A GPBAR1 (TGR5) Small Molecule Agonist Shows Specific Inhibitory Effects on Myeloid Cell Activation In Vitro and Reduces Experimental Autoimmune Encephalitis (EAE) In Vivo

Abstract

GPBAR1 is a G protein-coupled receptor that is activated by certain bile acids and plays an important role in the regulation of bile acid synthesis, lipid metabolism, and energy homeostasis. Recent evidence suggests that GPBAR1 may also have important effects in reducing the inflammatory response through its expression on monocytes and macrophages. To further understand the role of GPBAR1 in inflammation, we generated a novel, selective, proprietary GPBAR1 agonist and tested its effectiveness at reducing monocyte and macrophage activation in vitro and in vivo. We have used this agonist, together with previously described agonists to study agonism of GPBAR1, and shown that they can all induce cAMP and reduce TLR activation-induced cytokine production in human monocytes and monocyte-derived macrophages in vitro. Additionally, through the usage of RNA sequencing (RNA-Seq), we identified a select set of genes that are regulated by GPBAR1 agonism during LPS activation. To further define the in vivo role of GPBAR1 in inflammation, we assessed GPBAR1 expression and found high levels on circulating mouse monocytes. Agonism of GPBAR1 reduced LPS-induced cytokine production in mouse monocytes ex vivo and serum cytokine levels in vivo. Agonism of GPBAR1 also had profound effects in the experimental autoimmune encephalomyelitis (EAE) mouse model of multiple sclerosis, where monocytes play an important role. Mice treated with the GPBAR1 agonist exhibited a significant reduction in the EAE clinical score which correlated with reduced monocyte and microglial activation and reduced trafficking of monocytes and T cells into the CNS. These data confirm the importance of GPBAR1 in controlling monocyte and macrophage activation in vivo and support the rationale for selective agonists of GPBAR1 in the treatment of inflammatory diseases.

TUDCA: An Agonist of the Bile Acid Receptor GPBAR1/TGR5 With Anti‐Inflammatory Effects in Microglial Cells

“…Recently, a small molecule agonist of the bile acids receptor GPBAR1/TGR5 has exerted the same anti‐inflammatory effect on myeloid cell activation in vitro (Lewis et al, ) as shown by other agonists like TUDCA (Yanguas‐Casás et al, ) and betulinic acid (McMillin et al, ) on microglia. Mice treated with that TGR5 agonist showed reduced monocyte and microglial activation and reduced trafficking of monocytes and T cells into the CNS, correlating with a reduced clinical score in an animal model of experimental autoimmune encephalomyelitis (EAE, Lewis et al, ). We believe that TUDCA might have the same effect as this GPBAR1/TGR5 agonist, inhibiting by itself both the activation of microglia and the infiltration of blood monocytes into the neural parenchyma (Yanguas‐Casás et al, ).…”

Effects of bile acids on neurological function and disease

“…More recently, the use of agonists for bile acid receptors has been proposed for the management of multiple sclerosis, as bile acid signaling can modulate inflammation. Indeed, Lewis et al (79) developed a novel agonist for TGR5 that reduces proinflammatory cytokine production from mouse monocytes stimulated with LPS, and this therapeutic was found to reduce EAE severity in mice. FXR also seems to play a role in the progression of EAE, as mice with genetic knockout of FXR have a more severe grade of EAE compared to wild-type EAE mice (80).…”

The Role of Bile Acid Receptors in Chronic Inflammatory Diseases

“…Furthermore, rs11554825, a TGR5 single-nucleotide polymorphism, is associated with primary sclerosing cholangitis and ulcerative colitis development, and homozygous individuals for the G allele of rs3731859 which is in perfect linkage disequilibrium (LD) with the risk allele C of rs11554825 demonstrate low TGR5 expression levels, suggesting TGR5 may be important in the development of primary sclerosing cholangitis and ulcerative colitis pathogenesis [35]. In the multiple sclerosis animal model, experimental autoimmune encephalomyelitis (EAE) mice, TGR5 agonist resulted in decreased activation of monocyte and microglial activation, decreased trafficking of monocytes and T cells into the central nervous system (CNS), and improvement of EAE clinical scores, suggesting TGR5 may be a potential therapeutic target in multiple sclerosis [16].…”

“…Recently, bile acids were found to regulate inflammation and mediate immune homeostasis [9][10][11][12][13][14][15][16]. Moreover, natural, semi-synthetic, and fully synthetic drugs that target these receptors were developed and are currently being studied for use in various inflammatory disorders such as alcoholic hepatitis, non-alcoholic steatohepatitis, primary biliary cirrhosis, primary sclerosing cholangitis [17,18].…”