Multi‐drug‐resistant tuberculosis is a worldwide problem, and there is an urgent need for host‐derived therapeutic targets, circumventing emerging drug resistance. We have previously shown that hypoxia‐inducible factor‐1α (Hif‐1α) stabilisation helps the host to clear mycobacterial infection via neutrophil activation. However, Hif‐1α stabilisation has also been implicated in chronic inflammatory diseases caused by prolonged neutrophilic inflammation. Comorbid infection and inflammation can be found together in disease settings, and it remains unclear whether Hif‐1α stabilisation would be beneficial in a holistic disease setting. Here, we set out to understand the effects of Hif‐1α on neutrophil behaviour in a comorbid setting by combining two well‐characterised in vivo zebrafish models – TB infection (Mycobacterium marinum infection) and sterile injury (tailfin transection). Using a local Mm infection near to the tailfin wound site caused neutrophil migration between the two sites that was reduced during Hif‐1α stabilisation. During systemic Mm infection, wounding leads to increased infection burden, but the protective effect of Hif‐1α stabilisation remains. Our data indicate that Hif‐1α stabilisation alters neutrophil migration dynamics between comorbid sites and that the protective effect of Hif‐1α against Mm is maintained in the presence of inflammation, highlighting its potential as a host‐derived target against TB infection.

26Multi-drug resistant tuberculosis is a worldwide problem and there is an urgent need 27 for host-derived therapeutic targets, circumventing emerging drug resistance. We 28 have previously shown that hypoxia inducible-1 (Hif-1) stabilisation helps the host 29 to clear mycobacterial infection via neutrophil activation. However, Hif-1 stabilisation 30 has also been implicated in chronic inflammatory diseases caused by prolonged 31 neutrophilic inflammation. Comorbid infection and inflammation can be found together 32 in disease settings, so it is unclear as to whether Hif-1 stabilisation would be 33 beneficial in a holistic disease setting. Here, we set out to understand the effects of 34Hif-1 on neutrophil behaviour in disease-relevant settings by combining two well-35 characterised in vivo zebrafish models: TB infection (Mycobacterium marinum 36 infection) and wounding (tailfin transection). We demonstrate during systemic 37 infection, that wounding leads to increased infection burden, but the protective effect 38 of Hif-1 stabilisation remains. A local Mm infection near to the tailfin wound site 39 caused neutrophil migration between sites that was reduced by Hif-1 stabilisation. 40Our data indicate that the protective effect of Hif-1 against Mm is maintained in the 41 presence of inflammation, highlighting its potential as a host-derived target against TB 42 infection in a disease relevant setting. 43 44 and could work in combination with current antimicrobials to completely clear patients 51 of TB burden more rapidly [2]. 52

The interplay between hypoxia-inducible factors (HIFs) and transforming growth factor beta (TGF-β) is critical for both inflammation and angiogenesis. In hereditary hemorrhagic telangiectasia (HHT), we have previously observed that impairment of the TGF-β pathway is associated with downregulation of HIF-1α. HIF-1α accumulation is mandatory in situations of altered energy demand, such as during infection or hypoxia, by adjusting cell metabolism. Leukocytes undergo a HIF-1α-dependent switch from aerobic mitochondrial respiration to anaerobic glycolysis (glycolytic switch) after stimulation and during differentiation. We postulate that the decreased HIF-1α accumulation in HHT leads to a clinically observed immunodeficiency in these patients. Examination of HIF-1α and its target genes in freshly isolated peripheral blood mononuclear cells (PBMCs) from HHT patients revealed decreased gene expression and protein levels of HIF-1α and HIF-1α-regulated glycolytic enzymes. Treatment of these cells with the HIF–prolyl hydroxylase inhibitor, Roxadustat, rescued their ability to accumulate HIF-1α protein. Functional analysis of metabolic flux using a Seahorse FX extracellular flux analyzer showed that the extracellular acidification rate (indicator of glycolytic turnover) after Roxadustat treatment was comparable to non-HHT controls, while oxygen consumption (indicator of mitochondrial respiration) was slightly reduced. HIF stabilization may be a potential therapeutic target in HHT patients suffering from infections.