Sex-Based Differences in Persistent Lung Inflammation Following Influenza Infection of Juvenile Outbred Mice.

Children are susceptible to influenza infections and can experience severe disease presentation due to a lack of or limited pre-existing immunity. Despite the disproportionate impact influenza has on this population, there is a lack of focus on pediatric influenza research, particularly when it comes to identifying the pathogenesis of long-term outcomes that persist beyond the point of viral clearance. In this study, juvenile outbred male and female mice were infected with influenza and analyzed following viral clearance to determine how sex impacts the persistent inflammatory responses to influenza. It was found that females maintained a broader cytokine response in the lung following clearance of influenza, with innate, type I and type II cytokine signatures in almost all mice. Males, on the other hand, had higher levels of IL-6 and other macrophage-related cytokines, but no evidence of a type I or type II response. The immune landscape was similar in the lungs between males and females post-infection, but males had a higher regulatory T cell to TH1 ratio compared to female mice. Cytokine production positively correlated with the frequency of TH1 cells and exudate macrophages, as well as the number of cells in the bronchoalveolar lavage fluid. Furthermore, female lungs were enriched for metabolites involved in the glycolytic pathway, suggesting glycolysis is higher in female lungs compared to males after viral clearance. These data suggest juvenile female mice have persistent and excessive lung inflammation beyond the point of viral clearance, while juvenile males had a more immunosuppressive phenotype.

Empagliflozin restores cardiac metabolic flexibility in diet-induced obese C57BL6/J mice.

Sodium-glucose co-transporter type 2 (SGLT2) inhibitor therapy to treat type 2 diabetes unexpectedly reduced all-cause mortality and hospitalization due to heart failure in several large-scale clinical trials, and has since been shown to produce similar cardiovascular disease-protective effects in patients without diabetes. How SGLT2 inhibitor therapy improves cardiovascular disease outcomes remains incompletely understood. Metabolic flexibility refers to the ability of a cell or organ to adjust its use of metabolic substrates, such as glucose or fatty acids, in response to physiological or pathophysiological conditions, and is a feature of a healthy heart that may be lost during diabetic cardiomyopathy and in the failing heart. We therefore undertook studies to determine the effects of SGLT2 inhibitor therapy on cardiac metabolic flexibility in vivo in obese, insulin resistant mice using a [U13C]-glucose infusion during fasting and hyperinsulinemic euglycemic clamp. Relative rates of cardiac glucose versus fatty acid use during fasting were unaffected by EMPA, whereas insulin-stimulated rates of glucose use were significantly increased by EMPA, alongside significant improvements in cardiac insulin signaling. These metabolic effects of EMPA were associated with reduced cardiac hypertrophy and protection from ischemia. These observations suggest that the cardiovascular disease-protective effects of SGLT2 inhibitors may in part be explained by beneficial effects on cardiac metabolic substrate selection.

Fungal sensing enhances neutrophil metabolic fitness by regulating antifungal Glut1 activity.

Combating fungal pathogens poses metabolic challenges for neutrophils, key innate cells in anti-Candida albicans immunity, yet how host-pathogen interactions cause remodeling of the neutrophil metabolism is unclear. We show that neutrophils mediate renal immunity to disseminated candidiasis by upregulating glucose uptake via selective expression of glucose transporter 1 (Glut1). Mechanistically, dectin-1-mediated recognition of ß-glucan leads to activation of PKCδ, which triggers phosphorylation, localization, and early glucose transport by a pool of pre-formed Glut1 in neutrophils. These events are followed by increased Glut1 gene transcription, leading to more sustained Glut1 accumulation, which is also dependent on the ß-glucan/dectin-1/CARD9 axis. Card9-deficient neutrophils show diminished glucose incorporation in candidiasis. Neutrophil-specific Glut1-ablated mice exhibit increased mortality in candidiasis caused by compromised neutrophil phagocytosis, reactive oxygen species (ROS), and neutrophil extracellular trap (NET) formation. In human neutrophils, ß-glucan triggers metabolic remodeling and enhances candidacidal function. Our data show that the host-pathogen interface increases glycolytic activity in neutrophils by regulating Glut1 expression, localization, and function.

Graft IL-33 regulates infiltrating macrophages to protect against chronic rejection.

Alarmins, sequestered self-molecules containing damage-associated molecular patterns, are released during tissue injury to drive innate immune cell proinflammatory responses. Whether endogenous negative regulators controlling early immune responses are also released at the site of injury is poorly understood. Herein, we establish that the stromal cell-derived alarmin interleukin 33 (IL-33) is a local factor that directly restricts the proinflammatory capacity of graft-infiltrating macrophages early after transplantation. By assessing heart transplant recipient samples and using a mouse heart transplant model, we establish that IL-33 is upregulated in allografts to limit chronic rejection. Mouse cardiac transplants lacking IL-33 displayed dramatically accelerated vascular occlusion and subsequent fibrosis, which was not due to altered systemic immune responses. Instead, a lack of graft IL-33 caused local augmentation of proinflammatory iNOS+ macrophages that accelerated graft loss. IL-33 facilitated a metabolic program in macrophages associated with reparative and regulatory functions, and local delivery of IL-33 prevented the chronic rejection of IL-33-deficient cardiac transplants. Therefore, IL-33 represents what we believe is a novel regulatory alarmin in transplantation that limits chronic rejection by restraining the local activation of proinflammatory macrophages. The local delivery of IL-33 in extracellular matrix-based materials may be a promising biologic for chronic rejection prophylaxis.