Post-doctoral scientist, Hudson Institute of Medical Research
Hero turned villain: the role of inflammasomes during influenza virus infections
Severe influenza virus infections, such as those involving 'bird flu' are associated with an over reaction of the immune system which can cause fatal tissue damage. The hosts immune system utilises a protein called an inflammasome, which detects influenza virus infection resulting in promotion of inflammation. We have discovered using small molecule inhibitors, that inflammasomes are protective to the host in the initial phase (0-48 hours) of severe influenza virus infection. However, during the later stages we found inflammasomes contribute to disease by promoting hyperinflammation. Our studies suggest that targeting the inflammasome may be a viable therapeutic option for patients who present to hospital with severe influenza virus infections.
Furthermore, we have discovered a protein expressed by severe influenza viruses called PB1-F2, which can directly activate inflammasomes. Importantly, PB1-F2 protein from influenza viruses which cause mild disease did not activate the inflammasome. Our studies suggest that PB1-F2 protein expressed by severe and fatal influenza viruses may 'over activate' host inflammasomes leading to hyperinflammation.
Abstract: The ability for a host to recognize infection is critical for virus clearance and often begins with induction of inflammation. The PB1-F2 of pathogenic influenza A viruses (IAV) contributes to the pathophysiology of infection, although the mechanism for this is unclear. The NLRP3-inflammasome has been implicated in IAV pathogenesis, but whether IAV virulence proteins can be activators of the complex is unknown. We investigated whether PB1-F2-mediated activation of the NLRP3-inflammasome is a mechanism contributing to overt inflammatory responses to IAV infection. We show PB1-F2 induces secretion of pyrogenic cytokine IL-1β by activating the NLRP3-inflammasome, contributing to inflammation triggered by pathogenic IAV. Compared to infection with wild-type virus, mice infected with reverse engineered PB1-F2-deficient IAV resulted in decreased IL-1β secretion and cellular recruitment to the airways. Moreover, mice exposed to PB1-F2 peptide derived from pathogenic IAV had enhanced IL-1β secretion compared to mice exposed to peptide derived from seasonal IAV. Implicating the NLRP3-inflammasome complex specifically, we show PB1-F2 derived from pathogenic IAV induced IL-1β secretion was Caspase-1-dependent in human PBMCs and NLRP3-dependent in mice. Importantly, we demonstrate PB1-F2 is incorporated into the phagolysosomal compartment, and upon acidification, induces ASC speck formation. We also show that high molecular weight aggregated PB1-F2, rather than soluble PB1-F2, induces IL-1β secretion. Furthermore, NLRP3-deficient mice exposed to PB1-F2 peptide or infected with PB1-F2 expressing IAV were unable to efficiently induce the robust inflammatory response as observed in wild-type mice. In addition to viral pore forming toxins, ion channel proteins and RNA, we demonstrate inducers of NLRP3-inflammasome activation may include disordered viral proteins, as exemplified by PB1-F2, acting as host pathogen 'danger' signals. Elucidating immunostimulatory PB1-F2 mediation of NLRP3-inflammasome activation is a major step forward in our understanding of the aetiology of disease attributable to exuberant inflammatory responses to IAV infection.
Pub.: 06 Jun '13, Pinned: 24 Aug '17
Abstract: The emergence of avian H7N9 influenza A virus (IAV) in humans with associated high mortality, has highlighted the threat of a potential pandemic. Fatal H7N9 infections are characterised by hyperinflammation and increased cellular infiltrates in the lung. Currently there are limited therapies to address the pathologies associated with H7N9 infection and what virulence factors may contribute to these pathologies. We have found that PB1-F2 derived from H7N9 activates the NLRP3 inflammasome and induces lung inflammation and cellular recruitment that is NLRP3 dependent. We have also shown that H7N9 and A/Puerto Rico/H1N1 (PR8)PB1-F2 peptide treatment induces significant mitochondrial reactive oxygen production which contributes to NLRP3 activation. Importantly, treatment of cells or mice with the specific NLRP3 inhibitor MCC950 significantly reduces IL-1β maturation and lung cellular recruitment and cytokine production. Together, these results suggest that PB1-F2 from H7N9 avian IAV may be a major contributory factor to disease pathophysiology and excessive inflammation characteristic of clinical infections and that targeting the NLRP3 inflammasome may be an effective means to reduce the inflammatory burden associated with H7N9 infections.
Pub.: 02 Dec '16, Pinned: 24 Aug '17
Abstract: The inflammasome NLRP3 is activated by pathogen associated molecular patterns (PAMPs) during infection, including RNA and proteins from influenza A virus (IAV). However, chronic activation by danger associated molecular patterns (DAMPs) can be deleterious to the host. We show that blocking NLRP3 activation can be either protective or detrimental at different stages of lethal influenza A virus (IAV). Administration of the specific NLRP3 inhibitor MCC950 to mice from one day following IAV challenge resulted in hypersusceptibility to lethality. In contrast, delaying treatment with MCC950 until the height of disease (a more likely clinical scenario) significantly protected mice from severe and highly virulent IAV-induced disease. These findings identify for the first time that NLRP3 plays a detrimental role later in infection, contributing to IAV pathogenesis through increased cytokine production and lung cellular infiltrates. These studies also provide the first evidence identifying NLRP3 inhibition as a novel therapeutic target to reduce IAV disease severity.
Pub.: 11 Jun '16, Pinned: 24 Aug '17
Abstract: The severity of influenza A virus (IAV) infection can range from asymptotic to mild to severe. Infections, such as those seen following outbreaks of avian IAV, are associated with hyperinflammatory responses and the development of fatal disease. There is a continual threat that a novel or pandemic IAV will circulate in humans with high rates of mortality. The neuronal apoptosis inhibitor protein, class 2 transcription activator of the MHC, heterokaryon incompatibility, telomerase-associated protein 1, leucine-rich repeat, and pyrin domain-containing protein 3 (NLRP3) inflammasome is an innate immune sensor that has been shown to be critical for the secretion of the potent proinflammatory cytokines, IL-1β and IL-18, as well as chemokine production and cellular inflammation in vivo following IAV infection. Initial studies illustrated a protective role of NLRP3 during severe IAV infection in mice. However, the NLRP3 inflammasome may be a hero that turns villain in the later stages of severe IAV infection via the promotion of a hyperinflammatory state. Current treatments for patients who present to hospitals with a severe IAV infection are limited. The understanding of the mechanisms involved in the induction of NLRP3-dependent inflammation during severe IAV infections may provide new therapeutic targets that reduce human mortality.
Pub.: 07 Oct '16, Pinned: 24 Aug '17