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Diet-induced circadian enhancer remodeling synchronizes opposing hepatic lipid metabolic processes

ABSTRACT: Overnutrition disrupts circadian rhythms leading to dysregulated metabolism by mechanisms that are not well understood. Here we show that diet-induced obesity (DIO) causes massive remodeling of circadian enhancer activity and gene transcription in mouse liver. Remarkably, DIO triggers synchronous, high amplitude circadian rhythms of both fatty acid (FA) synthesis and oxidation. This gain of circadian rhythmicity in lipid metabolic pathways that oppose each other emphasizes the importance of balance and flux in normal hepatic lipid metabolism. DIO-promoted rhythmicity of Sterol Regulatory Element-Binding Protein (SREBP) activation, which was required not only for the induction of FA synthesis but also, surprisingly, for FA oxidation (FAO). DIO also brought about a high amplitude circadian rhythm of peroxisome proliferated receptor a (PPARa), which was required for FAO. Provision of a pharmacological ligand for PPARa abrogated the requirement of SREBP for FA oxidation (but not FA synthesis), suggesting that SREBP indirectly controls FA oxidation via production of an endogenous PPARa ligand. Moreover, the high amplitude circadian rhythm of PPARa imparts time-of-day-dependent responsiveness to lipid-lowering drugs. Thus, acquisition of rhythmicity for the non-core clock components PPARa and SREBP1 remodels metabolic gene transcription in response to a challenging nutritive environment and enables a chronopharmacological approach to metabolic disorders.

ORGANISM(S): Mus musculus

PROVIDER: GSE108878 | GEO | 2018/07/26

REPOSITORIES: GEO

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Transcriptomics informs design of a planar human enterocyte culture system that reveals metformin enhances fatty acid flux

Project description:Background & Aims: Absorption, metabolism, and secretion of lipids occurs in the small intestinal epithelium. Caco-2 and organoids have been used to study these processes but are limited in physiological relevance or preclude simultaneous apical and basal access. Here, we develop a dynamic and flexible planar absorptive enterocyte (AE) monolayer system, investigate how fatty acid oxidation (FAO) regulates FA mobilization mechanisms and probe a role for metformin in FA mobilization. Methods: Single-cell RNA-sequencing (scRNAseq) was performed on primary human jejunum. Transcriptomic signatures and trajectory analysis defined in vivo AE maturational signatures, which informed culture methods to differentiate ISCs and mimic in vivo AEs. The system was scaled for high-throughput drug screening and FAO was pharmacologically modulated. BODIPY (B)-labelled fatty acids (FAs) were used to easily and sensitively evaluate FA handling via fluorescence, and thin layer chromatography (TLC). Results: scRNAseq shows increasing expression of lipid-handling genes as AEs mature. In vitro, ISCs differentiate into AEs that mimic the in vivo maturational program, exhibit strong barrier function and express FA-handling genes. FA synthase inhibitor, C75, increased apical to basolateral mobilization of B-C16. Short-chain FA (B-C5) was unaffected and diffused freely through AEs. FAO inhibitor, etomoxir, decreased apical to basolateral mobilization of medium and long chain FAs (B-C12, B-C16) whereas anti-diabetic drug, metformin, augmented this mobilization. Conclusions: Primary human ISCs in culture undergo programmed maturation in vitro to generate a sensitive culture system of absorptive epithelium to investigate FA-handling. Modulating FAO impacts mobilization of FAs across absorptive epithelium and FAO enhanced by metformin increases basolateral mobilization pointing to an intestine-specific role.

2022-08-02 | GSE186583 | GEO

Vitamin B2 enables PPARa regulation of fasting glucose availability

Project description:Flavin adenine dinucleotide (FAD) mediates oxidation-reduction reactions required for cellular energy demands. Fatty acid oxidation (FAO) disorders caused by flavoprotein mutations and FAD depletion disrupt energy balance and glucose production during fasting. These FAO disorders are difficult to manage clinically, and their biochemical pathogenesis is poorly understood. Here, we identify a mechanistic connection between FAD levels and hepatic glucose production. Depleting the FAD pool in mice with a vitamin B2 deficient diet (B2D) resulted in phenotypes associated with organic acidemia phenotypes, including reduced body weight and whole-body fat oxidation rates coupled with hypoglycemia. Integrated discovery approaches revealed that B2D broadly tempered fasting activation of target genes for the nuclear receptor PPARa, including those required for gluconeogenesis. Consistent with this, Ppara knockout depleted liver FAD levels and worsened B2D hepatic glucose production. Treatment with the PPARa agonist fenofibrate overcame B2D phenotypes and rescued glucose availability and fatty liver signatures through activation of the integrated stress response and refilling anaplerotic amino acid substrates for glucose production. We conclude that PPARa governs metabolic responses to FAD availability and suggest pharmacologic activation as a strategy for treating disorders of riboflavin and FAD deficiency.

2022-06-18 | GSE206200 | GEO

Hepatocyte SREBP signaling mediates clock communication within the liver [ATAC-seq]

Project description:Rhythmic intraorgan communication coordinates environmental signals and cell-intrinsic clock to maintain organ homeostasis. Hepatocyte-specific knockout of core components of the molecular clock, Rev-erba and b (ReverbhDKO), alters cholesterol and lipid metabolism in hepatocytes as well as rhythmic gene expression in non-parenchymal cells (NPC) of the liver. Here we report that in diet induced obesity (DIO)-caused fatty liver, hepatocyte SREBP cleavage-activating protein (SCAP) is required for ReverbhDKO-induced diurnal rhythmic remodeling and epigenomic reprogramming in Kupffer cells (KC). Integrative analyses of isolated hepatocytes and Kupffer cells uncovered potential signals, including secreted polypeptides and metabolites, that gain rhythmicity in the absence of REV-ERBs in a SCAP-dependent manner. These results shed light on the signaling mechanisms by which hepatocytes regulate diurnal rhythms in NPCs in DIO and fatty liver disease.

2023-04-04 | GSE206318 | GEO

Hepatocyte SREBP signaling mediates clock communication within the liver [scRNA-seq]

2023-04-04 | GSE206317 | GEO

Hepatocyte SREBP signaling mediates clock communication within the liver [RNA-seq]

2023-04-04 | GSE206316 | GEO

Lipid metabolism genes in first trimester placenta

Project description:Placentas of obese women have low mitochondrial beta-oxidation of fatty acids (FA) and accumulate lipids in late pregnancy. This creates a lipotoxic environment, impairing placental efficiency. We assessed expression of key regulators of FA metabolism in first trimester placentas of lean and obese women. Expression of genes associated with FA oxidation (FAO; ACOX1, CPT2, AMPKα), FA uptake (LPL, LIPG, MFSD2A), FA synthesis (ACACA) and storage (PLIN2) were significantly reduced in placentas of obese compared to lean women. This effect was exacerbated in placentas of male fetuses. The PPARα pathway was enriched for placental genes impacted by obesity. These results demonstrate that obesity and hyperlipidemia impact placental FA metabolism as early as 7 weeks of pregnancy.

2022-10-12 | GSE206037 | GEO

DGAT1 phosphoproteome and long-term proteome

Project description:Enhanced fatty acid (FA) synthesis and uptake underpin the sustained membrane biogenesis and ATP production required for melanoma cell growth and division1-4. However, to thrive, melanoma cells must avoid a potential reduction in cell growth signalling, rampant reactive oxygen species (ROS) generation, and the build-up of toxic lipid species that can accompany excess free FA5. Here, we uncover and address the significance of frequent amplification and up-regulation of the Diacylglycerol O-acyltransferase 1 (DGAT1) gene in melanoma, whose encoded product catalyses the final step of Triacyglyceride (TAG) synthesis. Consistent with the classification of DGAT1 as an oncogene, we found that forced DGAT1 expression in p53 mutant zebrafish melanocytes was sufficient to induce melanoma, and accelerated melanoma progression initiated by co-expression of oncogenic BRAF or NRAS. Regarding DGAT1 function in human melanoma cells, its depletion, or alternatively pharmacological inhibition, suppressed mTOR-S6K signalling and increased levels of acyl carnitine species— FA derivatives that are the limiting substrate for FA oxidation (FAO). In turn, increased FAO induced mitochondrial malfunction, ROS generation, and lipid peroxidation. However, the resultant oxidative stress induced NRF2 and SESTRIN2 (SESN2) expression, which limited the extent of cell death. Conversely, DGAT1 over-expression enhanced mTOR-S6K signalling and cell growth, and protected against ROS, particularly in hypoxic conditions. Together, our data establish DGAT1 as a bona fide oncogene essential in melanoma cells for enabling FA accumulation.

2023-03-10 | PXD017487 | Pride

Temporal profiles of gene expression in Cry1/2 KO, Bmal1 KO under night restricted feeding and ad libitum feeding regimen

Project description:The circadian clock and rhythmic food intake are both important regulators of rhythmic gene expression in the liver. It remains, however, elusive to which extent the circadian clock network and natural feeding rhythms contribute to rhythmic gene expression. To systematically address this question, we developed an algorithm to investigate differential rhythmicity between a varying number of conditions. Mouse knockout models of different parts of the circadian clock network (Bmal1, Cry1/2, and Hlf/Dbp/Tef) exposed to controlled feeding regimens (ad libitum, night restricted feeding) were generated and analyzed for their temporal hepatic transcriptome. A genetical ablation of core loop elements altered feeding patterns that were restored by night restricted feeding. Mainly genes with a high amplitude were driven by the circadian clock but natural feeding patterns equally contributed to rhythmic gene expression with lower amplitude. We observed that Bmal1 and Cry1/2 KOs differed in rhythmic gene expression and identified differences in mean expression levels as a predictor for rhythmic gene expression. In Hlf/Dbp/Tef KO, mRNA levels of Hlf/Dbp/Tef target genes were decreased, albeit rhythmicity was overall preserved potentially due to the activity of the D-Box binding repressor NFIL3. Genes that lost rhythmicity in Hlf/Dbp/Tef KOs were identified to be no direct targets of PARbZip factors and presumably lost rhythmicity due to indirect effects. Collectively, our findings provide unprecedent insights into the diurnal transcriptome in mouse liver and defines the contribution of subloops of the circadian clock network and natural feeding cycles. The developed algorithm and a webapp to browse the outcomes of the study are publicly available to serve as a resource for the scientific community.

2020-12-03 | GSE135898 | GEO

Temporal profiles of hepatic gene expression in PAR bZip triple knockout mice

2020-12-03 | GSE135875 | GEO

Effect of p16 deficiency on gene expression in primary hepatocytes

Project description:*Objectives:* In addition to their well-known role in the control of cellular proliferation and cancer, cell cycle regulators are increasingly identified as important metabolic modulators. Genome wide association studies identified SNPs near the cell cycle regulator CDKN2A/p16INK4a (p16) as strongly associated with risk of developing type 2 diabetes (T2D). T2D is associated with numerous perturbations of hepatic lipid and glucose metabolism. We have recently shown that p16 controls fasting-induced hepatic gluconeogenesis in mice. However, whether p16 may also affect hepatic lipid homeostasis is unknown. *Results:* In primary hepatocytes, p16-deficiency was associated with elevated expression of genes involved in fatty acid catabolism and enhanced activation of PPAR. This led to increased mitochondrial fatty acid oxidation (FAO) through a mechanism requiring the catalytic AMPK 2 subunit and SIRT1. By contrast, *p16* overexpression was associated with triglyceride accumulation and increased lipid droplet numbers *in vitro*, and decreased ketogenesis and hepatic mitochondrial activity *in vivo*. Gene expression analysis of human liver samples revealed a negative correlation between *CDKN2A* expression and *PPARA* and its target genes, suggesting a potential association between hepatic p16 expression and FAO in obese humans. *Conclusions:* Our findings demonstrate that p16 plays a key role in hepatic lipid metabolism and may thus contribute to the development of metabolic diseases.

2020-10-09 | GSE134625 | GEO

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