Chronic COX-2 inhibition reduces medullary HSP70 expression and induces papillary apoptosis in dehydrated rats.
BACKGROUND
Papillary cells adapt to their hyperosmotic environment by accumulating organic osmolytes and by enhanced synthesis of heat shock protein 70 (HSP70), which protect against high-solute concentrations. Because cyclooxygenase-2 (COX-2) is expressed abundantly in the renal papilla and is induced by dehydration, and because HSP70 expression is stimulated by specific prostaglandins, COX-2 inhibition may interfere with cellular osmoadaptation.


METHODS
In vivo, rats received rofecoxib before water deprivation. Medullary expression of several tonicity-responsive genes was analyzed and apoptosis was monitored by transferase-mediated dUTP nick-end labeled (TUNEL) staining and determination of papillary caspase-3 activity. In vitro, inner medullary collecting duct 3 (IMCD3) cells were exposed to hypertonic medium containing a COX-2-specific inhibitor. Thereafter, expression of tonicity-responsive genes was analyzed and resistance to high-solute concentrations was examined. Further, the effect of Delta 12-PGJ2, a urinary prostaglandin, and of HSP70 overexpression on resistance against high urea concentration, was evaluated.


RESULTS
Rofecoxib treatment significantly increased urine osmolality due to higher urea concentrations, but reduced papillary HSP70 abundance by 50%. TUNEL staining showed numerous apoptotic cells in the papilla, associated with increased caspase-3 activity. These in vivo results were confirmed by experiments on cultured IMCD3 cells, in which COX-2 inhibition impaired the tonicity-induced up-regulation of HSP70 expression and rendered the cells susceptible to high urea concentrations. Furthermore, Delta 12-PGJ2 increased both HSP70 expression and resistance against high urea, which was causally linked to higher HSP70 levels.


CONCLUSIONS
These observations support the view that chronic COX-2 inhibition reduces medullary HSP70 expression, thus rendering papillary cells susceptible to damage by high urea concentrations, especially when accompanied by dehydration.
Neuhofer
Wolfgang
W
Department of Physiology, University of Munich, Germany. W.Neuhofer@physiol.med.uni-muenchen.de
Holzapfel
Konstantin
K
Fraek
Maria-Luisa
ML
Ouyang
Nengtai
N
Lutz
Jens
J
Beck
Franz-X
FX
D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects*; D002478:Cells, Cultured; D051546:Cyclooxygenase 2; D052246:Cyclooxygenase 2 Inhibitors; D016861:Cyclooxygenase Inhibitors / Q000494:pharmacology*; D003681:Dehydration / Q000503:physiopathology*; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics*; D006982:Hypertonic Solutions / Q000494:pharmacology; D007527:Isoenzymes / Q000037:antagonists & inhibitors*; D007671:Kidney Concentrating Ability / Q000187:drug effects; D007679:Kidney Medulla / Q000187:drug effects / Q000201:enzymology / Q000473:pathology; D007783:Lactones / Q000494:pharmacology*; D008297:Male; D009994:Osmolar Concentration; D015230:Prostaglandin D2 / Q000494:pharmacology / Q000031:analogs & derivatives; D011451:Prostaglandin-Endoperoxide Synthases; D051381:Rats; D017208:Rats, Wistar; D013450:Sulfones; D014868:Water Deprivation; D014882:Water-Electrolyte Balance / Q000187:drug effects
D000970:Antineoplastic Agents; D052246:Cyclooxygenase 2 Inhibitors; D016861:Cyclooxygenase Inhibitors; D018840:HSP70 Heat-Shock Proteins; D006982:Hypertonic Solutions; D007527:Isoenzymes; D007783:Lactones; D013450:Sulfones; C116926:rofecoxib; C040810:9-deoxy-9,10-didehydro-12,13-didehydro-13,14-dihydroprostaglandin D2; D051546:Cyclooxygenase 2; D011451:Prostaglandin-Endoperoxide Synthases; D015230:Prostaglandin D2