Extracellular Lactate Acts as a Metabolic Checkpoint and Shapes Monocyte Function Time Dependently

Staphylococcus aureus suppresses the pentose phosphate pathway in human neutrophils via the adenosine receptor A2aR to enhance intracellular survival

IMPORTANCE

Staphylococcus aureus is one of the leading causes of antimicrobial-resistant infections whose success as a pathogen is facilitated by its massive array of immune evasion tactics, including intracellular survival within critical immune cells such as neutrophils, the immune system's first line of defense. In this study, we describe a novel pathway by which intracellular S. aureus can suppress the antimicrobial capabilities of human neutrophils by using the anti-inflammatory adenosine receptor, adora2a (A2aR). We show that signaling through A2aR suppresses the pentose phosphate pathway, a metabolic pathway used to fuel the antimicrobial NADPH oxidase complex that generates reactive oxygen species (ROS). As such, neutrophils show enhanced ROS production and reduced intracellular S. aureus when treated with an A2aR inhibitor. Taken together, we identify A2aR as a potential therapeutic target for combatting intracellular S. aureus infection.

Staphylococci planktonic and biofilm environments differentially affect osteoclast formation

INTRODUCTION

The pathophysiology of chronic implant-related bone infections is characterized by an increase in osteoclast numbers and enhanced bone resorption. Biofilms are a major reason for chronicity of such infections as the biofilm matrix protects bacteria against antibiotics and impairs the function of immune cells. Macrophages are osteoclast precursor cells and therefore linked to inflammation and bone destruction.

OBJECTIVE AND METHOD

Investigations on the impact of biofilms on the ability of macrophages to form osteoclasts are yet missing and we, therefore, analyzed the effect of Staphylococcus aureus (SA) and Staphylococcus epidermidis (SE) planktonic and biofilm environments on osteoclastogenesis using RAW 264.7 cells and conditioned media (CM).

RESULTS

Priming with the osteoclastogenic cytokine RANKL before CM addition enabled the cells to differentiate into osteoclasts. This effect was highest in SE planktonic or SA biofilm CM. Simultaneous stimulation with CM and RANKL, however, suppressed osteoclast formation and resulted in formation of inflammation-associated multinucleated giant cells (MGCs) which was most pronounced in SE planktonic CM.

CONCLUSION

Our data indicate that the biofilm environment and its high lactate levels are not actively promoting osteoclastogenesis. Hence, the inflammatory immune response against planktonic bacterial factors through Toll-like receptors seems to be the central cause for the pathological osteoclast formation. Therefore, immune stimulation or approaches that aim at biofilm disruption need to consider that this might result in enhanced inflammation-mediated bone destruction.

Metabolic Reprogramming and Its Regulatory Mechanism in Sepsis-Mediated Inflammation

Sepsis is a systemic inflammatory disease caused by an infection that can lead to multiple organ failure. Sepsis alters energy metabolism, leading to metabolic reprogramming of immune cells, which consequently disrupts innate and adaptive immune responses, triggering hyperinflammation and immunosuppression. This review summarizes metabolic reprogramming and its regulatory mechanism in sepsis-induced hyperinflammation and immunosuppression, highlights the significance and intricacies of immune cell metabolic reprogramming, and emphasizes the pivotal role of mitochondria in metabolic regulation and treatment of sepsis. This review provides an up-to-date overview of the relevant literature to inform future research directions in understanding the regulation of sepsis immunometabolism. Metabolic reprogramming has great promise as a new target for sepsis treatment in the future.

Lactate: a pearl dropped in the ocean-an overlooked signal molecule in physiology and pathology

Lactate, once recognized as a wasty product from anaerobic glycolysis, is proved to be a pivotal signal molecule. Lactate accumulation occurs in diverse physiological and pathological settings due to the imbalance between lactate production and clearance. Under the condition with drastic changes in local microenvironment, such as tumorigenesis, inflammation, and microbial infection, the glycolysis turns to be active in surrounding cells leading to increased lactate release. Meanwhile, lactate can be utilized by these cells as an energy substrate and acts as a signal molecule to regulate cell functions through receptor-dependent or independent pathways. In this review, we tended to tease out the contribution of lactate in tumor progression and immunomodulation. And we also discussed the accessory role of lactate, beyond as the energy source only, in the growth of invading pathogens.

Understanding the Contribution of Lactate Metabolism in Cancer Progress: A Perspective from Isomers

Lactate mediates multiple cell-intrinsic effects in cancer metabolism in terms of development, maintenance, and metastasis and is often correlated with poor prognosis. Its functions are undertaken as an energy source for neighboring carcinoma cells and serve as a lactormone for oncogenic signaling pathways. Indeed, two isomers of lactate are produced in the Warburg effect: L-lactate and D-lactate. L-lactate is the main end-production of glycolytic fermentation which catalyzes glucose, and tiny D-lactate is fabricated through the glyoxalase system. Their production inevitably affects cancer development and therapy. Here, we systematically review the mechanisms of lactate isomers production, and highlight emerging evidence of the carcinogenic biological effects of lactate and its isomers in cancer. Accordingly, therapy that targets lactate and its metabolism is a promising approach for anticancer treatment.

Systematic Investigations on the Metabolic and Transcriptomic Regulation of Lactate in the Human Colon Epithelial Cells

Lactate, primarily produced by the gut microbiota, performs as a necessary “information transmission carrier” between the gut and the microbiota. To investigate the role of lactate in the gut epithelium cell–microbiota interactions as a metabolic signal, we performed a combinatory, global, and unbiased analysis of metabolomic and transcriptional profiling in human colon epithelial cells (Caco-2), using a lactate treatment at the physiological concentration (8 mM). The data demonstrated that most of the genes in oxidative phosphorylation were significantly downregulated in the Caco-2 cells due to lactate treatment. Consistently, the levels of fumarate, adenosine triphosphate (ATP), and creatine significantly decreased, and these are the metabolic markers of OXPHOS inhibition by mitochondria dysfunction. The one-carbon metabolism was affected and the polyol pathway was activated at the levels of gene expression and metabolic alternation. In addition, lactate significantly upregulated the expressions of genes related to self-protection against apoptosis. In conclusion, lactate participates in gut–gut microbiota communications by remodeling the metabolomic and transcriptional signatures, especially for the regulation of mitochondrial function. This work contributes comprehensive information to disclose the molecular mechanisms of lactate-mediated functions in human colon epithelial cells that can help us understand how the microbiota communicates with the intestines through the signaling molecule, lactate.

Metabolic Reprogramming Mediates Delayed Apoptosis of Human Neutrophils Infected With Francisella tularensis

Neutrophils (polymorphonuclear leukocytes, PMNs) have a distinctively short lifespan, and tight regulation of cell survival and death is imperative for their normal function. We demonstrated previously that Francisella tularensis extends human neutrophil lifespan, which elicits an impaired immune response characterized by neutrophil dysfunction. Herein, we extended these studies, including our transcriptional profiling data, and employed Seahorse extracellular flux analysis, gas chromatography-mass spectrometry metabolite analysis, flow cytometry and several other biochemical approaches to demonstrate that the delayed apoptosis observed in F. tularensis-infected neutrophils is mediated, in part, by metabolic reprogramming. Specifically, we show that F. tularensis-infected neutrophils exhibited a unique metabolic signature characterized by increased glycolysis, glycolytic flux and glucose uptake, downregulation of the pentose phosphate pathway, and complex glycogen dynamics. Glucose uptake and glycolysis were essential for cell longevity, although glucose-6-phosphate translocation into the endoplasmic reticulum was not, and we identify depletion of glycogen as a potential trigger of apoptosis onset. In keeping with this, we also demonstrate that ablation of apoptosis with the pan-caspase inhibitor Q-VD-OPh was sufficient to profoundly increase glycolysis and glycogen stores in the absence of infection. Taken together, our data significantly advance understanding of neutrophil immunometabolism and its capacity to regulate cell lifespan.