2.1. Targeting protein-protein interaction of macrophage migration inhibitory factor (MIF) in diabetes Research

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Macrophage migration inhibitory factor (MIF) has been identified as a versatile signalling protein that is involved in the pathogenesis of both type 1 and type 2 diabetes. MIF is a pro-inflammatory cytokine that activates immune cells by interaction with the CD74 receptor. Apart from its cytokine activity, MIF also harbours enzymatic activity mediated by distinct tautomerase and oxidoreductase active site pockets. Furthermore, MIF has been proposed to display chaperone activity for insulin, promoting correct insulin folding. The physical interaction between MIF and insulin appears to involve a MIF region that is distinct from the CD74 binding site and the tautomerase active site. Thus MIF harbours multiple functionalities on distinct structural locations that could potentially be targeted separately by small molecule modulators.

  • The MIF-CD74 interaction connects this cytokine to diabetes type 1. Patients with type 1 diabetes have significantly higher circulating MIF levels and higher levels of its receptor CD74 in monocytes (Drug Disc. Today, 2019, 24(2), 428-439). Importantly, the islets of MIF knock-out mice showed increased resistance to cytokine-induced death. This indicates that interference with the MIF-CD74 receptor interaction has potential to alleviate auto-immunity in type 1 diabetes. MIF is connected to the pathology of type 2 diabetes by its ability to modulate immune responses and insulin sensitivity in adipose tissue. Together with TNF, IL-6 and IL-1β, MIF is considered as one of the initiators of insulin resistance in adipocytes (J. Immunol., 179 (2007), pp. 5399-5406). Increased insulin resistance can be explained by interference of MIF with the phosphorylation of insulin receptor substrate-1 (IRS-1) as part of the insulin reponse pathway. Indirectly, MIF increases the production of adipokines and pro-inflammatory cytokines, which also reduces insulin sensitivity. In addition, MIF reportedly has chaperone activity, supporting correct insulin folding, which improves insulin bioactivity (Cytokine, 2014, 69(1), 39-46). Indeed, insulin derived from MIF knock-out mice is poorly functional, and the direct physical interaction between MIF and insulin was shown in an ELISA assay. These effects were not blocked by inhibition of MIF’s tautomerase activity, thereby indicating that the tautomerase active site region is likely not involved in MIF’s chaperone function. Taken together, MIF exerts disadvantageous functions in diabetes via interaction with the CD74 receptor, while it also appears to have advantageous functions via its insulin chaperone activity. Seemingly, both activities are mediated by distinct regions on the MIF protein surface.

  • The overall aim of this project is to design and develop small molecule modulators that selectively target the MIF-CD74 binding site, which provides perspectives towards drug discovery. The hypothesis is that optimized MIF inhibitors will have profound effects on the course of the diabetes disease.

  • In this project, the following methods are used:

    1. Development of novel assays to study interactions of MIF with the CD74 receptor in its cellular environment using bioluminescence and fluorescence-based assay formats.
    2. Screening of currently known MIF inhibitors for interference with MIF-CD74 binding followed by synthesis and screening of focused compound collections around the most promising scaffolds.
    3. Identification of inhibitors that block MIF-CD74 downstream signalling in macrophages and adipocytes using western blotting and RT-PCR for relevant proteins and genes, respectively.
    4. Counter screening of the identified MIF-CD74 inhibitors in biochemical assays for MIF-insulin chaperone activity. The proposed physical interaction between MIF and insulin will be confirmed using biochemical and structural studies.