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.

Des-Acyl Ghrelin and Ghrelin O-Acyltransferase Regulate Hypothalamic-Pituitary-Adrenal Axis Activation and Anxiety in Response to Acute Stress.

Ghrelin exists in two forms in circulation, acyl ghrelin and des-acyl ghrelin, both of which have distinct and fundamental roles in a variety of physiological functions. Despite this fact, a large proportion of papers simply measure and refer to plasma ghrelin without specifying the acylation status. It is therefore critical to assess and state the acylation status of plasma ghrelin in all studies. In this study we tested the effect of des-acyl ghrelin administration on the hypothalamic-pituitary-adrenal axis and on anxiety-like behavior of mice lacking endogenous ghrelin and in ghrelin-O-acyltransferase (GOAT) knockout (KO) mice that have no endogenous acyl ghrelin and high endogenous des-acyl ghrelin. Our results show des-acyl ghrelin produces an anxiogenic effect under nonstressed conditions, but this switches to an anxiolytic effect under stress. Des-acyl ghrelin influences plasma corticosterone under both nonstressed and stressed conditions, although c-fos activation in the paraventricular nucleus of the hypothalamus is not different. By contrast, GOAT KO are anxious under both nonstressed and stressed conditions, although this is not due to corticosterone release from the adrenals but rather from impaired feedback actions in the paraventricular nucleus of the hypothalamus, as assessed by c-fos activation. These results reveal des-acyl ghrelin treatment and GOAT deletion have differential effects on the hypothalamic-pituitary-adrenal axis and anxiety-like behavior, suggesting that anxiety-like behavior in GOAT KO mice is not due to high plasma des-acyl ghrelin.

Metformin Prevents Nigrostriatal Dopamine Degeneration Independent of AMPK Activation in Dopamine Neurons.

Metformin is a widely prescribed drug used to treat type-2 diabetes, although recent studies show it has wide ranging effects to treat other diseases. Animal and retrospective human studies indicate that Metformin treatment is neuroprotective in Parkinson's Disease (PD), although the neuroprotective mechanism is unknown, numerous studies suggest the beneficial effects on glucose homeostasis may be through AMPK activation. In this study we tested whether or not AMPK activation in dopamine neurons was required for the neuroprotective effects of Metformin in PD. We generated transgenic mice in which AMPK activity in dopamine neurons was ablated by removing AMPK beta 1 and beta 2 subunits from dopamine transporter expressing neurons. These AMPK WT and KO mice were then chronically exposed to Metformin in the drinking water then exposed to MPTP, the mouse model of PD. Chronic Metformin treatment significantly attenuated the MPTP-induced loss of Tyrosine Hydroxylase (TH) neuronal number and volume and TH protein concentration in the nigrostriatal pathway. Additionally, Metformin treatment prevented the MPTP-induced elevation of the DOPAC:DA ratio regardless of genotype. Metformin also prevented MPTP induced gliosis in the Substantia Nigra. These neuroprotective actions were independent of genotype and occurred in both AMPK WT and AMPK KO mice. Overall, our studies suggest that Metformin's neuroprotective effects are not due to AMPK activation in dopaminergic neurons and that more research is required to determine how metformin acts to restrict the development of PD.

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

Calorie restriction (CR) is neuroprotective in Parkinson's disease (PD) although the mechanisms are unknown. In this study we hypothesized that elevated ghrelin, a gut hormone with neuroprotective properties, during CR prevents neurodegeneration in an 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model of PD. CR attenuated the MPTP-induced loss of substantia nigra (SN) dopamine neurons and striatal dopamine turnover in ghrelin WT but not KO mice, demonstrating that ghrelin mediates CR's neuroprotective effect. CR elevated phosphorylated AMPK and ACC levels in the striatum of WT but not KO mice suggesting that AMPK is a target for ghrelin-induced neuroprotection. Indeed, exogenous ghrelin significantly increased pAMPK in the SN. Genetic deletion of AMPKß1 and 2 subunits only in dopamine neurons prevented ghrelin-induced AMPK phosphorylation and neuroprotection. Hence, ghrelin signaling through AMPK in SN dopamine neurons mediates CR's neuroprotective effects. We consider targeting AMPK in dopamine neurons may recapitulate neuroprotective effects of CR without requiring dietary intervention.

Acylated but not des-acyl ghrelin is neuroprotective in an MPTP mouse model of Parkinson's disease.

The gut hormone ghrelin is widely beneficial in many disease states. However, ghrelin exists in two distinctive isoforms, each with its own metabolic profile. In Parkinson's Disease (PD) acylated ghrelin administration is neuroprotective, however, the role of des-acylated ghrelin remains unknown. In this study, we wanted to identify the relative contribution each isoform plays using the MPTP model of PD. Chronic administration of acylated ghrelin in mice lacking both isoforms of ghrelin (Ghrelin KO) attenuated the MPTP-induced loss on tyrosine hydroxylase (TH) neuronal number and volume and TH protein expression in the nigrostriatal pathway. Moreover, acylated ghrelin reduced the increase in glial fibrillary acidic protein and Ionized calcium binding adaptor molecule 1 microglia in the substantia nigra. However, injection of acylated ghrelin also elevated plasma des-acylated ghrelin, indicating in vivo deacetylation. Next, we chronically administered des-acylated ghrelin to Ghrelin KO mice and observed no neuroprotective effects in terms of TH cell number, TH protein expression, glial fibrillary acidic protein and ionized calcium binding adaptor molecule 1 cell number. The lack of a protective effect was mirrored in ghrelin-O-acyltransferase KO mice, which lack the ability to acylate ghrelin and consequently these mice have chronically increased plasma des-acyl ghrelin. Plasma corticosterone was elevated in ghrelin-O-acyltransferase KO mice and with des-acylated ghrelin administration. Overall, our studies suggest that acylated ghrelin is the isoform responsible for in vivo neuroprotection and that pharmacological approaches preventing plasma conversion from acyl ghrelin to des-acyl ghrelin may have clinical efficacy to help slow or prevent the debilitating effects of PD. Ghrelin exists in the plasma as acyl and des-acyl ghrelin. We determined the form responsible for in vivo neuroprotection in a mouse model of Parkinson's disease. Although exogenous acyl ghrelin is deacylated in situ to des-acyl, only acyl ghrelin was neuroprotective by attenuating dopamine cell loss and glial activation. Acyl ghrelin is a therapeutic option to reduce Parkinson's Disease progression. Cover Image for this issue: doi: 10.1111/jnc.13316.

A stereological analysis of NPY, POMC, Orexin, GFAP astrocyte, and Iba1 microglia cell number and volume in diet-induced obese male mice.

The hypothalamic arcuate nucleus (ARC) contains 2 key neural populations, neuropeptide Y (NPY) and proopiomelanocortin (POMC), and, together with orexin neurons in the lateral hypothalamus, plays an integral role in energy homeostasis. However, no studies have examined total neuronal number and volume after high-fat diet (HFD) exposure using sophisticated stereology. We used design-based stereology to estimate NPY and POMC neuronal number and volume, as well as glial fibrillary acidic protein (astrocyte marker) and ionized calcium-binding adapter molecule 1 (microglia marker) cell number in the ARC; as well as orexin neurons in the lateral hypothalamus. Stereological analysis indicated approximately 8000 NPY and approximately 9000 POMC neurons in the ARC, and approximately 7500 orexin neurons in the lateral hypothalamus. HFD exposure did not affect total neuronal number in any population. However, HFD significantly increased average NPY cell volume and affected NPY and POMC cell volume distribution. HFD reduced orexin cell volume but had a bimodal effect on volume distribution with increased cells at relatively small volumes and decreased cells with relatively large volumes. ARC glial fibrillary acidic protein cells increased after 2 months on a HFD, although no significant difference after 6 months on chow diet or HFD was observed. No differences in ARC ionized calcium-binding adapter molecule 1 cell number were observed in any group. Thus, HFD affects ARC NPY or POMC neuronal cell volume number not cell number. Our results demonstrate the importance of stereology to perform robust unbiased analysis of cell number and volume. These data should be an empirical baseline reference to which future studies are compared.

Ghrelin as a neuroprotective and palliative agent in Alzheimer's and Parkinson's disease.

Ghrelin is a gastric hormone that stimulates growth hormone (GH) secretion and food intake to regulate energy homeostasis and body weight by binding to its receptor, GH secretagogue receptor (GHSR1a), which is most highly expressed in the pituitary and hypothalamus. Nowadays there is considerable evidence showing that the GHSR1a is also expressed in numerous extra-hypothalamic neuronal populations and the physiological role of ghrelin is by far wider than considered before including learning and memory, anxiety, depression and neuroprotection. The present review attempts to provide a comprehensive picture of the role of ghrelin in the central nervous system and to highlight recent findings showing its potential as an innovative therapeutic agent in neurodegenerative diseases including Alzheimer's disease and Parkinson's disease.

Neuropeptide Y (NPY) prevents depressive-like behavior, spatial memory deficits and oxidative stress following amyloid-ß (Aß(1-40)) administration in mice.

Neuropeptide Y (NPY) is a 36-amino acid peptide widely distributed in the central nervous system (CNS) that has been associated with the modulation of several functions including food intake, learning and memory, mood and neuroprotection. There is great interest in understanding the role of NPY in the deleterious effects induced by the central accumulation of amyloid-ß (Aß) peptides, a pathological hallmark of Alzheimer's disease (AD). Herein, we evaluated the effects of a single intracerebroventricular (i.c.v.) administration of NPY (0.0234 µmol/µL) 15 min prior to the i.c.v. injection of aggregated Aß1-40 peptide (400 pmol/mouse) in behavioral and neurochemical parameters related to oxidative stress in mice. Pretreatment with NPY prevented Aß1-40-induced depressive-like responses and spatial memory impairments evaluated in the tail suspension and object location tasks, respectively. The protective effects of NPY on spatial memory of Aß1-40-treated mice were abolished by the pretreatment with the selective Y2 receptor antagonist BIIE0246. On the other hand, the administration of NPY and Aß1-40 did not alter the performance of the animals in the elevated plus-maze and open field arena, indicating lack of effects on anxiety state and locomotor function. Although Aß1-40 infusion did not change hippocampal and cortical glutathione peroxidase (GPx) activity and glutathione (GSH) levels, Aß1-40-infused animals showed an increased lipid peroxidation in hippocampus and prefrontal cortex that were blunted by NPY administration. These findings indicate that central administration of NPY prevents Aß1-40-induced depressive-like behavior and spatial memory deficits in mice and that this response is mediated, at least in part, by the activation of Y2 receptors and prevention of oxidative stress.

Analysis of the temporal events in blood and tissues following fecal peritonitis in mice.

BACKGROUND: The kinetics of systemic responses triggered by bacterial peritonitis were analysed in the blood, bronchoalveolar lavage (BAL) and several organs. MATERIALS AND METHODS: The murine model of cecal ligation and puncture was employed. The parameters were analysed at different periods of time (4 to 72 h). RESULTS: Fecal peritonitis triggered a progressive, but not significant, decline of blood leukocytes between 4 and 6 h, becoming significant at 24 to 48 h (p<0.05). This profile was closely associated with the enhancement of leukocytes both in the abdomen (p<0.05) and in the BAL (p<0.05). A significant abdominal exudation was detected between 4 and 72 h (p<0.01), whereas maximal growth of aerobic bacteria in the blood and lungs was observed 24 and 72 h after. Maximal exudation in the studied tissues occurred at different time points (heart=24 h, spleen and kidney=48 h, liver and lung= 72 h). CONCLUSION: Using this model, evidence of sepsis can be easily measured in different body systems.