Neuroprotektive Wirkung von acyliertem und nicht-acyliertem Ghrelin in einem in vitro-Modell der Parkinson-Krankheit
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Philipps-Universität Marburg
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Abstract
Ghrelin is a polypeptide that exerts a wide range of functions, such as the regulation of growth hormone secretion, energy homeostasis, food intake, as well as the exocrine function of the pancreas. In regard to Parkinson’s disease (PD), patients who have been diagnosed with PD exhibit reduced levels of circulating ghrelin and a reduced postprandial ghrelin response. Experimental studies revealed neuroprotective effects of acylated ghrelin in different models of PD, which have not been further elucidated to date. There are two major molecular forms of ghrelin, an acylated (AG) and an unacylated (UAG) form. The acylation is catalyzed by the ghrelin-O-acyltransferase (GOAT) and only AG is able to bind to and activate the growth hormone secretagogue receptor 1a (GHS-R1a).
The issue we examined was whether ghrelin would exhibit neuroprotektive properties in our cell culture model and if this effect was limited to the acylated form. The study was conducted in primary mesencephalic cultures isolated from rat embryos at a gestational age of 15 days of pregnant Wistar rats. First, we investigated the neuroprotective effects of AG and UAG on dopaminergic neurons after treatment with the complex I inhibitor MPP+. Both ghrelin forms were neuroprotective, showing the maximum effect at a concentration of 0.1 nM AG and 1 nM UAG, ten times higher than the necessary concentration of AG. Concurrently, a tenfold higher concentration of UAG was also needed in experiments performed on pancreatic cells. Next, we investigated whether the observed effect was also evident when cells were treated with the complex II inhibitor 3-nitropropionic acid (3-NP). We found that both AG and UAG also protected midbrain neurons against complex II inhibition regardless of their neuronal phenotype, showing a maximum effect with the same concentrations as reported above.
There is a set of pathomechanisms responsible for the development of PD, such as the electrical activity of dopaminergic neurons. A massive influx of calcium or potassium ultimately leads to the loss of dopaminergic neurons. Chronic intake of calcium channel inhibitors (L-type / dihydropyridine-type) lowers the risk for PD. We analyzed whether co-treatment with the L-type channel blocker nicardipine could alter the neuroprotective effect of ghrelin after 3-NP exposition. Nicardipine abolished the neuroprotective effect of both AG and UAG on all mesencephalic neurons.
Traditionally, AG has been regarded as the only active form of ghrelin due to its receptor binding properties and UAG was thought to exhibit its effect after conversion to AG. To ascertain that the effects of UAG are not due to its in vitro acylation into AG, we assessed the effects of UAG in the presence of the GSH-R1a antagonist [D-Lys3]-GHRP-6 and the GOAT-inhibitor GO-CoA-Tat. Whereas the effect of AG on mitochondrial impairment required GSH-R1a binding, effects of UAG remained unaffected by treatment with a GSH-R1a antagonist. Importantly, inhibition of ghrelin-O-acyltransferase failed to reduce the activity of UAG.
In conclusion, our data suggests that both AG and UAG afford protection to dopaminergic neurons. This protective effect requires the activation of L-type calcium channels, however, it is transmitted through different mechanisms for both molecular forms of ghrelin.
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Created: 2015Issued: 2015-07-15
Faculty
Medizin
Publisher
Philipps-Universität Marburg
Language
ger
Data types
DoctoralThesis
Keywords
Ghrelin
DFG-subjects
Ghrelin
DDC-Numbers
610
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Wagner, Johanna Claudia (1074743814): Neuroprotektive Wirkung von acyliertem und nicht-acyliertem Ghrelin in einem in vitro-Modell der Parkinson-Krankheit. : Philipps-Universität Marburg 2015-07-15. DOI: https://doi.org/10.17192/z2015.0421.
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This item has been published with the following license: In Copyright