低碘膳食对大鼠脑组织同源盒基因Nkx-6．1和Nkx-6．2 mRNA表达的影响

Effects of low-iodine diet on the expression of homeobox gene NKX-6.1 and NKX-6.2 in rat cerebrum tissue

目的研究低碘膳食对大鼠脑组织同源盒基因Nkx-6．1、Nkx-6．2 mRNA表达的影响，探讨低碘导致脑发育迟滞的可能分子作用机制。方法20只雌性Wistar大鼠按体质量随机分为2组：低碘组和对照组，均饲以低碘饲料（含碘量为13．66μg／kg），分别饮用去离子水和含碘200μg／L的碘酸钾溶液，3个月时采用化学发光免疫分析法检测大鼠血清甲状腺激素水平，然后将雌鼠与正常饲养的Wistar雄鼠进行交配，分别取孕16d、新生期及生后20日龄仔鼠脑组织，采用实时荧光定量PCR检测Nkx-6．1、Nkx-6．2 mRNA的表达。结果①低碘组大鼠血清TT3、TT4、FT3、FT4水平[（0．89±0．20）、（0．32±0．16）nmol／L，（3．33±0．61）、（3．28±0．80）pmol／L]均明显低于对照组[（1．04±0．06）、（39．42±14．68）nmol/L，（4．83±0．33）、（26．99±4．48）pmol，t=2．71、6．52、5．70、12．89，P〈0．05或〈0．01]。②对照组孕16d、新生期及20日龄仔鼠脑组织Nkx-6．1 mRNA表达水平分别为（1．90±0．23）×10^-3、（1．86±0．40）×10^-4、（1．11±0．27）×10^-4，各日龄间比较差异有统计学意义（F=827．58．P〈0．01），随着日龄增加Nkx-6．1mRNA表达水平明显下降．两两比较差异均有统计学意义（P均〈0．01）；低碘组各日龄仔鼠脑组织Nkx-6．1mRNA表达水平分别为（1．16±0．16）×10^-3、（3．44±0．49）×10^-4、（3．58±0．64）×10^-4，差异有统计学意义（F=297．25，P〈0．01），但变化趋势与对照组不同，孕16d表达水平最高，与新生期及20日龄比较，差异有统计学意义（P〈0．01）；低碘组与对照组比较，孕16d明显降低（t=10．14，P〈0．01），而新生期及20日龄则明显增高（t值分别为9．69、13．81，P均〈0．01）。③对照组和低碘组各日龄仔鼠脑组织Nkx-6．2 mRNA表达水平分别为（1．03±0．19）×10^-2、（1．33±0.10）×10^-3、（8．79±0.87）×10^-2和（0.31±0．03）×10^-2、（1．53±0．13）×10^-3、（7．51±0．86）×10^-2，组间比较差异有统计学意义（F值分别为1293．02、1065．83，P均〈0．01），随着日龄增加，两组表达趋势一致，20日龄最高，孕16d次之，新生期最低；低碘组20日龄仔鼠与新生期及孕16d比较，差异有统计学意义（P均〈0．01），对照组新生期仔鼠与孕16d比较，差异有统计学意义（P〈0．01）；低碘组与对照组比较，孕16d及20日龄明显降低（t值分别为14．35、4．05，P均〈0．01），而新生期仔鼠则明显增高（t=4．78，P〈0．01）。结论同源盒基因Nkx-6．1、Nkx-6．2 mRNA表达水平改变可能与低碘导致脑发育迟滞有关。

Objective To study the influence of low-iodine diet on the expression of homeobox gene Nkx- 6.1 and Nkx-6.2 in rat cerebrum tissue, and to explore the possible molecular mechanism of cerebrum development retardation caused by low-iodine. Methods Twenty female Wistar rats were randomly equally divided into two groups： low-iodine group and control group, both fed with low-iodine diet as low as 13.66 μg/kg determinated by spectrophotometry in Tianjin Institute of Endocrinology and the former with deionized water, the later 200 μg/L potassium iodate. Thyroid hormone level was detected using chemiluminescence immunoassay 3 months later and they were mated with male rats normally fed. Rats of 16-day pregnancy, new-born and 20th davs old were detected the content of Nkx-6.1 and Nkx-6.2 mRNA in the cerebrum tissue by real-time fluorescence quantitative PCR techniques. Results ①TT3, TT4, FT3 and FT4 levels of low-iodine group[ （0.89 ± 0.20）, （0.32± 0.16）nmol/L, （3.33 ±0.61 ）, （3.28 ± 0.80）pmol/L] were lower than the control group [ （1.04 ± 0.06）, （39.42 ± 14.68）nmol/L, （4.83 ± 0.33）, （26.99 ± 4.48）pmol, t = 2.71,6.52,5.70,12.89, all P 〈 0.05 or 0.01]. ②Nkx-6.1 mRNA expression level in 16- day pregnancy, new-born and 20th days old of control group was （1.90 ± 0.23） × 10^-3, （1.86 ± 0.40） × 10^-4, （1.11 ± 0.27） × 10^-4（F = 827.58, P〈 0.01 ）, Nkx-6.1 mRNA expression level gradually decreased along with aging（all P 〈 0.05）. The intra-group difference was significant （F = 297.25, P 〈 0.01 ） and the Nkx6.1 mRNA expression level during 16 days of pregnancy was the highest（P 〈 0.01 ）. It was higher in the control group than in the low-iodine group during 16 days of pregnancy （t = 10.14, P 〈 0.01） as well as in the low-iodine group than in the control group during newborn and 20th days old（t = 9.69,13.81, all P 〈 0.01 ）. ③Nkx-6.2 mRNA expression level in 16-day pregnancy, new-born and 20th days old of control group was respeetively（1.03 ± 0.19） × 10^-2, （1.33 ±0.10） × 10^-3,（8.79 ± 0.87） × 10^-2, and that of low-iodine group was （0.31± 0.03） × 10^-2, （1.53 ± 0.13） × 10^-3, （7.51 ± 0.86） × 10^-2. The intra-group difference was significant（F = 1293.02,1065.83, all P 〈 0.01 ）. Nkx-6.2 expression level during 20th days old was the highest（P 〈 0.01 ） and that of newborn was the lowest（P 〈 0.01 ）. The Nkx6.2 mRNA expression level in control group were higher than the low-iodine group during 16-day pregnancy and 20th days old（t = 14.35, 4.05, all P 〈 0.01）. It was higher in the low-iodine group than in the control group during newborn （t = 4.78, P 〈 0.01 ）. Conclusions The difference in the expression of Nkx-6.1 and Nkx-6.2 is highly related to the brain development retardation caused by low-iodine.