Heat stress enhances recovery of hepatocyte bile acid and organic anion transporters in endotoxemic rats by multiple mechanisms.
Heat stress (HS) reduces the many sequelae of lipopolysaccharide (LPS)-induced endotoxemia. Without HS, endotoxins have been shown to induce a transcriptional down-regulation of hepatocyte transport proteins for bile acids and organic anions. We performed experiments in isolated perfused rat livers at various times after LPS administration with and without HS pretreatment to determine whether HS would correct deficient transport of bromosulfophthalein (BSP). Possible mechanisms involved were investigated in livers from intact animals. In isolated perfused livers, LPS injection reduced BSP excretion to 48% compared with saline-injected controls (P < 0.01). When HS was applied 2 hours prior to LPS, BSP excretion increased to 74% of controls (P < 0.05 vs LPS and controls). Expression of the basolateral (Oatp1a1) and canalicular (Mrp2) organic anion transporter involved in the transport of BSP recovered more rapidly when HS preceded LPS application. Recovery of mRNA levels of these transporters occurred also earlier. Coimmunoprecipitation experiments and immunoelectron microscopy using a double immunogold labeling of heat shock protein 70 (HSP70) and various hepatocyte transporters suggested colocalization with HSP70 for the canalicular bile acid transporter (Bsep) in the subcanalicular space. In contrast, no colocalization was shown for Ntcp and anion transporters. In conclusion, we could show that HS enhances recovery of organic anion transporters and bile acid transporters following endotoxemia. Faster recovery of mRNA seems to be a key mechanism for anion transporters, whereas physical interaction with HSP70 plays a role in preservation of bile acid transporters. This interaction of HSP70 and canalicular transporters occurs only in pericanalicular vesicles but not when the protein is integrated into the plasma membrane.
Department of Surgery, University of Regensburg, Franz-Josef-Strauss-Allee 11, 93053 Regensburg, Germany. ulrich_bolder@yahoo.com
Ulrich
U
Bolder
Marc Gerhard
MG
Jeschke
Lukas
L
Landmann
Francine
F
Wolf
Corina
C
de Sousa
Hans-Jürgen
HJ
Schlitt
René
R
Przkora
D000818:Animals; D000911:Antibodies, Monoclonal / Q000378:metabolism; D001647:Bile Acids and Salts / Q000378:metabolism*; D015152:Blotting, Northern; D019446:Endotoxemia / Q000209:etiology / Q000378:metabolism*; D005455:Fluorescent Antibody Technique; D018840:HSP70 Heat-Shock Proteins / Q000032:analysis / Q000648:ultrastructure; D018882:Heat Stress Disorders / Q000378:metabolism*; D022781:Hepatocytes / Q000378:metabolism* / Q000648:ultrastructure; D016753:Interleukin-10 / Q000378:metabolism; D007700:Kinetics; D008070:Lipopolysaccharides / Q000494:pharmacology; D008297:Male; D008856:Microscopy, Fluorescence; D027361:Organic Anion Transporters / Q000378:metabolism* / Q000648:ultrastructure; D011233:Precipitin Tests; D051381:Rats; D017207:Rats, Sprague-Dawley; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism
D000911:Antibodies, Monoclonal; D001647:Bile Acids and Salts; D018840:HSP70 Heat-Shock Proteins; D008070:Lipopolysaccharides; D027361:Organic Anion Transporters; D014409:Tumor Necrosis Factor-alpha; D016753:Interleukin-10