A28 TIME-RESTRICTED FEEDING REDUCES INFLAMMATORY BOWEL DISEASE AND IMPROVES EPITHELIUM COLON REGENERATION

Background

The circadian clock is a time keeping mechanism that drives daily rhythms in the body, including behavior and gastrointestinal digestion, inflammation, and metabolism. These daily rhythms are endogenous to cells, and they must adjust themselves to cyclic environmental cues like feeding schedules and light dark cycles. However, when the cyclical environment is chrono-disrupted (ex. shiftwork and jetlag), the temporal organization in the body is lost. Chrono-disruption is linked to an increase in the risk of Inflammatory Bowel Disease (IBD); studies in rodents shown that IBD is more severe in mice without a circadian clock and intestinal regeneration is compromised

Purpose

Recent studies have shown that time-restricted feeding (TRF, the provision of food at times of peak behavior activity – without caloric restriction), that aligns with circadian behavior improves daily organization in the body and health. Therefore, we hypothesized that time-restricted feeding would be an effective strategy to ameliorate IBD and improve regeneration in chrono-disrupted animals.

Method

To test this, we used the DSS induction of colitis in mutant mice without clock function (Bmal1^-/-) and controls with an intact clock (Bmal1^+/+) and compared ad libitum feeding vs. TRF conditions (food available from 7pm to 7am).

Result(s)

Our results show that TRF ameliorates IBD symptoms and protects against epithelium colon damage in animals without clock function. Our preliminary results suggest that TRF may function by increasing the expression of the anti-inflammatory signal PPARg in the colon. Currently, we are testing if the circadian clock controls the daily expression of PPARg in vivo and in vitro. To further test the effect of TRF during regeneration after colitis, we tested proliferation (Ki67) and regeneration in the colon. (Hopx). Our results show that TRF increases the number of Ki67 positive cells and the expression of fetal-like regenerative precursor Hopx in both animals with and without a functional clock.

Conclusion(s)

Together these data suggest that TRF enhances regeneration in the colon after colitis. Moving forward, we are testing transcriptional pathways that are activated during regeneration in animals under TRF. Our results show that time restricted feeding can ameliorate IBD and highlight the role of circadian rhythms in regeneration and intestinal stem cell biology.

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CIHR, Other

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Crohn's and Colitis Canada

Disclosure of Interest

None Declared

A30 EPITHELIAL FUNCTION OF THE CIRCADIAN CLOCK GENE, BMAL1, IS NECESSARY FOR COLONIC REGENERATION

Background

The circadian clock is a self-sustained molecular oscillator which drives 24-hour physiological rhythms. It consists of the genes Bmal1 and Clock that positively regulate Cry and Per, their negative regulators, resulting in a 24-hour transcription/translation feedback loop. Shift work, which causes disruptions to 24-hour physiological rhythms, has been shown to lead to an increased incidence of inflammatory bowel disease (IBD). We have previously established that mice lacking the non-redundant circadian regulator, Bmal1, exhibit more severe colitis compared to controls.

Purpose

This study aims to investigate the epithelial function of Bmal1 in colonic regeneration during colitis.

Method

In order to assess the cell-specific role of the clock, we tested the regenerative effects of Bmal1 in intestinal epithelial tissue using Vil^+/+;Bmal1^flox/flox (control) and Vil^Cre/+;Bmal1^flox/flox (conditional mutant) mice. Dextran Sulfate Sodium (DSS) was applied to induce acute colitis. Disease progression was evaluated during colitis and during recovery upon removal of DSS treatment. We hypothesized that the absence of a functional circadian clock disrupts effective proliferation and regeneration of intestinal epithelial cells during colitis remission.

Result(s)

Vil^+/+;Bmal1^flox/flox control and Vil^Cre/+;Bmal1^flox/flox conditional mutant mice exhibit no significant differences in disease severity or tissue histopathology during colitis. However, after the removal of DSS, Vil^Cre/+;Bmal1^flox/flox conditional mutants show increased total lesions and overall inflammation, decreased crypt density as well as a higher propensity of hyperplastic crypts in the tissue. Regenerative ability of the colon is decreased in conditional mutants: phosphorylated-histone H3 and Ki67 show persistent increases in mitosis and overall proliferation near ulcerated lesions. This suggests that, while controls complete the regenerative response, conditional mutants fail to recover from colitis and show inefficient regeneration when Bmal1 is disrupted in intestinal epithelial cells.

Conclusion(s)

Our results support a critical role for Bmal1 in intestinal epithelial cells during post-colitis regeneration and recovery.

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CIHR, Other

Please indicate your source of funding;

OGS, Crohn's & Colitis Canada

Disclosure of Interest

None Declared

Genetic and pharmacologic proteasome augmentation ameliorates Alzheimer's-like pathology in mouse and fly APP overexpression models

The proteasome has key roles in neuronal proteostasis, including the removal of misfolded and oxidized proteins, presynaptic protein turnover, and synaptic efficacy and plasticity. Proteasome dysfunction is a prominent feature of Alzheimer's disease (AD). We show that prevention of proteasome dysfunction by genetic manipulation delays mortality, cell death, and cognitive deficits in fly and cell culture AD models. We developed a transgenic mouse with neuronal-specific proteasome overexpression that, when crossed with an AD mouse model, showed reduced mortality and cognitive deficits. To establish translational relevance, we developed a set of TAT-based proteasome-activating peptidomimetics that stably penetrated the blood-brain barrier and enhanced 20S/26S proteasome activity. These agonists protected against cell death, cognitive decline, and mortality in cell culture, fly, and mouse AD models. The protective effects of proteasome overexpression appear to be driven, at least in part, by the proteasome's increased turnover of the amyloid precursor protein along with the prevention of overall proteostatic dysfunction.

A54 THE CIRCADIAN CLOCK INFLUENCES JAK/STAT SIGNALING AND GUT PERMEABILITY

Background

The circadian clock is a 24-hour feedback loop that drives rhythms in behaviours and physiological processes. This molecular timekeeper consists of the transcription factors, Clock-Cycle, that drive expression of thousands of clock-controlled genes, with two of these, Period and Timeless, acting as negative regulators of Clock-Cycle. This fundamental mechanism was initially characterized in the fruit fly, Drosophila melanogaster (Nobel Prize in Physiology & Medicine, 2017), and is highly conserved in humans. The intestine, or midgut, of Drosophila, is also similar to the human small intestine consisting of similar cellular lineage, signaling pathways, and physiological functions. The lineage of the Drosophila intestine contains the same four cell types as humans: intestinal stem cells (ISCs), progenitors called enteroblasts, enterocytes and enteroendocrine cells. This simplified lineage as well as the genetic tools available, make Drosophila an ideal model for intestinal regeneration in health and disease. We have previously shown that the circadian clock is active in ISCs, EBs and ECs during both homeostatic and regenerating conditions. Furthermore, the circadian clock regulates the mitosis of ISCs under regenerating conditions.

Aims

We sought to uncover if Jak/STAT signaling, one of the key pathways involved in ISC proliferation in the Drosophila intestine, shows a circadian rhythm and if there is a time-of-day difference in the regenerative response.

Methods

To test whether the clock regulates Jak/STAT during acute injury, we developed an irradiation assay that does not affect survival but acutely disrupts intestinal barrier function.

Results

Using a dynamic reporter of Jak/STAT activity we show that Period circadian clock mutants have low Jak/STAT signaling and a leaky gut phenotype. Wildtype controls show time-dependent gut leakiness upon irradiation, which is higher and time-independent in Period mutants. The level of Jak/STAT response differs depending on the time of irradiation in the controls, but is higher at all times in the mutants.

Conclusions

The Jak/Stat pathway regulates intestinal immunity and epithelial cell proliferation in humans, thus playing a role in colorectal cancer and inflammatory bowel disease. Our results suggest Jak/Stat is controlled by the circadian clock, which has implications for intestinal recovery following medical treatments, including radiation therapy.

Funding Agencies

NRC

A3 THE LOSS OF THE CIRCADIAN CLOCK GENE BMAL1 INCREASES TUMOUR INITIATION IN APCMIN MICE

Background

Circadian rhythms are autonomously running 24h cycles in bodily processes. In animals these rhythms are driven by a molecular time keeper known as the circadian clock. The clock is a transcription-translation feedback loop composed of the transcription factors Bmal1 and Clock as well as their repressors Per and Cry. The circadian clock regulates over 40% of the genome rhythmically. Chronic circadian disruption, in the case of shift work, can lead to pathologies including cancer. Colorectal cancer is most frequently initiated through a mutation in the Wnt pathway regulator, Apc. Several studies have attempted to provide a mechanistic link between cancer and circadian clock disruption but the use of mice on mixed genetic backgrounds and poor circadian models have made this link unclear.

Aims

We aim to determine if the circadian clock plays a role in intestinal tumourigenesis.

Methods

We crossed the Apcmin mouse strain, a common intestinal tumour model, with Bmal1 mutant mice, which lack a functioning circadian clock. After creating an isogenic strain, we examined the number of tumours in control (Bmal1+/+) and clock dead (Bmal1-/-) animals. We derived organoids, a 3D cell culture method, from Apc+/+; Bmal1+/+ (healthy, clock-live), Apc+/+, Bmal1-/-(healthy, clock-dead), Apcmin; Bmal1+/+(adenoma, clock-live), Apcmin; Bmal1-/- (adenoma, clock-live) mouse ileum and collected every 2h from 24-48h after synchronizing their circadian clock. Collected samples were sent for RNA sequencing and assessed for circadian regulated transcripts. This experiment was followed up by in vitro organoid assays.

Results

The circadian clock controls 41 genes in the intestinal epithelium, including genes like Tead4 which are known to be important in intestinal biology. There are twofold more tumours in Bmal1-/- mice than their Bmal1+/+ littermates, and Bmal1-/- tumours upregulate Tead4 and Hippo pathway targets and downregulate Wnt pathway targets. Bmal1-/- adenoma organoids show increased self-renewal when compared to Bmal1+/+ adenoma organoids. However, this increase in self-renewal is lost when organoids are treated with inhibitors of the hippo pathway.

Conclusions

The circadian clock is important in maintaining the health of an organism, and disruption of the clock can lead to many health consequences including cancer. We show for the first time that the circadian clock controls the hippo signaling mediator Tead4. Additionally, we show that the loss of the clock leads to an increase in the number of tumours present in the epithelium which are characterized by an increase in hippo signaling. This research shows the important of considering time of day when studying stem cells during homeostasis and in cancer.

Funding Agencies

CIHRNSERC

AFM Imaging Reveals Topographic Diversity of Wild Type and Z Variant Polymers of Human α1-Proteinase Inhibitor

α1-Proteinase inhibitor (antitrypsin) is a canonical example of the serpin family member that binds and inhibits serine proteases. The natural metastability of serpins is crucial to carry out structural rearrangements necessary for biological activity. However, the enhanced metastability of the mutant Z variant of antitrypsin, in addition to folding defect, may substantially contribute to its polymerization, a process leading to incurable serpinopathy. The metastability also impedes structural studies on the polymers. There are no crystal structures of Z monomer or any kind of polymers larger than engineered wild type (WT) trimer. Our understanding of polymerization mechanisms is based on biochemical data using in vitro generated WT oligomers and molecular simulations. Here we applied atomic force microscopy (AFM) to compare topography of monomers, in vitro formed WT oligomers, and Z type polymers isolated from transgenic mouse liver. We found the AFM images of monomers closely resembled an antitrypsin outer shell modeled after the crystal structure. We confirmed that the Z variant demonstrated higher spontaneous propensity to dimerize than WT monomers. We also detected an unexpectedly broad range of different types of polymers with periodicity and topography depending on the applied method of polymerization. Short linear oligomers of unit arrangement similar to the Z polymers were especially abundant in heat-treated WT preparations. Long linear polymers were a prominent and unique component of liver extracts. However, the liver preparations contained also multiple types of oligomers of topographies undistinguishable from those found in WT samples polymerized with heat, low pH or guanidine hydrochloride treatments. In conclusion, we established that AFM is an excellent technique to assess morphological diversity of antitrypsin polymers, which is important for etiology of serpinopathies. These data also support previous, but controversial models of in vivo polymerization showing a surprising diversity of polymer topography.

The proteasome in health and disease

The giant proteolytic factory called the proteasome came a long way from a biochemical curio to a major regulator of cellular physiology and a renowned drug target within the ubiquitin proteasome pathway (UPP). Thanks to availability of highly specific inhibitors of the proteasome, in less than twenty years it was possible to identify major transcription factors, cyclins, and products of oncogenes as crucial substrates for the UPP. Nine years passed since the FDA speedily approved bortezomib, the inhibitor of proteasome, for treatment of multiple myeloma. One year after its approval, the field was honored by awarding the Nobel Prize to Hershko, Ciechanover and Rose for introducing the concept of controlled proteolysis of ubiquitin-tagged substrates, with proteasome as the intracellular recycling facility. Taking into consideration the universal involvement of the proteasome in the life of all cells in human body, it comes to no surprise that the enzyme is deeply implicated in etiology, progression, diagnosis or cure of multiple diseases. Below we discuss some aspects of the involvement: from direct causative links to changes in proteasome properties that correlate with pathological conditions. We start with diseases collectively known as cancer, and with immune system-related pathologies. Here, the proteasome inhibitors are either already used in clinics, or undergo advanced preclinical screening. Then, we will continue with cardiovascular disorders, followed by aging. Changes of the proteasome make-up during aging may be a priming factor for neurodegenerative diseases, described last. We discuss the potential for proteasome regulation: inhibition, activation or specificity modulation, to successfully enter the clinical setting.

Pressure as a denaturing agent in studies of single-point mutants of an amyloidogenic protein human cystatin c

Recently, we presented a convenient method combining a deuterium-hydrogen exchange and electrospray mass spectrometry for studying high-pressure denaturation of proteins (Stefanowicz et al., Biosci Rep 2009; 30:91-99). Here, we present results of pressure-induced denaturation studies of an amyloidogenic protein-the wild-type human cystatin C (hCC) and its single-point mutants, in which Val57 residue from the hinge region was substituted by Asn, Asp or Pro, respectively. The place of mutation and the substituting residues were chosen mainly on a basis of theoretical calculations. Observation of H/D isotopic exchange proceeding during pressure induced unfolding and subsequent refolding allowed us to detect differences in the proteins stability and folding dynamics. On the basis of the obtained results we can conclude that proline residue at the hinge region makes cystatin C structure more flexible and dynamic, what probably facilitates the dimerization process of this hCC variant. Polar asparagine does not influence stability of hCC conformation significantly, whereas charged aspartic acid in 57 position makes the protein structure slightly more prone to unfolding. Our experiments also point out pressure denaturation as a valuable supplementary method in denaturation studies of mutated proteins.