Enhanced oligodendrocyte maturation and myelination in a mouse model of Timothy syndrome

To study the role of L-type voltage-gated Ca⁺⁺ channels in oligodendrocyte development, we used a mouse model of Timothy syndrome (TS) in which a gain-of-function mutation in the α1 subunit of the L-type Ca⁺⁺ channel Cav1.2 gives rise to an autism spectrum disorder (ASD). Oligodendrocyte progenitor cells (OPCs) isolated from the cortex of TS mice showed greater L-type Ca⁺⁺ influx and displayed characteristics suggestive of advanced maturation compared to control OPCs, including a more complex morphology and higher levels of myelin protein expression. Consistent with this, expression of Cav1.2 channels bearing the TS mutation in wild-type OPCs triggered process formation and promoted oligodendrocyte-neuron interaction via the activation of Ca⁺⁺ /calmodulin-dependent protein kinase II. To ascertain whether accelerated OPC maturation correlated with functional enhancements, we examined myelination in the TS brain at different postnatal time points. The expression of myelin proteins was significantly higher in the corpus callosum, cortex and striatum of TS animals, and immunohistochemical analysis for oligodendrocyte stage-specific markers revealed an increase in the density of myelinating oligodendrocytes in several areas of the TS brain. Along the same line, electron microscopy studies in the corpus callosum of TS animals showed significant increases both in the percentage of myelinated axons and in the thickness of myelin sheaths. In summary, these data indicate that OPC development and oligodendrocyte myelination is enhanced in the brain of TS mice, and suggest that this mouse model of a syndromic ASD is a useful tool to explore the role of L-type Ca⁺⁺ channels in myelination.