High fat diet disrupts diurnal interactions between small intestinal host innate immune factor REG3γ and gut microbiota resulting in metabolic dysfunction

BACKGROUND: Circadian rhythms are ubiquitous in nature, driving many bodily processes and behaviors, including sleep-wake cycles and feeding patterns over 24 hours. We and others revealed gut microbes and their functional outputs also exhibit diurnal rhythms that are responsive to how much, what, and when food is consumed. These microbial cues are integrated into host circadian networks, serving as key regulators of metabolism. High fat (HF) diet disrupts diurnal microbial oscillations, impacting diet-induced obesity (DIO). Apart from feeding, host factors that drive microbial oscillations, specifically in the small intestine, are complex and remain poorly understood. We hypothesized that HF diet disrupts coordination of diurnal rhythms between host-derived antimicrobial peptides, particularly the host C-type lectin Regenerating islet-derived 3 gamma(Reg3γ), and gut microbial community membership, contributing to DIO and metabolic dysfunction. RESULTS: Distal ileal tissue and luminal contents were collected every 4 hours over a 12:12 LD cycle from regular chow (RC) vs. HF-fed germ-free (GF) and conventionally raised (CONV) C57Bl/6 age and sex-matched mice. Ileal tissue gene expression analysis reveals diurnal Reg3γ expression is only observed in RC-fed, but not HF-fed, CONV mice. Illumina MiSeq 16S rRNA gene amplicon sequencing of ileal luminal contents indicates that HF diet significantly shifts microbial community membership with a corresponding reduction in oscillations relative to RC. Specific Lactobacillaceae bacteria selected by RC oscillate and exhibit positive correlation with Reg3γ expression, while HF promotes expansion of Clostridiales bacteria that negatively correlate with Reg3γ. Using both in vitro intestinal organoid and in vivomonoassociation of GF mice, we identified that exposure to bacterial strains representative of those selected by RC or HF diet elicit a bi-directional interaction with Reg3γ; only RC-driven Lactobacillus rhamnosus GG (LGG) induces diurnal Reg3γ expression, suggesting a bacteria-specific effect. While dietary composition remains the primary driver of microbial oscillators, host factors such as Reg3γ provide secondary cues to drive abundance and oscillation of key gut microbes that are essential for host metabolic homeostasis. CONCLUSIONS: Together, these results demonstrate transkingdom co-evolved biological rhythms that are primarily influenced by diet, and reciprocal sensor-effector signals between host and microbial components. The diurnal dynamics of host innate immune factors and specific diet-induced ileal gut microbes are key for the maintenance of regional intestinal host-microbe interactions and metabolic homeostasis. © FASEB.