The cerebellar projection from the trigeminal nuclear complex is one of the major populations of the cerebellar inputs. Although this projection is essential in cerebellar functional processing and organization, its morphological organization has not been systematically clarified. The present study addressed this issue by lobule-specific retrograde neuronal labeling and single axonal reconstruction with anterograde labeling. The cerebellar projection arose mainly from the interpolaris subdivision of the spinal trigeminal nucleus (Sp5I) and the principal trigeminal sensory nucleus (Pr5). Although crus II, paramedian lobule, lobule IX, and simple lobule were the major targets, paraflocculus, and other lobules received some projections. Reconstructed single trigeminocerebellar axons showed 77.8 mossy fiber terminals on average often in multiple lobules but no nuclear collaterals. More terminals were located in zebrin-negative or lightly-positive compartments than in zebrin-positive compartments. While Pr5 axons predominantly projected to ipsilateral crus II, Sp5I axons projected either predominantly to crus II and paramedian lobule often bilaterally, or predominantly to lobule IX always ipsilaterally. Lobule IX-predominant-type Sp5I neurons specifically expressed Gpr26. Gpr26-tagged neuronal labeling produced a peculiar mossy fiber distribution, which was dense in the dorsolateral lobule IX and extending transversely to the dorsal median apex in lobule IX. The projection to the cerebellar nuclei was observed in collaterals of ascending Sp5I axons that project to the diencephalon. In sum, multiple populations of trigeminocerebellar projections showed divergent projections to cerebellar lobules. The projection was generally complementary with the pontine projection and partly matched with the reported orofacial receptive field arrangement.

Neuropeptides and G protein-coupled receptors (GPCRs) have long been, and continue to be, one of the most popular target classes for drug discovery in CNS disorders, including alcohol use disorder (AUD). Yet, orphaned neuropeptide systems and receptors (oGPCR), which have no known cognate receptor or ligand, remain understudied in drug discovery and development. Orphan neuropeptides and oGPCRs are abundantly expressed within the brain and represent an unprecedented opportunity to address brain function and may hold potential as novel treatments for disease. Here, we describe the current literature regarding orphaned neuropeptides and oGPCRs implicated in AUD. Specifically, in this review, we focus on the orphaned neuropeptide cocaine- and amphetamine-regulated transcript (CART), and several oGPCRs that have been directly implicated in AUD (GPR6, GPR26, GPR88, GPR139, GPR158) and discuss their potential and pitfalls as novel treatments, and progress in identifying their cognate receptors or ligands.

Diabetes is the ninth leading cause of death, with an estimated 1.5 million deaths worldwide. Type 2 diabetes (T2D) results from the body\'s ineffective use of insulin and is largely the result of excess body weight and physical inactivity. T2D increases the risk of cardiovascular diseases, retinopathy, and kidney failure by two-to three-fold. Hyperglycemia, as a hallmark of diabetes, acts as a potent stimulator of inflammatory condition by activating endothelial cells and by dysregulating monocyte activation. G-protein couple receptors (GPCRs) can both exacerbate and promote inflammatory resolution. Genome-wide association studies (GWAS) indicate that GPCRs are differentially regulated in inflammatory and vessel cells from diabetic patients. However, most of these GPCRs are orphan receptors, for which the mechanism of action in diabetes is unknown. Our data indicated that orphan GPCR26 is downregulated in the PBMC isolated from T2D patients. In contrast, GPR26 was initially upregulated in human monocytes and PBMC treated with high glucose (HG) levels and then decreased upon chronic and prolonged HG exposure. GPR26 levels were decreased in T2D patients treated with insulin compared to non-insulin treated patients. Moreover, GPR26 inversely correlated with the BMI and the HbA1c of diabetic compared to non-diabetic patients. Knockdown of GPR26 enhanced monocyte ROS production, MAPK signaling, pro-inflammatory activation, monocyte adhesion to ECs, and enhanced the activity of Caspase 3, a pro-apoptotic molecule. The same mechanisms were activated by HG and exacerbated when GPR26 was knocked down. Hence, our data indicated that GPR26 is initially activated to protect monocytes from HG and is inhibited under chronic hyperglycemic conditions.

G protein-coupled receptors (GPCRs) play important roles in many physiological functions and numerous diseases. In addition to the classic ligand-stimulated receptor activity, an increasing number of studies have established that many GPCRs function constitutively in a receptor dose-dependent manner. Previous observations showed that following gene transfection, little or no protein was detectable for certain GPCRs (designated apparent state A), such as GPR26, GPR39, GPR78, GPR133, GPR139, BRS3, and LGR5, which showed strong constitutive activities. When we lysed cells in the immediate presence of western blot loading buffer, a significant increase of protein levels was detected (actual state B), which was much closer to the true expression levels under physiological conditions. GPR26 was chosen for further functional experiments as the actual state B. We identified an important ubiquitination site, K286, as well as the ubiquitin ligase E3 homologous to the E6-associated protein carboxyl terminus domain containing 3 interacting with GPR26. The pronounced differences in the protein expression and constitutive activity of GPR26 were a consequence of the ubiquitin-mediated rapid degradation mechanism. Furthermore, we identified in vitro and in vivo antitumor activity associated with high expression levels and constitutive activity of GPR26 in liver cancer cells. Hence, GPR26 could act as an antitumor gene for hepatocellular carcinoma. This study also represents the actual state B of a batch of GPCRs that actually play potentially important roles in physiological functions by their constitutive activity, which is controlled by rapid ubiquitin-dependent degradation.

Background: Glioblastoma (GBM) is recognized as a malignant brain tumor with frequent mortality. Extensive evidence indicated that miR-188-3p exerts an important role in various tumors. However, the role of miR-188-3p in GBM has not been elucidated. The purpose of the present investigation was to explore the biological effect of miR-188-3p, as well as to determine its target gene in GBM.Methods: The miR-188-3p and G Protein-Coupled Receptor 26 (GPR26) expressional profiles were obtained from The Cancer Genome Atlas (TCGA) database. The proliferative ability, invasive and migratory capabilities of GBM cells were measured using Cell Counting Kit-8 and transwell assays. Bioinformatics tool and luciferase reporter gene analysis were utilized to assess the correlation between miR-188-3p and GPR26. Reverse transcription-quantitative polymerase chain reaction (RT-PCR) and western blotting were performed to detect the indicated gene expression.Results: MiR-188-3p expression was highly regulated in GBM tissue and cell lines, while GPR26 was significantly decreased in GBM. Depletion of miR-188-3p significantly retarded the cell proliferation, invasion and migration in the U-87 MG cell. Luciferase reporter gene assay showed that GPR26 was a target gene of miR-188-3p in GBM. The expression of GPR26 was negatively regulated by miR-188-3p. The inhibitory effect of miR-188-3p inhibitor on cell behaviors was further strengthened by the overexpression of GPR26 in GBM.Conclusion: These findings provided evidence for the cancer-promoting effect of miR-188-3p in GBM cells and demonstrated that GPR26 was directly targeted by miR-188-3p, which might contribute to the therapeutic therapy of GBM.

OBJECTIVE: Metabolic syndrome (MS) is composed of several metabolic abnormalities that increase the risk of cardiovascular diseases and diabetes. Although there are treatments for the components of MS, this pathology maintains a high mortality, suggesting that there are other mechanisms in which orphan receptors such as GPR26 and GPR39 may be involved. For this reason, the aim of this work was to evaluate the expression of GPR26 and GPR39 orphan receptors in two models of MS (diet and genetics).
METHODS: We used male Wistar rats, which received 70% fructose in drinking water for 9 weeks, and obese Zucker rats. We measured weight, blood pressure, glucose, triglycerides, total cholesterol, HDL cholesterol, LDL cholesterol to determine the MS and the expression of the orphan receptors GPR26 and GPR39 in brain, heart, aorta, liver, and kidney by RT-PCR.
RESULTS: The analysis of the expression of the orphan receptors GPR26 and GPR39 showed that the receptors are expressed in some tissues, but the expression of the GPR26 tends to decrease in the heart and aorta, whereas in the brain, no changes were observed, this receptor is not expressed in the liver and kidney of both strains. The expression of GPR39 isoforms depends on the tissue and MS model.
CONCLUSIONS: We conclude that the orphan receptors GPR26, GPR39v1, and GPR39v2 are expressed in different tissues and their profile expression is dependent on the etiology of the MS.