Model Of Circadian Disruption Research Articles

Genetic and environmental circadian disruption induce weight gain through changes in the gut microbiome

ObjectiveInternal clocks time behavior and physiology, including the gut microbiome, in a circadian (∼24 h) manner. Mismatch between internal and external time, e.g. during shift work, disrupts circadian system coordination promoting the development of obesity and type 2 diabetes (T2D). Conversely, body weight changes induce microbiota dysbiosis. The relationship between circadian disruption and microbiota dysbiosis in metabolic diseases, however, remains largely unknown. MethodsCore and accessory clock gene expression in different gastrointestinal (GI) tissues were determined by qPCR in two different models of circadian disruption - mice with Bmal1 deficiency in the circadian pacemaker, the suprachiasmatic nucleus (Bmal1SCNfl/-), and wild-type mice exposed to simulated shift work (SSW). Body composition and energy balance were evaluated by nuclear magnetic resonance (NMR), bomb calorimetry, food intake and running-wheel activity. Intestinal permeability was measured in an Ussing chamber. Microbiota composition and functionality were evaluated by 16S rRNA gene amplicon sequencing, PICRUST2.0 analysis and targeted metabolomics. Finally, microbiota transfer was conducted to evaluate the functional impact of SSW-associated microbiota on the host's physiology. ResultsBoth chronodisruption models show desynchronization within and between peripheral clocks in GI tissues and reduced microbial rhythmicity, in particular in taxa involved in short-chain fatty acid (SCFA) fermentation and lipid metabolism. In Bmal1SCNfl/- mice, loss of rhythmicity in microbial functioning associates with previously shown increased body weight, dysfunctional glucose homeostasis and adiposity. Similarly, we observe an increase in body weight in SSW mice. Germ-free colonization experiments with SSW-associated microbiota mechanistically link body weight gain to microbial changes. Moreover, alterations in expression of peripheral clock genes as well as clock-controlled genes (CCGs) relevant for metabolic functioning of the host were observed in recipients, indicating a bidirectional relationship between microbiota rhythmicity and peripheral clock regulation. ConclusionsCollectively, our data suggest that loss of rhythmicity in bacteria taxa and their products, which likely originates in desynchronization of intestinal clocks, promotes metabolic abnormalities during shift work.

Beneficial effects of voluntary wheel running on activity rhythms, metabolic state, and affect in a diurnal model of circadian disruption

Emerging evidence suggests that disruption of circadian rhythmicity contributes to development of comorbid depression, cardiovascular diseases (CVD), and type 2 diabetes mellitus (T2DM). Physical exercise synchronizes the circadian system and has ameliorating effects on the depression- and anxiety-like phenotype induced by circadian disruption in mice and sand rats. We explored the beneficial effects of voluntary wheel running on daily rhythms, and the development of depression, T2DM, and CVD in a diurnal animal model, the fat sand rat (Psammomys obesus). Voluntary exercise strengthened general activity rhythms, improved memory and lowered anxiety- and depressive-like behaviors, enhanced oral glucose tolerance, and decreased plasma insulin levels and liver weight. Animals with access to a running wheel had larger heart weight and heart/body weight ratio, and thicker left ventricular wall. Our results demonstrate that exercising ameliorates pathological-like daily rhythms in activity and blood glucose levels, glucose tolerance and depressive- and anxiety-like behaviors in the sand rat model, supporting the important role of physical activity in modulating the “circadian syndrome” and circadian rhythm-related diseases. We suggest that the utilization of a diurnal rodent animal model may offer an effective way to further explore metabolic, cardiovascular, and affective-like behavioral changes related to chronodisruption and their underlying mechanisms.

0103 Novel Prebiotic Enhances Sleep-Wake Cycle and Memory Consolidation in 5xFAD Mice

Abstract Introduction Prior studies have shown that the gut microbiomes of Alzheimer’s Disease (AD) patients differ from unaffected individuals. Sleep and circadian rhythm disturbances are common in AD and often precede dementia symptoms. Gut microbiome alterations have also been observed in models of circadian disruption. Therefore, we hypothesized that altering the gut microbiome could improve sleep/circadian rhythms and cognition in an AD mouse model. Methods Mice were given a dietary polysaccharide, Modified Resistant Maltodextrin (MRM), as a 1% solution in the drinking water beginning at 2 months of age. 5xFAD and wild-type (WT) littermates were tested. Sleep-wake was recorded by EEG/EMG, memory consolidation was tested by the Object-Location Memory test, and beta amyloid deposition in the brain was assayed (dot blot). Composition of the gut microbiota was determined from amplicon sequencing of the 16s ribosomal RNA gene from fecal DNA. Results MRM treatment reduced dark (active)-phase sleep and the phase scattering of REM sleep in 5xFAD mice, indices of circadian consolidation. 6-month-old 5xFAD mice given plain water exhibited no 24hr retention of object location memory. However, MRM-treated 5xFAD mice demonstrated 24-hour memory, even at 12 months of age. Both improved memory and increased consolidation of sleep were also observed in WT mice. Two unclassified species of bacteria from the family Tannerellaceae were significantly increased in MRM-treated 5xFAD and WT mice. At 12 months of age, synaptic and neuronal loss become prominent in this AD model. However, the level of beta amyloid deposition in the brain was not significantly different between MRM and water control groups. Conclusion MRM treatment altered the gut microbiome, improved circadian timing of sleep and memory retention, but did not impact beta amyloid deposition in 5xFAD mice. Because these effects were also present in WT mice, MRM-induced microbiome changes may affect sleep and cognition independently from beta amyloid. Support Northwestern University Feinberg School of Medicine Center for Circadian and Sleep Medicine

Bromocriptine improves glucose tolerance independent of circadian timing, prolactin, or the melanocortin-4 receptor.

Bromocriptine, a dopamine D2 receptor agonist originally used for the treatment of hyperprolactinemia, is largely successful in reducing hyperglycemia and improving glucose tolerance in type 2 diabetics. However, the mechanism behind bromocriptine's effect on glucose intolerance is unclear. Here, we tested three hypotheses, that bromocriptine may exert its effects on glucose metabolism by 1) decreasing prolactin secretion, 2) indirectly increasing activity of key melanocortin receptors in the central nervous system, or 3) improving/restoring circadian rhythms. Using a diet-induced obese (DIO) mouse model, we established that a 2-wk treatment of bromocriptine is robustly effective at improving glucose tolerance. We then demonstrated that bromocriptine is effective at improving the glucose tolerance of both DIO prolactin-deficient and melanocortin-4 receptor (MC4R)-deficient mice, pointing to bromocriptine's ability to affect glucose tolerance independently of prolactin or MC4R signaling. Finally, we tested bromocriptine's dependence on the circadian system by testing its effectiveness in environmental (e.g., repeated shifts to the light-dark cycle) and genetic (e.g., the Clock mutant mouse) models of circadian disruption. In both models of circadian disruption, bromocriptine was effective at improving glucose tolerance, indicating that a functional or well-aligned endogenous clock is not necessary for bromocriptine's effects on glucose metabolism. Taken together, these results do not support the role of prolactin, MC4R, or the circadian clock as integral to bromocriptine's underlying mechanism. Instead, we find that bromocriptine is a robust diabetic treatment and resilient to genetically induced obesity, diabetes, and circadian disruption.

SAT-182 AN OMICS APPROACH TO UNDERSTANDING MUSCLE-KIDNEY CROSSTALK IN A BMAL1-DEPENDENT MODEL OF CIRCADIAN RHYTHM DISRUPTION

Skeletal muscle tissue is highly metabolically active and yields wastes that kidneys must excrete in order to maintain a homeostatic internal environment. Within skeletal muscle exists an intrinsic molecular clock mechanism that regulates the timing of such physiological processes. BMAL1 is a core transcription factor responsible for regulating this mechanism. The clock is able to anticipate patterns of behavior to prepare skeletal muscle cells for stressors, however, the relationship of these cycles with the kidney is unknown. The purpose of this study was to determine how kidneys are affected when the clock in skeletal muscle tissue is disrupted, using a model of circadian disruption and premature aging. Our mouse model was generated using floxed exon 8 BMAL1 mice crossed with skeletal muscle-specific Cre-recombinase mice (human skeletal actin-MerCreMer) to yield male tamoxifen-inducible skeletal muscle-specific BMAL1 knockout mice (KO). Littermate vehicle treated floxed mice were used as control mice (CNTL). Metabolic cages were used to collect urine samples 5 weeks after knockout induction. Additionally, a microarray was used on kidney tissue to determine gene expression and proteomic analysis was performed on serum collections. Body weight and food intake was similar between genotypes (P=0.1; P=0.2; N=5). Urinary sodium and potassium retention (intake minus excretion) was similar between KO and CNTL (Na: 0.07±0.02 vs. 0.06±0.02 mmol; P=0.7; K: 0.2±0.02 vs. 0.2±0.04 mmol; P=0.3; N=4-5). Microarray transcriptomic studies revealed that several genes connected to fibrosis and inflammation were higher in KO compared to CNTL (% increase in KO: VCAM1-25%; TNF 13b-45%; IL22-40%; IL10-30%; IL6a-30%; NFkB-30%). Proteomic evaluation of serum samples demonstrated altered levels of several proteins linked to chronic kidney diseases in humans. Serum albumin levels in KO were nearly half of CNTL levels (P<0.0001). The subunits of fibrinogen levels were higher in KO than CNTL serum (alpha, 1.3 fold, P=0.003; beta, 1.6 fold, P=0.003; gamma, 1.8 fold, P=0.01). Histidine-rich glycoprotein was nearly 40 fold higher in KO serum than CNTL (P=0.002). Renal handling of solutes was comparable between the genotypes at baseline. The protein markers in serum that were elevated in KO have been previously linked to the development of kidney disease in humans. These findings together with the increased renal expression of inflammatory genes in KO indicate that BMAL1-dependent mechanisms in skeletal muscle tissue may be associated with kidney health. Future studies will examine differences in kidney morphology as well as renal function in the face of a dietary electrolyte challenge.

Environmental disruption of the circadian clock leads to altered sleep and immune responses in mouse.

In mammals, one of the most salient outputs of the circadian (daily) clock is the timing of the sleep-wake cycle. Modern industrialized society has led to a fundamental breakdown in the relationship between our endogenous timekeeping systems and the solar day, disrupting normal circadian rhythms. We have argued that disrupted circadian rhythms could lead to changes in allostatic load, and the capacity of organisms to respond to other environmental challenges. In this set of studies, we apply a model of circadian disruption characterized in our lab in which mice are housed in a 20h long day, with 10h of light and 10h of darkness. We explored the effects of this environmental disruption on sleep patterns, to establish if this model results in marked sleep deprivation. Given the interaction between circadian, sleep, and immune systems, we further probed if our model of circadian disruption also alters the innate immune response to peripheral bacterial endotoxin challenge. Our results demonstrate that this model of circadian disruption does not lead to marked sleep deprivation, but instead affects the timing and quality of sleep. We also show that while circadian disruption does not lead to basal changes in the immune markers we explored, the immune response is affected, both in the brain and the periphery. Together, our findings further strengthen the important role of the circadian timing system in sleep regulation and immune responses, and provide evidence that disrupting the circadian clock increases vulnerability to further environmental stressors, including immunological challenges.