Agonists of galanin subtype 2 receptor may prevent pancreatic cancer and agonists of angiotensin II type 2 receptor may prevent colorectal cancer.

Pancreatic ductal adenocarcinoma (PDAC) remains a dreadful disease with poor prognosis. While the prognosis of colorectal carcinoma (CRC) is better than that of PDAC, it still is the second-leading cause of cancer deaths worldwide. Recently, a (methyl)lanthionine-stabilized, highly receptor-specific agonist of galanin subtype 2 (GAL2) receptor inhibited the growth of GAL2 receptor-expressing patient-derived xenografts (PDX) of pancreatic cancer. Furthermore, a lanthionine-constrained agonist of angiotensin II type 2 (AT2) receptor inhibited PDX of colorectal cancer in mice. Stimulation of GAL2 receptor may modulate immune surveillance and inhibits PDAC via cell cycle inhibition and apoptosis. Consistent with GAL2 receptor-mediated tumor inhibition, for PDAC, survival is much higher for patients with high GAL2 receptor expression. Importantly, a (methyl)lanthionine-stabilized GAL2 receptor-specific agonist enhances expression of GAL2 receptor, not only in PDAC-PDX but also in healthy tissue indicating therapeutic and preventive potentials for GAL2 receptor agonists. AT2 receptor is interacting with four tumor suppressor proteins, Src homology phosphatase 1, Src homology phosphatase 2, Promyelocytic Leukemia Zinc Finger protein and Microtuble-Associated Scaffold Protein1, the latter also known as Angiotensin-II type 2 receptor-Interacting Protein. Pathways linked to these tumor suppressor proteins may enhance immune surveillance, prevent carcinogenesis, counter proliferation and stimulate apoptosis. Taken together, current data are prompting the hypothesis of a prophylactic treatment option with stable, specific and safe agonists of GAL2 receptor and AT2 receptor to prevent the emergence of pancreatic and colorectal cancer in individuals at risk.

Spexin Diminishes Atrial Fibrillation Vulnerability by Acting on Galanin Receptor 2.

BACKGROUND: G protein-coupled receptors play a critical role in atrial fibrillation (AF). Spexin is a novel ligand of galanin receptors (GALRs). In this study, we investigated the regulation of spexin and GALRs on AF and the underlying mechanisms. METHODS: Global spexin knockout (SPX-KO) and cardiomyocyte-specific GALRs knockout (GALR-cKO) mice underwent burst pacing electrical stimulation. Optical mapping was used to determine atrial conduction velocity and action potential duration. Atrial myocyte action potential duration and inward rectifying K+ current (IK1) were recorded using whole-cell patch clamps. Isolated cardiomyocytes were stained with Fluo-3/AM dye, and intracellular Ca2+ handling was examined by CCD camera. A mouse model of AF was established by Ang-II (angiotensin II) infusion. RESULTS: Spexin plasma levels in patients with AF were lower than those in subjects without AF, and knockout of spexin increased AF susceptibility in mice. In the atrium of SPX-KO mice, potassium inwardly rectifying channel subfamily J member 2 (KCNJ2) and sarcolipin (SLN) were upregulated; meanwhile, IK1 current was increased and Ca2+ handling was impaired in isolated atrial myocytes of SPX-KO mice. GALR2-cKO mice, but not GALR1-cKO and GALR3-cKO mice, had a higher incidence of AF, which was associated with higher IK1 current and intracellular Ca2+ overload. The phosphorylation level of CREB (cyclic AMP responsive element binding protein 1) was upregulated in atrial tissues of SPX-KO and GALR2-cKO mice. Chromatin immunoprecipitation confirmed the recruitment of p-CREB to the proximal promoter regions of KCNJ2 and SLN. Finally, spexin treatment suppressed CREB signaling, decreased IK1 current and decreased intracellular Ca2+ overload, which thus reduced the inducibility of AF in Ang-II-infused mice. CONCLUSIONS: Spexin reduces atrial fibrillation susceptibility by inhibiting CREB phosphorylation and thus downregulating KCNJ2 and SLN transcription by GALR2 receptor. The spexin/GALR2/CREB signaling pathway represents a novel therapeutic avenue in the development of agents against atrial fibrillation.

Long-term enhancements in antidepressant efficacy and neurogenesis: Effects of intranasal co-administration of neuropeptide Y 1 receptor (NPY1R) and galanin receptor 2 (GALR2) agonists in the ventral hippocampus.

This study evaluates the sustained antidepressant-like effects and neurogenic potential of a 3-day intranasal co-administration regimen of galanin receptor 2 (GALR2) agonist M1145 and neuropeptide Y Y1 receptor (NPY1R) agonist [Leu31, Pro34]NPY in the ventral hippocampus of adult rats, with outcomes analyzed 3 weeks post-treatment. Utilizing the forced swimming test (FST), we found that this co-administration significantly enhances antidepressant-like behaviors, an effect neutralized by the GALR2 antagonist M871, highlighting the synergistic potential of these neuropeptides in modulating mood-related behaviors. In situ proximity ligation assay (PLA) indicated a significant increase in GALR2/NPYY1R heteroreceptor complexes in the ventral hippocampal dentate gyrus, suggesting a molecular basis for the behavioral outcomes observed. Moreover, proliferating cell nuclear antigen (PCNA) immunolabeling revealed increased cell proliferation in the subgranular zone of the dentate gyrus, specifically in neuroblasts as evidenced by co-labeling with doublecortin (DCX), without affecting quiescent neural progenitors or astrocytes. The study also noted a significant uptick in the number of DCX-positive cells and alterations in dendritic morphology in the ventral hippocampus, indicative of enhanced neuronal differentiation and maturation. These morphological changes highlight the potential of these agonists to facilitate the functional integration of new neurons into existing neural circuits. By demonstrating the long-lasting effects of a brief, 3-day intranasal administration of GALR2 and NPY1R agonists, our findings contribute significantly to the understanding of neuropeptide-mediated neuroplasticity and herald novel therapeutic strategies for the treatment of depression and related mood disorders, emphasizing the therapeutic promise of targeting neurogenesis and neuronal maturation processes.

Glyphosate-induced changes in the expression of galanin and GALR1, GALR2 and GALR3 receptors in the porcine small intestine wall.

Glyphosate is the active ingredient of glyphosate-based herbicides and the most commonly used pesticide in the world. The goal of the present study was to verify whether low doses of glyphosate (equivalent to the environmental exposure) evoke changes in galanin expression in intramural neurons in the small intestine in pigs and to quantitatively determine changes in the level of galanin receptor encoding mRNA (GALR1, GALR2, GALR3) in the small intestine wall. The experiment was conducted on 15 sexually immature gilts divided into three study groups: control (C)-animals receiving empty gelatin capsules; experimental 1 (G1)-animals receiving a low dose of glyphosate (0.05 mg/kg b.w./day); experimental 2 (G2)-animals receiving a higher dose of glyphosate (0.5 mg/kg b.w./day) orally in gelatine capsules for 28 days. Glyphosate ingestion led to an increase in the number of GAL-like immunoreactive intramural neurons in the porcine small intestine. The results of RT-PCR showed a significant increase in the expression of mRNA, which encodes the GAL-receptors in the ileum, a decreased expression in the duodenum and no significant changes in the jejunum. Additionally, intoxication with glyphosate increased the expression of SOD2-encoding mRNA in the duodenum and decreased it in the jejunum and ileum, but it did not affect SOD1 expression. The results suggest that it may be a consequence of the cytotoxic and/or neurotoxic properties of glyphosate and/or its ability to induce oxidative stress.

Enhanced neuronal survival and BDNF elevation via long-term co-activation of galanin 2 (GALR2) and neuropeptide Y1 receptors (NPY1R): potential therapeutic targets for major depressive disorder.

BACKGROUND: Major Depressive Disorder (MDD) is a prevalent and debilitating condition, necessitating novel therapeutic strategies due to the limited efficacy and adverse effects of current treatments. We explored how galanin receptor 2 (GALR2) and Neuropeptide Y1 Receptor (NPYY1R) agonists, working together, can boost brain cell growth and increase antidepressant-like effects in rats. This suggests new ways to treat Major Depressive Disorder (MDD). RESEARCH DESIGN AND METHODS: In a controlled laboratory setting, adult naive Sprague-Dawley rats were administered directly into the brain's ventricles, a method known as intracerebroventricular (ICV) administration, with GALR2 agonist (M1145), NPYY1R agonist, both, or in combination with a GALR2 antagonist (M871). Main outcome measures included long-term neuronal survival, differentiation, and behavioral. RESULTS: Co-administration of M1145 and NPYY1R agonist significantly enhanced neuronal survival and maturation in the ventral dentate gyrus, with a notable increase in Brain-Derived Neurotrophic Factor (BDNF) expression. This neurogenic effect was associated with an antidepressant-like effect, an outcome partially reversed by M871. CONCLUSIONS: GALR2 and NPYY1R agonists jointly promote hippocampal neurogenesis and exert antidepressant-like effects in rats without adverse outcomes, highlighting their therapeutic potential for MDD. The study's reliance on an animal model and intracerebroventricular delivery warrants further clinical exploration to confirm these promising results.

An update on galanin and spexin and their potential for the treatment of type 2 diabetes and related metabolic disorders.

Spexin (SPX) and galanin (GAL) are two neuropeptides widely expressed in the central nervous system as well as within peripheral tissues in humans and other species. SPX and GAL mediate their biological actions through binding and activation of galanin receptors (GALR), namely GALR1, GALR2 and GLAR3. GAL appears to trigger all three galanin receptors, whereas SPX interacts more specifically with GALR2 and GLAR3. Whilst the biological effects of GAL have been well-described over the years, in-depth knowledge of physiological action profile of SPX is still in its preliminary stages. However, it is recognised that both peptides play a significant role in modulating overall energy homeostasis, suggesting possible therapeutically exploitable benefits in diseases such as obesity and type 2 diabetes mellitus. Accordingly, although both peptides activate GALR's, it appears GAL may be more useful for the treatment of eating disorders such as anorexia and bulimia, whereas SPX may find therapeutic application for obesity and obesity-driven forms of diabetes. This short narrative review aims to provide an up-to-date account of SPX and GAL biology together with putative approaches on exploiting these peptides for the treatment of metabolic disorders.

Galanin 2 Receptor: A Novel Target for a Subset of Pancreatic Ductal Adenocarcinoma.

Galanin is a 30 amino acid peptide that stimulates three subtype receptors (GAL1-3R). M89b is a lanthionine-stabilized, C-terminally truncated galanin analog that specifically stimulates GAL2R. We investigated the potential of M89b as a therapeutic for pancreatic ductal adenocarcinoma (PDAC) and assessed its safety. The anti-tumor activity of subcutaneously injected M89b on the growth of patient-derived xenografts of PDAC (PDAC-PDX) in mice was investigated. In addition, the safety of M89b was assessed in vitro using a multi-target panel to measure the off-target binding and modulation of enzyme activities. In a PDAC-PDX with a high GAL2R expression, M89b completely inhibited the growth of the tumor (p < 0.001), while in two PDAC-PDXs with low GAL2R expression, low or negligeable inhibition of tumor growth was measured, and in the PDX without GAL2R expression no influence on the tumor growth was observed. The M89b treatment of the GAL2R high-PDAC-PDX-bearing mice led to a reduction in the expression of RacGap1 (p < 0.05), PCNA (p < 0.01), and MMP13 (p < 0.05). In vitro studies involving a multi-target panel of pharmacologically relevant targets revealedexcellent safety of M89b. Our data indicated that GAL2R is a safe and valuable target for treating PDACs with high GAL2R expression.

Detection of galanin receptors in the spinal cord in experimental autoimmune encephalomyelitis.

AIMS: The neuropeptide galanin is a widely distributed neurotransmitter/neuromodulator that regulates a variety of physiological processes and also participates in the regulation of stress responses. The aims of the present study were to investigate the expression of galanin receptors (GalR1, GalR2, GalR3) in the spinal cords in a murine model of multiple sclerosis, experimental autoimmune encephalomyelitis (EAE) using qPCR analysis and to determine GalR1 cellular localization (oligodendrocytes, microglia, astrocytes, ependymal cells, and endothelial cells in the capillaries) by immunohistochemistry. METHODS: Twelve samples from the EAE group and 14 samples from the control group were analyzed. Spinal cords samples were obtained at the peak of the EAE disease. RESULTS: The GalR1 mRNA level was significantly decreased in the EAE mice compared with the controls (P=0.016), whereas the mRNA levels of GalR2 and GalR3 were not significantly different for the EAE and the control mice. No significant correlations were found between the severity of the EAE disease and the mRNA levels of GalR1, GalR2 and GalR3. Immunochemical detection of the GalR1 revealed its expression in the ependymal and endothelial cells. Additionally, a weak GalR1 immunoreactivity was occasionally detected in the oligodendrocytes. CONCLUSION: This study provides additional evidence of galanin involvement in EAE pathophysiology, but this has to be further investigated.

Galanin Receptors (GALR1, GALR2, and GALR3) Immunoexpression in Enteric Plexuses of Colorectal Cancer Patients: Correlation with the Clinico-Pathological Parameters.

Galanin (GAL) is an important neurotransmitter released by the enteric nervous system (ENS) neurons located in the muscularis externa and submucosa enteric plexuses that acts by binding to GAL receptors 1, 2 and 3 (GALR1, 2 and 3). In our previous studies, the GAL immunoexpression was compared in colorectal cancer (CRC) tissue and the adjacent parts of the large intestine wall including myenteric and submucosal plexuses. Recently we have also found that expression levels of GALR1 and GALR3 proteins are elevated in CRC tissue as compared with their expression in epithelial cells of unchanged mucosa. Moreover, higher GALR3 immunoreactivity in CRC cells correlated with better prognosis of CRC patients. To understand the distribution of GALRs in enteric plexuses distal and close to CRC invasion, in the present study we decided to evaluate GALRs expression within the myenteric and submucosal plexuses located proximally and distally to the cancer invasion and correlated the GALRs expression levels with the clinico-pathological data of CRC patients. The immunohistochemical and immunofluorescent methods showed only slightly decreased immunoexpression of GALR1 and GALR3 in myenteric plexuses close to cancer but did not reveal any correlation in the immunoexpression of all three GAL receptors in myenteric plexuses and tumour progression. No significant changes were found between the expression levels of GALRs in submucosal plexuses distal and close to the tumour. However, elevated GALR1 expression in submucosal plexuses in vicinity of CRC correlated with poor prognosis, higher tumour grading and shorter overall survival. When myenteric plexuses undergo morphological and functional alterations characteristic for atrophy, GALRs maintain or only slightly decrease their expression status. In contrast, the correlation between high expression of GALR1 in the submucosal plexuses and overall survival of CRC patients suggest that GAL and GALRs can act as a components of local neuro-paracrine pro-proliferative pathways accelerating the invasion and metastasis of cancer cell. The obtained results suggest an important role of GALR1 in submucosal plexuses function during the progression of CRC and imply that GALR1 expression in submucosal plexuses of ENS could be an important predictive factor for CRC progression.

Levels of spexin and its receptors GALR2 and GALR3 in the hypothalamus and ovary of letrozole-induced polycystic ovary syndrome in rats.

Spexin (SPX) is a newly identified neuropeptide, a natural ligand for the galanin receptors (GALR) 2/3, which is involved in maintaining physiological functions including female reproduction. One of the most common endocrine disorder in reproductive system is polycystic ovary syndrome (PCOS), however the role of SPX in PCOS is still unknown. The objective of this study was to determine the expression of mRNA and peptide levels of SPX and its receptors GALR2/3 in the hypothalamus and ovary (by real time PCR and Western blot) as well as plasma levels of SPX (ELISA) in letrozole - induced PCOS rats. We observed that SPX plasma level does not change in PCOS rats. In the hypothalamus transcript level of Spx and Galr3 were significantly higher in PCOS rats compared to the control, while mRNA of Galr2 and protein expression of GALR2/3 were lower. Moreover, expression of Spx and Galr2/3 mRNA as well as GALR2/3 peptide production were lower in the ovary of PCOS rats. In summary, while our results did not show differences in plasma SPX levels, we observed tissue-dependent significant differences in the SPX/GALR2/3 levels between PCOS and control rats, what indicates possible new mechanisms of PCOS neuroendocrinology.

Galanin N-terminal fragment (1-15) reduces alcohol seeking and alcohol relapse in rats: Involvement of mesocorticolimbic system.

Alcohol Use Disorder (AUD) is among the most prevalent mental illnesses, and due to the low efficacy of the current medication, it is essential to find new biological targets that could modulate alcohol consumption. Since Galanin (1-15) [GAL(1-15)] produces a loss of motivational behaviour by an artificial reinforcer and decreases the preference an alcohol consumption in a voluntary alcohol intake, we have studied the role of GAL(1-15) in alcohol-seeking behaviour and the involvement of the corticomesolimbic system as well as the role of GAL(1-15) in context-induced alcohol relapse. In rats, we have studied GAL(1-15)-effects on alcohol-seeking in self-administration, in fixed-ratio (FR1) and progressive-ratio (PR), and the involvement of GAL receptors using siRNA GALR1 or GALR2 knockdown animals. We have analysed the transcriptional changes of C-Fos, dopamine receptors, GAL receptors and 5HT1A receptors in the corticomesolimbic system. Also, we have examined the effect of GAL(1-15) in context-induced alcohol relapse. GAL(1-15) substantially reduced alcohol-seeking behaviour in the operant self-administration model in an FR1 protocol and at the breaking point in a PR schedule. GALR1and GALR2 were involved in these effects, as indicated by the analysis by GALR2 antagonist and GALR1 and GALR2 knockdown animals. Notably, the mechanism of GAL(1-15)-mediated actions involved changes in C-Fos, Dopamine receptors and 5HT1A expression in the ventral tegmental area, accumbens nucleus and prefrontal cortex. Significantly, GAL(1-15) reduced the context-induced alcohol relapse. These results open up the possibility to use GAL(1-15) as a novel strategy in AUD.

Structure of the human galanin receptor 2 bound to galanin and Gq reveals the basis of ligand specificity and how binding affects the G-protein interface.

Galanin is a neuropeptide expressed in the central and peripheral nervous systems, where it regulates various processes including neuroendocrine release, cognition, and nerve regeneration. Three G-protein coupled receptors (GPCRs) for galanin have been discovered, which is the focus of efforts to treat diseases including Alzheimer's disease, anxiety, and addiction. To understand the basis of the ligand preferences of the receptors and to assist structure-based drug design, we used cryo-electron microscopy (cryo-EM) to solve the molecular structure of GALR2 bound to galanin and a cognate heterotrimeric G-protein, providing a molecular view of the neuropeptide binding site. Mutant proteins were assayed to help reveal the basis of ligand specificity, and structural comparison between the activated GALR2 and inactive hß2AR was used to relate galanin binding to the movements of transmembrane (TM) helices and the G-protein interface.

Treatment with spexin mitigates diet-induced hepatic steatosis in vivo and in vitro through activation of galanin receptor 2.

It was reported that spexin as an adipocyte-secreted protein could regulate obesity and insulin resistance. However, the specific metabolic contribution of spexin to fatty liver remains incompletely understood. Herein, we investigated the effects of spexin on hepatosteatosis and explored the underlying molecular mechanisms. HFD-fed mice were injected with spexin and/or GALR2 antagonist M871, while PA-induced HepG2 cells were treated with spexin in the absence or presence of M871 for 12 h, respectively. Gene expression in liver tissues and hepatocytes was assessed by qRT-PCR and western blotting, respectively. The results showed that body weight, visceral fat content, liver lipid droplet formation, hepatic intracellular triglyceride, and serum triglyceride were reduced in spexin-treated mice. Furthermore, spexin increased the expression of hepatic CPT1A, PPARα, SIRT1, KLF9, PGC-1α and PEPCK in vivo and in vitro. Additionally, spexin treatment improved glucose tolerance and insulin sensitivity in mice fed the HFD. Interestingly, these spexin-mediated beneficial effects were abolished by the GALR2 antagonist M871 in mice fed HFD and PA-induced HepG2 cells, suggesting that spexin mitigated HFD-induced hepatic steatosis by activating the GALR2, thereby increasing CPT1A, PPARα, SIRT1, KLF9, PGC-1α and PEPCK expression. Taken together, these data suggest that spexin ameliorates NAFLD by improving lipolysis and fatty acid oxidation via activation of GALR2 signaling.

Galanin Receptors (GalR1, GalR2, and GalR3) Expression in Colorectal Cancer Tissue and Correlations to the Overall Survival and Poor Prognosis of CRC Patients.

Colorectal cancer (CRC) is the second most common cause of cancer in women and the third in men. The postoperative pathomorphological evaluation of patients with CRC is extremely important for future therapeutic decisions. Although our previous studies demonstrated high galanin (GAL) presence within tumor tissue and an elevated concentration of GAL in the serum of CRC patients, to date, there is a lack of data regarding GAL receptor (GalR) protein expression in CRC cells. Therefore, the aim of this study was to evaluate the presence of all three types of GalRs (GalR1, GalR2 and GalR3) within epithelial cells of the human colon and CRC tissue with the use of the immunohistochemical method and to correlate the results with the clinical-pathological data. We found stronger immunoreactivity of GalR1 and GalR3 in CRC cells compared to epithelial cells of the unchanged mucosa of the large intestine. No differences in the GalR2 protein immunoreactivity between the studied tissues were noted. We also found that the increased immunoexpression of the GalR3 in CRC tissue correlated with the better prognosis and longer survival (p < 0.0079) of CRC patients (n = 55). The obtained results suggest that GalR3 may play the role of a prognostic factor for CRC patients. Based on data from the TCGA-COAD project deposited in the GDC Data Portal, we also found that GalR mRNA in cancer samples and the adjacent normal tissue did not correlate with immunoexpression of the GalR proteins in CRC cells and epithelial cells of the unchanged mucosa.

Galanin mediates tumor-induced immunosuppression in head and neck squamous cell carcinoma.

PURPOSE: Galanin receptor 2 (GALR2) plays a significant role in the progression of head and neck squamous cell carcinomas (HNSCC). Since there is virtually no information on immunomodulation mediated by its ligand in the tumor microenvironment, we assessed the effects of galanin on peripheral blood mononuclear cells (PBMCs). METHODS: After verification of GALR2 expression and it activity in PBMCs we evaluated the effect of galanin and conditioned media from HNSCC cell lines silenced for galanin or antibody-depleted, on proliferation, apoptosis, cytokine expression and activation/differentiation of immune cells. RESULTS: We found that galanin alone and as a component of the HNSCC secretome decreased HNSCC cell proliferation and expression of pro-inflammatory cytokines (IFNγ, IL-12, IL-17A, IL-1α, IL-6 and TNF-α), whilst increasing apoptosis and expression of pro-tumoral cytokines/growth factors (IL-10, IL-4, PDGF and GM-CSF). T cell activation (using CD69 as activation marker) and anti-tumoral phenotypes in CD4+ T cells (Th1 and Th17) were found to be suppressed. In vivo, tumor growth was found to be increased in the presence of galanin-stimulated PBMCs. Data from The Cancer Genome Atlas (TCGA) revealed that high expression of galanin was associated with a reduced overall survival of patients with HNSCC. CONCLUSION: Our data indicate that galanin secreted by HNSCC cells exhibits immune-suppressive and pro-tumoral effects.

Theoretical investigation of selective ligand binding mode of galanin receptors.

The Galaninergic system consist of Galanin and its receptors, involved in neuromodulation and neurotransmission. Galanin regulate its physiologic and pathologic functions by interacting with three G-protein coupled receptors; GalR1, GalR2 and GalR3. The widespread distribution of Galanin and its receptor subtypes in central and peripheral nervous system makes them an attractive drug target for the treatment of neurological diseases. However, subtypes selective ligands paucity and little structural information related to either Galanin receptors and Galanin receptor-ligand complexes hampered the structure-based drug design. Thus computational modeling characterization strategy was utilized for Galanin receptor 3D structure prediction and subtypes ligands binding selectivity. Reported ligands with experimental activity were docked against the homology model of Galanin receptors. Further, the MD simulation and binding free energy calculation were carried out to determine the binding interactions pattern consistency and selectivity towards receptor subtype. Results of binding free energy of per residue indicate key contribution of GalR1 Phe115 and His267 in the selective binding of ligands while Tyr103, Tyr270 and His277 play major role in the selective binding of GalR3 ligands. Our study provide rationale for further in silico virtual screening of small molecules for the development of selective ligands against Galanin receptor subtypes.Communicated by Ramaswamy H. Sarma.

Baicalin protects against insulin resistance and metabolic dysfunction through activation of GALR2/GLUT4 signaling.

BACKGROUND: Type 2 diabetes mellitus is a complex metabolic disorder associated with obesity, glucose intolerance and insulin resistance. Activation of GALR2 has been proposed as a therapeutic target for the treatment of insulin resistance. The previous studies showed that baicalin could mitigate insulin resistance, but the detailed mechanism of baicalin on insulin resistance has not been fully explored yet. PURPOSE: In the present study, we evaluated whether baicalin mitigated insulin resistance via activation of GALR2 signaling pathway. STUDY DESIGN/METHODS: Baicalin (25 mg/kg/d and 50 mg/kg/d) and/or GALR2 antagonist M871 (10 mg/kg/d) were injected individually or in combinations into obese mice once a day for three weeks, and normal and GALR2 knockdown myotubes were treated with baicalin (100 µM and 400 µM) or metformin (4 mM) in the absence or presence of M871 (800 nM) for 12 h, respectively. The molecular mechanism was explored in skeletal muscle and L6 myotubes. RESULTS: The present findings showed that baicalin mitigated hyperglycemia and insulin resistance and elevated the levels of PGC-1α, GLUT4, p-p38MAPK, p-AKT and p-AS160 in skeletal muscle of obese mice. Strikingly, the baicalin-induced beneficial effects were abolished by GALR2 antagonist M871 in obese mice. In vitro, baicalin dramatically augmented glucose consumption and the activity of PGC1α-GLUT4 axis in myotubes through activation of p38MAPK and AKT pathways. Moreover, baicalin-induced elevations in glucose consumption related genes were abolished by GALR2 antagonist M871 or silencing of GALR2 in myotubes. CONCLUSIONS: The present study for the first time demonstrated that baicalin protected against insulin resistance and metabolic dysfunction mainly through activation of GALR2-GLUT4 signal pathway. Our findings identified that activation of GALR2-GLUT4 signal pathway by baicalin could be a new therapeutic approach to treat insulin resistance and T2DM in clinic.

Involvement of galanin and galanin receptor 2 in a mouse model of allergic rhinitis.

BACKGROUND: Allergic rhinitis (AR) is caused by allergic reaction to allergens such as pollen. Galanin (GAL), a neuropeptide that regulates inflammatory processes, is widely expressed in the central and peripheral nervous systems. Although neuropeptides are implicated in arthritis and chemically induced ileitis, their roles in AR remain unclear. METHODS: We developed a murine model of AR and generated control, systemic sensitization, mild AR, and severe AR groups. We examined GAL and GAL receptor (GALR) mRNA and protein levels and localization patterns in each group using reverse transcription PCR, western blotting, and immunohistochemical analyses. Additionally, we evaluated the effects of M871, a GALR2 antagonist, on mice with severe AR. RESULTS: Gal and Galr2 are expressed in nasal mucosa and brain (control) samples from control and AR mice. GAL and GALR2 were expressed at similar levels and localized to ciliated epithelial and submucosal gland cells of the nasal mucosa in all four groups. Intranasal M871 administration significantly reduced the incidence of nose rubbing behaviors and sneezing (p < 0.001 in 30 min, respectively) in severe AR mice relative to that in controls. Mechanistically, we postulate that GALR2 is expressed in B cells, and M871 administration reduces IgE production, as well as the number of B cells in tissues. CONCLUSIONS: GAL signaling may not change progressively with increasing nasal sensitization, suggesting that this signaling process exacerbates, rather than directly trigger, AR. GAL-GALR2 signaling likely mediates AR development, suggesting that its inhibition represents a novel therapeutic strategy for AR.

Intranasal Delivery of a Methyllanthionine-Stabilized Galanin Receptor-2-Selective Agonist Reduces Acute Food Intake.

The regulatory (neuro)peptide galanin is widely distributed in the central and peripheral nervous systems, where it mediates its effects via three G protein-coupled receptors (GAL1-3R). Galanin has a vast diversity of biological functions, including modulation of feeding behavior. However, the clinical application of natural galanin is not practicable due to its rapid in vivo breakdown by peptidases and lack of receptor subtype specificity. Much effort has been put into the development of receptor-selective agonists and antagonists, and while receptor selectivity has been attained to some degree, most ligands show overlapping affinity. Therefore, we aimed to develop a novel ligand with specificity to a single galanin receptor subtype and increased stability. To achieve this, a lanthionine amino acid was enzymatically introduced into a galanin-related peptide. The residue's subsequent cyclization created a conformational constraint which increased the peptide's receptor specificity and proteolytic resistance. Further exchange of certain other amino acids resulted in a novel methyllanthionine-stabilized galanin receptor agonist, a G1pE-T3N-S6A-G12A-methyllanthionine[13-16]-galanin-(1-17) variant, termed M89b. M89b has exclusive specificity for GAL2R and a prolonged half-life in serum. Intranasal application of M89b to unfasted rats significantly reduced acute 24 h food intake inducing a drop in body weight. Combined administration of M89b and M871, a selective GAL2R antagonist, abolished the anorexigenic effect of M89b, indicating that the effect of M89b on food intake is indeed mediated by GAL2R. This is the first demonstration of in vivo activity of an intranasally administered lanthipeptide. Consequently, M89b is a promising candidate for clinical application as a galanin-related peptide-based therapeutic.

Serotonin Heteroreceptor Complexes and Their Integration of Signals in Neurons and Astroglia-Relevance for Mental Diseases.

The heteroreceptor complexes present a novel biological principle for signal integration. These complexes and their allosteric receptor-receptor interactions are bidirectional and novel targets for treatment of CNS diseases including mental diseases. The existence of D2R-5-HT2AR heterocomplexes can help explain the anti-schizophrenic effects of atypical antipsychotic drugs not only based on blockade of 5-HT2AR and of D2R in higher doses but also based on blocking the allosteric enhancement of D2R protomer signaling by 5-HT2AR protomer activation. This research opens a new understanding of the integration of DA and 5-HT signals released from DA and 5-HT nerve terminal networks. The biological principle of forming 5-HT and other heteroreceptor complexes in the brain also help understand the mechanism of action for especially the 5-HT hallucinogens, including putative positive effects of e.g., psilocybin and the indicated prosocial and anti-stress actions of MDMA (ecstasy). The GalR1-GalR2 heterodimer and the putative GalR1-GalR2-5-HT1 heteroreceptor complexes are targets for Galanin N-terminal fragment Gal (1-15), a major modulator of emotional networks in models of mental disease. GPCR-receptor tyrosine kinase (RTK) heteroreceptor complexes can operate through transactivation of FGFR1 via allosteric mechanisms and indirect interactions over GPCR intracellular pathways involving protein kinase Src which produces tyrosine phosphorylation of the RTK. The exciting discovery was made that several antidepressant drugs such as TCAs and SSRIs as well as the fast-acting antidepressant drug ketamine can directly bind to the TrkB receptor and provide a novel mechanism for their antidepressant actions. Understanding the role of astrocytes and their allosteric receptor-receptor interactions in modulating forebrain glutamate synapses with impact on dorsal raphe-forebrain serotonin neurons is also of high relevance for research on major depressive disorder.