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IL-4 and IL-13 are closely related canonical type-2 cytokines in mammals and have overlapping bioactivities via shared receptors. They are frequently activated together as part of the same immune response and are the signature cytokines produced by T-helper (Th)2 cells and type-2 innate lymphoid cells (ILC2), mediating immunity against extracellular pathogens. Little is known about the origin of type-2 responses, and whether they were an essential component of the early adaptive immune system that gave a fitness advantage by limiting collateral damage caused by metazoan parasites. Two evolutionary related type-2 cytokines, IL-4/13A and IL-4/13B, have been identified recently in several teleost fish that likely arose by duplication of an ancestral IL-4/13 gene as a consequence of a whole genome duplication event that occurred at the base of this lineage. However, studies of their comparative expression levels are largely missing and bioactivity analysis has been limited to IL-4/13A in zebrafish. Through interrogation of the recently released salmonid genomes, species in which an additional whole genome duplication event has occurred, four genomic IL-4/13 loci have been identified leading to the cloning of three active genes, IL-4/13A, IL-4/13B1 and IL-4/13B2, in both rainbow trout and Atlantic salmon. Comparative expression analysis by real-time PCR in rainbow trout revealed that the IL-4/13A expression is broad and high constitutively but less responsive to pathogen-associated molecular patterns (PAMPs) and pathogen challenge. In contrast, the expression of IL-4/13B1 and IL-4/13B2 is low constitutively but is highly induced by viral haemorrhagic septicaemia virus (VHSH) infection and during proliferative kidney disease (PKD) in vivo, and by formalin-killed bacteria, PAMPs, the T cell mitogen PHA, and the T-cell cytokines IL-2 and IL-21 in vitro. Moreover, bioactive recombinant cytokines of both IL-4/13A and B were produced and found to have shared but also distinct bioactivities. Both cytokines rapidly induce the gene expression of antimicrobial peptides and acute phase proteins, providing an effector mechanism of fish type-2 cytokines in immunity. They are anti-inflammatory via up-regulation of IL-10 and down-regulation of IL-1β and IFN-γ. They modulate the expression of cellular markers of T cells, macrophages and B cells, the receptors of IFN-γ, the IL-6 cytokine family and their own potential receptors, suggesting multiple target cells and important roles of fish type-2 cytokines in the piscine cytokine network. Furthermore both cytokines increased the number of IgM secreting B cells but had no effects on the proliferation of IgM+ B cells in vitro. Taken as a whole, fish IL-4/13A may provide a basal level of type-2 immunity whilst IL-4/13B, when activated, provides an enhanced type-2 immunity, which may have an important role in specific cell-mediated immunity. To our knowledge this is the first in-depth analysis of the expression, modulation and bioactivities of type-2 cytokines in the same fish species, and...

Mammalian interleukin-4 (IL-4) and IL-13 are T helper type 2 (Th2) cytokines with pleiotropic functions in immunity. They signal through receptors containing IL-4Rα and IL-2Rγ or IL-13Rα1. In addition, a decoy receptor, IL-13Rα2, is known to exist and modulates the function of IL-13. The existence of fish orthologues to mammalian IL-4 and IL-13 is still under debate. However, the receptor chains have been predicted in zebrafish, and we have previously cloned IL-2Rγ and IL-13Rα2 in rainbow trout. In this study, we have cloned a further five novel trout IL-4/13 receptors. Thus, each of the IL-4Rα, IL-13Rα1 and IL-13Rα2 chains has two copies. The identities of the receptors is supported by homology analysis, characteristic domain structure, phylogenetic tree analysis and synteny analysis in zebrafish. However, the characteristic WSXWS motif of structural importance in mammalian type I cytokine receptors is missing in all fish IL-4Rα and IL-13Rα1 molecules. All the receptors have a characteristic domain structure that is similar to their mammalian counterparts except for IL-13Rα1b that has the N-terminal Ig domain missing. Since this Ig domain is a specific and critical binding unit for IL-13 but not for IL-4 signalling, its absence potentially converts the IL-13Rα1b into a receptor that can only signal via IL-4 ligation. The existence of duplicated receptor genes perhaps suggests that more ligands still remain to be discovered that will bind these receptors. The duplicated receptors are differentially expressed in most tissues and cell lines examined, and their expression can be modulated by LPS, polyIC and IFN-γ in cell lines. In contrast, the T-cell stimulant phytohaemagglutinin increased the expression of IL-4Rα1 and IL-4Rα2, but not IL-13Rα1/2, suggesting a role of an IL-4-like molecule in T-cell growth/activation in fish.

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A series of novel indole-based PPAR agonists is described leading to discovery of 10k, a highly potent PPAR pan-agonist. The structural biology and molecular docking studies revealed that the distances between the acidic group and the linker, when a ligand was complexed with PPARgamma protein, were important for the potent activity. The hydrophobic tail part of 10k makes intensive hydrophobic interaction with the PPARgamma protein resulting in potent activity.

The synthesis and structure-activity relationship studies of novel indole derivatives as peroxisome proliferator-activated receptor (PPAR) agonists are reported. Indole, a drug-like scaffold, was studied as a core skeleton for the acidic head part of PPAR agonists. The structural features (acidic head, substitution on indole, and linker) were optimized first, by keeping benzisoxazole as the tail part, based on binding and functional activity at PPARgamma protein. The variations in the tail part, by introducing various heteroaromatic ring systems, were then studied. In vitro evaluation led to identification of a novel series of indole compounds with a benzisoxazole tail as potent PPAR agonists with the lead compound 14 (BPR1H036) displaying an excellent pharmacokinetic profile in BALB/c mice and an efficacious glucose lowering activity in KKA(y) mice. Structural biology studies of 14 showed that the indole ring contributes strong hydrophobic interactions with PPARgamma and could be an important moiety for the binding to the protein.