title: Phosphodiesterase-5 inhibition abolishes neuron apoptosis induced by chronic hypoxia independently of hypoxia-inducible factor-1alpha signaling.
abstract: Exposure to hypoxia triggers a variety of adverse effects in the brain that arise from metabolic stress and induce neuron apoptosis. Overexpression of the hypoxia-inducible factor-1alpha (HIF-1alpha) is believed to be a major candidate in orchestrating the cell's defense against stress. To test the impact of HIF-1alpha on apoptosis during chronic hypoxia in vivo, we examined the protective effect of modulating the nitric oxide (NO)/cGMP pathway by sildenafil, a selective inhibitor of phosphodiesterase-5 (PDE-5). Male ICR/CD-1 mice were divided into 3 groups (n = 6/group): normoxic (21% O(2)), hypoxic (9.5% O(2)), and hypoxic with sildenafil (1.4-mg/kg intraperitoneal injections daily). At the end of the 8-day treatment period, the mice were euthanized and cerebral cortex biopsies were harvested for analyses. We found that sildenafil: (1) did not significantly alter the hypoxia-induced weight loss and hemoglobin increase, but did augment plasma nitrates+nitrites and the tissue content of cGMP and phosphorylated (P) NO synthase III; (2) reversed the hypoxia-induced neuron apoptosis (terminal deoxynucleotidyl transferase positivity and double-staining immunofluorescence, P = 0.009), presumably through increased bcl-2/Bax (P = 0.0005); and (3) did not affect HIF-1alpha, but rather blunted the hypoxia-induced increase in P-ERK1/2 (P = 0.0002) and P-p38 (P = 0.004). We conclude that upregulating the NO/cGMP pathway by PDE-5 inhibition during hypoxia reduces neuron apoptosis, regardless of HIF-1alpha, through an interaction involving ERK1/2 and p38.
authors.affiliation: University of Milan, San Paolo Hospital, via di Rudinì 8 I-20142 Milan, Italy.
authors.forename: Anna
authors.initials: A
authors.lastname: Caretti
authors.forename: Paola
authors.initials: P
authors.lastname: Bianciardi
authors.forename: Raffaella
authors.initials: R
authors.lastname: Ronchi
authors.forename: Monica
authors.initials: M
authors.lastname: Fantacci
authors.forename: Marco
authors.initials: M
authors.lastname: Guazzi
authors.forename: Michele
authors.initials: M
authors.lastname: Samaja
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D006152:Cyclic GMP / Q000378:metabolism; D054706:Cyclic Nucleotide Phosphodiesterases, Type 5 / Q000378:metabolism; D000860:Hypoxia / Q000378:metabolism* / Q000473:pathology / Q000503:physiopathology*; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000378:metabolism*; D008297:Male; D051379:Mice; D008813:Mice, Inbred ICR; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D023421:Models, Animal; D009474:Neurons / Q000187:drug effects / Q000473:pathology*; D009569:Nitric Oxide / Q000378:metabolism; D058986:Phosphodiesterase 5 Inhibitors; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D010879:Piperazines / Q000494:pharmacology; D011687:Purines / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D000068677:Sildenafil Citrate; D013450:Sulfones / Q000494:pharmacology; D042461:Vascular Endothelial Growth Factor A / Q000378:metabolism; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
chemical_list: C497443:Hif1a protein, mouse; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D058986:Phosphodiesterase 5 Inhibitors; D010726:Phosphodiesterase Inhibitors; D010879:Piperazines; D011687:Purines; D013450:Sulfones; D042461:Vascular Endothelial Growth Factor A; D009569:Nitric Oxide; D000068677:Sildenafil Citrate; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D048051:p38 Mitogen-Activated Protein Kinases; D054706:Cyclic Nucleotide Phosphodiesterases, Type 5; D006152:Cyclic GMP