Structural Plasticity of Neurexin 1α: Implications for its Role as Synaptic Organizer

α-Neurexins are synaptic organizing molecules implicated in neuropsychiatric disorders. They bind and arrange an array of different partners in the synaptic cleft. The extracellular region of neurexin 1α (n1α) contains six LNS domains (L1–L6) interspersed by three Egf-like repeats. N1α must encode highly evolved structure–function relationships in order to fit into the narrow confines of the synaptic cleft, and also recruit its large, membrane-bound partners. Internal molecular flexibility could provide a solution; however, it is challenging to delineate because currently no structural methods permit high-resolution structure determination of large, flexible, multi-domain protein molecules. To investigate the structural plasticity of n1α, in particular the conformation of domains that carry validated binding sites for different protein partners, we used a panel of structural techniques. Individual particle electron tomography revealed that the N-terminally and C-terminally tethered domains, L1 and L6, have a surprisingly limited range of conformational freedom with respect to the linear central core containing L2 through L5. A 2.8-Å crystal structure revealed an unexpected arrangement of the L2 and L3 domains. Small-angle X-ray scattering and electron tomography indicated that incorporation of the alternative splice insert SS6 relieves the restricted conformational freedom between L5 and L6, suggesting that SS6 may work as a molecular toggle. The architecture of n1α thus encodes a combination of rigid and flexibly tethered domains that are uniquely poised to work together to promote its organizing function in the synaptic cleft, and may permit allosterically regulated and/or concerted protein partner binding.     

A New Function for the LDL Receptor: Transcytosis of LDL across the Blood–Brain Barrier

Lipoprotein transport across the blood–brain barrier (BBB) is of critical importance for the delivery of essential lipids to the brain cells. The occurrence of a low density lipoprotein (LDL) receptor on the BBB has recently been demonstrated. To examine further the function of this receptor, we have shown using an in vitro model of the BBB, that in contrast to acetylated LDL, which does not cross the BBB, LDL is specifically transcytosed across the monolayer. The C7 monoclonal antibody, known to interact with the LDL receptor-binding domain, totally blocked the transcytosis of LDL, suggesting that the transcytosis is mediated by the receptor. Furthermore, we have shown that cholesterol-depleted astrocytes upregulate the expression of the LDL receptor at the BBB. Under these conditions, we observed that the LDL transcytosis parallels the increase in the LDL receptor, indicating once more that the LDL is transcytosed by a receptor-mediated mechanism. The nondegradation of the LDL during the transcytosis indicates that the transcytotic pathway in brain capillary endothelial cells is different from the LDL receptor classical pathway. The switch between a recycling receptor to a transcytotic receptor cannot be explained by a modification of the internalization signals of the cytoplasmic domain of the receptor, since we have shown that LDL receptor messengers in growing brain capillary ECs (recycling LDL receptor) or differentiated cells (transcytotic receptor) are 100% identical, but we cannot exclude posttranslational modifications of the cytoplasmic domain, as demonstrated for the polymeric immunoglobulin receptor. Preliminary studies suggest that caveolae are likely to be involved in the potential transport of LDL from the blood to the brain.The maintenance of the homeostasis of brain interstitial fluid, which constitutes the special microenvironment for neurons, is established by the presence of the blood–brain barrier (BBB)¹ at the transition area from endothelial cells (ECs) to brain tissue. Of primary importance in the formation of a permeability barrier by these cells is the presence of continuous tight junctions that seal together the margins of the ECs and restrict the passage of substances from the blood to the brain. Furthermore, in contrast to ECs in many other organs, the brain capillary ECs contain no direct transendothelial passageways such as fenestrations or channels. But obviously, the BBB cannot be absolute. The brain is dependent upon the blood to deliver metabolic substrates and remove metabolic waste, and the BBB therefore facilitates the exchange of selected solutes. Carrier-mediated transport systems that facilitate the uptake of hexoses, amino acids, purine compounds, and mono-carboxylic acids have been revealed in the cerebral endothelium (Betz and Goldstein, 1978), but until now little information has come to light regarding the cerebral uptake of lipids.There is growing evidence that the brain is equipped with a relatively self-sufficient transport system for maintaining cholesterol and lipid homeostasis. The presence of a low density lipoprotein (LDL) receptor has been demonstrated by immunocytochemistry in rat and monkey brains; and apolipoprotein (apo) E and apo AI-containing particles have been detected in human cerebrospinal fluid (Pitas et al., 1987). Furthermore, enzymes involved in lipid metabolism have been located within the brain: LCAT mRNA has been shown to be expressed in rat brains and cholesteryl ester transfer protein, which plays a key role in cholesterol homeostasis, has been detected in human cerebrospinal fluid and seems to be synthesized in the brain (Albers et al., 1992). The distribution of the LDL receptor-related protein, a multifunctional receptor that binds apoE, is highly restricted and limited to the gray matter, primarily associated with neuronal cell population (Wolf et al., 1992). The difference in cellular expression of ligand (apoE) and receptor (LDL receptor-related protein) may provide a pathway for intracellular transport of apoE-containing lipoproteins in the central nervous system. All these data leave little doubt that the brain is equipped with a relatively self-sufficient transport system for cholesterol.Cholesterol could be derived from de novo synthesis within the brain and from plasma via the BBB. Malavolti et al. (1991) indicate the presence of unexpectedly close communications between extracerebral and brain cholesterol. Changes in the extracerebral cholesterol levels are readily sensed by the LDL receptor in the brain and promptly provoke appropriate modifications in its activity. Méresse et al. (1989a) provided direct evidence for the occurrence in vivo of an LDL receptor on the endothelium of brain capillaries. Furthermore, the fact that enzymes involved in the lipoprotein metabolism are present in the brain microvasculature (Brecher and Kuan, 1979) and that the entire fraction of the drug bound to lipoproteins is available for entry into the brain strongly suggest that this cerebral endothelial receptor plays a role in the interaction of plasma lipoproteins with brain capillaries. These results pinpoint the critical importance of the interactions between brain capillary ECs and lipoproteins. Owing to the fact that the neurological abnormalities that result from the inadequate absorption of dietary vitamin E can be improved by the oral administration of pharmacological doses of vitamin E, Traber and Kayden (1984) have suggested that LDL functions as a transport system for tocopherol to the brain. Furthermore, the trace amounts of apolipoprotein B that were detected by Salem et al. (1987) in cerebrospinal fluid from healthy patients using a very sensitive immunoblot technique confirm that, at most, small amounts of apolipoprotein B normally pass through the BBB. However, whether LDL is involved in the exchange is not known.Using an in vitro model of the BBB that imitates an in vivo situation by culturing capillary ECs and astrocytes on opposite sides of a filter (Dehouck et al., 1990a , 1992), we have demonstrated that in culture, like in vivo, in contrast to peripheral endothelium and in spite of the tight apposition of ECs and their contact with physiological concentrations of lipoproteins, brain capillary ECs express an LDL receptor (Méresse et al., 1991; Dehouck et al., 1994). The capacity of ECs to bind LDLs is greater when cocultured with astrocytes than in their absence. Futhermore, we have shown that the lipid requirement of astrocytes increases the expression of the LDL receptor on brain capillary ECs. Taken together, the presence of LDL receptors on brain capillary ECs and the modulation of the expression of these receptors by the lipid composition of astrocytes suggest that cholesterol used by cells in the central nervous system may be derived, at least in part, from the periphery via transport across the BBB.In the present study, we provide direct evidence that after binding to brain capillary ECs, there is a specific mechanism for the transport of LDL across the endothelial monolayer from the apical to the abluminal surface. This mechanism might be best explained by a process of receptor-mediated transcytosis. Preliminary results pinpoint the role of caveolae in the transcellular transport of LDL across the brain endothelium.     

Protein Prenylation and Synaptic Plasticity: Implications for Alzheimer’s Disease

Protein prenylation is an important lipid posttranslational modification of proteins. It includes protein farnesylation and geranylgeranylation, in which the 15-carbon farnesyl pyrophosphate or 20-carbon geranylgeranyl pyrophosphate is attached to the C-terminus of target proteins, catalyzed by farnesyl transferase or geranylgeranyl transferases, respectively. Protein prenylation facilitates the anchoring of proteins into the cell membrane and mediates protein–protein interactions. Among numerous proteins that undergo prenylation, small GTPases represent the largest group of prenylated proteins. Small GTPases are involved in regulating a plethora of cellular functions including synaptic plasticity. The prenylation status of small GTPases determines the subcellular locations and functions of the proteins. Dysregulation or dysfunction of small GTPases leads to the development of different types of disorders. Emerging evidence indicates that prenylated proteins, in particular small GTPases, may play important roles in the pathogenesis of Alzheimer’s disease. This review focuses on the prenylation of Ras and Rho subfamilies of small GTPases and its relation to synaptic plasticity and Alzheimer’s disease.     

Therapeutic targeting of RAS: New hope for drugging the “undruggable”

RAS is the most frequently mutated oncogene in cancer and a critical driver of oncogenesis. Therapeutic targeting of RAS has been a goal of cancer research for more than 30 years due to its essential role in tumor formation and maintenance. Yet the quest to inhibit this challenging foe has been elusive. Although once considered “undruggable”, the struggle to directly inhibit RAS has seen recent success with the development of pharmacological agents that specifically target the KRAS(G12C) mutant protein, which include the first direct RAS inhibitor to gain entry to clinical trials. However, the limited applicability of these inhibitors to G12C-mutant tumors demands further efforts to identify more broadly efficacious RAS inhibitors. Understanding allosteric influences on RAS may open new avenues to inhibit RAS. Here, we provide a brief overview of RAS biology and biochemistry, discuss the allosteric regulation of RAS, and summarize the various approaches to develop RAS inhibitors.     

DNA Methylation and Replication: Implications for the “Deletion Hotspot” Region of FMR1

Expansion and hyper-methylation of a CGG repeat tract are the main causes of fragile X syndrome (FRAXA). In some rare instances, FRAXA patients harbor not only an expanded CGG tract, but a deletion encompassing the CGG repeat and flanking sequences as well. Through the use of an SV40 primate replication system, it was possible to determine that CpG methylation and DNA replication may actually mediate the formation of these rare events. Also, the genetically stabilizing AGG interruptions can be lost by replication-mediated CGG deletions.     

Neural Plasticity in Human Brain Connectivity: The Effects of Long Term Deep Brain Stimulation of the Subthalamic Nucleus in Parkinson’s Disease

Background

Positive clinical outcomes are now well established for deep brain stimulation, but little is known about the effects of long-term deep brain stimulation on brain structural and functional connectivity. Here, we used the rare opportunity to acquire pre- and postoperative diffusion tensor imaging in a patient undergoing deep brain stimulation in bilateral subthalamic nuclei for Parkinson’s Disease. This allowed us to analyse the differences in structural connectivity before and after deep brain stimulation. Further, a computational model of spontaneous brain activity was used to estimate the changes in functional connectivity arising from the specific changes in structural connectivity.

Results

We found significant localised structural changes as a result of long-term deep brain stimulation. These changes were found in sensory-motor, prefrontal/limbic, and olfactory brain regions which are known to be affected in Parkinson’s Disease. The nature of these changes was an increase of nodal efficiency in most areas and a decrease of nodal efficiency in the precentral sensory-motor area. Importantly, the computational model clearly shows the impact of deep brain stimulation-induced structural alterations on functional brain changes, which is to shift the neural dynamics back towards a healthy regime. The results demonstrate that deep brain stimulation in Parkinson’s Disease leads to a topological reorganisation towards healthy bifurcation of the functional networks measured in controls, which suggests a potential neural mechanism for the alleviation of symptoms.

Conclusions

The findings suggest that long-term deep brain stimulation has not only restorative effects on the structural connectivity, but also affects the functional connectivity at a global level. Overall, our results support causal changes in human neural plasticity after long-term deep brain stimulation and may help to identify the underlying mechanisms of deep brain stimulation.     

Evolution of Mhc–DRB Introns: Implications for the Origin of Primates

Introns are generally believed to evolve too rapidly and too erratically to be of much use in phylogenetic reconstructions. Few phylogenetically informative intron sequences are available, however, to ascertain the validity of this supposition. In the present study the supposition was tested on the example of the mammalian class II major histocompatibility complex (Mhc) genes of the DRB family. Since the Mhc genes evolve under balancing selection and are believed to recombine or rearrange frequently, the evolution of their introns could be expected to be particularly rapid and subject to scrambling. Sequences of intron 4 and 5 DRB genes were obtained from polymerase chain reaction-amplified fragments of genomic DNA from representatives of six eutherian orders—Primates, Scandentia, Chiroptera, Dermoptera, Lagomorpha, and Insectivora. Although short stretches of the introns have indeed proved to be unalignable, the bulk of the intron sequences from all six orders, spanning >85 million years (my) of evolution, could be aligned and used in a study of the tempo and mode of intron evolution. The analysis has revealed the Mhc introns to evolve at a rate similar to that of other genes and of synonymous sites of non-Mhc genes. No evidence of homogenization or large-scale scrambling of the intron sequences could be found. The Mhc introns apparently evolve largely by point mutations and insertions/deletions. The phylogenetic signals contained in the intron sequences could be used to identify Scandentia as the sister group of Primates, to support the existence of the Archonta superorder, and to confirm the monophyly of the Chiroptera. Received: 26 October 1998 / Accepted: 21 December 1998     

Preconditioning Strategies for Kidney Ischemia Reperfusion Injury: Implications of the “Time-Window” in Remote Ischemic Preconditioning

Remote ischemic preconditioning (IP) is a potential renoprotective strategy. However, there has been no demonstrated result in large animals and the role of time window in remote IP remains to be defined. Using a single-kidney porcine model, we evaluated organ protective function of remote IP in renal ischemia reperfusion injury. Fifteen Yorkshire pigs, 20 weeks old and weighing 35–38 kg were used. One week after left nephrectomy, we performed remote IP (clamping right external iliac artery, 2 cycles of 10 minutes) and right renal artery clamping (warm ischemia; 90 minutes). The animals were randomly divided into three groups: control group, warm ischemia without IP; group 1 (remote IP with early window [IP-E]), IP followed by warm ischemia with a 10-minute time window; and group 2 (remote IP with late window [IP-L]), IP followed by warm ischemia after a 24-hour time window. There were no differences in serum creatinine changes between groups. The IP-L group had lower urinary neutrophil gelatinase-associated lipocalin than control and IP-E at 72 hours post-ischemia. At 72 hours post-ischemia, the urinary kidney injury molecule-1 (KIM-1) was lower in the IP-L group than in the control and IP-E groups, and the IP-L group KIM-1 was near pre-ischemic levels, whereas the control and IP-E group KIM-1 levels were rising. Microalbumin also tended to be lower in the IP-L group. Taken together, remote IP showed a significant reduction in renal injury biomarkers from ischemia reperfusion injury. To effectively provide kidney protection, remote IP might require a considerable, rather than short, time window of ischemia.     

The dynamic NMR structure of the TΨC-loop: Implications for the specificity of tRNA methylation

tRNA (m5U54)-methyltransferase (RUMT) catalyzes the S-adenosylmethionine-dependentmethylation of uridine-54 in the TC-loop of all transfer RNAs in E. coli to form the 54-ribosylthymine residue. However, in all tRNA structures, residue 54 is completely buried andthe question arises as to how RUMT gains access to the methylation site. A 17-mer RNAhairpin consisting of nucleotides 49–65 of the T-loop is a substrate for RUMT.Homonuclear NMR methods in conjunction with restrained molecular dynamics (MD)methods were used to determine the solution structure of the 17-mer T-arm fragment. Theloop of the hairpin exhibits enhanced flexibility which renders the conventional NMR averagestructure less useful compared to the more commonly found situation where a molecule existsin predominantly one major conformation. However, when resorting to softer refinementmethods such as MD with time-averaged restraints, the conflicting restraints in the loop canbe satisfied much better. The dynamic structure of the T-arm is represented as an ensembleof 10 time-clusters. In all of these, U54 is completely exposed. The flexibility of the T-loop in solution in conjunction with extensive binding studies of RUMT with the TC-loop and tRNA suggest that the specificity of the RUMT/tRNA recognition is associated withtRNA tertiary structure elements. For the methylation, RUMT would simply have to breakthe tertiary interactions between the D- and T-loops, leading to a melting of the T-armstructure and making U54 available for methylation.     

Methionine oxidation: Implications for the mechanism of toxicity of the β-amyloid peptide from Alzheimer's disease

Summary The amyloid β-peptide, Aβ is toxic to neurons and this toxicity plays a central role in the progression of Alzheimer's disease. The mechanism(s) by which Aβ exerts its toxicity has been hotly debated with several theories postulated. Here we discuss the role of oxidation of the sulfur atom of Met35 in Aβ42 (Met(O)Aβ), a modification that has significant implications for the mechanism of Aβ toxicity. Both Met(O)Aβ and its native form display toxicity to primary neuronal cells in culture which can be rescued by catalase, a H₂O₂ inhibitor and clioquinol a mild copper chelator. However both native Aβ and Met(O)Aβ differ substantially in primary and secondary structures, solubility, ability to penetrate lipid membranes, and oligomerization profiles. It is clearly evident that metals play an important role in the oxidation of Aβ to Met(O)Aβ via Fenton chemistry and that regulation of this pathway has a potential therapeutic application for the regulation of Alzheimer's disease.     

Education for sexuality—the rˆle of the school

Education for sexuality and healthy relationships should be viewed within a broad context of health education and social education in schools. However, this is not merely a matter for the formal curriculum of a school, but relates to the totality of the experience that young people receive there. The concept of the health promoting school encapsulates tfie formal curriculum, the ‘hidden curriculum’, and the interaction of the school with parents, the community, and other agencies, which can affect the health and well-being of all school users. One cannot view a school's rôle in this area out of the societal context. Research indicates that young people, as they move through their teenage years, get most of their information relating to sexuality from friends and yet they acknowledge that this is not a reliable source. Examples of current knowledge levels and attitudes relating to sexuality and HIV/AIDS are given. The strengths and weaknesses of schools as settings for sex education are explored, and 10 key points for consideration within a school policy on education for sexuality and relationships are proposed.     

Special Issue on “Big Data in Brain Science”

正The journal Genomics,ProteomicsBioinformatics(GPB)is now inviting submissions for a special issue(to be published in the winter of 2017)on the topic of‘‘Big data in brain science’’.It took 15 years,3 billion USD,and thousands of top scientists from all over the world to complete the Human Genome Project(HGP).Our next grand challenge in biological sciences,the     

Special Issue on “Big Data in Brain Science”

<正>The journal Genomics,ProteomicsBioinformatics(GPB)is now inviting submissions for a special issue(to be published in the summer of 2018)on the topic of‘‘Big data in brain science’’.It took 15 years,3 billion USD,and thousands of top scientists from all over the world to     

Special Issue on “Big Data in Brain Science”

<正>The journal Genomics,ProteomicsBioinformatics(GPB)is now inviting submissions for a special issue(to be published in the Winter of 2017)on the topic ofBig data in brain science.It took 15 years,3 billion USD,and thousands of top scientists from all over the world to complete the Human Genome Project(HGP).Our next grand challenge in biological sciences,the worldwide Human Brain Project(HBP),will be much more complex than HGP.Human brain is     

Special Issue on “Big Data in Brain Science”

正The journal Genomics,ProteomicsBioinformatics(GPB)is now inviting submissions for a special issue(to be published in the spring of 2019)on the topic of"Big data in brain science".It took 15 years,3 billion USD,and thousands of top scientists from all over the world to complete the Human Genome Project(HGP).Our next grand challenge in biological sciences,the worldwide Human Brain Project(HBP),will be much more complex than HGP.Human brain is     

Special Issue on “Big Data in Brain Science”

正The journal Genomics,ProteomicsBioinformatics(GPB)is now inviting submissions for a special issue(to be published in the Winter of 2017)on the topic of "Big data in brain science".It took 15 years,3 billion USD,and thousands of top scientists from all over the world to complete the Human Genome Project(HGP).Our next grand challenge in biological sciences,the     

Special Issue on “Big Data in Brain Science”

<正>The journal Genomics,ProteomicsBioinformatics(GPB)is now inviting submissions for a special issue(to be published in the winter of 2017)on the topic of‘‘Big data in brain science’’.It took 15 years,3 billion USD,and thousands of top scientists from all over the world to     

Special Issue on “Big Data in Brain Science”

正The journal Genomics,ProteomicsBioinformatics(GPB)is now inviting submissions for a special issue(to be published in the summer of 2018)on the topic of‘‘Big data in brain science’’.It took 15 years,3 billion USD,and thousands of top scientists from all over the world to complete the Human Genome Project(HGP).Our next grand challenge in biological sciences,the worldwide Human Brain Project(HBP),will be much more complex than HGP.Human brain is     

Special Issue on “Big Data in Brain Science”

正The journal Genomics,ProteomicsBioinformatics(GPB)is now inviting submissions for a special issue(to be published in the spring of 2019)on the topic of‘‘Big data in brain science’’.It took 15 years,3 billion USD,and thousands of top scientists from all over the world to complete the Human Genome Project(HGP).Our next grand challenge in biological sciences,the     

A Review of “Maritime Power and the Law of the Sea: Expeditionary Operations in World Politics”

Abstract

The purpose of the London Dumping Convention (LDC) is the protection of the marine environment including its seabed and subsoil. The preamble, articles, and annexes of the LDC make clear that the Convention must be interpreted in a manner which ensures that this responsibility is met. As a partial response to that mandate, the LDC prohibits the dumping at sea of certain wastes, including high‐level radioactive wastes. Disposal of high‐level wastes in seabed sediments is the subject of ongoing technical, environmental, and engineering feasibility studies by several countries. In the LDC's definition of dumping, the phrase “disposal at sea”; could be interpreted narrowly to mean the final resting place of wastes—with seabed disposal excluded from coverage because those wastes are not in direct contact with “marine waters.”; Given the LDC's object and purpose, though, the only harmonious and reasonable interpretation is that which defines “disposal at sea”; to mean the place where the dumping activities occur. Other international agreements also support this object and purpose‐based interpretation which concludes that seabed disposal is covered and prohibited. In addition, this approach is preferred because it contributes to the continued effectiveness of the LDC.