Toxoplasma gondii Toxolysin 4 Contributes to Efficient Parasite Egress from Host Cells.

Egress from host cells is an essential step in the lytic cycle of T. gondii and other apicomplexan parasites; however, only a few parasite secretory proteins are known to affect this process. The putative metalloproteinase toxolysin 4 (TLN4) was previously shown to be an extensively processed microneme protein, but further characterization was impeded by the inability to genetically ablate TLN4. Here, we show that TLN4 has the structural properties of an M16 family metalloproteinase, that it possesses proteolytic activity on a model substrate, and that genetic disruption of TLN4 reduces the efficiency of egress from host cells. Complementation of the knockout strain with the TLN4 coding sequence significantly restored egress competency, affirming that the phenotype of the Δtln4 parasite was due to the absence of TLN4. This work identifies TLN4 as the first metalloproteinase and the second microneme protein to function in T. gondii egress. The study also lays a foundation for future mechanistic studies defining the precise role of TLN4 in parasite exit from host cells. IMPORTANCE After replicating within infected host cells, the single-celled parasite Toxoplasma gondii must rupture out of such cells in a process termed egress. Although it is known that T. gondii egress is an active event that involves disruption of host-derived membranes surrounding the parasite, very few proteins that are released by the parasite are known to facilitate egress. In this study, we identify a parasite secretory protease that is necessary for efficient and timely egress, laying the foundation for understanding precisely how this protease facilitates T. gondii exit from host cells.

Severe Acute Respiratory Syndrome-Associated Coronavirus 2 Infection and Organ Dysfunction in the ICU: Opportunities for Translational Research.

OBJECTIVES: Since the beginning of the coronavirus disease 2019 pandemic, hundreds of thousands of patients have been treated in ICUs across the globe. The severe acute respiratory syndrome-associated coronavirus 2 virus enters cells via the angiotensin-converting enzyme 2 receptor and activates several distinct inflammatory pathways, resulting in hematologic abnormalities and dysfunction in respiratory, cardiac, gastrointestinal renal, endocrine, dermatologic, and neurologic systems. This review summarizes the current state of research in coronavirus disease 2019 pathophysiology within the context of potential organ-based disease mechanisms and opportunities for translational research. DATA SOURCES: Investigators from the Research Section of the Society of Critical Care Medicine were selected based on expertise in specific organ systems and research focus. Data were obtained from searches conducted in Medline via the PubMed portal, Directory of Open Access Journals, Excerpta Medica database, Latin American and Caribbean Health Sciences Literature, and Web of Science from an initial search from December 2019 to October 15, 2020, with a revised search to February 3, 2021. The medRxiv, Research Square, and clinical trial registries preprint servers also were searched to limit publication bias. STUDY SELECTION: Content experts selected studies that included mechanism-based relevance to the severe acute respiratory syndrome-associated coronavirus 2 virus or coronavirus disease 2019 disease. DATA EXTRACTION: Not applicable. DATA SYNTHESIS: Not applicable. CONCLUSIONS: Efforts to improve the care of critically ill coronavirus disease 2019 patients should be centered on understanding how severe acute respiratory syndrome-associated coronavirus 2 infection affects organ function. This review articulates specific targets for further research.

Ticagrelor Reduces Thromboinflammatory Markers in Patients With Pneumonia.

Despite treatment advances for sepsis and pneumonia, significant improvements in outcome have not been realized. Antiplatelet therapy may improve outcome in pneumonia and sepsis. In this study, the authors show that ticagrelor reduced leukocytes with attached platelets as well as the inflammatory biomarker interleukin (IL)-6. Pneumonia patients receiving ticagrelor required less supplemental oxygen and lung function tests trended toward improvement. Disruption of the P2Y12 receptor in a murine model protected against inflammatory response, lung permeability, and mortality. Results indicate a mechanistic link between platelets, leukocytes, and lung injury in settings of pneumonia and sepsis, and suggest possible therapeutic approaches to reduce complications.(Targeting Platelet-Leukocyte Aggregates in Pneumonia With Ticagrelor [XANTHIPPE]; NCT01883869).

Thromboinflammatory response and predictors of outcomes in patients undergoing transcatheter aortic valve replacement.

Transcatheter aortic valve replacement (TAVR) has been increasingly used to treat patients with symptomatic aortic stenosis. Despite improvements in valve deployment, patients that have undergone TAVR are at high risk for major adverse events following the procedure. Blood cell numbers, platelet function, and biomarkers of systemic inflammation were analyzed in 58 patients undergoing TAVR with the Edward's SAPIEN valve. Following valve deployment, platelet count and agonist-induced platelet activity declined and plasma markers of systemic inflammation (interleukin-6 and S100A8/A9) increased. Baseline platelet activity prior to TAVR correlated with perioperative changes plasma interleukin-6 levels. Moreover, perioperative changes in plasma inflammatory markers predicted the decline in platelet count in the days following the TAVR procedure. Additionally, a significant effect of gender on platelet count following TAVR and was observed. Finally, post-procedural mortality was associated with sustained thrombocytopenia after TAVR. Our findings suggest that TAVR elicits a thromboinflammatory state that may contribute to post-procedural thrombocytopenia. Importantly, our results add to the growing body of literature that suggests the thromboinflammatory changes that occur early after TAVR may predict long-term outcomes.

The effect of rosuvastatin on thromboinflammation in the setting of acute coronary syndrome.

In patients with acute coronary syndromes (ACS), early therapy with high-dose statins may reduce short-term adverse clinical outcomes. The mechanisms responsible are not known but could involve anti-inflammatory or anti-thrombotic effects. Compelling evidence from experimental models and clinical studies suggests that the interplay between inflammatory and thrombotic systems, typified by platelet-monocyte and platelet-neutrophil interactions, might be a key regulator of ischemic vascular events. The study sought to determine if early, high-dose administration of the HMG-CoA reductase inhibitor rosuvastatin in the setting of ACS exerts beneficial vascular effects by reducing, and inhibiting biomarkers of thromboinflammation, such as platelet-monocyte and platelet-neutrophil interactions, and biomarkers of myocardial necrosis. A total of 54 patients presenting with ACS within 8 h of symptom onset were randomized to rosuvastatin 40 mg or placebo. Rosuvastatin significantly reduced interactions between platelets and circulating neutrophils (P = 0.015) and monocytes (P = 0.009) within 24 h. No significant effects were observed on platelet aggregation or plasma levels of PF4, sP-selectin, or sCD40L, whereas significant reductions of RANTES occurred over time in both treatment groups. Plasma levels of myeloperoxidase (MPO) declined more rapidly with rosuvastatin therapy than placebo. In a subset of patients with normal cardiac necrosis biomarkers at randomization, rosuvastatin therapy was associated with less myocardial damage as measured by troponin-I or CK-MB. Early administration of high-dose statin therapy in patients with ACS appears to improve biomarkers of inflammation within 8 h, which may translate into fewer ischemic events.

Pleiotropy of the Drosophila JAK pathway cytokine Unpaired 3 in development and aging.

The Janus kinase (JAK) pathway is an essential, highly re-utilized developmental signaling cascade found in most metazoans. In vertebrates, the JAK intracellular cascade mediates signaling by dozens of cytokines and growth factors. In Drosophila, the Unpaired (Upd) family, encoded by three tandemly duplicated genes, is the only class of ligands associated with JAK stimulation. Unpaired has a central role in activation of JAK for most pathway functions, while Unpaired 2 regulates body size through insulin signaling. We show here that the third member of the family, unpaired 3 (upd3), overlaps upd in expression in some tissues and is essential for a subset of JAK-mediated developmental functions. First, consistent with the known requirements of JAK signaling in gametogenesis, we find that mutants of upd3 show an age-dependent impairment of fertility in both sexes. In oogenesis, graded JAK activity stimulated by Upd specifies the fates of the somatic follicle cells. As upd3 mutant females age, defects arise that can be attributed to perturbations of the terminal follicle cells, which require the highest levels of JAK activation. Therefore, in oogenesis, the activities of Upd and Upd3 both appear to quantitatively contribute to specification of those follicle cell fates. Furthermore, the sensitization of upd3 mutants to age-related decline in fertility can be used to investigate reproductive senescence. Second, loss of Upd3 during imaginal development results in defects of adult structures, including reduced eye size and abnormal wing and haltere posture. The outstretched wing and small eye phenotypes resemble classical alleles referred to as outstretched (os) mutations that have been previously ascribed to upd. However, we show that os alleles affect expression of both upd and upd3 and map to untranscribed regions, suggesting that they disrupt regulatory elements shared by both genes. Thus the upd region serves as a genetically tractable model for coordinate regulation of tandemly duplicated gene families that are commonly found in higher eukaryotes.

Obesity and diabetes cause cognitive dysfunction in the absence of accelerated ß-amyloid deposition in a novel murine model of mixed or vascular dementia.

Mid-life obesity and type 2 diabetes mellitus (T2DM) confer a modest, increased risk for Alzheimer's disease (AD), though the underlying mechanisms are unknown. We have created a novel mouse model that recapitulates features of T2DM and AD by crossing morbidly obese and diabetic db/db mice with APPΔNL/ΔNLx PS1P264L/P264L knock-in mice. These mice (db/AD) retain many features of the parental lines (e.g. extreme obesity, diabetes, and parenchymal deposition of ß-amyloid (Aß)). The combination of the two diseases led to additional pathologies-perhaps most striking of which was the presence of severe cerebrovascular pathology, including aneurysms and small strokes. Cortical Aß deposition was not significantly increased in the diabetic mice, though overall expression of presenilin was elevated. Surprisingly, Aß was not deposited in the vasculature or removed to the plasma, and there was no stimulation of activity or expression of major Aß-clearing enzymes (neprilysin, insulin degrading enzyme, or endothelin-converting enzyme). The db/AD mice displayed marked cognitive impairment in the Morris Water Maze, compared to either db/db or APPΔNLx PS1P264L mice. We conclude that the diabetes and/or obesity in these mice leads to a destabilization of the vasculature, leading to strokes and that this, in turn, leads to a profound cognitive impairment and that this is unlikely to be directly dependent on Aß deposition. This model of mixed or vascular dementia provides an exciting new avenue of research into the mechanisms underlying the obesity-related risk for age-related dementia, and will provide a useful tool for the future development of therapeutics.

Glypicans regulate JAK/STAT signaling and distribution of the Unpaired morphogen.

In Drosophila, ligands of the Unpaired (Upd) family activate the Janus kinase/signal transducers and activators of transcription (JAK/STAT) pathway. The JAK/STAT pathway controls many developmental events, including multiple functions in the ovary. These include an early role in the germarium for specification of stalk cells and a later role in the vitellarium to pattern the follicular epithelium surrounding each cyst. In this latter role, graded JAK/STAT activation specifies three distinct anterior follicular cell fates, suggesting that Upd is a morphogen in this system. Consistent with the JAK/STAT activation pattern in the vitellarium, Upd forms a concentration gradient on the apical surface of the follicular epithelium with a peak at its source, the polar cells. Like many morphogens, signaling and distribution of Upd are regulated by the heparan sulfate proteoglycans (HSPGs) Dally and Dally-like. Mutations in these glypican genes and in heparan sulfate biosynthetic genes result in disruption of JAK/STAT signaling, loss or abnormal formation of the stalk and significant reduction in the accumulation of extracellular Upd. Conversely, forced expression of Dally causes ectopic accumulation of Upd in follicular cells. Furthermore, biochemical studies reveal that Upd and Dally bind each other on the surface of the cell membrane. Our findings demonstrate that Drosophila glypicans regulate formation of the follicular gradient of the Upd morphogen, Upd. Furthermore, we establish the follicular epithelium as a new model for morphogen signaling in complex organ development.