Thyroid Hormone Regulates SNAREs Proteins Expression In The Prefrontal Cortex Of Adult-onset Hypothyroidism Rats

ObjectiveThe hypothyroid rats were induced by daily intraperitoneal injection of6-n-propyl-2-thiouracil（PTU）1mg/100g body weight. The expression of solubleN-ethylmaleimide-sensitive factor attachment protein receptor （SNARE） in theprefrontal cortex of adult-onset hypothyroidism rats and the effect of Levothyroxin（L-T₄） treatment were detected by Western blot method. Further to explore themolecular mechanism of brain impairment by hypothyroidism.MethodsFouty-five adult male Sprague-Dawley rats were used in current experiments anddivided into4groups randomly as indicated below:（1） Hypothyroid group（H group）.Twelve hypothyroid rats were induced by daily intraperitoneal injection ofPTU（dissolved in saline solution,1mg/100g body weight（BW））for six weeks;（2） T₄-5group. Eleven rats were treated with PTU for six weeks as described above. But fromthe fifth week, they were also treated with intraperitoneally injected L-T₄（dissolved insaline solution,50μg/kg BW） every day for two weeks;（3）T₄-20group. Eleven rats weretreated according to the same protocols as the T₄-5group except increasing the dosageof L-T₄to200μg/kg BW.（4）Control group（C group）. Eleven control rats were givensame volume of saline solution for six weeks with hypothyroid rats. Theradioimmunoassay kits were applied to assay the levels of serum T₃and T₄, andWestern blot method was used to determine the level of SNAREs proteins expression inthe prefrontal cortex. All statistical analysis was performed using SPSS software（version13.0）. Values are expressed as mean±S.E.M. The data among the groups werecompared using one-way ANOVA. Statistical significance was defined as Ps<0.05. Results（1） Thyroid Hormone LevelsThe serum T₃and T₄levels were significantly lower （P <0.05） in hypothyroid rats thanthose of control rats.5μg/100g BW T₄treatment restored T₃and T₄similar to the levelsof control rats, but both of them were significantly higher （vs the C group, P <0.001）after20μg/100g BW T₄treatment.（2） Protein Levels of Syntaxin-1in the prefrontal cortexWestern blot analysis was performed to determine whether thyroid hormone regulatedthe expression of SNAP-25, syntaxin-1, and VAMP-2in the PFC. Our results showedthat the amount of SNAP-25was increased by25.6%in the hypothyroid rats comparedto controls （P=0.027）, but SNAP-25levels were only8.2%higher in hypothyroid ratstreated with5μg T₄/100g BW （P>0.05） and0.2%higher in hypothyroid rats treatedwith20μg T₄/100g BW （P>0.05）. Compared to controls, syntaxin-1levels were lowerin the hypothyroid rats compared to controls （P <0.05）, but not significantly different inthe T₄-5and T₄-20groups. In contrast, the levels of VAMP-2did not differ significantlyamong groups（P>0.05）.Conclusion（1） Adult-onset hypothyroidism can increase the expression of SNAP-25and decreasethe expression of syntaxin-1in the prefrontal cortex.（2） T₄treatment can reverse the changed expressions of SNAP-25and syntaxin-1, andthe recovery degree is related to the T₄dosage.