Cerebrospinal fluid tau, A beta, and phosphorylated tau protein for the diagnosis of Alzheimer's disease

The diagnosis of AD is still largely based on exclusion criteria of secondary causes and other forms of dementia with similar clinical pictures, than the diagnostic accuracy of AD is low. Improved methods of early diagnosis are needed, particularly because drugs treatment is more effective in the early stages of the disease. Recent research focused the attention to biochemical diagnostic markers (biomarkers) and according to the proposal of a consensus group on biomarkers, three candidate CSF markers reflecting the pathological AD processes, have recently been identified: total tau protein (t-tau), amyloid beta(1-42) protein (A beta42), and tau protein phosphorylated at AD-specific epitopes (p-tau). Several articles report reduced CSF levels of A beta42 and increased CSF levels of t-tau and p-tau in AD; the sensitivity and specificity of these data are able for discrimination of AD patients from controls. However, the specificity for other dementias is low. According to the literature analysis reported in the present review, we can conclude that the combination of the CSF markers and their ratios may significantly increase the specificity and the accuracy of AD diagnosis.     

Structure-function relationship in a variant hemoglobin: a combined computational-experimental approach

Our study examines the functional and structural effects of amino acid substitution in the distal side of beta-chains of human Hb Duarte (alpha(2)beta(2)(62Ala-->Pro)). We have compared the functional properties of the purified Hb Duarte with those of HbA, and through proton NMR and molecular dynamics simulations we have investigated their tertiary and quaternary structures. The variant exhibits an increased oxygen affinity with a normal Hill coefficient and Bohr effect. The abnormal function of Hb Duarte is attributed to the presence of a proline residue at the beta62 position, since the functional properties of another Hb variant in the same position, Hb J-Europa (beta(62Ala-->Asp)), have been described as normal. Thereafter (1)H-NMR studies have shown that the beta62 Ala-->Pro substitution causes structural modifications of the tertiary structure of the beta globins, leaving the quaternary structure unaltered. These results have been confirmed by extensive all-atom molecular dynamics simulations. All these findings lead to the conclusion that the beta62 Ala-->Pro substitution produces a destabilization of the E-helix extending downward to the CD corner. Particularly, a cavity near the distal histidine of the beta-chains, connecting the heme pocket to the solvent, is affected, altering the functional properties of the protein molecule.     

Highly structured Asian Drosophila melanogaster populations: a new tool for hitchhiking mapping?

Mark-recapture experiments showed that D. melanogaster has high dispersal capabilities. Consistent with a highly migratory species, only very low levels of differentiation were described for D. melanogaster populations from the same continent. We reinvestigated the population structure in D. melanogaster using 49 polymorphic markers in 23 natural populations. While European and American D. melanogaster populations showed very low differentiation, Asian D. melanogaster populations were highly structured. Despite the high differentiation of Asian flies, we confirm that all non-African populations are derived from a single colonization event. We propose that the availability of D. melanogaster populations with high and low population structure provides a novel tool for the identification of ecologically important adaptations by hitchhiking mapping.     

Symmetry breaking in interspecific Drosophila hybrids is not due to developmental noise

Hybrids from crosses of different species have been reported to display decreased developmental stability when compared to their pure species, which is conventionally attributed to a breakdown of coadapted gene complexes. Drosophila subobscura and its close relative D. madeirensis were hybridized in the laboratory to test the hypothesis that genuine fluctuating asymmetry, measured as the within-individual variance between right and left wings that results from random perturbations in development, would significantly increase after interspecific hybridization. When sires of D. subobscura were mated to heterospecific females following a hybrid half-sib breeding design, F1 hybrid females showed a large bilateral asymmetry with a substantial proportion of individuals having an asymmetric index larger than 5% of total wing size. Such an anomaly, however, cannot be plainly explained by an increase of developmental instability in hybrids but is the result of some aberrant developmental processes. Our findings suggest that interspecific hybrids are as able as their parents to buffer developmental noise, notwithstanding the fact that their proper bilateral development can be harshly compromised. Together with the low correspondence between the co-variation structures of the interindividual genetic components and the within-individual ones from a Procrustes analysis, our data also suggest that the underlying processes that control (genetic) canalization and developmental stability do not share a common mechanism. We argue that the conventional account of decreased developmental stability in interspecific hybrids needs to be reappraised.     

Very low additive genetic variance and evolutionary potential in multiple populations of two rainforest Drosophila species

Most quantitative traits are thought to exhibit high levels of genetic variance and evolutionary potential. However, this conclusion may be biased by a lack of studies on nonmodel organisms and may not generalize to restricted species. A recent study on a single, southern population of the rainforest-restricted Drosophila birchii failed to find significant additive genetic variance for the desiccation resistance trait; however, it is unclear whether this pattern extends to other D. birchii populations or to other rainforest species. Here we use an animal model design to show very low levels of additive genetic variance for desiccation resistance in multiple populations of two highly sensitive rainforest species of Drosophila from tropical northeastern Australia. In contrast, relatively high levels of genetic variance were found for morphological traits in all populations of the species tested. This indicates limited evolutionary potential for evolving increased desiccation resistance in these rainforest restricted species.     

Islet-specific glucose-6-phosphatase catalytic subunit-related protein-reactive CD4+ T cells in human subjects

Islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP) is recognized as a major autoantigen for autoimmune type 1 diabetes (T1D) in the NOD mouse model. This study was undertaken to examine CD4+ T cell responses toward IGRP in human subjects. The tetramer-guided epitope mapping approach was used to identify IGRP-specific CD4+ T cell epitopes. IGRP(23-35) and IGRP(247-259) were identified as DRA1*0101/DRB1*0401-restricted epitopes. IGRP(13-25) and IGRP(226-238) were identified as DRA1*0101/DRB1*0301-restricted epitopes. IGRP-specific tetramers were used to evaluate the prevalence of IGRP-reactive T cells in healthy and T1D subjects. More than 80% of subjects with either DRB1*0401 or DRB1*0301 haplotype have IGRP-specific CD4+ T cell responses for at least one IGRP epitope. IGRP-specific T cells from both healthy and T1D groups produce both gamma-IFN and IL-10. DRA1*0101/DRB1*0401 IGRP(247-259)-restricted T cells also show cross-reactivity to an epitope derived from liver/kidney glucose-6-phosphatase. The detection of IGRP-reactive T cells in both type 1 diabetic subjects and healthy subjects and recent reports of other autoreactive T cells detected in healthy subjects underscore the prevalence of potentially autoreactive T cells in the peripheral immune system of the general population.     

Multiple interactions of FbsA, a surface protein from Streptococcus agalactiae, with fibrinogen: affinity, stoichiometry, and structural characterization

Streptococcus agalactiae is an etiological agent of several infective diseases in humans. We previously demonstrated that FbsA, a fibrinogen-binding protein expressed by this bacterium, elicits a fibrinogen-dependent aggregation of platelets. In the present communication, we show that the binding of FbsA to fibrinogen is specific and saturable, and that the FbsA-binding site resides in the D region of fibrinogen. In accordance with the repetitive nature of the protein, we found that FbsA contains multiple binding sites for fibrinogen. By using several biophysical methods, we provide evidence that the addition of FbsA induces extensive fibrinogen aggregation and has noticeable effects on thrombin-catalyzed fibrin clot formation. Fibrinogen aggregation was also found to depend on FbsA concentration and on the number of FbsA repeat units. Scanning electron microscopy evidentiated that, while fibrin clot is made of a fine fibrillar network, FbsA-induced Fbg aggregates consist of thicker fibers organized in a cage-like structure. The structural difference of the two structures was further indicated by the diverse immunological reactivity and capability to bind tissue-type plasminogen activator or plasminogen. The mechanisms of FbsA-induced fibrinogen aggregation and fibrin polymerization followed distinct pathways since Fbg assembly was not inhibited by GPRP, a specific inhibitor of fibrin polymerization. This finding was supported by the different sensitivity of the aggregates to the disruptive effects of urea and guanidine hydrochloride. We suggest that FbsA and fibrinogen play complementary roles in contributing to thrombogenesis associated with S. agalactiae infection.     

Haemochromatosis gene (HFE) mutations in viral-associated neoplasia: Linkage to cervical cancer

The present study examines the frequency of the two main HFE mutations (C282Y and H63D) in a randomly selected population of 346 individuals including 201 DNA samples from women with cervical neoplasia (including high-grade squamous intraepithelial lesions and invasive squamous cell carcinoma) and a control population of 146 women from the same geographical area. We found a significantly lower risk of development of cervical neoplasia in H63D carriers (OR = 0.56; 95% CI 0.35-0.92; p = 0.01). Multivariate logistic regression analysis confirms this observation (OR = 0.55; 95% CI 0.35-0.88, p = 0.01). Regarding the C282Y mutation no association was found (OR = 1.32; 95% CI 0.53-3.33; p = 0.52). In addition, a significant difference between H63D carrier and non-carrier women on the time-to-onset of cervical lesions was observed (log-rank test: p = 0.0012). These results indicate that HFE could be considered a candidate modifier gene of viral-related neoplasia such as cervical carcinoma possibly by a dual role on iron metabolism and immunological system.     

Role of loop bundle hydrogen bonds in the maturation and activity of (Pro)caspase-3

During maturation, procaspase-3 is cleaved at D175, which resides in a linker that connects the large and small subunits. The intersubunit linker also connects two active site loops that rearrange following cleavage and, in part, form the so-called loop bundle. As a result of chain cleavage, new hydrogen bonds and van der Waals contacts form among three active site loops. The new interactions are predicted to stabilize the active site. One unresolved issue is the extent to which the loop bundle residues also stabilize the procaspase active site. We examined the effects of replacing four loop bundle residues (E167, D169, E173, and Y203) on the biochemical and structural properties of the (pro)caspase. We show that replacing the residues affects the activity of the procaspase as well as the mature caspase, with D169A and E167A replacements having the largest effects. Replacement of D169 prevents caspase-3 autoactivation, and its cleavage at D175 no longer leads to an active enzyme. In addition, the E173A mutation, when coupled to a second mutation in the procaspase, D175A, may alter the substrate specificity of the procaspase. The mutations affected the active site environment as assessed by changes in fluorescence emission, accessibility to quencher, and cleavage by either trypsin or V8 proteases. High-resolution X-ray crystallographic structures of E167A, D173A, and Y203F caspases show that changes in the active site environment may be due to the increased flexibility of several residues in the N-terminus of the small subunit. Overall, the results show that these residues are important for stabilizing the procaspase active site as well as that of the mature caspase.