The role of TSH-THSR-cAMP-PKA signal pathway in the process of iodine uptake in lactating rat mammary gland / 中华地方病学杂志

ABSTRACT

Objective:To observe the mRNA and protein expression levels of thyroid stimulating hormone receptor (TSHR), protein kinase A (PKA) and sodium iodine transporter (NIS) in mammary gland tissue of lactating rats with different iodine nutrition levels, and to explore the role of thyroid stimulating hormone (TSH)-THSR-cyclic adenosine monophosphate (cAMP)-PKA signal pathway in the process of mammary iodine uptake during lactation.Methods:Using a group design, according to body weight (80 - 100 g), 110 Wistar female rats were randomly divided into normal iodine (NI) group, severe iodine deficiency (SID) group, moderately iodine deficiency (MID) group, moderately iodine excess (MIE) group and severe iodine excess (SIE) group, with 22 rats in each group. Another 22 Wistar male rats were selected, and the feeding situation was consistent with that of NI group. After 3 months of feeding, 24-hour urine samples of female rats were collected, and the female rats were caged with the male rats (5 ∶ 1). After mating, each female rat was fed separately. At 10 days of childbirth, the lactating rats were sacrificed and thyroid and mammary gland tissues were taken. The urinary iodine was determined by arsenic cerium catalytic spectrophotometry. The morphological changes of thyroid and mammary gland tissues were observed by HE staining. The mRNA expression levels of TSHR, PKA and NIS in thyroid and mammary gland tissues were measured by real-time PCR; the protein expression levels of TSHR, PKA, phosphorylated PKA (p-PKA), and NIS in mammary gland tissue were measured by Western blotting.Results:Compared with NI group (162.59 μg/L), the median urinary iodine of female rats in SID and MID groups (3.16, 6.36 μg/L) was lower, and the median urinary iodine of female rats in MIE and SIE groups (2 356.27, 11 507.29 μg/L) was higher ( P < 0.01). HE staining showed that different levels of iodine uptake had different effects on thyroid follicles most of the follicles in NI group were uniform round or oval; in MID group, the number of small follicles increased, the epithelial cells were monolayer columnar or cubic, the follicular cavity became smaller, and the glia decreased; the follicles in SID group became smaller, and the epithelial cells were columnar or high columnar, with reduced or absent glia in the follicular cavity; pleomorphic changes were found in thyroid follicles in SIE and MIE groups, with some follicles significantly enlarged and some small follicles hyperplasia. Different levels of iodine intake had different effects on mammary duct compared with NI group, the connective tissue around the mammary duct in SID and MID groups showed obvious fibrosis, while the fibrosis in MIE and SIE groups was significantly reduced. The results of real-time PCR showed that there were significant differences in the mRNA expression levels of TSHR, PKA and NIS in thyroid tissues of lactating rats with different levels of iodine nutrition ( F = 10.73, 92.37, 115.75, P < 0.01). There were statistically differences in the mRNA expression levels of TSHR, PKA and NIS in mammary gland tissues of lactating rats with different levels of iodine nutrition ( F = 40.25, 39.63, 14.92, P < 0.05). Western blotting results showed that there were significant differences in the protein expression levels of TSHR, PKA, p-PKA and NIS in mammary gland tissues of lactating rats with different levels of iodine nutrition ( F = 4.14, 6.73, 8.48, 4.51, P < 0.05). Among them, the protein expression level of TSHR in MIE and SIE groups was lower than that in NI group ( P < 0.05); the protein expression level of PKA in SID and MID groups was higher than that in NI group ( P < 0.05); the protein expression level of p-PKA in SID group was higher than that in NI group, but that in SIE group was lower than that in NI group ( P < 0.05), the protein expression level of NIS in SID group was higher than that in NI group ( P < 0.05). Conclusions:The mRNA and protein expression levels of TSHR are decreased in mammary gland tissues of lactating rats with high iodine intake, while the mRNA and protein expression levels of PKA and NIS are increased in low iodine intake. TSH-TSHR-cAMP-PKA signal pathway may be involved in the regulation of iodine intake in mammary gland tissue of lactating rats, which may protect itself and its offspring.