Comparison of ANG II with other growth factors on Egr-1 and matrix gene expression in cardiac fibroblasts.
The purpose of the present investigation was to compare the effects of angiotensin II (ANG II) other growth factors implicated to play a role in ventricular hypertrophy on cardiac fibroblast changes associated with cardiac remodeling. These changes included induction of early growth response (Egr-1) gene and increases in message levels of extracellular matrix proteins. ANG II treatment (10(-10)-10(-6) M) of rat cardiac fibroblasts induced 1) Egr-1 and 2) a fourfold (P < 0.02) increase in fibronectin and a twofold (P = 0.05) increase in laminin mRNA levels but no increases in that of collagens I, III, or IV at 24-48 h, and 3) a decrease in AT1-receptor mRNA levels to 26% (P < 0.001) of basal at 4-6 h. These effects were all inhibited by the AT1-receptor blocker, losartan, but not AT2-receptor blockers. Immunostaining of cultured cells with antibody against rat fibronectin demonstrated positive staining of cells in serum-free medium; staining was more intense in cells treated with ANG II (10(-6) M, 48 h). Fluorescent-activated cell sorting using an antibody against rat AT1 receptor demonstrated a receptor signal in cells maintained in serum-free medium; however, the receptor signal was not detectable in ANG II-treated cells. Serum and epidermal growth factor (EGF) also induced Egr-1, but norepinephrine (NE) and endothelin (ET) had no effect. Serum increased fibronectin mRNA levels by twofold (P < 0.05). EGF, NE, and ET had no effect on matrix gene expression. Serum, EGF, and NE also transiently downregulated AT1-receptor mRNA levels at 4-6 h of treatment. These results demonstrate that 1) ANG II both induces protooncogene expression and enhances fibronectin mRNA levels in cultured cardiac fibroblasts, whereas EGF only induces Egr-1, and NE and ET have no effects on either function; 2) ANG II effects are primarily mediated by the AT1 receptor; and 3) growth factors can regulate AT1-receptor mRNA levels. Thus ANG II, relative to NE, ET, and EGF, appears to play a prominent and direct role in fibroblast changes associated with cardiac hypertrophy.
Iwami
K
K
Department of Medicine, University of Southern California School of Medicine, Los Angeles 90033, USA.
Ashizawa
N
N
Do
Y S
YS
Graf
K
K
Hsueh
W A
WA
D000803:Angiotensin I / Q000378:metabolism; D000804:Angiotensin II / Q000494:pharmacology*; D000818:Animals; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000235:genetics*; D051766:Early Growth Response Protein 1; D016326:Extracellular Matrix Proteins / Q000235:genetics* / Q000378:metabolism; D005347:Fibroblasts / Q000502:physiology; D015870:Gene Expression / Q000187:drug effects*; D006133:Growth Substances / Q000494:pharmacology*; D006321:Heart / Q000502:physiology*; D017874:Immediate-Early Proteins; D009206:Myocardium / Q000166:cytology; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D011945:Receptors, Angiotensin / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics*
D004268:DNA-Binding Proteins; D051766:Early Growth Response Protein 1; C486110:Egr1 protein, rat; D016326:Extracellular Matrix Proteins; D006133:Growth Substances; D017874:Immediate-Early Proteins; D012333:RNA, Messenger; D011945:Receptors, Angiotensin; D014157:Transcription Factors; D000804:Angiotensin II; D000803:Angiotensin I