Dataset Information

α-Melanocyte-stimulating hormone regulates vascular NO availability and protects against endothelial dysfunction.

ABSTRACT:

Aims

α-Melanocyte-stimulating hormone (α-MSH), derived from the precursor molecule pro-opiomelanocortin, exerts potent anti-inflammatory actions in the vasculature, but its role in circulatory regulation remains unclear. Therefore, we sought to investigate whether α-MSH could regulate the local control of blood vessel tone.

Methods and results

Using in vivo and ex vivo methods to assess vascular reactivity, we found that α-MSH improved endothelium-dependent vasodilatation in the mouse aorta and coronary circulation without directly contracting or relaxing blood vessels. α-MSH promoted vasodilatation by enhancing endothelial nitric oxide (NO) formation and by improving sensitivity to endothelium-independent blood vessel relaxation. Using cultured human endothelial cells to elucidate the involved molecular mechanisms, we show that α-MSH increased the expression and phosphorylation of endothelial NO synthase in these cells. The observed effects were regulated by melanocortin 1 (MC1) receptors expressed in the endothelium. In keeping with the vascular protective role of α-MSH, in vivo treatment with stable analogues of α-MSH ameliorated endothelial dysfunction associated with aging and diet-induced obesity in mice.

Conclusion

The present study identifies α-MSH and endothelial MC1 receptors as a new signalling pathway contributing to the regulation of NO availability and vascular function. These findings suggest applicability of α-MSH analogues for therapeutic use in pathological conditions that are characterized by vascular dysfunction.

SUBMITTER: Rinne P

PROVIDER: S-EPMC3543993 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:AimsOxidative stress and apoptosis are among the earliest lesions of diabetic retinopathy. This study sought to examine the anti-oxidative and anti-apoptotic effects of α-melanocyte-stimulating hormone (α-MSH) in early diabetic retinas and to explore the underlying mechanisms in retinal vascular endothelial cells.MethodsSprague-Dawley rats were injected intravenously with streptozocin to induce diabetes. The diabetic rats were injected intravitreally with α-MSH or saline. At week 5 after diabetes, the retinas were analyzed for reactive oxygen species (ROS) and gene expression. One week later, the retinas were processed for terminal deoxynucleotidyl transferase dUTP nick-end labeling staining and transmission electron microscopy. Retinal vascular endothelial cells were stimulated by high glucose (HG) with or without α-MSH. The expression of Forkhead box O genes (Foxos) was examined through real-time PCR. The Foxo4 gene was overexpressed in endothelial cells by transient transfection prior to α-MSH or HG treatment, and oxidative stress and apoptosis were analyzed through CM-H2DCFDA and annexin-V assays, respectively.ResultsIn diabetic retinas, the levels of H2O2 and ROS and the total anti-oxidant capacity were normalized, the apoptotic cell number was reduced, and the ultrastructural injuries were ameliorated by α-MSH. Treatment with α-MSH also corrected the aberrant changes in eNOS, iNOS, ICAM-1, and TNF-α expression levels in diabetic retinas. Furthermore, α-MSH inhibited Foxo4 up-regulation in diabetic retinas and in endothelial cells exposed to HG, whereas Foxo4 overexpression abrogated the anti-oxidative and anti-apoptotic effects of α-MSH in HG-stimulated retinal vascular endothelial cells.Conclusionsα-MSH normalized oxidative stress, reduced apoptosis and ultrastructural injuries, and corrected gene expression levels in early diabetic retinas. The protective effects of α-MSH in retinal vascular endothelial cells may be mediated through the inhibition of Foxo4 up-regulation induced by HG. This study suggests an α-MSH-mediated potential intervention approach to early diabetic retinopathy and a novel regulatory mechanism involving Foxo4.

Project description:ObjectiveDuring infection, metabolism and immunity react dynamically to promote survival through mechanisms that remain unclear. Pro-opiomelanocortin (POMC) cleavage products are produced and released in the brain and in the pituitary gland. One POMC cleavage product, alpha-melanocyte-stimulating hormone (α-MSH), is known to regulate food intake and energy expenditure and has anti-inflammatory effects. However, it is not known whether α-MSH is required to regulate physiological anti-inflammatory responses. We recently developed a novel mouse model with a targeted mutation in Pomc (Pomctm1/tm1 mice) to block production of all α-MSH forms which are required to regulate metabolism. To test whether endogenous α-MSH is required to regulate immune responses, we compared acute bacterial lipopolysaccharide (LPS)-induced inflammation between Pomctm1/tm1 and wild-type Pomcwt/wt mice.MethodsWe challenged 10- to 14-week-old male Pomctm1/tm1 and Pomcwt/wt mice with single i.p. injections of either saline or low-dose LPS (100 μg/kg) and monitored immune and metabolic responses. We used telemetry to measure core body temperature (Tb), ELISA to measure circulating cytokines, corticosterone and α-MSH, and metabolic chambers to measure body weight, food intake, activity, and respiration. We also developed a mass spectrometry method to measure three forms of α-MSH produced in the mouse hypothalamus and pituitary gland.ResultsLPS induced an exaggerated immune response in Pomctm1/tm1 compared to Pomcwt/wt mice. Both groups of mice were hypoactive and hypothermic following LPS administration, but Pomctm1/tm1 mice were significantly more hypothermic compared to control mice injected with LPS. Pomctm1/tm1 mice also had reduced oxygen consumption and impaired metabolic responses to LPS compared to controls. Pomctm1/tm1 mice had increased levels of key proinflammatory cytokines at 2 h and 4 h post LPS injection compared to Pomcwt/wt mice. Lastly, Pomcwt/wt mice injected with LPS compared to saline had increased total α-MSH in circulation 2 h post injection.ConclusionsOur data indicate endogenous α-MSH contributes to the inflammatory immune responses triggered by low-dose LPS administration and suggest that targeting the melanocortin system could be a potential therapeutic for the treatment of sepsis or inflammatory disease.

Project description:ImportanceCorneal endothelial cell (CEnC) damage and loss are major issues in eye banking and transplantation. The underlying mechanisms for CEnC loss are incompletely understood, and cytoprotective strategies that enhance CEnC viability could have a major effect on donor tissue quality and graft survival.ObjectiveTo investigate the cytoprotective role of neuropeptide α-melanocyte-stimulating hormone (α-MSH) in preventing CEnC loss in eye bank cold-stored corneas under oxidative and inflammatory cytokine-induced stress.Design, setting, and participantsThis single-center comparative research study conducted ex vivo experiments using 16 pairs of research-grade human donor corneas (courtesy of Eversight Eye Bank). Data were collected from June 2018 to November 2019, and data were analyzed from December 2019 to January 2020.ExposuresTwo corneas from the same donor were randomized to either control or 0.1 mmol/L of α-MSH treatment and then subjected to oxidative stress (1.4 mmol/L of hydrogen peroxide-phosphate-buffered saline for 15 minutes at 37 °C; n = 8 pairs) or cytokine-induced stress (100 ng/mL of tumor necrosis factor-α and 100 ng/mL of interferon γ for 18 hours at 37 °C; n = 8 pairs). Corneas were then stored at 4 °C. Specular images were taken at baseline and repeated twice per week using a calibrated wide-field specular microscope. CEnC viability was assessed using a fluorescent live/dead viability assay.Main outcome and measuresEndothelial morphometry analysis, central corneal thickness measurements, and percentage of dead cells at day 11.ResultsOf 16 donors who provided corneas, 9 (56%) were male, and the mean (SD) age was 57.9 (12.4) years. Corneas were paired, and baseline parameters were comparable between all groups. At all time points, CEnC loss was lower in the α-MSH groups compared with the control groups. This difference was statistically significant after cytokine-induced stress (20.2% vs 35.2%; sample estimate of median, -14.9; 95% CI, -23.6 to -6.3; P = .008). Compared with the control group, α-MSH treatment resulted in a smaller increase in central corneal thickness (cytokine-induced stress: 89.3 μm vs 169.8 μm; sample estimate of median, -84.9; 95% CI, -131.5 to -41.6; P = .008; oxidative stress: 43.6 μm vs 111.9 μm; sample estimate of median, -68.8; 95% CI, -100.0 to -34.5; P = .008) and a smaller proportion of cell death (cytokine-induced stress: 2.7% vs 10.4%; difference, -7.7; 95% CI, -13.1 to -2.4; P = .01; oxidative stress: 2.9% vs 12.4%; difference, 9.5; 95% CI, 5.1 to 13.9; P = .006).Conclusions and relevanceIn this study, α-MSH treatment attenuated CEnC loss during cold storage after acute oxidative and cytokine-induced stress in human eye bank cold-stored corneas. These data suggest that supplementation of corneal storage solution with α-MSH may positively affect CEnC survival after transplant and protect the endothelium from proinflammatory cytokines and oxidative stress after full-thickness or endothelial keratoplasty, which is particularly valuable in patients at high risk of graft failure.