The Activation of GPR27 Increases Cytosolic L-Lactate in 3T3 Embryonic Cells and Astrocytes

Development of Ligands for the Super Conserved Orphan G Protein-Coupled Receptor GPR27 with Improved Efficacy and Potency

The orphan G protein-coupled receptor GPR27 appears to play a role in insulin production, secretion, lipid metabolism, neuronal plasticity, and l-lactate homeostasis. However, investigations on the function of GPR27 are impaired by the lack of potent and efficacious agonists. We describe herein the development of di- and trisubstituted benzamide derivatives 4a-e, 7a-z, and 7aa-ai, which display GPR27-specific activity in a β-arrestin 2 recruitment-based assay. Highlighted compounds are PT-91 (7p: pEC50 6.15; Emax 100%) and 7ab (pEC50 6.56; Emax 99%). A putative binding mode was revealed by the docking studies of 7p and 7ab with a GPR27 homology model. The novel active compounds exhibited no GPR27-mediated activation of G proteins, indicating that the receptor may possess an atypical profile. Compound 7p displays high metabolic stability and brain exposure in mice. Thus, 7p represents a novel tool to investigate the elusive pharmacology of GPR27 and assess its potential as a drug target.

Characterizing the SREB G protein-coupled receptor family in fish: Brain gene expression and genomic differences in upstream transcription factor binding sites

The SREB (Super-conserved Receptors Expressed in Brain) family of orphan G protein-coupled receptors is highly conserved in vertebrates and consists of three members: SREB1 (orphan designation GPR27), SREB2 (GPR85), and SREB3 (GPR173). SREBs are associated with processes ranging from neuronal plasticity to reproductive control. Relatively little is known about similarities across the entire family, or how mammalian gene expression patterns compare to non-mammalian vertebrates. In fish, this system may be particularly complex, as some species have gained a fourth member (SREB3B) while others have lost genes. To better understand the system, the present study aimed to: 1) use qPCR to characterize sreb and related gene expression patterns in the brains of three fish species with different systems, and 2) identify possible differences in transcriptional regulation among the receptors, using upstream transcription factor binding sites across 70 ray-finned fish genomes. Overall, regional patterns of sreb expression were abundant in forebrain-related areas. However, some species-specific patterns were detected, such as abundant expression of receptors in zebrafish (Danio rerio) hypothalamic-containing sections, and divergence between sreb3a and sreb3b in pufferfish (Dichotomyctere nigroviridis). In addition, a gene possibly related to the system (dkk3a) was spatially correlated with the receptors in all three species. Genomic regions upstream of sreb2 and sreb3b, but largely not sreb1 or sreb3a, contained many highly conserved transcription factor binding sites. These results provide novel information about expression differences and transcriptional regulation across fish that may inform future research to better understand these receptors.

Prognostic significance and immune characteristics of GPR27 in gastric cancer

Gastric cancer (GC) is one of the most typical cancerous neoplasms occurring in the digestive system. For advanced GC, immunotherapy is the final option for them to prolong survival time. Hence, we aimed to identify new molecular targets to enhance the immunotherapy response in GC individuals. Then we applied bioinformatic analysis to explore the expression profiles of G-protein-coupled receptor 27 (GPR27) transcription and GPR27 methylation. The associations between survival of GC patients and GPR27 transcription and methylation were then analyzed. We also studied the link between GPR27 expression and levels of immune cell infiltration. Finally, we gained insights into the prognostic role of GPR27 protein in 97 cases of GC individuals. According to datasets gained from TCGA, GPR27 mRNA is expressed lower in GC tissues. Down-regulation of GPR27 transcription was related with better survival in GC individuals, and GPR27 cg03024619 had the most significant prognostic value (HR=0.553, P<0.0001). In addition, the expression level of GPR27 has a clear interaction with immune cells' infiltration and their markers. Single-cell analysis displayed that GPR27 is mainly expressed in macrophages. Finally, down-regulation of GPR27 protein was observed in GC tissues and correlated with better survival outcomes. GPR27 can serve as an important prognostic biomarker and exert an immunomodulatory role in GC. Our findings highlight the significance of GPR27 in a variety of cancers, including GC, and provide clues for a better understanding of GPR27 from bioinformatics and clinically validated perspective.

Astrocytes in the pathophysiology of neuroinfection

Key homeostasis providing cells in the central nervous system (CNS) are astrocytes, which belong to the class of cells known as atroglia, a highly heterogeneous type of neuroglia and a prominent element of the brain defence. Diseases evolve due to altered homeostatic state, associated with pathology-induced astroglia remodelling represented by reactive astrocytes, astroglial atrophy and astrodegeneration. These features are hallmarks of most infectious insults, mediated by bacteria, protozoa and viruses; they are also prominent in the systemic infection. The COVID-19 pandemic revived the focus into neurotropic viruses such as SARS-CoV2 (Coronaviridae) but also the Flaviviridae viruses including tick-borne encephalitis (TBEV) and Zika virus (ZIKV) causing the epidemic in South America prior to COVID-19. Astrocytes provide a key response to neurotropic infections in the CNS. Astrocytes form a parenchymal part of the blood-brain barrier, the site of virus entry into the CNS. Astrocytes exhibit aerobic glycolysis, a form of metabolism characteristic of highly morphologically plastic cells, like cancer cells, hence a suitable milieu for multiplication of infectious agent, including viral particles. However, why the protection afforded by astrocytes fails in some circumstances is an open question to be studied in the future.

Superconserved receptors expressed in the brain: Expression, function, motifs and evolution of an orphan receptor family

GPR27, GPR85 and GPR173 constitute a small family of G protein-coupled receptors (GPCR) that share the distinctive characteristics of being highly conserved throughout vertebrate evolution and predominantly expressed in the brain. Accordingly, they have been coined as "Superconserved Receptors Expressed in the Brain" (SREB), although their expression profile is more complex than what was originally thought. SREBs have no known validated endogenous ligands and are thus labeled as "orphan" receptors. The investigation of this particular category of uncharacterized receptors holds great promise both in terms of physiology and drug development. In the largest GPCR family, the Rhodopsin-like or Class A, around 100 receptors are considered orphans. Because GPCRs are the most successful source of drug targets, the discovery of a novel function or ligand most likely will lead to significant breakthroughs for the discovery of innovative therapies. The high level of conservation is one of the characteristic features of the SREBs. We propose herein a detailed analysis of the putative evolutionary origin of this family. We highlight the properties that distinguish SREBs from other rhodopsin-like GPCRs. We present the current evidence for these receptors downstream signaling pathways and functions. We discuss the pharmacological challenge for the identification of natural or synthetic ligands of orphan receptors like SREBs. The different SREB-related scientific questions are presented with a highlight on what should be addressed in the near future, including the confirmation of published evidence and their validation as drug targets. In particular, we discuss in which pathological conditions these receptors may be of great relevance to solve unmet medical needs.

Super-conserved receptors expressed in the brain: biology and medicinal chemistry efforts

The super-conserved receptors expressed in the brain (SREB) constitute a family of orphan G protein-coupled receptors that include GPR27 (SREB1), GPR85 (SREB2) and GPR173 (SREB3). Their sequences are highly conserved in vertebrates, and they are almost exclusively expressed in the central nervous system. This family of receptors has attracted much attention due to their putative physiological functions and their potential as novel drug targets. The SREB family has been postulated to play important roles in a wide range of different diseases, including pancreatic β-cell insulin secretion and regulation, schizophrenia, autism and atherosclerosis. This review intends to provide a comprehensive overview of the SREB family and its recent advances in biology and medicinal chemistry.