Obesity underpins the development of numerous chronic diseases, such as type II diabetes mellitus. It is well established that obesity negatively alters immune cell frequencies and functions. Mucosal-associated invariant T (MAIT) cells are a population of innate T cells, which we have previously reported are dysregulated in obesity, with altered circulating and adipose tissue frequencies and a reduction in their IFN-g production, which is a critical effector function of MAIT cells in host defense. Hence, there is increased urgency to characterize the key molecular mechanisms that drive MAIT cell effector functions and to identify those which are impaired in the obesity setting. In this study, we found that MAIT cells significantly upregulate their rates of glycolysis upon activation in an mTORC1-dependent manner, and this is essential for MAIT cell IFN-g production. Furthermore, we show that mTORC1 activation is dependent on amino acid transport via SLC7A5. In obese patients, using RNA sequencing, Seahorse analysis, and a series of in vitro experiments, we demonstrate that MAIT cells isolated from obese adults display defective glycolytic metabolism, mTORC1 signaling, and SLC7A5 aa transport. Collectively, our data detail the intrinsic metabolic pathways controlling MAIT cell cytokine production and highlight mTORC1 as an important metabolic regulator that is impaired in obesity, leading to altered MAIT cell responses.

Significance to metallomicsDithiol gliotoxin is a near-terminal biosynthetic intermediate from the gliotoxin biosynthetic pathway in the human pathogen Aspergillus fumigatus. Chemically reduced gliotoxin, dithiol gliotoxin (DTG), is revealed as a biological zinc chelator, and conversely, zinc can relieve the hitherto cryptic fungal autotoxicity of DTG. There is a systems-wide impact of zinc chelation by DTG on the fungal proteome, and we suggest it is DTG, as opposed to gliotoxin, which chelates zinc from metalloproteins. Since gliotoxin can be sequestered by both fungi and bacteria, our findings infer a new avenue to interfere with, and exploit, cellular zinc homeostasis in microorganisms. IntroductionGliotoxin and holomycin are microbial natural products, which are produced by fungal and bacterial spp., respectively (Fig. 1). [1][2][3] Both are low molecular mass metabolites, and each contains a disulphide bridge formed by the action of oxidoreductases, namely GliT and HlmI, on the respective dithiol precursor (Fig. 1). [4][5][6] Disulphide bridge formation is essential for microbial self-protection against these reactive dithiol intermediates, and is a pre-requisite for the Major Facilitator Superfamily transporter GliA-mediated secretion of gliotoxin by Aspergillus fumigatus. 5-8Both metabolites are also present as bis-thiomethylated forms, and gliotoxin bis-thiomethyltransferase GtmA converts dithiol gliotoxin (DTG) to bis-dethiobis(methylthio)gliotoxin (BmGT) in A. fumigatus, whereas the origin of the cognate activity against dithiol holomycin in Streptomyces clavuligeris is unknown (Fig. 1). 9,10Bernardo et al. have shown that upon uptake by eukaryotic cells,