Expression Of SNARE Proteins In Dorsal Hippocampus Of Adult-onset Hypothyroidism Rats

ObjectiveTo observe the effect of adult-onset hypothyroidism on the expression of SNAREproteins of SNAP-25(synaptosomal-associated protein of25kDa)、 syntaxin-1andVAMP-2(vesicular-associated membrance protein-2) in dorsal hippocampus, andwhether the altered protein expression could be restored by T4treatment.MethodsFifty-five adult Sprague-Dawley rats were used in our experiment, weighting from250to300gram. All rats were separated into4groups randomly:(1) hypothyroid rats(Hypo group, n=12), treated intraperitoneally by daily injection of6-n-propyl-2-thiouracil (PTU,1mg/100g body weight (BW)) for six weeks;(2) L-T4treated rats with common dose (T4-5group, n=11) were administrated by PTU for sixweeks, from the fifth week daily intraperitoneal injection of L-T4(5g/100g BW) fortwo weeks;(3) L-T4treated rats with high dose (T4-20group, n=11) received the sameprotocol as T4-5group, but the high dose of L-T4(20ug/100g BW);(4) normal controlrats (C group, n=11) were treated with saline solution for six weeks. Theradioimmunoassay kits were applied to assay the levels of serum T3and T4, andwestern blot method was used to determine the levels of SNAP-25、syntaxin-1andvamp-2in dorsal hippocampi from different groups rats. All statistical analysis wasperformed using SPSS software (version13.0). Values are expressed as mean±S.E.M.The datas among the groups were compared using one-way ANOVA. Statisticalsignificance was defined as Ps<0.05. Results1. Body weight gainBefore the study, body weights of all animals were not significantly different (F (3,42)=0.21, P=0.93). After the experiment the normal growth of body weight in thecontrols was increased by49.0%. However, body weight gain in Hypothyroid, T4-5andT4-20groups increased respectively by21.5%,32.5%and26.1%, all groupssignificantly lower than the controls (Ps <0.05).2. Thyroid hormone levelsThe serum T3and T4levels was significantly lower in hypothyroid group (Ps <0.02),for53.6%,77.5%of the contol group, respectively; In T4-5group the serum T3and T4levels was similar to normal value(Ps>0.05), respectively for96.9%,99.7%of thecontrol group; after treatment of high dose L-T4, the serum T3and T4levels wassignificantly higher than normal level in T4-20group(Ps <0.001), respectively for171.8%,175.1%of the control group.3.the protein levels of SNAP-25、syntaxin-1、VAMP-2in the the dosal hippocampus(1) Compared to the control group, the expression of SNAP-25in the hypothyroidgroup were markly increased by35.8%(Ps <0.05), and in T4-5and T4-20group, theexpressions of SNAP-25were decreased15.7%(Ps>0.05) and25.5(Ps <0.05)compared with hypothyroid group, but were higher20.1%(Ps>0.05) and10.3%(Ps>0.05) than control group, respectively.(2) The content of syntaxin-1in doasal hippocampus of hypothyroid rats was higherthan control group by39.4%(Ps <0.05), but in T4-5and T4-20group, the levels ofsyntaxin-1were decreased by11.5%(Ps>0.05) and18%(Ps>0.05), respectively,when compared to hypothyroid group; the levels of syntaxin-1were not significantlydifferent from control group (Ps>0.05), the levels of syntaxin-1were higher thannormal group by27.9%in T4-5group, and21.4%in T4-20group.(3) The level of VAMP-2in doasal hippocampus was not significantly different between four groups (Ps>0.05).Conclusion(1) These data suggested that adult-onset hypothyroidism could lead to increase ofSNAP-25and syntaxin-1in dorsal hippocampus.(2) After teated with low dose of L-T4, the serm T3and T4were similar to normal level,and the increased expression of SNAP-25and syntaxin-1were restored.(3) After teated with high dose of L-T4, the serm T3and T4were higher than nomallevel, and the expression of SNAP-25and syntaxin-1were restored more closely tonormal level.