Forkhead Transcription Factor FoxO1 in Adipose Tissue Regulates Energy Storage and Expenditure

Abstract

OBJECTIVE-Adipose tissue serves as an integrator of various physiological pathways, energy balance, and glucose homeostasis. Forkhead box-containing protein O subfamily (FoxO) 1 mediates insulin action at the transcriptional level. However, physiological roles of FoxO1 in adipose tissue remain unclear.RESEARCH DESIGN AND METHODS-In the present study, we generated adipose tissue-specific FoxO1 transgenic mice (adipocyte protein 2 [aP 2 ]-FLAG-⌬256) using an aP 2 promoter/ enhancer and a mutant FoxO1 (FLAG⌬256) in which the carboxyl terminal transactivation domain was deleted. Using these mice, we analyzed the effects of the overexpression of FLAG⌬256 on glucose metabolism and energy homeostasis. RESULTS-The aP 2 -FLAG-⌬256 mice showed improved glucose tolerance and insulin sensitivity accompanied with smallersized adipocytes and increased adiponectin (adipoq) and Glut 4 (Slc2a4) and decreased tumor necrosis factor ␣ (Tnf) and chemokine (C-C motif) receptor 2 (Ccr2) gene expression levels in white adipose tissue (WAT) under a high-fat diet. Furthermore, the aP 2 -FLAG-⌬256 mice had increased oxygen consumption accompanied with increased expression of peroxisome proliferator-activated receptor ␥ coactivator (PGC)-1␣ protein and uncoupling protein (UCP)-1 (Ucp1), UCP-2 (Ucp2), and ␤3-AR (Adrb3) in brown adipose tissue (BAT). Overexpression of FLAG⌬256 in T37i cells, which are derived from the hibernoma of SV40 large T antigen transgenic mice, increased expression of PGC-1␣ protein and Ucp1. Furthermore, knockdown of endogenous FoxO1 in T37i cells increased Pgc1␣ (Ppargc1a), Pgc1␤ (Ppargc1b), Ucp1, and Adrb3 gene expression.CONCLUSIONS-These data suggest that FoxO1 modulates energy homeostasis in WAT and BAT through regulation of adipocyte size and adipose tissue-specific gene expression in response to excessive calorie intake. Diabetes 57:563-576, 2008

PDK-1/FoxO1 pathway in POMC neurons regulatesPomcexpression and food intake

“…However, Pomc expression level in ⌬256FoxO1 POMC Pdk1 Ϫ/Ϫ was similar to that in POMCPdk1 Ϫ/Ϫ mice, and the hypothalamic phenotype of POMCPdk1 Ϫ/Ϫ mice was not rescued. We have to remember that this transactivation-defective FoxO1 is not sufficient for complete loss-of-function of FoxO1 and that ⌬256FoxO1 used in the present study still has the NH 2 terminus and forkhead DNAbinding domain, and these domains could bind to some cofactors for transcription of FoxO1 target genes in a tissue-or cell type-specific manner (24). Interestingly, the ChIP assay demonstrated that ⌬256FoxO1 bound to Pomc promoter and phosphorylated STAT3 dissociated from Pomc promoter in ⌬256FoxO1 POMC Pdk1 Ϫ/Ϫ mice as well as POMCPdk1 Ϫ/Ϫ and CNFoxO1 POMC Pdk1 Ϫ/Ϫ mice.…”

“…We carried out all assays in duplicate; each value represents the means of two independent determinations. Intraperitoneal glucose tolerance tests, insulin tolerance tests, and computed tomography (CT) scans were performed as previously described (24). The measurement of serum corticosterone was performed using the Corticosterone Correlate-EIA Kit (Assay Designs).…”

“…The measurement of serum T 4 was performed using the Rodent T4 ELISA Test Kit (Endocrine Technology). The measurements of serum insulin and leptin levels were performed as previously described (24).…”

“…Isolation of total RNA from the hypothalamus was performed using the SV Total RNA Isolation System (Promega) according to the manufacturer's protocol. Real-time PCR was also performed as previously described (24). The primers used in this study were described previously (24).…”

“…Real-time PCR was also performed as previously described (24). The primers used in this study were described previously (24). We used the following primers for amplification of Pomc 5=-AGACCTCCATAGATGTGTGGA-3= (sense) and 5=-AGCGGAAGTGACCCATGACGT-3= (antisense): AgRP 5=-ATGCT-GACTGCAATGTTGCTG-3= (sense) and 5=-TGAGGCCATTCAGACT-TAGAC-3= (antisense); Npy 5=-AAGCCGGACAATCCGGGCCGAGG-3= (sense) and 5=-GCTTTCCTCATTAAGAGGTCT-3= (antisense); Cart 5=-ATCTACTCTGCCGTGGATGAT-3= (sense) and 5=-TTCCTCACTGCG-CACTGCTGT-3= (antisense).…”