Aconitate Decarboxylase 1 Participates In The Control Of Pulmonary Brucella Infection In Mice

Author summaryBrucellosis is one of the most widespread bacterial zoonoses worldwide. Here, our aim was to identify the effector mechanisms controlling the early stages of intranasal infection with Brucella in mice. During the first 48 hours of infection, alveolar macrophages (AMs) are the main cells infected in the lungs. Using RNA sequencing, a hypothesis-free approach, we identified the aconitate decarboxylase 1 gene (Acod1) as one of the genes most upregulated in murine AMs in response to B. melitensis infection. We observed that mice deficient for Acod1 display a higher bacterial load in their lungs than wild-type (wt) mice following B. melitensis or B. abortus infection, demonstrating that Acod1 participates in the control of pulmonary Brucella infection. We observed that, unlike the wt strain of B. abortus, the isocitrate lyase (ICL) deficient B. abortus strain multiplies similarly in wt and Acod1 deficient mice, suggesting that bacterial ICL might be a target of Acod1 in AMs. As the mouse ACOD1 enzyme is similar to 80% identical in its amino acid sequence to the human ACOD1, the development of pharmacological agents that enhance ACOD1 function might help to control early stages of pulmonary Brucella infection.

Brucellosis is one of the most widespread bacterial zoonoses worldwide. Here, our aim was to identify the effector mechanisms controlling the early stages of intranasal infection with Brucella in C57BL/6 mice. During the first 48 hours of infection, alveolar macrophages (AMs) are the main cells infected in the lungs. Using RNA sequencing, we identified the aconitate decarboxylase 1 gene (Acod1; also known as Immune responsive gene 1), as one of the genes most upregulated in murine AMs in response to B. melitensis infection at 24 hours post-infection. Upregulation of Acod1 was confirmed by RT-qPCR in lungs infected with B. melitensis and B. abortus. We observed that Acod1(-/-) C57BL/6 mice display a higher bacterial load in their lungs than wild-type (wt) mice following B. melitensis or B. abortus infection, demonstrating that Acod1 participates in the control of pulmonary Brucella infection. The ACOD1 enzyme is mostly produced in mitochondria of macrophages, and converts cis-aconitate, a metabolite in the Krebs cycle, into itaconate. Dimethyl itaconate (DMI), a chemically-modified membrane permeable form of itaconate, has a dose-dependent inhibitory effect on Brucella growth in vitro. Interestingly, structural analysis suggests the binding of itaconate into the binding site of B. abortus isocitrate lyase. DMI does not inhibit multiplication of the isocitrate lyase deletion mutant Delta aceA B. abortus in vitro. Finally, we observed that, unlike the wt strain, the Delta aceA B. abortus strain multiplies similarly in wt and Acod1(-/-) C57BL/6 mice. These data suggest that bacterial isocitrate lyase might be a target of itaconate in AMs.