Protective actions of des-acylated ghrelin on brain injury and blood-brain barrier disruption after stroke in mice

The major ghrelin forms, acylated ghrelin and des-acylated ghrelin, are novel gastrointestinal hormones. Moreover, emerging evidence indicates that these peptides may have other functions including neuro- and vaso-protection. Here, we investigated whether post-stroke treatment with acylated ghrelin or des-acylated ghrelin could improve functional and histological endpoints of stroke outcome in mice after transient middle cerebral artery occlusion (tMCAo). We found that des-acylated ghrelin (1 mg/kg) improved neurological and functional performance, reduced infarct and swelling, and decreased apoptosis. In addition, it reduced blood-brain barrier (BBB) disruption in vivo and attenuated the hyper-permeability of mouse cerebral microvascular endothelial cells after oxygen glucose deprivation and reoxygenation (OGD + RO). By contrast, acylated ghrelin (1 mg/kg or 5 mg/kg) had no significant effect on these endpoints of stroke outcome. Next we found that des-acylated ghrelin's vasoprotective actions were associated with increased expression of tight junction proteins (occludin and claudin-5), and decreased cell death. Moreover, it attenuated superoxide production, Nox activity and expression of 3-nitrotyrosine. Collectively, these results demonstrate that post-stroke treatment with des-acylated ghrelin, but not acylated ghrelin, protects against ischaemia/reperfusion-induced brain injury and swelling, and BBB disruption, by reducing oxidative and/or nitrosative damage

Ghrelin

Background: The gastrointestinal peptide hormone ghrelin was discovered in 1999 as the endogenous ligand of the growth hormone secretagogue receptor. Increasing evidence supports more complicated and nuanced roles for the hormone, which go beyond the regulation of systemic energy metabolism. Scope of review: In this review, we discuss the diverse biological functions of ghrelin, the regulation of its secretion, and address questions that still remain 15 years after its discovery. Major conclusions: In recent years, ghrelin has been found to have a plethora of central and peripheral actions in distinct areas including learning and memory, gut motility and gastric acid secretion, sleep/wake rhythm, reward seeking behavior, taste sensation and glucose metabolism

Actions of NPY, and its Y1 and Y2 receptors on pulsatile growth hormone secretion during the fed and fasted state

The hypothalamic NPY system plays an important role in regulating food intake and energy expenditure. Different biological actions of NPY are assigned to NPY receptor subtypes. Recent studies demonstrated a close relationship between food intake and growth hormone (GH) secretion; however, the mechanism through which endogenous NPY modulates GH release remains unknown. Moreover, conclusive evidence demonstrating a role for NPY and Y-receptors in regulating the endogenous pulsatile release of GH does not exist. We used genetically modified mice (germline Npy, Y1, and Y2 receptor knock-out mice) to assess pulsatile GH secretion under both fed and fasting conditions. Deletion of NPY did not impact fed GH release; however, it reversed the fasting-induced suppression of pulsatile GH secretion. The recovery of GH secretion was associated with a reduction in hypothalamic somatotropin release inhibiting factor (Srif; somatostatin) mRNA expression. Moreover, observations revealed a differential role for Y1 and Y2 receptors, wherein the postsynaptic Y1 receptor suppresses GH secretion in fasting. In contrast, the presynaptic Y2 receptor maintains normal GH output under long-term ad libitum-fed conditions. These data demonstrate an integrated neural circuit that modulates GH release relative to food intake, and provide essential information to address the differential roles of Y1 and Y2 receptors in regulating the release of GH under fed and fasting states

Liver-expressed antimicrobial peptide 2 is associated with improved pancreatic insulin secretion in adults with overweight and obesity

Aims: To examine association of liver-expressed antimicrobial peptide 2 (LEAP2), an endogenous ghrelin antagonist with anorexiant effects, to key cardiometabolic risk factors in people with overweight and obesity. Methods: In this cross-sectional study, we sought to identify associations between LEAP2 levels and cardiometabolic risk factors, including body composition (dual X-ray absorptiometry), insulin and glucose metabolism (oral and intravenous glucose tolerance tests and hyperinsulinaemic-euglycaemic clamps), plasma lipids and inflammation markers (ELISA and multiplex assays). Results: In 65 participants with overweight or obesity (63.1% male, mean age 31.3 ± 8.5 years), LEAP2 levels were associated with total body fat, but not with body mass index or waist-hip ratio in both univariable and age- and sex-adjusted models (P < 0.05). Higher LEAP2 level was also positively associated with higher insulin secretion in univariable (P = 0.047) and multivariable models adjusted for age, sex and body fat (P = 0.03), but not with fasting glucose levels (P ≥ 0.05). Higher LEAP2 levels were associated insulin resistance (P = 0.07) after adjustment for age and sex, but the association disappeared after an additional adjustment for body fat (P = 0.2). There was an inverse association between LEAP2 levels and nuclear factor kappa-B (NFκB) activity in the peripheral blood mononuclear cells in age-, sex- and body fat-adjusted models (P = 0.04). There were no associations with cardiovascular risk factors (lipids, blood pressure) or other inflammation markers. Conclusions: These results provide important insights into the association between LEAP2 and cardiometabolic health in a high-risk population of individuals with overweight and obesity. This is a first report of an association between LEAP2 and insulin secretion, insulin sensitivity and NFκB activity. LEAP2 may represent an important potential therapeutic target to promote insulin secretion in people with type 2 diabetes and obesity

Ghrelin-AMPK Signaling Mediates the Neuroprotective Effects of Calorie Restriction in Parkinson's Disease

Jacqeline Bayliss, Romana Stark, Moyra Lemus, Vanessa Santos, Aiysha Thompson, Daniel Rees, Sandra Galic, John Elsworth, Bruce Kemp, Jeffrey Davies, and Zane Andrew

Leptin and Insulin Act on POMC Neurons to Promote the Browning of White Fat

SummaryThe primary task of white adipose tissue (WAT) is the storage of lipids. However, “beige” adipocytes also exist in WAT. Beige adipocytes burn fat and dissipate the energy as heat, but their abundance is diminished in obesity. Stimulating beige adipocyte development, or WAT browning, increases energy expenditure and holds potential for combating metabolic disease and obesity. Here, we report that insulin and leptin act together on hypothalamic neurons to promote WAT browning and weight loss. Deletion of the phosphatases PTP1B and TCPTP enhanced insulin and leptin signaling in proopiomelanocortin neurons and prevented diet-induced obesity by increasing WAT browning and energy expenditure. The coinfusion of insulin plus leptin into the CNS or the activation of proopiomelanocortin neurons also increased WAT browning and decreased adiposity. Our findings identify a homeostatic mechanism for coordinating the status of energy stores, as relayed by insulin and leptin, with the central control of WAT browning

Calorie restriction activates new adult born olfactory‐bulb neurones in a ghrelin‐dependent manner but acyl‐ghrelin does not enhance subventricular zone neurogenesis

The ageing and degenerating brain show deficits in neural stem/progenitor cell (NSPC) plasticity that are accompanied by impairments in olfactory discrimination. Emerging evidence suggests that the gut hormone ghrelin plays an important role in protecting neurones, promoting synaptic plasticity and increasing hippocampal neurogenesis in the adult brain. In the present study, we investigated the role of ghrelin with respect to modulating adult subventricular zone (SVZ) NSPCs that give rise to new olfactory bulb (OB) neurones. We characterised the expression of the ghrelin receptor, growth hormone secretagogue receptor (GHSR), using an immunohistochemical approach in GHSR‐eGFP reporter mice to show that GHSR is expressed in several regions, including the OB but not in the SVZ of the lateral ventricle. These data suggest that acyl‐ghrelin does not mediate a direct effect on NSPC in the SVZ. Consistent with these findings, treatment with acyl‐ghrelin or genetic silencing of GHSR did not alter NSPC proliferation within the SVZ. Similarly, using a bromodeoxyuridine pulse‐chase approach, we show that peripheral treatment of adult rats with acyl‐ghrelin did not increase the number of new adult‐born neurones in the granule cell layer of the OB. These data demonstrate that acyl‐ghrelin does not increase adult OB neurogenesis. Finally, we investigated whether elevating ghrelin indirectly, via calorie restriction (CR), regulated the activity of new adult‐born cells in the OB. Overnight CR induced c‐Fos expression in new adult‐born OB cells but not in developmentally born cells, whereas neuronal activity was absent following re‐feeding. These effects were not present in ghrelin−/− mice, suggesting that adult‐born cells are uniquely sensitive to changes in ghrelin mediated by fasting and re‐feeding. In summary, ghrelin does not promote neurogenesis in the SVZ and OB; however, new adult‐born OB cells are activated by CR in a ghrelin‐dependent manner

Unacylated-Ghrelin Impairs Hippocampal Neurogenesis and Memory in Mice and Is Altered in Parkinson’s Dementia in Humans

Blood-borne factors regulate adult hippocampal neurogenesis and cognition in mammals. We report that elevating circulating unacylated-ghrelin (UAG), using both pharmacological and genetic methods, reduced hippocampal neurogenesis and plasticity in mice. Spatial memory impairments observed in ghrelin-O-acyl transferase-null (GOAT/) mice that lack acyl-ghrelin (AG) but have high levels of UAG were rescued by acyl-ghrelin. Acyl-ghrelin-mediated neurogenesis in vitro was dependent on non-cell-autonomous BDNF signaling that was inhibited by UAG. These findings suggest that post-translational acylation of ghrelin is important to neurogenesis and memory in mice. To determine relevance in humans, we analyzed circulating AG:UAG in Parkinson disease (PD) patients diagnosed with dementia (PDD), cognitively intact PD patients, and controls. Notably, plasma AG:UAG was only reduced in PDD. Hippocampal ghrelin-receptor expression remained unchanged; however, GOAT+ cell number was reduced in PDD. We identify UAG as a regulator of hippocampal-dependent plasticity and spatial memory and AG:UAG as a putative circulating diagnostic biomarker of dementia