Genetically induced adult oligodendrocyte cell death is associated with poor myelin clearance, reduced remyelination, and axonal damage.

Loss of oligodendrocytes is a feature of many demyelinating diseases including multiple sclerosis. Here, we have established and characterized a novel model of genetically induced adult oligodendrocyte death. Specific primary loss of adult oligodendrocytes leads to a well defined and highly reproducible course of disease development that can be followed longitudinally by magnetic resonance imaging. Histological and ultrastructural analyses revealed progressive myelin vacuolation, in parallel to disease development that includes motor deficits, tremor, and ataxia. Myelin damage and clearance were associated with induction of oligodendrocyte precursor cell proliferation, albeit with some regional differences. Remyelination was present in the mildly affected corpus callosum. Consequences of acutely induced cell death of adult oligodendrocytes included secondary axonal damage. Microglia were activated in affected areas but without significant influx of B-cells, T-helper cells, or T-cytotoxic cells. Analysis of the model on a RAG-1 (recombination activating gene-1)-deficient background, lacking functional lymphocytes, did not change the observed disease and pathology compared with immune-competent mice. We conclude that this model provides the opportunity to study the consequences of adult oligodendrocyte death in the absence of primary axonal injury and reactive cells of the adaptive immune system. Our results indicate that if the blood-brain barrier is not disrupted, myelin debris is not removed efficiently, remyelination is impaired, and axonal integrity is compromised, likely as the result of myelin detachment. This model will allow the evaluation of strategies aimed at improving remyelination to foster axon protection.

De novo fatty acid synthesis by Schwann cells is essential for peripheral nervous system myelination.

Myelination calls for a remarkable surge in cell metabolism to facilitate lipid and membrane production. Endogenous fatty acid (FA) synthesis represents a potentially critical process in myelinating glia. Using genetically modified mice, we show that Schwann cell (SC) intrinsic activity of the enzyme essential for de novo FA synthesis, fatty acid synthase (FASN), is crucial for precise lipid composition of peripheral nerves and fundamental for the correct onset of myelination and proper myelin growth. Upon FASN depletion in SCs, epineurial adipocytes undergo lipolysis, suggestive of a compensatory role. Mechanistically, we found that a lack of FASN in SCs leads to an impairment of the peroxisome proliferator-activated receptor (PPAR) γ-regulated transcriptional program. In agreement, defects in myelination of FASN-deficient SCs could be ameliorated by treatment with the PPARγ agonist rosiglitazone ex vivo and in vivo. Our results reveal that FASN-driven de novo FA synthesis in SCs is mandatory for myelination and identify lipogenic activation of the PPARγ transcriptional network as a putative downstream functional mediator.