Integrin-linked Kinase Functions as a Cytoskeletal Scaffold in Oligodendrocyte Migration, Differentiation and Central Nervous System Myelination

Abstract

In the central nervous system (CNS), oligodendrocytes (OLs) generate myelin to facilitate the rapid propagation of neuronal impulses. In multiple sclerosis (MS), chronic demyelination leads to irreversible neurodegeneration that eventually impairs physical and cognitive function. Much effort is directed at elucidating the mechanisms underlying OL development in hope to unveil therapeutic targets for promoting remyelination in MS. Many aspects of OL biology are regulated by the integrins, a large family of transmembrane extracellular matrix (ECM) receptors. ECM components such as laminin and fibronectin bind to OL integrin receptors and initiate downstream signaling cascades involved in survival, proliferation, differentiation/myelination and migration. Integrin-linked kinase (ILK), an adaptor protein that binds to integrin cytosolic tails, works to stabilize the ECM-integrin connection by indirectly targeting the actin cytoskeleton to ECM adhesion sites. We hypothesized that ILK played an important role in OL migration, differentiation and capacity to myelinate neuronal projections. To address this hypothesis, we developed three cell culture techniques to assess these cellular phenomena in vitro. Conditional knockout of Ilk compromised both the morphological and molecular differentiation of primary mouse OLs in vitro, and reduced their capacity to produce myelin-like membrane. ILK was required for proper OL ensheathment of neuronal extensions when co-cultured with primary neurons. Conditional ablation of Ilk in vivo produced a transient amyelination defect that was endogenously compensated for at later time points. Loss of ILK in primary OLs was associated with upregulated RhoA signaling, and pharmacological inhibition of the RhoA axis restored the morphology of a distinct subset of NG2+ OPCs. ILK depletion in OL precursor cells (OPCs) resulted in a substrate-dependent defect in migration velocity and migration initiation. Inhibition of the RhoA signaling pathway enhanced the migratory velocity of wild-type OPCs, an effect that was dependent on ILK expression. In sum, we established three primary mouse OL cell culture techniques, with which we defined roles for ILK in OL biology. Our work highlights the importance of integrin signaling in OLs and provides new experimental methods useful in MS research.