Interaction between CD40, a member of the tumor necrosis factor receptor (TNFR) superfamily, and its ligand CD40L, a 39-kDa glycoprotein, is essential for the development of humoral and cellular immune responses 1,2 . Selective blockade or activation of this pathway provides the ground for the development of new treatments against immunologically based diseases 3,4 and malignancies 5,6 . Like other members of the TNF superfamily, CD40L monomers self-assemble around a threefold symmetry axis to form noncovalent homotrimers that can each bind three receptor molecules 7,8 . Here, we report on the structure-based design of small synthetic molecules with C 3 symmetry that can mimic CD40L homotrimers. These molecules interact with CD40, compete with the binding of CD40L to CD40, and reproduce, to a certain extent, the functional properties of the much larger homotrimeric soluble CD40L. Architectures based on rigid C 3 -symmetric cores may thus represent a general approach to mimicking homotrimers of the TNF superfamily.CD40L is expressed mainly on activated T cells, whereas its cognate receptor, CD40, is constitutively expressed on dendritic cells (DC), macrophages and B cells. The engagement of CD40 by its ligand contributes to regulation of B cell proliferation, immunoglobulin production, immunoglobulin class switching, germinal center formation and development of B cell memory 1 . Moreover, CD40-CD40L interaction has an essential role in cellular immune response in which CD40 ligation activates DCs, 'licensing' them to present antigen to cytotoxic T cells by increasing MHC and costimulatory molecule expression and by producing high levels of IL-12, a T cell-stimulating cytokine [9][10][11] . Antibodies against CD40 with agonist activity have been used to increase immune response in infectious diseases 12,13 and in cancer immunotherapy 5,6 . All of these results underscore the important therapeutic applications that could emerge from the development of small-molecule CD40 agonists.Although ligand-induced dimerization is a general mechanism for activating receptors of cytokines and growth factors 14 , signaling through receptors of the TNFR superfamily strongly relies on the formation of stoichiometrically defined C 3 -symmetric complexes 7 . The structures of several TNF family members in complex with their cognate receptors show that each ligand homotrimer interacts with three monomeric receptor chains 7,15,16 . The geometry of the resulting 3:3 hexameric complex is favorable to the formation of an internal 3:3 signaling complex between the intracellular tail of the receptor and transduction proteins, ultimately activating downstream effector pathways 7 .Despite the difficulty in identifying small molecules that can disrupt protein-protein interactions, synthetic agonists of homodimeric cytokine receptors have been reported 17,18 . The ability of these molecules to dimerize cell-surface receptors is a major determinant of their effector functions 19 . In the present study, we have developed CD40L mimetics by integr...

In the present study, we aimed to investigate the neuromodulatory role played by hypothalamic brain-derived neurotrophic factor (BDNF) in the regulation of acute cardiovascular and feeding responses to melanocortin-4 receptor (MC4R) activation. In vitro, a selective MC4R agonist, MK1, stimulated BDNF release from isolated rat hypothalami and this effect was blocked by preincubation with the MC3/4R antagonist SHU-9119. In vivo, peripheral administration of MK1 decreased food intake in rats and this effect was blocked by pretreatment with an anti-BDNF antibody administered into the third ventricle. When anorexia was induced with the cannabinoid-1 receptor (CB1R) antagonist AM251, the anti-BDNF antibody did not prevent the reduction in food intake. Peripheral administration of MK1 also increased mean arterial pressure, heart rate and body temperature. These effects were prevented by pretreatment with the anti-BDNF antibody whereas the intracerebroventricular administration of BDNF caused changes similar to those of MK1. These findings demonstrate for the first time that activation of MC4R leads to an acute release of BDNF in the hypothalamus. This release is a prerequisite for MC4R-induced effects on appetite, body temperature and cardiovascular function. By contrast, CB1R antagonist-mediated anorexia is independent of the MC4R/BDNF pathway. Overall, these results show that BDNF is an important downstream mediator of the MC4R pathway.

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