Molecular mechanisms for dysfunction of obese adipose tissue focusing on the network of NADPH producing enzymes and intracellular glucocorticoid reactivating enzyme

2007年度～2009年度科学研究費補助金（基盤研究(Ｂ)）研究成果報告書研究概要（和文）：肥満の脂肪組織で細胞内グルココルチコイド活性化酵素、11β-HSD1 の活性が亢進するメカニズムに関して 肥満脂肪組織で普遍的に観察される 炎症シグナルの亢進、セラミドシグナルの亢進、酸化ストレスの亢進との関連において ヒト、マウスの培養脂肪細胞と脂肪組織で検証した。前駆脂肪細胞における11β-HSD1 活性は種々の炎症性サイトカインやセラミド系によって誘導され、11β-HSD1 の阻害は細胞における炎症シグナルを有意に抑制した。また、ヒト、マウスの肥満脂肪組織では11β-HSD1 の最大活性化に必要な補因子、NADPH を供給し、それ自体が酸化ストレス誘導因子、中性脂肪合成を担うG6PD などペントース経路を構成する一連のNADPH 供給酵素の発現や活性が上昇しており、培養脂肪細胞系におけるヒト型Ｇ６ＰＤの過剰発現が11β-HSD1 酵素活性を顕著に誘導し、培地中へのコルチゾル分泌を有意に増加させることが明らかとなった。本研究により、肥満脂肪組織の機能異常に これらの酵素ネットワーク系の機能異常が関与することが初めて明らかとなった。研究概要（英文） : Elevated expression and activity of the intracellular glucocorticoid reactivating enzyme, 11beta-hydroxysteroid dehydrogenase type 1 (11 β -HSD1), contribute to dysfunction of obese adipose tissue. Although the pathophysiologic role of 11β-HSD1 in obese adipose tissue has long been investigated, the mechanism whereby 11β-HSD1 is augmented in obese adipose tissue still remains obscure. In this context, in the present study, we investigated the possible involvement of chronic inflammation, oxidative stress, ceramide signals and NADPH provision from enzymes comprising of pentose pathways. In cultured adipocytes and SVF cells from obese adipose tissue from mice, enzyme activity and expression of 11 β -HSD1 was augmented by TNF α , IL-1 β , LPS and ceramide. Pharmacological inhibition of 11β-HSD1 and RNA interference against 11β-HSD1 reduced a line of pro-inflammatory molecules as well as substantially attenuated NF-kβ and MAPK inflammatory signaling in cultured adipocytes. Expression of enzymes comprising of pentose pathways was elevated in obese adipose tissue in proportion to the degree of obesity in both humans and mice. Forced expression of glucose-6-phosphate ehydrogenase (G6PD), a member of pentose pathways, in adipocytes augmented intracellular glucocorticoid reamplification and resultant secretion of cortisol into the media, indicating a functional link between 11β-HSD1 and NADPH provision in obese adipose tissue. Our data highlight an unexpected role of reamplified glucocorticoids and molecular basis for augmented 11β-HSD1 in obese adipose tissue