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NG2-expressing cells in demyelination and remyelination: studies using new transgenic mouse models

Fachliche Zuordnung Molekulare Biologie und Physiologie von Nerven- und Gliazellen
Förderung Förderung von 2008 bis 2013
Projektkennung Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 103728416
 
Erstellungsjahr 2014

Zusammenfassung der Projektergebnisse

In this project we investigated the effect of genetically deleting oligodendrocytes to induce a demyelinating lesion on the behavior of NG2-expressing oligodendrocyte progenitor cells (OPC). In this mouse model MOG-promoter expressing oligodendrocyes express Cre recombinase which upregulates expression of a diptheria toxin receptor (DTR) on the cells allowing deletion via administration of Diptheria Toxin (DT). We crossed this double transgenic mouse line to our NG2-EYFP mice. Unfortunately we observed that upon injection of DT the mice became very sick and di not recover making it imposiible to study a regulated de- and remyelination. We think this is due to MOG promoter expression in many NG2 OPC, resulting in their additional deletion. Our staining and WBlot data support this. We also now have microarray data supporting this as well as published microarray data from another lab. Furthermore, we have published evidence that the Cre expression in the MOGiCre line also extends to many neurons. This is likely to cause neuronal death upon injection of DT. The combination of mature oligodendrocyte deletion, deletion of a subpopulation of the NG2-expressing cells and mostly likely some deletion of neurons, leads to an irreversible axonal pathology, loss of neurons and death of the mice. Remyelination and hence preservation of axonal and neuronal health cannot be accomplished. We continued working on the NG2-EYFP mouse and the relevance of the NG2 cells for disease including demyelination. We established a novel binding partner of the NG2 proteoglycan: the PDZ protein OMI/HtrA2 which under oxidative cell stress (such as occurs in Multiple Sclerosis) leaks out of the mitochondrial intermembrane space and promotes apoptosis by cleaving the Inhibtors of Apoptosis (IAPs). We found that binding to NG2 inhibits the OMI protease and protects cells against oxidative stress. We observed as published by others, that human glioma which express NG2 are more resistant to oxidative stress than those lacking NG2, and we have evidence that the OMI/NG2 interaction helps protect the cells here. Secondly, we found that the NG2 protein is sequentially cleaved in an activity- dependent fashion by alpha and gamma secretases. The NG2 ectodomain can then become part of the ECM. We observed that mice lacking NG2 in OPC have alterations of the neuronal network, this includes diminished NMDA-receptor dependent LTP and altered neuronal AMPA receptors. Pharmacological inhibition of NG2 ectodomain cleavage in wild-type (WT) brain slices converts the WT phenotype to NG2 knockout phenotype. From microarray data and analysis of isolated OPC from WT and NG2 KO mice, we observed that OPC express neuromodulatory factors and one of these appears to be regulated in expression level by the NG2 protein. These results show for the first time that OPC which are integrated into the neuronal network by synapsing with axons not only respond to neuronal signals but also signal back to the network. The NG2 proteoglycan plays a regulatory role in this process and we observed that our NG2 KO mice exhibit subtle behavioural differences to WT mice. Taken together, our results demonstrate the importance of NG2 cells in CNS homeostasis.

Projektbezogene Publikationen (Auswahl)

 
 

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