Monroy A, Kamath S, Chavez A O, Centonze V E, Veerasamy M, Barrentine A, Wewer J J, Coletta D K, Jenkinson C, Jhingan R M, Smokler D, Reyna S, Musi N, Khokka R, Federici M, Tripathy D, DeFronzo R A, Folli F
Department of Medicine, University of Texas Health Science Center at San Antonio, 78229-3900, USA.
Diabetologia. 2009 Oct;52(10):2169-81. doi: 10.1007/s00125-009-1451-3. Epub 2009 Jul 25.
AIMS/HYPOTHESIS: TNF-alpha levels are increased in obesity and type 2 diabetes. The regulation of TNF-alpha converting enzyme (TACE) and its inhibitor, tissue inhibitor of metalloproteinase 3 (TIMP3), in human type 2 diabetes is unknown.
We examined TACE/TIMP3 regulation: (1) in lean and obese normal glucose tolerant (NGT) individuals and in type 2 diabetes patients; (2) following 6 h of lipid/saline infusion in NGT individuals; and (3) in cultured human myotubes from lean NGT individuals incubated with palmitate. Insulin sensitivity was assessed by a euglycaemic clamp and TACE/TIMP3 was evaluated by confocal microscopy, RT-PCR, western blotting and an in vitro activity assay. Circulating TNF-alpha, TNF-alpha-receptor 1 (TNFR1), TNF-alpha-receptor 2 (TNFR2), IL-6 receptor (IL-6R), vascular cell adhesion molecule (VCAM) and intercellular adhesion molecule (ICAM) levels were evaluated.
TIMP3 levels were reduced and TACE enzymatic activity was increased in type 2 diabetes skeletal muscle. TACE expression, and TACE, TNF-alpha, TNFR1 and IL-6R levels were increased in type 2 diabetes, and positively correlated with insulin resistance. A 6 h lipid infusion into NGT individuals decreased insulin-stimulated glucose metabolism by 25% with increased TACE, decreased expression of the gene encoding TIMP3 and increased IL-6R release. Palmitate induced a dramatic reduction of TIMP3 and increased the TACE/TIMP3 ratio in cultured myotubes.
CONCLUSIONS/INTERPRETATION: TACE activity was increased in skeletal muscle of obese type 2 diabetes patients and in lipid-induced insulin resistance. We propose that dysregulation of membrane proteolysis by TACE/TIMP3 of TNF-alpha and IL-6R is an important factor for the development of skeletal muscle insulin resistance in obese type 2 diabetes patients by a novel autocrine/paracrine mechanism.
目的/假设：肥胖症和2型糖尿病患者体内的肿瘤坏死因子-α（TNF-α）水平升高。人类2型糖尿病中肿瘤坏死因子-α转换酶（TACE）及其抑制剂金属蛋白酶组织抑制剂3（TIMP3）的调节机制尚不清楚。
我们研究了TACE/TIMP3的调节情况：（1）在体重正常和肥胖的糖耐量正常（NGT）个体以及2型糖尿病患者中；（2）在NGT个体中输注脂质/生理盐水6小时后；（3）在来自体重正常的NGT个体的培养人肌管中用棕榈酸酯孵育。通过正常血糖钳夹评估胰岛素敏感性，通过共聚焦显微镜、逆转录-聚合酶链反应（RT-PCR）、蛋白质印迹法和体外活性测定评估TACE/TIMP3。评估循环中的TNF-α、TNF-α受体1（TNFR1）、TNF-α受体2（TNFR2）、白细胞介素-6受体（IL-6R）、血管细胞黏附分子（VCAM）和细胞间黏附分子（ICAM）水平。
2型糖尿病患者骨骼肌中TIMP3水平降低，TACE酶活性增加。2型糖尿病患者中TACE表达以及TACE、TNF-α、TNFR1和IL-6R水平升高，且与胰岛素抵抗呈正相关。向NGT个体输注脂质6小时使胰岛素刺激的葡萄糖代谢降低25%，同时TACE增加、编码TIMP3的基因表达降低以及IL-6R释放增加。棕榈酸酯使培养的肌管中TIMP3显著减少，并增加TACE/TIMP3比值。
结论/解读：肥胖的2型糖尿病患者骨骼肌以及脂质诱导的胰岛素抵抗中TACE活性增加。我们提出，TACE/TIMP3对TNF-α和IL-6R的膜蛋白水解失调是肥胖2型糖尿病患者通过一种新的自分泌/旁分泌机制发生骨骼肌胰岛素抵抗的重要因素。
