Effects of thyroid hormone on the expression of homeobox gene Nkx6.1 in the cerebrum tissue of offspring of hypothyroidism rat / 中国地方病学杂志

ABSTRACT

Objective To explore the effects of thyroid hormone on the expression of homeobox gene Nkx6.1 in offspring of hypothyroidism rats and the relationship between gene expression and hormone level by supplying their hypothyroidism pregnant mother with thyroid hormone. Method A total of 240 Wistar rats were half nude and half female. Female rats were randomly divided into eight groups control, hypothyroidism group, hypothyroidism groups which were supplied with thyroid hormone in high, medium and low dosage in early stage(1- 17 d) and in late stage( 18 - 20 d). According to 100 grams of body weight, the concentration of thyroid hormone 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 normal control group was given KIO_3 solution and the other groups were given deionized water. After three months female rats were mated with male rats. The content of Nkx6.1 mRNA in brain tissue of 17-day fetal rats, new-born and 20- day old offspring by real-time fluorescence quantitative PCR techniques. Results①A rat model of hypothyroidism was successfully established, there were statistical significance between 8 groups in TT_3,TT_4,FT_3,FT_4(F=4.08,31.99,5.79,26.34, all P < 0.01 ). ② The expression of Nkx6.1 mRNA had significant difference(F = 758.720, 1121.589,144.716, all P < 0.01 ) between groups in 17-day fetal rats, new-bern and 20-day old offsprings and intra- groups in different time (F=2898.863,325.605,716.285,56.329,236.727,196.678,7115.752,9152.306, all P < 0.01 ). ③The time factor and dosage factor had influence on Nkx6.1 mRNA expression(F = 1176.655,246.530, all P < 0.01 ). There were interaction between time and dosage factor(F = 1249.934, P < 0.01 ). ④Comparison of Nkx6.1 mRNA expression between hypothyroidism group and normal control group had significant difference in the above three time points(all P < 0.01 ). ⑤Comparisons of Nkx6.1 mRNA expression between 6 hypothyroidism groups which were supplied with thyroid hormone and hypothyroidism group had significant difference(all P < 0.01 ) in new-bern and 20-day old offspring; comparisons of Nkx6.1 mRNA expression between hypothyroidism groups which were supplied with high and medium thyroid hormone and hypothyroidism group had significant difference in 17-day fetal rats(all P < 0.01 ). ⑥Comparison of Nkx6.1 mRNA expression between hypothyroidism groups which were supplied with medium thyroid hormone in early stage and normal control group had no statistical significance (all P > 0.05), while between the other 5 groups which were supplied with thyroid hormone and normal control group had significant difference(all P < 0.01 ) in the above three time points.⑦Multiple comparison of early stage groups which were supplied with thyroid hormone showed that the expression of Nkx6.1 mRNA had significant difference(all P < 0.01) between high, low dosage groups and medium group in 17-day fetal rats, new-bern and 20-day offspring(all P< 0.01). ⑧Multiple comparison of late stage groups supplied with thyroid hormone showed that old offspring and between high dosage groups and low dosage groups in 17-day fetal rats and 20-day the expression of Nkx6.1 mRNA had significant difference(all P < 0.01 ) between three groups in new-bern and 20- day old offspring. Conclusion The expression of Nkx6.1 in rats offspring is highly related to the supply dosage and supply time of thyroid hormone in hypothyroidism pregnant rats.