Could a loss of α‐synuclein function put dopaminergic neurons at risk?

The alpha-synuclein gene is implicated in Parkinson's disease, the symptoms of which occur after a marked loss of substantia nigra dopamine neurons. While the function of alpha-synuclein is not entirely elucidated, one function appears to be as a normal regulatory protein that can bind to and inhibit tyrosine hydroxylase, the rate-limiting enzyme in dopamine synthesis. Soluble alpha-synuclein levels may be diminished in Parkinson's disease substantia nigra dopamine neurons both by reduced expression and by alpha-synuclein aggregation as Lewy bodies and Lewy neurites form. The loss of functional alpha-synuclein may then result in dysregulation of tyrosine hydroxylase, dopamine transport and dopamine storage, resulting in excess cytosolic dopamine. Because dopamine and its metabolites are reactive molecules capable of generating highly reactive quinones and reactive oxygen species, a failure to package dopamine into vesicles could cause irreversible damage to cellular macromolecules and contribute to resultant neurotoxicity. This review focuses on how a loss of normal alpha-synuclein function may contribute to the dopamine-related loss of substantia nigra neurons during Parkinson's disease pathogenesis.     

Can the combination of electrochemical regeneration of NAD+, selectivity of L‐α‐amino‐acid dehydrogenase,and reductive amination of α‐keto‐acid be applied to the inversion of configuration of a L‐α‐amino‐acid?

The inversion of configuration of L‐alanine can be carried out by combining its selective oxidation in the presence of NAD⁺ and L‐alanine dehydrogenase, electrochemical regeneration of the NAD⁺ at a carbon felt anode, and reductive amination of pyruvate, i.e., reduction of its imino derivative at a mercury cathode, the reaction mixture being buffered with concentrated ammonium/ammonia (1.28M / 1.28M). The dehydrogenase exhibits astonishing activity and stability under such extreme conditions of pH and ionic strength. The main drawback of the process is its slowness. At best, the complete inversion of a 10 mM solution of L‐alanine requires 140 h. A careful and detailed quantitative analysis of each of the key steps involved shows that the enzyme catalyzed oxidation is so thermodynamically uphill that it can be driven efficiently to completion only when both the coenzyme regeneration and the pyruvate reduction are very effective. The first condition is easily fulfilled. Under the best conditions, it is the rate of the chemical reaction producing the imine which controls the whole process kinetically. © 1999 John Wiley & Sons, Inc. Biotechnol Bioeng 64: 101–107, 1999.     

Interleukin‐1β: a bridge between inflammation and excitotoxicity?

Interleukin-1 (IL-1) is a proinflammatory cytokine released by many cell types that acts in both an autocrine and/or paracrine fashion. While IL-1 is best described as an important mediator of the peripheral immune response during infection and inflammation, increasing evidence implicates IL-1 signaling in the pathogenesis of several neurological disorders. The biochemical pathway(s) by which this cytokine contributes to brain injury remain(s) largely unidentified. Herein, we review the evidence that demonstrates the contribution of IL-1β to the pathogenesis of both acute and chronic neurological disorders. Further, we highlight data that leads us to propose IL-1β as the missing mechanistic link between a potential beneficial inflammatory response and detrimental glutamate excitotoxicity.     

Who Is the King? The α‐Hydroxy‐β‐oxo‐α,β‐enone Moiety or the Catechol B Ring: Relationship between the Structure of Quercetin Derivatives and Their Pro‐Oxidative Abilities

Quercetin and other flavonoids have been reported to exhibit both antioxidant and pro‐oxidant properties. Most studies about the pro‐oxidative ability were conducted in the presence of metal ions, and the essential functional moiety of quercetin responsible for the pro‐oxidative effect is still unclear. In this study, we evaluated the pro‐oxidative abilities in the absence of metal ions of two quercetin derivatives, i.e., quercetin‐3′‐O‐β‐D ‐glucoside ( 1 ) and quercetin‐3‐O‐β‐D ‐glucoside ( 2 ), by assessing DNA cleavage and HO^.‐radical production. The binding mode between these compounds and DNA was studied by fluorescence and viscometric titrations. The results showed that 1 can efficiently induce oxidative damage to plasmid DNA, while 2 shows poor activity. Both 1 and 2 bind to DNA via groove‐binding. These results proved that the α‐hydroxy‐β‐oxo‐α,β‐enone moiety contributes to the pro‐oxidative activity of quercetin.     

A gene for speed? The evolution and function of α‐actinin‐3

The alpha-actinins are an ancient family of actin-binding proteins that play structural and regulatory roles in cytoskeletal organisation and muscle contraction. alpha-actinin-3 is the most-highly specialised of the four mammalian alpha-actinins, with its expression restricted largely to fast glycolytic fibres in skeletal muscle. Intriguingly, a significant proportion ( approximately 18%) of the human population is totally deficient in alpha-actinin-3 due to homozygosity for a premature stop codon polymorphism (R577X) in the ACTN3 gene. Recent work in our laboratory has revealed a strong association between R577X genotype and performance in a variety of athletic endeavours. We are currently exploring the function and evolutionary history of the ACTN3 gene and other alpha-actinin family members. The alpha-actinin family provides a fascinating case study in molecular evolution, illustrating phenomena such as functional redundancy in duplicate genes, the evolution of protein function, and the action of natural selection during recent human evolution.     

Metalloproteases and γ‐secretase: new membrane partners regulating p75 neurotrophin receptor signaling?

Signaling by the p75 neurotrophin receptor (p75) has been implicated in diverse neuronal responses, including the control of neuronal survival versus death and axonal regeneration and growth cone collapse, involving p75 in different neuropathological conditions. There are different levels of complexity regulating p75-mediated signaling. First, p75 can interact with different ligands and co-receptors in the plasma membrane, forming tripartite complexes, whose activation result in different cellular outcomes. Moreover, it was recently described that trafficking capacities of p75 in neurons are regulating, in addition to p75 downstream interactions, also the sequential cleavage of p75. The proteolytical processing of p75 involves, first, a shedding event that releases a membrane-bound carboxiterminal fragment (p75-CTF), followed by a gamma-secretase mediated cleavage, generating a soluble intracellular domain (p75-ICD) with signaling capabilities. The first shedding event, generating a p75-CTF, is the key step to regulating the production of p75-ICD, and although the generation of p75-ICD is important for both p75-mediated control of neuronal survival and the control of neurite outgrowth, little is known how both cleavage events are regulated. In this review, we argue that both sheddases and gamma-secretase are key membrane components regulating p75-mediated signaling transduction; therefore, further attention should be paid to their roles as p75 signaling regulators.     

Role of α2‐macroglobulin in regulating amyloid β‐protein neurotoxicity: protective or detrimental factor?

alpha2-Macroglobulin (alpha2M) has been identified as a carrier protein for beta-amyloid (Abeta) decreasing fibril formation and affecting the neurotoxicity of this peptide. The alpha2-macroglobulin receptor/low density lipoprotein receptor related protein (LRP) is involved in the internalization and degradation of the alpha2M/Abeta complexes and its impairment has been reported to occur in Alzheimer's disease. Previous studies have shown alpha2M to determine an enhancement or a reduction of Abeta toxicity in different culture systems. In order to clarify the role of alpha2M in Abeta neurotoxicity, we challenged human neuroblastoma cell lines with activated alpha2M in combination with Abeta. Our results show that in neuroblastoma cells expressing high levels of LRP, the administration of activated alpha2M protects the cells from Abeta neurotoxicity. Conversely, when this receptor is not present alpha2M determines an increase in Abeta toxicity as evaluated by MTT and TUNEL assays. In LRP-negative cells transfected with the full-length human LRP, the addition of activated alpha2M resulted to be protective against Abeta-induced neurotoxicity. By means of recombinant proteins we ascribed the neurotoxic activity of alpha2M to its FP3 fragment which has been previously shown to bind and neutralize transforming growth factor-beta. These studies provide evidence for both a neuroprotective and neurotoxic role of alpha2M regulated by the expression of its receptor LRP.     

The α‐sheet: A missing‐in‐action secondary structure?

The α-sheet has been speculated to play a role as a toxic conformer in amyloid diseases. However, except for relatively short fragments, its detection has remained elusive. Here, we present molecular dynamics simulations that support the existence of the α-sheet as a stable, metastable, or long-lived secondary structure in polyglutamine and, to a lesser extent, in polyasparagine aggregates.     

Peptaibiomics: Towards a Myriad of Bioactive Peptides Containing Cα‐Dialkylamino Acids?

Fungi are generally regarded as a literally infinite resource of bioactive secondary metabolites displaying remarkable structural diversity. Research on a particular group of linear and cyclic peptide antibiotics comprehensively named peptaibiotics--as result of the abundance of the non-proteinogenic C(alpha)-dialkylated alpha-amino acids alpha-aminoisobutyric acid (Aib) and isovaline (Iva)--has been started 50 years ago. These peptides have gained constantly increasing interest because of their unique bioactivities and conformations. This review, reflecting the history of peptaibiotic research from 1958 to 2008, is focussed on introducing both the structural diversity and natural microheterogeneity of the peptaibiotics, as well as the biodiversity of their fungal producers. Recently introduced state-of-the-art methods for rapid screening and sequencing of peptaibiotics, such as peptaibiomics and intact-cell MALDI-TOF mass spectrometry, are discussed. Finally, future prospects in peptaibiotic research are presented. Owing to the ubiquity and biodiversity of the fungal producers in the biosphere, the discovery of a myriad of peptaibiotics within the next decade is predicted.     

Phylogeny of γ‐proteobacteria: resolution of one branch of the universal tree?

The reconstruction of bacterial evolutionary relationships has proven to be a daunting task because variable mutation rates and horizontal gene transfer (HGT) among species can cause grave incongruities between phylogenetic trees based on single genes. Recently, a highly robust phylogenetic tree was constructed for 13 gamma-proteobacteria using the combined alignments of 205 conserved orthologous proteins.1 Only two proteins had incongruent tree topologies, which were attributed to HGT between Pseudomonas species and Vibrio cholerae or enterics. While the evolutionary relationships among these species appears to be resolved, further analysis suggests that HGT events with other bacterial partners likely occurred; this alters the implicit assumption of gamma-proteobacteria monophyly. Thus, any thorough reconstruction of bacterial evolution must not only choose a suitable set of molecular markers but also strive to reduce potential bias in the selection of species.     

Levels of polymorphism on the sex‐limited chromosome: a clue to Y from W?

Nucleotide diversity of the human Y chromosome is much lower than that in the rest of the genome. A new hypothesis postulates that this invariance may result from mutations in maternally inherited mitochondrial DNA (mtDNA), leading to impaired reproduction among males and lowered male effective population size. If correct, we should expect to see low levels of polymorphism in the male-specific Y chromosome of many organisms but not necessarily in the female-specific W chromosome in organisms with female heterogamety. However, recent observations from birds suggest that the avian W chromosome is very low in nucleotide diversity. This indicates that mtDNA mutations cannot broadly explain the evolution of the sex-limited chromosome. Other work has suggested that sexual selection at loci involved in sex determination or secondary sexual characteristics might reduce levels of genetic variability on Y through hitch-hiking effects. Although the W chromosome does not seen to play a dominant role for sex determination in birds, it cannot be excluded that selective sweeps arising from natural or sexual selection contribute to the low levels of genetic variability seen on this chromosome.     

Beyond taxonomic diversity patterns: how do α, β and γ components of bird functional and phylogenetic diversity respond to environmental gradients across France?

Aim To test how far can macroecological hypotheses relating diversity to environmental factors be extrapolated to functional and phylogenetic diversities, i.e. to the extent to which functional traits and evolutionary backgrounds vary among species in a community or region. We use a spatial partitioning of diversity where regional or γ‐diversity is calculated by aggregating information on local communities, local or α‐diversity corresponds to diversity in one locality, and turnover or β‐diversity corresponds to the average turnover between localities and the region. Location France. Methods We used the Rao quadratic entropy decomposition of diversity to calculate local, regional and turnover diversity for each of three diversity facets (taxonomic, phylogenetic and functional) in breeding bird communities of France. Spatial autoregressive models and partial regression analyses were used to analyse the relationships between each diversity facet and environmental gradients (climate and land use). Results Changes in γ‐diversity are driven by changes in both α‐ and β‐diversity. Low levels of human impact generally favour all three facets of regional diversity and heterogeneous landscapes usually harbour higher β‐diversity in the three facets of diversity, although functional and phylogenetic turnover show some relationships in the opposite direction. Spatial and environmental factors explain a large percentage of the variation in the three diversity facets (>60%), and this is especially true for phylogenetic diversity. In all cases, spatial structure plays a preponderant role in explaining diversity gradients, suggesting an important role for dispersal limitations in structuring diversity at different spatial scales. Main conclusions Our results generally support the idea that hypotheses that have previously been applied to taxonomic diversity, both at local and regional scales, can be extended to phylogenetic and functional diversity. Specifically, changes in regional diversity are the result of changes in both local and turnover diversity, some environmental conditions such as human development have a great impact on diversity levels, and heterogeneous landscapes tend to have higher diversity levels. Interestingly, differences between diversity facets could potentially provide further insights into how large‐ and small‐scale ecological processes interact at the onset of macroecological patterns.     

Proteasomal dysfunction induced by 4‐hydroxy‐2,3‐trans‐nonenal,an end‐product of lipid peroxidation: a mechanism contributing to neurodegeneration?

4-Hydroxy-2,3-trans-nonenal (HNE) is a neurotoxic unsaturated aldehyde end-product of lipid peroxidation. The addition of HNE to NT-2 and SK-N-MC cell lines induces apoptosis and we now investigated the time-course of events occurring prior to apoptosis. Treatment of both NT-2 and SK-N-MC cell lines with HNE led to HNE association with the proteasome, increased levels of protein carbonyls and ubiquitinated proteins, and decreased proteasomal function. There was also decreased metabolic activity, cytochrome c release and activation of caspase 3, followed by apoptotic changes including chromatin condensation, cell shrinkage and DNA fragmentation and laddering. Overexpression of mutant superoxide dismutase 1 proteins associated with amyotrophic lateral sclerosis decreased proteasomal activities in the absence of HNE and accelerated the apoptosis induced by HNE. By contrast, overexpression of wild-type superoxide dismutase 1 did not affect basal levels of proteasomal activity. The data suggest that accumulation of ubiquitinated proteins and impairment of proteasomal function are important events in HNE toxicity. We propose that the proteasomal system is a significant target of HNE neurotoxicity in a wide range of neurodegenerative diseases, especially if abnormal proteins are being expressed.     

Are communities saturated? On the relationship between α, β and γ diversity

A popular way to suggest a regional influence on local species diversity has been to plot local versus regional diversity. The form of these curves has been interpreted as evidence for or against "community saturation" due to species interactions. This interpretation, however, is unwarranted. Using the concepts of α, β and γ diversity, I show that local–regional richness curves are determined by the way total diversity is partitioned between its α and β components, which itself is a matter of scale. Changing the scale of the local community amounts to changing the scale at which the heterogeneity of the interactions between organisms and their environment manifests itself, and hence the balance between α and β diversity. Community saturation may occur because of physical limitations, but there are no theoretical grounds for the belief that species interactions set an absolute upper limit to diversity at any scale. A distinction between different meanings of the concept of "saturation" is proposed to clarify this issue. I argue that the challenge now is to understand the relationship between α and β diversity at multiple scales, and the processes that determine it.     

How and why does β‐actin mRNA target?

beta-Actin mRNA is localized near the leading edge in several cell types where actin polymerization is actively promoting forward protrusion. The localization of the beta-actin mRNA near the leading edge is facilitated by a short sequence in the 3'UTR (untranslated region), the 'zipcode'. Localization of the mRNA at this region is important physiologically. Treatment of chicken embryo fibroblasts with antisense oligonucleotides complementary to the localization sequence (zipcode) in the 3'UTR leads to delocalization of beta-actin mRNA, alteration of cell phenotype and a decrease in cell motility. The dynamic image analysis system (DIAS) used to quantify movement of cells in the presence of sense and antisense oligonucleotides to the zipcode showed that net pathlength and average speed of antisense-treated cells were significantly lower than in sense-treated cells. This suggests that a decrease in persistence of direction of movement and not in velocity results from treatment of cells with zipcode-directed antisense oligonucleotides. We postulate that delocalization of beta-actin mRNA results in delocalization of nucleation sites and beta-actin protein from the leading edge followed by loss of cell polarity and directional movement. Hence the physiological consequences of beta-actin mRNA delocalization affect the stability of the cell phenotype.