The RIPK3 Scaffold Regulates Lung Inflammation During Pseudomonas Aeruginosa Pneumonia

Qingfei Yin alleviates Streptococcus pneumoniae pneumonia by promoting complete autophagy to suppress necroptosis

BACKGROUND

Bacterial pneumonia is most prevalent among all pneumonia types, with Streptococcus pneumoniae being the main pathogen. Qingfei Yin (QFY) is a traditional Chinese medicine formula used in the clinical treatment of bacterial pneumonia. Previous studies have confirmed the multi-target and -effect characteristics of QFY in treating S. pneumoniae pneumonia.

PURPOSE

The purpose of this study was to explore the mechanism underlying QFY in treating pneumonia produced by S. pneumoniae.

METHODS

First, an in vivo model of S. pneumoniae-induced pneumonia was established in mice and evaluated the efficacy of QFY by hematoxylin-eosin (HE) staining and measuring cytokine levels in bronchoalveolar lavage fluid. Next, single-cell transcriptomics was used to identify the targeted cell subtypes, signaling pathways, and biological processes affected by QFY. Finally, the findings were validated using a pneumolysin (PLY) -induced mouse lung epithelial cells (TC-1) model in vitro using western blot analysis, immunofluorescence (IF), acridine orange (AO) staining, and propidium iodide (PI) staining.

RESULTS

QFY was shown to alleviate lung inflammation and reduce the TNF-α and IL-6 levels in bronchoalveolar lavage fluid in vivo. A total of 113,353 cells were classified using single-cell transcriptomics and 12 major cell types were identified. By single-cell transcriptomics, QFY was confirmed to primarily target lung epithelial cells. Differentially expressed genes were shown to be enriched in autophagy and necroptosis signaling pathways, and the key differentially expressed gene, Sequestosome 1 (p62/SQSTM1), was identified. PLY was shown to induce RIPK1-dependent necroptosis and incomplete autophagy in TC-1 cells. QFY was shown to promote complete autophagy by downregulating the expression of p62, thereby reducing phosphorylation of RIPK1 and MLKL, and alleviating necroptosis in S. pneumoniae-induced lung epithelial cell death.

CONCLUSION

This study demonstrated that QFY can effectively alleviate S. pneumoniae pneumonia. The mechanism of action may be that QFY promotes complete autophagy by downregulating p62 expression, thereby alleviating necroptosis of S. pneumoniae-induced lung epithelial cells and reducing lung injury. It provides a scientific basis for clinical prevention and treatment of S. pneumoniae pneumonia.

Targeting necroptosis: a promising avenue for respiratory disease treatment

Respiratory diseases are a growing concern in public health because of their potential to endanger the global community. Cell death contributes critically to the pathophysiology of respiratory diseases. Recent evidence indicates that necroptosis, a unique form of programmed cell death (PCD), plays a vital role in the molecular mechanisms underlying respiratory diseases, distinguishing it from apoptosis and conventional necrosis. Necroptosis is a type of inflammatory cell death governed by receptor-interacting serine/threonine protein kinase 1 (RIPK1), RIPK3, and mixed-lineage kinase domain-like protein (MLKL), resulting in the release of intracellular contents and inflammatory factors capable of initiating an inflammatory response in adjacent tissues. These necroinflammatory conditions can result in significant organ dysfunction and long-lasting tissue damage within the lungs. Despite evidence linking necroptosis to various respiratory diseases, there are currently no specific alternative treatments that target this mechanism. This review provides a comprehensive overview of the most recent advancements in understanding the significance and mechanisms of necroptosis. Specifically, this review emphasizes the intricate association between necroptosis and respiratory diseases, highlighting the potential use of necroptosis as an innovative therapeutic approach for treating these conditions.

Necroptosis in bacterial infections

Necroptosis, a recently discovered form of cell-programmed death that is distinct from apoptosis, has been confirmed to play a significant role in the pathogenesis of bacterial infections in various animal models. Necroptosis is advantageous to the host, but in some cases, it can be detrimental. To understand the impact of necroptosis on the pathogenesis of bacterial infections, we described the roles and molecular mechanisms of necroptosis caused by different bacterial infections in this review.

Cell death proteins in sepsis: key players and modern therapeutic approaches

Cell death proteins play a central role in host immune signaling during sepsis. These interconnected mechanisms trigger cell demise via apoptosis, necroptosis, and pyroptosis while also driving inflammatory signaling. Targeting cell death mediators with novel therapies may correct the dysregulated inflammation seen during sepsis and improve outcomes for septic patients.

Cell type-specific molecular mechanisms and implications of necroptosis in inflammatory respiratory diseases

Necroptosis is generally considered as an inflammatory cell death form. The core regulators of necroptotic signaling are receptor-interacting serine-threonine protein kinases 1 (RIPK1) and RIPK3, and the executioner, mixed lineage kinase domain-like pseudokinase (MLKL). Evidence demonstrates that necroptosis contributes profoundly to inflammatory respiratory diseases that are common public health problem. Necroptosis occurs in nearly all pulmonary cell types in the settings of inflammatory respiratory diseases. The influence of necroptosis on cells varies depending upon the type of cells, tissues, organs, etc., which is an important factor to consider. Thus, in this review, we briefly summarize the current state of knowledge regarding the biology of necroptosis, and focus on the key molecular mechanisms that define the necroptosis status of specific cell types in inflammatory respiratory diseases. We also discuss the clinical potential of small molecular inhibitors of necroptosis in treating inflammatory respiratory diseases, and describe the pathological processes that engage cross talk between necroptosis and other cell death pathways in the context of respiratory inflammation. The rapid advancement of single-cell technologies will help understand the key mechanisms underlying cell type-specific necroptosis that are critical to effectively treat pathogenic lung infections and inflammatory respiratory diseases.

Fine Particulate Matter Perturbs the Pulmonary Microbiota in Broiler Chickens

(1) Fine particulate matter (PM2.5) seriously affects the respiratory tract health of both animals and humans. Growing evidence indicates that the pulmonary microbiota is involved in the development of respiratory tract health; however, there is still much that is unknown about the specific changes of pulmonary microbiota caused by PM2.5 in broilers. (2) In this experiment, a total of 48 broilers were randomly divided into a control group and PM-exposure group. The experiment lasted for 21 days. Microbiota, inflammation biomarkers, and histological markers in the lungs were determined. (3) On the last day of the experiment, PM significantly disrupted the structure of lung tissue and induced chronic pulmonary inflammation by increasing IL-6, TNFα, and IFNγ expression and decreasing IL-10 expression. PM exposure significantly altered the α and β diversity of pulmonary microbiota. At the phylum level, PM exposure significantly decreased the Firmicutes abundance and increased the abundance of Actinobacteria and Proteobacteria. At the genus level, PM exposure significantly increased the abundance of Rhodococcus, Achromobacter, Pseudomonas, and Ochrobactrum. We also observed positive associations of the above altered genera with lung TNFα and IFNγ expression. (4) The results suggest that PM perturbs the pulmonary microbiota and induces chronic inflammation, and the pulmonary microbiota possibly contributes to the development of lung inflammation.