Ghrelin Promotes Cortical Neurites Growth in Late Stage After Oxygen-Glucose Deprivation/Reperfusion Injury

Hypoxic Preconditioned Neural Stem Cell-Derived Extracellular Vesicles Contain Distinct Protein Cargo from Their Normal Counterparts

Hypoxic preconditioning has been demonstrated to increase the resistance of neural stem cells (NSCs) to hypoxic conditions, as well as to improve their capacity for differentiation and neurogenesis. Extracellular vesicles (EVs) have recently emerged as critical mediators of cell–cell communication, but their role in this hypoxic conditioning is presently unknown. Here, we demonstrated that three hours of hypoxic preconditioning triggers significant neural stem cell EV release. Proteomic profiling of EVs from normal and hypoxic preconditioned neural stem cells identified 20 proteins that were upregulated and 22 proteins that were downregulated after hypoxic preconditioning. We also found an upregulation of some of these proteins by qPCR, thus indicating differences also at the transcript level within the EVs. Among the upregulated proteins are CNP, Cyfip1, CASK, and TUBB5, which are well known to exhibit significant beneficial effects on neural stem cells. Thus, our results not only show a significant difference of protein cargo in EVs consequent to hypoxic exposure, but identify several candidate proteins that might play a pivotal role in the cell-to-cell mediated communication underlying neuronal differentiation, protection, maturation, and survival following exposure to hypoxic conditions.

Ghrelin Regulates Expression of the Transcription Factor Pax6 in Hypoxic Brain Progenitor Cells and Neurons

The nature of brain impairment after hypoxia is complex and recovery harnesses different mechanisms, including neuroprotection and neurogenesis. Experimental evidence suggests that hypoxia may trigger neurogenesis postnatally by influencing the expression of a variety of transcription factors. However, the existing data are controversial. As a proof-of-principle, we subjected cultured cerebral cortex neurons, cerebellar granule neurons and organotypic cerebral cortex slices from rat brains to hypoxia and treated these cultures with the hormone ghrelin, which is well-known for its neuroprotective functions. We found that hypoxia elevated the expression levels and stimulated nuclear translocation of ghrelin’s receptor GHSR1 in the cultured neurons and the acute organotypic slices, whereas ghrelin treatment reduced the receptor expression to normoxic levels. GHSR1 expression was also increased in cerebral cortex neurons of mice with induced experimental stroke. Additional quantitative analyses of immunostainings for neuronal proliferation and differentiation markers revealed that hypoxia stimulated the proliferation of neuronal progenitors, whereas ghrelin application during the phase of recovery from hypoxia counteracted these effects. At the mechanistic level, we provide a link between the described post-ischemic phenomena and the expression of the transcription factor Pax6, an important regulator of neural progenitor cell fate. In contrast to the neurogenic niches in the brain where hypoxia is known to increase Pax6 expression, the levels of the transcription factor in cultured hypoxic cerebral cortex cells were downregulated. Moreover, the application of ghrelin to hypoxic neurons normalised the expression levels of these factors. Our findings suggest that ghrelin stimulates neurogenic factors for the protection of neurons in a GHSR1-dependent manner in non-neurogenic brain areas such as the cerebral cortex after exposure to hypoxia.

In Vitro Oxygen Glucose Deprivation Model of Ischemic Stroke: A Proteomics-Driven Systems Biological Perspective

Oxygen glucose deprivation (OGD) of brain cells is the commonest in vitro model of ischemic stroke that is used extensively for basic and preclinical stroke research. Protein mass spectrometry is one of the most promising and rapidly evolving technologies in biomedical research. A systems-level understanding of cell-type-specific responses to oxygen and glucose deprivation without systemic influence is a prerequisite to delineate the response of the neurovascular unit following ischemic stroke. In this systematic review, we summarize the proteomics studies done on different OGD models. These studies have followed an expression or interaction proteomics approach. They have been primarily used to understand the cellular pathophysiology of ischemia-reperfusion injury or to assess the efficacy of interventions as potential treatment options. We compile the limitations of OGD model and downstream proteomics experiment. We further show that despite having limitations, several proteins shortlisted as altered in in vitro OGD-proteomics studies showed comparable regulation in ischemic stroke patients. This showcases the translational potential of this approach for therapeutic target and biomarker discovery. We next discuss the approaches that can be adopted for cell-type-specific validation of OGD-proteomics results in the future. Finally, we briefly present the research questions that can be addressed by OGD-proteomics studies using emerging techniques of protein mass spectrometry. We have also created a web resource compiling information from OGD-proteomics studies to facilitate data sharing for community usage. This review intends to encourage preclinical stroke community to adopt a hypothesis-free proteomics approach to understand cell-type-specific responses following ischemic stroke.

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.

Severe Zinc Deficiency Causes the Loss and Apoptosis of Olfactory Ensheathing Cells (OECs) and Olfactory Deficit

Dietary zinc deficiency may lead to olfactory deficits, whose mechanism remains largely elusive. Olfactory ensheathing cells (OECs), a type of glial cells that support the function and neurogenesis in the olfactory bulb (OB), may play a pivotal role in the maintenance of the olfactory system. In the present study, we established a rat model of dietary zinc deficiency and found that severe zinc deficiency, but not marginal zinc deficiency, caused significantly reduced food intake, growth retardation, and apparent olfactory deficit in growing rats. We showed that severe zinc deficiency resulted in the loss of OECs in the olfactory nerve layer (ONL) of the olfactory bulb. In addition, we revealed that the number of TUNEL-positive cells increased markedly in the region, suggesting an involvement of apoptotic cell death in zinc deficiency-induced loss of OECs. Moreover, we found that treatment with zinc chelator N,N,N'N',-tetrakis (2-pyridylmethyl)ethylenediamine (TPEN) triggered the apoptosis of in vitro-cultured primary OECs. The apoptosis of OECs was correlated with significantly elevated expression of p53. Importantly, TUNEL and CCK-8 assays both demonstrated that treatment with p53 antagonist pifithrin-α (PFT-α) markedly attenuated TPEN-induced OEC apoptosis. These findings implicated that p53-triggered apoptosis of OECs might play an integral role in zinc deficiency-induced olfactory malfunction.