Changes in gene expression with iron loading and chelation in cardiac myocytes and non-myocytic fibroblasts

Iron overload is associated with long-term cardiac iron accumulation and ti ssue changes such as fibrosis. To determine short-term iron-dependent chang es in expression of genes associated with iron homeostasis and fibrosis we measured mRNA on Northern blots prepared from cultured rat neonatal cardiom yocytes and non-myocytes (fibroblasts) as a function of iron loading and ch elation. Transferrin receptor mRNA was reduced in myocytes exposed to vario us concentrations of iron for 3 days and this decline was associated with a 63% decline in iron-response element (IRE) binding of iron regulatory prot ein-1, indicating that myocytes utilize IRE-dependent mechanisms to modulat e gene expression. In myocytes iron caused a dose-dependent decline in mRNA s coding for transforming growth factor-beta(1) (TGF-beta(1)), biglycan, an d collagen type I while plasminogen activator inhibitor-1 mRNA was unaffect ed 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 fo r 1 day did not have any significant effect on any of these genes. Parallel changes in gene expression were exhibited by non-myocytes (fibroblasts), w here chelation also decreased TGF-beta, mRNA and activity, and mRNA for col lagen type I and biglycan, and collagen synthesis. In addition to these cha nges in transcripts associated with matrix formation the mRNA of the metabo lic enzyme glyceraldehyde-3-phosphate dehydrogenase was unaffected by iron loading but doubled in both cell types upon treatment with deferoxamine. Th ese findings suggest that in both cardiac myocytes and non-myocyte fibrobla sts gene expression is coupled to intracellular iron pools by gene-specific and IRE-dependent and idependent mechanisms. This linkage may influence ma trix deposition, a significant component of cardiac injury. (C) 2000 Academ ic Press.