The research described in this thesis has, using the zebrafish as a model system, shed new light on the intricate relationship between TB and DM2, in particular on the role of leptin, SHP-1 and... Show moreThe research described in this thesis has, using the zebrafish as a model system, shed new light on the intricate relationship between TB and DM2, in particular on the role of leptin, SHP-1 and glucocorticoids.Leptin plays an important role during TB infection and has a huge impact on insulin sensitivity in zebrafish larvae. Similarly to what has been observed in the murine model, leptin deficiency in zebrafish increased the bacterial burden and mortality during the infection, leading to hyperglycemia and the development of insulin resistance. In addition, a novel SHP-1/SHP-2 inhibitor, NSC-87877, was shown to represent a promising anti-diabetic drug that can be used for further DM2 research, as it is able to rescue the phenotype of the leptin-deficient zebrafish and to restore glucose transport to the tissues. In contrast to metformin, NSC-87877 can act at very early developmental stages and inhibits the function of SHP-1 and factors that underlay impaired glucose metabolism, whereas metformin is mostly known to improve insulin sensitivity. Additionally, treatment with the glucocorticoid beclomethasone attenuates the metabolic changes associated with the infection, and transcriptional alterations induced by beclomethasone treatment suggest that genes involved in glucose metabolism, insulin and leptin signaling all play an important role in the modulation of the metabolism.Our data show that zebrafish larvae represent an interesting model system to investigate the complex pathology of TB, and the studies described in this thesis in which this model has been used have provided novel insights into the molecular mechanisms underlying wasting syndrome and the possibilities for adjunctive glucocorticoid therapy to alleviate this metabolic state. Show less
Tuberculosis (TB) is the most prevalent bacterial infectious disease in the world, caused by the pathogen Mycobacterium tuberculosis (Mtb). In this study, we have used Mycobacterium marinum (Mm)... Show moreTuberculosis (TB) is the most prevalent bacterial infectious disease in the world, caused by the pathogen Mycobacterium tuberculosis (Mtb). In this study, we have used Mycobacterium marinum (Mm) infection in zebrafish larvae as an animal model for this disease to study the role of the myeloid differentiation factor 88 (Myd88), the key adapter protein of Toll-like receptors. Previously, Myd88 has been shown to enhance innate immune responses against bacterial infections, and in the present study, we have investigated the effect of Myd88 deficiency on the granuloma morphology and the intracellular distribution of bacteria during Mm infection. Our results show that granulomas formed in the tail fin from myd88 mutant larvae have a more compact structure and contain a reduced number of leukocytes compared to the granulomas observed in wild-type larvae. These morphological differences were associated with an increased bacterial burden in the myd88 mutant. Electron microscopy analysis showed that the majority of Mm in the myd88 mutant are located extracellularly, whereas in the wild type, most bacteria were intracellular. In the myd88 mutant, intracellular bacteria were mainly present in compartments that were not electron-dense, suggesting that these compartments had not undergone fusion with a lysosome. In contrast, approximately half of the intracellular bacteria in wild-type larvae were found in electron-dense compartments. These observations in a zebrafish model for tuberculosis suggest a role for Myd88-dependent signalling in two important phenomena that limit mycobacterial growth in the infected tissue. It reduces the number of leukocytes at the site of infection and the acidification of bacteria-containing compartments inside these cells. Show less
