胸腺肽a1对小鼠新生期感染所致学习记忆障碍的影响

Protective effect of thymosin alpha-1 on postnatal systemic inflammation induced learning and memory impairment in mice

目的探讨胸腺肽a1对新生小鼠持续感染所致学习记忆障碍的影响及其相关机制。方法（1）新生C57BL／6小鼠24只按随机数字表法分为生理盐水组、0-3mg／kg脂多糖（LPS）剂量组、0．6mg/kgLPS剂量组、0．9mg／kgLPS剂量组，分别连续5d注射等量生理盐水和不同剂量LPS。观察各组小鼠体质量、相对肝重变化及血清、脑组织肿瘤坏死因子-α（TNF-α）含量，以确定模拟临床新生儿感染的LPS剂量。（2）取60只新生小鼠按随机数字表分为3组：对照组、LPS组、胸腺肽a1处理组，分别连续5d注射等量生理盐水、LPS（0．6mg／kg）和胸腺肽a1（0．4mg／kg）＋LPS（0．6mg／kg）。在4周和8周时，采用Morris水迷宫实验检测各组小鼠的学习记忆能力，采用ELISA法检测海马组织TNF-α、白介素-1β（IL-1β）、脑源性神经营养因子（BDNF）和神经生长因子（NGF）含量，采用Western blotting检测海马组织Toll样受体4（TLR4）和核转录因子-κB（NF-κB）蛋白表达水平。结果（1）与生理盐水组相比，0．6mg／kgLPS剂量组小鼠生长缓慢[（2．23±0．22）g vs （1．18±0．21）g]、相对肝重增加（0．052±0．004 vs 0．072±0．007）、血清及脑组织TNF-α含量[（62．01±3．32）pg／mL vs（151．06±14．51）pg／mL；（186．03±13．24）pg／mL vs（298．71±41．61）pg／mL]明显增高，差异均有统计学意义（P〈0．05）。（2）与LPS组相比，胸腺肽a1处理组小鼠定位航行实验中逃避潜伏期明显缩短，空间探索实验中目标象限停留时间明显延长，海马组织TNF-α、IL．1B、TLR4、NF-κB蛋白表达明显降低[（73．32±5．18）pg／mL vs（58．61±4．03）pg／mL；（99．15±8．30）pg／mL vs（75．56±6．13）pg／mL；2．32±0．29 vs 1．71±0．26；1．77±0．24 vs 1．26±0．141，BDNF、NGF蛋白表达明显增高[（1．33±0．12）pg／mL／）8（1．69±0．25）pg／mL；（41．45±3．47）pg／mL vs（50．38±5．02）pg／mL]，差异均有统计学意义（P＜0．05）。结论胸腺肽a1可以改善小鼠新生期感染导致的学习记忆障碍和神经炎症，其途径是通过抑制TLR4／NF-κB信号通路传导和提高神经营养因子水平。

Objective To explore the effect ofthymosin alpha-1 （Tal） on postnatal systemic inflammation-induced learning and memory impairment in mice and their relevant mechanism. Methods （I） Twenty-four neonatal C57BL/6 mice were randomly assigned into normal saline group, lipopolysaccharide （LPS, 0.3 mg/kg） group, LPS （0.6 mg/kg） group, and LPS （0.9 mg/kg） group. And the animals were intraperitoneally injected with different doses of LPS or equal volume of saline for 5 days. The variations of body weight, liver weight relative to the body and tumor necrosis factor-α （TNF-α） level in serum and brain tissues were observed to determine the appropriate dose of LPS for simulating neonatal clinical infection. （2） A total of 60 newborn mice were randomly divided into three groups： control group, LPS group and Tal treatment group; mice in each group were continuously injected with equal volume saline, LPS （0.6 mg/kg） and Tal （0.4 mg/kg）±LPS （0.6 mg/kg） for 5 days. On day 28 and on day 56, Morris water maze was used to measure the spatial learning and memory abilities of mice; the concentrations of TNF-α, interleukin-1β （IL-1β）, brain-derived neurotrophic factor （BDNF） and nerve growth factor （NGF） in the hippocampus were examined by ELISA, and the expressions of toll-like receptor 4 （TLR4） and nuclear factor-κB （NF-κB） were measured by Western blotting. Results （1） As compared with the normal saline group, the mice in the LPS group （0.6 mg/kg） had significantly slower growth （[2.23±0.22] g vs. [1.18±0.21] g）, increased relative liver weight to the body （0.052±0.004 vs. 0.072±0.007） and increased TNF-α levels in serum and brain tissues （[62.01 ±3.32] pg/mL vs. [151.06± 14.51] pg/mL; [186.03±13.24] pg/mL vs. [298.71±41.61] pg/mL, P〈0.05）. （2） As compared with the LPS group, Tal treatment group had significantly shortened average escape latency in place navigation test, prolonged active time in spatial probe test, statistically decreased hippocampal TNF-α, IL-1β, TLR4 and NF-κB levels （[73.32±5.18] pg/mL vs. [58.61±4.03] pg/mL; [99.15±8.30] pg/mL vs. [75.56±6.13] pg/mL; 2.32±0.29 vs. 1.71±0.26; 1.77±0.24 vs. 1.26±0.14） and significantly increased BDNF and NGF levels （[1.33±0.12] pg/mL vs. [1.69±0.25] pg/mL; [41.45±3.47] pg/mL vs. [50.38±5.02] pg/mL, P〈0.05）. Conclusion Tal improves learning and memory functions and alleviates neuro-inflammation in postnatal infection of mice, and the underlying mechanism probably involves in inhibiting TLR4/NF-κB signaling pathway activation and increasing neurotrophic factors.