Timing-Dependent Effects of Dexamethasone in a Mouse Model of Neonatal Hypoxic-Ischemic Brain Injury: A...

The optimal timing and therapeutic role of dexamethasone for neuroprotection in neonatal hypoxic-ischemic (HI) brain injury remain unclear. We investigated whether dexamethasone-mediated neuroprotection is time-dependent and explored its underlying molecular mechanisms in a neonatal HI mouse model. The Rice-Vannucci model (unilateral carotid artery ligation followed by 8% O₂ for 90 min) was constructed utilizing postnatal day 7 mice who received vehicle (n = 5), dexamethasone pre-treatment (0.5 mg/kg, 6 h before HI; n = 6), or dexamethasone post-treatment (0.5 mg/kg, 6 h after HI; n = 6). Brain injury severity was evaluated by two blinded investigators 72 h after HI, who measured the whitish discoloration in the ipsilateral hemisphere. Transcriptomic analysis was performed using five representative brain samples from each group. Dexamethasone pre-treatment significantly reduced the area of whitish discoloration compared with the vehicle (p < 0.001); dexamethasone post-treatment exerted no significant protective effect. Transcriptomic profiling identified 962 (407 upregulated and 555 downregulated) differentially expressed genes. Genes with upregulated expressions were enriched in pathways related to central nervous system development, synaptic signaling, and calcium homeostasis; those with downregulated expressions were associated with cellular metabolic processes. Protein-protein interaction network analysis identified Dlg4, Calm1, and Grin1 as hub genes. qRT-PCR validation confirmed significant upregulation of Grin1 and Calm1, whereas Dlg4 showed a concordant but non-significant trend. These findings suggest that dexamethasone pre-treatment may be associated with time-dependent changes in synaptic- and calcium-related gene expression following neonatal HI injury, providing insight into the optimal therapeutic window for neonatal HI brain injury.