Hypoxia-inducible factor-1alpha signaling in aquaporin upregulation after traumatic brain injury.
Previous studies have demonstrated that traumatic brain injury (TBI) causes brain edema via aquaporins (AQPs), the water-transporting proteins. In the present study, we determined the role of hypoxia inducible factor-1alpha (HIF-1alpha), which is a transcription factor in response to physiological hypoxia, in regulating expression of AQP4 and AQP9. Adult male Sprague-Dawley rats (400-425g) received a closed head injury using the Marmarou weight drop model with a 450g weight and survived for 1, 4, 24 and 48h. Some animals were administered 30min after injury with 2-methoxyestradiol (2ME2), a naturally occurring metabolite of estradiol which is known to post-transcriptionally down-regulate HIF-1alpha expression, and sacrificed 4h after injury. Real-time PCR and Western blot were used, respectively, to detect gene and protein expressions of manganese superoxide dismutase (MnSOD, showing hypoxic stress), HIF-1alpha, AQP4, and AQP9. ANOVA analysis demonstrated a significant (p<0.05) increase in gene expression of MnSOD, HIF-1alpha, AQP4, and AQP9, starting at 1h after injury through 48h. Western blot analysis further indicated a significant (p<0.05) increase in protein expression of these molecules at the same time points. Pharmacological inhibition of HIF-1alpha by 2ME2 reduced the up-regulated levels of AQP4 and AQP9 after TBI. The present study suggests that hypoxic conditions determined by MnSOD expression after closed head injury contribute to HIF-1alpha expression. HIF-1alpha, in turn, up-regulates expression of AQP4 and AQP9. These results characterize the pathophysiological mechanisms, and suggest possible therapeutic targets for TBI patients.
Anatomy and Cell Biology, Wayne State University, School of Medicine, Detroit, MI, United States.
Jamie Y
JY
Ding
Christian W
CW
Kreipke
Susan L
SL
Speirs
Patrick
P
Schafer
Steven
S
Schafer
José A
JA
Rafols
D000077584:2-Methoxyestradiol; D000704:Analysis of Variance; D000818:Animals; D051401:Aquaporin 4 / Q000378:metabolism*; D020346:Aquaporins / Q000378:metabolism*; D015153:Blotting, Western; D001930:Brain Injuries / Q000378:metabolism*; D004958:Estradiol / Q000031:analogs & derivatives / Q000494:pharmacology; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000378:metabolism*; D008297:Male; D016133:Polymerase Chain Reaction; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction; D013482:Superoxide Dismutase / Q000378:metabolism; D013997:Time Factors; D015854:Up-Regulation
C496032:Aqp4 protein, rat; C491637:Aqp9 protein, rat; D051401:Aquaporin 4; D020346:Aquaporins; C497444:Hif1a protein, rat; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D004958:Estradiol; D000077584:2-Methoxyestradiol; D013482:Superoxide Dismutase