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Inhibition of GGPPS1 attenuated LPS-induced acute lung injury by suppressing the NLRP3 inflammasome

ABSTRACT: Rationale: Geranylgeranyl pyrophosphate synthase large subunit 1 (GGPPS1), a catalase downstream of the mevalonate pathway, regulates various pathological processes through balancing the production of farnesyl pyrophosphate and geranylgeranyl pyrophosphate. We sought to investigate whether GGPPS1 plays a role in mediating acute lung injury (ALI) using a mouse model of inflammation. Methods: Lipopolysaccharide (LPS) was intra-tracheally instilled to induce ALI in lung specific GGPPS1 knockout and wild-type mice. Expression of GGPPS1 in lung tissues and alveolar epithelial cells (AECs) was examined at different time points. Alveolar exudate, neutrophil infiltration, lung injury and cell death were determined. Change in global gene expression in response to GGPPS1 depletion was measured using mRNA microarray and verified in vivo and in vitro. Results: GGPPS1 levels increased significantly in lung tissues from LPS-induced ALI mice, where it showed a time- and dose-dependent increase in alveolar epithelial cells. Specific deletion of pulmonary GGPPS1 reduced the alveolar exudate and attenuated the severity of lung injury through inhibiting apoptosis of AECs. However, GGPPS1 deletion had limited effect on neutrophil counts and TNF-α levels in alveolar fluids. Deletion of GGPPS1 inhibited LPS-induced inflammasome activation, in terms of IL-1β release and pyroptosis, by down-regulating NLRP3 expression. Conclusions: Inhibition of pulmonary GGPPS1 attenuated LPS-induced ALI, predominantly by suppressing NLRP3 inflammasome activation.

ORGANISM(S): Mus musculus

PROVIDER: GSE89311 | GEO | 2017/08/15

SECONDARY ACCESSION(S): PRJNA351748

REPOSITORIES: GEO

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Project description:Acute lung injury (ALI)/acute respiratory distress syndrome (ARDS) is an inflammatory process of the lungs characterized by increased permeability of the alveolar-capillary membrane with subsequent interstitial/alveolar edema and diffuse alveolar damage. ALI/ARDS can be the results of either direct or indirect lung injury, with pneumonia being the most common direct pulmonary insult and sepsis the most common extra-pulmonary cause. In this study, we employed the murine lipopolysaccharide (LPS)-induced direct and indirect lung injury model to explore the pathogenic mechanisms of pulmonary and extra-pulmonary ARDS, using an unbiased, discovery and quantitative proteomic approach. A total of 1,017 proteins were both identified and quantified in bronchoalveolar lavage fluid (BALF) from control, intratracheal LPS (I.T. LPS, 0.1 mg/kg) and intraperitoneal LPS (I.P. LPS, 5 mg/kg) treated mice. The two LPS groups shared 13 up-regulated and 22 down-regulated proteins compared to the control group. Among them, molecules related to bronchial and type II alveolar epithelial cell functions including cell adhesion molecule 1 and surfactant protein B were reduced, whereas lactotransferrin and resistin like alpha involved in lung innate immunity were upregulated in both LPS groups. Proteomic profiling also identified significant differences in BALF proteins between I.T. and I.P. LPS groups. Ingenuity pathway analysis revealed that acute-phase response signaling was activated by both I.T. and I.P. LPS, however, the magnitude of activation is much greater in I.T. LPS group compared to I.P. LPS group. Intriguingly, two canonical signaling pathways, liver X receptor/retinoid X receptor activation and the production of nitric oxide and reactive oxygen species in macrophages, were activated by I.T. LPS but suppressed by I.P. LPS. In addition, CXCL15 (also known as lungkine) was also up-regulated by I.T LPS but down-regulated by I.P. LPS. In conclusion, our quantitative discovery-based proteomic approach identified commonalities as well as significant differences in BALF protein expression profiles in LPS-induced direct and indirect lung injury, and importantly, LPS-induced indirect lung injury results in suppression of select components of lung innate immunity, which could contribute to the so-called “immunoparalysis” in sepsis patients.

Project description:Inflammasome, activated by pathogen-derived and host-derived danger signals, constitutes a multimolecular signaling complex that serves as a platform for caspase-1 (CASP1) activation and interleukin-1beta (IL1B) maturation. The activation of NLRP3 inflammasome requires two-step signals. The first “priming” signal (Signal 1) enhances gene expression of inflammasome components. The second “activation” signal (Signal 2) promotes the assembly of inflammasome components. Deregulated activation of NLRP3 inflammasome contributes to the pathological processes of Alzheimer’s disease (AD) and multiple sclerosis (MS). However, at present, the precise mechanism regulating NLRP3 inflammasome activation and deactivation remains largely unknown. By genome-wide gene expression profiling, we studied the molecular network of NLRP3 inflammasome activation-responsive genes in a human monocyte cell line THP-1 sequentially given two-step signals. We identified the set of 83 NLRP3 inflammasome activation-responsive genes. Among them, we found the NR4A nuclear receptor family NR4A1, NR4A2, and NR4A3, the EGR family EGR1, EGR2, and EGR3, the IkappaB family NFKBIZ, NFKBID, and NFKBIA as a key group of the genes that possibly constitute a negative feedback loop for shutting down inflammation following NLRP3 inflammasome activation. By molecular network analysis, we identified a complex network of NLRP3 inflammasome activation-responsive genes involved in cellular development and death, and immune and inflammatory responses, where transcription factors AP-1, NR4A, and EGR serve as a hub. Thus, NLRP3 inflammasome activation-responsive genes constitute the molecular network composed of a set of negative feedback regulators for prompt resolution of inflammation. To load the Signal 1 (S1), THP-1 cells were incubated for 3 hours in the culture medium with or without inclusion of 0.2 microgram/ml lipopolysaccharide (LPS). To load the Signal 2 (S2), they were incubated further for 2 hours in the culture medium with inclusion of 10 microM nigericin sodium salt dissolved in ethanol or the equal v/v% concentration of ethanol (vehicle), followed by processing for microarray analysis on Human Gene 1.0 ST Array (Affymetrix).

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Inhibition of GGPPS1 attenuated LPS-induced acute lung injury by suppressing the NLRP3 inflammasome

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