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BHLHE40 role in hepatocytes exposed to high sugar content

ABSTRACT: BHLHE40/DEC1 is a basic helix-loop-helix transcription factor (TF) that regulates circadian rhythm and T cell responses. In hepatocytes, its function and cooperativity with other TFs are poorly understood. Employing genome-wide approached, we show that its genomic binding strongly overlapped with that of carbohydrate response-element binding protein (ChREBP), a sugar sensing TF and known inducer of BHLHE40 expression. Transcriptomic analysis of primary mouse hepatocytes revealed a pervasive repressive role for BHLHE40 on genes involved in genomic stability. Bhlhe40 depletion potentiated fructose responsiveness of genes involved in cell cycle regulation. Strikingly, genomic binding of BHLHE40 overlapped with enhancers occupied by PPARα, RXRα, and HNF4 nuclear receptors and BHLHE40 fine-tuned the expression of PPARα target genes. Consistently, BHLHE40 physically interacted with RXRα and proteins of PPARα-related regulators. Collectively, our data suggest that through cooperation with ChREBP and nuclear receptors, BHLHE40 is a central regulator of hepatic gene expression with potential to integrate inputs from nutrient signals contributing to the metabolic flexibility of the liver.

ORGANISM(S): Mus musculus

PROVIDER: GSE316769 | GEO | 2026/09/16

REPOSITORIES: GEO

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Project description:Using both global and conditional knockout mice, we demonstrated that the transcription factor Basic Helix-Loop-Helix Family Member E40 (BHLHE40/DEC1) is required in T cells for rejection of mouse syngeneic tumors upon immune checkpoint therapy (ICT) with anti-PD-1 or anti-CTLA-4 monoclonal antibody (mAb) treatment. Using single cell RNA sequencing (scRNAseq) we profiled intratumoral CD45+ cells from syngeneic mouse sarcomas that (a) grow progressively with control treatment in either Bhlhe40+/+ or Bhlhe40-/- tumor-bearing mice, (b) reject following anti-PD-1 or anti-CTLA-4 ICT in Bhlhe40+/+ tumor-bearing mice, or (c) grow progressively following anti-PD-1 or anti-CTLA-4 in Bhlhe40-/- mice. We performed two separate scRNAseq experiments with the same conditions but harvested tumors on either day 9 post-tumor transplant or day 11 post-tumor transplant. The groups were as follows: (1) Control mAb Bhlhe40+/+, (2) Control mAb Bhlhe40-/-, (3) anti-PD-1 Bhlhe40+/+, (4) anti-PD-1 Bhlhe40-/-, (5) anti-CTLA-4 Bhlhe40+/+, and (6) anti-CTLA-4 Bhlhe40-/-. scRNAseq of intratumoral immune cells in BHLHE40-deficient mice revealed differential ICT-induced immune cell remodeling. These BHLHE40-dependent gene expression alterations were associated with altered metabolism, NF-kB signaling, and IFN- response in subpopulations of intratumoral CD4+ and CD8+ T cells. Intratumoral T cells from tumor-bearing Bhlhe40-/- mice also had higher transcript expression of the inhibitory receptor gene Tigit, along with altered transcript expression of chemokine/chemokine receptor granzyme family members. Bhlhe40-/- CD4+ and CD8+ T cells also had reduced ICT-driven IFN- production. Furthermore, BHLHE40 was required for ICT-induced remodeling of macrophages from a CX3CR1+ CD206+ subpopulation to an iNOS+ subpopulation. While anti-PD-1 or anti-CTLA-4 ICT in tumor-bearing Bhlhe40-/- mice led to tumor outgrowth—several BHLHE40-dependent changes were specific to the ICT treatment that was administered.

Project description:Background: Evidence has recently accumulated suggesting that mature hepatocytes have the unique capacity to autonomously decide their replication fate. The molecular mechanism by which hepatocytes switch from an essentially quiescent state to rapidly proliferation after liver injury is not fully understood. To provide molecular insights into the self-renewal of mature hepatocytes, we have applied an ex vivo liver slice culture system. Results: After liver injury, activation of p38 and Erk1/2 began in mature hepatocytes within 5 min. Erk1/2 was activated at the edge of the cut as well as on the surface of liver slices. The number of hepatocytes that contain activated Erk1/2 increased within 1 h and then decreased. Concomitantly, immediate early genes (IEGs), such as Jun, early gene response 1 (Egr1) and Myc were induced and Ki67 positive hepatocytes appeared 24 h after liver injury in the slices. In agreement with in vivo studies, transcriptome analysis using 2 h slice culture reveals that 63% of upregulated genes were downstream of lipopolysaccharide (LPS) stimulation which induces interleukin 6 (IL 6) or tumor necrosis factor (TNF) alpha pathways. Furthermore, circadian clock regulator, such as members of the basic helix-loop-helix family, Bhlhe40 and Bhlhe41, were highly upregulated for 4 h after injury. Although upon injury Jun or Egr1 were induced in liver slices from proliferation-defective liver, no circadian clock regulator genes were upregulated. Moreover, using an in vitro cell culture system we show that Bhlhe40 is required for the G0-G1 transition. Conclusion: Our data suggest that the circadian clock regulator, Bhlhe40, is involved in the G0-G1 transition. An ex vivo system using normal and proliferation defective KO liver is a useful tool for identification of genes that trigger cell proliferation shortly after liver injury. This method may also be applied for measurement of the liver regeneration potential of individual livers at the priming phase. In one dual-color microarray hybridization, mRNA expression changes after 2h ex vivo incubation of liver slices were examined.

Project description:Nuclear receptor activation in liver leads to coordinated alteration of the expression of multiple gene products with attendant phenotypic changes of hepatocytes. Peroxisome proliferators including endogenous fatty acids, environmental chemicals, and drugs induce a multi-enzyme metabolic response that affects lipid and fatty acid processing. We studied the signaling network for the peroxisome proliferator-associated receptor alpha (PPARα) in primary human hepatocytes using the selective PPARα ligand, GW7647. We measured gene expression over multiple concentrations and times and conducted ChIP-seq studies at 2 and 24 hours to assess genomic binding of PPARα. Over all treatments there were 192 genes differentially expressed. Of these only 51% showed evidence of PPARα binding – either directly at PPARα response elements or via alternative mechanisms. Almost half of regulated genes had no PPARα binding. We then developed two novel bioinformatics methods to visualize the dose-dependent activation of both the transcription factor circuitry for PPARα and the downstream metabolic network in relation to functional annotation categories. Available databases identified several key transcription factors involved with the non-genomic targets after GW7647 treatment, including SP1, STAT1, ETS1, ERα, and HNF4α. The linkage from PPARα binding through gene expression likely requires intermediate protein kinases to activate these transcription factors. We found enrichment of functional annotation categories for organic acid metabolism and cell lipid metabolism among the differentially expressed genes. Lipid transport processes showed enrichment at the highest concentration of GW7647 (10μM). While our strategy for mapping transcriptional networks is evolving, these approaches are necessary in moving from toxicogenomic methods that derive signatures of activity to methods that establish pathway structure, showing the coordination of the activated nuclear receptor with other signaling pathways. Primary hepatocytes from four donors were exposed to 0, 0.001, 0.01, 0.1, 1.0, or 10.0μM GW7647 for 2, 6, 12, 24, or 72 hours.

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BHLHE40 role in hepatocytes exposed to high sugar content

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