Stimulation of Hypoxia-Inducible Factor-1 Alpha (HIF-1α) Protein in the Adult Rat Testis Following Ischemic Injury Occurs Without an Increase in HIF-1α Messenger RNA Expression1

Abstract

Hypoxia-inducible factor 1 (HIF-1) is a transcription factor composed of α and β subunits. Stabilized from proteasome degradation and activated by hypoxia, HIF-1 stimulates expression of hypoxia-sensitive genes that mediate oxygen homeostasis in many tissues. Our hypothesis is that HIF-1 is involved in the cellular response to hypoxia in the ischemic testis. Goals of this study were to determine if HIF-1α mRNA is expressed in the testis, epididymis, and accessory sex glands of adult Sprague-Dawley rats and to determine if HIF-1α mRNA and protein expression in the testis is affected by experimentally induced ischemia. Total RNA from reproductive organs of adult rats was analyzed by relative reverse transcription-polymerase chain reaction (RT-PCR) analysis. HIF-1α mRNA showed equal expression in testis, all segments of epididymis, ductus deferens, accessory sex glands, and penis. To examine the effects of ischemia on HIF-1α mRNA and protein expression in the testis, rats were subjected to unilateral testicular ischemia by placing a ligature around spermatic artery or ischemia-inducing experimental torsion and reperfusion. RT-PCR revealed that HIF-1α mRNA expression at all times of ischemic treatment and reperfusion was unchanged compared with normoxic controls. HIF-1α protein was detected by immunoblot analysis of nuclear protein extracts from normoxic testes. Steady-state levels of HIF-1α protein were stimulated by 15 min of ischemia and showed a 2-fold increase at 30 min and 1, 3, and 6 h. HIF-1α protein was also elevated by experimental torsion and reperfusion compared with normoxic controls. These results support the hypothesis that HIF-1 may play a role in the cellular response to hypoxia in the ischemic testis.