STRAIN ACTIVATION OF BOVINE AORTIC SMOOTH-MUSCLE CELL-PROLIFERATION AND ALIGNMENT - STUDY OF STRAIN DEPENDENCY AND THE ROLE OF PROTEIN-KINASE-A AND PROTEIN-KINASE-C SIGNALING PATHWAYS

Smooth muscle cell BMC) phenotype can be altered by physical forces as demonstrated by cyclic strain-induced changes in proliferation, orien tation, and secretion of macromolecules. However, the magnitude of str ain required and the intracellular coupling pathways remain ill define d. To examine the strain requirements for SMC proliferation, we select ively seeded bovine aortic SMC either on the center or periphery of si lastic membranes which were deformed with 150 mm Hg vacuum (0-7% cente r; 7-24% periphery). SMC located in either the center or peripheral re gions showed enhanced proliferation compared to cells grown under the absence of cyclic strain. Moreover, SMC located in the center region d emonstrated significantly (P < 0.005) greater proliferation as compare d to those in the periphery. In contrast, SMC exposed to high strain ( 7-24%) demonstrated alignment perpendicular to the strain gradient, wh ereas SMC in the center (0-7%) remained aligned randomly. To determine the mechanisms of these phenomena, we examined the effect of cyclic s train on bovine aortic SMC signaling pathways. We observed strain-indu ced stimulation of the cyclic AMP pathway including adenylate cyclase activity and cyclic AMP accumulation. In addition, exposure of SMC to cyclic strain caused a significant increase in protein kinase C (PKC) activity and enzyme translocation from the cytosol to a particulate fr action. Further study was conducted to examine the effect of strain ma gnitude on signaling, particularly protein kinase A !PKA) activity as well as cAMP response element (CRE) binding protein levels. We observe d significantly (P < 0.05) greater PKA activity and CRE binding protei n levels in SMC located in the center as compared to the peripheral re gion. However, inhibition of PKA (with 10 mu M Rp-cAMP) or PKC (with 5 -20 ng/ml staurosporine) failed to alter either the strain-induced inc rease in SMC proliferation or alignment. These data characterize the s train determinants for activation of SMC proliferation and alignment. Although strain activated both the AC/cAMP/PKA and the PKC pathways in SMC, singular inhibition of PKA and PKC failed to prevent strain-indu ced alignment and proliferation, suggesting either their lack of invol vement or the multifactorial nature of these responses. (C) 1997 Wiley -Liss, Inc.