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.
Ding
Jamie Y
JY
Anatomy and Cell Biology, Wayne State University, School of Medicine, Detroit, MI, United States.
Kreipke
Christian W
CW
Speirs
Susan L
SL
Schafer
Patrick
P
Schafer
Steven
S
Rafols
José A
JA
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