In vivo regulation of the A disintegrin and metalloproteinase 10 (ADAM10) by the tetraspanin 15

A disintegrin and metalloproteinase 10 (ADAM10) plays a major role in the ectodomain shedding of important surface molecules with physiological and pathological relevance including the amyloid precursor protein (APP), the cellular prion protein, and different cadherins. Despite its therapeutic potential, there is still a considerable lack of knowledge how this protease is regulated. We have previously identified tetraspanin15 (Tspan15) as a member of the TspanC8 family to specifically associate with ADAM10. Cell-based overexpression experiments revealed that this binding affected the maturation process and surface expression of the protease. Our current study shows that Tspan15 is abundantly expressed in mouse brain, where it specifically interacts with endogenous ADAM10. Tspan15 knockout mice did not reveal an overt phenotype but showed a pronounced decrease of the active and mature form of ADAM10, an effect which augmented with aging. The decreased expression of active ADAM10 correlated with an age-dependent reduced shedding of neuronal (N)-cadherin and the cellular prion protein. APP α-secretase cleavage and the expression of Notch-dependent genes were not affected by the loss of Tspan15, which is consistent with the hypothesis that different TspanC8s cause ADAM10 to preferentially cleave particular substrates. Analyzing spine morphology revealed no obvious differences between Tspan15 knockout and wild-type mice. However, Tspan15 expression was elevated in brains of an Alzheimer’s disease mouse model and of patients, suggesting that upregulation of Tspan15 expression reflects a cellular response in a disease state. In conclusion, our data show that Tspan15 and most likely also other members of the TspanC8 family are central modulators of ADAM10-mediated ectodomain shedding in vivo.     

Protein misfolding and disease: the case of prion disorders

Recent findings strongly support the hypothesis that diverse human disorders, including the most common neurodegenerative diseases, arise from misfolding and aggregation of an underlying protein. Despite the good evidence for the involvement of protein misfolding in disease pathogenesis, the mechanism by which protein conformational changes participate in the disease is still unclear. Among the best-studied diseases of this group are the transmissible spongiform encephalopathies or prion-related disorders, in which misfolding of the normal prion protein plays a key role in the disease. In this article we review recent data on the link between prion protein misfolding and the pathogensis of spongiform encephalopathies. Received 15 July 2002; received after revision 19 August 2002; accepted 23 August 2002 RID="*" ID="*"Corresponding author.     

疼痛的神经生物学--理解大脑机制及神经疾病治疗的机理

中枢神经系统的神经元和突触具有可塑性，他们能够发生贯穿整个生命过程的长时程改变。研究这种长时程变化的分子和细胞学机制，不仅可以帮助我们了解大脑如何学习和储存新的知识，而且还可以揭示机体损伤后病理变化的机制。我认为，一方面学习和记忆等生理学功能的神经机制可能与大脑在疼痛期间的反常或机体损伤相关的变化过程共用一些信号分子；另一方面，一些不参与认知学习和记忆过程的突触和神经元网络机制也可能与疼痛的病理过程相关。伤害性感受可以从脊髓传递到前脑并在不同水平受到调节。其中，前扣带脑皮质(anterior cingulate cortex，ACC)在痛觉的感受和调节中具有重要作用。我们的实验结果表明，ACC中的N-甲基-D-门冬氨酸(NMDA)受体依赖的、钙／钙调蛋白激活的腺苷酸环化酶(adenylyl cyclases，AC)(ACl和ACB)在慢性痛的表达过程中起着重要的作用。ACC还可以通过激活内源性易化系统影响脊髓背角的痛觉信号传递。这些结果为机体对损伤的生理反应如痛行为反应、情绪变化和不良记忆等提供了重要的突触和分子水平的机制。加强对疼痛机制研究，会带动中国的神经科学的基础和临床研究。     

NLRP3 inflammasome activation in macrophage cell lines by prion protein fibrils as the source of IL-1β and neuronal toxicity

Prion diseases are fatal transmissible neurodegenerative diseases, characterized by aggregation of the pathological form of prion protein, spongiform degeneration, and neuronal loss, and activation of astrocytes and microglia. Microglia can clear prion plaques, but on the other hand cause neuronal death via release of neurotoxic species. Elevated expression of the proinflammatory cytokine IL-1β has been observed in brains affected by several prion diseases, and IL-1R-deficiency significantly prolonged the onset of the neurodegeneration in mice. We show that microglial cells stimulated by prion protein (PrP) fibrils induced neuronal toxicity. Microglia and macrophages release IL-1β upon stimulation by PrP fibrils, which depends on the NLRP3 inflammasome. Activation of NLRP3 inflammasome by PrP fibrils requires depletion of intracellular K⁺, and requires phagocytosis of PrP fibrils and consecutive lysosome destabilization. Among the well-defined molecular forms of PrP, the strongest NLRP3 activation was observed by fibrils, followed by aggregates, while neither native monomeric nor oligomeric PrP were able to activate the NLRP3 inflammasome. Our results together with previous studies on IL-1R-deficient mice suggest the IL-1 signaling pathway as the perspective target for the therapy of prion disease.     

慢性酒精中毒小鼠小脑的超微结构实验研究

目的 探讨慢性酒精中毒导致神经系统损伤的机制.方法 建立小鼠慢性酒精中毒动物模型,观察动物行为学的改变,测量血浆酒精浓度,通过透射电镜了解小脑的超微结构变化.结果 酒精处理组的血浆酒精浓度为101.4±20.5 mg/dL,与对照组和配对对照组比较,酒精处理组小鼠行动欠灵活,小脑线粒体形状多样、大小多变、数量增加和平均横断面面积显著减小;突触的数量减少、突触后膜致密物质厚度变薄、突触活性区长度变短及突触间隙宽度变宽,突触前结构内附着于突触的囊泡较多.结论 酒精对线粒体和突触结构、功能的损害可能是慢性酒精中毒的神经系统损伤机制之一.     

The Janus kinase family of protein tyrosine kinases and their role in signaling

In the early 1990s, the search for protein kinases led to the discovery of a novel family of non-receptor tyrosine kinases, the Janus kinases or JAKs. These proteins were unusual because they contained two kinase homology domains and no other known signaling modules. It soon became clear that these were not ‘just another’ type of kinase. Their ability to complement mutant cells insensitive to interferons and to be activated by a variety of cytokines demonstrated their central signaling function. Now, as we approach the end of the decade, it is evident from biochemical studies to knockout mice that JAKs play non-redundant functions in development, differentiation, and host defense mechanisms. Here, recent progress is reviewed, with particular emphasis on structure-function studies aimed at revealing how this family of tyrosine kinases is regulated.     

The role of p53 in tumour suppression: lessons from mouse models

The use of mouse models has greatly contributed to our understanding of the role of p53 in tumour suppression. Mice homozygous for a deletion in the p53 gene develop tumours at high frequency, providing essential evidence for the importance of p53 as a tumour suppressor. Additionally, crossing these knockout mice or transgenic expression p53 dominant negative alleles with other tumour-prone mouse strains has allowed the effect of p53 loss on tumour development to be examined further. In a variety of mouse models, absence of p53 facilitates tumorigenesis, thus providing a means to study how the lack of p53 enhances tumour development and to define genetic pathways of p53 action. Depending on the particular model system, loss of p53 either results in deregulated cell-cylce entry or aberrant apoptosis (programmed cell death), confirming results found in cell culture systems and providing insight into in vitro function of p53. Finally, as p53 null mice rapidly develop tumours, they are useful for evaluating agents for either chemopreventative or therapeutic activities.     

Copper and zinc dismetabolism in the mouse brain upon chronic cuprizone treatment

Recent reports describe successful treatment using copper chelation therapy in neurodegenerative animal models. However, the success claimed for chelation therapy in neurodegenerative diseases is still rather controversial. To acquire new information on copper metabolism/homeostasis, we utilized cuprizone, a very sensitive and selective copper-chelating agent with well-known neurotoxic properties, as a relevant chemical model in mice. Upon cuprizone treatment, mice developed a pronounced astrocytosis, with brain oedema and spongiosis characterised by vacuolisations of the neuropil predominantly in the white matter. In addition, cuprizone treatment severely altered copper and zinc homeostasis in the central nervous system (CNS) as well as in all other tissues examined, with increasing metal ion concentrations particularly in the CNS. Concomitant with this increase in the Cu and Zn concentration in the brain, metallothionein-I and -II were also highly immunoreactive in astrocyte, consistent with the astrocytosis and demyelination observed in our and other laboratories.Received 23 February 2005; received after revision 3 May 2005; accepted 13 May 2005     

CD4<Superscript>+</Superscript> T cell-mediated immunity against prion proteins

The prion protein (PrP(C)) is essential for susceptibility to transmissible spongiform encephalopathies. A specific conformer of this protein (PrP(Sc)) is, according to the 'protein only' hypothesis, the principal or only component of the infectious agent, designated prion. Transmission of prions between species is often inefficient, resulting in low attack rates and/or prolonged incubation times and is ascribed to a 'species barrier' caused by differences in the amino acid sequence of PrP between recipient and donor. In this report, we demonstrate that these differences in amino acid sequence result in presentation of distinct peptides on major histocompatibility complex class II molecules. These peptides result in activation of specific CD4+ T cells which leads to the induction of an effective immune response against foreign PrP as demonstrated by antibody production. Therefore, CD4+ T cells represent a crucial component of the immune system to distinguish between foreign and self PrP.     

Sleeping sickness and the brain

Recent progress in understanding the neuro-pathological mechanisms of sleeping sickness reveals a complex relationship between the trypanosome parasite that causes this disease and the host nervous system. The pathology of late-stage sleeping sickness, in which the central nervous system is involved, is complicated and is associated with disturbances in the circadian rhythm of sleep. The blood-brain barrier, which separates circulating blood from the central nervous system, regulates the flow of materials to and from the brain. During the course of disease, the integrity of the blood-brain barrier is compromised. Dysfunction of the nervous system may be exacerbated by factors of trypanosomal origin or by host responses to parasites. Microscopic examination of cerebrospinal fluid remains the best way to confirm late-stage sleeping sickness, but this necessitates a risky lumbar puncture. Most drugs, including many trypanocides, do not cross the blood-brain barrier efficiently. Improved diagnostic and therapeutic approaches are thus urgently required. The latter might benefit from approaches which manipulate the blood-brain barrier to enhance permeability or to limit drug efflux. This review summarizes our current understanding of the neurological aspects of sleeping sickness, and envisages new research into blood-brain barrier models that are necessary to understand the interactions between trypanosomes and drugs active against them within the host nervous system. Received 10 October 2001; received after revision 29 November 2001; accepted 5 December 2001     

Ecdysteroid receptors located in the central nervous system of an insect

Summary Using thaw-mount autoradiography for steroid hormones, we obtained direct evidence for a nuclear localization of ecdysteroid binding sites in target organs of blowfly (Calliphora vicina) larvae. The binding sites revealed properties of ecdysteroid receptors. Endocrine cells of the ring gland were found to be target tissues of ecydysteroids. This observation provides morphological evidence for a network of complex interendocrine regulation. In the central nervous system receptorcontaining neurons were identified which include many, if not all, neurosecretory cells of the brain. A map of ecdysteroid sensitive cells of the larval brain is presented.     

Autotaxin (NPP-2) in the brain: cell type-specific expression and regulation during development and after neurotrauma

Autotaxin is a secreted cell motility-stimulating exo-phosphodiesterase with lysophospholipase D activity that generates bioactive lysophosphatidic acid. Lysophosphatidic acid has been implicated in various neural cell functions such as neurite remodeling, demyelination, survival and inhibition of axon growth. Here, we report on the in vivo expression of autotaxin in the brain during development and following neurotrauma. We found that autotaxin is expressed in the proliferating subventricular and choroid plexus epithelium during embryonic development. After birth, autotaxin is mainly found in white matter areas in the central nervous system. In the adult brain, autotaxin is solely expressed in leptomeningeal cells and oligodendrocyte precursor cells. Following neurotrauma, autotaxin is strongly up-regulated in reactive astrocytes adjacent to the lesion. The present study revealed the cellular distribution of autotaxin in the developing and lesioned brain and implies a function of autotaxin in oligodendrocyte precursor cells and brain injuries. Received 18 September 2006; received after revision 30 October 2006; accepted 4 December 2006     

Sensing life: regulation of sensory neuron survival by neurotrophins

Neurotrophins are a family of structurally and functionally related neurotrophic factors which, in mammals, include: nerve growth factor, brain-derived neurotrophic factor, neurotrophin-3 (NT-3), and NT-4/5. In addition to their canonical role in promoting neuronal survival, these molecules appear to regulate multiple aspects of the development of the nervous system in vertebrates, including neuronal differentiation, axon elongation and target innervation, among others. Actions of neurotrophins and of their receptors in vivo are being analyzed by loss-of-function or gain-of-function experiments in mice. Here, we review the phenotypes of the primary sensory system in these mutant mouse strains and the different strategies specifically involved in the regulation of neuronal survival by neurotrophins in this portion of the nervous system. Received 10 December 2001; received after revision 11 May 2002; accepted 13 May 2002 RID="*" ID="*"Corresponding author.     

Inhibition of protein misfolding and aggregation by natural phenolic compounds

Protein misfolding and aggregation into fibrillar deposits is a common feature of a large group of degenerative diseases affecting the central nervous system or peripheral organs, termed protein misfolding disorders (PMDs). Despite their established toxic nature, clinical trials aiming to reduce misfolded aggregates have been unsuccessful in treating or curing PMDs. An interesting possibility for disease intervention is the regular intake of natural food or herbal extracts, which contain active molecules that inhibit aggregation or induce the disassembly of misfolded aggregates. Among natural compounds, phenolic molecules are of particular interest, since most have dual activity as amyloid aggregation inhibitors and antioxidants. In this article, we review many phenolic natural compounds which have been reported in diverse model systems to have the potential to delay or prevent the development of various PMDs, including Alzheimer’s and Parkinson’s diseases, prion diseases, amyotrophic lateral sclerosis, systemic amyloidosis, and type 2 diabetes. The lower toxicity of natural compounds compared to synthetic chemical molecules suggest that they could serve as a good starting point to discover protein misfolding inhibitors that might be useful for the treatment of various incurable diseases.     

Chemical chaperone therapy for GM1-gangliosidosis

We have proposed a chemical chaperone therapy for lysosomal diseases, based on a paradoxical phenomenon that an exogenous competitive inhibitor of low molecular weight stabilizes the target mutant molecule and restores its catalytic activity as a molecular chaperone intracellularly. After Fabry disease experiments, we investigated a new synthetic chaperone compound N-octyl-4-epi-β-valienamine (NOEV) in a G_M1-gangliosidosis model mice. Orally administered NOEV entered the brain through the blood-brain barrier, enhanced β-galactosidase activity, reduced the substrate storage, and clinically improved neurological deterioration. We hope that chemical chaperone therapy will prove useful for some patients with G_M1-gangliosidosis and potentially other lysosomal storage diseases with central nervous system involvement. Received 10 October 2007; received after revision 31 October 2007; accepted 6 November 2007     

Scavenger, transducer, RNA chaperone? What ligands of the prion protein teach us about its function

Prion protein, a misfolded isoform of which is the essential component of the agent of prion diseases, still remains an enigmatic protein whose physiological functions are at best hypothetical. To gain a better insight into its putative role, many studies were undertaken to look for molecules that bind prion protein, and have notably identified divalent metal ions, several proteins, and nucleic acids. At first sight, the diversity of prion protein’s ligands seems of little help to infer a plausible function. However, the intrinsically disordered property of its N-terminal tail and the potential of the protein to adopt a transmembrane topology, can both be taken into account to predict its different states during its cellular cycle and its possible functions, of which the most promising correspond to a general scavenger, a sensor or adaptor in a signaling cascade, and an RNA chaperone. Received 16 August 2006; received after revision 7 November 2006; accepted 13 December 2006     

Monogenetic determinants of Alzheimer's disease: APP mutations

Mutations within exons 16 and 17 of the β-amyloid precursor protein (APP) gene were the first known cause of familial Alzheimer's disease. These mutations are rare and have been reported in a handful of families exhibiting autosomal dominant inheritance of Alzheimer's disease with age of onset around 50 years. In vitro and in vivo studies have demonstrated that each of these mutations alters proteolytic processing of APP, resulting in an increase in the production of Aβ42, a highly fibrillogenic peptide, that spontaneously aggregates and deposits in the brain. Transgenic mice carrying a mutant human APP gene also show age-dependent β-amyloid (Aβ) deposition in the brain. The rate of deposition in these mice can be modified by apolipoprotein E expression.     

Disinhibition of neurite growth to repair the injured adult CNS: Focusing on Nogo

Investigations into mechanisms that restrict the recovery of functions after an injury to the brain or the spinal cord have led to the discovery of specific neurite growth inhibitory factors in the adult central nervous system (CNS) of mammals. Blocking their growth-suppressive function resulted in disinhibition of axonal growth, i.e. growth of cultured neurons on inhibitory CNS tissue in vitro and regeneration of injured axons in vivo. The enhanced regenerative and compensatory fibre growth was often accompanied by a substantial improvement in the functional recovery after CNS injury. The first clinical studies to assess the therapeutic potential of compounds that neutralize growth inhibitors or interfere with their downstream signalling are currently in progress. This review discusses recent advances in the understanding of how the ‘founder molecule’ Nogo-A and other glialderived growth inhibitors restrict the regeneration and repair of disrupted neuronal circuits, thus limiting the functional recovery after CNS injuries. Received 5 April 2007; received after revision 28 September 2007; accepted 1 October 2007     

Identification of the bioactive peptide PEC-60 in brain

PEC-60 is a 60-residue peptide originally isolated from pig intestine. It inhibits glucose-induced insulin secretion from perfused pancreas in a hormonal manner and also has biological activity in the immune system. PEC-60-like immunoreactive material has been reported in catecholamine neurons of the central and peripheral nervous systems, but the peptide has not been identified from that material. We have now isolated PEC-60 from pig and rat brains with a method that combines column purification procedures with the specificity of a radioimmunoassay and the sensitivity of mass spectrometry to directly identify the peptide. The results show that PEC-60, like many other peptides, is expressed in the gastrointestinal tract and the central nervous system. The specific regional brain distribution and interaction with classical neurotransmitters raise the possibility that PEC-60may play a role in the central nervous system disorders involving dopamine dysregulation. Received 6 December 2002; received after revision 10 December 2002; accepted 11 December 2002 RID="*" ID="*"Corresponding author.