Adenosine-dependent activation of hypoxia-inducible factor-1 induces late preconditioning in liver cells.
The cellular mechanisms by which ischemic preconditioning increases liver tolerance to ischemia/reperfusion injury are still poorly understood. This study investigated the role of the hypoxia-inducible factor-1 (HIF-1) in the protection associated with the late phase of liver preconditioning. Late preconditioning was induced in primary cultured rat hepatocytes by a transient (10 minute) hypoxic stress or by 15 minutes incubation with the adenosine A(2A) receptors agonist CGS21680 24 hours before exposure to 90 minutes of hypoxia in a serum-free medium. Late preconditioning induced the nuclear translocation of HIF-1 and the expression of carbonic anhydrase IX (CAIX), a HIF-1-regulated transmembrane enzyme that catalyzes bicarbonate production. Such effects were associated with prevention of hepatocyte killing by hypoxia and the amelioration of intracellular acidosis and Na+ accumulation. The inhibition of PKC-mediated and PI3-kinase-mediated signals with, respectively, chelerythrine and wortmannin abolished HIF-1 activation and blocked both CAIX expression and the protective action of late preconditioning. CAIX expression was also prevented by interfering with the transcriptional activity of HIF-1 using a dominant negative HIF-1beta subunit. The inhibition of CAIX with acetazolamide or the block of bicarbonate influx with disodium-4-acetamido-4'-isothiocyanato-stilben-2,2'-disulfonate also reverted the protective effects of late preconditioning on intracellular acidosis and Na+ accumulation.


CONCLUSIONS
The stimulation of adenosine A(2A) receptors induced late preconditioning in liver cells through the activation of HIF-1. HIF-1-induced expression of CAIX increases hepatocyte tolerance to ischemia by maintaining intracellular Na+ homeostasis. These observations along with the importance of HIF-1 in regulating cell survival indicates HIF-1 activation as a possible key event in liver protection by late preconditioning.
Dipartimento di Scienze Mediche, Università "A. Avogadro", Novara, Italy.
Elisa
E
Alchera
Lorenza
L
Tacchini
Chiara
C
Imarisio
Caterina
C
Dal Ponte
Cristina
C
De Ponti
Elena
E
Gammella
Gaetano
G
Cairo
Emanuele
E
Albano
Rita
R
Carini
D000241:Adenosine / Q000031:analogs & derivatives / Q000378:metabolism* / Q000494:pharmacology; D058908:Adenosine A2 Receptor Agonists; D000818:Animals; D001692:Biological Transport; D030741:Carbonic Anhydrase IV / Q000378:metabolism; D015687:Cell Hypoxia / Q000502:physiology; D002467:Cell Nucleus / Q000378:metabolism; D002478:Cells, Cultured; D016895:Culture Media, Serum-Free; D019610:Cytoprotection; D022781:Hepatocytes / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D051793:Hypoxia-Inducible Factor 1 / Q000378:metabolism*; D019194:Ischemic Preconditioning; D008099:Liver / Q000098:blood supply*; D008297:Male; D010627:Phenethylamines / Q000494:pharmacology; D058906:Purinergic P1 Receptor Agonists; D051381:Rats; D017208:Rats, Wistar; D043705:Receptor, Adenosine A2A / Q000378:metabolism*; D018047:Receptors, Purinergic P1 / Q000378:metabolism*; D013997:Time Factors
D058908:Adenosine A2 Receptor Agonists; D016895:Culture Media, Serum-Free; D051793:Hypoxia-Inducible Factor 1; D010627:Phenethylamines; D058906:Purinergic P1 Receptor Agonists; D043705:Receptor, Adenosine A2A; D018047:Receptors, Purinergic P1; C061282:2-(4-(2-carboxyethyl)phenethylamino)-5'-N-ethylcarboxamidoadenosine; D030741:Carbonic Anhydrase IV; D000241:Adenosine