Increased susceptibility of irradiated mice to Aspergillus fumigatus infection via NLRP3/GSDMD pathway in pulmonary bronchial epithelia

NLRP3/GSDMD mediated pyroptosis induces lung inflammation susceptibility in diesel exhaust exposed mouse strains

BACKGROUND

Genetic diversity among species influences the disease severity outcomes linked to air pollution. However, the mechanism responsible for this variability remain elusive and needs further investigation.

OBJECTIVE

To investigate the genetic factors and pathways linked with differential susceptibility in mouse strains associated with diesel exhaust exposure.

METHODS

C57BL/6 and Balb/c mice were exposed to diesel exhaust (DE) for 5 days/week for 30 min/day for 8 weeks. Body weight of mice was recorded every week and airway hyperresponsiveness towards DE exposure was recorded after 24 h of last exposure. Mice were euthanised to collect BALF, blood, lung tissues for immunobiochemical assays, structural integrity and genetic studies.

RESULTS

C57BL/6 mice showed significantly decreased body weight in comparison to Balb/c mice (p < 0.05). Both mouse strains showed lung resistance and damage to elastance upon DE exposure compared to respective controls (p < 0.05) with more pronounced effects in C57BL/6 mice. Lung histology showed increase in bronchiolar infiltration and damage to the wall in C57BL/6 mice (p < 0.05). DE exposure upregulated pro-inflammatory and Th2 cytokine levels in C57BL/6 in comparison to Balb/c mice. C57BL/6 mice showed increase in Caspase-1 and ASC expression confirming activation of downstream pathway. This showed significant activation of inflammasome pathway in C57BL/6 mice with ∼2-fold increase in NLRP3 and elevated IL-1β expression. Gasdermin-D levels were increased in C57BL/6 mice demonstrating induction of pyroptosis that corroborated with IL-1β secretion (p < 0.05). Genetic variability among both species was confirmed with sanger's sequencing suggesting presence of SNPs in 3'UTRs of IL-1β gene influencing expression between mouse strains.

CONCLUSIONS

C57BL/6 mice exhibited increased susceptibility to diesel exhaust in contrast to Balb/c mice via activation of NLRP3-related pyroptosis. Differential susceptibility between strains may be attributed via SNPs in the 3'UTRs of the IL-1β gene.

Pyroptosis and airway homeostasis regulation

Pyroptosis is a form of cell death associated with inflammation. In the maintenance of airway homeostasis, pyroptosis goes through activation and assembly of Inflammasome. The pyroptosis pathway is mediated by caspase which activates the pore-forming effect of substrate gasdermin family members. It eventually leads to lysis and release of the cell contents and then induces an inflammatory response. In this process, it participates in airway homeostasis regulation by affecting airway immunity, airway epithelial structure and airway microbiota. Therefore, we discussed the correlation between airway immunity, airway epithelial structure, airway microbiota and the mechanism of pyroptosis to describe the role of pyroptosis in airway homeostasis regulation which is of great significance for understanding the occurrence and treatment of airway inflammatory diseases.

Effect of Aspergillus fumigatus on infection in immunosuppressed rats

Background

Immunosuppression is believed to increase the risk of invasive pulmonary aspergillosis (IPA), but information on the mechanism is limited. Therefore, we analyze the effect and mechanism of the pathogenesis and disease progression of IPA in a combined immunosuppressed rat model.

Methods

The immunosuppressed rat model was established by intraperitoneal injection of cyclophosphamide (CTX) and dexamethasone (DXM). IPA was established by nasal inoculation of Aspergillus fumigatus spore suspension. Pathological sections and tissue homogenate culture were used to evaluate the lung tissue. Routine blood and inflammatory indexes were dynamically observed. The expressions of NLRP3/caspase-1/GSDMD protein and gene were determined using western blot and quantitative polymerase chain reaction (q-PCR) respectively. T-test or one-way repeated measures analysis were used to do statistical analysis on the groups.

Results

Following intraperitoneal of CTX and DXM injections, the rats showed depression, weight loss, and significant decreases in the numbers of leukocytes and classified cells. Pathological sections revealed more severe lung lesions in the immunosuppressed rats infected with Aspergillus fumigatus. The expression of NLRP3/caspase-1/GSDMD protein increased significantly in both the aspergillosis and immunosuppressed plus aspergillosis groups.

Conclusions

The pathological development of IPA in the immunosuppressed rats had the most serious effects, and the findings strongly implicated NLRP3/caspase-1/GSDMD pathway involvement.

Hunting down NLRP3 inflammasome: An executioner of radiation-induced injury

Radiotherapy is one of the mainstream treatment modalities for several malignancies. However, radiation-induced injury to surrounding normal tissues limits its efficacy. The NLRP3 inflammasome is an essential mechanism of innate immunity that reacts to challenges from endogenous danger signals and pathological microbes. A growing body of evidence has demonstrated a key role of NLRP3 inflammasome in the pathogenesis of radiation-induced tissue injury. Despite accumulating evidence, the potential value of the NLRP3 inflammasome in the management of radiation-induced tissue injury is not adequately recognized. We conducted a literature review to characterize the relationship between NLRP3 inflammasome and radiation injury. By analyzing recent evidence, we identify NLRP3 inflammasome as one of the executioners of radiation-induced injury, since it responds to the challenges of radiation, induces cell pyroptosis and tissue dysfunction, and initiates non-resolving inflammation and fibrosis. Based on these concepts, we propose early intervention/prevention strategies targeting NLRP3 inflammasome in a radiation context, which may help resolve imperative clinical problems.

Clostridium difficile Induced Inflammasome Activation and Coagulation Derangements

C. difficile enterocolitis (CDAC) is the most common hospital infection, burdened by an increased incidence of coagulation-related complications such as deep vein thrombosis (DVT) and disseminated intravascular coagulation (DIC) as well as a significant sepsis-related mortality. In this review, we analyzed the available data concerning the correlation between coagulation complications related to C. difficile infection (CDI) and inflammasome activation, in particular the pyrin-dependent one. The little but solid available preclinical and clinical evidence shows that inflammasome activation increases the risk of venous thromboembolism (VTE). As proof of this, it has been observed that in vitro inhibition of the molecules (e.g., tissue factor) mainly involved in coagulation activation could block the process. In vivo studies show that it could be possible to reduce the incidence of complications associated with C. difficile infection (CDI) and mortality due to a state of hypercoagulability. A personalized therapeutic approach to reduce the inflammatory activity and prevent thromboembolic complications could be preliminarily defined to reduce mortality.