2Developmental abnormalities of myelination are observed in the brains of laminin-deficient humans and mice. The mechanisms by which these defects occur remain unknown. It has been proposed that, given their central role in mediating extracellular matrix (ECM) interactions, integrin receptors are likely to be involved. However, it is a non-integrin ECM receptor, dystroglycan, that provides the key linkage between the dystrophin-glycoprotein complex (DGC) and laminin in skeletal muscle basal lamina, such that disruption of this bridge results in muscular dystrophy. In addition, the loss of dystroglycan from Schwann cells causes myelin instability and disorganization of the nodes of Ranvier. To date, it is unknown whether dystroglycan plays a role during central nervous system (CNS) myelination. Here, we report that the myelinating glia of the CNS, oligodendrocytes, express and use dystroglycan receptors to regulate myelin formation. In the absence of normal dystroglycan expression, primary oligodendrocytes showed substantial deficits in their ability to differentiate and to produce normal levels of myelin-specific proteins. After blocking the function of dystroglycan receptors, oligodendrocytes failed both to produce complex myelin membrane sheets and to initiate myelinating segments when co-cultured with dorsal root ganglion neurons. By contrast, enhanced oligodendrocyte survival in response to the ECM, in conjunction with growth factors, was dependent on interactions with beta-1 integrins and did not require dystroglycan. Together, these results indicate that laminins are likely to regulate CNS myelination by interacting with both integrin receptors and dystroglycan receptors, and that oligodendrocyte dystroglycan receptors may have a specific role in regulating terminal stages of myelination, such as myelin membrane production, growth, or stability.

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The adhesion receptor dystroglycan positively regulates terminal differentiation of oligodendrocytes, however the mechanism by which this occurs remains unclear. Using primary oligodendrocyte cultures, we identified and examined a connection between dystroglycan expression and the ability of insulin-like growth factor-1 (IGF-1) to promote oligodendrocyte differentiation. Consistent with previous reports, treatment with exogenous IGF-1 caused an increase in MBP protein that was preceded by activation of PI3K (AKT) and MAPK (ERK) signaling pathways. The extracellular matrix protein laminin was furthermore shown to potentiate the effect of IGF-1 on oligodendrocyte differentiation. Depletion of the laminin receptor dystroglycan using siRNA, however, blocked the ability of IGF-1 to promote oligodendrocyte differentiation of cells grown on laminin, suggesting a role for dystroglycan in IGF-1-mediated differentiation. Indeed, loss of dystroglycan led to a reduction in the ability of IGF-1 to activate MAPK, but not PI3K, signaling pathways. Pharmacological inhibition of MAPK signaling also prevented IGF-1-induced increases in MBP, indicating that MAPK signaling was necessary to drive IGF-1-mediated enhancement of oligodendrocyte differentiation. Using immunoprecipitation, we found that dystroglycan, the adaptor protein Grb2, and insulin receptor substrate-1 (IRS1), were associated in a protein complex. Taken together, our results suggest that the positive regulatory effect of laminin on oligodendrocyte differentiation may be attributed, at least in part, to dystroglycan’s ability to promote IGF-1-induced differentiation.

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This study shows that melanogenesis can be induced by AGI-1140 without many of the deleterious effects associated with UVB.