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

The role of orphan G protein-coupled receptors in pain

G protein-coupled receptors (GPCRs), which form the largest family of membrane protein receptors in humans, are highly complex signaling systems with intricate structures and dynamic conformations and locations. Among these receptors, a specific subset is referred to as orphan GPCRs (oGPCRs) and has garnered significant interest in pain research due to their role in both central and peripheral nervous system function. The diversity of GPCR functions is attributed to multiple factors, including allosteric modulators, signaling bias, oligomerization, constitutive signaling, and compartmentalized signaling. This review primarily focuses on the recent advances in oGPCR research on pain mechanisms, discussing the role of specific oGPCRs including GPR34, GPR37, GPR65, GPR83, GPR84, GPR85, GPR132, GPR151, GPR160, GPR171, GPR177, and GPR183. The orphan receptors among these receptors associated with central nervous system diseases are also briefly described. Understanding the functions of these oGPCRs can contribute not only to a deeper understanding of pain mechanisms but also offer a reference for discovering new targets for pain treatment.

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.

Proximity Interactome Analysis of Super Conserved Receptors Expressed in the Brain Identifies EPB41L2, SLC3A2, and LRBA as Main Partners

The Super-Conserved Receptors Expressed in the Brain (SREBs) form a subfamily of orphan G protein-coupled receptors, highly conserved in evolution and characterized by a predominant expression in the brain. The signaling pathways activated by these receptors (if any) are presently unclear. Given the strong conservation of their intracellular loops, we used a BioID2 proximity-labeling assay to identify protein partners of SREBs that would interact with these conserved domains. Using streptavidin pull-down followed by mass spectrometry analysis, we identified the amino acid transporter SLC3A2, the AKAP protein LRBA, and the 4.1 protein EPB41L2 as potential interactors of these GPCRs. Using co-immunoprecipitation experiments, we confirmed the physical association of these proteins with the receptors. We then studied the functional relevance of the interaction between EPB41L2 and SREB1. Immunofluorescence microscopy revealed that SREB1 and EPB41L2 co-localize at the plasma membrane and that SREB1 is enriched in the β-catenin-positive cell membranes. siRNA knockdown experiments revealed that EPB41L2 promotes the localization of SREB1 at the plasma membrane and increases the solubilization of SREB1 when using detergents, suggesting a modification of its membrane microenvironment. Altogether, these data suggest that EPB41L2 could regulate the subcellular compartmentalization of SREBs and, as proposed for other GPCRs, could affect their stability or activation.

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.

Comprehensive analysis of a pyroptosis-related gene signature of clinical and biological values in spinal cord injury

Background

Since some of the clinical examinations are not suitable for patients with severe spinal cord injury (SCI), blood biomarkers have been reported to reflect the severity of SCI. The objective of this study was to screen out the potential biomarkers associated with the diagnosis of SCI by bioinformatics analysis.

Methods

The microarray expression profiles of SCI were obtained from the Gene Expression Omnibus (GEO) database. Core genes correlated to pyroptosis were obtained by crossing the differential genes, and module genes were obtained by WGCNA analysis and lasso regression. The immune infiltration analysis and GSEA analysis revealed the essential effect of immune cells in the progression of SCI. In addition, the accuracy of the biomarkers in diagnosing SCI was subsequently evaluated and verified using the receiver operating characteristic curve (ROC) and qRT-PCR.

Results

A total of 423 DEGs were identified, among which 319 genes were upregulated and 104 genes were downregulated. Based on the WGCNA analysis, six potential biomarkers were screened out, including LIN7A, FCGR1A, FGD4, GPR27, BLOC1S1, and GALNT4. The results of ROC curves demonstrated the accurate value of biomarkers related to SCI. The immune infiltration analysis and GSEA analysis revealed the essential effect of immune cells in the progression of SCI, including macrophages, natural killer cells, and neutrophils. The qRT-PCR results verified that FGD4, FCAR1A, LIN7A, BLOC1S1, and GPR27 were significantly upregulated in SCI patients.

Conclusion

In this study, we identified and verified five immune pyroptosis-related hub genes by WGCNA and biological experiments. It is expected that the five identified potential biomarkers in peripheral white blood cells may provide a novel strategy for early diagnosis.