无生长追赶出生低体重幼鼠生长激素/胰岛素样生长因子1轴抵抗与胰岛素抵抗的相关研究

目的探讨生后无生长追赶的出生低体重（NCU—SGA）幼鼠的胰岛素抵抗对生长激素（GH）抵抗的影响及其受体后信号转导机制。方法以母鼠孕期限制饮食法建立雄性NCU．SGA模型研究：（1）GH和胰岛素抵抗的关系：测定4周龄时24h尿GH排泄率（24hU—GH）,血胰岛素样生长因子（IGF）-1、空腹胰岛素（FINS）、血糖以及肝组织IGF-1mRNA和STATS信号表达;（2）胰岛素抵抗对生长轴的影响：3周龄时注射P13K阻断剂1周后（设溶剂对照组）,测定大鼠体格生长,血IGF-1、FINS水平及肝IGF-1mRNA和STATS信号表达。结果（1）NCU—SGA鼠血清IGF-1浓度、肝IGF-1mRNA表达以及磷酸化与总STAT蛋白表达水平的比率均显著低于健康对照组（C组）,分别为（248±58）ng／ml,（6．1±0．3）拷贝和（61±22）％;C组为（383±62）ng／ml,（6．6±0．4）拷贝和（91±29）％（均P〈0．01）;NCU—SGA组与C组的24hU-GH差异无统计学意义（P〉0．05）;NCU—SGA组FINS及空腹血糖为（24．7±9．6）mU／ml和（5．4±0．3）mmol／L显著高于C组的（9．8±2．8）mmol／L和（4．5±1．7）mmol／L（均P〈0．05）。24hU—GH与FINS显著正相关（r=0．680,P=0．000）。（2）PBK阻断后NCU．SGA鼠胰岛素抵抗加重,体重下降,血清IGF-1及肝IGF-1mRNA为（218±60）ng／ml及（6．1±0．3）拷贝,显著低于溶剂对照组的（286±45）ng／ml及（6．3±0．3）拷贝,均P〈0．05。但两组间肝组织总的及磷酸化STATS信号表达水平差异无统计学意义。结论NCU—SGA幼鼠的胰岛素抵抗与GH抵抗密切相关。生后无追赶与GH受体后JAK2-STATS通路受损所致的GH抵抗有关。胰岛素抵抗可能经非STATS依赖途径加重了GH抵抗及生长障碍。

Correlation between growth hormone/insulin-like growth factor-1 resistance and insulin resistance in non catch-up growth rats born small for gestational age

OBJECTIVE: To investigate the post-receptor signaling mechanism responsible for insulin resistance-induced growth hormone (GH) resistance in non-catch-up (NCU) growth rats born small for gestational age (SGA). METHODS: Twenty pregnant female SD rats were fed with restricted food (40% of normal intake, 9 g/d) throughout the pregnancy so as to develop NCU-SGA rats. The rats with their length and body weight < or = -2SD were out into the NCU-SGA group, and those with their length and body weight > -2SD were out into the catch-up (CU) growth group. Rats born to normally-fed pregnant rats were set as normal control (control Group, C Group, n = 17). The body weight and length were measured every 2 weeks. At the age of 4 weeks, 24 h urine was collected to measure the urine GH (U-GH). Then blood samples were collected to measure the serum insulin-like growth factor-1 (IGF-1), fasting insulin (FINS), and glucose levels, and the liver was taken out to detect the expression of STAT5 signal. Twelve 3-week NCU-SGA rats were divided into 2 equal groups: P13K blocking group, undergoing intraperitoneal injection of LY294002, blocker of P13K twice every 3 days, and solvent control group, undergoing intraperitoneal injection of DMSO. At the age of 4 weeks, blood samples were collected and then the liver was taken out to detect the IGF-1 mRNA and STAT5 signal. RESULTS: (1) The body weight and length at birth of the NCU-SGA group were (4.4 +/- 0.5) g and (4.5 +/- 0.2) cm, both significantly lower than those of Group C (6.8 +/- 0.6) g and (5.3 +/- 0.2) cm respectively], and the body weight and length at 4 weeks of age of the NCU-SGA group were (63 +/- 12) g and (13.2 +/- 1.0) cm respectively, both significantly lower than those of the C group (88 +/- 12) g and (15.3 +/- 0.5) cm respectively, all P < 0.01]. The serum IGF-1 level, IGF-1 mRNA expression, and total and phosphate STAT5 level in liver of the NCU-SGA group were (248 +/- 58) ng/ml, (6.1 +/- 0.3) copies, and (61 +/- 22)% respectively, all significantly lower than those of the C group (383 +/- 62) ng/ml, (6.6 +/- 0.4) copies, and (91 +/- 29)%, all P < 0.01]. There was no statistic difference in 24 h U-GH between the NCU-SGA and C groups (P > 0.05). The FINS and glucose level of the NCU-SGA group were (24.7 +/- 9.6) mU/ml and (5.4 +/- 0.3) mmol/L respectively, both significantly higher than those of the C group (9.8 +/- 2.8) mU/ml and (4.5 +/- 1.7) mmol/L respectively, both P < 0.05]. The level of 24 h U-GH was positively correlated with FINS (r = 0.680, P = 0.000). No correlation was found between IGF-1 and fasting insulin level. (2) After the PI3K pathway was chronically blocked, the NCU-SGA rats lost weight and developed a more severe insulin resistance, decreased serum IGF-1 level and the IGF-1 mRNA expression level of the PI3K inhibitor group were (218 +/- 60) ng/ml and (6.1 +/- 0.3) copies respectively, both significantly lower than those of the solvent control group (286 +/- 45) ng/ml and (6.3 +/- 0.3) copies, both P < 0.05]. No statistically significant difference in total and phosphate STAT5 levels in liver between the P13K blocker and solvent groups. CONCLUSION: GH resistance is closely associated with insulin resistance in the NCU-SGA rats. GH resistance-induced failure of catch-up growth is related to the impairment of JAK2-STAT5 pathway. Insulin resistance exacerbates growth axis resistance and growth retardation in NCU-SGA rats via a non-STAT5 dependent pathway.