Yao Jun, Zhang Ting-ting, Duan Yu-min, Guo Xiao-hui
Department of Endocrinology, Peking University First Hospital, Beijing 100034, China.
Beijing Da Xue Xue Bao Yi Xue Ban. 2010 Oct 18;42(5):514-9.
To observe the characteristics of lipolysis in epididymal adipose tissues of spontaneously type 2 diabetic animal model-Otsuka Long-Evans Tokushima Fatty (OLETF) rats-in different stages of disease and explore the possible molecular mechanism.
We adopted OLETF rats as subjects, and Long-Evans Tokushima Otsuka (LETO) rats were used as age-matched normal controls. Oral glucose tolerance tests (OGTT) and fasting serum insulin levels were performed respectively at the ages of 8, 18 and 28 weeks. The animals were sacrificed and epididymal fat pads were obtained in corresponding weeks. Glycerol released in the culture medium was determined by use of a colorimetric assay and served as an index of lipolysis. The protein levels of hormone-sensitive lipase (HSL), adipose triglyceride lipase (ATGL), perilipin, extracellular signal-regulated kinase (ERK) and its phosphorylated form (p-ERK) in epididymal fat were examined by immunoblotting.
(1) Compared with the age-matched normal control, the ratio of epididymal adipose tissues to total body weight was heavier at the end of 18 weeks [(1.80±0.09)% vs (1.23±0.07)%, P<0.01] and 28 weeks [(2.51±0.12)% vs (1.56±0.08)%, P<0.01]; In OGTT 1 h plasma glucose levels of OLETF rats were higher at the age of 18 weeks [(26.00±3.09) vs (10.50±0.82) mmol/L, P<0.01] and 28 weeks [(23.15±0.55) vs (9.72±0.17) mmol/L, P<0.01] and 2 h plasma glucose levels were higher at the age of 18 weeks [(16.19±1.22) vs (7.47±0.35) mmol/L, P<0.01] and 28 weeks [(17.96±2.00) vs (9.24±0.47) mmol/L, P<0.01]. The level of fasting insulin was higher in OLETF rats than that of LETO rats only at the age of 28 weeks [(68.17±13.35)×10(-3) vs (19.61±0.20)×10(-3) U/L, P<0.01]. (2) Glycerol released from epididymal adipose tissues of OLETF rats was increased by 34.7% compared with LETO rats at the age of 18 weeks [(213.0±12.5) vs (158.2±11.7) nmol/(g×h), P<0.05], whereas at the age of 28 weeks, it was reduced by 33.5% [(210.2±37.8) vs (315.9±25.0) nmol/(g×h), P<0.05]. (3) In OLETF rats, HSL protein level was not altered at the age of 18 weeks, but down-regulated at the age of 28 weeks. Nevertheless, the expressions of ATGL and perilipin were decreased, while p-ERK protein expression was increased at the age of both 18 and 28 weeks.
With the development of disease in spontaneously type 2 diabetic animal model of OLETF rats, the lipolysis in epididymal adipose tissue presented a pattern of initial increase followed by subsequent reduction. The earlier augment may contribute to the higher expression of p-ERK and the lower content of perilipin, however the later decrease may result from the reduction of both HSL and ATGL level.
观察自发性2型糖尿病动物模型——大冢长- Evans德岛肥胖（OLETF）大鼠附睾脂肪组织在疾病不同阶段的脂解特征，并探讨其可能的分子机制。
以OLETF大鼠为研究对象，选用年龄匹配的长- Evans德岛大冢（LETO）大鼠作为正常对照。分别在8周、18周和28周龄时进行口服葡萄糖耐量试验（OGTT）和空腹血清胰岛素水平检测。在相应周龄处死动物并获取附睾脂肪垫。采用比色法测定培养基中释放的甘油，作为脂解指标。通过免疫印迹法检测附睾脂肪中激素敏感性脂肪酶（HSL）、脂肪甘油三酯脂肪酶（ATGL）、围脂滴蛋白、细胞外信号调节激酶（ERK）及其磷酸化形式（p - ERK）的蛋白水平。
（1）与年龄匹配的正常对照相比，18周龄末附睾脂肪组织与总体重的比值较重[（1.80±0.09）%对（1.23±0.07）%，P<0.01]，28周龄时亦如此[（2.51±0.12）%对（1.56±0.08）%，P<0.01]；18周龄时OLETF大鼠OGTT 1小时血浆葡萄糖水平较高[（26.00±3.09）对（10.50±0.82）mmol/L，P<0.01]，28周龄时同样较高[（23.15±0.55）对（9.72±0.17）mmol/L，P<0.01]，且18周龄时OGTT 2小时血浆葡萄糖水平较高[（16.19±1.22）对（7.47±0.35）mmol/L，P<0.01]，28周龄时也较高[（17.96±2.00）对（9.24±0.47）mmol/L，P<0.01]。仅在28周龄时，OLETF大鼠的空腹胰岛素水平高于LETO大鼠[（68.17±13.35）×10⁻³对（19.61±0.20）×10⁻³U/L，P<0.01]。（2）18周龄时，OLETF大鼠附睾脂肪组织释放的甘油较LETO大鼠增加34.7%[（213.0±12.5）对（158.2±11.7）nmol/（g·h），P<0.05]，而在28周龄时，减少了33.5%[（210.2±37.8）对（315.9±25.0）nmol/（g·h），P<0.05]。（3）在OLETF大鼠中，18周龄时HSL蛋白水平未改变，但在28周龄时下调。然而，18周龄和28周龄时ATGL和围脂滴蛋白的表达均降低，而p - ERK蛋白表达增加。
在自发性2型糖尿病OLETF大鼠动物模型中，随着疾病发展，附睾脂肪组织的脂解呈现出先增加后减少的模式。早期增加可能与p - ERK表达升高和围脂滴蛋白含量降低有关，而后期减少可能是由于HSL和ATGL水平降低所致。
