Thermodynamics of small systems by nanocalorimetry: from physical to biological nano-objects

Membrane based nanocalorimeters have been developed for ac calorimetry experiments. It has allowed highly sensitive measurements of heat capacity from solid state physics to complex systems like polymers and proteins. In this article we review what has been developed in ac calorimetry toward the measurement of very small systems. Firstly, at low temperature ac calorimetry using silicon membrane permits the measurement of superconducting sample having geometry down to the nanometer scale. New phase transitions have been found in these nanosystems illustrated by heat capacity jumps versus the applied magnetic field. Secondly, a sensor based on ultra-thin polymer membrane will be presented. It has been devoted to thermal measurements of nanomagnetic systems at intermediate temperature (20K to 300K). Thirdly, three specific polyimide membrane based sensors have been designed for room temperature measurements. One is devoted to phase transitions detection in polymer, the second one to protein folding/unfolding studies and the third one will be used for the study of heat release in living cells. The possibility of measuring systems out of equilibrium will be emphasized

Intermediate filaments control collective migration by restricting traction forces and sustaining cell-cell contacts

Mesenchymal cell migration relies on the coordinated regulation of the actin and microtubule networks that participate in polarized cell protrusion, adhesion, and contraction. During collective migration, most of the traction forces are generated by the acto-myosin network linked to focal adhesions at the front of leader cells, which transmit these pulling forces to the followers. Here, using an in vitro wound healing assay to induce polarization and collective directed migration of primary astrocytes, we show that the intermediate filament (IF) network composed of vimentin, glial fibrillary acidic protein, and nestin contributes to directed collective movement by controlling the distribution of forces in the migrating cell monolayer. Together with the cytoskeletal linker plectin, these IFs control the organization and dynamics of the acto-myosin network, promoting the actin-driven treadmilling of adherens junctions, thereby facilitating the polarization of leader cells. Independently of their effect on adherens junctions, IFs influence the dynamics and localization of focal adhesions and limit their mechanical coupling to the acto-myosin network. We thus conclude that IFs promote collective directed migration in astrocytes by restricting the generation of traction forces to the front of leader cells, preventing aberrant tractions in the followers, and by contributing to the maintenance of lateral cell-cell interactions

Dynamic measurement of the height and volume of migrating cells by a novel fluorescence microscopy technique

We propose a new technique to measure the volume of adherent migrating cells. The method is based on a negative staining where a fluorescent, non cell-permeant dye is added to the extracellular medium. The specimen is observed with a conventional fluorescence microscope in a chamber of uniform height. Given that the fluorescence signal depends on the thickness of the emitting layer, the objects excluding the fluorescent dye (i.e., cells) appear dark, and the decrease of the fluorescent signal with respect to the background is expected to give information about the height and the volume of the object. Using a glass microfabricated pattern with steps of defined heights, we show that the drop in fluorescence intensity is indeed proportional to the height of the step and obtain calibration curves relating fluorescence intensity to height. The technique, termed fluorescence displacement method, is further validated by comparing our measurements with the ones obtained by atomic force microscopy (AFM). We apply our method to measure the real-time volume dynamics of migrating fish epidermal keratocytes subjected to osmotic stress. The fluorescence displacement technique allows fast and precise monitoring of cell height and volume, thus providing a valuable tool for characterizing the three-dimensional behaviour of migrating cells

Evaluation of a Gender-Relevant Physical Activity After-School Program

Background: Physical activity rates have decreased in the past 30 years. Physical activity rates decline further among girls as they reach adolescence, yet studies suggest girls are more inclined to participate in moderate-to-vigorous physical activity (MVPA) while among peers. When in close social networks, girls who have more physically active friends report being more active themselves. Several mentor-based programs throughout the United States have increased physical activity among preadolescent girls, indicating that gender-relevant physical activity programs may reverse their declining rates of physical activity. Purpose: To evaluate if participation in a gender-relevant physical activity after-school program influenced participants\u27 aerobic fitness, body composition, and physical activity self-efficacy. Methods: Data were collected at baseline (T1) and mid-program (3 months, T2) for each variable (estimated VO2max, body fat mass, lean body mass, and physical activity self-efficacy) within the control and intervention groups. Two-way ANOVA was conducted to examine the effect of the program intervention and time on each outcome variable. Results: There were no significant differences for estimated VO2max or physical activity self-efficacy. There was a statistically significant effect on body fat mass by group, by time, and for the interaction (group x time): control (14.69±7.09kg at T1 and 16.05±7.27kg at T2) and Aggie Play (10.49±7.96kg at T1 and 10.61±7.91kg at T2); group F(df 1)=3.87, p\u3c0.01; time F(df 1)=22.9, p\u3c0.01; and group x time F(df 1)=16.03, p\u3c0.01. There was a statistically significant effect on lean body mass by time and interaction (group x time), but not for the group effect: control (28.82 ± 6.56kg at T1 and 29.05 ± 6.63kg at T2) and Aggie Play (26.12 ± 5.47kg at T1 and 26.98 ± 5.70kg at T2); group F(df 1)= 1.69, p=0.02; time F(df 1)=15.7, p\u3c0.01; and group x time F(df 1)=5.09, p\u3c0.01. Conclusion: The results of this study indicate that after a three-month midpoint analysis a mentor-based after-school physical activity program can be beneficial. A major finding of the effectiveness of the program was the improvement in body composition

Evaluation of a Gender-Relevent Physical Activity Afterschool Program

Background: Physical activity rates have decreased in the past 30 years. Physical activity rates decline further among girls as they reach adolescence, yet studies suggest girls are more inclined to participate in moderate-to-vigorous physical activity (MVPA) while among peers. When in close social networks, girls who have more physically active friends report being more active themselves. Several mentor-based programs throughout the United States have increased physical activity among preadolescent girls, indicating that gender-relevant physical activity programs may reverse their declining rates of physical activity. Purpose: To evaluate if participation in a gender-relevant physical activity after-school program influenced participants’ aerobic fitness, body composition, and physical activity self-efficacy. Methods: Data were collected at baseline (T1) and mid-program (3 months, T2) for each variable (estimated VO2max, body fat mass, lean body mass, and physical activity self-efficacy) within the control and intervention groups. Two-way ANOVA was conducted to examine the effect of the program intervention and time on each outcome variable. Results: There were no significant differences for estimated VO2max or physical activity self-efficacy. There was a statistically significant effect on body fat mass by group, by time, and for the interaction (group x time): control (14.69±7.09kg at T1 and 16.05±7.27kg at T2) and Aggie Play (10.49±7.96kg at T1 and 10.61±7.91kg at T2); group F(df 1)=3.87, p\u3c0.01; time F(df 1)=22.9, p\u3c0.01; and group x time F(df 1)=16.03, p\u3c0.01. There was a statistically significant effect on lean body mass by time and interaction (group x time), but not for the group effect: control (28.82 ± 6.56kg at T1 and 29.05 ± 6.63kg at T2) and Aggie Play (26.12 ± 5.47kg at T1 and 26.98 ± 5.70kg at T2); group F(df 1)= 1.69, p=0.02; time F(df 1)=15.7, p\u3c0.01; and group x time F(df 1)=5.09, p\u3c0.01. Conclusion: The results of this study indicate that after a three-month midpoint analysis a mentor-based after-school physical activity program can be beneficial. A major finding of the effectiveness of the program was the improvement in body composition

Adhérence de cellules uniques sur supports micro-structurés

The cell adhesion is a critical process involved in many fundamental biological phenomena as dierentiation, tissue repair or cell development. This thesis focuses on a study combining experiments and modelization of single cells spreading on micro-fabricated substrates. Experimental results show that the geometrical constraint imposed by the adhesiveness contrast limits the adhesion. Beyond this limitation, a reproducible organization of the actin cytoskeleton of cells spreading on micro-structured materials suggests that simple physical laws govern the process. We have developed a classication method of basic geometrical shapes observed experimentally to obtain robust statistics. Based on the Cellular Potts model, we reproduced experimental results. This energetical model shows that the basic shapes are metastable states used by cells during spreading. The model parameters are linked to relevant biological parameters. We present results that connect the curvature of interfaces to biological parameters. We show that the experimental measurement of this curvature represents the competition between the contractility of stress bers and the elasticity of the actin gel. A correspondence between the physical properties in the model and the biochemical processes that regulate and organize the cellular adhesion is possible.L'adhérence cellulaire est un processus vital impliqué dans de nombreux phénomènes biologiques fondamentaux comme la diérenciation, la réparation tissulaire ou encore le développement cellulaire. Cette thèse porte sur une étude alliant expériences et modélisation de cellules uniques en adhérence sur des supports micro-structurés Les résultats montrent que la contrainte géomé- trique imposée par les supports à contraste adhésif limite l'adhérence. Au-delà de cette limitation, une organisation reproductible du cytosquelette d'actine est observée cela suggère l'existence de lois physiques simples régissant ce processus. Nous avons développé une méthode de classication des formes géométriques élémentaires observées expérimentalement nous permettant d'obtenir des statistiques robustes. En nous basant sur le modèle de Potts Cellulaire, nous avons pu reproduire les résultats expérimentaux. Ce modèle énergétique démontre que les formes élémentaires sont des états métastables utilisés par les cellules au cours de l'adhérence. Les paramètres du modèle sont reliés aux paramètres biologiques pertinents. Nous présentons des résultats qui relient la courbure des interfaces aux paramètres biologiques. Nous montrons que la mesure expérimentale de cette courbure est une représentation de la compétition entre la contractilité des bres de stress et l'élasticité du gel d'actine. Une correspondance entre les propriétés physiques issues du modèle et les processus biochimiques régulant et organisant l'adhérence cellulaire est ainsi possible

Adhérence de cellules uniques sur supports micro-structurés

L'adhérence cellulaire est un processus vital impliqué dans de nombreux phénomènes biologiques fondamentaux comme la diérenciation, la réparation tissulaire ou encore le développement cellulaire. Cette thèse porte sur une étude alliant expériences et modélisation de cellules uniques en adhérence sur des supports micro-structurés Les résultats montrent que la contrainte géomé- trique imposée par les supports à contraste adhésif limite l'adhérence. Au-delà de cette limitation, une organisation reproductible du cytosquelette d'actine est observée cela suggère l'existence de lois physiques simples régissant ce processus. Nous avons développé une méthode de classication des formes géométriques élémentaires observées expérimentalement nous permettant d'obtenir des statistiques robustes. En nous basant sur le modèle de Potts Cellulaire, nous avons pu reproduire les résultats expérimentaux. Ce modèle énergétique démontre que les formes élémentaires sont des états métastables utilisés par les cellules au cours de l'adhérence. Les paramètres du modèle sont reliés aux paramètres biologiques pertinents. Nous présentons des résultats qui relient la courbure des interfaces aux paramètres biologiques. Nous montrons que la mesure expérimentale de cette courbure est une représentation de la compétition entre la contractilité des bres de stress et l'élasticité du gel d'actine. Une correspondance entre les propriétés physiques issues du modèle et les processus biochimiques régulant et organisant l'adhérence cellulaire est ainsi possible.The cell adhesion is a critical process involved in many fundamental biological phenomena as dierentiation, tissue repair or cell development. This thesis focuses on a study combining experiments and modelization of single cells spreading on micro-fabricated substrates. Experimental results show that the geometrical constraint imposed by the adhesiveness contrast limits the adhesion. Beyond this limitation, a reproducible organization of the actin cytoskeleton of cells spreading on micro-structured materials suggests that simple physical laws govern the process. We have developed a classication method of basic geometrical shapes observed experimentally to obtain robust statistics. Based on the Cellular Potts model, we reproduced experimental results. This energetical model shows that the basic shapes are metastable states used by cells during spreading. The model parameters are linked to relevant biological parameters. We present results that connect the curvature of interfaces to biological parameters. We show that the experimental measurement of this curvature represents the competition between the contractility of stress bers and the elasticity of the actin gel. A correspondence between the physical properties in the model and the biochemical processes that regulate and organize the cellular adhesion is possible.GRENOBLE1-BU Sciences (384212103) / SudocSudocFranceF