Postnatal glucocorticoids suppress myelination in a dose-dependent manner by genomic mechanism

Objective: Postnatal glucocorticoids (GCs) are widely used in the prevention of chronic lung disease in premature infants. However, their use is associated with neurodevelopmental delay and cerebral palsy. We hypothesized that postnatal dexamethasone or betamethasone in high-dose, but not low-dose, would induce hypomyelination, astrogliosis, and motor impairment in premature rabbit pups. Additionally, these effects would be mediated by glucocorticoid receptors (GRs). Methods: Preterm rabbit pups, delivered by C-section at E29 (term=32d), were treated with a high dose of dexamethasone or vehicle. Myelin basic protein (MBP), glial fibrillary basic protein (GFAP), oligodendrocyte proliferation and maturation, and alteration of transcriptomic profile were evaluated in these pups. Neurobehavioral assessments were performed at 14d. Results: High-dose dexamethasone treatment reduced MBP expression and induced motor-impairment compared with controls. High-dose dexamethasone induced astrogliosis and altered genes associated with myelination, cell-cycle, GR, and MAP-Kinase signaling. Interpretation: High-dose postnatal dexamethasone arrested maturation of oligodendrocytes, and induced hypomyelination, gliosis and motor deficits. GC treatment reduced myelination by genomic GR-dependent mechanisms, and caused astrogliosis by non-genomic mechanisms. Two-condition experiment: forebrains of HDD (high dose dexamethasone) vs. CTR (saline) post-natally exposed rabbit pups. Biological replicates: 4 CTR replicates, 4 HDD replicates.