Publication date: Nov 20, 2024

The role of macrophage (McD8) cellular metabolism and reprogramming during TB infection is of great interest due to the influence of Mycobacterium spp. on McD8 bioenergetics. Recent studies have shown that M. tuberculosis induces a TLR2-dependent shift towards aerobic glycolysis, comparable to the established LPS induced pro-inflammatory M1 McD8 polarisation. Distinct differences in the metabolic profile of murine and human McD8 indicates species-specific differences in bioenergetics. So far, studies examining the metabolic potential of bovine McD8 are lacking, thus the basic bioenergetics of bovine and human McD8 were explored in response to a variety of innate immune stimuli. Cellular energy metabolism kinetics were measured concurrently for both species on a Seahorse XFe96 platform to generate bioenergetic profiles for the response to the bona-fide TLR2 and TLR4 ligands, FSL-1 and LPS respectively. Despite previous reports of species-specific differences in TLR signalling and cytokine production between human and bovine McD8, we observed similar respiratory profiles for both species. Basal respiration remained constant between stimulated McD8 and controls, whereas addition of TLR ligands induced increased glycolysis, as measured by the surrogate parameter ECAR. In contrast to McD8 stimulation with M. tuberculosis PPD, another TLR2 ligand, M. bovis PPD treatment significantly enhanced basal respiration rates and glycolysis only in human McD8. Respiratory profiling further revealed significant elevation of ATP-linked OCR and maximal respiration suggesting a strong OXPHOS activation upon M. bovis PPD stimulation in human McD8. Our results provide an exploratory set of data elucidating the basic respiratory profile of bovine vs. human McD8 that will not only lay the foundation for future studies to investigate host-tropism of the M. tuberculosis complex but may explain inflammatory differences observed for other zoonotic diseases.

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Original Article