title: Transcriptional regulatory factor X6 (Rfx6) increases gastric inhibitory polypeptide (GIP) expression in enteroendocrine K-cells and is involved in GIP hypersecretion in high fat diet-induced obesity.
abstract: Gastric inhibitory polypeptide (GIP) is an incretin released from enteroendocrine K-cells in response to nutrient ingestion. GIP potentiates glucose-stimulated insulin secretion and induces energy accumulation into adipose tissue, resulting in obesity. Plasma GIP levels are reported to be increased in the obese state. However, the molecular mechanisms of GIP secretion and high fat diet (HFD)-induced GIP hypersecretion remain unclear, primarily due to difficulties in separating K-cells from other intestinal epithelial cells in vivo. In this study, GIP-GFP knock-in mice that enable us to visualize K-cells by enhanced GFP were established. Microarray analysis of isolated K-cells from these mice revealed that transcriptional regulatory factor X6 (Rfx6) is expressed exclusively in K-cells. In vitro experiments using the mouse intestinal cell line STC-1 showed that knockdown of Rfx6 decreased mRNA expression, cellular content, and secretion of GIP. Rfx6 bound to the region in the gip promoter that regulates gip promoter activity, and overexpression of Rfx6 increased GIP mRNA expression. HFD induced obesity and GIP hypersecretion in GIP-GFP heterozygous mice in vivo. Immunohistochemical and flow cytometry analysis showed no significant difference in K-cell number between control fat diet-fed (CFD) and HFD-fed mice. However, GIP content in the upper small intestine and GIP mRNA expression in K-cells were significantly increased in HFD-fed mice compared with those in CFD-fed mice. Furthermore, expression levels of Rfx6 mRNA were increased in K-cells of HFD-fed mice. These results suggest that Rfx6 increases GIP expression and content in K-cells and is involved in GIP hypersecretion in HFD-induced obesity.
authors.affiliation: Department of Diabetes and Clinical Nutrition, Graduate School of Medicine, Kyoto University, 54 Kawahara-cho, Shogoin, Kyoto 606-8507, Japan.
authors.forename: Kazuyo
authors.initials: K
authors.lastname: Suzuki
authors.forename: Norio
authors.initials: N
authors.lastname: Harada
authors.forename: Shunsuke
authors.initials: S
authors.lastname: Yamane
authors.forename: Yasuhiko
authors.initials: Y
authors.lastname: Nakamura
authors.forename: Kazuki
authors.initials: K
authors.lastname: Sasaki
authors.forename: Daniela
authors.initials: D
authors.lastname: Nasteska
authors.forename: Erina
authors.initials: E
authors.lastname: Joo
authors.forename: Kimitaka
authors.initials: K
authors.lastname: Shibue
authors.forename: Takanari
authors.initials: T
authors.lastname: Harada
authors.forename: Akihiro
authors.initials: A
authors.lastname: Hamasaki
authors.forename: Kentaro
authors.initials: K
authors.lastname: Toyoda
authors.forename: Kazuaki
authors.initials: K
authors.lastname: Nagashima
authors.forename: Nobuya
authors.initials: N
authors.lastname: Inagaki
mesh_terms: D000273:Adipose Tissue / Q000378:metabolism* / Q000473:pathology; D000818:Animals; D004268:DNA-Binding Proteins / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism; D059305:Diet, High-Fat / Q000009:adverse effects; D019858:Enteroendocrine Cells / Q000378:metabolism* / Q000473:pathology; D005749:Gastric Inhibitory Polypeptide / Q000235:genetics* / Q000378:metabolism; D015870:Gene Expression; D055879:Gene Knock-In Techniques; D017930:Genes, Reporter; D005947:Glucose / Q000378:metabolism; D049452:Green Fluorescent Proteins; D007328:Insulin / Q000378:metabolism; D007413:Intestinal Mucosa / Q000378:metabolism / Q000473:pathology; D051379:Mice; D008822:Mice, Transgenic; D009765:Obesity / Q000209:etiology / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D020411:Oligonucleotide Array Sequence Analysis; D061251:Primary Cell Culture; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D034741:RNA, Small Interfering; D000071701:Regulatory Factor X Transcription Factors; D015398:Signal Transduction; D014157:Transcription Factors / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism
chemical_list: D004268:DNA-Binding Proteins; D007328:Insulin; D034741:RNA, Small Interfering; D000071701:Regulatory Factor X Transcription Factors; C547963:Rfx6 protein, mouse; D014157:Transcription Factors; D049452:Green Fluorescent Proteins; D005749:Gastric Inhibitory Polypeptide; D005947:Glucose