人類腹部脂肪組織中visfatin/PBEF訊息核糖核酸表現量與新陳代謝表現型之關連以及其調節機轉

Abstract

脂肪組織會產生許多分泌性物質, 稱為脂肪激素(adipokines), 在人體的能量新陳代謝中扮演重要角色。 最近, 以基因差異表現方法(differential display method)找尋到一種新的可能的脂肪激素, 稱為visfatin/PBEF。研究顯示visfatin/PBEF在人類和小鼠身體中, 主要是表現在內臟脂肪組織(visceral fat), 而非皮下脂肪組織(subcutaneous fat), 而且其血清濃度會隨著肥胖而增高。Visfatin/PBEF在週邊組織會和胰島素受器結合, 具有類似胰島素的作用, 可以降低血糖。 為了釐清visfatin/PBEF在人體內的作用, 我們利用定量即時聚合酶鍊反應(quantitative real-time polymerase chain reaction, RT-PCR), 測定62位臺灣成年人中, 腹部內臟脂肪組織及皮下脂肪組織中visfatin/PBEF mRNA表現量, 並研究其與新陳代謝表現型(metabolic phenotypes)的關連。 我們發現visfatin/PBEF mRNA表現量在皮下脂肪組織中較在內臟脂肪組織中高(以比較閾值次數值comparative threshold cycle values △Ct 表示: -0.75 ± 2.71 v.s. –1.36 ± 2.47; p= 0.04), 尤其是在肥胖的人身上 (△Ct: -0.53 ± 2.57 v.s. –1.46 ± 2.41; p= 0.006)。兩者和身體質量指數(body mass index)皆無相關。皮下脂肪組織中visfatin/PBEF mRNA和飯前血清中胰島素濃度呈現正相關(r= 0.40, p= 0.008), 和胰島素阻抗指標Homeostasis Model Assessment (HOMA-IR) 也呈現正相關(r= 0.35, p= 0.02)。 我們進一步利用小鼠RAW 267.4 巨噬細胞株以及3T3-L1脂肪細胞株(這兩種細胞為脂肪組織中兩種主要表現visfatin/PBEF的細胞類型)為模型, 釐清脂肪組織中visfatin/PBEF 蛋白質表現可能的調節機轉。我們發現長時間(96小時)的游離脂肪酸(free fatty acids), 包括palmitate和oleate, 會大量增加巨噬細胞visfatin/PBEF的表現, 同時也會增加iNOS表現。NF-κB 抑制劑 parthenolide會抑制此作用, 而NF-κB促進劑 lipopolysaccharide會增加visfatin/PBEF表現。依此推測, 游離脂肪酸可能會經由活化NF-κB 而增加visfatin/PBEF表現。 Aspirin 及sodium salicylate為已知具有抑制 NF-κB 活性之非類固醇抗發炎藥物, 也會抑制visfatin/PBEF在巨噬細胞的表現, 相反的, ketorolac或indomethacin等其他非類固醇抗發炎藥物則沒有此作用。15-deoxy-Δ12,14-prostaglandin J2 是已知具有抑制NF-κB 活化作用的內生性peroxisome proliferator-activated receptor-γ(PPAR-γ)促進劑, 也會抑制visfatin/PBEF在巨噬細胞的表現, 相反的, 合成PPAR-γ促進劑rosiglitazone則沒有此作用。 簡言之, 我們的研究顯示高胰島素阻抗性的人其腹部皮下脂肪組織visfatin/PBEF mRNA表現量增加, 這增加可能和脂肪組織內巨噬細胞受游離脂肪酸刺激而活化有關。

Context: Visfatin/PBEF was recently identified as an adipocytokine predominantly expressed and secreted in visceral adipose tissue with insulin-mimetic effect in peripheral tissues. Objectives: The goals were to investigate the association of visfatin/PBEF gene expresion in human abdominal adipose tissue with metabolic phenotypes and to identify the regulatory mechanism of visfatin/PBEF expression in cultured cells. Subjects and Methods: Relative visfatin/PBEF mRNA levels in human abdominal visceral and subcutaneous adipose tissues were determined by quantitative real-time polymerase chain reaction for correlation with metabolic phenotypes. Regulation of visfatin/PBEF expression by humoral factors was examined using cultured murine3T3-L1 adipocytes and RAW 264.7 macrophages. Results: Relative visfatin/PBEF mRNA levels in abdominal subcutaneous adipose tissue were higher than those in visceral adipose tissue and neither correlated with BMI. Relative visfatin/PBEF mRNA levels in abdominal subcutaneous adipose tissue correlated positively with fasting plasma insulin concentrations and with the insulin resistance index by Homeostasis Model Assessment(HOMA-IR). Free fatty acids (palmitate and oleate) and lipopolysaccharide stimulated visfatin/PBEF expression in RAW 264.7 macrophages but not 3T3-L1 adipocytes; the stimulation was mediated by NF-κB activation. Treatment with aspirin, sodium salicylate, or 15-deoxy-Δ12,14-prostaglandin J2 (15-d-PGJ2), but not indomethacin, ketorolac or rosiglitazone, suppressed visfatin/PBEF expression in RAW 264.7 macrophages.

Conclusions: Visfatin/PBEF mRNA expression in abdominal subcutaneous adipose tissue is increased in hyperinsulinemic and insulin-resistant subjects. Visfatin/PBEF expression is induced by free fatty acids and inflammatory stimuli in macrophages rather than adipocytes. These findings support linkages among insulin resistance, macrophage activation, and increased visfatin/PBEF expression.