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Author: Donna Huber

cGAS-STING Pathway Activation during Trypanosoma cruzi Infection Leads to Tissue-Dependent Parasite Control

FIGURE 1. T. cruzi activates the cGAS-STING pathway in primary cells to induce a modest IFN-I response.


Host cell invasion by Trypanosoma cruzi is a markedly silent process, with limited host transcriptional changes indicative of innate immune recognition, except for a modest type I IFN (IFN-I) response. In this study, we show that T. cruzi-induced IFN-β production was nearly abolished in primary murine cGAS-/- or stimulator of IFN genes (STING)-deficient (STINGGt) macrophages and fibroblasts. T. cruzi infection did not impact the ability of IFN-regulatory factor reporter macrophages to respond to classical cGAS-STING agonists, indicating that the limited IFN-β induction is not due to active parasite suppression. cGAS-/-, STINGGt, and IFN-α/β receptor-/- (IFNAR-/-) macrophages infected with T. cruzi yielded significantly higher numbers of amastigotes compared with wild-type macrophages; however, the impact of the STING pathway during infection in vivo is more complex. Despite an initial increase in parasite growth, STINGGt and IFNAR-/- mice ultimately had lower parasite burden in footpads as compared with wild-type mice, demonstrating a role for IFN-I expression in potentiating parasite growth at the infection site. STING pathway activation had little impact on parasite levels in the skeletal muscle; however, in the heart, cGAS-/- and STINGGt mice, but not IFNAR-/- mice, accumulated higher acute parasite loads, suggesting a protective role of STING sensing of T. cruzi in this organ that was independent of IFN-I. Together, these results demonstrate that host cGAS-STING senses T. cruzi infection, enhancing parasite growth at the site of entry, and contributes to acute-phase parasite restriction in the heart, a major site of tissue damage in chronic T. cruzi infection.

Natasha Perumal, Brooke White, Fernando Sanchez-Valdez, Rick L Tarleton. J Immunol. 2023 Aug 21;ji2300373. doi: 10.4049/jimmunol.2300373.

Interorganellar Communication Through Membrane Contact Sites in Toxoplasma gondii

Figure 1. Reported and potential MCSs between organelles of Toxoplasma gondii. Schematic representation showing proteins recently reported to be involved in MCSs, along with putative MCS candidates (indicated with “?”). For clarity purposes, only the central part of the parasite is shown. Abbreviations: AP, apicoplast; ER, endoplasmic reticulum; PLVAC, plant-like vacuolar compartment; IMC, inner membrane complex; TgTPC, T. gondii two pore channel; VDAC, voltage-dependent anion channel; LMF1, lasso maintenance factor 1.; MCS, membrane contact site.
Figure 1. Reported and potential MCSs between organelles of Toxoplasma gondii. Schematic representation showing proteins recently reported to be involved in MCSs, along with putative MCS candidates (indicated with “?”). For clarity purposes, only the central part of the parasite is shown. Abbreviations: AP, apicoplast; ER, endoplasmic reticulum; PLVAC, plant-like vacuolar compartment; IMC, inner membrane complex; TgTPC, T. gondii two pore channel; VDAC, voltage-dependent anion channel; LMF1, lasso maintenance factor 1.; MCS, membrane contact site.


Apicomplexan parasites are a group of protists that cause disease in humans and include pathogens like Plasmodium spp., the causative agent of malaria, and Toxoplasma gondii, the etiological agent of toxoplasmosis and one of the most ubiquitous human parasites in the world. Membrane contact sites (MCSs) are widespread structures within eukaryotic cells but their characterization in apicomplexan parasites is only in its very beginnings. Basic biological features of the T. gondii parasitic cycle support numerous organellar interactions, including the transfer of Ca2+ and metabolites between different compartments. In T. gondii, Ca2+ signals precede a series of interrelated molecular processes occurring in a coordinated manner that culminate in the stimulation of key steps of the parasite life cycle. Calcium transfer from the endoplasmic reticulum to other organelles via MCSs would explain the precision, speed, and efficiency that is needed during the lytic cycle of T. gondii. In this short review, we discuss the implications of these structures in cellular signaling, with an emphasis on their potential role in Ca2+ signaling.

Diego Huet, Silvia N J Moreno. Contact (Thousand Oaks). 2023 Aug 6;6:25152564231189064. doi: 10.1177/25152564231189064. eCollection 2023 Jan-Dec.

Effects of doxycycline dose rate and pre-adulticide wait period on heartworm-associated pathology and adult worm mass

graphical abstract

Background: The American Heartworm Society canine guidelines recommend treatment with doxycycline prior to adulticide administration to reduce levels of Wolbachia and its associated metabolites, which are known to be a leading cause of pulmonary pathology. Studies have determined that doxycycline administered at 10 mg/kg BID for 28 days is an effective dose for eliminating Wolbachia, but what has not been determined is the clinical relevance of this elimination. The current guidelines also recommend a 30-day wait period following administration of doxycycline to allow for clearance of metabolites, such as Wolbachia surface protein, and for further reduction in heartworm biomass before administration of adulticide. Reducing the doxycycline dose and eliminating the wait period may carry practical benefits for the animal, client, and practitioner.

Methods: To investigate these treatment practices, Dirofilaria immitis adults were surgically transplanted into each of 45 dogs, which were divided into nine study groups of five dogs each. Seventy-five days after transplantation, two groups each were administered 5, 7.5, or 10 mg/kg BID doxycycline orally for 28 days and 6 µg/kg ivermectin monthly, with three untreated groups serving as controls. Study animals were necropsied and examined prior to treatment as well as 30 and 60 days post-treatment.

Results: Mean worm weight was unaffected by dosage but exhibited a significant increase at 30 days and significant decrease at 60 days post-treatment, including in control groups. Histopathology lesion scores did not significantly differ among groups, with the exception of the lung composite score for one untreated group. Liver enzymes, the levels of which are a concern in doxycycline treatment, were also examined, with no abnormalities in alanine aminotransferase or alkaline phosphatase observed.

Conclusions: No consistent worsening of tissue lesions was observed with or without the AHS-recommended 30-day wait period, nor did reduced dosages of doxycycline lead to worsening of pathology or any change in efficacy in depleting worm weight. Mean worm weight did significantly increase prior to, and decrease following, the wait period. Future work that also includes adulticide treatment (i.e. melarsomine) will study treatment recommendations that may improve both animal health and owner compliance.

Andrew R Moorhead, Christopher C Evans, Kaori Sakamoto, Michael T Dzimianski, Abdelmoneim Mansour, Utami DiCosty, Crystal Fricks, Scott McCall, Ben Carson, C Thomas Nelson, John W McCall. Parasit Vectors. 2023 Jul 25;16(1):251. doi: 10.1186/s13071-023-05858-2.

Diagnosis and Treatment of a Natural Infection with Trypanosoma Cruzi (Chagas Disease) in a Symptomatic De Brazza’s Monkey (Cercopithecus Neglectus) in Alabama

Trypanosoma cruzi, the causative agent of Chagas disease, is a zoonotic, vector-borne, protozoan hemoflagellate with a wide host range. An 11-yr-old, captive-bred male De Brazza’s monkey (Cercopithecus neglecus) presented with weight loss despite normal appetite. Examination revealed hypoglycemia, nonregenerative anemia, and many trypanosomes on a blood smear. A whole blood sample was PCR-positive for T. cruzi discrete typing unit TcIV and the monkey seroconverted using two different methods. The monkey was treated with the standard human dose of benznidazole twice daily for 60 d; however, blood obtained over the next 1.5 yr posttreatment remained PCR-positive for T. cruzi. A second course of benznidazole at a higher dose but lower frequency for 26 wk was required for the monkey to convert to sustained PCR-negative status. The monkey recovered with no apparent lasting effects.

Stephanie McCain, Richard R Sim, Bridget Weidner, Anne E Rivas, Brooke White, Lisa D Auckland, Rick L Tarleton, Sarah Hamer. J Zoo Wildl Med. 2023 Jul;54(2):412-416. doi: 10.1638/2022-0095

Understanding heterogeneity of human bone marrow plasma cell maturation and survival pathways by single-cell analyses

Human bone marrow (BM) plasma cells are heterogeneous, ranging from newly arrived antibody-secreting cells (ASCs) to long-lived plasma cells (LLPCs). We provide single-cell transcriptional resolution of 17,347 BM ASCs from five healthy adults. Fifteen clusters are identified ranging from newly minted ASCs (cluster 1) expressing MKI67 and high major histocompatibility complex (MHC) class II that progress to late clusters 5–8 through intermediate clusters 2–4. Additional ASC clusters include the following: immunoglobulin (Ig) M predominant (likely of extra-follicular origin), interferon responsive, and high mitochondrial activity. Late ASCs are distinguished by G2M checkpoints, mammalian target of rapamycin (mTOR) signaling, distinct metabolic pathways, CD38 expression, utilization of tumor necrosis factor (TNF)-receptor superfamily members, and two distinct maturation pathways involving TNF signaling through nuclear factor κB (NF-κB). This study provides a single-cell atlas and molecular roadmap of LLPC maturation trajectories essential in the BM microniche. Altogether, understanding BM ASC heterogeneity in health and disease enables development of new strategies to enhance protective ASCs and to deplete pathogenic ones.

Meixue Duan, Doan C Nguyen, Chester J Joyner, Celia L Saney, Christopher M Tipton, Joel Andrews, Sagar Lonial, Caroline Kim, Ian Hentenaar, Astrid Kosters, Eliver Ghosn, Annette Jackson, Stuart Knechtle, Stalinraja Maruthamuthu, Sindhu Chandran, Tom Martin, Raja Rajalingam, Flavio Vincenti, Cynthia Breeden, Ignacio Sanz, Greg Gibson, F Eun-Hyung Lee. Cell Rep. 2023 Jun 23;42(7):112682. doi: 10.1016/j.celrep.2023.112682

A cathepsin C-like protease mediates the post-translation modification of Toxoplasma gondii secretory proteins for optimal invasion and egress

Microbial pathogens use proteases for their infections, such as digestion of proteins for nutrients and activation of their virulence factors. As an obligate intracellular parasite, Toxoplasma gondii must invade host cells to establish its intracellular propagation. To facilitate invasion, the parasites secrete invasion effectors from microneme and rhoptry, two unique organelles in apicomplexans. Previous work has shown that some micronemal invasion effectors experience a series of proteolytic cleavages within the parasite’s secretion pathway for maturation, such as the aspartyl protease (TgASP3) and the cathepsin L-like protease (TgCPL), localized within the post-Golgi compartment and the endolysosomal system, respectively. Furthermore, it has been shown that the precise maturation of micronemal effectors is critical for Toxoplasma invasion and egress. Here, we show that an endosome-like compartment (ELC)-residing cathepsin C-like protease (TgCPC1) mediates the final trimming of some micronemal effectors, and its loss further results in defects in the steps of invasion, egress, and migration throughout the parasite’s lytic cycle. Notably, the deletion of TgCPC1 completely blocks the activation of subtilisin-like protease 1 (TgSUB1) in the parasites, which globally impairs the surface-trimming of many key micronemal invasion and egress effectors. Additionally, we found that Toxoplasma is not efficiently inhibited by the chemical inhibitor targeting the malarial CPC ortholog, suggesting that these cathepsin C-like orthologs are structurally different within the apicomplexan phylum. Collectively, our findings identify a novel function of TgCPC1 in processing micronemal proteins within the Toxoplasma parasite’s secretory pathway and expand the understanding of the roles of cathepsin C protease.Toxoplasma gondii is a microbial pathogen that is well adapted for disseminating infections. It can infect virtually all warm-blooded animals. Approximately one-third of the human population carries toxoplasmosis. During infection, the parasites sequentially secrete protein effectors from the microneme, rhoptry, and dense granule, three organelles exclusively found in apicomplexan parasites, to help establish their lytic cycle. Proteolytic cleavage of these secretory proteins is required for the parasite’s optimal function. Previous work has revealed that two proteases residing within the parasite’s secretory pathway cleave micronemal and rhoptry proteins, which mediate parasite invasion and egress. Here, we demonstrate that a cathepsin C-like protease (TgCPC1) is involved in processing several invasion and egress effectors. The genetic deletion of TgCPC1 prevented the complete maturation of some effectors in the parasites. Strikingly, the deletion led to a full inactivation of one surface-anchored protease, which globally impaired the trimming of some key micronemal proteins before secretion. Therefore, this finding represents a novel post-translational mechanism for the processing of virulence factors within microbial pathogens.

L Brock Thornton, Melanie Key, Chiara Micchelli, Andrew J Stasic, Samuel Kwain, Katherine Floyd, Silvia N J Moreno, Brian N Dominy, Daniel C Whitehead, Zhicheng Dou. mBio. 2023 Jun 16;e0017423. doi: 10.1128/mbio.00174-23.

Evaluation of renal values during treatment for heartworm disease in 27 client-owned dogs

Background: Canine heartworm disease (CHD) caused by Dirofilaria immitis remains a common preventable disease with increasing incidence in some parts of the USA. The treatment guidelines of the American Heartworm Society (AHS) currently recommend monthly macrocyclic lactone administration, 28 days of doxycycline given orally every 12 h and three injections of melarsomine dihydrochloride (1 injection on day 2 of treatment followed 30 days later by 2 injections 24 h apart). Minocycline has also been utilized when doxycycline is unavailable. The systemic effects of CHD, which particularly impact cardiac and renal function, have been described, with infected dogs often experiencing renal damage characterized by an increase in serum concentrations of renal biomarkers. Although the AHS treatment protocol for CHD has been shown to be safe and effective in most cases, the potential for complications remains. No study as of yet has evaluated changes in symmetric dimethylarginine (SDMA), a sensitive marker of renal function, during treatment for CHD. The purpose of the present study was to evaluate renal function in dogs by measuring serum creatinine and SDMA concentrations during the adulticide treatment period.

Methods: Serum creatinine and SDMA concentrations were measured in 27 client-owned dogs affected by CHD at the following time points: prior to starting doxycycline or minocycline therapy (baseline), during doxycycline or minocycline therapy (interim), at the time of the first dose of melarsomine (first dose), at the time of the second dose of melarsomine (second dose) and at the dog’s follow-up visit after treatment, occurring between 1 and 6 months after completion of therapy (post-treatment). Concentrations of creatinine and SDMA were compared between time points using a mixed effects linear model.

Results: Mean SDMA concentrations following the second dose of melarsomine were significantly lower (-1.80 ug/dL, t-test, df = 99.067, t = -2.694, P-Value = 0.00829) than baseline concentrations. There were no other statistically significant differences in the concentration of either biomarker between the baseline and the other time points in CHD dogs undergoing treatment.

Conclusions: The results suggest that the current AHS protocol may not have a substantial impact on renal function.

C Autumn M Vetter, Alison G Meindl, Bianca N Lourenço, Michael Coyne, Corie Drake, Rachel Murphy, Ira G Roth, Andrew R Moorhead. Parasit Vectors. 2023 Jun 9;16(1):191. doi: 10.1186/s13071-023-05779-0.

Christopher West named 2023 Distinguished Research Professor

Christopher West

Christopher West, head of the Department of Biochemistry and Molecular Biology, a researcher in the Complex Carbohydrate Research Center and a member of CTEGD, belongs to a small group of internationally recognized parasite glycobiologists. His rigorous, transformative research explores cellular processes involving various structures, enzymes and roles of glycans, or sugar chains. His studies have identified fundamental cell-to-cell mechanisms of environmental sensing and signaling in glycobiology. Some of his seminal discoveries involve the biosynthesis and roles of novel glycan molecules in the model organism, Dictyostelium discoideum. One of his crucial contributions to glycobiology has been to describe at molecular resolution that organism’s biochemical response pathway to altered oxygen levels, allowing it to respond to its environment’s available oxygen. Since arriving at UGA, he has translated these findings to an opportunistic human pathogen, Toxoplasma gondii, which can grow and infect cells in low-oxygen environments. His research with collaborators at UGA and internationally has opened a new field of oxygen-sensing in protists, exploring how this environmental factor can control the behavior and virulence of pathogenic parasites.

Monitoring transmission intensity of trachoma with serology

Trachoma, caused by ocular Chlamydia trachomatis infection, is targeted for global elimination as a public health problem by 2030. To provide evidence for use of antibodies to monitor C. trachomatis transmission, we collated IgG responses to Pgp3 antigen, PCR positivity, and clinical observations from 19,811 children aged 1-9 years in 14 populations. We demonstrate that age-seroprevalence curves consistently shift along a gradient of transmission intensity: rising steeply in populations with high levels of infection and active trachoma and becoming flat in populations near elimination. Seroprevalence (range: 0-54%) and seroconversion rates (range: 0-15 per 100 person-years) correlate with PCR prevalence (r: 0.87, 95% CI: 0.57, 0.97). A seroprevalence threshold of 13.5% (seroconversion rate 2.75 per 100 person-years) identifies clusters with any PCR-identified infection at high sensitivity ( >90%) and moderate specificity (69-75%). Antibody responses in young children provide a robust, generalizable approach to monitor population progress toward and beyond trachoma elimination.

Christine Tedijanto, Anthony W Solomon, Diana L Martin, Scott D Nash, Jeremy D Keenan, Thomas M Lietman, Patrick J Lammie, Kristen Aiemjoy, Abdou Amza, Solomon Aragie, Ahmed M Arzika, E Kelly Callahan, Sydney Carolan, Adisu Abebe Dawed, E Brook Goodhew, Sarah Gwyn, Jaouad Hammou, Boubacar Kadri, Khumbo Kalua, Ramatou Maliki, Beido Nassirou, Fikre Seife, Zerihun Tadesse, Sheila K West, Dionna M Wittberg, Taye Zeru Tadege, Benjamin F Arnold. Nat Commun. 2023 Jun 5;14(1):3269. doi: 10.1038/s41467-023-38940-5.

Poly(A)-binding protein is an ataxin-2 chaperone that regulates biomolecular condensates

Biomolecular condensation underlies the biogenesis of an expanding array of membraneless assemblies, including stress granules (SGs), which form under a variety of cellular stresses. Advances have been made in understanding the molecular grammar of a few scaffold proteins that make up these phases, but how the partitioning of hundreds of SG proteins is regulated remains largely unresolved. While investigating the rules that govern the condensation of ataxin-2, an SG protein implicated in neurodegenerative disease, we unexpectedly identified a short 14 aa sequence that acts as a condensation switch and is conserved across the eukaryote lineage. We identify poly(A)-binding proteins as unconventional RNA-dependent chaperones that control this regulatory switch. Our results uncover a hierarchy of cis and trans interactions that fine-tune ataxin-2 condensation and reveal an unexpected molecular function for ancient poly(A)-binding proteins as regulators of biomolecular condensate proteins. These findings may inspire approaches to therapeutically target aberrant phases in disease.

Steven Boeynaems, Yanniv Dorone, Yanrong Zhuang, Victoria Shabardina, Guozhong Huang, Anca Marian, Garam Kim, Anushka Sanyal, Nesli-Ece Şen, Daniel Griffith, Roberto Docampo, Keren Lasker, Iñaki Ruiz-Trillo, Georg Auburger, Alex S Holehouse, Edor Kabashi, Yi Lin, Aaron D Gitler. Mol Cell. 2023 Jun 1;S1097-2765(23)00381-7. doi: 10.1016/j.molcel.2023.05.025.