Ghrelin regulates cell cycle-related gene expression in cultured hippocampal neural stem cells

Ghrelin/GHSR Axis Induced M2 Macrophage and Alleviated Intestinal Barrier Dysfunction in a Sepsis Rat Model by Inactivating E2F1/NF-κB Signaling

Sepsis is an inflammatory reaction disorder state that is induced by infection. The activation and regulation of the immune system play an essential role in the development of sepsis. Our previous studies have shown that ghrelin ameliorates intestinal dysfunction in sepsis. Very little is known about the mechanism of ghrelin and its receptor (GHSR) on the intestinal barrier and the immune function of macrophage regulation. Our research is to investigate the regulatory effect and molecular mechanism of the ghrelin/GHSR axis on intestinal dysfunction and macrophage polarization in septic rats. A rat model of sepsis was established by cecal ligation and puncture (CLP) operation. Then, the sepsis rats were treated with a ghrelin receptor agonist (TZP-101) or ghrelin inhibitor (obestatin). The results suggested that TZP-101 further enhanced ghrelin and GHSR expressions in the colon and spleen of septic rats and obestatin showed the opposite results. Ghrelin/GHSR axis ameliorated colonic structural destruction and intestinal epithelial tight junction injury in septic rats. In addition, the ghrelin/GHSR axis promoted M2-type polarization of macrophages, which was characterized by the decreases of IL-1β, IL-6, and TNF-α, as well as the increase of IL-10. Mechanistically, the ghrelin/GHSR axis promoted E2F2 expression and suppressed the activation of the NF-κB signaling pathway in septic rats. Collectively, targeting ghrelin/GHSR during sepsis may represent a novel therapeutic approach for the treatment of intestinal barrier injury.

Molecular Mechanisms and Clinical Application of Multipotent Stem Cells for Spinal Cord Injury

Spinal Cord Injury (SCI) is a common neurological disorder with devastating psychical and psychosocial sequelae. The majority of patients after SCI suffer from permanent disability caused by motor dysfunction, impaired sensation, neuropathic pain, spasticity as well as urinary complications, and a small number of patients experience a complete recovery. Current standard treatment modalities of the SCI aim to prevent secondary injury and provide limited recovery of lost neurological functions. Stem Cell Therapy (SCT) represents an emerging treatment approach using the differentiation, paracrine, and self-renewal capabilities of stem cells to regenerate the injured spinal cord. To date, multipotent stem cells including mesenchymal stem cells (MSCs), neural stem cells (NSCs), and hematopoietic stem cells (HSCs) represent the most investigated types of stem cells for the treatment of SCI in preclinical and clinical studies. The microenvironment of SCI has a significant impact on the survival, proliferation, and differentiation of transplanted stem cells. Therefore, a deep understanding of the pathophysiology of SCI and molecular mechanisms through which stem cells act may help improve the treatment efficacy of SCT and find new therapeutic approaches such as stem-cell-derived exosomes, gene-modified stem cells, scaffolds, and nanomaterials. In this literature review, the pathogenesis of SCI and molecular mechanisms of action of multipotent stem cells including MSCs, NSCs, and HSCs are comprehensively described. Moreover, the clinical efficacy of multipotent stem cells in SCI treatment, an optimal protocol of stem cell administration, and recent therapeutic approaches based on or combined with SCT are also discussed.

Microbiota-Gut-Brain Axis Regulation of Adult Hippocampal Neurogenesis

The birth, maturation, and integration of new neurons in the adult hippocampus regulates specific learning and memory processes, responses to stress, and antidepressant treatment efficacy. This process of adult hippocampal neurogenesis is sensitive to environmental stimuli, including peripheral signals from certain cytokines, hormones, and metabolites, which can promote or hinder the production and survival of new hippocampal neurons. The trillions of microorganisms resident to the gastrointestinal tract, collectively known as the gut microbiota, also demonstrate the ability to modulate adult hippocampal neurogenesis. In doing so, the microbiota-gut-brain axis can influence brain functions regulated by adult hippocampal neurogenesis. Unlike the hippocampus, the gut microbiota is highly accessible to direct interventions, such as prebiotics, probiotics, and antibiotics, and can be manipulated by lifestyle choices including diet. Therefore, understanding the pathways by which the gut microbiota shapes hippocampal neurogenesis may reveal novel targets for non-invasive therapeutics to treat disorders in which alterations in hippocampal neurogenesis have been implicated. This review first outlines the factors which influence both the gut microbiome and adult hippocampal neurogenesis, with cognizance that these effects might happen either independently or due to microbiota-driven mechanisms. We then highlight approaches for investigating the regulation of adult hippocampal neurogenesis by the microbiota-gut-brain axis. Finally, we summarize the current evidence demonstrating the gut microbiota's ability to influence adult hippocampal neurogenesis, including mechanisms driven through immune pathways, microbial metabolites, endocrine signalling, and the nervous system, and postulate implications for these effects in disease onset and treatment.

HDAC5 promotes intestinal sepsis via the Ghrelin/E2F1/NF-κB axis

In the current study, we sought to determine the roles of histone deacetylase 5 (HDAC5) on the promotion of intestinal sepsis in a mouse model. Dual luciferase reporter gene assay was used to determine the binding relationship between HDAC5 and Ghrelin. Cecal ligation and puncture (CLP) was used as an animal model of intestinal sepsis. The roles of HDAC5 on intestinal sepsis were determined by HDAC5 knockdown, overexpression, and inhibitor (LMK-235) in vivo. Mice intestinal permeability and intestinal epithelial damage were evaluated, and HE staining was used to evaluate the intestinal mucosal injury index. Lipopolysaccharide (LPS)-treated intestinal-derived macrophages served as a cell model of sepsis, followed by the loss-of-function and gain-of-function assays. ELISA was used to determine the levels of inflammatory factors, and TUNEL staining was used to detect intestinal cell apoptosis. HDAC5 was upregulated in the intestine of sepsis patients. This increased HDAC5 expression was positively correlated with the expression of inflammatory factors TNF-α, IL-1β, IL-6, and HMGB1, as well as the intestinal dysfunction-related factors IFABP. In sepsis mice, the expression of inflammatory factors was reduced by HDAC5 knockdown. HDAC5 knockdown also improved survival, morphology of intestinal tissue, intestinal permeability, and epithelial damage. Ghrelin was bound and inhibited by HDAC5, but E2F1 expression was increased by Ghrelin overexpression, leading to inhibition of the NF-κB pathway. Ghrelin and E2F1 expression were increased by the treatment with HDAC5 inhibitor LMK-235, which inhibited the NF-κB pathway to improve intestinal dysfunction in the sepsis model. In conclusion, HDAC5 inhibits Ghrelin to reduce E2F1 and thus activate the NF-κB pathway, thereby promoting intestinal sepsis.

Ghrelin-Mediated Regeneration and Plasticity After Nervous System Injury

The nervous system is highly vulnerable to different factors which may cause injury followed by an acute or chronic neurodegeneration. Injury involves a loss of extracellular matrix integrity, neuronal circuitry disintegration, and impairment of synaptic activity and plasticity. Application of pleiotropic molecules initiating extracellular matrix reorganization and stimulating neuronal plasticity could prevent propagation of the degeneration into the tissue surrounding the injury. To find an omnipotent therapeutic molecule, however, seems to be a fairly ambitious task, given the complex demands of the regenerating nervous system that need to be fulfilled. Among the vast number of candidates examined so far, the neuropeptide and hormone ghrelin holds within a very promising therapeutic potential with its ability to cross the blood-brain barrier, to balance metabolic processes, and to stimulate neurorepair and neuroactivity. Compared with its well-established systemic effects in treatment of metabolism-related disorders, the therapeutic potential of ghrelin on neuroregeneration upon injury has received lesser appreciation though. Here, we discuss emerging concepts of ghrelin as an omnipotent player unleashing developmentally related molecular cues and morphogenic cascades, which could attenuate and/or counteract acute and chronic neurodegeneration.

Effects of Ghrelin on Olfactory Ensheathing Cell Viability and Neural Marker Expression

Ghrelin (Ghre), a gut-brain peptide hormone, plays an important role in the entire olfactory system and in food behavior regulation. In the last years, it has aroused particular interest for its antioxidant, anti-inflammatory, and anti-apoptotic properties. Our previous research showed that Ghre and its receptor are expressed by peculiar glial cells of the olfactory system: Olfactory Ensheathing Cells (OECs). These cells are able to secrete different neurotrophic factors, promote axonal growth, and show stem cell characteristics. The aim of this work was to study, in an in vitro model, the effect of Ghre on both cell viability and the expression of some neural markers, such as Nestin (Ne), Glial Fibrillary Acid Protein (GFAP), Neuregulin (Neu), and β-III-tubulin (Tuj1), in primary mouse OEC cultures. The MTT test and immunocytochemical procedures were used to highlight cell viability and marker expression, respectively. Our results demonstrate that Ghre, after 7 days of treatment, exerted a positive effect, stimulating OEC viability compared with cells without Ghre treatment. In addition, Ghre was able to modify the expression of some biomarkers, increasing Neu and Tuj1 expression, while GFAP was constant; on the contrary, the presence of positive Ne cells was drastically reduced after 7 days, and this showed a loss of stem cell characteristic and therefore the possible orientation towards an adult neural phenotype.

Ghrelin in Alzheimer's disease: Pathologic roles and therapeutic implications

Ghrelin, which has many important physiological roles, such as stimulating food intake, regulating energy homeostasis, and releasing insulin, has recently been studied for its roles in a diverse range of neurological disorders. Despite the several functions of ghrelin in the central nervous system, whether it works as a therapeutic agent for neurological dysfunction has been unclear. Altered levels and various roles of ghrelin have been reported in Alzheimer's disease (AD), which is characterized by the accumulation of misfolded proteins resulting in synaptic loss and cognitive decline. Interestingly, treatment with ghrelin or with the agonist of ghrelin receptor showed attenuation in several cases of AD-related pathology. These findings suggest the potential therapeutic implications of ghrelin in the pathogenesis of AD. In the present review, we summarized the roles of ghrelin in AD pathogenesis, amyloid beta (Aβ) homeostasis, tau hyperphosphorylation, neuroinflammation, mitochondrial deficit, synaptic dysfunction and cognitive impairment. The findings from this review suggest that ghrelin has a novel therapeutic potential for AD treatment. Thus, rigorously designed studies are needed to establish an effective AD-modifying strategy.

The protective effects of Ghrelin/GHSR on hippocampal neurogenesis in CUMS mice

Ghrelin is an orexigenic hormone that also plays an important role in mood disorders. Our previous studies demonstrated that ghrelin administration could protect against depression-like behaviors of chronic unpredictable mild stress (CUMS) in rodents. However, the mechanism related to the effect of ghrelin on CUMS mice has yet to be revealed. This article shows that ghrelin (5 nmol/kg/day for 2 weeks, i.p.) decreased depression-like behaviors induced by CUMS and increased hippocampal integrity (neurogenesis and spine density) measured via Ki67, 5-bromo-2-deoxyuridine (BrdU), doublecortin (DCX) labeling and Golgi-cox staining, which were decreased under CUMS. The behavioral phenotypes of Growth hormone secretagogue receptor (Ghsr)-null and wild type (WT) mice were evaluated under no stress condition and after CUMS exposure to determine the effect of Ghsr knockout on the behavioral phenotypes and stress susceptibility of mice. Ghsr-null mice exhibited depression-like behaviors under no stress condition. CUMS induced similar depression- and anxiety-like behavioral manifestations in both Ghsr-null and WT mice. A similar pattern of behavioral changes was observed after hippocampal GHSR knockdown. Additionally, both Ghsr knockout as well as CUMS exhibited deleterious effects on neurogenesis and spine density in the dentate gyrus (DG). Besides, CCK8 assay and 5-Ethynyl-2'-deoxyuridine (EdU) incorporation assay showed that ghrelin has a proliferative effect on primary cultured hippocampal neural stem cells (NSCs) and this proliferation was blocked by D-Lys3-GHRP-6 (DLS, the antagonist of GHSR, 100 μM) pretreatment. Ghrelin-induced proliferation is associated with the inhibition of G1 arrest, and this inhibition was blocked by LY294002 (specific inhibitor of PI3K, 20 μM). Furthermore, the in vivo data displayed that LY294002 (50 nmol, i.c.v.) can significantly block the antidepressant-like action of exogenous ghrelin treatment. All these results suggest that ghrelin/GHSR signaling maintains the integrity of hippocampus and has an inherent neuroprotective effect whether facing stress or not.

The Neurocognitive Effects of Ghrelin-induced Signaling on the Hippocampus: A Promising Approach to Alzheimer's Disease

The communication between the gastrointestinal tract and the central nervous system (CNS) allows for certain peptide hormones to influence neurocognitive function. Ghrelin, also known as the 'hunger hormone,' has the unique ability to enter the CNS and interact with the growth hormone secretagogue receptor (GHS-R) within the hippocampus. Upon interaction with ghrelin, a conformational change in the receptor causes an increase in transcription factors to foster a wide array of physiologic changes in response to caloric deprivation. With the GHS-R in a relatively high concentration within the hippocampus, ghrelin can promote memory, spatial, learning, and behavioral effects. In fact, ghrelin appears to also have a neuroprotective and neuromodulatory response once active within the hippocampal dentate gyrus. Through the GHS-R, higher levels of ghrelin may alter cognitive circuitry and offer a possible link to the treatment of some pathologies implicated in neurological dysfunction. Alzheimer's disease (AD) is already becoming a significant target for ghrelin neuroreceptor therapy. In such experimental models, ghrelin has been shown to combat this degenerative process by eliciting an ameliorative and regenerative response. Although trials and research are still ongoing, further studies are indicated as early research into this adjuvant therapy is promising. The research team explored the effects of ghrelin by reviewing the downstream signaling modifications of ghrelin's interaction with a specific CNS receptor, the GHS-R. Although the GHS-R is found in multiple locations within the CNS, the team investigated the role of the GHS-R within the hippocampus to focus solely on the neurocognitive implications of ghrelin. The team noted which signaling pathways in particular that ghrelin initiated and used this approach to determine whether ghrelin may have any therapeutic benefits. The team explored the possible therapeutic indications of ghrelin by looking at studies conducted with a specific neurodegenerative disease known to target the hippocampus.

Methylation of Cdkn1c may be involved in the regulation of tooth development through cell cycle inhibition

Cdkn1c, a member of the Cip/Kip cyclin-dependent kinase inhibitor family, is critically involved in regulating cell cycle and cellular differentiation during development in mammals. However, the functional role of Cdkn1c and the underlying mechanisms by which Cdkn1c affects odontogenesis remain largely unknown. In our study, we found that Cdkn1c expression dynamically changes from embryonic day 11.5 (E11.5) to postnatal day 3 (P3), and exhibits tissue-specific expression profiles. Evaluation of CDKN1C protein by immunohistochemistry and western blot, revealed that CDKN1C protein expression peaks at P3 and then is reduced at P5 and P7. Interestingly, we observed that CDKN1C expression is higher in immature odontoblasts than preodontoblasts, is lower in mature odontoblasts, and is practically absent from ameloblasts. We evaluated cell cycle progression to further investigate the mechanisms underlying CDKN1C-mediated regulation of odontogenesis, and found that pRB, cyclin D1 and CDK2 expression decreased from P1 to P3, and reduced at P5 and P7. In addition, we observed increased methylation of KvDMR1 at P1 and P3, and reduced KvDMR1 methylation at P5 and P7. However, the methylation levels of Cdkn1c-sDMR were relatively low from P1 to P7. In summary, we demonstrated that Cdkn1c expression and methylation status may be involved in early postnatal tooth development through regulating the cell cycle inhibition activity of Cdkn1c. Notably, Cdkn1c expression and methylation may associate with cell cycle exit and differentiation of odontoblasts.

MK-0677, a Ghrelin Agonist, Alleviates Amyloid Beta-Related Pathology in 5XFAD Mice, an Animal Model of Alzheimer's Disease

Alzheimer’s disease (AD) is a progressive neurodegenerative disorder characterized by cognitive deficits, neuroinflammation, and neuronal death. The primary pathogenic cause is believed to be the accumulation of pathogenic amyloid beta (Aβ) assemblies in the brain. Ghrelin, which is a peptide hormone predominantly secreted from the stomach, is an endogenous ligand for the growth hormone secretagogue-receptor type 1a (GHS-R1a). MK-0677 is a ghrelin agonist that potently stimulates the GHS-R1a ghrelin receptor. Interestingly, previous studies have shown that ghrelin improves cognitive impairments and attenuates neuronal death and neuroinflammation in several neurological disorders. However, it is unknown whether MK-0677 can affect Aβ accumulation or Aβ-mediated pathology in the brains of patients with AD. Therefore, we examined the effects of MK-0677 administration on AD-related pathology in 5XFAD mice, an Aβ-overexpressing transgenic mouse model of AD. MK-0677 was intraperitoneally administered to three-month-old 5XFAD mice. To visualize Aβ accumulation, neuroinflammation, and neurodegeneration, thioflavin-S staining and immunostaining with antibodies against Aβ (4G8), ionized calcium-binding adaptor molecule 1 (Iba-1), glial fibrillary acidic protein (GFAP), neuronal nuclear antigen (NeuN), and synaptophysin were conducted in the neocortex of 5XFAD and wild-type mice, and to evaluate changes of phosphorylated cyclic adenosine monophosphate (cAMP) response element binding protein (pCREB) levels, immunostaining with antibody against pCREB was performed in dentate gyrus of the hippocampus of 5XFAD and wild-type mice. The histological analyses indicated that MK-0677-treated 5XFAD mice showed reduced Aβ deposition, gliosis, and neuronal and synaptic loss in the deep cortical layers, and inhibited the decrement of pCREB levels in dentate gyrus of the hippocampus compared to vehicle-treated 5XFAD mice. Our results showed that activation of the ghrelin receptor with MK-0677 inhibited the Aβ burden, neuroinflammation, and neurodegeneration, which suggested that MK-0677 might have potential as a treatment of the early phase of AD.

Being a Neural Stem Cell: A Matter of Character But Defined by the Microenvironment

The cells that build the nervous system, either this is a small network of ganglia or a complicated primate brain, are called neural stem and progenitor cells. Even though the very primitive and the very recent neural stem cells (NSCs) share common basic characteristics that are hard-wired within their character, such as the expression of transcription factors of the SoxB family, their capacity to give rise to extremely different neural tissues depends significantly on instructions from the microenvironment. In this chapter we explore the nature of the NSC microenvironment, looking through evolution, embryonic development, maturity and even disease. Experimental work undertaken over the last 20 years has revealed exciting insight into the NSC microcosmos. NSCs are very capable in producing their own extracellular matrix and in regulating their behaviour in an autocrine and paracrine manner. Nevertheless, accumulating evidence indicates an important role for the vasculature, especially within the NSC niches of the postnatal brain; while novel results reveal direct links between the metabolic state of the organism and the function of NSCs.

Synergistic effect of melatonin and ghrelin in preventing cisplatin-induced ovarian damage via regulation of FOXO3a phosphorylation and binding to the p27Kip1 promoter in primordial follicles

Premature ovarian failure during chemotherapy is a serious problem for young women with cancer. To preserve the fertility of these patients, approaches to prevent chemotherapy-induced ovarian failure are needed. In a previous study, we reported that melatonin treatment prevents the depletion of the dormant follicle pool via repression of the simultaneous activation of dormant primordial follicles by cisplatin. However, melatonin's protective effect was only partial and thus insufficient. In this study, we found that the hormone ghrelin enhances the protective effect of melatonin against cisplatin-induced ovarian failure in mouse model. Co-administration of melatonin and ghrelin more effectively prevented cisplatin-induced follicle disruption. Simultaneous treatment with melatonin and ghrelin almost restored the number of primordial follicles and the corpus luteum in cisplatin-treated ovaries, compared with single administration. We found melatonin and ghrelin receptors on the cell membrane of premature oocytes of primordial follicles. In addition, melatonin and ghrelin co-administration inhibited the cisplatin-induced phosphorylation of PTEN and FOXO3a that induces cytoplasmic translocation of FOXO3a. Inhibition of FOXO3a phosphorylation by melatonin and ghrelin increased the binding affinity of FOXO3a for the p27^Kip1 promoter in primordial follicles. Co-administration of melatonin and ghrelin in cisplatin-treated ovaries restored the expression of p27^Kip1 , which is critical for retention of the dormant status of primordial follicles. In conclusion, these findings suggest that melatonin and ghrelin co-administration is suitable for use as a fertoprotective adjuvant therapy during cisplatin chemotherapy in young female cancer patients.

Neurogenic Effects of Ghrelin on the Hippocampus

Mammalian neurogenesis continues throughout adulthood in the subventricular zone of the lateral ventricle and in the subgranular zone of the dentate gyrus in the hippocampus. It is well known that hippocampal neurogenesis is essential in mediating hippocampus-dependent learning and memory. Ghrelin, a peptide hormone mainly synthesized in the stomach, has been shown to play a major role in the regulation of energy metabolism. A plethora of evidence indicates that ghrelin can also exert important effects on neurogenesis in the hippocampus of the adult brain. The aim of this review is to discuss the current role of ghrelin on the in vivo and in vitro regulation of neurogenesis in the adult hippocampus. We will also discuss the possible role of ghrelin in dietary restriction-induced hippocampal neurogenesis and the link between ghrelin-induced hippocampal neurogenesis and cognitive functions.