Differential expression of stress-inducible proteins in chronic hepatic iron overload.
BACKGROUND
Oxidative stress can trigger a cellular stress response characterized by induction of antioxidants, acute phase reactants (APRs) and heat shock proteins (HSPs), which are presumed to play a role in limiting tissue damage. In rodents, hepatic iron overload causes oxidative stress that results in upregulation of antioxidant defenses with minimal progressive liver injury. The aim of this study was to determine whether iron overload modulates expression of other stress-responsive proteins such as APRs and HSPs that may confer protection against iron-induced damage in rodent liver.


METHODS
Male rats received repeated injections of iron dextran or dextran alone over a 6-month period. Hepatic transcript levels for a panel of APRs and HSPs were quantitated by real-time PCR and protein expression was evaluated by Western blot and immunohistochemistry.


RESULTS
Hepatic iron concentrations were increased >50-fold in the iron-loaded rats compared to controls. Iron loading resulted in striking increases in mRNAs for Hsp32 (heme oxygenase-1; 12-fold increase vs. controls) and metallothionein-1 and -2 (both increased approximately 6-fold). Transcripts for alpha1-acid glycoprotein, the major rat APR, were increased approximately 3-fold, while expression of other classical APRs was unaltered. Surprisingly, although mRNA levels for the HSPs were not altered by iron, the abundance of Hsp25, Hsp70 and Hsp90 proteins was uniformly reduced in the iron-loaded livers, as were levels of NAD(P)H:quinone oxidoreductase 1, an Hsp70 client protein.


CONCLUSIONS
Chronic iron administration elicits a unique pattern of stress protein expression. These alterations may modulate hepatic responses to iron overload, as well as other injury processes.
Brown
Kyle E
KE
Iowa City Veterans Administration Medical Center, Division of Gastroenterology-Hepatology, University of Iowa Roy J. and Lucille A. Carver College of Medicine, Iowa City 52242, USA. kyle-brown@uiowa.edu
Broadhurst
Kimberly A
KA
Mathahs
M Meleah
MM
Weydert
Jamie
J
D000209:Acute-Phase Proteins / Q000235:genetics* / Q000378:metabolism; D000818:Animals; D001052:Apoferritins / Q000235:genetics / Q000378:metabolism; D001798:Blood Proteins / Q000235:genetics / Q000378:metabolism; D015153:Blotting, Western; D002908:Chronic Disease; D004305:Dose-Response Relationship, Drug; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation / Q000187:drug effects; D006023:Glycoproteins / Q000235:genetics / Q000378:metabolism; D006360:Heat-Shock Proteins / Q000235:genetics* / Q000378:metabolism; D051547:Heme Oxygenase-1 / Q000235:genetics / Q000378:metabolism; D022781:Hepatocytes / Q000187:drug effects / Q000378:metabolism; D007150:Immunohistochemistry; D007274:Injections, Intraperitoneal; D019190:Iron Overload / Q000139:chemically induced / Q000503:physiopathology*; D007505:Iron-Dextran Complex / Q000008:administration & dosage / Q000633:toxicity; D035925:Iron-Regulatory Proteins / Q000235:genetics / Q000378:metabolism; D007728:Kupffer Cells / Q000187:drug effects / Q000378:metabolism; D008099:Liver / Q000187:drug effects / Q000378:metabolism; D008297:Male; D008668:Metallothionein / Q000235:genetics / Q000378:metabolism; D016660:NAD(P)H Dehydrogenase (Quinone) / Q000235:genetics / Q000378:metabolism; D009961:Orosomucoid; D051381:Rats; D017207:Rats, Sprague-Dawley; D020133:Reverse Transcriptase Polymerase Chain Reaction
D000209:Acute-Phase Proteins; D001798:Blood Proteins; D006023:Glycoproteins; D006360:Heat-Shock Proteins; D035925:Iron-Regulatory Proteins; C506108:Orm1 protein, rat; D009961:Orosomucoid; D007505:Iron-Dextran Complex; D001052:Apoferritins; D008668:Metallothionein; D051547:Heme Oxygenase-1; D016660:NAD(P)H Dehydrogenase (Quinone); C507703:NQO1 protein, rat