Wortmannin, ein spezifischer Inhibitor der Phosphatidylinositol-3-Kinase, beeinflusst das neurotrophin-induzierte Wachstum von Spiralganglienneuriten

Zusammenfassung

Hintergrund: Der Phosphatidylinositol-3-Kinase (PI3K) wird eine wesentliche Rolle bei der intrazellulären Übertragung von Neurotrophin-Signalen vom Rezeptor an der Zellmembran zum Zellkern zugesprochen.

Methode: In dieser Studie wurde die Beteiligung der PI3K bei der Vermittlung von Neurotrophin-Effekten im Spiralganglion (SG) neugeborener Ratten untersucht. Die SG-Explantate wurden in vitro mit Neurotrophin-3 (NT-3) stimuliert und zusätzlich mit Wortmannin, einem spezifischen Inhibitor der PI3K behandelt. Nach Fixierung und immunhistochemischer Färbung der Explantate erfolgte die Auswertung des Neuritenwachstums.

Ergebnisse: Die Stimulation mit NT-3 führte zu dem bereits bekannten Effekt einer Zunahme sowohl der Anzahl, als auch der Länge der auswachsenden SG-Neuriten im Vergleich zu Kontrollexplantaten. Die Behandlung NT-3-stimulierter SG-Explantate mit Wortmannin resultierte in einer konzentrationsabhängigen Reduktion beider Parameter, während nach der Inkubation von Kontrollexplantaten mit Wortmannin keine Änderung des Neuritenwachstums beobachtet wurde.

Schlussfolgerung: Die Ergebnisse der Untersuchung zeigen, dass neurotrophin-induziertes Neuritenwachstum von SG-Explantaten durch den PI3K-Inhibitor Wortmannin moduliert werden kann und deuten darauf hin, dass die PI3K ein wichtiges Schlüsselenzym bei der Vermittlung von Effekten des Wachstumfaktors NT-3 in cochleären Neuronen darstellt. Zusammen mit den Ergebnissen früherer Untersuchungen deuten die aktuellen Resultate darauf hin, dass sowohl die Aktivierung der PI3K, als auch des G-Proteins Ras und der mitogen-aktivierten Proteinkinase Kinase (MEK) für das Neuritenwachstum von SG-Neuronen notwendig sind. Die weitere Aufklärung dieser, das Wachstum der SG-Neuriten beeinflussenden molekulären Mechanismen lässt für die Zukunft neue therapeutische Ansätze für Innenohrerkrankungen erwarten.

Abstract

Background: Phosphatidylinositol 3-kinase (PI3K) is considered to be an important enzyme in cell signaling, mediating certain aspects of neurotrophin signals from the cell surface receptor to the nucleus.

Methods: The participation of PI3K in the mediation of neurotrophin-induced effects in the spiralganglion (SG) of neonatal rats was investigated in vitro. SG explants were stimulated with neurotrophin (NT)-3 and treated with Wortmannin, a specific inhibitor of PI3K. After fixation and immunhistochemical staining, the growth of the SG neurites was evaluated.

Results: Stimulation with NT-3 lead to significant increases in number and length of neurites, when compared to non-stimulated controls. Treatment of NT-3 stimulated SG explants resulted in a dose-dependent reduction of both parameters, whereas the neurite growth of non-stimulated control explants was not significantly influenced by the incubation with Wortmannin.

Conclusions: The results demonstrate that neurotrophin-induced neurite growth from SG explants can be modulated with the PI3K inhibitor Wortmannin and indicate that PI3K is a key enzyme in the mediation of NT-3 effects in cochlear neurons. These observations together with results of previous studies suggest that the activation of PI3K as well as Ras and MEK are essential for neurite growth in cochlear neurons. Further knowledge of cell signaling mechanisms influencing SG neurite growth could lead to new therapeutical strategies for the treatment of inner ear diseases.

NT-3, Wortmannin - PI3K - Spiralganglion - Neuritenwachstum

NT-3, Wortmannin - PI3K - Spiralganglion - Neurite growth

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