scholarly journals An Extracellular Redox Signal Triggers Calcium Release and Impacts the Asexual Development of Toxoplasma gondii

2021 ◽  
Vol 11 ◽  
Author(s):  
Eduardo Alves ◽  
Henry J. Benns ◽  
Lilian Magnus ◽  
Caia Dominicus ◽  
Tamás Dobai ◽  
...  
Keyword(s):  
Toxoplasma Gondii ◽  
Calcium Release ◽  
Parasitophorous Vacuole ◽  
Human Fibroblasts ◽  
Calcium Dependent ◽  
Intracellular Parasites ◽  
Intracellular Ca ◽  
The Rich ◽  
Sense And Respond ◽  
The Impact

The ability of an organism to sense and respond to environmental redox fluctuations relies on a signaling network that is incompletely understood in apicomplexan parasites such as Toxoplasma gondii. The impact of changes in redox upon the development of this intracellular parasite is not known. Here, we provide a revised collection of 58 genes containing domains related to canonical antioxidant function, with their encoded proteins widely dispersed throughout different cellular compartments. We demonstrate that addition of exogenous H2O2 to human fibroblasts infected with T. gondii triggers a Ca2+ flux in the cytosol of intracellular parasites that can induce egress. In line with existing models, egress triggered by exogenous H2O2 is reliant upon both Calcium-Dependent Protein Kinase 3 and diacylglycerol kinases. Finally, we show that the overexpression a glutaredoxin-roGFP2 redox sensor fusion protein in the parasitophorous vacuole severely impacts parasite replication. These data highlight the rich redox network that exists in T. gondii, evidencing a link between extracellular redox and intracellular Ca2+ signaling that can culminate in parasite egress. Our findings also indicate that the redox potential of the intracellular environment contributes to normal parasite growth. Combined, our findings highlight the important role of redox as an unexplored regulator of parasite biology.

scholarly journals An extracellular redox signal triggers calcium release and impacts the asexual development of Toxoplasma gondii

2021 ◽  
Author(s):  
Eduardo Alves ◽  
Henry J. Benns ◽  
Lilian Magnus ◽  
Caia Dominicus ◽  
Tamás Dobai ◽  
...  
Keyword(s):  
Toxoplasma Gondii ◽  
Calcium Release ◽  
Catalytic Domain ◽  
Parasitophorous Vacuole ◽  
Human Fibroblasts ◽  
Calcium Dependent ◽  
Intracellular Ca ◽  
The Rich ◽  
Sense And Respond ◽  
The Impact

AbstractThe ability of an organism to sense and respond to environmental redox fluctuations relies on a signaling network that is incompletely understood in the apicomplexan parasite Toxoplasma gondii. The impact of changes in redox upon the development of this intracellular parasite is not known. Here, we provide a revised collection of 49 genes containing domains related to canonical antioxidant groups, with their encoded proteins widely dispersed throughout different cellular compartments. We demonstrate that addition of exogenous H2O2 to human fibroblasts infected with T. gondii triggers a Ca2+ flux in the cytosol of intracellular parasites that can induce egress. In line with existing models, egress triggered by exogenous H2O2 is reliant upon both Calcium-Dependent Protein Kinase 3 and diacylglycerol kinases. Finally, we show that the overexpression of the active catalytic domain of glutaredoxin in the parasitophorous vacuole severely impacts parasite replication. These data shed light on the rich redox network that exists in T. gondii, evidencing a link between extracellular redox and intracellular Ca2+ signaling that can culminate in parasite egress. Our findings also indicate that the redox potential of the intracellular environment contributes to normal parasite growth. Combined, our findings highlight the important role of redox as an unexplored regulator of parasite biology.

A SIMPLE MODEL FOR INTERACTION OF VOLTAGE AND CALCIUM DYNAMICS IN VIRTUAL VENTRICULAR TISSUE

2003 ◽  
Vol 13 (12) ◽  
pp. 3873-3886
Author(s):  
O. V. ASLANIDI ◽  
A. V. HOLDEN
Keyword(s):  
Intracellular Calcium ◽  
Calcium Release ◽  
Cell Model ◽  
Excitation Threshold ◽  
Calcium Dynamics ◽  
Variable Model ◽  
Ventricular Cell ◽  
Calcium Dependent ◽  
Intracellular Ca ◽  
A Site

A simple two-variable model is used to replace the formulation of calcium dynamics in the Luo–Rudy ventricular cell model. Virtual ventricular cell and tissue are developed and validated to reproduce restitution properties and calcium-dependent voltage patterns present in the original model. Basic interactions between the membrane potential and Ca 2+ dynamics in the virtual cell and a strand of the virtual tissue are studied. Intracellular calcium waves can be linked to both action potentials (APs) and delayed afterdepolarizations (DADs). An intracellular calcium wave propagating from the cell interior can induce an AP upon reaching the cell membrane. The voltage and the intracellular Ca 2+ patterns within the same cell can be highly desynchronized. In a one-dimensional strand of the virtual tissue calcium motion is driven by the AP propagation. However, calcium release can be induced upon certain conditions (e.g. Na + overload of the cells), which results in DADs propagating in the wake of AP. Such propagating DADs can reach the excitation threshold, generating a pair of extrasystolic APs. Collision of a propagating AP with a site of elevated intracellular Ca 2+ concentration does not affect the propagation under the normal conditions. Under Na + overload local elevation of the intracellular Ca 2+ leads to generation of an extrasystolic AP, which destroys the original propagating AP.

Besnoitia besnoiti and Toxoplasma gondii: two apicomplexan strategies to manipulate the host cell centrosome and Golgi apparatus

Parasitology ◽  
2014 ◽  
Vol 141 (11) ◽  
pp. 1436-1454 ◽  
Author(s):  
RITA CARDOSO ◽  
SOFIA NOLASCO ◽  
JOÃO GONÇALVES ◽  
HELDER C. CORTES ◽  
ALEXANDRE LEITÃO ◽  
...  
Keyword(s):  
Toxoplasma Gondii ◽  
Golgi Apparatus ◽  
Host Cell ◽  
Parasitophorous Vacuole ◽  
Host Cells ◽  
Besnoitia Besnoiti ◽  
Microtubule Cytoskeleton ◽  
Cytoskeleton Organization ◽  
Evolutionary Paths ◽  
The Impact

SUMMARYBesnoitia besnoiti and Toxoplasma gondii are two closely related parasites that interact with the host cell microtubule cytoskeleton during host cell invasion. Here we studied the relationship between the ability of these parasites to invade and to recruit the host cell centrosome and the Golgi apparatus. We observed that T. gondii recruits the host cell centrosome towards the parasitophorous vacuole (PV), whereas B. besnoiti does not. Notably, both parasites recruit the host Golgi apparatus to the PV but its organization is affected in different ways. We also investigated the impact of depleting and over-expressing the host centrosomal protein TBCCD1, involved in centrosome positioning and Golgi apparatus integrity, on the ability of these parasites to invade and replicate. Toxoplasma gondii replication rate decreases in cells over-expressing TBCCD1 but not in TBCCD1-depleted cells; while for B. besnoiti no differences were found. However, B. besnoiti promotes a reorganization of the Golgi ribbon previously fragmented by TBCCD1 depletion. These results suggest that successful establishment of PVs in the host cell requires modulation of the Golgi apparatus which probably involves modifications in microtubule cytoskeleton organization and dynamics. These differences in how T. gondii and B. besnoiti interact with their host cells may indicate different evolutionary paths.

scholarly journals A Member of the Ferlin Calcium Sensor Family Is Essential for Toxoplasma gondii Rhoptry Secretion

mBio ◽  
2018 ◽  
Vol 9 (5) ◽  
Author(s):  
Bradley I. Coleman ◽  
Sudeshna Saha ◽  
Seiko Sato ◽  
Klemens Engelberg ◽  
David J. P. Ferguson ◽  
...  
Keyword(s):  
Toxoplasma Gondii ◽  
Host Cell ◽  
Cell Invasion ◽  
Host Cells ◽  
Model Organisms ◽  
Host Cell Invasion ◽  
Content Type ◽  
Calcium Dependent ◽  
Calcium Sensing ◽  
Intracellular Ca

ABSTRACT Invasion of host cells by apicomplexan parasites such as Toxoplasma gondii is critical for their infectivity and pathogenesis. In Toxoplasma, secretion of essential egress, motility, and invasion-related proteins from microneme organelles is regulated by oscillations of intracellular Ca2+. Later stages of invasion are considered Ca2+ independent, including the secretion of proteins required for host cell entry and remodeling from the parasite’s rhoptries. We identified a family of three Toxoplasma proteins with homology to the ferlin family of double C2 domain-containing Ca2+ sensors. In humans and model organisms, such Ca2+ sensors orchestrate Ca2+-dependent exocytic membrane fusion with the plasma membrane. Here we focus on one ferlin that is conserved across the Apicomplexa, T. gondii FER2 (TgFER2). Unexpectedly, conditionally TgFER2-depleted parasites secreted their micronemes normally and were completely motile. However, these parasites were unable to invade host cells and were therefore not viable. Knockdown of TgFER2 prevented rhoptry secretion, and these parasites failed to form the moving junction at the parasite-host interface necessary for host cell invasion. Collectively, these data demonstrate the requirement of TgFER2 for rhoptry secretion in Toxoplasma tachyzoites and suggest a possible Ca2+ dependence of rhoptry secretion. These findings provide the first mechanistic insights into this critical yet poorly understood aspect of apicomplexan host cell invasion. IMPORTANCE Apicomplexan protozoan parasites, such as those causing malaria and toxoplasmosis, must invade the cells of their hosts in order to establish a pathogenic infection. Timely release of proteins from a series of apical organelles is required for invasion. Neither the vesicular fusion events that underlie secretion nor the observed reliance of the various processes on changes in intracellular calcium concentrations is completely understood. We identified a group of three proteins with strong homology to the calcium-sensing ferlin family, which are known to be involved in protein secretion in other organisms. Surprisingly, decreasing the amounts of one of these proteins (TgFER2) did not have any effect on the typically calcium-dependent steps in invasion. Instead, TgFER2 was essential for the release of proteins from organelles called rhoptries. These data provide a tantalizing first look at the mechanisms controlling the very poorly understood process of rhoptry secretion, which is essential for the parasite’s infection cycle.

scholarly journals NADPH oxidase-2 inhibition restores contractility and intracellular calcium handling and reduces arrhythmogenicity in dystrophic cardiomyopathy

2014 ◽  
Vol 307 (5) ◽  
pp. H710-H721 ◽  
Author(s):  
Daniel R. Gonzalez ◽  
Adriana V. Treuer ◽  
Guillaume Lamirault ◽  
Vera Mayo ◽  
Yenong Cao ◽  
...  
Keyword(s):  
Nadph Oxidase ◽  
Calcium Release ◽  
Calcium Handling ◽  
Mdx Mouse ◽  
No Production ◽  
Wild Type ◽  
Intracellular Ca ◽  
Dystrophic Cardiomyopathy ◽  
The Impact ◽  
Phospholamban Phosphorylation

Duchenne muscular dystrophy may affect cardiac muscle, producing a dystrophic cardiomyopathy in humans and the mdx mouse. We tested the hypothesis that oxidative stress participates in disrupting calcium handling and contractility in the mdx mouse with established cardiomyopathy. We found increased expression (fivefold) of the NADPH oxidase (NOX) 2 in the mdx hearts compared with wild type, along with increased superoxide production. Next, we tested the impact of NOX2 inhibition on contractility and calcium handling in isolated cardiomyocytes. Contractility was decreased in mdx myocytes compared with wild type, and this was restored toward normal by pretreating with apocynin. In addition, the amplitude of evoked intracellular Ca2+ concentration transients that was diminished in mdx myocytes was also restored with NOX2 inhibition. Total sarcoplasmic reticulum (SR) Ca2+ content was reduced in mdx hearts and normalized by apocynin treatment. Additionally, NOX2 inhibition decreased the production of spontaneous diastolic calcium release events and decreased the SR calcium leak in mdx myocytes. In addition, nitric oxide (NO) synthase 1 (NOS-1) expression was increased eightfold in mdx hearts compared with wild type. Nevertheless, cardiac NO production was reduced. To test whether this paradox implied NOS-1 uncoupling, we treated cardiac myocytes with exogenous tetrahydrobioterin, along with the NOX inhibitor VAS2870. These agents restored NO production and phospholamban phosphorylation in mdx toward normal. Together, these results demonstrate that, in mdx hearts, NOX2 inhibition improves the SR calcium handling and contractility, partially by recoupling NOS-1. These findings reveal a new layer of nitroso-redox imbalance in dystrophic cardiomyopathy.

scholarly journals Effects of aqueous leaf extracts of Azadirachta indica A. Juss. (neem) and Melia azedarach L. (Santa Barbara or cinnamon) on the intracellular development of Toxoplasma gondii

2011 ◽  
Vol 13 (2) ◽  
pp. 215-222 ◽  
Author(s):  
E.J.T Melo ◽  
K.J Vilela ◽  
C.S Carvalho
Keyword(s):  
Toxoplasma Gondii ◽  
Azadirachta Indica ◽  
Parasitophorous Vacuole ◽  
Biologically Active ◽  
In Vitro Assays ◽  
Melia Azedarach ◽  
Aqueous Extracts ◽  
Leaf Extracts ◽  
Intracellular Parasites

Melia azedarach (cinnamon) and Azadirachta indica (neem) have a variety of biologically active ingredients against virus, bacteria and protozoan parasites; however, little is known about their action on Toxoplasma gondii intracellular development. Toxoplasma gondii infects all eukaryotic cells, where it establishes and multiplies inside a modified vacuole called the parasitophorous vacuole until the cell ruptures, re-infecting other cells and establishing the infection. There are no efficient chemotherapies for the elimination of T. gondii, minimizing side effects. In this study, we performed in vitro assays with neem and cinnamon aqueous extracts against the intracellular development of T. gondii tachyzoites. After treatment with neem and cinnamon for 24 h, the percentage of infected cells and the number of intracellular parasites drastically decreased. This effect was concentration-dependent. During the incubation of the extracts, progressive morphological and ultrastructure alterations led to intense vesiculation and complete elimination of the parasite from the intracellular medium. However, during the treatment with extracts, no morphological effects were observed in the structure of the host cell. These results suggest that the aqueous extracts of neem and cinnamon were capable of interfering with and eliminating the intracellular development of Toxoplasma gondii.

scholarly journals Nonlinear Dynamic Modeling of 2-Dimensional Interdependent Calcium and Inositol 1,4,5-Trisphosphate in Cardiac Myocyte

2019 ◽  
Vol 14 (1) ◽  
pp. 290-305 ◽  
Author(s):  
N. Singh ◽  
N. Adlakha
Keyword(s):  
Cardiac Myocyte ◽  
Calcium Release ◽  
Feedback Regulation ◽  
Calcium Oscillations ◽  
The Body ◽  
Calcium Dependent ◽  
Coupled Equations ◽  
Calcium Modulation ◽  
Inositol 1,4,5 Trisphosphate ◽  
The Impact

Calcium (Ca2+) and inositol 1,4,5-trisphosphate (IP3) is critically important actors for a vast array of cellular processes. The most significant of the functions is One of the main functions is communication in all parts of the body which is achieved through cell signaling. Abnormalities in Ca2+signaling have been implicated in clinically important conditions such as heart failure and cardiac arrhythmias. We propose a mathematical model which systematically investigates complex Ca2+and IP3dynamics in cardiac myocyte. This two dimensional model is based on calcium-induced calcium release via inositol 1,4,5-trisphosphate receptors and includes calcium modulation of IP3levels through feedback regulation of degradation and production. Forward-Time Centered-Space method has been used to solve the coupled equations. We were able to reproduce the observed oscillatory patterns in Ca2+as well as IP3signals. The model predicts that calcium-dependent production and degradation of IP3is a key mechanism for complex calcium oscillations in cardiac myocyte. The impact and sensitivity of source, leak, diffusion coefficients on both Ca2+and IP3dynamics have been investigated. The results show that the relationship between Ca2+and IP3dynamics is nonlinear.

scholarly journals Substrate-mediated regulation of the arginine transporter of Toxoplasma gondii

2021 ◽  
Vol 17 (8) ◽  
pp. e1009816
Author(s):  
Esther Rajendran ◽  
Morgan Clark ◽  
Cibelly Goulart ◽  
Birte Steinhöfel ◽  
Erick T. Tjhin ◽  
...  
Keyword(s):  
Amino Acid ◽  
Toxoplasma Gondii ◽  
Apicomplexan Parasite ◽  
Upstream Open Reading Frame ◽  
Amino Acid Transporters ◽  
Reading Frame ◽  
Intracellular Parasites ◽  
Biosensor Strain ◽  
Sense And Respond

Intracellular parasites, such as the apicomplexan Toxoplasma gondii, are adept at scavenging nutrients from their host. However, there is little understanding of how parasites sense and respond to the changing nutrient environments they encounter during an infection. TgApiAT1, a member of the apicomplexan ApiAT family of amino acid transporters, is the major uptake route for the essential amino acid L-arginine (Arg) in T. gondii. Here, we show that the abundance of TgApiAT1, and hence the rate of uptake of Arg, is regulated by the availability of Arg in the parasite’s external environment, increasing in response to decreased [Arg]. Using a luciferase-based ‘biosensor’ strain of T. gondii, we demonstrate that the expression of TgApiAT1 varies between different organs within the host, indicating that parasites are able to modulate TgApiAT1-dependent uptake of Arg as they encounter different nutrient environments in vivo. Finally, we show that Arg-dependent regulation of TgApiAT1 expression is post-transcriptional, mediated by an upstream open reading frame (uORF) in the TgApiAT1 transcript, and we provide evidence that the peptide encoded by this uORF is critical for mediating regulation. Together, our data reveal the mechanism by which an apicomplexan parasite responds to changes in the availability of a key nutrient.

Host cells: mobilizable lipid resources for the intracellular parasite Toxoplasma gondii

2002 ◽  
Vol 115 (15) ◽  
pp. 3049-3059 ◽  
Author(s):  
Audra J. Charron ◽  
L. David Sibley
Keyword(s):  
Fatty Acids ◽  
Toxoplasma Gondii ◽  
Host Cell ◽  
Parasitophorous Vacuole ◽  
Host Cells ◽  
Intracellular Parasite ◽  
Head Groups ◽  
Intracellular Parasites ◽  
Successful Replication ◽  
Conjugated Compounds

Successful replication of the intracellular parasite Toxoplasma gondii within its parasitophorous vacuole necessitates a substantial increase in membrane mass. The possible diversion and metabolism of host cell lipids and lipid precursors by Toxoplasma was therefore investigated using radioisotopic and fluorophore-conjugated compounds. Confocal microscopic analyses demonstrated that Toxoplasma is selective with regards to both the acquisition and compartmentalization of host cell lipids. Lipids were compartmentalized into parasite endomembranes and, in some cases, were apparently integrated into the surrounding vacuolar membrane. Additionally,some labels became concentrated in discrete lipid bodies that were biochemically and morphologically distinct from the parasite apical secretory organelles. Thin layer chromatography established that parasites readily scavenged long-chain fatty acids as well as cholesterol, and in certain cases modified the host-derived lipids. When provided with radiolabeled phospholipid precursors, including polar head groups, phosphatidic acid and small fatty acids, intracellular parasites preferentially accrued phosphatidylcholine(PtdCho) over other phospholipids. Moreover, Toxoplasma was found to be competent to synthesize PtdCho from radiolabeled precursors obtained from its environment. Together, these studies underscore the ability of Toxoplasma gondii to divert and use lipid resources from its host, a process that may contribute to the biogenesis of parasite membranes.

scholarly journals Acidification of the parasitophorous vacuole containing Toxoplasma gondii in the presence of hydroxyurea

2006 ◽  
Vol 78 (3) ◽  
pp. 475-484 ◽  
Author(s):  
Cristiane S. Carvalho ◽  
Edésio J.T. Melo
Keyword(s):  
Acid Phosphatase ◽  
Toxoplasma Gondii ◽  
Parasitophorous Vacuole ◽  
Vero Cells ◽  
Cellular Mechanism ◽  
Host Cells ◽  
Oxidative Defense ◽  
Intracellular Parasites ◽  
Vital Stains ◽  
Acidic Organelles

Toxoplasma gondii multiplies within parasitophorous vacuole that is not recognized by the primary no oxidative defense of host cells, mainly represented by the fusion with acidic organelles. Recent studies have already shown that hydroxyurea arrested the intracellular parasites leading to its destruction. In the present work we investigated the cellular mechanism involved in the destruction of intracellular Toxoplasma gondii. Fluorescent vital stains were used in order to observe possible acidification of parasitophorous vacuole-containing Toxoplasma gondii in presence of hydroxyurea. Vero cells infected with tachyzoites were treated with hydroxyurea for 12, 24 or 48 hours. Fluorescence, indicative of acidification, was observed in the parasitophorous vacuole when the cultures were incubated in presence of acridine orange. LysoTracker red was used in order to determine whether lysosomes were involved in the acidification process. An intense fluorescence was observed after 12 and 24 hours of incubation with hydroxyurea, achieving it is highly intensity after 48 hours of treatment. Ultrastructural cytochemistry for localization of the acid phosphatase lysosomal enzyme was realized. Treated infected cultures showed reaction product in vesicles fusing with vacuole or associated with intravacuolar parasites. These results suggest that fusion with lysosomes and acidification of parasitophorous vacuole leads to parasites destruction in the presence pf hydroxyurea.

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