Evolutionary analyses of the gasdermin family suggest conserved roles in infection response despite loss of pore-forming functionality

Background Gasdermins are ancient (>500million-years-ago) proteins, constituting a family of pore-forming proteins that allow the release of intracellular content including proinflammatory cytokines. Despite their importance in the immune response, and although gasdermin and gasdermin-like genes have been identified across a wide range of animal and non-animal species, there is limited information about the evolutionary history of the gasdermin family, and their functional roles after infection. In this study, we assess the lytic functions of different gasdermins across Metazoa species, and use a mouse model of sepsis to evaluate the expression of the different gasdermins during infection. Results We show that the majority of gasdermin family members from distantly related animal clades are pore-forming, in line with the function of the ancestral proto-gasdermin and gasdermin-like proteins of Bacteria. We demonstrate the first expansion of this family occurred through a duplication of the ancestral gasdermin gene which formed gasdermin E and pejvakin prior to the divergence of cartilaginous fish and bony fish ~475 mya. We show that pejvakin from cartilaginous fish and mammals lost the pore-forming functionality and thus its role in cell lysis. We describe that the pore-forming gasdermin A formed ~320 mya as a duplication of gasdermin E prior to the divergence of the Sauropsida clade (the ancestral lineage of reptiles, turtles, and birds) and the Synapsid clade (the ancestral lineage of mammals). We then demonstrate that the gasdermin A gene duplicated to form the rest of the gasdermin family including gasdermins B, C, and D: pore-forming proteins that present a high variation of the exons in the linker sequence, which in turn allows for diverse activation pathways. Finally, we describe expression of murine gasdermin family members in different tissues in a mouse sepsis model, indicating function during infection response. Conclusions In this study we explored the evolutionary history of the gasdermin proteins in animals and demonstrated that the pore-formation functionality has been conserved from the ancient proto-gasdermin protein. We also showed that one gasdermin family member, pejvakin, lost its pore-forming functionality, but that all gasdermin family members, including pejvakin, likely retained a role in inflammation and the physiological response to infection.

Prospective international validation of the predisposition, infection, response and organ dysfunction (PIRO) clinical staging system among intensive care and general ward patients

Background Stratifying patients with sepsis was the basis of the predisposition, infection, response and organ dysfunction (PIRO) concept, an attempt to resolve the heterogeneity in treatment response. The purpose of this study is to perform an independent validation of the PIRO staging system in an international cohort and explore its utility in the identification of patients in whom time to antibiotic treatment is particularly important. Methods Prospective international cohort study, conducted over a 6-month period in five Portuguese hospitals and one Australian institution. All consecutive adult patients admitted to selected wards or the intensive care, with infections that met the CDC criteria for lower respiratory tract, urinary, intra-abdominal and bloodstream infections were included. Results There were 1638 patients included in the study. Patients who died in hospital presented with a higher PIRO score (10 ± 3 vs 8 ± 4, p < 0.001). The observed mortality was 3%, 15%, 24% and 34% in stage I, II, III and IV, respectively, which was within the predicted intervals of the original model, except for stage IV patients that presented a lower mortality. The hospital survival rate was 84%. The application of the PIRO staging system to the validation cohort resulted in a positive predictive value of 97% for stage I, 91% for stage II, 85% for stage III and 66% for stage IV. The area under the receiver operating characteristics curve (AUROC) was 0.75 for the all cohort and 0.70 if only patients with bacteremia were considered. Patients in stage III and IV who did not have antibiotic therapy administered within the desired time frame had higher mortality rate than those who have timely administration of antibiotic. Conclusions To our knowledge, this is the first external validation of this PIRO staging system and it performed well on different patient wards within the hospital and in different types of hospitals. Future studies could apply the PIRO system to decision-making about specific therapeutic interventions and enrollment in clinical trials based on disease stage.

Parenteral glucose supply and pharmacological glycolysis inhibition determine the clinical fate of infected preterm newborns

Preterm infants are susceptible to bloodstream infection that can lead to sepsis. High parenteral glucose supplement is commonly used to support their growth and energy expenditure, but may exceed endogenous regulation during infection, causing dysregulated immune response and clinical deterioration. Using a preterm piglet model of neonatal sepsis induced by Staphylococcus epidermidis infection, we demonstrate the delicate interplay between immunity and energy metabolism to regulate the host infection response. Circulating glucose levels, glycolysis and inflammatory response to infection are closely connected across the states of tolerance, resistance and immunoparalysis. Further, high parenteral glucose provision during infection induces hyperglycemia, elevated glycolysis and inflammation, leading to lactate acidosis and sepsis, whereas glucose restricted individuals are clinically unaffected with increased gluconeogenesis to maintain moderate hypoglycemia. Finally, pharmacological glycolysis inhibition during normoglycemia enhances bacterial clearance and dampens inflammation but fails to prevent sepsis. Our results uncover how blood glucose controls immune cell metabolism and function, in turn determining the clinical fate of infected preterm neonates. This also questions the current practice of parenteral glucose supply for infected preterm infants.

Familial aggregation of COVID-19 severity suggests a genetic component to host infection response

Familial aggregation of COVID-19 cases suggest transmission occurs by contact but can also be evidence of a genetic component to the disease presentation. The goal of this work was to evaluate the disease pattern in families that many individuals have been affected by the disease. A case series analysis of six families that had many individuals affected by COVID-19 and the pattern of the severity of the disease is reported. Families were from two densely populated cities in Brazil. Participants included family members of six unrelated families, with some individuals that showed signs of COVID-19. The exposure was SARS-CoV-2 in the same household. The main outcomes and measures were disease affection and severity, including mortality. From the six families, two had mild cases only, whereas the other four families showed severe disease and death in the same sibship. The two families that had mild disease could be followed for six months and one showed reinfection after six months. This cases series suggest that disease severity aggregates in families, which suggests a genetic component for individual host response to SARS-CoV-2 infection.

Identification and characterization of novel infection associated transcripts in macrophages

Regulated expression of genes in response to internal and external stimuli is primarily responsible for the enormous plasticity and robustness of biological systems. Recent studies have elucidated complex regulatory non protein coding transcript (lncRNA) circuits in coordinated response of immune cells. By analysis of lncRNA expression profiles of macrophages in response to Mtb infection, we identified novel highly expressed transcripts, unique in encompassing one functional protein coding transcript- CMPK2 and a previously identified type I IFN responsive lncRNA- NRIR. While these RNA are induced by virulent Mtb early, the complete absence of expression in non-viable Mtb infected cells coupled to a more protracted expression profile in the case of BCG suggest an important role in macrophage response to mycobacteria. Moreover, enhanced expression was observed in macrophages from TB patients. The elevated expression by 1h in response to fast growing bacteria further emphasizes the importance of these RNAs in the macrophage infection response. These transcripts (TILT1, 2,3 - TLR4 and Infection induced Long Transcript) are triggered exclusively by TLR4 stimulation (LPS) with faster and stronger kinetics in comparison to the lncRNA–NRIR. Overall, we provide evidence for the presence of numerous transcripts that is a part of the early infection response program of macrophages.

Blood purification for sepsis: an overview

Sepsis is a life-threatening organ failure exacerbated by a maladaptive infection response from the host, and is one of the major causes of mortality in the intensive care unit. During the past decades, several extracorporeal blood purification techniques have been developed to manage sepsis by acting on both the infectious agents themselves and the host immune response. This research aims to summarize recent progress on the extracorporeal blood purification technologies applied for sepsis, discuss the unanswered questions of RRT for septic patients and present a decision-making strategy for practitioners.

Epithelial Infection With Candida albicans Elicits a Multi-System Response in Planarians

Candida albicans is one of the most common fungal pathogens of humans. Prior work introduced the planarian Schmidtea mediterranea as a new model system to study the host response to fungal infection at the organismal level. In the current study, we analyzed host–pathogen changes that occurred in situ during early infection with C. albicans. We found that the transcription factor Bcr1 and its downstream adhesin Als3 are required for C. albicans to adhere to and colonize the planarian epithelial surface, and that adherence of C. albicans triggers a multi-system host response that is mediated by the Dectin signaling pathway. This infection response is characterized by two peaks of stem cell divisions and transcriptional changes in differentiated tissues including the nervous and the excretory systems. This response bears some resemblance to a wound-like response to physical injury; however, it takes place without visible tissue damage and it engages a distinct set of progenitor cells. Overall, we identified two C. albicans proteins that mediate epithelial infection of planarians and a comprehensive host response facilitated by diverse tissues to effectively clear the infection.