神经元胞浆转运与外周神经病

外周神经系统的神经元在结构和功能上有明显的特点:轴突的表面积或容积比胞体大上千倍,但轴浆中没有合成蛋白质的粗面内质网,核蛋白体也很少;轴突生长发育、代谢更新以及再生修复所需的结构物质必须由胞体合成,经轴浆转运到轴突的特定部位;轴突传导冲动、释放递质所需的能源、递质和有关的代谢酶,以及其他功能物质也有赖于胞体内合成与胞浆中转运。外周神经这种分化上的特异性,不仅说明胞浆转运有重要的生理意义,还说     

线粒体T12338C突变可能是与Leber遗传性视神经病变相关的突变位点

Leber遗传性视神经病变变(Leber’s hereditary optic neuropathy,LHON)是一种与线粒体DNA(Mito-chondrial DNA,mtDNA)突变相关的母系遗传性眼科疾病。文章报道了两例具有典型LHON临床、分子遗传特征的中国汉族家系。首先通过对家系先证者和其他成员进行眼科相关检查,发现两个家系成员中视力都仅有先证者一人损害严重,即外显率很低。经常规的方法对母系成员进行mtDNA测序及相关软件分析,结果发现携带ND4 G11696A和ND5 T12338C同质性突变位点,多态性变异位点均属于东亚单体型F2。线粒体DNA ND4 G11696A是一个已知的与LHON相关的突变位点,而T12338C位于线粒体氧化磷酸化复合体I亚基ND5的第2个碱基,该突变使起始密码子由蛋氨酸转变成苏氨酸,并且紧连tRNALeu(CUN)的3′末端。这可能影响tRNA Leu(CUN)空间结构和稳定性发生改变,以及起始密码子改变导致线粒体ND5蛋白合成功能受损和ATP障碍,最终导致需求能量高的视神经受损和视力损害。因此,线粒体ND4 G11696A和ND5 T12338C突变可能协同作用Leber遗传性视神经病变的发生,是与LHON相关的mtDNA突变位点,但外显率很低说明突变本身不足以造成LHON的表型表达,提示其他修饰因子(核修饰基因、环境等)可能对这两个家系发病起协同作用。     

神经元维持不对称性新机制

科学家发现在接近神经元胞体的轴突起始段存在一个由肌动蛋白和Ankyrin G构成的分子筛,像滤网一样限制了大分子蛋白在轴突和胞体之间的扩散,但允许某些依赖特定马达蛋白转运的膜蛋白通过。马达蛋白驱动力的强弱,以及膜蛋白-马达蛋白复合体运输效能的高低,是膜蛋白能否通过分子筛的决定条件。     

青年猫和老年猫视神经超微结构观察比较

目的探讨青年猫和老年猫视神经年龄相关的形态学变化及可能造成的生理影响。方法取4只青年猫(2-3岁,2-2.5kg)和4只老年猫(10-13岁,2.5-3.5kg)颅内相对应部分视神经,制作横向半薄切片和超薄切片,半薄切片用甲苯胺蓝硼砂溶液染色,光镜观察、测量视神经的直径(不含外层神经膜);超薄切片标本用醋酸和柠檬酸铅染色,电镜观察、计数视神经纤维密度、测量视神经纤维外径D(含髓鞘)和内径d(不含髓鞘),按一定分级范围算出各种直径的纤维及各种d/D比值的纤维所占百分比,分别画出直方图,对实验结果进行统计学分析并绘制纤维直径谱。结果与青年猫相比,老年猫视神经直径显著增大(P0.05);纤维数量显著下降(P0.05)。纤维直径谱分析结果显示,青、老年猫纤维直径分布范围相似,但老年猫纤维的峰直径及纤维平均直径比青年猫的显著减小(P0.05),老年猫视神经纤维的d/D比值亦明显降低。另外,老年猫视神经中部分轴突肿胀,髓鞘疏松、结构紊乱,板层脱离、空泡化,有的轴索髓鞘溶解。结论在衰老过程中,老年猫视神经纤维丢失,纤维直径减小,d/D比值下降,以及纤维髓鞘的松散解体,这些变化均可能导致视神经纤维对视觉信息的传导速度减慢,是老年个体视觉分析速度下降的重要原因。     

线粒体tRNAGlu A14693G可能是与Leber遗传性视神经病变相关的基因突变

收集了3个具有典型临床特征的中国汉族Leber遗传性视神经病变(Leber's hereditary optic neuropathy, LHON)家系。通过对先证者和家系其他成员进行眼科临床(如视力损害程度和发病年龄)检查, 发现这些家系成员中视力损害的外显率很低, 经mtDNA测序分析, 在tRNA^Glu 上发现了A14693G同质性突变位点, 多态性位点分别属于东亚单体型Y1b、Y1和Y1, 没有发现其他高度保守和有功能意义的突变位点。A14693G突变位于线粒体tRNAGlu高度保守区(通用位点为54位), 可能导致tRNA空间结构和稳定性发生改变, 继而影响tRNA的代谢, 导致线粒体蛋白合成功能受损和ATP障碍, 最终导致视力损害。所以, tRNAGlu A14693G突变可能是与视神经病变相关的致病性线粒体突变位点。     

神经元细胞器和囊泡运输

神经元是高度极化的细胞,典型的神经元由胞体、轴突及树突构成。神经元的胞体和神经末梢之间的物质和信息传递以及神经元之间的通讯都依赖于胞内的细胞器和囊泡运输。神经元中的运输系统对于神经元形态和功能的建成和维持以及突触的功能和可塑性至关重要。胞内运输的调控机制是细胞神经生物学领域的重大科学问题。该文重点总结了近年来关于神经元内细胞器和囊泡运输的研究进展,并对神经活性依赖的运输调控机制进行了初步探讨。此外,该文还简要介绍了神经元胞内运输与人类疾病之间的关系。     

Leber遗传性视神经病变研究进展和挑战

Leber遗传性视神经病变(Leber hereditary optic neuropathy, LHON; MIM535000)是最典型的线粒体遗传病之一, 主要由线粒体DNA (Mitochondrial DNA, mtDNA)3个原发突变(Primary mutation, m.11778G>A、m.3460G> A 和m.14484T>C)引起。患者表现为无痛性双侧视力下降或丧失, 主要易感人群为青壮年男性。不完全外显(Incomplete penetrance)和性别偏好(Gender bias)是该病亟待解决的两大难题, 目前尚无有效的预防及治疗措施。文章对近年来LHON 的分子发病机制、临床症状及特点、体外实验和动物模型研究、预防及治疗等方面的研究进展进行综述, 并集中介绍了我们近期对于我国LHON患者的研究结果。     

中国人群携带m.14484T>C突变的Leber’s遗传性视神经病变线粒体单体型及多态位点分析

线粒体ND6基因(MT-ND6)上的m.14484TC突变是Leber’s遗传性视神经病变(Leber’s hereditary optic neuropathy,LHON)的一个原发性突变,但该突变自身不足以产生视力损伤。为研究线粒体单体型对携带该突变人群LHON发病的影响,文章对1 177例中国汉族LHON患者MT-ND6基因进行了全面系统的筛查,共筛查到67例患者携带m.14484TC同质性突变,在该研究群体中所占比例为5.7%。携带m.14484TC突变的51例家系LHON的外显率从5.6%~100.0%不等,平均外显率为21.5%。对家系中51例先证者线粒体全基因组进行分析,各表现为不同的多态性,分别属于18个东亚线粒体单体型。其中单体型A和单体型F在病例组频率均明显低于106例对照组。另外,单体型M10a在病例组中占9.8%,在对照组中未被发现,进一步发现该单体型家系LHON的平均外显率(46.13%)显著高于其他单体型家系的平均外显率,提示线粒体单体型M10a可能增加视力损伤的风险。     

猫视神经中S100蛋白表达的年龄相关变化

比较老年猫和青年猫视神经S100蛋白表达及胶质细胞的年龄相关变化,探讨其可能的生理作用.取老年猫(10～13龄)和青年猫(1～3龄)各4只的颅内视神经相应部分作组织切片,用免疫组织化学ABC法标记S100免疫阳性(S100～IR)细胞,Marsland-Gless染色显示胶质细胞.光镜下采用图像分析系统计数视神经中S100-IR细胞密度、胶质细胞密度及阳性反应灰度值.视神经中棕黄色S100-IR细胞分布均匀,Marsland-Gless染色的纤维横断面及胶质细胞均呈棕红色.与青年猫相比,老年猫视神经中胶质细胞密度明显增大;S100-IR细胞密度显著增加(P<0.01),胞体较大,阳性较强(灰度值显著减小,P<0.01);S100-IR细胞在胶质细胞中所占比例亦显著增大.结果表明S100-IR细胞呈明显的年龄相关性增生,这可能对衰老的神经纤维起保护作用.     

脂质过氧化物酶体增殖物激活受体在心脏生理与病理中的作用

心肌能量代谢状况是其结构与功能的重要决定因素,调节能量代谢是心脏疾病的有效疗法之一.脂质过氧化物酶体增殖物激活受体(PPARs)是一组具有复杂功能的核受体超家族成员,与脂肪形成、糖脂代谢、炎症及肿瘤发生等多种生物过程有关.PPARs可通过调控编码脂肪酸与糖类氧化相关酶的基因转录而调节心肌代谢,在心脏多种疾病病理过程中其表达与活性均有明显变化,因此已被作为心脏病的治疗靶点之一.本文对PPARs在心脏生理与病理中的作用进行简要介绍.     

OPA1-associated disorders: Phenotypes and pathophysiology

The OPA1 gene, encoding a dynamin-like mitochondrial GTPase, is involved in autosomal dominant optic atrophy (ADOA, OMIM #165500). ADOA, also known as Kjer's optic atrophy, affects retinal ganglion cells and the axons forming the optic nerve, leading to progressive visual loss. OPA1 gene sequencing in patients with hereditary optic neuropathies indicates that the clinical spectrum of ADOA is larger than previously thought. Specific OPA1 mutations are responsible for several distinct clinical presentations, such as ADOA with deafness (ADOAD), and severe multi-systemic syndromes, the so-called “ADOA plus” disorders, which involve neurological and neuromuscular symptoms similar to those due to mitochondrial oxidative phosphorylation defects or mitochondrial DNA instability. The study of the various clinical presentations of ADOA in conjunction with the investigation of OPA1 mutations in fibroblasts from patients with optic atrophy provides new insights into the pathophysiological mechanisms of the disease while underscoring the multiple physiological roles played by OPA1 in energetic metabolism, mitochondrial structure and maintenance, and cell death. Finally, OPA1 represents an important new paradigm for emerging neurodegenerative diseases affecting mitochondrial structure, plasticity and functions.     

Optic nerve degeneration and mitochondrial dysfunction: genetic and acquired optic neuropathies

Selective degeneration of the smallest fibers (papillo-macular bundle) of the human optic nerve occurs in a large number of optic neuropathies characterized primarily by loss of central vision. The pathophysiology that underlies this peculiar pattern of cell involvement probably reflects different forms of genetic and acquired mitochondrial dysfunction.Maternally inherited Leber's hereditary optic neuropathy (LHON), dominant optic atrophy (Kjer disease), the optic atrophy of Leigh's syndrome, Friedreich ataxia and a variety of other conditions are examples of inherited mitochondrial disorders with different etiologies. Tobacco-alcohol amblyopia (TAA), the Cuban epidemic of optic neuropathy (CEON) and other dietary (Vitamins B, folate deficiencies) optic neuropathies, as well as toxic optic neuropathies such as due to chloramphenicol, ethambutol, or more rarely to carbon monoxide, methanol and cyanide are probably all related forms of acquired mitochondrial dysfunction.Biochemical and cellular studies in LHON point to a partial defect of respiratory chain function that may generate either an ATP synthesis defect and/or a chronic increase of oxidative stress. Histopathological studies in LHON cases and a rat model mimicking CEON revealed a selective loss of retinal ganglion cells (RGCs) and the corresponding axons, particularly in the temporal-central part of the optic nerve. Anatomical peculiarities of optic nerve axons, such as the asymmetric pattern of myelination, may have functional implications on energy dependence and distribution of mitochondrial populations in the different sections of the nerve. Histological evidence suggests impaired axonal transport of mitochondria in LHON and in the CEON-like rat model, indicating a possible common pathophysiology for this category of optic neuropathies. Histological evidence of myelin pathology in LHON also suggests a role for oxidative stress, possibly affecting the oligodendrocytes of the optic nerves.     

Mitochondrial Optic Neuropathies: How Two Genomes may Kill the Same Cell Type?

Ocular involvement is a prevalent feature in mitochondrial diseases. Leber’s hereditary optic neuropathy (LHON) and dominant optic atrophy (DOA) are both non-syndromic optic neuropathies with a mitochondrial etiology. LHON is associated with point mutations in the mitochondrial DNA (mtDNA), which affect subunit genes of complex I. The majority of DOA patients harbor mutations in the nuclear-encoded protein OPA1, which is targeted to mitochondria and participates to cristae organization and mitochondrial network dynamics. In both disorders the retinal ganglion cells (RGCs) are specific cellular targets of the degenerative process. We here review the clinical features and the genetic bases, and delineate the possible common pathomechanism for both these disorders.     

Mitochondrial oxidative phosphorylation compensation may preserve vision in patients with OPA1-linked autosomal dominant optic atrophy

Autosomal Dominant Optic Atrophy (ADOA) is the most common inherited optic atrophy where vision impairment results from specific loss of retinal ganglion cells of the optic nerve. Around 60% of ADOA cases are linked to mutations in the OPA1 gene. OPA1 is a fission-fusion protein involved in mitochondrial inner membrane remodelling. ADOA presents with marked variation in clinical phenotype and varying degrees of vision loss, even among siblings carrying identical mutations in OPA1. To determine whether the degree of vision loss is associated with the level of mitochondrial impairment, we examined mitochondrial function in lymphoblast cell lines obtained from six large Australian OPA1-linked ADOA pedigrees. Comparing patients with severe vision loss (visual acuity [VA]<6/36) and patients with relatively preserved vision (VA>6/9) a clear defect in mitochondrial ATP synthesis and reduced respiration rates were observed in patients with poor vision. In addition, oxidative phosphorylation (OXPHOS) enzymology in ADOA patients with normal vision revealed increased complex II+III activity and levels of complex IV protein. These data suggest that OPA1 deficiency impairs OXPHOS efficiency, but compensation through increases in the distal complexes of the respiratory chain may preserve mitochondrial ATP production in patients who maintain normal vision. Identification of genetic variants that enable this response may provide novel therapeutic insights into OXPHOS compensation for preventing vision loss in optic neuropathies.     

A retinal projection to the lateral hypothalamus in the rat

Summary This study presents evidence for a retinal projection to neurons in the lateral hypothalamic area (LHA) of the albino rat. In Golgi-Kopsch material dendrites from LHA-neurons are observed to extend through the supraoptic commissures into the optic tract. The presence of dendrites in the optic tract is confirmed by electron microscopy. Numerous axon terminals are observed forming asymmetric synaptic contacts with these dendritic profiles. Following bilateral enucleation, many of the preterminal axons and terminals in synaptic contact with dendrites in the optic tract demonstrate dark degeneration. After intraocular injection of horseradish peroxidase, there is marked labeling of preterminal axons and terminals in the optic tract. These observations indicate that LHA neurons receive a direct retinal projection from terminals making synaptic contact with dendrites of LHA-neurons extending into the optic tract.     

Leber Hereditary Optic Neuropathy: How Do Mitochondrial DNA Mutations Cause Degeneration of the Optic Nerve?

Leber hereditary optic neuropathy (LHON) is an inherited form of bilateral optic atrophy in which the primary etiological event is a mutation in the mitochondrial genome. The optic neuropathy involves a loss of central vision due to degeneration of the retinal ganglion cells and optic nerve axons that subserve central vision. The primary mitochondrial mutation is necessary—but not sufficient—for development of the optic neuropathy, and secondary genetic and/or epigenetic risk factors must also be present although they are poorly defined at the present time. There is broad agreement that mutations at nucleotides 3460, 11778, and 14484 are primary LHON mutations, but there may also be other rare primary mutations. It appears that the three primary LHON mutations are associated with respiratory chain dysfunction, but the derangements may be relatively subtle. There is also debate on whether there are mitochondrial mutations that have a secondary etiological or pathogenic role in LHON. The specific pattern of the optic neuropathy may arise from a chokepoint in the optic nerve in the region of the nerve head and lamina cribosa, and which may be more severe in those LHON family members who become visually affected. It is hypothesized that the respiratory chain dysfunction leads to axoplasmic stasis and swelling, thereby blocking ganglion cell function and causing loss of vision. In some LHON patients, this loss of function is reversible in a substantial number of ganglion cells, but in others, a cell death pathway (probably apoptotic) is activated with subsequent extensive degeneration of the retinal ganglion cell layer and optic nerve.     

Functions of retrograde axonal transport

Retrograde axonal transport conveys materials from axon to cell body. One function of this process is recycling of materials originally transported from cell body to axon. In motoneurons, 50% of fast-transported protein is returned. Reversal probably occurs mainly at nerve terminals and, for labeled proteins, is nonselective. Proteolysis is not required, although changes in tertiary protein structure may occur with a repackaging of molecules in organelles different from those in which they were anterograde-transported. A second function is transfer of information about axonal status and terminal environment. Premature reversal of transport adjacent to an axon injury may be a component of a signal that initiates cell body chromatolysis. Transport of target cell-derived molecules with trophic effects on the cell body is exemplified by nerve growth factor transport in neurons dependent on it, and is probably a widespread phenomenon in the developing nervous system. Disorders in retrograde transport or reversal occur in some experimental neuropathies, and certain viruses, as well as tetanus toxin, may gain access to the central nervous system by this route.     

Hereditäre Optikusatrophien

Hereditary optic neuropathies comprise a group of clinically and genetically heterogeneous disorders, which can be divided into 2 subgroups: isolated hereditary optic atrophies and optic neuropathies as part of complex disorders. In the first group of isolated hereditary optic neuropathies, optic nerve dysfunction is typically the only manifestation of the disease. This group comprises autosomal dominant, autosomal recessive and X-linked recessive optic atrophy, and the mitochondrial inherited Leber’s hereditary optic neuropathy (LHON). In the second group of complex disorders, various neurologic and other systemic abnormalities are regularly observed. The most frequent cause in this group are mitochondrial DNA (mtDNA) mutations, inherited peripheral neuropathies, Charcot–Marie–Tooth disorders (CMT2A2, CMTX5), hereditary sensory neuropathy type 3 (HSAN3), Friedreich ataxia, leukodystrophies, sphingolipidoses, ceroid-lipofuscinoses, and neurodegeneration with brain iron accumulation (NBIA). In the present article, the clinical phenotypes and underlying genetic predispositions are described.     

The <Emphasis Type="Italic">OPA1</Emphasis> Gene Mutations Are Frequent in Han Chinese Patients with Suspected Optic Neuropathy

While many patients with hereditary optic neuropathies are caused by mitochondrial DNA (mtDNA) mutations of Leber’s hereditary optic neuropathy (LHON), a significant proportion of them does not have mtDNA mutation and is caused by mutations in genes of the nuclear genome. In this study, we investigated whether the OPA1 gene, which is a pathogenic gene for autosomal dominant optic atrophy (ADOA), is frequently mutated in these patients. We sequenced all 29 exons of the OPA1 gene in 105 Han Chinese patients with suspected LHON. mtDNA copy number was quantified in blood samples from patients with and without OPA1 mutation and compared to healthy controls. In silico program-affiliated prediction, evolutionary conservation analysis, and in vitro cellular assays were performed to show the potential pathogenicity of the mutations. We identified nine OPA1 mutations in eight patients; six of them are located in exons and three are located in splicing sites. Mutation c.1172T?>?G has not been reported before. When we combined our data with 193 reported Han Chinese patients with optic neuropathy and compared to the available data of 4327 East Asians by the Exome Aggregation Consortium (ExAC), we found a significant enrichment of potentially pathogenic OPA1 mutations in Chinese patients. Cellular assays for OPA1 mutants c.869G?>?A and c.2708_2711del showed abnormalities in OPA1 isoforms, mitochondrial morphology, and cellular reactive oxygen species (ROS) level. Our results indicated that screening OPA1 mutation is needed for clinical diagnosis of patients with suspected optic neuropathy.