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Ceruloplasmin (Cp) is a ferroxidase enzyme that is essential for cell iron efflux and has been postulated to have a neuroprotective role. During the myelination process, oligodendrocytes (OLs) and Schwann cells (SCs) express high levels of Cp, but the role of this enzyme in glial cell development and function is completely unknown. To define the function of Cp in the myelination of the central and peripheral nervous systems, we have conditionally knocked-out Cp specifically in OLs and SCs during early postnatal development as well as in aged mice. Cp ablation in early OLs (postnatal day 2, P2) significantly affects the differentiation of these cells and the synthesis of myelin through the first four postnatal weeks. The total number of mature myelinating OLs was reduced, and the density of apoptotic OLs was increased. These changes were accompanied with reductions in the percentage of myelinated axons and increases in the g-ratio of myelinated fibers. Cp ablation in young myelinating OLs (P30 or P60) did not affect myelin synthesis and/or OL numbers, however, Cp loss in aged OLs (8 months) induced cell iron overload, apoptotic cell death, brain oxidative stress, neurodegeneration and myelin disruption. Furthermore, Cp deletion in SCs affected postnatal SC development and myelination and produced motor coordination deficits as well as oxidative stress in young and aged peripheral nerves. Together, our data indicate that Cp ferroxidase activity is essential for OLs and SCs maturation during early postnatal development and iron homeostasis in matured myelinating cells. Additionally, our results suggest that Cp expression in myelinating glial cells is crucial to prevent oxidative stress and neurodegeneration in the central and peripheral nervous systems., (Copyright © 2021 The Authors. Published by Elsevier B.V. All rights reserved.)