2-Methoxyestradiol confers neuroprotection and inhibits a maladaptive HIF-1α response after traumatic brain injury in mice

Abstract

HIF-1α is pivotal for cellular homeostasis in response to cerebral ischemia. Pharmacological inhibition of HIF-1α may reduce secondary brain damage by targeting post-translational mechanisms associated with its proteasomal degradation and nuclear translocation. This study examined the neuroprotective effects of 2-methoxyestradiol (2ME2), the involved HIF-1α-dependent response, and alternative splicing in exon 14 of HIF-1α (HIF-1α∆Ex14) after traumatic brain injury (TBI) in mice. Intraperitoneal 2ME2 administration 30 min after TBI caused a dose-dependent reduction in secondary brain damage after 24 h. 2ME2 was physiologically tolerated, showed no effects on immune cell brain migration, and mitigated trauma-induced brain expression of neuropathologically relevant HIF-1α target genes encoding for Plasminogen activator inhibitor 1 and tumor necrosis factor alpha. Moreover, TBI-induced expression of pro-apoptotic BNIP3 was attenuated by 2ME2 treatment. Alternatively, spliced HIF-1α∆Ex14 was substantially up-regulated from 6 to 48 h after TBI. In vitro, nuclear location and gene transcription activity of HIF-1α∆Ex14 were impaired compared to full-length HIF-1α, but no effects on nuclear translocation of the transcriptional complex partner HIF-1β were observed. This study demonstrates that 2ME2 confers neuroprotection after TBI. While the role of alternatively spliced HIF-1α∆Ex14 remains elusive, the in vivo data provide evidence that inhibition of a maladaptive HIF-1α-dependent response contributes to the neuroprotective effects of 2ME2. We examined neuroprotective effects of 2-methoxyestradiol (2ME2) and the hypoxia-inducible factor 1-α (HIF-1α) response following traumatic brain injury in mice. Early 2ME2 administration reduced the secondary brain damage and neuronal HIF-1α probably involving ubiquitin proteasome system-mediated degradation. The up-regulation of neuropathological HIF-1α target genes and pro-apoptotic BNIP3 protein was attenuated. We propose that the inhibition of a maladaptive HIF-1α response may contribute to 2ME2-mediated neuroprotection.

Keywords: 2-methoxyestradiol; HIF-1; alternative splicing; cerebral ischemia; neuroprotection; traumatic brain injury.