Abstract
This study investigated whether gene expression profiles of myofibroblasts derived from infarcted myocardium differ from normal cardiac fibroblasts. We compared the expression of cytoskeletal proteins in cultured ovine cardiac fibroblasts derived from infarcted (ID) and noninfarcted ovine myocardium (NID) and the levels of expression of the natriuretic peptide receptors (NPR)-A and NPR-B in response to treatment with transforming growth factor (TGF)-beta 1 and/or platelet-derived growth factor ( PDGF). Transformation of cultured cardiac fibroblasts to myofibroblasts, as indicated by alpha-smooth muscle actin and vimentin expression, was independent of the presence of TGF-beta 1, PDGF, or cell origin. ID fibroblasts had higher basal levels than NID fibroblasts of NPR-A (ID: 58.0 +/- 32.2 arbitrary density units, NID: undetectable), NPR-B (ID: 780 +/- 155, NID: 330 +/- 38 arbitrary density units) and collagen I (ID: 17.2 +/- 0.5, NID: 10.5 +/- 1.7 pg mRNA/mu g total RNA, P < 0.05) but lower levels of alpha-SMa expression (ID: 50.2 +/- 7.9, NID: 76.9 +/- 3.2 fluorescence units, P < 0.05). NPR-A mRNA in ID fibroblasts showed a rapid fourfold increase in response to TGF-beta 1 and/or PDGF at 4 and 2 h, respectively, followed by a profound decline; in NID cells, NPR-A mRNA was undetectable. In ID fibroblasts, cytokines reduced NPR-B mRNA below control levels; in NID fibroblasts, TGF-beta 1 and PDGF elicited prompt increments in expression: a fourfold increase with TGF-beta 1 at 8 h and a twofold increase with PDGF at 4 h (P < 0.05). In summary, transformation of cardiac fibroblasts to myofibroblasts in culture is independent of cytokine treatment. Moreover, whether the cultured cardiac fibroblasts are from infarct tissue is a major determinant of NPR expression levels and cytokine responses, even after four to five passages.