A forward-backward view of some primal-dual optimization methods in image recovery

A wide array of image recovery problems can be abstracted into the problem of minimizing a sum of composite convex functions in a Hilbert space. To solve such problems, primal-dual proximal approaches have been developed which provide efficient solutions to large-scale optimization problems. The objective of this paper is to show that a number of existing algorithms can be derived from a general form of the forward-backward algorithm applied in a suitable product space. Our approach also allows us to develop useful extensions of existing algorithms by introducing a variable metric. An illustration to image restoration is provided

Approches expérimentale et de modélisation de la signalisation calcique dans les cellules

In many cell types, specific and robust signalling relies on a high level of spatiotemporal organization of Ca2+ dynamics. In response to external stimulation, Ca2+ signals ranging from a small increase of a few tens of nanomolar concentrations ot the mouth of an inositol 1, 4, 5-trisphosphate receptor to the periodic propagation of waves invading an organ or a tissue, can be observed. Here, we review our combined experimental and computational approach of Ca2+ dynamics, which has been mainly carried out on liver hepotocytes. We focus in particular on the understanding of the relationship between elementary Ca2+ increases, Ca2+ oscillations and intra- or intercellular Ca2+ waves. The physiological impact of such signalling on liver function is also discussed.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Role of Sigma-1 Receptor in Calcium Modulation: Possible Involvement in Cancer

Ca2+ signaling plays a pivotal role in the control of cellular homeostasis and aberrant regulation of Ca2+ fluxes have a strong impact on cellular functioning. As a consequence of this ubiquitous role, Ca2+ signaling dysregulation is involved in the pathophysiology of multiple diseases including cancer. Indeed, multiple studies have highlighted the role of Ca2+ fluxes in all the steps of cancer progression. In particular, the transfer of Ca2+ at the ER-mitochondrial contact sites, also known as mitochondrial associated membranes (MAMs), has been shown to be crucial for cancer cell survival. One of the proteins enriched at this site is the sigma-1 receptor (S1R), a protein that has been described as a Ca2+-sensitive chaperone that exerts a protective function in cells in various ways, including the modulation of Ca2+ signaling. Interestingly, S1R is overexpressed in many types of cancer even though the exact mechanisms by which it promotes cell survival are not fully elucidated. This review summarizes the findings describing the roles of S1R in the control of Ca2+ signaling and its involvement in cancer progression

Approche expérimentale et computationnelle de la signalisation calcique

info:eu-repo/semantics/publishe

Role of Sigma-1 Receptor in Calcium Modulation: Possible Involvement in Cancer

Ca2+ signaling plays a pivotal role in the control of cellular homeostasis and aberrant regulation of Ca2+ fluxes have a strong impact on cellular functioning. As a consequence of this ubiquitous role, Ca2+ signaling dysregulation is involved in the pathophysiology of multiple diseases including cancer. Indeed, multiple studies have highlighted the role of Ca2+ fluxes in all the steps of cancer progression. In particular, the transfer of Ca2+ at the ER-mitochondrial contact sites, also known as mitochondrial associated membranes (MAMs), has been shown to be crucial for cancer cell survival. One of the proteins enriched at this site is the sigma-1 receptor (S1R), a protein that has been described as a Ca2+-sensitive chaperone that exerts a protective function in cells in various ways, including the modulation of Ca2+ signaling. Interestingly, S1R is overexpressed in many types of cancer even though the exact mechanisms by which it promotes cell survival are not fully elucidated. This review summarizes the findings describing the roles of S1R in the control of Ca2+ signaling and its involvement in cancer progression

What can we learn from the irregularity of Ca2+ oscillations?

In most cells, Ca(2+) increases in response to external stimulation are organized in the form of oscillations and waves that sometimes propagate from one cell to another. Numerous experimental and theoretical studies reveal that this spatiotemporal organization contains a non-negligible level of stochasticity. In this study, we extend the previous work based on a statistical analysis of experimental Ca(2+) traces in isolated, hormone-stimulated hepatocytes and on stochastic simulations of Ca(2+) oscillations based on the Gillespie's algorithm. Comparison of the coefficients of variation in the periods of experimental and simulated Ca(2+) spikes provides information about the clustering and the specific subtypes of the Ca(2+) channels. In hepatocytes coupled by gap junctions, the global perfusion with a hormone leads to successive Ca(2+) responses, giving the appearance of an intercellular wave. Statistical analysis of experimental Ca(2+) oscillations in coupled hepatocytes confirms that this coordinated Ca(2+) spiking corresponds to a phase wave but suggests the existence of an additional coupling mechanism.Journal ArticleResearch Support, Non-U.S. Gov'tSCOPUS: ar.jinfo:eu-repo/semantics/publishe

Expression des récepteurs P2X dans le foie et implication de la signalisation purinergique dans la régénération et la fibrose hépatique

LE KREMLIN-B.- PARIS 11-BU Méd (940432101) / SudocSudocFranceF

Fine tuning of cytosolic Ca2+ oscillations [version 1; referees: 3 approved]

Ca2+ oscillations, a widespread mode of cell signaling, were reported in non-excitable cells for the first time more than 25 years ago. Their fundamental mechanism, based on the periodic Ca2+ exchange between the endoplasmic reticulum and the cytoplasm, has been well characterized. However, how the kinetics of cytosolic Ca2+ changes are related to the extent of a physiological response remains poorly understood. Here, we review data suggesting that the downstream targets of Ca2+ are controlled not only by the frequency of Ca2+ oscillations but also by the detailed characteristics of the oscillations, such as their duration, shape, or baseline level. Involvement of non-endoplasmic reticulum Ca2+ stores, mainly mitochondria and the extracellular medium, participates in this fine tuning of Ca2+ oscillations. The main characteristics of the Ca2+ exchange fluxes with these compartments are also reviewed