Ornithine-A urea cycle metabolite enhances autophagy and controls Mycobacterium tuberculosis infection

Abstract

Abstract Alveolar macrophages (AMs) are the first cells encountered by TB pathogen and serve as the primary defense against Mycobacterium tuberculosis (Mtb) in the lungs. Studies have shown that liver macrophages (Kupffer cells; KCs) can control Mtb growth but, it is not clear how KCs completely eliminate mycobacterial infections. Thus, identification of these mechanisms will facilitate the development of immunomodulatory strategies to boost AM-mediated immunity to Mtb. In the current study, we compared Mtb growth in murine AMs, peritoneal (PMs), liver macrophages (Kupffer cells; KCs) and bone marrow-derived monocytes (BDMs). KCs restricted Mtb growth more efficiently than all other macrophages and monocytes despite equivalent infections. Differences in Mtb growth restriction were not due to differences in cytokine production, expression of Toll-like receptors 2 and 4, M1/M2 paradigm or apoptosis. We provide evidence that the enhanced autophagy efficiently restricts Mtb growth in KCs using flow cytometry, western blot, RT-PCR and confocal microscopy. A metabolomic comparison of Mtb-infected macrophages by liquid chromatography mass spectrometry indicated that ornithine (VIP=1.8) and imidazole (VIP=1.6) were two top-scoring metabolites found in Mtb-infected KCs and that acetylcholine was top-scoring in Mtb-infected AMs. Ornithine and imidazole inhibited Mtb growth in AMs by enhancing AMPK mediated autophagy whereas imidazole directly killed Mtb by reducing cytochrome P450 activity. Intranasal delivery of ornithine or imidazole or together restricted Mtb growth in Mtb-infected mouse lungs. Our study demonstrates that the metabolic differences in Mtb-infected AMs and KCs leads to differences in the restriction of Mtb growth.