综述与专论: 白质消融性白质脑病研究进展

白质消融性白质脑病（leukoencephalopathy with vanishing white matter,VWM）是一种常染色体隐性遗传性脑白质病,其致病基因EIF2B 1~5分别编码真核细胞蛋白质翻译起始因子2B（eukaryotic initiation factor 2B,eIF2B）的5个亚基α~ε,其中任一编码基因突变均可引起发病。起病多见于婴幼儿及儿童期,临床表型差异大,典型表现为进行性运动功能退行,可伴共济失调和癫痫。应激（发热、外伤等）可导致发作性加重。影像学显示大脑白质进行性液化。尸解神经病理学特征主要表现为广泛性白质稀疏和囊性变性,无神经胶质细胞反应性增生,星形胶质细胞形态异常,过表达祖细胞标志物巢蛋白（Nestin）和胶质纤维酸性蛋白δ（GFAPδ）,少突前体细胞数量增加和成熟少突胶质细胞减少、泡沫化且凋亡增加。VWM致病基因EIF2B 1~5是管家基因,但多数患者通常仅脑白质受累。少数胎儿期及婴儿早期发病的患者可出现多系统受累,成年女性患者可有卵巢功能障碍。目前认为,星形胶质细胞在其致病机制中起着核心作用,病理性星形胶质细胞继发性引起少突胶质细胞成熟障碍和髓鞘形成异常,进而导致脑白质病变。其他疾病机制包括内质网应激后未折叠蛋白反应（UPR）过度激活、线粒体功能障碍、自噬抑制等,尚不完全明确。     

研究报告: 一个白质消融性白质脑病家系新基因突变及临床表型研究

目的 探讨白质消融性脑病的临床及影像学特点。方法 回顾分析一例白质消融性白质脑病患儿家系的临床资料，并复习相关文献。结果 先证者1，女，4岁10个月，因步态异常起病。头颅磁共振成像（MRI）示白质异常，且弥漫对称。基因检测发现患儿EIF2B4基因存在2个错义突变，均位于外显子13，分别为C. 1544 T→A（p.Leu515Gln）和C. 1445 G→T （p.Arg 482Leu）杂合变异，国内外均未报道，为新发现的基因变异。结合国外临床诊断标准及基因分析结果确诊为白质消融性白质脑病。另一患儿为其同卵妹妹，与其发病时间、发病表现、头颅MRI及基因检测结果均大致相同，但随访1年发现先证者1退步更快。结论 发现2个新的EIF2B4基因错义突变，基因分析有助明确诊断白质消融性白质脑病。     

巨脑性白质脑病伴皮层下囊肿MLC1基因突变对星形胶质细胞功能的影响

单基因病是一种天然存在的致病基因突变模型,对这些基因突变引起的细胞功能障碍的分子机制研究越来越受到关注。巨脑性白质脑病伴皮层下囊肿(MLC)是儿童较常见的遗传性白质脑病之一,其致病基因为MLC1。新近研究表明,MLC1蛋白主要在星形胶质细胞的终足(end foot)表达,对其功能研究尚处于起步阶段,在分子水平上探讨MLC1基因突变对星形胶质细胞功能影响可以阐明其可能的分子机制,这些研究结果将为了解本病及类似疾病的共同发生机制、新的治疗靶点及早期干预,提供理论依据。     

可逆性后部白质脑病综合征

可逆性后部白质脑病综合征(reversible posterior leukoencephalopathy syndrome,RPLS)是一种以头痛、癫痫发作、视觉障碍、意识和精神障碍为主要临床症状;可逆性后部白质损害为主要神经影像学表现的临床综合征.该病如治疗及时准确疾病的临床和影像学改变完全可逆,故早期诊断治疗非常重要.本文就目前对该疾病的研究现状和进展作一综述.     

研究报告: EIF2B5表达下调的人星形胶质细胞与人神经元在内质网应激后细胞存活及miRNA表达的差异

目的 探讨白质消融性白质脑病中胶质细胞选择性受累而神经元受累轻微的原因。方法 将EIF2B5-RNAi表达载体转染至人星形胶质细胞和人神经元,检测基础状态下及内质网应激（endoplasmic reticulum stress,ERS）后细胞凋亡和活力,检测参与ERS调控的已知和未知miRNA,筛选EIF2B5-RNAi人星形胶质细胞在ERS后miRNA变化。结果 与EIF2B5-RNAi人神经元相比,星形胶质细胞自发凋亡及细胞活力下降。较之神经元,更多miRNA参与星形胶质细胞ERS刺激后的调控,EIF2B5-RNAi组参与调控的miRNA数目显著减少。聚类分析发现,5条已知miRNA是通路连接的关键组分。结论 人星形胶质细胞在ERS后可能更加依赖众多促细胞增殖分化的miRNA修复,而EIF2B5-RNAi人星形胶质细胞存在自发凋亡,ERS后严重减少的miRNA可能导致细胞无法存活。     

伴皮层下囊肿的巨脑性白质脑病星形胶质细胞肿胀与囊肿形成机制

MLC1/GlialCAM突变导致伴皮层下囊肿的巨脑性白质脑病(MLC)预后不同的常染色体隐性/显性的一类中枢神经系统髓鞘变性病,病理特征为星形胶质细胞肿胀与囊肿形成。MLC1与GlialCAM蛋白在星形胶质细胞定位于终足处,参与MLC1/GlialCAM/CLCN2三聚体结构的形成,MLC1突变影响EGFR信号转导通路参与星形胶质细胞体积调节与RVD活化,影响EGFR-KCa3. 1信号通路使得星形胶质细胞功能障碍,影响水和离子平衡,最终导致疾病发生。     

内质网应激与胰岛素抵抗

肥胖是一种影响人群健康的重要致病因素 ,肥胖导致胰岛素抵抗和Ⅱ型糖尿病的机制目前尚不清楚 .最近Umut zcan等人在细胞培养和动物模型研究的基础上认为 ,内质网应激可能参与肥胖时胰岛素抵抗的发病过程 .研究者以PKR likekinase(PERK ,内质网膜上的一种蛋白激酶 )和翻译起始因子eIF2α的磷酸化水平为内质网应激指标 ,发现饮食诱导肥胖组及遗传性肥胖组小鼠肝组织和脂肪组织PERK和eIF2α磷酸化水平较正常饮食组和遗传性消瘦组明显升高 .同时 ,葡萄糖调节蛋白 78(GRP78,内质网应激指标 )mRNA的表达水平增高 ,且GRP78mRNA表达的…     

敲除eIF4B基因对小鼠胚胎肝脏细胞凋亡的影响北大核心CSCD

真核翻译起始因子4B(eukaryotic translation initiation factor 4B,eIF4B)在mRNA翻译起始、细胞存活和增殖过程中发挥着关键作用,然而其在生物体内的生物学功能仍存在许多疑问。本研究利用eIF4B基因敲除小鼠模型,结合苏木精和伊红(hematoxylin-eosin,HE)染色、流式细胞术、Western blotting和免疫组化等一系列实验技术手段,探究了eIF4B在胚胎发育过程中的功能及作用机理。结果显示,eIF4B敲除小鼠胚胎的肝脏呈现严重病理损伤,主要表现为胚肝细胞的凋亡和坏死,而小鼠胚胎的肺脏、脑、胃和胰腺则发育正常。进一步研究发现,在eIF4B敲除小鼠的胚胎肝脏中活化型caspase 3(cleaved-caspase 3)的表达水平显著升高。此外,eIF4B敲除小鼠的胚胎成纤维细胞和胚胎肝脏中mTOR通路下游信号分子p70S6K的表达和磷酸化水平以及4EBP1的磷酸化水平显著升高。综上所述,eIF4B敲除导致cleaved-caspase 3表达增加和mTOR信号通路过度活化,促进胚肝细胞的凋亡,致使小鼠胚肝发育异常,最终引发小鼠胚胎死亡。本研究揭示了eIF4B在胚胎发育过程中的重要作用,为深入了解eIF4B在生物体内的生物学功能提供了新的科学依据。     

eIF4E作用及调节机制

eIF4E作为翻译启动因子复合体eIF4-F的关键部分,调节细胞的蛋白质合成的限速步骤,ras基因加强eIF4E的磷酸化,c-myc基因增加eIF4E mRNA水平,eIF4E活性随其本身磷酸化的加强而加强,随其结合蛋白的磷酸化加强而减弱。eIF4E是新近发现的原癌,这量的eIF4E选择性地加强原癌基因等“弱mRNA”的翻译：可以通过加强蛋白质合成的速度,也可以加速mRNA由细胞核由胞浆转移。     

Scurvy in capybaras bred in captivity in Argentine

In order to determine if the absence of vitamin C in the diet of capybaras (Hydrochoerus hydrochaeris) causes scurvy, a group of seven young individuals were fed food pellets without ascorbic acid, while another group of eight individuals received the same food with 1 g of ascorbic acid per animal per day. Animals in the first group developed signs of scurvy-like gingivitis, breaking of the incisors and death of one animal. Clinical signs appeared between 25 and 104 days from the beginning of the trial in all individuals. Growth rates of individuals deprived of vitamin C was considerably less than those observed in the control group. Deficiency of ascorbic acid had a severe effect on reproduction of another population of captive capybaras. We found that the decrease in ascorbic acid content in the diet affected pregnancy, especially during the first stages. The results obtained suggest that it is necessary to supply a suitable quantity of vitamin C in the diet of this species in captivity.     

Changes in lactate dehydrogenase activity in chicken tissues in hyperthyreosis in ontogenesis

The lactate dehydrogenase activity in reactions of lactate oxidation and synthesis was studied in subfractions of the chicken brain, heart and liver at the embryonal, early postembryonal and adult stages of development after thyroxine administration. It has been shown that during embryogenesis thyroxine predominantly enhanced the rate of lactate oxidation in the mitochondrial tissues. A marked increase in the lactate synthesis was found in cytoplasm of the adult chicken tissues. Specificity of enzyme activity alterations was detected in the chicken brain during ontogenesis after thyroxine administration.     

Role for dopamine in malonate-induced damage in vivo in striatum and in vitro in mesencephalic cultures

Defects in mitochondrial energy metabolism have been implicated in the pathology of several neurodegenerative disorders. In addition, the reactive metabolites generated from the metabolism and oxidation of the neurotransmitter dopamine (DA) are thought to contribute to the damage to neurons of the basal ganglia. We have previously demonstrated that infusions of the metabolic inhibitor malonate into the striata of mice or rats produce degeneration of DA nerve terminals. In the present studies, we demonstrate that an intrastriatal infusion of malonate induces a substantial increase in DA efflux in awake, behaving mice as measured by in vivo microdialysis. Furthermore, pretreatment of mice with tetrabenazine (TBZ) or the TBZ analogue Ro 4-1284 (Ro-4), compounds that reversibly inhibit the vesicular storage of DA, attenuates the malonate-induced DA efflux as well as the damage to DA nerve terminals. Consistent with these findings, the damage to both DA and GABA neurons in mesencephalic cultures by malonate exposure was attenuated by pretreatment with TBZ or Ro-4. Treatment with these compounds did not affect the formation of free radicals or the inhibition of oxidative phosphorylation resulting from malonate exposure alone. Our data suggest that DA plays an important role in the neurotoxicity produced by malonate. These findings provide direct evidence that inhibition of succinate dehydrogenase causes an increase in extracellular DA levels and indicate that bioenergetic defects may contribute to the pathogenesis of chronic neurodegenerative diseases through a mechanism involving DA.     

SSTR5 ablation in islet results in alterations in glucose homeostasis in mice

Somatostatin (SST) peptide is a potent inhibitor of insulin secretion and its effect is mediated via somatostatin receptor 5 (SSTR5) in the endocrine pancreas. To investigate the consequences of gene ablation of SSTR5 in the mouse pancreas, we have generated a mouse model in which the SSTR5 gene was specifically knocked down in the pancreatic beta cells (betaSSTR5Kd) using the Cre-lox system. Immunohistochemistry analysis showed that SSTR5 gene expression was absent in beta cells at three months of age. At the time of gene ablation, betaSSTR5Kd mice demonstrated glucose intolerance with lack of insulin response and significantly reduced serum insulin levels. Insulin tolerance test demonstrated a significant increase of insulin clearance in vivo at the same age. In vitro studies demonstrated an absence of response to SST-28 stimulation in the betaSSTR5Kd mouse islet, which was associated with a significantly reduced SST expression level in betaSSTR5Kd mice pancreata. In addition, betaSSTR5Kd mice had significantly reduced serum glucose levels and increased serum insulin levels at 12 months of age. Glucose tolerance test at an older age also indicated a persistently higher insulin level in betaSSTR5Kd mice. Further studies of betaSSTR5Kd mice had revealed elevated serum C-peptide levels at both 3 and 12 months of age, suggesting that these mice are capable of producing and releasing insulin to the periphery. These results support the hypothesis that SSTR5 plays a pivotal role in the regulation of insulin secretion in the mouse pancreas.