Connective tissue growth factor expression and induction by transforming growth factor-beta is abrogated by simvastatin via a Rho signaling mechanism.
Connective tissue growth factor (CTGF), a potent profibrotic mediator, acts downstream and in concert with transforming growth factor (TGF)-beta to drive fibrogenesis. Significant upregulation of CTGF has been reported in fibrogenic diseases, including idiopathic pulmonary fibrosis (IPF), and is partly responsible for associated excessive fibroblast proliferation and extracellular matrix deposition, but no effective therapy exists for averting such fibrogeneic events. Simvastatin has reported putative antifibrotic actions in renal fibroblasts; this study explores such actions on human IPF-derived and normal lung fibroblasts and examines associated driving mechanisms. Simvastatin reduces basal CTGF gene and protein expression in all fibroblast lines, overriding TGF-beta induction through inhibition of the cholesterol synthesis pathway. Signaling pathways driving simvastatin's effects on CTGF/TGF-beta interaction were evaluated using transient reporter transfection of a CTGF promoter construct. Inhibition of CTGF promoter activity by simvastatin was most marked at 10 muM concentration, reducing activity by 76.2 and 51.8% over TGF-beta-stimulated cultures in IPF and normal fibroblasts, respectively. We also show that geranylgeranylpyrophosphate (GGPP), but not farnesylpyrophosphate, induces CTGF promoter activity following simvastatin inhibition by 55.3 and 31.1% over GGPP-negative cultures in IMR90 and IPF-derived fibroblasts, respectively, implicating small GTPase Rho involvement rather than Ras in these effects. Indeed, the specific Rho inhibitor C3 exotoxin significantly (P < 0.05) suppressed TGF-beta-induced CTGF promoter activity in transfected lung fibroblasts, a finding further supported by transfection of dominant-negative and constitutively active RhoA constructs, thus demonstrating that simvastatin through a Rho signaling mechanism in lung fibroblasts can modulate CTGF expression and interaction with TGF-beta.
Watts
Keira L
KL
Lung Research, Institute of Science and Technology in Medicine, University Hospital of North Staffordshire/Keele University, Stoke on Trent, United Kingdom. keira_watts@yahoo.co.uk
Spiteri
Monica A
MA
D002460:Cell Line; D055513:Connective Tissue Growth Factor; D005347:Fibroblasts / Q000187:drug effects / Q000502:physiology; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D017874:Immediate-Early Proteins / Q000235:genetics*; D018969:Insulin-Like Growth Factor Binding Proteins / Q000235:genetics; D036341:Intercellular Signaling Peptides and Proteins / Q000235:genetics*; D008168:Lung / Q000187:drug effects / Q000502:physiology*; D011994:Recombinant Proteins / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D019821:Simvastatin / Q000494:pharmacology*; D016212:Transforming Growth Factor beta / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D020741:rho GTP-Binding Proteins / Q000502:physiology*
C526317:CCN2 protein, human; D017874:Immediate-Early Proteins; D018969:Insulin-Like Growth Factor Binding Proteins; D036341:Intercellular Signaling Peptides and Proteins; D011994:Recombinant Proteins; D016212:Transforming Growth Factor beta; D055513:Connective Tissue Growth Factor; D019821:Simvastatin; D020741:rho GTP-Binding Proteins