Correlation between IL1β expression level and morphological parameters proves the usefulness of morphology measures to predict the degree of activation of microglial cells

It is well known that microglial cells undergo an important change in morphology upon activation, so that form and function are intimately related. Upon activation, microglia cell body enlarges, its ramifications shortens and become thicker. In parallel, a variety of cytokines and inflammatory mediators such as IL1β are released. However the activation process is not all-or-nothing. Rather, cells in subtle activation states or in a deactivation process can occur, so intermediate not obvious phenotypes may appear. Thus, we aimed to correlate the expression level of a well-defined marker of activation, IL1β, with different morphological parameters. To do so, we used an intracerebroventricular injection of neuraminidase to produce an acute inflammation in rats. Brain sections were double-stained with IBA1 to have an image of the whole cell and its ramifications, and with IL1β to assess the level of activation. Images were captured from septofimbria (close to the injection site) and from the hypothalamus. A ratio of IL1β-positive pixels to IBA1-positive pixels was used to estimate the level of IL1β expression for each cell. Single microglial cell images were processed with ImageJ software to obtain outlined and filled shapes, which were used to obtain (by means of FracLac plug in) the following morphological parameters: fractal dimension, lacunarity, area, density and perimeter. All parameters showed a significant correlation with the level of expression of IL1β. This occurred in cells sampled from the two brain areas studied. Density, lacunarity and perimeter resulted as the best predictor parameters of activation, that is, those with a better correlation with the level of expression of IL1β. Area, an extensively used parameter to assess microglial activation, presented the least significant correlation. Thus, objectively measured morphological parameters correlate with the level of expression of IL1β, and could therefore be used as predictors of the activation level of microglial cells.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Computational study of the mechanism of Bcl-2 apoptotic switch

Programmed cell death - apoptosis is one of the most studied biological phenomenon of recent years. Apoptotic regulatory network contains several significant control points, including probably the most important one - Bcl--2 apoptotic switch. There are two proposed hypotheses regarding its internal working - the indirect activation and direct activation models. Since these hypotheses form extreme poles of full continuum of intermediate models, we have constructed more general model with these two models as extreme cases. By studying relationship between model parameters and steady-state response ultrasensitivity we have found optimal interaction pattern which reproduces behavior of Bcl-2 apoptotic switch. Our results show, that stimulus-response ultrasensitivity is negatively related to spontaneous activation of Bcl-2 effectors - subgroup of Bcl-2 proteins. We found that ultrasensitivity requires effector's activation, mediated by another subgroup of Bcl-2 proteins - activators. We have shown that the auto-activation of effectors forms ultrasensitivity enhancing feedback loop, only if mediated by monomers, but not by oligomers. Robustness analysis revealed that interaction pattern proposed by direct activation hypothesis is able to conserve stimulus-response dependence and preserve ultrasensitivity despite large changes of its internal parameters. This ability is strongly reduced as for the intermediate to indirect side of the models. Computer simulation of the more general model presented here suggest, that stimulus-response ultrasensitivity is an emergent property of the direct activation model, that cannot originate within model of indirect activation. Introduction of indirect-model-specific interactions does not provide better explanation of Bcl-2 functioning compared to direct model

Integrin activation - the importance of a positive feedback

Integrins mediate cell adhesion and are essential receptors for the development and functioning of multicellular organisms. Integrin activation is known to require both ligand and talin binding and to correlate with cluster formation but the activation mechanism and precise roles of these processes are not yet resolved. Here mathematical modeling, with known experimental parameters, is used to show that the binding of a stabilizing factor, such as talin, is alone insufficient to enable ligand-dependent integrin activation for all observed conditions; an additional positive feedback is required.Comment: in press in Bulletin of Mathematical Biolog