Poster Presentation Lorne Infection and Immunity 2019

Characterising the role of guanylate binding proteins in tuberculosis (#166)

Nashied Peton 1 2 3 , Armin Deffur 3 4 , Daniel Fisch 5 , Eva Frickel 5 , Musa Mhlanga 3 , Anca Savulescu 3 , Allison Seeger 2 3 , Robert J Wilkinson 2 3 6 7 , Anna K Coussens 1 2 3
  1. Walter and Eliza Hall Institute, Parkville, Victoria, Australia
  2. Wellcome Centre for Infectious Diseases Research in Africa, Cape Town, South Africa
  3. Institute of Infectious Disease and Molecular Medicine, University of Cape Town, Cape Town, South Africa
  4. Department of Medicine, University of Cape Town, Cape Town, South Africa
  5. Host-Toxoplasma Interaction Laboratory, The Francis Crick Institute, London, United Kingdom
  6. Tuberculosis Laboratory, The Francis Crick Institute, London, United Kingdom
  7. Department of Medicine, Imperial College, London, United Kingdom

Guanylate Binding Proteins (GBPs) are a family of interferon (IFN)-inducible guanosine triphosphatases (GTPases) that mediate host protection in a number of bacterial and viral infections. Studies in mouse models of intracellular Gram-negative bacterial infection have shown that GBPs mediate pro-inflammatory cell death known as pyroptosis through inflammasome formation and Caspase-1 and -11 activation. In humans, Caspase-1, -4 and -5 mediate pyroptosis through activation of Gasdermin D producing an N-terminal cleavage product (GSDMD-NT) which binds inner membrane lipids forming pores and triggering cell death. Although the role of human GBPs in the context of mycobacterium tuberculosis (Mtb) infection is unclear, transcriptional signatures derived from whole blood of tuberculosis (TB) patients, compared to latent TB controls, invariantly include a disease-associated interferon signature dominated by upregulation of GBP1, 2, 4, 5 and 6. Moreover, upregulation of GBP1, 2, 5 has been seen more than 6 months before TB onset, suggestive of a contribution of GBPs to TB disease progression.

To characterise whether GBPs play a role in TB pathogenesis, we investigated the production and localisation of GBPs in human macrophages during in vitro Mtb infection and whether their induction results in pyroptosis via Caspase-mediated inflammasome activation. We characterised the gene expression profile of all 7 human GBP and both inflammatory and apoptotic Caspase genes in both type I & II IFN-stimulated and Mtb infected human monocyte-derived macrophages (MDM). We show that GBP induction is predominantly IFNγ driven, with GBP1-5 and Caspase-1 and -4 exhibiting the greatest induction in both IFN-stimulated and Mtb infected MDM. We also show that GBP induction correlates with cell death as measured by Lactate dehydrogenase (LDH) release in Mtb-infected MDM, an in vivo marker of cell death. Through siRNA-mediated knockdown of specific GBPs, we demonstrate that both LDH and IL1β levels (an indicator of Caspase-mediated inflammasome activation and pyroptosis) are reduced and cell death inhibited. These results suggest the utility of GBP genes as a potential target for host-directed therapies that prevent TB progression.