title: Changes in gene expression with iron loading and chelation in cardiac myocytes and non-myocytic fibroblasts.
abstract: Iron overload is associated with long-term cardiac iron accumulation and tissue changes such as fibrosis. To determine short-term iron-dependent changes in expression of genes associated with iron homeostasis and fibrosis we measured mRNA on Northern blots prepared from cultured rat neonatal cardiomyocytes and non-myocytes (fibroblasts) as a function of iron loading and chelation. Transferrin receptor mRNA was reduced in myocytes exposed to various concentrations of iron for 3 days and this decline was associated with a 63% decline in iron-response element (IRE) binding of iron regulatory protein-1, indicating that myocytes utilize IRE-dependent mechanisms to modulate gene expression. In myocytes iron caused a dose-dependent decline in mRNAs coding for transforming growth factor- beta(1)(TGF- beta(1)), biglycan, and collagen type I while plasminogen activator inhibitor-1 mRNA was unaffected by iron loading and decorin mRNA doubled. Total TGF- beta bioactivity was also decreased by iron loading. Thus, the effects of iron loading on genes related to cardiac fibrosis are gene-specific. Addition of deferoxamine for 1 day did not have any significant effect on any of these genes. Parallel changes in gene expression were exhibited by non-myocytes (fibroblasts), where chelation also decreased TGF- beta(1)mRNA and activity, and mRNA for collagen type I and biglycan, and collagen synthesis. In addition to these changes in transcripts associated with matrix formation the mRNA of the metabolic enzyme glyceraldehyde-3-phosphate dehydrogenase was unaffected by iron loading but doubled in both cell types upon treatment with deferoxamine. These findings suggest that in both cardiac myocytes and non-myocyte fibroblasts gene expression is coupled to intracellular iron pools by gene-specific and IRE-dependent and idependent mechanisms. This linkage may influence matrix deposition, a significant component of cardiac injury.
authors.affiliation: Department of Laboratory Medicine and Pathobiology, University of Toronto, 100 College St, Toronto, M5G 1L5, Canada.
authors.forename: J G
authors.initials: JG
authors.lastname: Parkes
authors.forename: Y
authors.initials: Y
authors.lastname: Liu
authors.forename: J B
authors.initials: JB
authors.lastname: Sirna
authors.forename: D M
authors.initials: DM
authors.lastname: Templeton
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D002478:Cells, Cultured / Q000187:drug effects; D015913:Chelation Therapy; D003094:Collagen / Q000096:biosynthesis / Q000235:genetics; D017077:Culture Media, Conditioned / Q000494:pharmacology; D003676:Deferoxamine / Q000494:pharmacology; D018450:Disease Progression; D016326:Extracellular Matrix Proteins / Q000096:biosynthesis / Q000235:genetics; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism*; D005355:Fibrosis; D005786:Gene Expression Regulation / Q000187:drug effects*; D006321:Heart / Q000187:drug effects*; D007501:Iron / Q000378:metabolism / Q000494:pharmacology*; D007502:Iron Chelating Agents / Q000494:pharmacology; D019190:Iron Overload / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D035925:Iron-Regulatory Proteins; D007506:Iron-Sulfur Proteins / Q000096:biosynthesis / Q000235:genetics; D008168:Lung; D008907:Mink; D009124:Muscle Proteins / Q000096:biosynthesis* / Q000235:genetics; D009206:Myocardium / Q000378:metabolism* / Q000473:pathology; D017395:Plasminogen Activator Inhibitor 1 / Q000096:biosynthesis / Q000235:genetics; D012333:RNA, Messenger / Q000096:biosynthesis; D016601:RNA-Binding Proteins / Q000096:biosynthesis / Q000235:genetics; D051381:Rats; D017207:Rats, Sprague-Dawley; D012045:Regulatory Sequences, Nucleic Acid; D016212:Transforming Growth Factor beta / Q000096:biosynthesis* / Q000235:genetics; D017211:Treatment Failure
chemical_list: D017077:Culture Media, Conditioned; D016326:Extracellular Matrix Proteins; D007502:Iron Chelating Agents; D035925:Iron-Regulatory Proteins; D007506:Iron-Sulfur Proteins; D009124:Muscle Proteins; D017395:Plasminogen Activator Inhibitor 1; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; D016212:Transforming Growth Factor beta; D003094:Collagen; D007501:Iron; D003676:Deferoxamine