AbstractsBiology & Animal Science

Disturbed actin dynamics have been associated with aging, neurodegenerative conditions and cell death. The current thesis investigates the interplay between microglia activation and the state of the actin cytoskeleton. Models of actin stabilization included microglia from gelsolin-deficient (Gsn-/-) mice as well as treatment with actin polymerization agent jasplakinolide. Cytochalasin D served as a blocker of actin polymerization. Disruption of actin dynamics did not affect transcription of genes involved in the LPS-triggered classical inflammatory response. However, genes involved in IL-4 induced alternative activation were strongly transcriptionally downregulated by disturbed actin dynamics, which was related to impaired nuclear translocation of phospho-Stat6. Functionally, disturbed actin dynamics resulted in reduced NO secretion and reduced release of TNF- and IL-6 from LPS-stimulated microglia and of IGF-1 from IL-4 stimulated microglia. Reduced NO secretion was associated with reduced cytoplasmic iNOS protein expression and reduced arginine uptake. However, stabilization of the actin cytoskeleton increased LPS-induced release of IL-1b, which belongs to a non-classical release pathway. Furthermore, disruption of actin dynamics resulted in reduced microglia migration, proliferation and phagocytosis in vitro. Similarly, proliferation of IBA1-expressing cells was reduced in Gsn-/- mice after facial nerve axotomy as well as in a model of mild brain ischemia. Finally, baseline and ATP-induced intracellular calcium levels were significantly increased in Gsn-/- microglia. Together, disruption of actin dynamics attenuates both classical and alternative microglia activation. While alternative activation is strongly downregulated at the level of gene transcription, the mechanisms operating in classical activation are post-transcriptional and primarily relate to impaired uptake, transport and release. Neurodegenerative Pathologien, Alterungsprozesse und Zelltod gehen oft mit einer Dysfunktion des Aktinzytoskeletts einher. Ziel vorliegender Arbeit war es, den Einfluss des Aktinzytoskeletts auf den Prozess der Mikrogliaaktivierung näher zu erforschen und zu charakterisieren. Das Modell zur Untersuchung dieser Aktinstabilisierungsprozesse basiert auf der gelsolindefizienten Mauslinie (Gsn-/-) und dem Einsatz pharmazeutischer Interventionen mit Jasplakinolid und Cytochalasin D. Während Jasplakinolid zur Stabilisierung (Polymerisation) des Aktinfilamentes führt, resultieren Interventionen mit Cytochalsin D in einer Destabilisierung (Depolymerisation). Die Arbeit zeigt, dass gezielte Störungen des Auf- und Abbaus von Aktinfilamenten in klassisch aktivierter Mikroglia (mittels LPS) keinen Einfluss auf die Transkription von typischen „M1“ Genen haben. Unterdessen resultierten Eingriffe in die Aktinfilamentstabilität bei alternativer Aktivierung von Mikroglia (mittels IL-4) in einer deutlichen Herabregulierung der Transkriptionsrate typischer „M2“ Gene, was auf einen verminderten Transport des Transkriptionsaktivators pStat6 in…