4 research outputs found
Déchiffrage des mécanismes d’assemblage des filaments de septines
Les septines sont des protéines conservées de la levure à l’homme qui sont impliquées
dans divers processus cellulaires tels que la cytokinèse, le transport vésiculaire et l’organisation
du cortex cellulaire. Il existe 13 gènes de septines retrouvés en plusieurs isoformes chez
l’humain, et seulement cinq chez Drosophila melanogaster, Sep1, Sep2, Pnut, Sep4 et Sep5, ce
qui en fait un modèle idéal vu son génome simple. Les septines sont composées d’un domaine
de liaison au GTP très conservé entre les espèces, dont le rôle reste à ce jour ambiguë, ainsi que
de régions N et C-terminales variables. Les septines s’assemblent entre elles pour former un
hexamère, composé de Sep1, Sep2 et Pnut chez Drosophila melanogaster, via l’interface N-C
et G des septines. Ces hexamères s’assemblent bout à bout afin de former les filaments de
septines. Ces filaments peuvent ensuite se regrouper et s’assembler en structures hautement
ordonnées telles que des anneaux, des tubes, des faisceaux de filaments, des cages et elles sont
retrouvées au sillon de clivage durant la cytokinèse. Le but était de déchiffrer les mécanismes
d’assemblage des filaments de septines qui mènent à la formation des différentes structures, afin
de mieux comprendre les mécanismes d’interaction entre les septines. Au sein des cellules S2
de Drosophila melanogaster, les septines sont retrouvées à trois structures hautement ordonnées
et dépendantes de Pnut endogène : des tubes cytoplasmiques, des anneaux cytoplasmiques et le
sillon de clivage durant la cytokinèse. Notre hypothèse est qu’il existe plusieurs mécanismes
qui régissent la formation des structures hautement ordonnées et que ceux-ci sont dépendants
des régions N et C terminales variables des septines qui sont impliquées dans plusieurs
interactions. Divers mutants de Sep1, Sep2 et Pnut tronqués en N et en C-terminal ont été
fusionnés à une protéine fluorescente et caractérisés par microscopie confocale. La localisation
de ces mutants a été répertoriée et analysée en présence des septines endogènes ou lors de la
déplétion de celles-ci. Nos résultats suggèrent que le domaine de liaison au GTP est suffisant
pour le recrutement des septines au sillon de clivage durant la cytokinèse, mais que la région N-terminale
est requise la formation des tubes et des anneaux cytoplasmiques dépendants de Pnut.Septins are conserved from yeast to humans and are implicated in diverse cellular
processes such as cytokinesis, vesicular transport and cellular cortical organization. There are
13 known genes that encode for human septins, which also have many isoforms, while there
are only five septin genes in Drosophila melanogaster: Sep1, Sep2, Pnut, Sep4 and Sep5, which
makes it an ideal model system. Septins have a conserved GTP binding domain, whose role is
still not fully understood, and variable N-C-termini. Septins assemble together, via N-C and G
interfaces, to form a hexamer, that is composed of Sep1, Sep2 and Pnut in Drosophila
melanogaster, which assemble end-to-end to form non polar filaments. These filaments can
subsequently assemble together to form higher-ordered structures, such as rings, tubes, bundles,
and gauzes. Furthermore, septins are recruited to the cleavage furrow during cytokinesis
although their organization there is unclear. The aim of this project is to define septin assembly
mechanisms that can lead to the formation of different higher ordered structures. In Drosophila
melanogaster S2 cells, septins are recruited to three, readily observable septin dependent
structures: cytoplasmic rings, cytoplasmic tubes, and the cleavage furrow during cytokinesis.
Our hypothesis is that multiple mechanisms govern septin incorporation into these structures
and that these mechanisms differentially depend on septin N-C variable termini. A panel of
mutants of Sep1, Sep2 and Pnut truncated in N-C-termini were fused to fluorescent proteins and
their localization in S2 cells monitored by confocal microscopy, with or without depletion of
endogenous septins. My results suggest that the GTP binding domain is sufficient for septin
recruitment to the cleavage furrow during cytokinesis, but that the septin N-termini are required
for recruitment to the cytoplasmic tubes and rings
Patients with acute heart failure treated with the CARRESS-HF diuretic protocol in association with canrenoate potassium: Tolerance of high doses of canrenoate potassium
International audienceBackground: Oral mineralocorticoid receptor antagonists have failed to prove their efficacy for decongestion and potassium homeostasis in acute heart failure. Intravenous mineralocorticoid receptor antagonists have yet to be studied.Aim: The aim of this study was to confirm the safety of high-dose potassium canrenoate in association with classic diuretics in acute heart failure.Methods: This retrospective single-centre study included consecutive patients who were hospitalized with acute heart failure between 2013 and 2018. One hundred patients with overload treated with the standardized diuretic protocol from the CARRESS-HF trial were included. There were no exclusion criteria relating to creatinine or kalaemia at the time of admission. Two groups were constituted on the basis of potassium canrenoate posology: a low-dose group (<300mg/day) and a high-dose group (≥300mg/day); the groups were similar in terms of baseline characteristics.Results: Mean daily potassium canrenoate doses were 198mg/day (range 100-280mg/day) in the low-dose group and 360mg/day (range 300-600mg/day) in the high-dose group. There was no significant difference between the high-dose and low-dose groups in terms of mortality, dialysis, renal function, hyperkalaemia, haemorrhage, sepsis or confusion.Conclusions: Potassium canrenoate at high doses can be used safely in association with standard diuretics in acute heart failure, even in patients with altered renal function. A prospective study is required to evaluate the efficacy of high-dose potassium canrenoate in preventing hypokalaemia and improving decongestion