Nrf2 signaling increases expression of ATP-binding cassette subfamily C mRNA transcripts at the blood-brain barrier following hypoxia-reoxygenation stress.

TitleNrf2 signaling increases expression of ATP-binding cassette subfamily C mRNA transcripts at the blood-brain barrier following hypoxia-reoxygenation stress.
Publication TypeJournal Article
Year of Publication2017
AuthorsIbbotson K, Yell J, Ronaldson PT
JournalFluids Barriers CNS
Date Published2017 Mar 16
KeywordsAnimals, Anticarcinogenic Agents, Blood-Brain Barrier, Brain, Chromatin Immunoprecipitation, Disease Models, Animal, Electrophoretic Mobility Shift Assay, Female, Gene Expression Regulation, Hyperbaric Oxygenation, Hypoxia, Isothiocyanates, Microvessels, Multidrug Resistance-Associated Proteins, NF-E2-Related Factor 2, Rats, Rats, Sprague-Dawley, RNA, Messenger, Signal Transduction, Time Factors

BACKGROUND: Strategies to maintain BBB integrity in diseases with a hypoxia/reoxygenation (H/R) component involve preventing glutathione (GSH) loss from endothelial cells. GSH efflux transporters include multidrug resistance proteins (Mrps). Therefore, characterization of Mrp regulation at the BBB during H/R is required to advance these transporters as therapeutic targets. Our goal was to investigate, in vivo, regulation of Abcc1, Abcc2, and Abcc4 mRNA expression (i.e., genes encoding Mrp isoforms that transport GSH) by nuclear factor E2-related factor (Nrf2) using a well-established H/R model.

METHODS: Female Sprague-Dawley rats (200-250 g) were subjected to normoxia (Nx, 21% O2, 60 min), hypoxia (Hx, 6% O2, 60 min) or H/R (6% O2, 60 min followed by 21% O2, 10 min, 30 min, or 1 h) or were treated with the Nrf2 activator sulforaphane (25 mg/kg, i.p.) for 3 h. Abcc mRNA expression in brain microvessels was determined using quantitative real-time PCR. Nrf2 signaling activation was examined using an electrophoretic mobility shift assay (EMSA) and chromatin immunoprecipitation (ChIP) respectively. Data were expressed as mean ± SD and analyzed via ANOVA followed by the post hoc Bonferroni t test.

RESULTS: We observed increased microvascular expression of Abcc1, Abcc2, and Abcc4 mRNA following H/R treatment with reoxygenation times of 10 min, 30 min, and 1 h and in animals treated with sulforaphane. Using a biotinylated Nrf2 probe, we observed an upward band shift in brain microvessels isolated from H/R animals or animals administered sulforaphane. ChIP studies showed increased Nrf2 binding to antioxidant response elements on Abcc1, Abcc2, and Abcc4 promoters following H/R or sulforaphane treatment, suggesting a role for Nrf2 signaling in Abcc gene regulation.

CONCLUSIONS: Our data show increased Abcc1, Abcc2, and Abcc4 mRNA expression at the BBB in response to H/R stress and that Abcc gene expression is regulated by Nrf2 signaling. Since these Mrp isoforms transport GSH, these results may point to endogenous transporters that can be targeted for BBB protection during H/R stress. Experiments are ongoing to examine functional implications of Nrf2-mediated increases in Abcc transcript expression. Such studies will determine utility of targeting Mrp isoforms for BBB protection in diseases with an H/R component.

Alternate JournalFluids Barriers CNS
PubMed ID28298215
PubMed Central IDPMC5353788
Grant ListR01 NS084941 / NS / NINDS NIH HHS / United States
Faculty Member Reference: 
Patrick T Ronaldson, PhD, FAAPS