Targeted deletions of Mel1a and Mel1b melatonin receptors affect pCREB levels in lactotroph and pars intermedia cells of mice

Several studies have revealed that melatonin affects the insulin secretion via MT(1) and MT(2) receptor isoforms. Owing to the lack of selective MT(1) receptor antagonists, we used RNA interference technology to generate an MT(1) knockdown in a clonal β-cell line to evaluate whether melatonin modulates insulin secretion specifically via the MT(1) receptor. Incubation experiments were carried out, and the insulin concentration in supernatants was measured using a radioimmunoassay. Furthermore, the intracellular cAMP was determined using an enzyme-linked immunosorbent assay. Real-time RT-PCR indicated that MT(1) knockdown resulted in a significant increase in the rIns1 mRNA and a significantly elevated basal insulin secretion of INS-1 cells. Incubation with melatonin decreased the amount of glucagon-like peptide 1 or inhibited the glucagon-stimulated insulin release of INS-1 cells, while, in MT(1) -knockdown cells, no melatonin-induced reduction in insulin secretion could be found. No decrease in 3-isobutyl-1-methylxanthine-stimulated intracellular cAMP in rMT(1) -knockdown cells was detectable after treatment with melatonin either, and immunocytochemistry proved that MT(1) knockdown abolished phosphorylation of cAMP-response-element-binding protein. In contrast to the INS-1 cells, preincubation with melatonin did not sensitize the insulin secretion of rMT(1) -knockdown cells. We also monitored insulin secretion from isolated islets of wild-type and melatonin-receptor knockout mice ex vivo. In islets of wild-type mice, melatonin treatment resulted in a decrease in insulin release, whereas melatonin treatment of islets from MT(1) knockout and MT(1/2) double-knockout mice did not show a significant effect. The data indicate that melatonin inhibits insulin secretion, primarily via the MT(1) receptor in rat INS-1 cells and isolated mouse islets.

Section: Influence Of Melatonin On Insulin Secretionmentioning

confidence: 79%

Melatonin influences insulin secretion primarily via MT1 receptors in rat insulinoma cells (INS-1) and mouse pancreatic islets

Mühlbauer¹,

Albrecht²,

Bazwinsky-Wutschke³

et al. 2012

“…Secondly, we and others reported previously that myocardial melatonin membrane receptors participated in its cardioprotective action [25,71]. As melatonin membrane receptors (Mel1a receptor and Mel1b receptor) conduct different signaling pathways in different cell types [72][73][74], further study is required to determine the role and mechanism of melatonin membrane receptors in its protective action in diabetic state.…”

Section: Discussionmentioning

confidence: 93%

Reduced silent information regulator 1 signaling exacerbates myocardial ischemia–reperfusion injury in type 2 diabetic rats and the protective effect of melatonin

Liu

Dong

et al. 2015

109

Diabetes mellitus (DM) increases myocardial oxidative stress and endoplasmic reticulum (ER) stress. Melatonin confers cardioprotective effect by suppressing oxidative damage. However, the effect and mechanism of melatonin on myocardial ischemia-reperfusion (MI/R) injury in type 2 diabetic state are still unknown. In this study, we developed high-fat diet-fed streptozotocin (HFD-STZ) rat, a well-known type 2 diabetic model, to evaluate the effect of melatonin on MI/R injury with a focus on silent information regulator 1 (SIRT1) signaling, oxidative stress, and PERK/eIF2α/ATF4-mediated ER stress. HFD-STZ treated rats were exposed to melatonin treatment in the presence or the absence of sirtinol (a SIRT1 inhibitor) and subjected to MI/R surgery. Compared with nondiabetic animals, type 2 diabetic rats exhibited significantly decreased myocardial SIRT1 signaling, increased apoptosis, enhanced oxidative stress, and ER stress. Additionally, further reduced SIRT1 signaling, aggravated oxidative damage, and ER stress were found in diabetic animals subjected to MI/R surgery. Melatonin markedly reduced MI/R injury by improving cardiac functional recovery and decreasing myocardial apoptosis in type 2 diabetic animals. Melatonin treatment up-regulated SIRT1 expression, reduced oxidative damage, and suppressed PERK/eIF2α/ATF4 signaling. However, these effects were all attenuated by SIRT1 inhibition. Melatonin also protected high glucose/high fat cultured H9C2 cardiomyocytes against simulated ischemia-reperfusion injury-induced ER stress by activating SIRT1 signaling while SIRT1 siRNA blunted this action. Taken together, our study demonstrates that reduced cardiac SIRT1 signaling in type 2 diabetic state aggravates MI/R injury. Melatonin ameliorates reperfusion-induced oxidative stress and ER stress via activation of SIRT1 signaling, thus reducing MI/R damage and improving cardiac function.

“…In conclusion, the observed alterations of pancreatic islet hormones, in the present study, were possibly caused by melatonin receptor‐dependent CREB modulation. MT1‐modulated pCREB levels have been observed in the lactotroph cell of the pituitary gland by use of mouse lines with a targeted deletion of the receptor . Jin et al.…”

Section: Discussionmentioning

confidence: 99%

“…In conclusion, the observed alterations of pancreatic islet hormones, in the present study, were possibly caused by melatonin receptor-dependent CREB modulation. MT1-modulated pCREB levels have been observed in the lactotroph cell of the pituitary gland by use of mouse lines with a targeted deletion of the receptor [56]. Jin et al [31] have shown for the suprachiasmatic nucleus that both melatonin receptor subtypes contribute to regulation of CREB phosphorylation, although the MT1 receptor mediates responses to low concentrations of melatonin, while the residual response at higher concentrations is mediated by the MT2 receptor.…”

Section: Discussionmentioning

confidence: 99%

Influence of melatonin receptor signalling on parameters involved in blood glucose regulation

Bazwinsky-Wutschke

Bieseke

Mühlbauer

et al. 2013

The pineal hormone melatonin is known to influence insulin secretion via the G-protein-coupled receptor isoforms MT1 and MT2. The present study was aimed to further elucide the impact of melatonin on blood glucose regulation. To this end, mouse lines were used, in which one of the two or both melatonin receptors were deleted. In comparison with wild-type mice of the same age (8-12 months old), increased plasma insulin and melatonin levels and decreased blood glucose levels and body weights were detected in the MT1- and double-knockout lines. The elimination of melatonin receptor signalling also altered blood glucose concentrations, body weight and melatonin and insulin levels when comparing wild-type and receptor knockout mice of different ages (6 wk and 8-12 months old); such changes, however, were dependent on the type of receptor deleted. Furthermore, reverse transcription polymerase chain reaction results provided evidence that melatonin receptor deficiency has an impact on transcript levels of pancreatic islet hormones as well as on pancreatic and hepatic glucose transporters (Glut1 and 2). Under stimulated insulin secretion in the presence of melatonin in the rat insulinoma β-cells INS-1, the Glut1 transcript level was decreased. In conclusion, the present findings demonstrate that melatonin receptor knockout types affect blood glucose levels, body weight, plasma levels of melatonin and insulin, as well as pancreatic hormone and Glut1 expression in significantly different manners.