Response to Angiotensin II–Induced Proliferation of Neonatal and Adult Rat Cardiac Fibroblasts
In response to Dr Lijnen’s letter,1 it is indeed the case that several reports focused on the proliferative effects of angiotensin (Ang) II on isolated adult rat cardiac fibroblasts vary widely in the magnitude of effect. We have studied the proliferative effects of Ang II on these cells for the past 5 years, finding that Ang II has a modest but significant effect on proliferation that routinely reaches a 50% to 70% increase over the vehicle-treated controls. Other studies have demonstrated more robust responses to Ang II, whereas others have reported less. Certainly the confluence of the cultures along with the serum starvation period have a significant impact on the overall 3H-thymidine incorporation. As stated in our recent article, we plate the adult cardiac fibroblasts at 40% to 50% confluence to ensure that the cells have ample room to proliferate (free of contact inhibition), and we routinely serum-starve the cells for 18 to 24 hours before agonist stimulation to help synchronize them in the cell cycle. Furthermore, we only use early passage fibroblasts (passage 2 or 3), because we have determined that the fibroblasts, by passage 4 or 5, will differentiate in culture to the myofibroblast phenotype.2 Once differentiated, the growth of the myofibroblasts is significantly attenuated compared to the undifferentiated fibroblasts. Each of the above tissue culture parameters, which differ from laboratory to laboratory, likely contributes to the varied results relating to Ang II–induced proliferation of adult cardiac fibroblasts.
Sources of Funding
Funding provided by the American Heart Association-B61A (016012B) and Ohio Board of Regents Research Challenge (34177).
Lijnen P. Angiotensin II–induced proliferation of neonatal and adult rat cardiac fibroblasts. Hypertension. 2008; 51: e50.
Swaney J, Naugle JE, Olson ER, Meszaros JG, Roth DM, Insel PA. Inhibition of cardiac myofibroblast formation and collagen synthesis by activation and overexpression of adenylyl cyclase. Proc Natl Acad Sci U S A. 2005; 102: 437–442.