Guanylate-binding protein 5 licenses caspase-11 for Gasdermin-D mediated host resistance to Brucella abortus infection

Abstract

Innate immune response against Brucella abortus involves activation of Toll-like receptors (TLRs) and NOD-like receptors (NLRs). Among the NLRs involved in the recognition of B. abortus are NLRP3 and AIM2. Here, we demonstrate that B. abortus triggers non-canonical inflammasome activation dependent on caspase-11 and gasdermin-D (GSDMD). Additionally, we identify that Brucella-LPS is the ligand for caspase-11 activation. Interestingly, we determine that B. abortus is able to trigger pyroptosis leading to pore formation and cell death, and this process is dependent on caspase-11 and GSDMD but independently of caspase-1 protease activity and NLRP3. Mice lacking either caspase-11 or GSDMD were significantly more susceptible to infection with B. abortus than caspase-1 knockout or wild-type animals. Additionally, guanylate-binding proteins (GBPs) present in mouse chromosome 3 participate in the recognition of LPS by caspase-11 contributing to non-canonical inflammasome activation as observed by the response of Gbpchr3-/- BMDMs to bacterial stimulation. We further determined by siRNA knockdown that among the GBPs contained in mouse chromosome 3, GBP5 is the most important for Brucella LPS to be recognized by caspase-11 triggering IL-1β secretion and LDH release. Additionally, we observed a reduction in neutrophil, dendritic cell and macrophage influx in spleens of Casp11-/- and Gsdmd-/- compared to wild-type mice, indicating that caspase-11 and GSDMD are implicated in the recruitment and activation of immune cells during Brucella infection. Finally, depletion of neutrophils renders wild-type mice more susceptible to Brucella infection. Taken together, these data suggest that caspase-11/GSDMD-dependent pyroptosis triggered by B. abortus is important to infection restriction in vivo and contributes to immune cell recruitment and activation.

Guanylate-binding proteins at the crossroad of noncanonical inflammasome activation during bacterial infections

“…Indeed, due to the hydrophobic nature of lipid A moiety of LPS, GBPs may facilitate caspase‐11 binding to intracellular LPS itself and also LPS from experimental transfected liposomal membranes . Accordingly, our recent data support the idea that mGBP5 contributes to the recognition of B. abortus LPS incorporated within liposomal membranes by caspase‐11 …”

“…Further experiments established that among the GBPs contained in mouse chromosome 3, mGBP5 is the most relevant for the recognition of Brucella LPS by caspase‐11, triggering BMDM pore formation and IL‐1β secretion . Collectively, these results suggest that the GBPs are central to target and disrupt the PCV revealing B. abortus LPS to caspase‐11 …”

“…Moreover, a decreased number of disrupted PCVs was observed in cells deficient in GBP chr3 when compared to wild‐type cells, suggesting that GBPs orchestrate host surveillance during B. abortus infection. Besides, GBP chr3 machinery is essential for B. abortus induction of noncanonical inflammasome activation and pyroptosis in BMDMs . Further experiments established that among the GBPs contained in mouse chromosome 3, mGBP5 is the most relevant for the recognition of Brucella LPS by caspase‐11, triggering BMDM pore formation and IL‐1β secretion .…”

“…Similarly, caspase‐11 controlled Brucella melitensis joint infection and exacerbated joint inflammatory response against this pathogen . Moreover, recent data revealed that during B. abortus systemic infection, caspase‐11 −/− mice are more susceptible compared to wild‐type animals and they recruited fewer immune cells such as neutrophils, Mϕ s, and dendritic cells (DCs) in mouse spleens . Additionally, Gram‐negative bacteria such as Burkholderia pseudomallei and B. thailandensis that naturally invade the cytosol are targeted by caspase‐11.…”

“…Interestingly, the levels of CD62L on neutrophils were higher in Gsdmd −/− infected animals compared to wild‐type, which is related to less activated neutrophils. In addition, depletion of neutrophils in wild‐type mice increases susceptibility to bacterial infection, indicating a prominent role of GSDMD in B. abortus infection restriction …”