Activation of galanin receptor 2 stimulates large conductance Ca2+-dependent K+ (BK) channels through the IP3 pathway in human embryonic kidney (HEK293) cells

Downregulation of the expression of galanin impairs erectile function in hypoandrogenic rats

Background

The relationship between galanin and erectile function under low androgen levels is still unclear.

Aim

To explore whether a low testosterone level damages the erection of a rat by regulating the expression of galanin and GalR in penile cavernous tissue.

Methods

Thirty-six male Sprague-Dawley rats, 8 weeks of age, were randomly grouped as follows (n = 6): control, castration, castration + testosterone replacement, control + transfection, castration + transfection, and castration + empty transfection. At 4 weeks after castration, rats in the transfection group were injected with lentivirus carrying the targeting galanin gene (2 × 10⁸ TU/mL, 10 μL) in the corpus cavernosum. After 1 week of injection, the intracavernosal pressure (ICP), mean arterial blood pressure (MAP), nitric oxide (NO), serum testosterone concentration, galanin, GalR1-3, ROCK1, ROCK2, and p-eNOS/eNOS in the rat penile tissues were evaluated.

Outcomes

ICPmax/MAP and the expression of galanin in the corpus cavernosum in castrated rats were obviously decreased as compared with those in the control rats.

Results

The castrated rats showed remarkably lower ICPmax/MAP, galanin, GalR1-3, p-eNOS/eNOS, and NO content and markedly higher ROCK1 and ROCK2 in penile tissues than the control group (P < .05). The transfected rats administrated with LV Gal had obviously higher ICPmax/MAP, p-eNOS/eNOS, and NO content and less ROCK1 and ROCK2 protein expression in the corpus cavernosum when compared with the castration group (P < .05).

Clinical Translation

Upregulating the expression of galanin in the penile corpus cavernosum might be a novel method of treating erectile dysfunction caused by a low androgen level.

Strengths and Limitations

The conclusions obtained in the animal experiments need to be confirmed in human data.

Conclusion

The erectile function of hypoandrogen rats might be inhibited by downregulating the level of galanin and GalR1-3, upregulating ROCK1 and ROCK2 levels, and inhibiting the eNOS/NO signaling pathway in penile corpus cavernosum.

Effects of Intracerebroventricular Injection of Spexin and its Interaction with NPY, GalR2 and GalR3 Receptors on the Central Food Intake Regulation and Nutritional Behavior in Broiler Chickens

Food intake and appetite in birds can be adjusted by the complex homeostatic control mechanisms. There seem to be many similarities between mammalian and avian species in terms of the regulatory feeding systems. Therefore, the aim of this study was to investigate the effects of ICV injection of spexin and its interaction with GalR and NPY receptors on central food intake regulation and nutritional behavior in broiler chickens. In experiment 1, chicken received ICV injection of saline, spexin (2.5nmol), spexin (5nmol) and spexin (10nmol). In experiment 2, birds received ICV injection of saline, B5063 (NPY₁ receptor antagonist 1.25µg), spexin (10nmol) and B5063+spexin. In experiments 3-6, SF22 (NPY₂ receptor antagonist ,1.25µg), ML0891 (NPY₅ receptor antagonist ,1.25µg), M871 (GalR₂ receptor antagonist ,10nmol) and SNAP37889 (GalR₃ receptor antagonist,10nmol) were injected in chickens instead of B5063. Then food intake was measured until 120 minutes after the injection and nutritional behavior was monitored at 30 minutes after the injection. Based on the data, a dose-dependent hypophagia was observed by the injection of spexin (P<0.05). Concomitant injection of B5063+spexin enhanced spexin-induced hypophagia (P<0.05). Co-injection of SNAP37889+spexin (10nmol) attenuated -induced hypophagia (P<0.05). Spexin (5 and 10 nmol) decreased number of steps, jumps, the exploratory food and pecks at 15 minutes after the injection (P<0.05). Spexin (5 and 10nmol) decreased standing time while siting time and rest time increased at 10 minutes after injection (P<0.05). Based on observations, spexin-induced hypophagia could be mediated by NPY₁ and GalR₃ receptors in neonatal broiler chickens.

Galanin suppresses proliferation of human U251 and T98G glioma cells via its subtype 1 receptor

Galanin is a neuropeptide with a widespread distribution throughout the nervous and endocrine systems, and recent studies have shown an anti-proliferative effect of galanin on several types of tumors. However, whether and how galanin and its receptors are involved in the regulation of cell proliferation in glioma cells remains unclear. In this study, the roles of galanin and its subtype 1 receptor (GAL1) in the proliferation of human U251 and T98G glioma cells were investigated. We found that galanin significantly suppressed the proliferation of U251 and T98G cells as well as tumor growth in nude mice. However, galanin did not exert apoptotic or cytotoxic effects on these two cell lines. In addition, we showed that galanin decreased the proliferation of U251 and T98G cells via its GAL1 receptor. Finally, we found that the GAL1 receptor was involved in the suppressive effects of galanin by activating ERK1/2.

Characterization of the Rat GAL2R Promoter: Positive Role of ETS-1 in Regulation of the Rat GAL2R Gene in PC12 Cells

Galanin receptor 2 (GAL2R) is a G protein-coupled receptor for the neuropeptide galanin that regulates many important physiological functions and pathological processes. To investigate the molecular mechanism governing GAL2R gene transcription, the rat GAL2R promoter was isolated and analyzed. We found that the region from -320 to -300 of the GAL2R promoter contains two putative ETS-1 elements and plays an important role in regulating GAL2R promoter activity. We also showed that transcription factor ETS-1 bound to this region in vitro and in vivo. Overexpression of ETS-1 significantly increased GAL2R promoter activity and transcription of the GAL2R gene, whereas knockdown of ETS-1 produced the opposite effects. In addition, we showed that ETS-1 recruited co-activator p300 to the GAL2R promoter. These data indicate a role for ETS-1 in the control of the GAL2R gene expression and provide a basis for understanding the transcriptional regulation of the GAL2R gene.

Galanin and its receptor system promote the repair of injured sciatic nerves in diabetic rats

Various studies have reported that galanin can promote axonal regeneration of dorsal root ganglion neurons in vitro and inhibit neuropathic pain. However, little is known about its effects on diabetic peripheral neuropathy, and in vivo experimental data are lacking. We hypothesized that repeated applications of exogenous galanin over an extended time frame may also repair nerve damage in diabetic peripheral neuropathy, and relieve pain in vivo. We found that neuropathic pain occurred in streptozotocin-induced diabetic rats and was more severe after sciatic nerve pinch injury at 14 and 28 days than in diabetic sham-operated rats. Treatment with exogenous galanin alleviated the neuropathic pain and promoted sciatic nerve regeneration more effectively in diabetic rats than in non-diabetic rats after sciatic nerve pinch injury. This was accompanied by changes in the levels of endogenous galanin, and its receptors galanin receptor 1 and galanin receptor 2 in the dorsal root ganglia and the spinal dorsal horn when compared with nerve pinch normal rats. Our results show that application of exogenous galanin daily for 28 days can promote the regeneration of injured sciatic nerves, and alleviate neuropathic pain in diabetic rats.

Spexin Enhances Bowel Movement through Activating L-type Voltage-dependent Calcium Channel via Galanin Receptor 2 in Mice

A novel neuropeptide spexin was found to be broadly expressed in various endocrine and nervous tissues while little is known about its functions. This study investigated the role of spexin in bowel movement and the underlying mechanisms. In functional constipation (FC) patients, serum spexin levels were significantly decreased. Consistently, in starved mice, the mRNA of spexin was significantly decreased in intestine and colon. Spexin injection increased the velocity of carbon powder propulsion in small intestine and decreased the glass beads expulsion time in distal colon in mice. Further, spexin dose-dependently stimulated the intestinal/colonic smooth muscle contraction. Galanin receptor 2 (GALR2) antagonist M871, but not Galanin receptor 3 (GALR3) antagonist SNAP37899, effectively suppressed the stimulatory effects of spexin on intestinal/colonic smooth muscle contraction, which could be eliminated by extracellular [Ca²⁺] removal and L-type voltage-dependentCa²⁺ channel (VDCC) inhibitor nifedipine. Besides, spexin dramatically increased the [Ca²⁺]i in isolated colonic smooth muscle cells. These data indicate that spexin can act on GALR2 receptor to regulate bowel motility by activating L-type VDCC. Our findings provide evidence for important physiological roles of spexin in GI functions. Selective action on spexin pathway might have therapeutic effects on GI diseases with motility disorders.

Physiology, signaling, and pharmacology of galanin peptides and receptors: three decades of emerging diversity

Galanin was first identified 30 years ago as a "classic neuropeptide," with actions primarily as a modulator of neurotransmission in the brain and peripheral nervous system. Other structurally-related peptides-galanin-like peptide and alarin-with diverse biologic actions in brain and other tissues have since been identified, although, unlike galanin, their cognate receptors are currently unknown. Over the last two decades, in addition to many neuronal actions, a number of nonneuronal actions of galanin and other galanin family peptides have been described. These include actions associated with neural stem cells, nonneuronal cells in the brain such as glia, endocrine functions, effects on metabolism, energy homeostasis, and paracrine effects in bone. Substantial new data also indicate an emerging role for galanin in innate immunity, inflammation, and cancer. Galanin has been shown to regulate its numerous physiologic and pathophysiological processes through interactions with three G protein-coupled receptors, GAL1, GAL2, and GAL3, and signaling via multiple transduction pathways, including inhibition of cAMP/PKA (GAL1, GAL3) and stimulation of phospholipase C (GAL2). In this review, we emphasize the importance of novel galanin receptor-specific agonists and antagonists. Also, other approaches, including new transgenic mouse lines (such as a recently characterized GAL3 knockout mouse) represent, in combination with viral-based techniques, critical tools required to better evaluate galanin system physiology. These in turn will help identify potential targets of the galanin/galanin-receptor systems in a diverse range of human diseases, including pain, mood disorders, epilepsy, neurodegenerative conditions, diabetes, and cancer.