A biologic role of HIF-1 in the renal medulla.
BACKGROUND
Activation of hypoxia-inducible factor-1 (HIF-1) is the primary defensive mechanism against hypoxia. HIF-1 activation generally occurs in pathologic disruption of tissue oxygenation. However, a biologic role of HIF-1 in the medulla of the kidney, which is considered perpetually hypoxic under physiologic conditions due to its unique circulation, remains to be elucidated.


METHODS
The expression of HIF-1alpha was detected by immunohistochemical analysis. Functional studies of HIF in medulla were carried out by gene transfer of various plasmids by retrograde injection via ureter.


RESULTS
Our immunohistochemical analysis detected HIF-1alpha in the inner stripe and the inner medulla of normal rats. Water deprivation increased the number of HIF-1alpha-positive cells, which may be mediated by an increase in medullar workload and a decrease in local blood flow. To perform functional studies, we performed gene transfer. Efficient expression of the transgene was confirmed using an enhanced green fluorescent protein (E-GFP) expressing vector. Our histologic and immunoblotting analysis detected the transgene product at the inner medulla and the inner stripe 48 hours after injection. Administration of negative-dominant HIF induced severe damage in the medulla of normal rats. In contrast, gene transfer of constitutively active HIF (HIF/VP16) induced expression of various HIF-regulated genes and protected the medulla against ischemic insults.


CONCLUSIONS
Our studies demonstrated a crucial role of HIF in the renal medulla under normal and hypoxic circumstances.
Manotham
Krissanapong
K
Division of Nephrology and Endocrinology, University of Tokyo School of Medicine, Tokyo, Japan.
Tanaka
Tetsuhiro
T
Ohse
Takamoto
T
Kojima
Ichiro
I
Miyata
Toshio
T
Inagi
Reiko
R
Tanaka
Hirotoshi
H
Sassa
Ryoji
R
Fujita
Toshiro
T
Nangaku
Masaomi
M
D000818:Animals; D017209:Apoptosis; D001806:Blood Urea Nitrogen; D015687:Cell Hypoxia / Q000502:physiology; D017931:DNA Primers; D004268:DNA-Binding Proteins / Q000235:genetics / Q000502:physiology*; D018014:Gene Transfer Techniques; D017930:Genes, Reporter; D049452:Green Fluorescent Proteins / Q000235:genetics; D051793:Hypoxia-Inducible Factor 1; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D007679:Kidney Medulla / Q000166:cytology / Q000502:physiology*; D009687:Nuclear Proteins / Q000235:genetics / Q000502:physiology*; D016133:Polymerase Chain Reaction; D051381:Rats; D017207:Rats, Sprague-Dawley; D014157:Transcription Factors / Q000032:analysis / Q000235:genetics / Q000502:physiology*
D017931:DNA Primers; D004268:DNA-Binding Proteins; C497444:Hif1a protein, rat; D051793:Hypoxia-Inducible Factor 1; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D009687:Nuclear Proteins; D014157:Transcription Factors; D049452:Green Fluorescent Proteins