Prolyl hydroxylase inhibitor treatment confers whole-animal hypoxia tolerance.
OBJECTIVE
Recently a family of O(2)-dependent prolyl hydroxylase domain-containing enzymes (PHD) has been identified as a cellular oxygen-sensing mechanism. Reduced prolyl hydroxylase activity initiates a signalling cascade that includes the accumulation, as well as the activation, of hypoxia-inducible factor (HIF-1alpha). In turn the transcription factor HIF-1alpha, and other targets of the PHD, elicit a myriad of incompletely understood cellular responses. In these studies we have tested: (1) whether a small-molecule prolyl hydroxylase inhibitor (PHI) can effectively activate the oxygen-sensing pathway when administered systemically to mice, and (2) whether the activation of the PHD signalling pathway at the cellular level results in whole-animal hypoxic tolerance.


METHODS
Mice received daily injections of the PHI, ethyl-3,4 dihydroxybenzoate (EDHB, 100-250 mg kg(-1)) or vehicle. Tissue levels of HIF-1alpha and the serum levels of the HIF-inducible gene, erythropoietin (EPO), were measured to evaluate PHD-pathway activation. To evaluate hypoxic tolerance, the endurance and survival ability of these animals was tested in sublethal (8% O(2)) and lethal hypoxia (5% O(2)) respectively.


RESULTS
Systemic treatment of mice with the PHD inhibitor, EDHB, leads to elevated levels of HIF-1alpha in liver and HIF-inducible EPO in serum, indicating activation of the cellular oxygen-sensing pathway. Animals treated with EDHB display significantly increased viability and enhanced exercise performance in hypoxia.


CONCLUSIONS
These results demonstrate a novel pharmacological strategy to induce hypoxic tolerance and are the first to demonstrate that the activation of the PHD oxygen-sensing pathway at the cellular level is sufficient to produce a hypoxic-tolerant phenotype at the physiological level of the whole animal.
Kasiganesan
H
H
Department of Pharmaceutical Sciences, Medical University of South Carolina, Charleston, SC 29425, USA.
Sridharan
V
V
Wright
G
G
D000600:Amino Acids, Dicarboxylic / Q000008:administration & dosage; D000818:Animals; D004791:Enzyme Inhibitors / Q000008:administration & dosage*; D004921:Erythropoietin / Q000097:blood; D006400:Hematocrit; D062385:Hydroxybenzoates / Q000008:administration & dosage*; D000860:Hypoxia / Q000378:metabolism*; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000032:analysis; D007274:Injections, Intraperitoneal; D008099:Liver / Q000378:metabolism; D008297:Male; D051379:Mice; D008815:Mice, Inbred Strains; D010100:Oxygen / Q000502:physiology; D010805:Physical Conditioning, Animal / Q000379:methods; D010807:Physical Endurance / Q000502:physiology; D011393:Procollagen-Proline Dioxygenase / Q000037:antagonists & inhibitors*; D015398:Signal Transduction / Q000502:physiology
D000600:Amino Acids, Dicarboxylic; D004791:Enzyme Inhibitors; C497443:Hif1a protein, mouse; D062385:Hydroxybenzoates; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D004921:Erythropoietin; C018063:ethyl protocatechuate; D011393:Procollagen-Proline Dioxygenase; D010100:Oxygen; C040947:oxalylglycine