Toxoplasma Effector MAF1 Mediates Recruitment of Host Mitochondria and Impacts the Host Response

Recent information has revealed the functional diversity and importance of mitochondria in many cellular processes including orchestrating the innate immune response. Intriguingly, several infectious agents, such as Toxoplasma, Legionella, and Chlamydia, have been reported to grow within vacuoles surrounded by host mitochondria. Although many hypotheses have been proposed for the existence of host mitochondrial association (HMA), the causes and biological consequences of HMA have remained unanswered. Here we show that HMA is present in type I and III strains of Toxoplasma but missing in type II strains, both in vitro and in vivo. Analysis of F1 progeny from a type II×III cross revealed that HMA is a Mendelian trait that we could map. We use bioinformatics to select potential candidates and experimentally identify the polymorphic parasite protein involved, mitochondrial association factor 1 (MAF1). We show that introducing the type I (HMA+) MAF1 allele into type II (HMA-) parasites results in conversion to HMA+ and deletion of MAF1 in type I parasites results in a loss of HMA. We observe that the loss and gain of HMA are associated with alterations in the transcription of host cell immune genes and the in vivo cytokine response during murine infection. Lastly, we use exogenous expression of MAF1 to show that it binds host mitochondria and thus MAF1 is the parasite protein directly responsible for HMA. Our findings suggest that association with host mitochondria may represent a novel means by which Toxoplasma tachyzoites manipulate the host. The existence of naturally occurring HMA+ and HMA- strains of Toxoplasma, Legionella, and Chlamydia indicates the existence of evolutionary niches where HMA is either advantageous or disadvantageous, likely reflecting tradeoffs in metabolism, immune regulation, and other functions of mitochondria. © 2014 Pernas et al

Cellular metabolism in the defense against microbes

The study of metabolic changes associated with host-pathogen interactions have largely focused on the strategies that microbes use to subvert host metabolism to support their own proliferation. However, recent reports demonstrate that changes in host cell metabolism can also be detrimental to pathogens and restrict their growth. In this Review, I present a framework to consider how the host cell exploits the multifaceted roles of metabolites to defend against microbes. I also highlight how the rewiring of metabolic processes can strengthen cellular barriers to microbial invasion, regulate microbial virulence programs and factors, limit microbial access to nutrient sources and generate toxic environments for microbes. Collectively, the studies described here support a critical role for the rewiring of cellular metabolism in the defense against microbes. Further study of host-pathogen interactions from this framework has the potential to reveal novel aspects of host defense and metabolic control, and may inform how human metabolism impacts the progression of infectious disease

Move it to lose it: Mitocytosis expels damaged mitochondria

Mechanisms by which cells remove damaged mitochondria extracellularly are unclear. Recent work by Jiao and colleagues in Cell shows that migrating cells expel dysfunctional mitochondria in membrane-bound structures called migrasomes to maintain mitochondrial homeostasis

RevAMPing Mitochondrial Shape to Live Longer

Whether and how mitochondria connect reduced energy intake to healthy aging are unclear. In this issue of Cell Metabolism, Weir et al. (2017) find that constitutive AMPK activation and dietary restriction promote longevity in C. elegans via remodeling of the mitochondrial network and fatty acid oxidation in peripheral tissues

Mito-Morphosis: Mitochondrial Fusion, Fission, and Cristae Remodeling as Key Mediators of Cellular Function

Permanent residency in the eukaryotic cell pressured the prokaryotic mitochondrial ancestor to strategize for intracellular living. Mitochondria are able to autonomously integrate and respond to cellular cues and demands by remodeling their morphology. These processes define mitochondrial dynamics and inextricably link the fate of the mitochondrion and that of the host eukaryote, as exemplified by the human diseases that result from mutations in mitochondrial dynamics proteins. In this review, we delineate the architecture of mitochondria and define the mechanisms by which they modify their shape. Key players in these mechanisms are discussed, along with their role in manipulating mitochondrial morphology during cellular action and development. Throughout, we highlight the evolutionary context in which mitochondrial dynamics emerged and consider unanswered questions whose dissection might lead to mitochondrial morphology-based therapies

Contact and competition between mitochondria and microbes

Invading microbes occupy the host cytosol and take up nutrients on which host organelles are also dependent. Thus, host organelles are poised to interact with intracellular microbes. Despite the essential role of host mitochondria in cellular metabolic homeostasis and in mediating cellular responses to microbial infection, we know little of how these organelles interact with intracellular pathogens, and how such interactions affect disease pathogenesis. Here, we give an overview of the different classes of physical and metabolic interactions reported to occur between mitochondria and eukaryotic pathogens. Investigating the underlying molecular mechanisms and functions of such interactions will reveal novel aspects of infection biology

Mitochondria Restrict Growth of the Intracellular Parasite Toxoplasma gondii by Limiting Its Uptake of Fatty Acids

How intracellular pathogens acquire essential non-diffusible host metabolites and whether the host cell counteracts the siphoning of these nutrients by its invaders are open questions. Here we show that host mitochondria fuse during infection by the intracellular parasite Toxoplasma gondii to limit its uptake of fatty acids (FAs). A combination of genetics and imaging of FA trafficking indicates that Toxoplasma infection triggers lipophagy, the autophagy of host lipid droplets (LDs), to secure cellular FAs essential for its proliferation. Indeed, Toxoplasma FA siphoning and growth are reduced in host cells genetically deficient for autophagy or triglyceride depots. Conversely, Toxoplasma FA uptake and proliferation are increased in host cells lacking mitochondrial fusion, required for efficient mitochondrial FA oxidation, or where mitochondrial FA oxidation is pharmacologically inhibited. Thus, mitochondrial fusion can be regarded as a cellular defense mechanism against intracellular parasites, by limiting Toxoplasma access to host nutrients liberated by lipophagy

TGGT1_053770 is a novel secreted <i>Toxoplasma</i> protein and candidate mediator of HMA.

<p>(A) Schematic diagram of the TGGT1_053770 protein. Signal peptide (SP), TM domain, and phosphorylation sites (P sites) are indicated where predicted by SignalP 4.0 (<a href="http://www.cbs.dtu.dk/services/SignalP/" target="_blank">http://www.cbs.dtu.dk/services/SignalP/</a>), TMHMM v. 2.0 (<a href="http://www.cbs.dtu.dk/services/TMHMM/" target="_blank">http://www.cbs.dtu.dk/services/TMHMM/</a>), and ToxoDB (<a href="http://www.toxodb.org" target="_blank">www.toxodb.org</a>). (B) Microarray expression values (log2 ratios of sample intensity over control intensity) for 17 of the HMA-phenotyped progeny (black data points). Red, green, and blue data points represent expression values for type I (RH; HMA+), II (PDS; HMA⁻), and III (CTG; HMA+) strains, respectively. Data shown are averages across 10 probes on the cDNA expression array that map to the <i>MAF1</i> locus. (C) Lysates from extracellular type I parasites and type I–infected HFFs (intracellular) were treated with and without CIP and loaded in each lane. The membrane was probed with anti-HA antibody conjugated to peroxidase. (D) Normalized sequence coverage (<i>y</i>-axis) reflective of the number of copies of TGGT1_<i>053770</i> on chromosome II (<i>x</i>-axis) for types I (GT1), II (ME49), and III (VEG). The region putatively encoding TGGT1_053770 is indicated by a black bar. (E) Type I parasites expressing HA-tagged TGGT1_053770 were added to HFFs, and cultures were fixed 6 hpi. Following permeabilization, TGGT1_053770 was visualized using anti-HA antibodies. Scale bar, 5 µm. (F) Type I parasites were added to HFFs, and cultures were fixed 6 hpi. Following permeabilization, TGGT1_053770 was visualized using polyclonal anti-TGGT1_053770 mouse sera. Scale bar, 5 µm. (G) Western blot showing expression of TGGT1_053770 in type I, II, III and type II parasites. Blots were probed with antibodies to recombinant TGGT1_053770 (upper panels), then probed for surface antigen SAG1 as a loading control (lower panels); white vertical lines indicate that the order of the lanes shown is different from the original loading of the gel. Note that the product of the type III allele has a reproducibly slower electrophoretic mobility than type I. (H) Syringe-lysed parasites were plated on coverslips and fixed, labeled with anti-HA (TGGT1_053770) and anti-GRA7 antibodies, and visualized using confocal microscopy.</p