Defense Date

2013

Document Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Integrative Life Sciences

First Advisor

Christopher Waggener

Second Advisor

Babette Fuss

Abstract

Oligodendrocytes are cells located in the central nervous system (CNS) that are responsible for the production of the lipid rich membrane, myelin. Myelin and the process of making and wrapping myelin around an axon (also known as myelination) are critical for normal development since they ensure proper signal conduction in the vertebrate CNS. The loss or damage of this myelin, which is typically associated with the demyelinating disease multiple sclerosis (MS), is associated with improper axonal protection along with disrupted nerve signaling which can lead to a variety of different debilitating phenotypic responses. It has been shown that there are MS lesions in which oligodendrocyte progenitors are present. However, while these cells are thought to possess the intrinsic ability to myelinate, they do not efficiently mature and/or repair the myelin sheath within the MS lesion. The reasons for this block in differentiation are currently not fully understood. A critical and thorough understanding of oligodendrocyte ix development provides the foundation needed for future research to potentially provide therapeutic targets for stimulating proper maturation and efficient remyelination from the oligodendrocyte progenitors that are present within the MS brain. In the search for regulators of oligodendrocyte development and potential therapeutic targets, the data generated as part of my thesis provided evidence that CaMKII (more specifically CaMKIIβ) is a regulator of oligodendrocyte myelination and maturation. Using pharmacological inhibitors or siRNA-mediated knockdown of this protein resulted in improper formation of the oligodendrocyte process network. Interestingly, siRNA-mediated knockdown of CaMKIIβ appeared to play no noticeable role in the genetic regulation of specific oligodendrocyte developmental markers. Furthermore, an overall reduction of the thickness of the compact myelin was observed in the ventral spinal cord of CaMKIIβ knockout mice. These findings emphasize the importance of CaMKIIβ in oligodendrocyte myelination and maturation. To further investigate CaMKIIβ’s role in the regulation of CNS myelination, the effect of glutamate signaling on CaMKIIβ and in particular its actin binding site were assessed. These data showed that signaling via glutamate transporters promote an increase of process network in oligodendrocytes. This effect was associated with a transient increase in intracellular calcium concentration and a change in the phosphorylation of at least one serine residue present within CaMKIIβ’s actin binding site. Changes in phosphorylation of CaMKIIβ’s actin binding site suggested that CaMKIIβ detaches from filamentous F-actin and x allows for remodeling of the oligodendrocyte’s actin cytoskeleton. This was demonstrated by overexpressing CaMKIIβ actin binding mutant constructs to alter phosphorylation of serine residues to either always allow actin binding (CaMKIIβallA) or never allow actin binding (CaMKIIβallD). The overexpression of CaMKIIβallD alone demonstrated a decrease in the process network of oligodendrocytes and inhibited the effect of glutamate on the process network. In contrast, the overexpression of CaMKIIβallA and CaMKIIβWT alone showed normal process network formation along with a significant increase in the process network after stimulation of glutamate. The above data strongly suggest that there is a significant relationship between sodium dependent glutamate transporters/CaMKIIβ activation and the oligodendrocyte cytoskeleton in the role of regulation of oligodendrocyte differentiation and CNS myelination. The data presented in this dissertation provides overwhelming evidence that CaMKIIβ plays a significant role in the proper formation of the oligodendrocyte complex process network and myelination. CaMKIIβ’s relationship with glutamate and the actin cytoskeleton could lay the foundation for future research not only for the signaling of oligodendrocyte process formation and remyelination but also for future targets for MS therapies.

Rights

© The Author

Is Part Of

VCU University Archives

Is Part Of

VCU Theses and Dissertations

Date of Submission

8-13-2013

Available for download on Tuesday, August 14, 2018

Included in

Life Sciences Commons

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