2017 Cardiovascular Research Day Abstract Book

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Gut Microbial Trimethylamine (TMA) Lyase Activity Coordinates Circadian Rhythms in Host
Hepatic Lipid and Bile Acid Metabolism
Christy Gliniak, PhD 1 • Rebecca Schugar, PhD 1 • Robert Helsley, PhD 1 • Anthony Gromovsky 1 •
Chase Neumann 1 • Zeneng Wang, PhD 1 • Stanley Hazen, MD, PhD 2 • J. Mark Brown, PhD 2
1Department of Cellular and Molecular Medicine, Cleveland Clinic • 2 Department of Cellular and
Molecular Medicine, Center for Microbiome & Human Health, Cleveland Clinic
Faculty
From cyanobacteria to humans, circadian rhythms evolved to allow an organism to adapt and
anticipate environmental cues, particularly events that regulate energy metabolism. Misalignment
of circadian rhythms are associated with increased incidence of obesity, diabetes, cardiovascular
disease, cancer, and other inflammatory disorders. Intestinal microbial composition and structure
displays circadian rhythmicity, and the gut microbiome itself can regulate host endogenous
circadian rhythms. However, it is not well understood how gut microbes regulate host metabolism
and circadian rhythms. Gut microbes contribute to the production of the circulating metabolite
trimethlyamine-N-oxide (TMAO), which is associated with cardiovascular disease in humans, and
has been shown to enhance atherosclerosis and thrombosis potential in mice. Microbes produce
trimethlyamine (TMA) from dietary choline or carnitine, which is later converted by the host to
TMAO, primarily by host liver flavin monooxygenase 3 (FMO3). Previous studies have shown that
pharmacologic inhibition of microbial TMA lyase activity or inhibition of FMO3 results in decreased
atherosclerosis in mice, and the expression of the TMAO producing enzyme FMO3 exhibits
circadian rhythmic patterns in the liver. Here we hypothesized that the co-metabolites TMA and
TMAO may serve as gut microbe-derived signals that entrain host metabolic circadian rhythms,
thereby impacting cardiometabolic disease. To test this we treated C57BL/6 mice with a highly
potent and selective second-generation TMA lyase inhibitor CC08, and examined effects on
circadian rhythms in host metabolism. As expected, mice treated with CC08 displayed reduced
plasma TMA/TMAO levels across an entire 24-hour period. Unexpectedly, TMA lyase inhibition
resulted in increased expression of the key nuclear receptors that regulate the circadian clock
including Bmal1 (Arntl1) and Rev-erbα (Nr1d1) during the light cycle in the liver. The well known
circadian cycling of transcription factors orchestrating hepatic fatty acid metabolism such as
Srebp1c and Pparα were markedly altered in CC08-treated mice. TMA lyase inhibition resulted in
elevated hepatic expression of Srebp1c during the light cycle, yet suppressed hepatic Pparα
expression during the dark cycle. Furthermore, the expression of the bile acid-sensing nuclear
receptor Fxr was lower in TMA lyase-inhibited animals during the dark cycle, which is associated
with alterations in hepatic Fxr target gene expression and circulating bile acid levels. Collectively,
these data suggest that pharmacologic inhibition of gut microbial TMA lyase activity can alter host
transcriptional programs that dictate hepatic circadian rhythms in lipid and bile acid metabolism.
These data provide the first clues into mechanisms by which TMA lyase inhibitors may protect mice
against cardiometabolic disease.
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