甲状腺功能减低孕鼠补充甲状腺素对子代脑组织同源盒基因Nkx2.1mRNA表达的影响

目的 通过对妊娠期甲状腺功能减低(甲低)大鼠补充左旋甲状腺素(L-thyroxine,L-T4),探讨甲状腺素对子代鼠脑组织同源盒基因Nkx2.1mRNA表达影响,探讨该基因的表达与甲状腺素水平之间的关系.方法 Wistar雌性大鼠120只,按体重分层随机分为对照组、甲低非治疗组,甲低孕鼠妊娠早期(妊娠第1～17天)补充L-T4高、中、低剂量组,甲低孕鼠妊娠晚期(妊娠第18天至分娩后第20天)补充L-T4高、中、低剂量组,共8组,每组15只;补充L-T4高、中、低剂量分别为:3.5、2.0、0.5μg/100 g体重.各组均给予低碘饮食,对照组饮用碘浓度为200 μg/L碘酸钾溶液,其余7组饮用去离子水.3个月后各组均与正常雄性大鼠交配,确定受孕后各甲低给药组于不同时期给予补充L-T4.各组分别取孕第17天胎鼠、新生及出生后第20天龄仔鼠前脑组织,实时荧光定量PCR(Real-time PCR)检测Nkx2.1mRNA水平.结果 甲低孕鼠妊娠早期补充L-T4高、中、低剂量组,甲低孕鼠妊娠晚期补充L-T4高、中、低剂量组,甲低非治疗组、对照组大鼠血清TT3分别为(0.85±0.17)、(0.81±0.18)、(0.86±0.21)、(0.85±0.20)、(0.89±0.18)、(0.85±0.20)、(0.86±0.20)、(1.08±0.07)nmol/L(F=4.08,P＜0.01);TT4分别为(0.43±0.16)、(0.39±0.11)、(0.39±0.13)、(0.43±0.17)、(0.51±0.19)、(0.43±0.16)、(0.41±0.15)、(39.43±14.16)nmol/L(F=31.99,P＜0.01);FT3分别为(3.29±0.61)、(3.29±0.61)、(3.24±0.61)、(3.28±0.63)、(3.31±0.59)、(3.28±0.50)、(3.24±0.49)、(4.93±0.46)pmol/L(F=5.79,P＜0.01);FT4分别为(3.38±0.80)、(3.31±0.67)、(3.29±0.73)、(3.27±0.71)、(3.48±0.81)、(3.56±0.66)、(3.29±0.61)、(27.29±4.53)pmol/L(F=26.34,P＜0.01).甲低非治疗组在妊娠第17天胎鼠Nkx2.1mRNA水平(9.15×10-5±9.17 × 10-5)低于对照组胎鼠(65.1×10-5±40.90×10-5)(t=66.224,P＜0.05);甲低非治疗组在新生期仔鼠Nkx2.1mRNA水平(3.16×10-5±0.142×10-5)低于对照组仔鼠(55.6×10-5±51.05×10-5)(t=102.225,P＜0.05);甲低非治疗组在生后第20天仔鼠Nkx2.1mRNA水平(8.09×10-5±8.21×10-5)低于对照组仔鼠(13.9×10-5±7.43×10-5)(t=9.235,P＜0.05).甲低孕鼠妊娠早期补充L-T4中等剂量组在妊娠第17天胎鼠、新生、生后第20天仔鼠脑组织Nkx2.1mRNA表达水平逐渐降低,分别为(57.1×10-5±22.90×10-5)、(30.8×10-5±27.20×10-5)、(17.1×10-5±0.623×10-5)(F=13.394,P＜0.01).甲低孕鼠妊娠早期补充L-T4中等剂量组妊娠第17天胎鼠、新生、生后第20天仔鼠脑组织Nkx2.1mRNA水平接近对照组,差异无统计学意义(t值分别为0.225、0.336、0.345,P值均＞0.05).结论 大鼠脑组织同源盒基因Nkx2.1mRNA的表达与甲状腺素水平存在关联.

Effects of supplement of thyroxine for hypothyroid pregnant rat on the expression of homeobox gene Nkx2.1 mRNA in the offspring's cerebrum tissue

Objective To explore the effects of thyroid hormone on the expression of homeobox gene Nkx2.1 mRNA in child rat by supplying their hypothyroidism pregnant mother with different dose of levothyroxine( L-thyroxine , L-T4 ) in different times. Methods 120 female Wistar rats were randomly divided into eight groups according to the body weight: control group, non-treatment hypothyroidism group,hypothyroidism groups supplied with L-T4 in high,medium and low dosage in early stage (1st-17th day of pregnancy) and in late stage ( 18th day of pregnancy-20th day after childbirth). According to 100 grams of body weight, the concentrations of L-T4 were 3.5,2.0,0.5 μg/d in high, medium and low dosage group. All the rats were fed with low-iodine food. The control group was given 200 μg/L potassium iodate solution as drinking water and the other groups were given deionized water. After three months, the rats were mated with normal male rats. After the pregnancy was confirmed, hypothyroidism groups were supplied with L-T4 of different concentrations. Brain samples were taken from the 17-day fetal rats, new-born and 20-day old offsprings and the levels of Nkx2.1 mRNA in brain tissue were analyzed by real-time fluorescence quantitative PCR techniques. Results The levels of TT3 in hypothyroidism groups supplied with L-T4 in high, medium and low dosages in early and late pregnant stages, non-treatment hypothyroidism group and control group were (0.85 ± 0.17), (0.81 ± 0.18), (0.86 ± 0.21), (0.85 ± 0.20), (0.89 ± 0.18),(0.85 ± 0.20), (0.86 ± 0.20 ), (1.08 ± 0.07) nmol/L (F = 4.08, P ＜ 0.01); the levels of TT4 in each group were (0.43 ± 0.16), (0.39 ± 0.11), (0.39 ± 0.13), (0.43 ± 0.17), (0.51 ±0.19), (0.43 ±0.16),(0.41 ± 0.15),(39.43 ± 14.16) nmol/L (F=31.99,P＜0.01); the levels of FT3 in each group were (3.29 ± 0.61),(3.29 ± 0.61),(3.24 ± 0.61), (3.28 ± 0.63),(3.31 ± 0.59),(3.28 ± 0.50),(3.24 ± 0.49), (4.93 ± 0.46) pmol/L (F = 5.79, P ＜ 0.01); the levels of FT4 in each group were(3.38 ± 0.80), (3.31 ± 0.67), (3.29 ± 0.73), (3.27 ± 0.71), (3.48 ± 0.81), (3.506 ± 0.66), (3.29 ±0.61), (27.29 ± 4.53) pmol/L (F = 26.34, P ＜ 0.01). The expression of Nkx2.1 mRNA in non-treatment hypothyroidism group (9.15 × 10-5 ± 9.17 × 10-5) was lower than control group (65.1 × 10-5 ± 40.90 ×10-5 ) in 17th day of pregnancy (t = 66.224 ,P ＜ 0.05); the expression of Nkx2.1 mRNA in non-treatment hypothyroidism group (3.16 × 10-5 ± 0.142 × 10-5) was lower than control group (55.6 × 10-5 ± 51.05 ×10-5) in new-born (t = 102.225, P ＜ 0.05); the expression of Nkx2.1 mRNA in non-treatment hypothyroidism group (8.09 × 10-5 ± 8.21 × 10-5 ) was lower than control group (13.9 × 10-5 ± 7.43 ×10-5) in 20th day after birth (t = 9.235, P ＜ 0.05). The trend of Nkx2.1 mRNA in hypothyroidism groups was decreased in group supplied with L-T4 in medium dosage in early stage descends in 17th day of pregnancy, new-born and 20th day after birth (57.1 × 10-5 ± 22.90 × 10-5), (30.8 × 10-5 ± 27.20 ×10-5), (17.1 × 10-5 ± 0.623 × 10-5) (F = 13.394, P ＜ 0.01). The expression of Nkx2.1 mRNA in hypothyroidism groups supplied with L-T4 in medium dosage in early stage in 17th day of pregnancy, newborn and 20th day after childbirth was closest to the control group in every period ( t values were 0.225,0.336,0.345, all P values ＞ 0.05 ). Conclusion The difference in the expression of homeobox gene Nkx2.1 mRNA is highly related to the level of thyroid hormone.