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Conditional overexpression of PPARα in intestinal epithelium diminishes GIP enteroendocrine cells and circulating hormone levels

ABSTRACT: PPARα transcriptional programs have tissue-dependent features, yet there is a lack of genetic research tools to study tissue-specific signaling activation without the addition of a systemic agonist. Our aim was to investigate intestinal epithelial-specific roles of PPARα signaling using a novel transgenic mouse that enables spatial and temporal control of Ppara overexpression. CAG-Ppara,-EGFP mice were bred to Villin-CreERT2 to establish the IEC-Ppara mouse, which was compared to littermate controls 2 weeks after tamoxifen exposure. Transcriptional analysis of intestinal tissue from IEC-Ppara mice showed upregulation of PPARα target genes and functional enrichment for fatty acid catabolic processes. Unexpectedly, the enteroendocrine hormone Gip was among the most downregulated genes. GIP-positive enteroendocrine cell number, GIP circulating hormone, and the incretin response were also reduced in IEC-Ppara mice. These findings reveal PPARα as a regulator of GIP and support a new framework in which PPARα signaling influences glucose homeostasis via a gut hormone axis

ORGANISM(S): Mus musculus

PROVIDER: GSE336031 | GEO | 2026/08/14

REPOSITORIES: GEO

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Project description:Immune-mediated beta cell destruction and lack of alpha cell responsiveness to hypoglycaemia are hallmarks of type 1 diabetes pathology. The incretin hormone glucose-dependent insulinotropic polypeptide (GIP) may hold therapeutic potential for type 1 diabetes due to its insulinotropic and glucagonotropic effects as well as its beta cell protective effects shown in rodent islets. Here, we examined the functional and transcriptomic effects of GIP treatment upon diabetogenic cytokine exposure to interleukin (IL)-1β ± interferon (IFN)-γ in human EndoC-βH5 beta cells and isolated human islets, respectively. GIP dose-dependently augmented glucose-stimulated insulin secretion from EndoC-βH5 cells and increased insulin and glucagon secretion from human islets during high and low glucose concentrations, respectively. The insulinotropic effect of GIP in EndoC-βH5 cells was abrogated by KN-93, an inhibitor of calcium/calmodulin-dependent protein kinase 2 (CaMK2). GIP did not prevent cytokine-induced apoptosis or cytokine-induced functional impairment of human EndoC-βH5 cells. GIP also did not prevent cytokine-induced apoptosis in human islets. GIP treatment of human islets with or without cytokines for 24 hours did not significantly impact the transcriptome. GIP potentiated cytokine-induced secretion of IL-10 and c-c motif chemokine ligand (CCL)-2 from human islets while decreasing the secretion of c-x-c motif chemokine ligand (CXCL)-8. In EndoC-βH5 cells, GIP reduced IFN-γ-induced secretion of tumor necrosis factor (TNF)-α, IL-2, IL-6, and IL-10, but increased the secretion of CXCL8, CCL2, CCL4, and CCL11. In conclusion, our results suggest that the insulinotropic effect of GIP is CaMK2-dependent. Furthermore, our results indicate that GIP does not provide substantial cytoprotective effects against diabetogenic cytokine challenge or significantly modulate the transcriptome of human islets when applied at a supraphysiological level. GIP may, however, still exert selective inflammation-modulatory effects upon diabetogenic cytokine exposure.

Project description:Abstract submitted to the Journal of clinical encodcrinology and metabolism: The molecular mechanisms responsible for the ectopic expression of the GIP receptor in the adrenal cortex of patients with GIP-dependent Cushing’s syndrome (CS) are unknown. Chronic adrenal stimulation by ACTH in Cushing’s disease (CD) or by GIP in GIP-dependent AIMAH both lead to induction of a set of genes which stimulate adrenal proliferation and steroidogenesis. The objective of this study was to compare the whole genome expression profile of adrenal glands of five cases of GIP-dependent bilateral macronodular adrenal hyperplasia with CS, one case of GIP-dependent adenoma, compared to five cases of ACTH-dependant hyperplasias (CD) and a pool of adrenals from 62 normal individuals. We used the genome-spanning Affymetrix U133 plus 2.0 microarray oligochips to identify genes differentially expressed specifically in GIP-dependent CS and which would be candidate genes implicated in the ectopic expression of the GIP receptor in the adrenal cortex. After data normalization and filtering, genes with differential expression were identified with a multi-step statistical analysis involving a student’s t-test, a filter on flags and a SAM analysis. A total of 721 probesets were thus isolated with intensity levels robustly related to the presence of a GIP-dependent hyperplasia. We performed a functional classification to further define potentially important biological processes and signaling mechanism for the formation of GIP-dependent AIMAH. Various probesets were related to metabolic processes, cell-surface and intracellular signaling, tumorigenesis, transport and transcription factors. The most relevant genes had their expression profile confirmed by real-time RT-PCR. This study reports an extensive series of potentially novel targets in the identification of the molecular mechanisms of ectopic expression of the GIP-receptor in this pathology. Keywords: Comparative genomic analysis

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Conditional overexpression of PPARα in intestinal epithelium diminishes GIP enteroendocrine cells and circulating hormone levels

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