Masanori A. Murayama

Free Fatty Acids-Sensing G Protein-Coupled Receptors in Drug Targeting and Therapeutics

G protein-coupled receptor (GPCR) (also known as seven-transmembrane domain receptor) superfamily represents the largest protein family in the human genome. These receptors respond to various physiological ligands such as photons, odors, pheromones, hormones, ions, and small molecules including amines, amino acids to large peptides and steroids. Thus, GPCRs are involved in many diseases and the target of around half of all conventional drugs. The physiological roles of free fatty acids (FFAs), in particular, long-chain FFAs, are important for the development of many metabolic disease including obesity, diabetes, and atherosclerosis. In the past half decade, deorphanization of several GPCRs has revealed that GPR40, GPR41, GPR43, GPR84 and GPR120 sense concentration of extracellular FFAs with various carbon chain lengths. GPR40 and GPR120 are activated by medium- and long-chain FFAs. GPR84 is activated by medium- chain, but not long-chain, FFAs. GPR41 and GPR43 are activated by short-chain FFAs. GPR40 is highly expressed in pancreatic beta cells and plays a crucial role in FFAs-induced insulin secretion. GPR120 is mainly expressed in enteroendocrine cells and plays an important role for FFAs-induced glucagon-like peptide-1. GPR43 is abundant in leukocytes and adipose tissue, whilst GPR41 is highly expressed in adipose tissue, the pancreas and leukocytes. GPR84 is expressed in leukocytes and monocyte/macrophage. This review aims to shed light on the physiological roles and development of drugs targeting these receptors.

Excess IL-1 Signaling Enhances the Development of Th17 Cells by Downregulating TGF-β–Induced Foxp3 Expression

IL-1R antagonist–deficient (Il1rn−/−) mice develop autoimmune arthritis in which IL-17A plays a crucial role. Although many studies have shown that Th17 cell differentiation is dependent on TGF-β and IL-6, we found that Th17 cells developed normally in Il1rn−/−Il6−/− mice in vivo. Then, we analyzed the mechanisms of Th17 cell differentiation in Il1rn−/−Il6−/− mice. We found that IL-21 production was increased in the lymph nodes of Il1rn−/− mice, naive Il6−/− CD4+ T cells differentiated into Th17 cells when cultured with TGF-β and IL-21, and the differentiation was greatly enhanced when IL-1 was added to the culture. Th17 cell differentiation was not induced by either TGF-β or IL-1 alone or in combination. IL-21 induced IL-1R expression in naive CD4+ T cells, and IL-1 inhibited TGF-β–induced Foxp3 expression, resulting in the promotion of Th17 cell differentiation. Furthermore, IL-1 augmented the expression of Th17 cell–specific transcription factors such as Nfkbiz and Batf. These results indicate that excess IL-1 signaling can overcome the requirement of IL-6 in the differentiation of Th17 cells by suppressing Foxp3 expression and inducing Th17 cell–specific transcription factors.

CTRP3 plays an important role in the development of collagen-induced arthritis in mice

Rheumatoid arthritis (RA) is an autoimmune inflammatory disease exhibited most commonly in joints. We found that the expression of C1qtnf3, which encodes C1q/TNF-related protein 3 (CTRP3), was highly increased in two mouse RA models with different etiology. To elucidate the pathogenic roles of CTRP3 in the development of arthritis, we generated C1qtnf3(-/-) mice and examined the development of collagen-induced arthritis in these mice. We found that the incidence and severity score was higher in C1qtnf3(-/-) mice compared with wild-type (WT) mice. Histopathology of the joints was also more severe in C1qtnf3(-/-) mice. The levels of antibodies against type II collagen and pro-inflammatory cytokine mRNAs in C1qtnf3(-/-) mice were higher than WT mice. These observations indicate that CTRP3 plays an important role in the development of autoimmune arthritis, suggesting CTRP3 as a possible medicine to treat RA.

Optical monitoring of progressive synchronization in dentate granule cells during population burst activities

Monitoring multiple neurons is essential for understanding neuronal network activities. While calcium imaging from a population of cells is an effective method to study the network dynamics of a neural structure, it has been difficult to image from densely packed structures, such as the granule cell layer of the dentate gyrus, due to overlap of the cells. We have developed a novel method to label multiple granule cells with a Ca2+ indicator in rat hippocampal slices using Oregon Green 488u2003BAPTA‐1u2003(OGB‐1)u2003AM. Synchronized burst activities (0.3–1.4u2003Hz), which were induced by applying 50u2003µm 4‐aminopyridine, were monitored extracellularly with a glass electrode placed at the granule cell layer in the dentate gyrus. During the burst activities, spontaneously occurring action potential‐induced Ca2+ transients from multiple (4–12) granule cells were monitored with a cooled CCD camera with single‐cell resolution. Temporal structures of firing patterns from the multiple neurons were determined from Ca2+ transients. In each single‐burst‐event recorded from the extracellular electrode, each neuron fired synchronously within a 200u2003ms time window. The latency and its variance from the onset time of the single‐burst‐events to one of the Ca2+ transients decreased over time (<u20037.5u2003min). These results indicate that the synchrony of the action potentials within a single‐burst‐event was enhanced as the burst activities proceeded. This progressive synchronization may be a key feature in making self‐organizing neuronal networks.

CTRP6 is an endogenous complement regulator that can effectively treat induced arthritis

The complement system is important for the host defence against infection as well as for the development of inflammatory diseases. Here we show that C1q/TNF-related protein 6 (CTRP6; gene symbol C1qtnf6) expression is elevated in mouse rheumatoid arthritis (RA) models. C1qtnf6−/− mice are highly susceptible to induced arthritis due to enhanced complement activation, whereas C1qtnf6-transgenic mice are refractory. The Arthus reaction and the development of experimental autoimmune encephalomyelitis are also enhanced in C1qtnf6−/− mice and C1qtnf6−/− embryos are semi-lethal. We find that CTRP6 specifically suppresses the alternative pathway of the complement system by competing with factor B for C3(H2O) binding. Furthermore, treatment of arthritis-induced mice with intra-articular injection of recombinant human CTRP6 cures the arthritis. CTRP6 is expressed in human synoviocytes, and CTRP6 levels are increased in RA patients. These results indicate that CTRP6 is an endogenous complement regulator and could be used for the treatment of complement-mediated diseases.

IL-1R2 deficiency suppresses dextran sodium sulfate-induced colitis in mice via regulation of microbiota

Ulcerative colitis (UC) is an inflammatory disease of the colon. IL1R2, which encodes IL-1 receptor type 2 (IL-1R2), was reported as a risk gene for UC. To elucidate the roles of IL-1R2 in the development of colitis, we examined the development of dextran sodium sulfate-induced colitis, a mouse model for UC using Il1r2-/- mice. We found the severity score of colitis was milder in Il1r2-/- mice compared with wild-type (WT) mice when they were housed separately, however the severity score was similar when they were housed in a cage. In the separate housing condition, relative contents of Actinobacteria and Bacilli in feces of Il1r2-/- mice were lower than that of WT mice. Furthermore, IL-1β induced the expression of antimicrobial peptides (AMPs) from colon. Thus, we show that IL-1R2 is harmful for the development of colitis, because IL-1R2 promotes the growth of proinflammatory intestinal microbiota by suppressing IL-1β-induced AMP production.

IL-36α from Skin-Resident Cells Plays an Important Role in the Pathogenesis of Imiquimod-Induced Psoriasiform Dermatitis by Forming a Local Autoamplification Loop

IL-36α (gene symbol Il1f6), a member of the IL-36 family, is closely associated with inflammatory diseases, including colitis and psoriasis. In this study, we found that Il1f6−/− mice developed milder psoriasiform dermatitis upon treatment with imiquimod, a ligand for TLR ligand 7 (TLR7) and TLR8, whereas Il1f6−/− mice showed similar susceptibility to dextran sodium sulfate–induced colitis to wild-type mice. These effects were observed in both cohoused and separately housed conditions, and antibiotic treatment did not cancel the resistance of Il1f6−/− mice to imiquimod-induced dermatitis. Bone marrow (BM) cell transfer revealed that IL-36α expression in skin-resident cells is important for the pathogenesis of dermatitis in these mice. Following stimulation with IL-36α, the expression of Il1f6 and Il1f9 (IL-36γ), but not Il1f8 (IL-36β), was enhanced in murine BM-derived Langerhans cells (BMLCs) and murine primary keratinocytes but not in fibroblasts from mice. Upon stimulation with agonistic ligands of TLRs and C-type lectin receptors (CLRs), Il1f6 expression was induced in BMLCs and BM-derived dendritic cells. Furthermore, IL-36α stimulation resulted in significantly increased gene expression of psoriasis-associated Th17-related cytokines and chemokines such as IL-1α, IL-1β, IL-23, CXCL1, and CXCL2 in BMLCs and fibroblasts, and IL-1α, IL-1β, IL-17C, and CXCL2 in keratinocytes. Collectively, these results suggest that TLR/CLR signaling–induced IL-36α plays an important role for the development of psoriasiform dermatitis by enhancing Th17-related cytokine/chemokine production in skin-resident cells via a local autoamplification loop.