SCN2b mRNA在快速老化小鼠额叶和海马中的表达及变化

本实验目的在于探讨SCN2bmRNA在快速老化小鼠SAMP8的不同生长发育阶段海马和额叶中的表达及变化。按月龄将SAMP8小鼠分为3组:2周龄组、8月龄组和13月龄组,每组5只;并分别以8月龄和13月龄SAMR1小鼠为对照组,每组5只。运用RT-PCR技术,观察SCN2bmRNA在各组额叶和海马内的表达及变化。结果显示:SCN2bmRNA在各组小鼠海马和额叶中均有表达,但仅额叶内SCN2bmRNA的表达在SAMP8小鼠2周龄组分别与8月龄组和13月龄组的比较有统计学差异(P<0.05)。以上结果提示,SCN2b参与了海马和额叶正常生理功能的维持,其在额叶随月龄增加的表达变化可能与衰老、认知记忆功能的减退有关。     

SAMP8小鼠在不同发育阶段海马和额叶中人类同源衰老相关基因的表达

目的探讨13个与人类同源的衰老相关基因在不同月龄快速老化小鼠海马和额叶中的表达及变化,从中筛选出与脑老化最相关的基因。方法采用SAMP8快速老化小鼠,以同月龄SAMR1为对照,运用RT-PCR技术,观察SAMP8幼年组2周龄、成年组8月龄、老年组13月龄海马和额叶中13个同源衰老相关基因的表达及变化。结果13个基因在各组小鼠海马和额叶中均有表达。SCN2b基因在快速老化小鼠额叶的表达在幼年组与成年组和老年组之间比较有统计学意义(P<0.05),其它基因的表达无统计学意义。结论被调查的13个基因可能参与维持海马和额叶的生理功能,SCN2b在额叶衰老进程中可能发挥作用。     

快速老化小鼠海马突触体内NMDA受体的表达变化

目的:观察NMDA受体在SAMP8小鼠海马突触体内的表达变化。方法:首先应用生物化学的方法分离海马突触蛋白,并对其进行鉴定。其次,Western Blot检测NMDA受体的主要亚基NR1、NR2A和NR2B在SAMP8小鼠海马突触体内的表达变化。结果:PSD-95和synaptophysin特异性抗体检测显示突触蛋白的分离是成功的。SAMP8小鼠海马内NR1、NR2A和NR2B在突触的表达均显著低于SAMR1小鼠。进一步分析NR1、NR2A和NR2B蛋白在突触的表达量占总表达量的比值,SAMP8小鼠同样显著低于SAMR1小鼠,而SAMR1和CD-1小鼠间没有显著性差异。结论:SAMP8小鼠海马突触体内NR1、NR2A和NR2B的蛋白表达水平均显著性降低,推测NMDA受体在突触表达水平的降低可能是导致受体功能失调,激发突触功能损伤信号途径的原因之一,进而导致SAMP8小鼠学习记忆功能的下降。     

快速老化小鼠P8海马神经元突触可塑性相关的AMPA受体表达异常

目的比较快速老化小鼠P8(SAMP8)与抗快速老化小鼠R1(SAMR1)海马神经元突触可塑性相关的谷氨酸α-氨基-3-羟基-5-甲基-4-异唑丙酸(AMPA)受体表达差异,为阿尔兹海默病(AD)的发病机制提供实验依据。方法取雄性10月龄SAMP8 10只和SAMR1 9只,应用Morris水迷宫实验评价动物学习记忆能力,透射电子显微镜观察海马CA1区神经元突触界面超微结构,蛋白质免疫印迹法检测海马AMPA受体亚基GluR1、GluR2的表达。结果与SAMR1比较,SAMP8逃避潜伏期延长,目标象限时间百分比下降,穿台次数减少;海马CA1区神经元突触后致密带变薄,突触间隙增宽,突触界面曲率下降;海马GluR2含量下降,GluR1含量有下降趋势,但差异无统计学意义。结论海马AMPA受体异常可能是导致突触可塑性受损,引发SAMP8认知障碍的原因之一,AMPA受体在AD的发病中可能占有重要地位。     

衰老相关miRNAs的筛选及鉴定

目的以快速老化模型SAM小鼠的海马组织作为研究对象,通过miRNA芯片大规模筛选与衰老相关的miRNAs,为探讨衰老的机制提供线索。方法随机各选取3只4、8和12月龄SAMP8及SAMR1小鼠,提取海马组织RNA进行芯片检测;以snRNA U6作为内参,SYBR Green作为染料,用real-time PCR方法进行验证,对miRNA的表达进行相对定量分析。结果对比miRNA芯片和real-time PCR验证结果,证实芯片结果具有相对较好的重复性和真实度。对3张miRNA芯片结果进行综合分析,在4和8月龄均表现出表达差异的miRNA共7个,在8和12月龄均表现出表达差异的miRNA共8个,4和12月龄均表现出表达差异的miRNA共3个,在3个月龄间均表现出明显表达差异的1个(miR-9*)。结论 miRNAs在SAMP8及SAMR1的差异表达提示其在SAMP8衰老进程中发挥重要作用。     

快速老化小鼠海马中细胞外基质金属蛋白酶诱导因子的年龄相关性变化

目的:观察细胞外基质金属蛋白酶诱导因子(extracellular matrix metalloproteinase inducer,CD147)在快速老化小鼠(senescence-accelerated-prone mouse 8,SAMP8)海马中随年龄变化的趋势。方法:应用免疫组织化学和Western blot的方法,观察CD147在SAMP8小鼠海马中的年龄相关性变化。结果:免疫组织化学结果显示SAMP8小鼠海马区CD147免疫反应呈阳性,且随年龄增加无明显的细胞分布变化。Western blot分析数据表明随年龄增加CD147蛋白水平逐渐下降;相对于3月龄小鼠,12月龄小鼠的CD147蛋白水平下降了约53%(P<0.05)。结论:随年龄的增加,海马区CD147蛋白水平逐渐下降,推测其与阿尔茨海默病(Alzheimer’s disease,AD)相关。     

快速老化小鼠胸腺细胞分化与Notch信号相关基因表达关系的研究

目的：研究快速老化小鼠（Senescence-accelerated mice，SAM）增龄过程中胸腺T细胞亚群的变化与Notch 1、Presenilin 1、2（PS1、2）、HES1等Notch信号转导通路相关基因mRNA表达变化及这两种变化的关系。方法：选择出生后1—8周龄SAM，采用流式细胞技术检测胸腺细胞亚群变化、用荧光实时定量PCR的方法检测Notch1、PS1、PS2、HES1基因mRNA表达的动态变化。结果：SAM出生1-2周，胸腺中CD4^＋CD8^＋细胞所占比例较高，4周龄后逐渐降低，各周龄SAMP8与SAMR1之间无显著性差异；在CD4^＋CD8^＋。细胞比例上，SAM呈增龄性增加，1—6周龄的SAMP8与SAMR1之间无显著性差异，8周龄的SAMP8低于SAMR1；在CD4^＋CD8^＋细胞比例上，SAM呈增龄性增加，4周龄后的SAMP8均明显高于SAMR1；Notch1、PS2、HES1基因mRNA表达量呈增龄性增加，各周龄SAMP8的Notch1基因表达水平高于SAMR1，4周龄后SAMP8的PS2、HES1基因表达水平高于SAMR1；PS1基因mRNA表达量呈增龄性降低，4周龄后的SAMP8低于SAMR1。结论：Notch1、PS2、HES1的表达与胸腺CD4^＋CD8^＋细胞的分化呈正相关，PS1表达与胸腺CD4^＋CD8^＋细胞的分化呈负相关。     

EphB2在快速老化小鼠海马中的增龄性变化

目的:观察受体酪氨酸激酶EphB2在快速老化小鼠海马中表达的年龄相关性。方法:应用免疫组织化学和免疫印迹,检测EphB2在3、6、9、12月龄的快速老化和对照组抗快速老化小鼠(SAMR1)海马中的表达。结果:免疫组织化学结果显示,EphB2表达在快速老化和对照组小鼠的海马CA1、CA3和门区都出现年龄依赖性减少,快速老化小鼠各区的减少更为显著。免疫印迹结果显示,快速老化小鼠中,与3月龄相比,EphB2的表达从6月龄开始出现年龄依赖性的降低;而对照组小鼠,EphB2的表达到12月龄才有所降低。结论:快速老化小鼠海马区EphB2的蛋白表达水平呈现年龄依赖性的降低,推测EphB2表达水平的降低可能在阿尔茨海默病发病过程中起到重要作用。     

MPTP处理的SAMP8小鼠黑质纹状体损伤中血红素加氧酶-1的表达变化

目的:研究1-甲基-4-苯基-1、2、3、6-四氢吡啶(MPTP)诱导6月龄快速老化小鼠(SAMP8)黑质纹状体急性损伤,以及血红素加氧酶-1(HO-1)的表达变化,探讨其与MPTP导致的SAMP8小鼠黑质纹状体系统损害的关系.方法:给6月龄健康雄性SAMP8小鼠背部皮下注射MPTP 20mg/(kg·次),连续注射4次,每次间隔2h;对照组注射等量生理盐水.在注射后6h、24h、3d和8d处死小鼠留取脑组织标本,用免疫组织化学技术检测小鼠黑质、纹状体的酪氨酸羟化酶(TH)和HO-1,以计数黑质多巴胺能神经元数量及其投射纤维的改变,及HO-1阳性细胞的变化;用Western blot方法检测TH和HO-1蛋白表达的变化.结果:MPTP致6月龄SAMP8小鼠各时间点TH阳性神经元分别减少14.23％(P＜0.05),23.85％ (P＜0.01),36.77％ (P ＜0.01),45.9％(P＜O.01),24 h与3d比较有显著性差异(P＜0.05),神经元的丢失以24 h至3d最为显著;MPTP组随时间延长纹状体区酪氨酸羟化酶免疫反应阳性染色逐渐变浅淡,不均匀,于注射后24h明显,第8天最为浅淡;同时TH蛋白表达具有相同变化.但仅在注射后3d小鼠纹状体区见到大量HO-1阳性细胞,同时HO-1蛋白表达增高,具有统计学意义,其余各时间点及对照组未见HO-1阳性细胞.中脑区HO-1阳性细胞及蛋白表达在各时间点均未见显著变化.结论:MPTP导致6月龄SAMP8小鼠黑质纹状体系统急性损伤,产生多巴胺能神经元数量减少及蛋白表达降低;其黑质纹状体HO-1的高表达是一过性短暂的,它在PD中的作用是有限的.     

神经元型一氧化氮合酶在快速衰老小鼠额叶皮质中的增龄性改变

为了观察快速衰老小鼠(senescence accelerated mouse,SAM)衰老过程中大脑额叶皮质中nNOS的分布和表达变化,探讨NO/nNOS在中枢神经系统衰老中的作用。采用雄性快速衰老亚系8小鼠(senescence accelerated mouse/prone8,SAMP8)及抗快速衰老亚系1小鼠(senescence accelerated mouse/resistance1,SAMR1)为研究对象,其中SAMP8为实验组,SAMR1为对照组,每组动物再分为青年组(2月龄)和老年组(10月龄)两组。用免疫组织化学方法观察SAM额叶皮质中的nNOS神经元的形态和分布,并计数nNOS阳性神经元在额叶皮质中的数量;用RT-PCR法检测额叶皮质中nNOS mRNA表达水平。结果显示:SAMP8老年组与青年组相比,额叶皮质中nNOS阳性神经元的数量显著增加(15.8±6.3vs8.0±4.9,P<0.05);SAMP8与SAMR1比较,青年组额叶皮质nNOS阳性神经元的数量差异无统计学意义,老年组额叶皮质nNOS阳性神经元的数量显著增加(15.8±6.3vs7.5±5.3,P<0.05)。SAMP8老年组额叶皮质nNOS mRNA水平明显高于SAMP8青年组(1.00±0.17vs0.67±0.13,P<0.01)和老年组SAMR1(1.00±0.17vs0.67±0.11,P<0.01)。以上结果提示:额叶皮质中nNOS神经元的数量增加可能产生过量NO,NO可能参与了SAMP8快速衰老的过程。本研究的结果为通过调节额叶皮质NO产量来延缓衰老及衰老相关功能障碍提供了依据。     

Chronic stress impairs learning and hippocampal cell proliferation in senescence-accelerated prone mice

Chronic stress can induce cognitive impairment. It is unclear whether a higher susceptibility to chronic stress is associated with the progression of pathological brain aging. Senescence-accelerated prone mouse 8 (SAMP8) is a naturally occurring animal model of accelerated brain aging. Senescence-accelerated resistant mouse 1 (SAMR1) is usually used as the normal control. In this study, we examined the effects of chronic restraint stress (CRS) on learning in the Y-maze, hippocampal cell proliferation, and the expression of brain-derived neurotrophic factor (BDNF) in the hippocampus of 4-month-old SAMP8 and SAMR1. The results showed that exposure to CRS impaired learning and hippocampal cell proliferation in SAMP8 and SAMR1 but to a much greater extent in SAMP8. Furthermore, CRS significantly decreased the expression of BDNF protein and mRNA in the hippocampus of SAMP8 and SAMR1. These data indicated that SAMP8 is more sensitive to the deleterious effects of CRS on learning than SAMR1. A greater decrease in hippocampal cell proliferation caused by chronic stress may be part of the underlying mechanism for the more severe learning deficit observed in SAMP8. In addition, our findings suggested a role of BDNF in the stress-induced impairment of learning and hippocampal cell proliferation in both strains.     

Disturbance of rapid eye movement sleep in senescence-accelerated mouse prone/8 mice is improved by retinoic acid receptor agonist Am80 (tamibarotene)

Senescence-accelerated mouse prone/8 (SAMP8) mice are known to exhibit age-related deterioration in sleep–wake architecture compared with senescence-accelerated mouse resistant/1 (SAMR1) mice. We investigated whether treatment with Am80 (Tamibarotene), a retinoic acid receptor agonist, would improve sleep in 9–10-month-old SAMP8 mice. One week of Am80 administration improved the decrease in rapid eye movement (REM) sleep shown by SAMP8 mice. Real-time RT-PCR analysis demonstrated an impairment in the hippocampal retinoid cascade (retinoic acid receptor alpha and transthyretin) in SAMP8 in comparison to SAMR1 mice. Am80 treatment induced an increase in mRNA expression in the vesicular acetylcholine transporter in the brainstem and transthyretin in the hippocampus. Furthermore, decreased cortical acetylcholine content in SAMP8 was improved by Am80 administration. Decreased non-REM sleep and delta oscillation were also observed in SAMP8 mice; however, this was not improved by Am80 administration. These results partially support the hypothesis that the effects of aging on sleep–wake architecture are improved by the activation of retinoic acid receptors. The improvement may be induced by the activation of the cholinergic pathway.     

Proteomic data show an increase in autoantibodies and alpha-fetoprotein and a decrease in apolipoprotein A-II with time in sera from senescence-accelerated mice

We evaluated changes in levels by comparing serum proteins in senescence-accelerated mouse-prone 8 (SAMP8) mice at 2, 6, 12, and 15 months of age (SAMP8-2 m, -6 m, -12 m, -15 m) to age-matched SAM-resistant 1 (SAMR1) mice. Mice were sacrificed, and blood was analyzed by 2-dimensional electrophoresis combined with mass spectrometry. Five protein spots were present in all SAMP8 serum samples, but only appeared in SAMR1 samples at 15 months of age except for spot 3, which also showed a slight expression in SAMR1-12 m sera. Two proteins decreased in the sera from SAMP8-2 m, -6 m, and -12 m mice, and divided into 2 spots each in SAMP8-15 m sera. Thus, the total number of altered spots in SAMP8 sera was 7; of these, 4 were identified as Ig kappa chain V region (M-T413), chain A of an activity suppressing Fab fragment to cytochrome P450 aromatase (32C2_A), alpha-fetoprotein, and apolipoprotein A-II. M-T413 is a monoclonal CD4 antibody, which inhibits T cell proliferation. We found that M-T413 RNA level was significantly enhanced in splenocytes from SAMP8-2 m mice. This agreed with serum M-T413 protein alterations and a strikingly lower blood CD4⁺ T cell count in SAMP8 mice when compared to the age-matched SAMR1 mice, with the latter negatively correlating with serum M-T413 protein volume. Age-related changes in serum proteins favored an increase in autoantibodies and alpha-fetoprotein and a decrease of apolipoprotein A-II, which occurred in SAMP8 mice at 2 months of age and onwards. These proteins may serve as candidate biomarkers for early aging.     

Increased permeability of blood-brain barrier on the hippocampus of a murine model of senescence

SAMP8 mice show several indicative characteristics of accelerated aging and have been used to study the physiological and physiopathological processes that take place during senescence. There is some controversy about the presence of a functional blood-brain barrier (BBB) disturbance on these animals, which could be related to the oxidative stress or the amyloidosis present in their brain. In order to elucidate BBB status in the hippocampus of SAMP8 mice, in this study we have determined the extravasation from brain microvessels of endogenous IgG in SAMP8 mice aged 3, 7 and 12 months and in age-matched control SAMR1 mice. Immunohistochemistry, confocal microscopy and an imaging methodology specially designed to quantify IgG extravasation have been used. The choroid plexus was analyzed as a control for positive extravasation in SAMP8 and SAMR1 mice and, as expected, in all studied ages high IgG immunoreactivity was observed in both strains. We have found significantly higher levels of IgG extravasation in the hippocampus of 12-month-old SAMP8 mice compared to SAMR1 mice, indicating an increased permeability of BBB in aged senescence-accelerated mice.     

Tubular aggregates in the skeletal muscle of the senescence-accelerated mouse; SAM

We investigated the skeletal muscles of nine strains of senescence accelerated mouse (SAM), DDD, AKR/J, C57BL/6J, A/J and BALB/c mice. We found that male SAMP8, SAMP7, C57BL/6J, A/J and BALB/c mice expressed tubular aggregates (TAs) in their skeletal muscle. Among these strains, the SAMP8 strain, which exhibits a short life span and various age-associated neurodegenerative disorders plus mitochondrial dysfunction, showed TAs more markedly than the others. Thus, we compared SAMP8 mice against SAMR1 mice, an accelerated senescence-resistant strain. Light- and electron micrographs showed that male SAMP8 mice exhibited an age-dependent aggravation of TA accumulation. There were no significant differences in the serum lactate/pyruvate levels between the SAMP8 and SAMR1 mice. However, the serum creatine kinase (CK) levels of the 3 and 6-month-old SAMP8 mice were higher than that of the corresponding SAMR1 mice. Considering the serum CK levels and the mitochondrial dysfunction of SAMP8 mice, we conclude that the TAs may be involved in the homeostasis of energy metabolism that is not appropriately regulated in the SAMP8 mouse mitochondrion.     

Age-related difference in nociceptive behavior between SAMP6 and SAMR1 strains

Senescence accelerated prone mouse 6 (SAMP6) mice have been known to be a model for accelerated aging. Compared with the normal control senescence accelerated resistant mouse 1 (SAMR1) mice, although the SAMP6 mice have normal bone mass at 4 months, they exhibit a significantly lower bone mass at 8 months. It was recently reported that SAMP6 has memory deficit at 4 months of age, indicating that the change of nervous function might be already detected at 4 months of age. To assess whether SAMP6 mice exhibit an age-related abnormality of nociceptive transmission, we examined a battery of tests using the von Frey test for mechanically induced response, the hot plate test for thermally induced response, and the formalin paw test for chemically induced response. SAMP6 and SAMR1 showed similar response patterns in the von Frey test and the hot plate test. In the formalin paw test, 1-month-old SAMP6 and SAMR1 had similar responses, while 4-month-old SAMP6 exhibited attenuated phase 2 response, but normal phase 1 response. These findings indicate that onset of age-related phenotypes in SAMP6 differs in different tissues. SAMP6 could be useful to delineate the involvement of age-related nociceptive mechanisms.     

Differential gene expression profiles in the hippocampus of senescence-accelerated mouse

The senescence-accelerated mouse (SAM) is an animal model for studying senescence and age-associated disorders due to its inherited aging phenotype. The SAM/prone8 (SAMP8) is a useful animal model to investigate the fundamental mechanisms involved in age-related learning and memory deficits that may have relevance to age-associated AD, while SAM/resistant1 (SAMR1) shows normal. To identify genes rendering the cognitive deterioration with aging, the subtractive cDNA libraries containing 1924 clones with the positive ratio of 96.18% were generated and the microarray containing 3136 cDNA was prepared. The results of screening libraries by the microarray showed that of all 91 differentially expressed genes, 50 were over-expressed and 41 were low-expressed in SAMP8. Some of the identified genes were confirmed by the real time quantitative RT-PCR. These results indicated the profiles of gene expression in the hippocampus of SAMP8 and SAMR1 were significantly different, which may play important roles in the age-related cognitive deficit in SAMP8, suggesting those genes related to the cognitive deficient or pathology change in the brain of SAMP8 may be potential gene targets for Alzheimer's disease therapy.     

Age-related changes in anxiety are task-specific in the senescence-accelerated prone mouse 8

In the senescence-accelerated prone mouse 8 (SAMP8), an excellent model of brain aging, aged individuals have impairments in learning and memory. One study has indicated that the anxiety is also reduced in those mice. However, increased anxiety with aging has been observed in other models, such as C57BL mice and rats. Altered emotion is linked to impairments in learning and memory. Thus, we were interested in further characterizing the pattern of age-related changes in anxiety in this strain. In the present study, a battery of tasks (i.e., elevated plus maze, open field, black-white alley, food neophobia and hole-board) was used to determine the age-related alterations in anxiety in the SAMP8 mice. Three age groups (2, 6, and 10 months of age) of SAMP8 mice and their control SAMR1 (senescence-accelerated resistant mouse 1) mice were used. The results showed that the effect of age was significant only in the elevated plus maze and black-white alley tasks. The SAMP8 showed a tendency toward increased anxiety with age as measured by the time spent on the open arms of elevated plus maze. When the sexes were separated for analysis, the increased anxiety was significant in the old (10-month-old) male SAMP8. In the black-white alley task, however, anxiety levels in the old male SAMP8 mice were lower than those of the middle-aged (6-month-old) mice, but similar to those in the young (2-month-old) mice. These results suggested that the age-related anxiety levels of SAMP8 mice are sex- and task-specific.