Maximum entropy determination of mammalian proteome dynamics.

Full understanding of proteostasis and energy utilization in cells will require knowledge of the fraction of cell proteins being degraded with different half-lives and their rates of synthesis. We therefore developed a method to determine such information that combines mathematical analysis of protein degradation kinetics obtained in pulse-chase experiments with Bayesian data fitting using the maximum entropy principle. This approach will enable rapid analyses of whole-cell protein dynamics in different cell types, physiological states, and neurodegenerative disease. Using it, we obtained surprising insights about protein stabilities in cultured cells normally and upon activation of proteolysis by mTOR inhibition and increasing cAMP or cGMP. It revealed that >90% of protein content in dividing mammalian cell lines is long-lived, with half-lives of 24 to 200 h, and therefore comprises much of the proteins in daughter cells. The well-studied short-lived proteins (half-lives < 10 h) together comprise <2% of cell protein mass, but surprisingly account for 10 to 20% of measurable newly synthesized protein mass. Evolution thus appears to have minimized intracellular proteolysis except to rapidly eliminate misfolded and regulatory proteins.

Force scaling and efficiency of elongated median fin propulsion.

Several fishes swim by undulating a thin and elongated median fin while the body is mostly kept straight, allowing them to perform forward and directional maneuvers. We used a robotic vessel with similar fin propulsion to determine the thrust scaling and efficiency. Using precise force and swimming kinematics measurements with the robotic vessel, the thrust generated by the undulating fin was found to scale with the square of the relative velocity between the free streaming flow and the wave speed. A hydrodynamic efficiency is presented based on propulsive force measurements and modelling of the power required to oscillate the fin laterally. It was found that the propulsive efficiency has a broadly high performance versus swimming speed, with a maximum efficiency of 75%. An expression to calculate the swimming speed over wave speed was found to depend on two parameters:Ap/Ae(ratio between body frontal area to fin swept area) andCD/Cx(ratio of body drag to fin thrust coefficient). The models used to calculate propulsive force and free-swimming speed were compared with experimental results. The broader impacts of these results are discussed in relation to morphology and the function of undulating fin swimmers. In particular, we suggest that the ratio of fin and body height found in natural swimmers could be due to a trade-off between swimming efficiency and swimming speed.

Apexificación en una cita utilizando material biocerámico como tapón apical / Apexification in a single appointment using a bioceramic material as an apical plug

El objetivo fue realizar una técnica de apexificación en una cita, evaluando clínica y radiográficamente la formación de barrera dura apical, con seguimiento a nueve meses, al utilizar material biocerámico en dien-tes permanentes jóvenes. Se trataron 30 incisivos su-periores permanentes con ápice abierto y anteceden-tes de trauma, en pacientes de ambos géneros y 18-40 años. Las piezas (n=30) se dividieron en dos grupos (n=15). Grupo experimental: tratamiento de apexifica-ción con EndoSequence Root Repair Material (EERR), y grupo control: tratamiento con impresión apical. Se determinaron distribuciones de frecuencias y esta-dísticas descriptivas para cada variable, según es-cala de medición y distribución. Se realizaron IC 95%, test de Chi cuadrado con cálculo de residuos estan-darizados ajustados y test de Fisher. Se fijó nivel de significación p=0.05. Las diferencias de manifestacio-nes preoperatorias y postoperatorias según grupo fueron no significativas (p Fisher = 0.9140) y (p Fisher = 0.992), respectivamente. No se hallaron diferencias entre proporciones de hallazgos radiológicos preope-ratorios según grupo. Medidas trimestralmente, no hubo diferencias significativas entre proporciones de piezas con continuidad de cortical ósea y radiolucidez periapical postoperatoria según grupo, (p Fisher = 0.7780) y (p Fisher = 0.7909), respectivamente. Debi-do la escasa cantidad de trabajos que reportan el uso de EERR para esta técnica, se requiere de nuevos en-sayos clínicos con tamaños muestrales amplios, para compararlo con otros materiales y técnicas, y deter-minar si su tasa de éxito a largo plazo es mayor que a de los materiales y técnicas usadas actualmente (AU)

To perform apexification technique in one appointment, clinically and radiographically evaluating the formation of apical hard barrier, with follow-up at nine months, when using bioceramic material in young permanent teeth. Materials and methods: 30 permanent upper incisors with open apex and history of trauma were treated, in patients of both genders and 18-40 years of ages. The teeth (n=30) were divided into two groups (n=15). Experimental group: apexification treatment was performed with EndoSequence Root Repair Material (EERR), control group: treatment with apical impression. Frequency distributions and descriptive statistics were determined for each variable according to scale of measurement and distribution. 95% CI, Chi-square test with calculation of adjusted standardized residuals and Fisher's test were performed. The level of significance p=0.05 was set. The differences in preoperative and postoperative manifestations according to group were not statistically significant (Fisher's p = 0.9140) and (Fisher's p = 0.992), respectively. No differences were found between proportions of preoperative radiological findings according to group. Measured quarterly, there were no significant differences between proportions of teeth with bone cortical continuity and with postoperative periapical radiolucency according to group, (p Fisher = 0.7780) and (p Fisher = 0.7909), respectively. Due to the small number of works that report its use for this technique, is necessary to carry out new clinical trials with larger sample sizes, to compare it with other materials and techniques, and determine if its success rate in the long term is greater than that of currently used materials and techniques (AU)

Quantifying Co-Oligomer Formation by α-Synuclein.

Small oligomers of the protein α-synuclein (αS) are highly cytotoxic species associated with Parkinson's disease (PD). In addition, αS can form co-aggregates with its mutational variants and with other proteins such as amyloid-ß (Aß) and tau, which are implicated in Alzheimer's disease. The processes of self-oligomerization and co-oligomerization of αS are, however, challenging to study quantitatively. Here, we have utilized single-molecule techniques to measure the equilibrium populations of oligomers formed in vitro by mixtures of wild-type αS with its mutational variants and with Aß40, Aß42, and a fragment of tau. Using a statistical mechanical model, we find that co-oligomer formation is generally more favorable than self-oligomer formation at equilibrium. Furthermore, self-oligomers more potently disrupt lipid membranes than do co-oligomers. However, this difference is sometimes outweighed by the greater formation propensity of co-oligomers when multiple proteins coexist. Our results suggest that co-oligomer formation may be important in PD and related neurodegenerative diseases.

Quantitative analysis of co-oligomer formation by amyloid-beta peptide isoforms.

Multiple isoforms of aggregation-prone proteins are present under physiological conditions and have the propensity to assemble into co-oligomers with different properties from self-oligomers, but this process has not been quantitatively studied to date. We have investigated the amyloid-ß (Aß) peptide, associated with Alzheimer's disease, and the aggregation of its two major isoforms, Aß40 and Aß42, using a statistical mechanical modelling approach in combination with in vitro single-molecule fluorescence measurements. We find that at low concentrations of Aß, corresponding to its physiological abundance, there is little free energy penalty in forming co-oligomers, suggesting that the formation of both self-oligomers and co-oligomers is possible under these conditions. Our model is used to predict the oligomer concentration and size at physiological concentrations of Aß and suggests the mechanisms by which the ratio of Aß42 to Aß40 can affect cell toxicity. An increased ratio of Aß42 to Aß40 raises the fraction of oligomers containing Aß42, which can increase the hydrophobicity of the oligomers and thus promote deleterious binding to the cell membrane and increase neuronal damage. Our results suggest that co-oligomers are a common form of aggregate when Aß isoforms are present in solution and may potentially play a significant role in Alzheimer's disease.

Kinetic model of the aggregation of alpha-synuclein provides insights into prion-like spreading.

The protein alpha-synuclein (αS) self-assembles into small oligomeric species and subsequently into amyloid fibrils that accumulate and proliferate during the development of Parkinson's disease. However, the quantitative characterization of the aggregation and spreading of αS remains challenging to achieve. Previously, we identified a conformational conversion step leading from the initially formed oligomers to more compact oligomers preceding fibril formation. Here, by a combination of single-molecule fluorescence measurements and kinetic analysis, we find that the reaction in solution involves two unimolecular structural conversion steps, from the disordered to more compact oligomers and then to fibrils, which can elongate by further monomer addition. We have obtained individual rate constants for these key microscopic steps by applying a global kinetic analysis to both the decrease in the concentration of monomeric protein molecules and the increase in oligomer concentrations over a 0.5-140-µM range of αS. The resulting explicit kinetic model of αS aggregation has been used to quantitatively explore seeding the reaction by either the compact oligomers or fibrils. Our predictions reveal that, although fibrils are more effective at seeding than oligomers, very high numbers of seeds of either type, of the order of 10(4), are required to achieve efficient seeding and bypass the slow generation of aggregates through primary nucleation. Complementary cellular experiments demonstrated that two orders of magnitude lower numbers of oligomers were sufficient to generate high levels of reactive oxygen species, suggesting that effective templated seeding is likely to require both the presence of template aggregates and conditions of cellular stress.

Fast flow microfluidics and single-molecule fluorescence for the rapid characterization of α-synuclein oligomers.

α-Synuclein oligomers can be toxic to cells and may be responsible for cell death in Parkinson's disease. Their typically low abundance and highly heterogeneous nature, however, make such species challenging to study using traditional biochemical techniques. By combining fast-flow microfluidics with single-molecule fluorescence, we are able to rapidly follow the process by which oligomers of αS are formed and to characterize the species themselves. We have used the technique to show that populations of oligomers with different FRET efficiencies have varying stabilities when diluted into low ionic strength solutions. Interestingly, we have found that oligomers formed early in the aggregation pathway have electrostatic repulsions that are shielded in the high ionic strength buffer and therefore dissociate when diluted into lower ionic strength solutions. This property can be used to isolate different structural groups of αS oligomers and can help to rationalize some aspects of αS amyloid fibril formation.

Force generation by the growth of amyloid aggregates.

The generation of mechanical forces are central to a wide range of vital biological processes, including the function of the cytoskeleton. Although the forces emerging from the polymerization of native proteins have been studied in detail, the potential for force generation by aberrant protein polymerization has not yet been explored. Here, we show that the growth of amyloid fibrils, archetypical aberrant protein polymers, is capable of unleashing mechanical forces on the piconewton scale for individual filaments. We apply microfluidic techniques to measure the forces released by amyloid growth for two systems: insulin and lysozyme. The level of force measured for amyloid growth in both systems is comparable to that observed for actin and tubulin, systems that have evolved to generate force during their native functions and, unlike amyloid growth, rely on the input of external energy in the form of nucleotide hydrolysis for maximum force generation. Furthermore, we find that the power density released from growing amyloid fibrils is comparable to that of high-performance synthetic polymer actuators. These findings highlight the potential of amyloid structures as active materials and shed light on the criteria for regulation and reversibility that guide molecular evolution of functional polymers.

A mechanistic model of tau amyloid aggregation based on direct observation of oligomers.

Protein aggregation plays a key role in neurodegenerative disease, giving rise to small oligomers that may become cytotoxic to cells. The fundamental microscopic reactions taking place during aggregation, and their rate constants, have been difficult to determine due to lack of suitable methods to identify and follow the low concentration of oligomers over time. Here we use single-molecule fluorescence to study the aggregation of the repeat domain of tau (K18), and two mutant forms linked with familial frontotemporal dementia, the deletion mutant ΔK280 and the point mutant P301L. Our kinetic analysis reveals that aggregation proceeds via monomeric assembly into small oligomers, and a subsequent slow structural conversion step before fibril formation. Using this approach, we have been able to quantitatively determine how these mutations alter the aggregation energy landscape.

Asymptotic solutions of the Oosawa model for the length distribution of biofilaments.

Nucleated polymerisation phenomena are general linear growth processes that underlie the formation of a range of biofilaments in nature, including actin and tubulin that are key components of the cellular cytoskeleton. The conventional theoretical framework for describing this process is the Oosawa model that takes into account homogeneous nucleation coupled to linear growth. In his original work, Oosawa provided an analytical solution to the total mass concentration of filaments; the time evolution of the full length distribution has, however, been challenging to access, in large part due to the nonlinear nature of the rate equations inherent in the description of such phenomena and to date analytical solutions for the filament distribution are known only in certain special cases. Here, by exploiting a technique based on the method of matched asymptotics, we present an analytical treatment of the Oosawa model that describes the shape of the length distribution of biofilaments reversibly growing through primary nucleation and filament elongation. Our work highlights the power of matched asymptotics for obtaining closed-form analytical solutions to nonlinear master equations in biophysics and allows us to identify the key time scales that characterize biological polymerization processes.

Nucleation-conversion-polymerization reactions of biological macromolecules with prenucleation clusters.

The self-assembly of biomolecules, such as peptides and proteins, into filaments is conventionally understood as a nucleated polymerization reaction. However, detailed analysis of experimental observation has revealed recently that nucleation pathways generate growth-competent nuclei via a cascade of metastable intermediate species, which are omitted in conventional models of filamentous growth based on classical nucleation theory. Here we take an analytical approach to generalizing the classical theory of nucleated polymerization to include the formation of these prenucleation clusters, providing a quantitative general classification of the behavior exhibited by these nucleation-conversion-polymerization reactions. A phase diagram is constructed, and analytical predictions are derived for key experimental observables. Using this approach, we delineate the characteristic time scales that determine the nature of biopolymer growth phenomena.

sEMG-based detection of poor posture: a feasibility study.

The cost of the medical treatment of low back pain (LBP) was estimated to be $24 billion in the early 90s. Also, 80% of the LBP is estimated to be due to poor or inappropriate posture. The ultimate goal of the project is to develop a surface electromyography (sEMG)-based device that could be used to prevent and treat LBP by postural re-education or simply for on-the-spot sEMG feedback. In this paper we present the results and conclusions of a feasibility study for sEMG-based poor posture classifier. The results show that a s-EMG based poor posture classifier could be possible. The sensitivity for the best linear classifier model was 72% and the specificity was 78%. The same signal feature returned very different results from one participant to another. This inter-subject variability could be due to different muscular activation patterns during posture correction.

Evaluación clínica de un nuevo dispositivo electrónico en la determinación de la longitud de trabajo / Clinical evaluation of a new electronic device for work length determination

El presente estudio clínico evaluó, en 67 conductos radiculares, el grado de precisión de un nuevo dispositivo electrónico en la determinación de la longitud de trabajo, comparándolo con el método radiográfico. Los resultados mostraron un total del 92,5 por ciento de mediciones aceptables. No se observaron diferencias estadísticamente significativas entre las mediciones obtenidas en piezas dentarias con pulpa vital y pulpa mortificada

Evaluación clínica de un nuevo dispositivo electrónico en la determinación de la longitud de trabajo / Clinical evaluation of a new electronic device for work length determination

El presente estudio clínico evaluó, en 67 conductos radiculares, el grado de precisión de un nuevo dispositivo electrónico en la determinación de la longitud de trabajo, comparándolo con el método radiográfico. Los resultados mostraron un total del 92,5 por ciento de mediciones aceptables. No se observaron diferencias estadísticamente significativas entre las mediciones obtenidas en piezas dentarias con pulpa vital y pulpa mortificada (AU)

Maxi program at IEEE EMBS Student Club of Beijing University of Posts and Telecommunications.

This paper presents the recently launched Maxi Program at IEEE EMBS Student Club of Beijing University of Posts and Telecommunications. The program initiates a variety of seminar series covering biomedical expertise and professional communication skills, forms a cooperative partnership between students, university and industry through guest speakers events and industry tours, and sets in motion personal consultative services (PCS) to foster the individualized competence of students. This extended program could be an innovative model of self-development as an affiliated student chapter/club with IEEE EMBS.

Torsión del epiplón mayor, causa de abdomen agudo en escolares y adolescentes / Great omuntum torsion, cause of acute abdomen in scholars and adolescents

La torsión del delantal epiploico, segmento libre del epiplón mayor, es un evento clínico poco frecuente sobre todo entre los infantes. En el Hospital de Especialidades No. 1 del Centro Médico Nacional del Noroeste, Ciudad Obregón, Sonora, en los últimos cinco años se han identificado cuatro casos en tres niños y una niña, con edades entre ocho y 10 años. Todos tuvieron como rasgo común la obesidad moderada o marcada y el antecedente de contusión abdominal reciente. El principal dato clínico fue el dolor abdominal continuo y progresivo en los cuadrantes derechos, con una evolución de tres días sin estar acompañado de síndrome infeccioso. En ningún caso se estableció diagnóstico preoperatorio, indicándose el procedimiento quirúrgico por la sospecha de apendicitis aguda. Durante la laparotomía se encontró el apéndice cecal sano y al palpar internamente el alto abdomen derecho se identificó el plastrón hemorrágico de un segmento del epiplón mayor, muy cercano a su borde derecho, en el que histopatológicamente se documentó necrosis y hemorragía. La resección fue curativa en todos