Accumulating evidences suggest a strong correlation between metabolic changes and neurodegeneration in CNS demyelinating diseases such as multiple sclerosis (MS). Biotin, an essential cofactor for five carboxylases, is expressed by oligodendrocytes and involved in fatty acid synthesis and energy production. The metabolic effect of biotin or high-dose-biotin (MD1003) has been reported on rodent oligodendrocytes in vitro, and in neurodegenerative or demyelinating animal models. However, clinical studies, showed mild or no beneficial effect of MD1003 in amyotrophic lateral sclerosis (ALS) or MS. Here, we took advantage of a mouse model of myelin deficiency to study the effects of MD1003 on the behavior of murine and grafted human oligodendrocytes in vivo. We show that MD1003 increases the number and the differentiation potential of endogenous murine oligodendroglia over time. Moreover, the levels of MD1003 are increased in the plasma and brain of pups born to treated mothers, indicating that MD1003 can pass through the mother\'s milk. The histological analysis of the grafted animals shows that MD1003 increased proliferation and accelerates differentiation of human oligodendroglia, but without enhancing their myelination potential. These findings provide important insights into the role of MD1003 on murine and human oligodendrocyte maturation/myelination that may explain the mitigated outcome of ALS/MS clinical trials.

OBJECTIVE: To perform a quantitative evaluation of myelination on WT and myelin-deficient (shiverer) mouse spinal cords using ultrahigh-b diffusion-weighted imaging (UHb-DWI).
METHODS: UHb-DWI of ex vivo on spinal cord specimens of two shiverer (C3HeB/FeJ-shiverer, homozygous genotype for MbPshi ) and six WT (Black Six, C3HeB/FeJ) mice were acquired using 3D multishot diffusion-weighted stimulated-echo EPI, a homemade RF coil, and a small-bore 7T MRI system. Imaging was performed in transaxial plane with 75 × 75 μm2 in-plane resolution, 1-mm-slice thickness, and radial DWI using bmax = 42,890 s/mm2 . Histological evaluation was performed on upper thoracic sections using optical and transmission electron microscopy. Numerical Monte Carlo simulations (MCSs) of water diffusion were performed to facilitate interpretation of UHb-DWI signal-b curves.
RESULTS: The white matter ultrahigh-b radial DWI (UHb-rDWI) signal-b curves of WT mouse cords behaved biexponentially with high-b diffusion coefficient DH < 0.020 × 10-3 mm2 /s. However, as expected with less myelination, the signal-b of shiverer mouse cords behaved monoexponentially with significantly greater DH = 0.162 × 10-3 , 0.142 × 10-3 , and 0.164 × 10-3 mm2 /s at anterodorsal, posterodorsal, and lateral columns, respectively. The axial DWI signals of all mouse cords behaved monoexponentially with D = (0.718-1.124) × 10-3 mm2 /s. MCS suggests that these elevated DH are mainly induced by increased water exchange at the myelin sheath. Microscopic results were consistent with the UHb-rDWI findings.
CONCLUSIONS: UHb-DWI provides quantitative differences in myelination of spinal cords from myelin-deficit shiverer and WT mice. UHb-DWI may become a powerful tool to evaluate myelination in demyelinating disease models that may translate to human diseases, including multiple sclerosis.

Lack of axon regeneration following spinal cord injury has been mainly ascribed to the inhibitory environment of the injury site, i.e., to chondroitin sulfate proteoglycans (CSPGs) and myelin-associated inhibitors (MAIs). Here, we used shiverer (shi) mice to assess axon regeneration following spinal cord injury in the presence of MAIs and CSPG but in the absence of compact myelin. Although in vitro shi neurons displayed a similar intrinsic neurite outgrowth to wild-type neurons, in vivo, shi fibers had increased regenerative capacity, suggesting that the wild-type spinal cord contains additional inhibitors besides MAIs and CSPG. Our data show that besides myelin protein, myelin lipids are highly inhibitory for neurite outgrowth and suggest that this inhibitory effect is released in the shi spinal cord given its decreased lipid content. Specifically, we identified cholesterol and sphingomyelin as novel myelin-associated inhibitors that operate through a Rho-dependent mechanism and have inhibitory activity in multiple neuron types. We further demonstrated the inhibitory action of myelin lipids in vivo, by showing that delivery of 2-hydroxypropyl-β-cyclodextrin, a drug that reduces the levels of lipids specifically in the injury site, leads to increased axon regeneration of wild-type (WT) dorsal column axons following spinal cord injury. In summary, our work shows that myelin lipids are important modulators of axon regeneration that should be considered together with protein MAIs as critical targets in strategies aiming at improving axonal growth following injury.