Modulation of TLR4 Signalling by Novel Synthetic Glycolipids

Background: Vascular diseases represent a significant burden on healthcare systems in the developed world, heavily contributing to mortality and morbidity. TLR4 is an innate immune receptor integral to host defence against pathogens. However, overactivation of this response can be detrimental and is associated with development and progression of chronic inflammatory based conditions such as vascular diseases. Modulation of TLR4 activity therefore represents a potential avenue for development of pharmacological interventions. Objective: Professor Peri (University of Milano) has developed a series of synthetic glycolipid small molecule modulators of TLR4. The current body of work aimed to screen and assess the potential of several predicted agonist and antagonists to affect TLR4 signalling in a cellular system, investigate the mechanism of action of these compounds and to determine their validity as modulators of haematopoietic TLR4 signalling in human and mouse cell lines. Methods: Human and mouse monocyte and macrophages were used as a model. MTT was used to determine cytotoxic effects of ligands and small molecule antagonists and agonists. TLR4 activation was stimulated by exposure of cells to bacterial endotoxin or sterile oxidised lipids and effects. FP compounds were tested in the presence or absence of TLR4 ligands. Two readouts were used: activation of signalling mediators and endpoint proinflammatory protein production. These were measured using Western blot, ELISA, and a proinflammatory protein antibody array. Results: Screening revealed two antagonists and one agonist which were selected for further mechanistic studies. FP7 and FP12 were shown to negatively regulate both human and mouse MyD88-dependent signalling and human TRIF-dependent pathways. FP11 and FP18 were more effective at inducing MyD88-dependent signalling than TRIF-dependent but may still activate signalling via IFNAR. Conclusions: Results from the current body of work provide novel evidence towards the effects and mechanism of action of FP antagonists and agonists as modulators of TLR4-dependent proinflammatory signalling. Together, this helps to validate two antagonist and two agonist molecules as potential novel therapeutics for further preclinical investigations for treatment of inflammatory based disorders.