Fatty acid–induced NLRP3-ASC inflammasome activation interferes with insulin signaling

High-fat diet (HFD) and inflammation are key contributors to insulin resistance and type 2 diabetes (T2D). Interleukin (IL)-1β plays a role in insulin resistance; yet, how IL-1β is induced by fatty acid with HFD, and how this alters insulin signaling is unclear. We show that the saturated fatty acid, palmitate, but not unsaturated oleate, induces the activation of NLRP3-PYCARD inflammasome, causing caspase-1, IL-1β, and IL-18 production. This involves mitochondrial reactive oxygen species and the AMP-activated protein kinase and ULK1 autophagy signaling cascade. Inflammasome activation in hematopoietic cells impairs insulin signaling in several target tissues to reduce glucose tolerance and insulin sensitivity. Furthermore, IL-1β affects insulin sensitivity via TNF-independent and dependent pathways. These findings provide insights into the association of inflammation, diet and T2D

Atopic asthmatic patients have reduced airway inflammatory cell recruitment after inhaled endotoxin challenge compared with healthy volunteers

Atopic asthmatic patients are reported to be more sensitive to the effects of environmental endotoxin (LPS) than healthy volunteers (HVs). It is unknown whether this sensitivity is due to dysregulated inflammatory responses after LPS exposure in atopic asthmatic patients

NLRP3 (NALP3, Cryopyrin) Facilitates In Vivo Caspase-1 Activation, Necrosis, and HMGB1 Release via Inflammasome-Dependent and -Independent Pathways

Bacterial infection elicits a range of beneficial as well as detrimental host inflammatory responses. Key among these responses are macrophage/monocyte necrosis, release of the pro-inflammatory factor high-mobility group box 1 protein (HMGB1), and induction of the cytokine IL-1. While the control of IL-1β has been well-studied, processes that control macrophage cell death and HMGB-1 release in animals are poorly understood. This study utilizes Klebsiella pneumonia as a model organism since it elicits all three responses in vivo. The regulation of these responses is studied in the context of the inflammasome components, NLRP3 and ASC, which are important for caspase-1 activation and IL-1β release. Using a pulmonary infection model that reflects human infection, we show that K. pneumonia-induced mouse macrophage necrosis, HMGB-1 and IL-1β release are dependent on NLRP3 and ASC. K. pneumoniae infection of mice lacking Nlrp3 results in decreased lung inflammation and reduced survival relative to control indicating the overall protective role of this gene. Macrophage/monocyte necrosis and HMGB1 release are controlled independently of caspase-1 suggesting that the former two responses are separable from inflammasome-associated functions. These results provide critical in vivo validation that the physiologic role of NLRP3 and ASC is not limited to inflammasome formation

Radiation Combined With Thermal Injury Induces Immature Myeloid Cells

The continued development of nuclear weapons and the potential for thermonuclear injury necessitates the further understanding of the immune consequences after radiation combined with injury (RCI). We hypothesized that sub-lethal ionization radiation exposure combined with a full thickness thermal injury would result in the production of immature myeloid cells. Mice underwent either a 20% total body surface area (TBSA) full-thickness contact burn or sham procedure followed by a single whole body dose of 5-Gy radiation. Serum, spleen and peripheral lymph nodes were harvested at 3 and 14 days post-injury. Flow cytometry was performed to identify and characterize adaptive and innate cell compartments. Elevated pro- and anti-inflammatory serum cytokines and profound leukopenia were observed after RCI. A population of cells with dual expression of the cell surface markers Gr-1 and CD11b were identified in all experimental groups, but was significantly elevated after burn alone and RCI at 14 days post-injury. In contrast to the T-cell suppressive nature of myeloid-derived suppressor cells (MDSC) found after trauma and sepsis, myeloid cells after RCI augmented T-cell proliferation and were associated with a weak but significant increase in IFN-γ and a decrease in IL-10. This is consistent with previous work in burn injury indicating that a MDSC-like population increases innate immunity. RCI results in the increase of distinct populations of Gr-1+ CD11b+cells within the secondary lymphoid organs, and we propose these immature inflammatory myeloid cells provide innate immunity to the severely injured and immunocompromised host

Deletion of ripA Alleviates Suppression of the Inflammasome and MAPK by Francisella tularensis

Francisella tularensis is a facultative intracellular pathogen and potential biothreat agent. Evasion of the immune response contributes to the extraordinary virulence of this organism although the mechanism is unclear. Whereas wild-type strains induced low levels of cytokines, an F. tularensis ripA deletion mutant (LVSΔripA) provoked significant release of IL-1β, IL-18, and TNF-α by resting macrophages. IL-1β and IL-18 secretion was dependent on inflammasome components pyrin-caspase recruitment domain/apoptotic speck-containing protein with a caspase recruitment domain and caspase-1, and the TLR/IL-1R signaling molecule MyD88 was required for inflammatory cytokine synthesis. Complementation of LVSΔripA with a plasmid encoding ripA restored immune evasion. Similar findings were observed in a human monocytic line. The presence of ripA nearly eliminated activation of MAPKs including ERK1/2, JNK, and p38, and pharmacologic inhibitors of these three MAPKs reduced cytokine induction by LVSΔripA. Animals infected with LVSΔripA mounted a stronger IL-1β and TNF-α response than that of mice infected with wild-type live vaccine strain. This analysis revealed novel immune evasive mechanisms of F. tularensis

GvHD-associated, inflammasome-mediated loss of function in adoptively transferred myeloid-derived suppressor cells

Myeloid-derived suppressor cells (MDSC) are a naturally occurring immune regulatory population associated with inhibition of ongoing inflammatory responses. In vitro generation of MDSC from bone marrow have been shown to enhance survival in an acute model of lethal graft-versus-host disease (GvHD). However, donor MDSC infusion only partially ameliorates GvHD lethality. In order to improve the potential therapeutic benefit and ultimately survival outcomes we set out to investigate the fate of MDSC after transfer in the setting of acute GvHD (aGvHD). MDSC transferred to lethally irradiated recipients of allogeneic donor hematopoietic grafts are exposed to an intense inflammatory environment associated with aGvHD, which we now show directly undermines their suppressive capacity. Under conditioning regimen and GvHD inflammatory settings, MDSC rapidly lose suppressor function and their potential to inhibit GvHD lethality, which is associated with their induced conversion towards a mature inflammasome-activated state. We find even brief in vitro exposure to inflammasome-activating mediators negates the suppressive potential of cultured murine and human-derived MDSCs. Consistent with a role for the inflammasome, donor MDSC deficient in the adaptor ASC (Apoptosis-associated speck-like protein containing a CARD), that assembles inflammasome complexes, conferred improved survival of mice developing GvHD compared to wild-type donor MDSC. These data suggest the use of MDSC as a therapeutic approach for preventing GvHD and other systemic inflammatory conditions will be more effective when combined with approaches limiting in vivo MDSC inflammasome activation empowering MDSCs to maintain their suppressive potential

Atopic asthmatic patients have reduced airway inflammatory cell recruitment after inhaled endotoxin challenge compared with healthy volunteers

BACKGROUND: Atopic asthmatic patients are reported to be more sensitive to the effects of environmental endotoxin (LPS) than healthy volunteers (HVs). It is unknown whether this sensitivity is due to dysregulated inflammatory responses after LPS exposure in atopic asthmatic patients. OBJECTIVE: We sought to test the hypothesis that atopic asthmatic patients respond differentially to inhaled LPS challenge compared with HVs. METHODS: Thirteen allergic asthmatic (AA) patients and 18 nonallergic nonasthmatic subjects (healthy volunteers [HVs]) underwent an inhalation challenge to 20,000 endotoxin units of Clinical Center Reference Endotoxin (LPS). Induced sputum and peripheral blood were obtained at baseline and 6 hours after inhaled LPS challenge. Sputum and blood samples were assayed for changes in inflammatory cell numbers and cytokine and cell-surface marker levels on monocytes and macrophages. RESULTS: The percentage of neutrophils in sputum (%PMN) in induced sputum similarly and significantly increased in both HVs and AA patients after inhaled LPS challenge. However, the absolute numbers of leukocytes and PMNs recruited to the airways were significantly lower in AA patients compared with those seen in HVs with inhaled LPS challenge. Sputum levels of IL-6 and TNF-α were significantly increased in both cohorts, but levels of IL-1β and IL-18 were only significantly increased in the HV group. Cell-surface expression of Toll-like receptors 4 and 2 were significantly enhanced only in the HV group. CONCLUSIONS: The airway inflammatory response to inhaled LPS challenge is blunted in AA patients compared with that seen in HVs and accompanied by reductions in airway neutrophilia and inflammasome-dependent cytokine production. These factors might contribute to increased susceptibility to airway microbial infection or colonization in AA patients

Radiation Combined With Thermal Injury Induces Immature Myeloid Cells

The continued development of nuclear weapons and the potential for thermonuclear injury necessitates the further understanding of the immune consequences after radiation combined with injury (RCI). We hypothesized that sub-lethal ionization radiation exposure combined with a full thickness thermal injury would result in the production of immature myeloid cells. Mice underwent either a 20% total body surface area (TBSA) full-thickness contact burn or sham procedure followed by a single whole body dose of 5-Gy radiation. Serum, spleen and peripheral lymph nodes were harvested at 3 and 14 days post-injury. Flow cytometry was performed to identify and characterize adaptive and innate cell compartments. Elevated pro- and anti-inflammatory serum cytokines and profound leukopenia were observed after RCI. A population of cells with dual expression of the cell surface markers Gr-1 and CD11b were identified in all experimental groups, but was significantly elevated after burn alone and RCI at 14 days post-injury. In contrast to the T-cell suppressive nature of myeloid-derived suppressor cells (MDSC) found after trauma and sepsis, myeloid cells after RCI augmented T-cell proliferation and were associated with a weak but significant increase in IFN-γ and a decrease in IL-10. This is consistent with previous work in burn injury indicating that a MDSC-like population increases innate immunity. RCI results in the increase of distinct populations of Gr-1(+) CD11b(+)cells within the secondary lymphoid organs, and we propose these immature inflammatory myeloid cells provide innate immunity to the severely injured and immunocompromised host