The Role of Pericytes in Lipopolysaccharide-Induced Murine Acute Respiratory Distress Syndrome.

Acute respiratory distress syndrome (ARDS) is a heterogeneous clinical syndrome that is most commonly triggered by infection-related inflammation. Lung pericytes can respond to infection and act as immune and proangiogenic cells; moreover, these cells can differentiate into myofibroblasts in nonresolving ARDS and contribute to the development of pulmonary fibrosis. Here, we aimed to characterize the role of lung cells, which present characteristics of pericytes, such as peri-endothelial location and expression of a panel of specific markers. To study their role in ARDS, we used a murine model of lipopolysaccharide (LPS)-induced resolving ARDS. We confirmed the development of ARDS after LPS instillation, which was resolved 14 days after onset. Using immunofluorescence and flow cytometry, we observed early expansion of neural-glial antigen 2+ ß-type platelet-derived growth factor receptor+ pericytes in murine lungs with loss of CD31+ ß-type platelet-derived growth factor receptor+ endothelial cells. These changes were accompanied by specific changes in lung structure and loss of vascular integrity. On day 14 after ARDS onset, the composition of pericytes and endothelial cells returned to baseline values. LPS-induced ARDS activated NOTCH signaling in lung pericytes, the inhibition of which during LPS stimulation reduced the expression of its downstream target genes, pericyte markers, and angiogenic factors. Together, lung pericytes in response to inflammatory injury activate NOTCH signaling that supports their maintenance and in turn can contribute to recovery of the microvascular endothelium.

1-Methylnicotinamide (1-MNA) inhibits the activation of the NLRP3 inflammasome in human macrophages.

The NLRP3 inflammasome is among the most potent intracellular sensors of danger and disturbances of cellular homeostasis that can lead to the release of IL-1ß and cell death, or pyroptosis. Despite its protective role, this mechanism is involved in the pathogenesis of numerous inflammatory diseases; therefore, it is seen as a potential therapeutic target. 1-methylnicotinamide (1-MNA) is a direct metabolite of nicotinamide and was previously shown to display several immunomodulatory properties, including a reduction in the reactive oxygen species (ROS). Here, we investigated whether 1-MNA could influence the activation of the NLRP3 inflammasome in human macrophages. In differentiated human macrophages we observed that 1-MNA specifically reduced the activation of the NLRP3 inflammasome. This effect was related to the scavenging of ROS, as exogenous H2O2 was able to restore NLRP3 activation. Additionally, 1-MNA increased the mitochondrial membrane potential, indicating that it did not inhibit oxidative phosphorylation. Moreover, at high but not low concentrations, 1-MNA decreased NF-κB activation and the level of pro-IL-1ß. Interestingly, 1-MNA did not reduce the secretion of IL-6 upon endotoxin stimulation, confirming that its primary immunomodulatory effect on human macrophages is dependent on the NLRP3 inflammasome. Taken together, we have shown for the first time that 1-MNA reduced the activation of the NLRP3 inflammasome in human macrophages via an ROS-dependent pathway. Our results indicate a novel potential use of 1-MNA in NLRP3-related disorders.

A Bittersweet Kiss of Gram-Negative Bacteria: The Role of ADP-Heptose in the Pathogenesis of Infection.

Due to the global crisis caused by the dramatic rise of drug resistance among Gram-negative bacteria, there is an urgent need for a thorough understanding of the pathogenesis of infections of such an etiology. In light of the limited availability of new antibiotics, therapies aimed at host-pathogen interactions emerge as potential treatment modalities. Thus, understanding the mechanism of pathogen recognition by the host and immune evasion appear to be the key scientific issues. Until recently, lipopolysaccharide (LPS) was recognized as a major pathogen-associated molecular pattern (PAMP) of Gram-negative bacteria. However, recently, ADP-L-glycero-ß-D-manno-heptose (ADP-heptose), an intermediate carbohydrate metabolite of the LPS biosynthesis pathway, was discovered to activate the hosts' innate immunity. Therefore, ADP-heptose is regarded as a novel PAMP of Gram-negative bacteria that is recognized by the cytosolic alpha kinase-1 (ALPK1) protein. The conservative nature of this molecule makes it an intriguing player in host-pathogen interactions, especially in the context of changes in LPS structure or even in its loss by certain resistant pathogens. Here, we present the ADP-heptose metabolism, outline the mechanisms of its recognition and the activation of its immunity, and summarize the role of ADP-heptose in the pathogenesis of infection. Finally, we hypothesize about the routes of the entry of this sugar into cytosol and point to emerging questions that require further research.