinal tract (Clemente, Ursell, et al., 2012). There is an intimate relationship between the intestine and its contents (Bernardo, Sanchez, et al., 2012; Wells, Rossi, et al., 2011) and there are several factors that can have significant proinflammatory changes in the host, including alterations in the intestinal microbiota leading to dysfunction of intestinal barrier integrity (Caricilli, Castoldi, et al., 2014; Malago, 2015). Our group has demonstrated that both environmental circadian rhythm disruption (once weekly changes in the light–dark cycle) and genetic perturbation of the molecular clock (mutation in the core molecular clock, the Clock△19 mouse) cause intestinal microbiota dysbiosis, especially when paired with a dietary stress such as a high-fat diet (HFD) or alcohol consumption (Voigt, Forsyth, et al., 2014; Voigt, Summa, et al., 2016). The changes in the microbiota are characterized by an increase in proinflammatory bacteria, a decrease in putative antiinflammatory, butyrate-producing bacteria, and a shift in the Bacteroidetes/Firmicutes ratio (Voigt et al., 2014, 2016). Our group has also demonstrated disrupted intestinal barrier function in mice exhibiting circadian
Circadian Rhythm and the Gut Microbiome
199
rhythm disruption (both environmental and genetic manipulation) (Summa, Voigt, et al., 2013). The integrity of the intestinal barrier is critical for keeping the proinflammatory contents of the intestine separate from the intestinal mucosa and the systemic circulation (Farhadi, Banan, et al., 2003). Intestinal dysbiosis and intestinal hyperpermeability can have proinflammatory consequences in the intestinal mucosa, but additionally, these factors can alter immune function. Under normal circumstances, the immune system is tightly regulated by circadian rhythmicity and disrupted circadian rhythms can have devastating consequences (Cermakian, Westfall, et al., 2014; Curtis, Bellet, et al., 2014; Logan & Sarkar, 2012). Circadian disruption by shifts in light– dark cycles results in increased intestinal Th17 cells (Yu, Rollins, et al., 2013). Circadian rhythm disruption is also associated with higher rates of infection (Everson, 1993; Mohren, Jansen, et al., 2002) and a clear time of day effect exists in response to Salmonella infections (Bellet, Deriu, et al., 2013). Finally, mice with disrupted circadian homeostasis have exaggerated proinflammatory responses to lipopolysaccharide (i.e., a component in the outer membrane of Gram-negative bacteria) exposure and greater mortality (Castanon-Cervantes, Wu, et al., 2010). These data suggest that an increased abundance of proinflammatory bacteria in the intestine, coupled with intestinal barrier dysfunction, can promote inflammation-mediated diseases.
3. CIRCADIAN RHYTHMS AND THE INTESTINAL MICROBIOTA It is well established that the intestinal microbiome changes according to dietary intake, and likewise, it is clear that different stages of life (birth to old age) are associated with shifts in bacterial populations (Bischoff, 2016; Clemente et al., 2012; Yatsunenko, Rey, et al., 2012). What was not known until recently was whether or not intestinal microbiota exhibit circadian patterns of composition or function (i.e., metabolism). While circadian fluctuations in metabolism have been observed in cyanobacteria (light-sensitive bacteria) (Cohen & Golden, 2015; Kondo, Mori, et al., 1997), it was not clear if microbes that are not light sensitive (or that are not exposed to sunlight) also have a genetically encoded endogenous circadian rhythm. Our work has shown that disrupted circadian rhythmicity in the host can influence bacterial populations in the intestine (Voigt et al., 2014, 2016); however, it is becoming clear that intestinal microbiota also have circadian fluctuations (Fig. 3). Thaiss et al. subsequently demonstrated that up to 20% of intestinal bacteria exhibit diurnal fluctuations in relative abundance and
200
R.M. Voigt et al.
Intestinal microbiota circadian rhythms Regulated by: Time of eating Diet Host circadian rhythms Disrupted by: Irregular eating patterns High-fat diet
Disruption = metabolic syndrome
Fig. 3 Circadian rhythms in the intestinal microbiota. Intestinal microbiota exhibit diurnal fluctuations community populations (shifts in dominant bacteria) as well as fluctuations in bacterial function including metabolism. These rhythmic changes in the microbiota appear to be driven by the host via time of eating (i.e., nutrient availability), diet composition (i.e., high-fat diet), and circadian status of the host (i.e., genetic mutations in the host circadian clock, Clock, Per1/2, and Bmal1). Several studies demonstrate a clear link between disruption of microbiota rhythms with host metabolic syndrome and obesity.
activity (Thaiss, Zeevi, et al., 2014). Other groups have also observed circadian oscillations in bacterial abundance (Liang, Bushman, et al., 2015; Zarrinpar et al., 2014). Interestingly, one study has shown that bacterial rhythms in female mice are more robust than those observed in male mice (Liang et al., 2015). These rhythmic changes in the microbiota appear to be driven by the host. Time of eating, via changes in nutrient availability, regulates a variety of microbial functions (e.g., energy harvest, cell growth, and DNA repair are predominant during the periods of nutrient availability, while detoxification is predominant during periods of fasting) and overall community populations (shifts in dominant bacteria) also appear to be driven by time of eating (Thaiss et al., 2014). Other studies have also shown evidence of clear circadian patterns of metabolism in intestinal bacterial populations (Liang et al., 2015; Thaiss et al., 2014). Thus, while light/dark cycles are zeitgebers for the central circadian clock in mammals, time of eating is the zeitgeber for intestinal circadian rhythms in mammals as well as the zeitgeber for circadian rhythms in intestinal bacteria. As previously mentioned, environmental factors can influence circadian rhythms and a recent study examined the impact of a (HFD) on circadian rhythmicity of intestinal microbiota (Leone et al., 2015). Circadian oscillations in bacterial abundance were dampened in mice fed a HFD. Affected
Circadian Rhythm and the Gut Microbiome
201
bacteria included members of the family Lachnospiraceae (a short-chain fatty acid (SCFA)-producing bacteria). Conversely, bacteria that previously had no rhythm, such as H2S-producing bacteria (i.e., sulfate-reducing bacteria), demonstrated a rhythm when the host mice were fed a HFD. However, circadian rhythms in intestinal bacteria can be partially restored when the HFD is fed only during the dark (i.e., time-restricted feeding). As might be expected based on these results, the HFD blunts the robust metabolic rhythms that are observed in chow-fed mice. SCFAs are a metabolic byproduct of fermentation by specific microbial taxa, including a number of members of the family Lachnospiraceae, and circadian oscillations in SCFA production are lost under certain conditions such as HFD consumption (Leone et al., 2015; Thaiss et al., 2014). Alterations in SCFA-producing bacteria and SCFA production could be important for several reasons: (1) SCFA (particularly butyrate) has beneficial effects on intestinal barrier function, (2) SCFA (particularly butyrate) is antiinflammatory via a histone deacetylase mechanism, and (3) SCFAs could be a feedback mechanism by which the intestinal bacteria communicate with the host (i.e., SCFAs may regulate the circadian metabolic clock in the brain and liver). In addition to environmental perturbations of circadian rhythms (e.g., light–dark cycles, HFD consumption), genetic mutations of the core circadian clock also can result in intestinal dysbiosis and/or disrupted circadian rhythmicity of intestinal bacteria. The circadian gene mutations studied thus far include Clock (Voigt et al., 2016), Per1/2 (Thaiss et al., 2014), and Bmal1 (Liang et al., 2015). The ClockΔ19 mutation is associated with significant dysbiosis (an increase in proinflammatory bacteria), an effect that was exacerbated by alcohol consumption (Voigt et al., 2016). Per1/2 KO mice exhibit dysbiosis and lack of circadian rhythmicity in the intestinal tract (Thaiss et al., 2014) with similar results found in Bmal1 KO mice (Liang et al., 2015). It is interesting that these effects appear to be sex specific with female mice displaying greater microbiota rhythmicity as well as differing responses to the BMAL1 KO (Liang et al., 2015). Taken together, these studies support a role for the host genome in regulating the circadian pattern of the microbiota, which may, in part, be driven by circadian rhythm-induced differences in eating patterns or circadian-induced changes in host immune function.
3.1 How Do Bacterial Circadian Rhythms Impact Host Metabolism? Host circadian rhythmicity can alter the composition and activity of the intestinal microbiota, and conversely, the intestinal microbiota can also
202
R.M. Voigt et al.
influence the host. Several studies demonstrate a clear link between intestinal dysbiosis and disruption of microbiota rhythms with host metabolic syndrome and obesity. A compelling study by Thaiss et al. showed that when intestinal microbiota from jet-lagged humans (i.e., circadian disrupted) was transferred into germ-free mice, this resulted in obesity and glucose intolerance, an effect that was not observed when microbiota was transferred from nonjet-lagged humans (Thaiss et al., 2014). Consumption of a HFD blunts intestinal bacterial rhythms and results in obesity and signs of metabolic syndrome; however, time-restricted feeding of the HFD restores glucose tolerance and prevents obesity in mice (Leone et al., 2015). These effects could be attributed to time-restricted feeding-induced partial restoration of intestinal microbiota rhythms in HFD-fed mice, a reduction in obesogenic bacteria and an increase in bacterial taxa that promote healthy metabolism (e.g., organisms from the genera Oscillibacter and Ruminococcus), or changes in abundance or function of SCFA-producing bacteria (Zarrinpar et al., 2014). Leone et al. proposed that butyrate produced by specific populations of intestinal bacteria is a powerful signal for the liver that entrains the liver circadian clock; however, under conditions where SCFA production is altered, that signal is no longer present and this can result in metabolic syndrome in the host. Data from our studies show that the jet-lagged mice fed a HFD exhibit dysbiosis and increased gut leakiness and endotoxemia (Summa et al., 2013). Such increased intestinal permeability and endotoxemia have been associated with increased systemic inflammation and metabolic syndrome and obesity that was eliminated when normal gut permeability was restored (Cani, Bibiloni, et al., 2008). Thus, increased gut leakiness resulting from microbiota circadian disruption could be a key pathogenic factor and target for therapy.
4. CONCLUSION Despite significant progress in intestinal microbiota research, the microbiota still seems to be characterized by more mystery than established principles and facts. The emerging consensus is of a dynamic system in which the host-associated microbiota is involved in a complex conversation with the host. Host-regulated conditions include those under endogenous circadian control, diet, time of feeding, and other factors can all lead to an altered microbial community structure and altered microbial activity. In turn, microbial metabolic activity, in part through the production of SCFAs, can serve as a key regulator of mammalian immune and metabolic function.
Circadian Rhythm and the Gut Microbiome
203
As such, it must now be considered in any model related to circadian homeostasis as a key component of circadian-related disease processes as well as potential therapies. The overall conclusion from these studies is that there is a clear circadian rhythm to the intestinal microbiota (i.e., largely regulated by food timing) and that this rhythm is closely tied to the microbiota function with substantial effects on the host in immunity and metabolism. We propose that this relationship holds the potential for microbiota-directed therapies such as probiotics and targeted prebiotics to ameliorate the effects of disrupted circadian homeostasis.
REFERENCES Asher, G., & Sassone-Corsi, P. (2015). Time for food: The intimate interplay between nutrition, metabolism, and the circadian clock. Cell, 161(1), 84–92. Bass, J., & Takahashi, J. S. (2011). Circadian integration of metabolism and energetics. Science, 330(6009), 1349–1354. Bechtold, D. A., Gibbs, J. E., et al. (2010). Circadian dysfunction in disease. Trends in Pharmacological Sciences, 31(5), 191–198. Bellet, M. M., Deriu, E., et al. (2013). Circadian clock regulates the host response to Salmonella. Proceedings of the National Academy of Sciences of the United States of America, 110(24), 9897–9902. Bernardo, D., Sanchez, B., et al. (2012). Microbiota/host crosstalk biomarkers: Regulatory response of human intestinal dendritic cells exposed to Lactobacillus extracellular encrypted peptide. PLoS One, 7(5), e36262. Bischoff, S. C. (2016). Microbiota and aging. Current Opinion in Clinical Nutrition and Metabolic Care, 19(1), 26–30. Bunger, M. K., Wilsbacher, L. D., et al. (2000). Mop3 is an essential component of the master circadian pacemaker in mammals. Cell, 103(7), 1009–1017. Burgess, H. J., & Molina, T. A. (2014). Home lighting before usual bedtime impacts circadian timing: A field study. Photochemistry and Photobiology, 90(3), 723–726. Cani, P. D., Bibiloni, R., et al. (2008). Changes in gut microbiota control metabolic endotoxemia-induced inflammation in high-fat diet-induced obesity and diabetes in mice. Diabetes, 57(6), 1470–1481. Caricilli, A. M., Castoldi, A., et al. (2014). Intestinal barrier: A gentlemen’s agreement between microbiota and immunity. World Journal of Gastrointestinal Pathophysiology, 5(1), 18–32. Castanon-Cervantes, O., Wu, M., et al. (2010). Dysregulation of inflammatory responses by chronic circadian disruption. The Journal of Immunology, 185(10), 5796–5805. Cermakian, N., Westfall, S., et al. (2014). Circadian clocks and inflammation: Reciprocal regulation and shared mediators. Archivum Immunologiae et Therapiae Experimentalis, 62(4), 303–318. Clemente, J. C., Ursell, L. K., et al. (2012). The impact of the gut microbiota on human health: An integrative view. Cell, 148(6), 1258–1270. Cohen, S. E., & Golden, S. S. (2015). Circadian rhythms in cyanobacteria. Microbiology and Molecular Biology Reviews, 79(4), 373–385. Curtis, A. M., Bellet, M. M., et al. (2014). Circadian clock proteins and immunity. Immunity, 40(2), 178–186. Ehret, C. F. (1974). The sense of time: Evidence for its molecular basis in the eukaryotic gene-action system. Advances in Biological and Medical Physics, 15, 47–77.
204
R.M. Voigt et al.
Everson, C. A. (1993). Sustained sleep deprivation impairs host defense. The American Journal of Physiology, 265(5 Pt 2), R1148–R1154. Farhadi, A., Banan, A., et al. (2003). Intestinal barrier: An interface between health and disease. Journal of Gastroenterology and Hepatology, 18(5), 479–497. Fonken, L. K., Weil, Z. M., et al. (2013). Mice exposed to dim light at night exaggerate inflammatory responses to lipopolysaccharide. Brain, Behavior, and Immunity, 34, 159–163. Fonken, L. K., Workman, J. L., et al. (2010). Light at night increases body mass by shifting the time of food intake. Proceedings of the National Academy of Sciences of the United States of America, 107(43), 18664–18669. Forsyth, C. B., Voigt, R. M., et al. (2015). Circadian rhythms, alcohol and gut interactions. Alcohol, 49(4), 389–398. Foster, R. G., Peirson, S. N., et al. (2013). Sleep and circadian rhythm disruption in social jetlag and mental illness. Progress in Molecular Biology and Translational Science, 119, 325–346. Golombek, D. A., Casiraghi, L. P., et al. (2013). The times they’re a-changing: Effects of circadian desynchronization on physiology and disease. Journal of Physiology (Paris), 107(4), 310–322. Grimaldi, B., Nakahata, Y., et al. (2009). Chromatin remodeling, metabolism and circadian clocks: The interplay of CLOCK and SIRT1. The International Journal of Biochemistry & Cell Biology, 41(1), 81–86. Guo, H., Brewer, J. M., et al. (2006). Suprachiasmatic regulation of circadian rhythms of gene expression in hamster peripheral organs: Effects of transplanting the pacemaker. The Journal of Neuroscience, 26(24), 6406–6412. Hastings, M. H., Reddy, A. B., et al. (2003). A clockwork web: Circadian timing in brain and periphery, in health and disease. Nature Reviews. Neuroscience, 4(8), 649–661. Kondo, T., Mori, T., et al. (1997). Circadian rhythms in rapidly dividing cyanobacteria. Science, 275(5297), 224–227. Leone, V., Gibbons, S. M., et al. (2015). Effects of diurnal variation of gut microbes and highfat feeding on host circadian clock function and metabolism. Cell Host & Microbe, 17(5), 681–689. Liang, X., Bushman, F. D., et al. (2015). Rhythmicity of the intestinal microbiota is regulated by gender and the host circadian clock. Proceedings of the National Academy of Sciences of the United States of America, 112(33), 10479–10484. Logan, R. W., & Sarkar, D. K. (2012). Circadian nature of immune function. Molecular and Cellular Endocrinology, 349(1), 82–90. Malago, J. J. (2015). Contribution of microbiota to the intestinal physicochemical barrier. Beneficial Microbes, 6(3), 295–311. Mattson, M. P., Allison, D. B., et al. (2014). Meal frequency and timing in health and disease. Proceedings of the National Academy of Sciences of the United States of America, 111(47), 16647–16653. Mendoza, J. (2007). Circadian clocks: Setting time by food. Journal of Neuroendocrinology, 19(2), 127–137. Mohawk, J. A., Green, C. B., et al. (2012). Central and peripheral circadian clocks in mammals. Annual Review of Neuroscience, 35, 445–462. Mohren, D. C., Jansen, N. W., et al. (2002). Prevalence of common infections among employees in different work schedules. Journal of Occupational and Environmental Medicine, 44(11), 1003–1011. Paulose, J. K., Wright, J. M., et al. (2016). Human gut bacteria are sensitive to melatonin and express endogenous circadian rhythmicity. PLoS One, 11(1), e0146643. Reddy, A. B., & O’Neill, J. S. (2010). Healthy clocks, healthy body, healthy mind. Trends in Cell Biology, 20(1), 36–44.
Circadian Rhythm and the Gut Microbiome
205
Reppert, S. M., & Weaver, D. R. (2002). Coordination of circadian timing in mammals. Nature, 418(6901), 935–941. Roenneberg, T., Allebrandt, K. V., et al. (2012). Social jetlag and obesity. Current Biology, 22(10), 939–943. Schibler, U. (2005). The daily rhythms of genes, cells and organs. Biological clocks and circadian timing in cells. EMBO Reports, 6 Spec No, S9–S13. Summa, K. C., Voigt, R. M., et al. (2013). Disruption of the circadian clock in mice increases intestinal permeability and promotes alcohol-induced hepatic pathology and inflammation. PLoS One, 8(6), e67102. Swanson, G. R., Gorenz, A., et al. (2015). Decreased melatonin secretion is associated with increased intestinal permeability and marker of endotoxemia in alcoholics. American Journal of Physiology. Gastrointestinal and Liver Physiology, 308(12), G1004–G1011. Thaiss, C. A., Zeevi, D., et al. (2014). Transkingdom control of microbiota diurnal oscillations promotes metabolic homeostasis. Cell, 159(3), 514–529. van der Horst, G. T., Muijtjens, M., et al. (1999). Mammalian Cry1 and Cry2 are essential for maintenance of circadian rhythms. Nature, 398(6728), 627–630. Voigt, R. M., Forsyth, C. B., et al. (2014). Circadian disorganization alters intestinal microbiota. PLoS One, 9(5), e97500. Voigt, R. M., Summa, K. C., et al. (2016). The circadian clock mutation promotes intestinal dysbiosis. Alcoholism, Clinical and Experimental Research, 40(2), 335–347. Wells, J. M., Rossi, O., et al. (2011). Epithelial crosstalk at the microbiota-mucosal interface. Proceedings of the National Academy of Sciences of the United States of America, 108(Suppl. 1), 4607–4614. Welsh, D. K., Takahashi, J. S., et al. (2010). Suprachiasmatic nucleus: Cell autonomy and network properties. Annual Review of Physiology, 72, 551–577. West, A. C., & Bechtold, D. A. (2015). The cost of circadian desynchrony: Evidence, insights and open questions. Bioessays, 37(7), 777–788. Wittmann, M., Dinich, J., et al. (2006). Social jetlag: Misalignment of biological and social time. Chronobiology International, 23(1–2), 497–509. Yatsunenko, T., Rey, F. E., et al. (2012). Human gut microbiome viewed across age and geography. Nature, 486(7402), 222–227. Yoo, S. H., Yamazaki, S., et al. (2004). PERIOD2::LUCIFERASE real-time reporting of circadian dynamics reveals persistent circadian oscillations in mouse peripheral tissues. Proceedings of the National Academy of Sciences of the United States of America, 101(15), 5339–5346. Youngstedt, S. D., Kline, C. E., et al. (2016). Circadian phase-shifting effects of bright light, exercise, and bright light + exercise. Journal of Circadian Rhythms, 14, 2. Yu, X., Rollins, D., et al. (2013). TH17 cell differentiation is regulated by the circadian clock. Science, 342(6159), 727–730. Zarrinpar, A., Chaix, A., et al. (2014). Diet and feeding pattern affect the diurnal dynamics of the gut microbiome. Cell Metabolism, 20(6), 1006–1017. Zelinski, E. L., Deibel, S. H., et al. (2014). The trouble with circadian clock dysfunction: Multiple deleterious effects on the brain and body. Neuroscience and Biobehavioral Reviews, 40C, 80–101.
Circadian Rhythm and the Gut Microbiome R.M. Voigt*, C.B. Forsyth*, S.J. Green†, P.A. Engen*, A. Keshavarzian*,{,1 *Rush University Medical Center, Chicago, IL, United States † DNA Services Facility, Research Resources Center, University of Illinois at Chicago, Chicago, IL, United States { Utrecht Institute for Pharmaceutical Sciences, Utrecht University, Utrecht, The Netherlands 1 Corresponding author: e-mail address: [email protected]
Contents 1. Circadian Rhythms in Health 1.1 What Are Circadian Rhythms? 1.2 Central vs Peripheral Circadian Clocks 2. Circadian Rhythms in Disease 2.1 What Factors Disrupt Circadian Rhythms? 2.2 Consequences of Circadian Rhythm Disruption 3. Circadian Rhythms and the Intestinal Microbiota 3.1 How Do Bacterial Circadian Rhythms Impact Host Metabolism? 4. Conclusion References
194 194 196 197 197 198 199 201 202 203
Abstract Circadian rhythms are 24-h patterns regulating behavior, organs, and cells in living organisms. These rhythms align biological functions with regular and predictable environmental patterns to optimize function and health. Disruption of these rhythms can be detrimental resulting in metabolic syndrome, cancer, or cardiovascular disease, just to name a few. It is now becoming clear that the intestinal microbiome is also regulated by circadian rhythms via intrinsic circadian clocks as well as via the host organism. Microbiota rhythms are regulated by diet and time of feeding which can alter both microbial community structure and metabolic activity which can significantly impact host immune and metabolic function. In this review, we will cover how host circadian rhythms are generated and maintained, how host circadian rhythms can be disrupted, as well as the consequences of circadian rhythm disruption. We will further highlight the newly emerging literature indicating the importance of circadian rhythms of the intestinal microbiota.
International Review of Neurobiology, Volume 131 ISSN 0074-7742 http://dx.doi.org/10.1016/bs.irn.2016.07.002
#
2016 Elsevier Inc. All rights reserved.
193
194
R.M. Voigt et al.
1. CIRCADIAN RHYTHMS IN HEALTH 1.1 What Are Circadian Rhythms? Circadian rhythms are rhythmic patterns of approximately 24 h that are exhibited by most organisms including bacteria, fungi, plants, and animals (Hastings, Reddy, et al., 2003). The circadian clock regulates and optimizes the function of cells, organs, systems, and behavior based on the 24-h day (Mohawk, Green, et al., 2012). Activity–rest cycles and feast–famine cycles that are features of our 24-h day drive physiological and cellular adaptations in a wide variety of processes including gastrointestinal function, metabolic processes, and cellular transcription and translation, just to name a few (Reddy & O’Neill, 2010). However, the ability to respond and adapt to changes in the environment is vital for survival; thus, physiological patterns controlled by circadian rhythms also can be influenced by external cues. Circadian rhythms are endogenous which means that they are observed independent of external cues and this rhythmicity is based on the function of the molecular circadian clock (Reppert & Weaver, 2002). The molecular clock is a transcriptional–translational autoregulatory feedback loop that takes approximately 24 h to complete, and while the specifics of the molecular clock differ amongst various organisms, they all exhibit an endogenous 24 h pattern. The mammalian core circadian clock is comprised of the transcription factors “Clock” (circadian locomotor output cycles kaput) and “Bmal1” (brain and muscle aryl hydrocarbon receptor nuclear translocatorprotein 1) which bind to the E-box promoter initiating transcription and subsequent translation of so-called clock-controlled genes (Bunger, Wilsbacher, et al., 2000; Mohawk et al., 2012; Schibler, 2005) (Fig. 1). Two clock-controlled genes are period (Per) and cryptochrome (Cry), and the accumulation and dimerization of PER and CRY proteins result in feedback inhibition whereby further CLOCK and BMAL1-mediated transcription is inhibited (van der Horst, Muijtjens, et al., 1999). Degradation of PER and CRY releases the feedback inhibition and the cycle begins anew. In addition to this core clock, there are other mechanisms of regulation including posttranscriptional and posttranslational modifications that result in “fine-tuning” of the clock, including nuclear receptors retinoic acid-related orphan receptor alpha (Rora), reverse erythroblastosis virus alpha (Rev-erba), and sirtuin 1 (Sirt1) (Bass & Takahashi, 2011; Grimaldi, Nakahata, et al., 2009).
195
Circadian Rhythm and the Gut Microbiome
PER1/2 CRY1/2
CLOCK
BMAL1
E-Box
Per1/Per2 Cry1/Cry2 CCG
PER1/2 CRY1/2
Fig. 1 The molecular circadian clock. The mammalian core circadian clock is comprised of the transcription factors “CLOCK” (circadian locomotor output cycles kaput) and “BMAL1” (brain and muscle aryl hydrocarbon receptor nuclear translocator-protein 1) which bind to the E-box promoter initiating transcription and subsequent translation of so-called clock-controlled genes (CCG). Two clock-controlled genes are period (Per1/Per2) and cryptochrome (Cry1/Cry2), and the accumulation and dimerization of PER and CRY proteins result in feedback inhibition whereby further CLOCK and BMAL1-mediated transcription is inhibited. Degradation of PER and CRY releases the feedback inhibition and the cycle begins anew.
Microorganisms colonize every accessible surface of the host organism. Thus, microorganisms are found on our skin, in our nasal passages, and in our gastrointestinal tract. Not surprisingly, given the importance and ubiquitous nature of circadian rhythms across the kingdoms, some bacteria also exhibit circadian rhythms. The bacterial clock has primarily been studied in Cyanobacteria (i.e., a bacterial phylum of photosynthetic microorganisms) which contain a molecular clock that is comprised of only three proteins KaiA, KaiB, and KaiC. These proteins function in a transcriptional feedback loop similar to that in mammals (Cohen & Golden, 2015). Also, one species of bacteria that is found in the human intestine, Enterobacter aerogenes, was recently shown to be responsive to the circadian hormone melatonin and exhibits an endogenous daily rhythm (Paulose, Wright, et al., 2016). Circadian rhythms can be entrained or adjusted by cues in the environment in order to synchronize the organism with external cues which are known as zeitgebers (i.e., time givers) (Fig. 2). Light–dark cycles strongly regulate the mammalian central clock via inputs from the eye into the master circadian pacemaker located in the suprachiasmatic nucleus (SCN) of the hypothalamus. The ability of circadian rhythms to entrain to the environment is important for several reasons: (1) the ability to adapt to changes
196
R.M. Voigt et al.
Central circadian rhythms Regulated by: Light–dark cycles Disrupted by: Shift work Rotating work schedules Social jet lag Light at night
Intestinal circadian rhythms Regulated by: Time of eating Disrupted by: Irregular eating schedules Late night eating
Fig. 2 Central and peripheral circadian clocks. Circadian rhythms and the molecular circadian clock are found in nearly every mammalian cell, with different molecular clocks regulated by different environmental cues. Light–dark cycles regulate the mammalian central circadian clock located in the suprachiasmatic nucleus (SCN) located in the hypothalamus. The SCN integrates inputs from the eye synchronizing circadian rhythms in the periphery via sympathetic and parasympathetic signals. Time of meal consumption (i.e., timing of nutrient availability) strongly regulates circadian clocks in the intestine and liver. Alterations in light:dark cycles or time of eating can disrupt central and peripheral rhythms, respectively, which can have detrimental health outcomes.
in the environment is critical for survival (e.g., seasonal changes in light–dark cycles and food availability) and (2) the molecular circadian clock is not exactly 24 h in duration and must constantly be readjusted to align with the environment. Human circadian rhythms average 24.2 h per day; however, variations among humans are observed, and this accounts for different chronotypes: night owls vs morning larks (Ehret, 1974). Without the ability of circadian rhythms to be adjusted by environmental cues, rhythms would gradually become desynchronized from the environment, with a resulting loss in the ability of the circadian rhythms to optimize biological functions.
1.2 Central vs Peripheral Circadian Clocks Circadian rhythms and the molecular circadian clock are found in nearly every mammalian cell, with different molecular clocks regulated by different environmental cues (Yoo, Yamazaki, et al., 2004) (Fig. 2). Light–dark cycles
Circadian Rhythm and the Gut Microbiome
197
are important regulators of the mammalian central circadian clock located in the SCN. The SCN has two essential functions: integrating inputs from the optic nerve and synchronizing circadian rhythms in the periphery through sympathetic and parasympathetic signals (Welsh, Takahashi, et al., 2010; West & Bechtold, 2015). For some time, it was believed that the ablation of the SCN would abolish circadian rhythms in the periphery. However, subsequent studies have shown that destruction or inactivation of the SCN does not prevent circadian rhythms from being observed in the periphery, but rather the rhythms become gradually desynchronized from one another without input from the SCN (Guo, Brewer, et al., 2006; Yoo et al., 2004). This observation is consistent with the idea that circadian rhythms are endogenous, but that cues from the environment help entrain the rhythms to synchronize them with the external environment. While light is a regulator of the central circadian clock, it is important to note that other external cues can regulate molecular clocks in peripheral tissues. For example, time of meal consumption (i.e., timing of nutrient availability) strongly regulates circadian clocks in the intestine and liver and these clocks are also impacted by diet composition (e.g., high-fat or high-sugar diets) (Mattson, Allison, et al., 2014; Mendoza, 2007). Exercise also can regulate circadian rhythms in muscle and lung tissue (Youngstedt, Kline, et al., 2016). Thus, regular and predictable patterns of eating or exercise will allow an organism to best adapt to and respond to stresses induced by these activities (e.g., oxidative stress).
2. CIRCADIAN RHYTHMS IN DISEASE 2.1 What Factors Disrupt Circadian Rhythms? Disruption of circadian rhythms in humans can be the consequence of numerous lifestyle factors, with shift work and traveling between time zones being some of the most obvious causes. However, other factors contribute to disrupted circadian homeostasis. These include (but are not limited to): (1) light exposure at night (e.g., use of light emitting electronic devices), which can alter rhythmicity via inputs from the eye directly to the SCN (Burgess & Molina, 2014; Fonken, Weil, et al., 2013; Fonken, Workman, et al., 2010); (2) time of eating close to or during the rest period (i.e., typically within 2 h of the normal rest time) can effectively uncouple central circadian rhythms from those in the intestine and liver (Asher & Sassone-Corsi, 2015; Mattson et al., 2014); (3) social jet lag, wherein daily schedules are altered on work-free days compared to work days a leading to disruptions in central and
198
R.M. Voigt et al.
peripheral circadian rhythmicity (Roenneberg, Allebrandt, et al., 2012; Wittmann, Dinich, et al., 2006); and (4) diet composition. For example, alcohol consumption disrupts central circadian rhythms (Forsyth, Voigt, et al., 2015; Swanson, Gorenz, et al., 2015) and diets high in fat can disrupt circadian rhythms in the intestine (Leone, Gibbons, et al., 2015; Zarrinpar, Chaix, et al., 2014).
2.2 Consequences of Circadian Rhythm Disruption A number of studies have demonstrated higher rates of cancer (breast and prostate), cardiovascular disease, obesity, psychiatric, and neurodegenerative diseases in shift workers (Bechtold, Gibbs, et al., 2010; Golombek, Casiraghi, et al., 2013; Zelinski, Deibel, et al., 2014). Individuals with a late chronotype (i.e., night owl) are at a higher risk for developing poor health outcomes than individuals with an early chronotype, possibly because these individuals tend to eat close to the rest period, thereby uncoupling rhythms in the liver/intestine from the central pacemaker (Foster, Peirson, et al., 2013; Golombek et al., 2013; Roenneberg et al., 2012; Zelinski et al., 2014). But why do these detrimental consequences occur? One common feature among the diseases associated with circadian rhythm disruption is that they appear to be triggered or promoted by inflammatory processes. One source of “sterile inflammation” is the intestine which is in constant contact with bacteria, fungi, and viruses in the intestinal tract (Clemente, Ursell, et al., 2012). There is an intimate relationship between the intestine and its contents (Bernardo, Sanchez, et al., 2012; Wells, Rossi, et al., 2011) and there are several factors that can have significant proinflammatory changes in the host, including alterations in the intestinal microbiota leading to dysfunction of intestinal barrier integrity (Caricilli, Castoldi, et al., 2014; Malago, 2015). Our group has demonstrated that both environmental circadian rhythm disruption (once weekly changes in the light–dark cycle) and genetic perturbation of the molecular clock (mutation in the core molecular clock, the Clock△19 mouse) cause intestinal microbiota dysbiosis, especially when paired with a dietary stress such as a high-fat diet (HFD) or alcohol consumption (Voigt, Forsyth, et al., 2014; Voigt, Summa, et al., 2016). The changes in the microbiota are characterized by an increase in proinflammatory bacteria, a decrease in putative antiinflammatory, butyrate-producing bacteria, and a shift in the Bacteroidetes/Firmicutes ratio (Voigt et al., 2014, 2016). Our group has also demonstrated disrupted intestinal barrier function in mice exhibiting circadian
Circadian Rhythm and the Gut Microbiome
199
rhythm disruption (both environmental and genetic manipulation) (Summa, Voigt, et al., 2013). The integrity of the intestinal barrier is critical for keeping the proinflammatory contents of the intestine separate from the intestinal mucosa and the systemic circulation (Farhadi, Banan, et al., 2003). Intestinal dysbiosis and intestinal hyperpermeability can have proinflammatory consequences in the intestinal mucosa, but additionally, these factors can alter immune function. Under normal circumstances, the immune system is tightly regulated by circadian rhythmicity and disrupted circadian rhythms can have devastating consequences (Cermakian, Westfall, et al., 2014; Curtis, Bellet, et al., 2014; Logan & Sarkar, 2012). Circadian disruption by shifts in light– dark cycles results in increased intestinal Th17 cells (Yu, Rollins, et al., 2013). Circadian rhythm disruption is also associated with higher rates of infection (Everson, 1993; Mohren, Jansen, et al., 2002) and a clear time of day effect exists in response to Salmonella infections (Bellet, Deriu, et al., 2013). Finally, mice with disrupted circadian homeostasis have exaggerated proinflammatory responses to lipopolysaccharide (i.e., a component in the outer membrane of Gram-negative bacteria) exposure and greater mortality (Castanon-Cervantes, Wu, et al., 2010). These data suggest that an increased abundance of proinflammatory bacteria in the intestine, coupled with intestinal barrier dysfunction, can promote inflammation-mediated diseases.
3. CIRCADIAN RHYTHMS AND THE INTESTINAL MICROBIOTA It is well established that the intestinal microbiome changes according to dietary intake, and likewise, it is clear that different stages of life (birth to old age) are associated with shifts in bacterial populations (Bischoff, 2016; Clemente et al., 2012; Yatsunenko, Rey, et al., 2012). What was not known until recently was whether or not intestinal microbiota exhibit circadian patterns of composition or function (i.e., metabolism). While circadian fluctuations in metabolism have been observed in cyanobacteria (light-sensitive bacteria) (Cohen & Golden, 2015; Kondo, Mori, et al., 1997), it was not clear if microbes that are not light sensitive (or that are not exposed to sunlight) also have a genetically encoded endogenous circadian rhythm. Our work has shown that disrupted circadian rhythmicity in the host can influence bacterial populations in the intestine (Voigt et al., 2014, 2016); however, it is becoming clear that intestinal microbiota also have circadian fluctuations (Fig. 3). Thaiss et al. subsequently demonstrated that up to 20% of intestinal bacteria exhibit diurnal fluctuations in relative abundance and
200
R.M. Voigt et al.
Intestinal microbiota circadian rhythms Regulated by: Time of eating Diet Host circadian rhythms Disrupted by: Irregular eating patterns High-fat diet
Disruption = metabolic syndrome
Fig. 3 Circadian rhythms in the intestinal microbiota. Intestinal microbiota exhibit diurnal fluctuations community populations (shifts in dominant bacteria) as well as fluctuations in bacterial function including metabolism. These rhythmic changes in the microbiota appear to be driven by the host via time of eating (i.e., nutrient availability), diet composition (i.e., high-fat diet), and circadian status of the host (i.e., genetic mutations in the host circadian clock, Clock, Per1/2, and Bmal1). Several studies demonstrate a clear link between disruption of microbiota rhythms with host metabolic syndrome and obesity.
activity (Thaiss, Zeevi, et al., 2014). Other groups have also observed circadian oscillations in bacterial abundance (Liang, Bushman, et al., 2015; Zarrinpar et al., 2014). Interestingly, one study has shown that bacterial rhythms in female mice are more robust than those observed in male mice (Liang et al., 2015). These rhythmic changes in the microbiota appear to be driven by the host. Time of eating, via changes in nutrient availability, regulates a variety of microbial functions (e.g., energy harvest, cell growth, and DNA repair are predominant during the periods of nutrient availability, while detoxification is predominant during periods of fasting) and overall community populations (shifts in dominant bacteria) also appear to be driven by time of eating (Thaiss et al., 2014). Other studies have also shown evidence of clear circadian patterns of metabolism in intestinal bacterial populations (Liang et al., 2015; Thaiss et al., 2014). Thus, while light/dark cycles are zeitgebers for the central circadian clock in mammals, time of eating is the zeitgeber for intestinal circadian rhythms in mammals as well as the zeitgeber for circadian rhythms in intestinal bacteria. As previously mentioned, environmental factors can influence circadian rhythms and a recent study examined the impact of a (HFD) on circadian rhythmicity of intestinal microbiota (Leone et al., 2015). Circadian oscillations in bacterial abundance were dampened in mice fed a HFD. Affected
Circadian Rhythm and the Gut Microbiome
201
bacteria included members of the family Lachnospiraceae (a short-chain fatty acid (SCFA)-producing bacteria). Conversely, bacteria that previously had no rhythm, such as H2S-producing bacteria (i.e., sulfate-reducing bacteria), demonstrated a rhythm when the host mice were fed a HFD. However, circadian rhythms in intestinal bacteria can be partially restored when the HFD is fed only during the dark (i.e., time-restricted feeding). As might be expected based on these results, the HFD blunts the robust metabolic rhythms that are observed in chow-fed mice. SCFAs are a metabolic byproduct of fermentation by specific microbial taxa, including a number of members of the family Lachnospiraceae, and circadian oscillations in SCFA production are lost under certain conditions such as HFD consumption (Leone et al., 2015; Thaiss et al., 2014). Alterations in SCFA-producing bacteria and SCFA production could be important for several reasons: (1) SCFA (particularly butyrate) has beneficial effects on intestinal barrier function, (2) SCFA (particularly butyrate) is antiinflammatory via a histone deacetylase mechanism, and (3) SCFAs could be a feedback mechanism by which the intestinal bacteria communicate with the host (i.e., SCFAs may regulate the circadian metabolic clock in the brain and liver). In addition to environmental perturbations of circadian rhythms (e.g., light–dark cycles, HFD consumption), genetic mutations of the core circadian clock also can result in intestinal dysbiosis and/or disrupted circadian rhythmicity of intestinal bacteria. The circadian gene mutations studied thus far include Clock (Voigt et al., 2016), Per1/2 (Thaiss et al., 2014), and Bmal1 (Liang et al., 2015). The ClockΔ19 mutation is associated with significant dysbiosis (an increase in proinflammatory bacteria), an effect that was exacerbated by alcohol consumption (Voigt et al., 2016). Per1/2 KO mice exhibit dysbiosis and lack of circadian rhythmicity in the intestinal tract (Thaiss et al., 2014) with similar results found in Bmal1 KO mice (Liang et al., 2015). It is interesting that these effects appear to be sex specific with female mice displaying greater microbiota rhythmicity as well as differing responses to the BMAL1 KO (Liang et al., 2015). Taken together, these studies support a role for the host genome in regulating the circadian pattern of the microbiota, which may, in part, be driven by circadian rhythm-induced differences in eating patterns or circadian-induced changes in host immune function.
3.1 How Do Bacterial Circadian Rhythms Impact Host Metabolism? Host circadian rhythmicity can alter the composition and activity of the intestinal microbiota, and conversely, the intestinal microbiota can also
202
R.M. Voigt et al.
influence the host. Several studies demonstrate a clear link between intestinal dysbiosis and disruption of microbiota rhythms with host metabolic syndrome and obesity. A compelling study by Thaiss et al. showed that when intestinal microbiota from jet-lagged humans (i.e., circadian disrupted) was transferred into germ-free mice, this resulted in obesity and glucose intolerance, an effect that was not observed when microbiota was transferred from nonjet-lagged humans (Thaiss et al., 2014). Consumption of a HFD blunts intestinal bacterial rhythms and results in obesity and signs of metabolic syndrome; however, time-restricted feeding of the HFD restores glucose tolerance and prevents obesity in mice (Leone et al., 2015). These effects could be attributed to time-restricted feeding-induced partial restoration of intestinal microbiota rhythms in HFD-fed mice, a reduction in obesogenic bacteria and an increase in bacterial taxa that promote healthy metabolism (e.g., organisms from the genera Oscillibacter and Ruminococcus), or changes in abundance or function of SCFA-producing bacteria (Zarrinpar et al., 2014). Leone et al. proposed that butyrate produced by specific populations of intestinal bacteria is a powerful signal for the liver that entrains the liver circadian clock; however, under conditions where SCFA production is altered, that signal is no longer present and this can result in metabolic syndrome in the host. Data from our studies show that the jet-lagged mice fed a HFD exhibit dysbiosis and increased gut leakiness and endotoxemia (Summa et al., 2013). Such increased intestinal permeability and endotoxemia have been associated with increased systemic inflammation and metabolic syndrome and obesity that was eliminated when normal gut permeability was restored (Cani, Bibiloni, et al., 2008). Thus, increased gut leakiness resulting from microbiota circadian disruption could be a key pathogenic factor and target for therapy.
4. CONCLUSION Despite significant progress in intestinal microbiota research, the microbiota still seems to be characterized by more mystery than established principles and facts. The emerging consensus is of a dynamic system in which the host-associated microbiota is involved in a complex conversation with the host. Host-regulated conditions include those under endogenous circadian control, diet, time of feeding, and other factors can all lead to an altered microbial community structure and altered microbial activity. In turn, microbial metabolic activity, in part through the production of SCFAs, can serve as a key regulator of mammalian immune and metabolic function.
Circadian Rhythm and the Gut Microbiome
203
As such, it must now be considered in any model related to circadian homeostasis as a key component of circadian-related disease processes as well as potential therapies. The overall conclusion from these studies is that there is a clear circadian rhythm to the intestinal microbiota (i.e., largely regulated by food timing) and that this rhythm is closely tied to the microbiota function with substantial effects on the host in immunity and metabolism. We propose that this relationship holds the potential for microbiota-directed therapies such as probiotics and targeted prebiotics to ameliorate the effects of disrupted circadian homeostasis.
REFERENCES Asher, G., & Sassone-Corsi, P. (2015). Time for food: The intimate interplay between nutrition, metabolism, and the circadian clock. Cell, 161(1), 84–92. Bass, J., & Takahashi, J. S. (2011). Circadian integration of metabolism and energetics. Science, 330(6009), 1349–1354. Bechtold, D. A., Gibbs, J. E., et al. (2010). Circadian dysfunction in disease. Trends in Pharmacological Sciences, 31(5), 191–198. Bellet, M. M., Deriu, E., et al. (2013). Circadian clock regulates the host response to Salmonella. Proceedings of the National Academy of Sciences of the United States of America, 110(24), 9897–9902. Bernardo, D., Sanchez, B., et al. (2012). Microbiota/host crosstalk biomarkers: Regulatory response of human intestinal dendritic cells exposed to Lactobacillus extracellular encrypted peptide. PLoS One, 7(5), e36262. Bischoff, S. C. (2016). Microbiota and aging. Current Opinion in Clinical Nutrition and Metabolic Care, 19(1), 26–30. Bunger, M. K., Wilsbacher, L. D., et al. (2000). Mop3 is an essential component of the master circadian pacemaker in mammals. Cell, 103(7), 1009–1017. Burgess, H. J., & Molina, T. A. (2014). Home lighting before usual bedtime impacts circadian timing: A field study. Photochemistry and Photobiology, 90(3), 723–726. Cani, P. D., Bibiloni, R., et al. (2008). Changes in gut microbiota control metabolic endotoxemia-induced inflammation in high-fat diet-induced obesity and diabetes in mice. Diabetes, 57(6), 1470–1481. Caricilli, A. M., Castoldi, A., et al. (2014). Intestinal barrier: A gentlemen’s agreement between microbiota and immunity. World Journal of Gastrointestinal Pathophysiology, 5(1), 18–32. Castanon-Cervantes, O., Wu, M., et al. (2010). Dysregulation of inflammatory responses by chronic circadian disruption. The Journal of Immunology, 185(10), 5796–5805. Cermakian, N., Westfall, S., et al. (2014). Circadian clocks and inflammation: Reciprocal regulation and shared mediators. Archivum Immunologiae et Therapiae Experimentalis, 62(4), 303–318. Clemente, J. C., Ursell, L. K., et al. (2012). The impact of the gut microbiota on human health: An integrative view. Cell, 148(6), 1258–1270. Cohen, S. E., & Golden, S. S. (2015). Circadian rhythms in cyanobacteria. Microbiology and Molecular Biology Reviews, 79(4), 373–385. Curtis, A. M., Bellet, M. M., et al. (2014). Circadian clock proteins and immunity. Immunity, 40(2), 178–186. Ehret, C. F. (1974). The sense of time: Evidence for its molecular basis in the eukaryotic gene-action system. Advances in Biological and Medical Physics, 15, 47–77.
204
R.M. Voigt et al.
Everson, C. A. (1993). Sustained sleep deprivation impairs host defense. The American Journal of Physiology, 265(5 Pt 2), R1148–R1154. Farhadi, A., Banan, A., et al. (2003). Intestinal barrier: An interface between health and disease. Journal of Gastroenterology and Hepatology, 18(5), 479–497. Fonken, L. K., Weil, Z. M., et al. (2013). Mice exposed to dim light at night exaggerate inflammatory responses to lipopolysaccharide. Brain, Behavior, and Immunity, 34, 159–163. Fonken, L. K., Workman, J. L., et al. (2010). Light at night increases body mass by shifting the time of food intake. Proceedings of the National Academy of Sciences of the United States of America, 107(43), 18664–18669. Forsyth, C. B., Voigt, R. M., et al. (2015). Circadian rhythms, alcohol and gut interactions. Alcohol, 49(4), 389–398. Foster, R. G., Peirson, S. N., et al. (2013). Sleep and circadian rhythm disruption in social jetlag and mental illness. Progress in Molecular Biology and Translational Science, 119, 325–346. Golombek, D. A., Casiraghi, L. P., et al. (2013). The times they’re a-changing: Effects of circadian desynchronization on physiology and disease. Journal of Physiology (Paris), 107(4), 310–322. Grimaldi, B., Nakahata, Y., et al. (2009). Chromatin remodeling, metabolism and circadian clocks: The interplay of CLOCK and SIRT1. The International Journal of Biochemistry & Cell Biology, 41(1), 81–86. Guo, H., Brewer, J. M., et al. (2006). Suprachiasmatic regulation of circadian rhythms of gene expression in hamster peripheral organs: Effects of transplanting the pacemaker. The Journal of Neuroscience, 26(24), 6406–6412. Hastings, M. H., Reddy, A. B., et al. (2003). A clockwork web: Circadian timing in brain and periphery, in health and disease. Nature Reviews. Neuroscience, 4(8), 649–661. Kondo, T., Mori, T., et al. (1997). Circadian rhythms in rapidly dividing cyanobacteria. Science, 275(5297), 224–227. Leone, V., Gibbons, S. M., et al. (2015). Effects of diurnal variation of gut microbes and highfat feeding on host circadian clock function and metabolism. Cell Host & Microbe, 17(5), 681–689. Liang, X., Bushman, F. D., et al. (2015). Rhythmicity of the intestinal microbiota is regulated by gender and the host circadian clock. Proceedings of the National Academy of Sciences of the United States of America, 112(33), 10479–10484. Logan, R. W., & Sarkar, D. K. (2012). Circadian nature of immune function. Molecular and Cellular Endocrinology, 349(1), 82–90. Malago, J. J. (2015). Contribution of microbiota to the intestinal physicochemical barrier. Beneficial Microbes, 6(3), 295–311. Mattson, M. P., Allison, D. B., et al. (2014). Meal frequency and timing in health and disease. Proceedings of the National Academy of Sciences of the United States of America, 111(47), 16647–16653. Mendoza, J. (2007). Circadian clocks: Setting time by food. Journal of Neuroendocrinology, 19(2), 127–137. Mohawk, J. A., Green, C. B., et al. (2012). Central and peripheral circadian clocks in mammals. Annual Review of Neuroscience, 35, 445–462. Mohren, D. C., Jansen, N. W., et al. (2002). Prevalence of common infections among employees in different work schedules. Journal of Occupational and Environmental Medicine, 44(11), 1003–1011. Paulose, J. K., Wright, J. M., et al. (2016). Human gut bacteria are sensitive to melatonin and express endogenous circadian rhythmicity. PLoS One, 11(1), e0146643. Reddy, A. B., & O’Neill, J. S. (2010). Healthy clocks, healthy body, healthy mind. Trends in Cell Biology, 20(1), 36–44.
Circadian Rhythm and the Gut Microbiome
205
Reppert, S. M., & Weaver, D. R. (2002). Coordination of circadian timing in mammals. Nature, 418(6901), 935–941. Roenneberg, T., Allebrandt, K. V., et al. (2012). Social jetlag and obesity. Current Biology, 22(10), 939–943. Schibler, U. (2005). The daily rhythms of genes, cells and organs. Biological clocks and circadian timing in cells. EMBO Reports, 6 Spec No, S9–S13. Summa, K. C., Voigt, R. M., et al. (2013). Disruption of the circadian clock in mice increases intestinal permeability and promotes alcohol-induced hepatic pathology and inflammation. PLoS One, 8(6), e67102. Swanson, G. R., Gorenz, A., et al. (2015). Decreased melatonin secretion is associated with increased intestinal permeability and marker of endotoxemia in alcoholics. American Journal of Physiology. Gastrointestinal and Liver Physiology, 308(12), G1004–G1011. Thaiss, C. A., Zeevi, D., et al. (2014). Transkingdom control of microbiota diurnal oscillations promotes metabolic homeostasis. Cell, 159(3), 514–529. van der Horst, G. T., Muijtjens, M., et al. (1999). Mammalian Cry1 and Cry2 are essential for maintenance of circadian rhythms. Nature, 398(6728), 627–630. Voigt, R. M., Forsyth, C. B., et al. (2014). Circadian disorganization alters intestinal microbiota. PLoS One, 9(5), e97500. Voigt, R. M., Summa, K. C., et al. (2016). The circadian clock mutation promotes intestinal dysbiosis. Alcoholism, Clinical and Experimental Research, 40(2), 335–347. Wells, J. M., Rossi, O., et al. (2011). Epithelial crosstalk at the microbiota-mucosal interface. Proceedings of the National Academy of Sciences of the United States of America, 108(Suppl. 1), 4607–4614. Welsh, D. K., Takahashi, J. S., et al. (2010). Suprachiasmatic nucleus: Cell autonomy and network properties. Annual Review of Physiology, 72, 551–577. West, A. C., & Bechtold, D. A. (2015). The cost of circadian desynchrony: Evidence, insights and open questions. Bioessays, 37(7), 777–788. Wittmann, M., Dinich, J., et al. (2006). Social jetlag: Misalignment of biological and social time. Chronobiology International, 23(1–2), 497–509. Yatsunenko, T., Rey, F. E., et al. (2012). Human gut microbiome viewed across age and geography. Nature, 486(7402), 222–227. Yoo, S. H., Yamazaki, S., et al. (2004). PERIOD2::LUCIFERASE real-time reporting of circadian dynamics reveals persistent circadian oscillations in mouse peripheral tissues. Proceedings of the National Academy of Sciences of the United States of America, 101(15), 5339–5346. Youngstedt, S. D., Kline, C. E., et al. (2016). Circadian phase-shifting effects of bright light, exercise, and bright light + exercise. Journal of Circadian Rhythms, 14, 2. Yu, X., Rollins, D., et al. (2013). TH17 cell differentiation is regulated by the circadian clock. Science, 342(6159), 727–730. Zarrinpar, A., Chaix, A., et al. (2014). Diet and feeding pattern affect the diurnal dynamics of the gut microbiome. Cell Metabolism, 20(6), 1006–1017. Zelinski, E. L., Deibel, S. H., et al. (2014). The trouble with circadian clock dysfunction: Multiple deleterious effects on the brain and body. Neuroscience and Biobehavioral Reviews, 40C, 80–101.