Mechanisms of Adsorption and Surface-Mediated Aggregation of Intrinsically Disordered Protein Tau at Model Surfaces

The adsorption and aggregation of an intrinsically disordered soluble protein, tau, into insoluble filaments is a defining hallmark of many neurodegenerative diseases, commonly referred to as tauopathies. In its native state, the protein tau’s function is to promote the assembly, and aid in the stabilization of microtubules. The microtubules allow for material transport through the axon, to and from the neuron. While the presence of aggregated tau protein fibrils are hypothesized to accelerate neuronal degradation, possibly by destabilizing microtubules, or disrupting cell membranes, more recent research has established the presence of soluble oligomeric species as being cytotoxic. These results necessitate a complete fundamental understanding of the governing principles that modulate the initial steps in the mechanisms of tau protein aggregation. The macromolecular environment, including the presence of surfaces such as the cell membrane, and the presence of macromolecules in a crowded environment, has been implicated in the aggregation of tau protein. However, the exact role of surfaces in modulating Tau protein aggregation has not been explored in detail. We hypothesize that Tau protein aggregation at model surfaces is modulated by two factors, the physicochemical properties of the surfaces, as well as the biochemistry of the protein molecules. The work presented in this thesis project employs a combination of biophysical techniques to study the adsorption and aggregation of a wild type and several mutations of tau protein at model surfaces. A Quartz Crystal Microbalance with Dissipation (QCM-D) was used to monitor the adsorption of different tau species at nanomolar concentrations, mimicking the in vivo situation, to surfaces with different surface charge, wettability and softness, while Atomic Force Microscopy (AFM) was utilized to obtain direct visualization of the proteins at these different surfaces. Our results indicate that the hydrophobic amino acid sequence in the microtubule binding region was the leading force driving the adsorption of tau proteins to different surfaces. Further, AFM images provided direct evidence of the presence of oligomeric tau species at the interfaces, establishing that the solid surface did in fact provide a template for the tau protein to form aggregates. Adsorption of different tau protein mutations to phospholipid covered surfaces of different fluidity indicated that tau protein oligomers can also cause destabilization or disintegration of lipid bilayers. Such disintegration may well be the cause of observed cell death in several tauopathies. In summary, this thesis establishes that both protein biochemistry and the physicochemical properties of the surface modulate surface mediated aggregation. The work described in this thesis also provides a foundation for further research focused on the role of surfaces as templates that mediate tau aggregation pathway in vivo. A complete understanding of the mechanisms of tau aggregation will ultimately lead to strategies for therapeutic solutions for neurodegenerative diseases

A second large plasmid encodes conjugative transfer and antimicrobial resistance in O119:H2 and some typical O111 enteropathogenic \u3ci\u3eEscherichia coli\u3c/i\u3e strains

A novel and functional conjugative transfer system identified in O119:H2 enteropathogenic Escherichia coli (EPEC) strain MB80 by subtractive hybridization is encoded on a large multidrug resistance plasmid, distinct from the well-described EPEC adherence factor (EAF) plasmid. Variants of the MB80 conjugative resistance plasmid were identified in other EPEC strains, including the prototypical O111:NM strain B171, from which the EAF plasmid has been sequenced. This separate large plasmid and the selective advantage that it confers in the antibiotic era have been overlooked because it comigrates with the virulence plasmid on conventional gels

The trans-sialidase from Trypanosoma cruzi induces thrombocytopenia during acute Chagas' disease by reducing the platelet sialic acid contents

Strong thrombocytopenia is observed during acute infection with Trypanosoma cruzi, the parasitic protozoan agent of American trypanosomiasis or Chagas' disease. The parasite sheds trans-sialidase, an enzyme able to mobilize the sialyl residues on cell surfaces, which is distributed in blood and is a virulence factor. Since the sialic acid content on the platelet surface is crucial for determining the half-life of platelets in blood, we examined the possible involvement of the parasite-derived enzyme in thrombocytopenia induction. We found that a single intravenous injection of trans-sialidase into naïve mice reduced the platelet count by 50%, a transient effect that lasted as long as the enzyme remained in the blood. CD43(−/−) mice were affected to a similar extent. When green fluorescent protein-expressing platelets were treated in vitro with trans-sialidase, their sialic acid content was reduced together with their life span, as determined after transfusion into naïve animals. No apparent deleterious effect on the bone marrow was observed. A central role for Kupffer cells in the clearance of trans-sialidase-altered platelets was revealed after phagocyte depletion by administration of clodronate-containing liposomes and splenectomy. Consistent with this, parasite strains known to exhibit more trans-sialidase activity induced heavier thrombocytopenia. Finally, the passive transfer of a trans-sialidase-neutralizing monoclonal antibody to infected animals prevented the clearance of transfused platelets. Results reported here strongly support the hypothesis that the trans-sialidase is the virulence factor that, after depleting the sialic acid content of platelets, induces the accelerated clearance of the platelets that leads to the thrombocytopenia observed during acute Chagas' disease

Duplication of the Gallbladder. A Case Report

Gallbladder duplication is a rare anatomic malformation, which can now be detected by preoperative imaging study. We report a case of a symptomatic duplicated gallbladder, successfully treated by laparoscopic cholecystectomy. This anomaly is important to know for surgeons because of associated anatomical variations of main bile duct and hepatic artery and increased risk of common bile duct injury

prebiotics offered to broiler chicken exert positive effect on meat quality traits irrespective of delivery route

Elimination of antibiotic growth promoters from poultry production has encouraged intensive search for relevant alternatives. Prebiotics are proposed as efficient replacements to stimulate colonization/expansion of beneficial microflora in chickens. The aim of this study was to deepen the knowledge on the effect of prebiotic administration on slaughter performance and meat quality traits of broiler chickens by evaluating different routes of their delivery (in ovo vs. in-water vs. in ovo + in-water). At d 12 of incubation, 1,500 eggs (Ross 308) containing viable embryos were randomly allotted into 4 groups and injected in ovo with 0.2 mL solution containing: 3.5 mg/embryo BI (Bi²tos, trans-galactooligosaccharides); 0.88 mg/embryo DN (DiNovo, extract of Laminaria spp.); 1.9 mg/embryo RFO (raffinose family oligosaccharides) and 0.2 mL physiological saline (C). All prebiotics increased final BW compared to C group (P < 0.01), irrespective of delivery route. The prebiotics injected in ovo (T1) or in ovo combined with in-water supplementation (T2) increased carcass weight as compared with in-water group (T3), while T3 had the lowest carcass yield compared to the other groups. All prebiotics increased breast muscle weight and yield (P < 0.01), as well as fiber diameter (P < 0.05). Ultimate meat pH was lower (P < 0.01) in T3 than in T2 group. Meat from chickens treated with prebiotics showed a lower redness index, while lightness and yellowness were not affected by the treatments. Saturated fatty acid (SFA), polyunsaturated fatty acid (PUFA) and n-3 fatty acids contents were higher (P < 0.01), and monounsaturated fatty acid (MUFA) level was lower (P < 0.01) in prebiotic groups compared with C group. Nutritional indexes (n-6/n-3, PUFA/SFA ratio and thrombogenic index) displayed favorable human health-promoting values in the meat of chickens which were treated with prebiotics, irrespective of delivery route. Muscle cholesterol content was not affected by prebiotics. In conclusion, this study has shown that prebiotics can exert positive effects on growth of broiler chickens, carcass and meat quality traits, irrespective of delivery route

Emerging Issues in Occupational Disease: Mental Health in the Aging Working Population and Cognitive Impairment - A Narrative Review

Cognitive impairment has often been reported in scientific literature as a concern derived from chronic exposure to work-related stress. Organizational factors can contribute to the onset of this concern especially in a susceptible population such as elderly workers. The aim of our study was to review the last five years of scientific literature, focusing on experimental and epidemiological studies, possible mechanisms implicated in the onset of cognitive decline due to work-related stress, and the recent organizational strategies to prevent detrimental effects of stress on cognitive processes. A literature search was performed in scientific platforms Medline and Web of Science, by means of specific string search terms, restricting the search to the years of publication 2014-2019. Thirty-three articles were identified and qualitatively evaluated, reporting narratively the main point of interest. At this stage, six articles were excluded because they did not meet the inclusion criteria. Only a few articles considered the population of the elderly workers, often with a short follow-up period. Strategies to manage stress with organizational procedures are scarce. Mechanisms implicated in the development of cognitive impairment due to stress are not fully explained and seem to include a chronical decrease in the inhibitory process of neurological pathways. Further research that focused on strategies to manage stress in elderly workers, with the aim of preventing cognitive impairment processes, is warranted

Emerging Issues in Occupational Disease: Mental Health in the Aging Working Population and Cognitive Impairment - A Narrative Review

Cognitive impairment has often been reported in scientific literature as a concern derived from chronic exposure to work-related stress. Organizational factors can contribute to the onset of this concern especially in a susceptible population such as elderly workers. The aim of our study was to review the last five years of scientific literature, focusing on experimental and epidemiological studies, possible mechanisms implicated in the onset of cognitive decline due to work-related stress, and the recent organizational strategies to prevent detrimental effects of stress on cognitive processes. A literature search was performed in scientific platforms Medline and Web of Science, by means of specific string search terms, restricting the search to the years of publication 2014–2019. Thirty-three articles were identified and qualitatively evaluated, reporting narratively the main point of interest. At this stage, six articles were excluded because they did not meet the inclusion criteria. Only a few articles considered the population of the elderly workers, often with a short follow-up period. Strategies to manage stress with organizational procedures are scarce. Mechanisms implicated in the development of cognitive impairment due to stress are not fully explained and seem to include a chronical decrease in the inhibitory process of neurological pathways. Further research that focused on strategies to manage stress in elderly workers, with the aim of preventing cognitive impairment processes, is warranted

Mal de Debarquement Syndrome: A Matter of Loops?

Introduction: Mal de Debarquement Syndrome (MdDS) is a poorly understood neurological disorder affecting mostly perimenopausal women. MdDS has been hypothesized to be a maladaptation of the vestibulo-ocular reflex, a neuroplasticity disorder, and a consequence of neurochemical imbalances and hormonal changes. Our hypothesis considers elements from these theories, but presents a novel approach based on the analysis of functional loops, according to Systems and Control Theory. Hypothesis: MdDS is characterized by a persistent sensation of self-motion, usually occurring after sea travels. We assume the existence of a neuronal mechanism acting as an oscillator, i.e., an adaptive internal model, that may be able to cancel a sinusoidal disturbance of posture experienced aboard, due to wave motion. Thereafter, we identify this mechanism as a multi-loop neural network that spans between vestibular nuclei and the flocculonodular lobe of the cerebellum. We demonstrate that this loop system has a tendency to oscillate, which increases with increasing strength of neuronal connections. Therefore, we hypothesize that synaptic plasticity, specifically long-term potentiation, may play a role in making these oscillations poorly damped. Finally, we assume that the neuromodulator Calcitonin Gene-Related Peptide, which is modulated in perimenopausal women, exacerbates this process thus rendering the transition irreversible and consequently leading to MdDS. Conclusion and Validation: The concept of an oscillator that becomes noxiously permanent can be used as a model for MdDS, given a high correlation between patients with MdDS and sea travels involving undulating passive motion, and an alleviation of symptoms when patients are re-exposed to similar passive motion. The mechanism could be further investigated utilizing posturography tests to evaluate if subjective perception of motion matches with objective postural instability. Neurochemical imbalances that would render individuals more susceptible to developing MdDS could be investigated through hormonal profile screening. Alterations in the connections between vestibular nuclei and cerebellum, notably GABAergic fibers, could be explored by neuroimaging techniques as well as transcranial magnetic stimulation. If our hypothesis were tested and verified, optimal targets for MdDS treatment could be found within both the neural networks and biochemical factors that are deemed to play a fundamental role in loop functioning and synaptic plasticity