ePoster Presentation 49th Annual Scientific Meeting of the Australian and New Zealand Society for Immunology 2021

Deciphering mechanisms of TLR-inducible mitochondrial fission and fission-mediated antimicrobial responses in macrophages (#205)

Syeda Farhana Afroz 1 , Divya Ramnath 1 , Kaustav Das Gupta 1 , Ina Kirmes 2 , Antje Blumenthal 3 , Steven Zuryn 2 , Ronan Kapetanovic 1 4 , Matt Sweet 1
  1. Institute for Molecular Bioscience (IMB), IMB Centre for Inflammation and Disease Research and Australian Infectious Diseases Research Centre, The University of Queensland, Brisbane, QLD, Australia
  2. Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, Brisbane, QLD, Australia
  3. The University of Queensland Diamantina Institute, Faculty of Medicine, The University of Queensland, Brisbane, QLD, Australia
  4. Friedrich Miescher Institute for Biomedical Research & Faculty of Sciences, University of Basel, Basel, Switzerland

Mitochondria have a multitude of functions beyond energy generation. Mitochondrial dynamics (the balance between mitochondrial fission and fusion) has been implicated in regulating key macrophage functions, such as inflammatory and antimicrobial responses. This study focused on deciphering the upstream mechanisms of mitochondrial fission, along with a novel role for fission in macrophage antimicrobial responses. Quantitative analysis of mitochondrial numbers and morphology reveal that treatment of mouse bone marrow-derived macrophages (BMM) with LPS promotes toll-like receptor 4 (Tlr4)-dependent mitochondrial fission. Fission is triggered as early as 1 h post-stimulation, is sustained over a 24 h time course, and is dependent on the TLR adaptor protein MyD88. Drp1, a GTPase that is essential for mitochondrial fission in other cellular systems, was recruited to mitochondria in response to LPS. Furthermore, the LPS-inducible fission response was defective in Drp1-silenced BMM, Drp1-deleted (CRISPR) RAW264.7 cells and Drp1-/- mouse embryonic fibroblasts. Since fission has been linked to LPS-inducible glycolysis, we next investigated a role for the glycolysis-promoting class IIa histone deacetylase (HDAC), Hdac7, in LPS-inducible fission. Fission was abrogated in Hdac7-deficient macrophages and amplified in primary macrophages overexpressing Hdac7. Moreover, the class IIa HDAC inhibitor TMP195 attenuated LPS-inducible fission in BMM. However, an enzyme-dead Hdac7 mutant was able to restore LPS-inducible fission in Hdac7-deficient BMM. This suggests that Hdac7 promotes LPS-inducible fission independently of its enzymatic activity. In investigating biological roles of Tlr4-inducible fission, we found that pharmacological or genetic targeting of this response compromised the ability of macrophages to clear infection by non-pathogenic E. coli. Investigation of potential antimicrobial mechanisms identified a likely role for inducible antimicrobial gene expression via the mitochondrial unfolded protein response (UPR) pathway. In summary, this study has thus far delineated a pathway in which TLR4 activation promotes Drp1-mediated mitochondrial fission via MyD88- and Hdac7, enabling effective macrophage antimicrobial responses.