ABSTRACT
ObjectiveTo find out if the immune system derived thyroid stimulating hormone(TSH) β splice variant(TSHβ-Ⅴ) would be regulated by circulating thyroid hormone levels to get a further understanding of the function and mechanism of this TSHβ-Ⅴ in thyroid homeostasis.MethodsA total of 20 weaning Balb/c mice (half male and half female) were selected and randomly divided into two groups according to their body mass and gender(n =10).Mice of control group were fed with common diet and deionized water.Mice of the low-iodine(LI) group were fed with low-iodine diet(containing iodine 20 - 40 μg/kg,iodine-intake about 0.25 μg/d) and deionized water.The experimental period was 3 months.At the end of the experiment,mice were executed and the blood was collected to observe the levels of TSH and thyroid hormone by chemiluminescence immunoassay (CIA) ; bone marrow (BM),peripheral blood(PBL),thyroid gland and pituitary were collected to assay the TSHβ-Ⅴ mRNA expression by real-time quantitative reverse transcriptase polymerase chain reaction (RT-PCR).ResultsThe serum free thyroxine(FT4) and total thyroxine(TT4) levels in LI group of mice[(0.47 ± 0.70)nmol/L,(2.41 ± 0.28)pmol/L] were significantly lower than that of the control group of mice [(55.2 ± 3.68) nmol/L, (32.72 ± 1.02) pmol/L,t =43.81,86.04 、all P ＜ 0.01 ] and the serum total triiodothyronine(TT3) and free triiodothyronine(FT3) reduction in LI group of mice[ (0.76 ± 0.08)nmol/L,(4.01 ± 0.40)pmol/L] were significantly lower than that of the control group of mice [ (1.10 ± 0.06)nmol/L,(5.40 ± 0.38)pmol/L,t =9.81,7.5 1,P ＜ 0.01 ].Iodine insufficiency strongly elevated the serum TSH in LI group of mice[ (35.67 ± 17.39)mU/L] than that in control group of mice[ (0.24 ± 0.10)mU/L,t =- 6.11,P ＜ 0.01 ].The mRNA levels of TSH β-Ⅴ in BM (9.62 ± 0.60) and in PBL( 9.25 ± 0.83 ) of LI group of mice were lower than those in control group of mice (7.69 ± 0.36,7.11 ± 0.41,t =6.77,5.64,P ＜ 0.01),while the mRNA level of TSH β-Ⅴ in pituitary of LI group of mice (1.99 ± 0.61) was increased compared with that in control group of mice (5.75 ± 0.98,t =- 8.02,P＜ 0.01).Compared with control group of mice(9.12 ± 0.62),the level of thyroid TSH β-Ⅴ mRNA in LI group of mice (9.32 ± 0.91 ) was not significantly changed (t =0.45,P ＞ 0.05).There was no detectable native TSHβ in BM,PBL and thyroid.The mRNA level of native TSHβ in pituitary in LI group of mice( - 7.17 ± 1.78) was dramatically elevated compared to that in control group of mice( - 1.43 ± 0.51,t =- 7.60,P ＜ 0.01 ).ConclusionsThe mRNA levels of TSHβ-Ⅴ are suppressed in BM and PBL in low iodinediet induced hypothyroidism mice,which suggest that immune system derived TSHβ-Ⅴ may be more important thannative TSHβ in immune-thyroid regulation.