Mature retinal ganglion cells (RGCs) cannot normally regenerate axons into the injured optic nerve but can do so after lens injury. Astrocyte-derived ciliary neurotrophic factor and leukemia inhibitory factor have been identified as essential key factors mediating this effect. However, the outcome of this regeneration is still limited by inhibitors associated with the CNS myelin and the glial scar. The current study demonstrates that Taxol markedly enhanced neurite extension of mature RGCs and PC12 cells by stabilization of microtubules and desensitized axons toward myelin and chondroitin sulfate proteoglycan (CSPG) inhibition in vitro without reducing RhoA activation. In vivo, the local application of Taxol at the injury site of the optic nerve of rats enabled axons to regenerate beyond the lesion site but did not affect the intrinsic regenerative state of RGCs. Furthermore, Taxol treatment markedly increased lens injury-mediated axon regeneration in vivo, delayed glial scar formation, suppressed CSPG expression, and transiently reduced the infiltration of macrophages at the injury site. Thus, microtubule-stabilizing compounds such as Taxol might be promising candidates as adjuvant drugs in the treatment of CNS injuries particularly when combined with interventions stimulating the intrinsic regenerative state of neurons.

Traumatic CNS injuries often cause permanent, devastating disabilities due to a lack of regeneration of damaged axons. Next to an insufficient intrinsic capability of CNS neurons to regrow axons, also inhibitory molecules that are associated with the CNS myelin and the glial scar contribute to the failure of axonal regeneration. Strategies targeting the inhibitory molecules, their receptors or downstream signaling pathways result in little improvement of regeneration in vivo. However, the combination of such approaches together with measures that increase the intrinsic growth potential of neurons reportedly lead to a significantly better outcome. In this mini-review we outline and discuss a novel therapeutic strategy facilitating axon regeneration by directly targeting microtubule dynamics in axonal growth cones and reducing the inhibitory scar formation at the injury site by the anticancer drug Taxol. Moreover, we portray the mechanisms underlying the beneficial effects of Taxol and its potential as an adjuvant drug to accomplish substantial regeneration and functional recovery after CNS injuries in vivo.

Retinal ganglion cells (RGCs) are central nervous system neurons with a very limited ability for axon regeneration. This unit details a cell culture technique, which can be used to functionally screen factors/compounds for their neuritogenic and neuroprotective effects on RGCs. In this protocol, the retina is isolated, digested in a papain solution, and after trituration, the RGCs are cultured. The neuritogenic effect of applied factors/compounds on RGCs in the medium is functionally determined by measuring the average neurite length of βIII-tubulin-positive RGCs in culture after 3 days. This protocol takes 3 to 7 days to perform depending on the application to complete, and is suitable to reliably test pharmacological and genetic approaches for their axon growth-promoting and neuroprotective potential on mature RGCs.

Patients with autosomal recessive microcephaly 15 caused by deficiency in the sodium-dependent lysophosphatidylcholine (LPC) transporter major facilitator superfamily domain–containing 2a (Mfsd2a) present with both microcephaly and hypomyelination, suggesting an important role for LPC uptake by oligodendrocytes in the process of myelination. Here we demonstrate that Mfsd2a is specifically expressed in oligodendrocyte precursor cells (OPCs) and is critical for oligodendrocyte development. Single-cell sequencing of the oligodendrocyte lineage revealed that OPCs from OPC-specific Mfsd2a-KO mice (2aOKO mice) underwent precocious differentiation into immature oligodendrocytes and impaired maturation into myelinating oligodendrocytes, correlating with postnatal brain hypomyelination. 2aOKO mice did not exhibit microcephaly, a finding consistent with the notion that microcephaly is the consequence of an absence of LPC uptake at the blood-brain barrier rather than a deficiency in OPCs. Lipidomic analysis showed that OPCs and iOLs from 2aOKO mice had significantly decreased levels of phospholipids containing omega-3 fatty acids, with a corresponding increase in unsaturated fatty acids, the latter being products of de novo synthesis governed by Srebp-1. RNA-Seq indicated activation of the Srebp-1 pathway and defective expression of regulators of oligodendrocyte development. Taken together, these findings indicate that the transport of LPCs by Mfsd2a in OPCs is important for maintaining OPC state to regulate postnatal brain myelination.