title: Strain activation of bovine aortic smooth muscle cell proliferation and alignment: study of strain dependency and the role of protein kinase A and C signaling pathways.
abstract: Smooth muscle cell (SMC) phenotype can be altered by physical forces as demonstrated by cyclic strain-induced changes in proliferation, orientation, and secretion of macromolecules. However, the magnitude of strain required and the intracellular coupling pathways remain ill defined. To examine the strain requirements for SMC proliferation, we selectively seeded bovine aortic SMC either on the center or periphery of silastic membranes which were deformed with 150 mm Hg vacuum (0-7% center; 7-24% periphery). SMC located in either the center or peripheral regions showed enhanced proliferation compared to cells grown under the absence of cyclic strain. Moreover, SMC located in the center region demonstrated significantly (P < 0.005) greater proliferation as compared to those in the periphery. In contrast, SMC exposed to high strain (7-24%) demonstrated alignment perpendicular to the strain gradient, whereas SMC in the center (0-7%) remained aligned randomly. To determine the mechanisms of these phenomena, we examined the effect of cyclic strain on bovine aortic SMC signaling pathways. We observed strain-induced 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 fraction. Further study was conducted to examine the effect of strain magnitude on signaling, particularly protein kinase A (PKA) activity as well as cAMP response element (CRE) binding protein levels. We observed significantly (P < 0.05) greater PKA activity and CRE binding protein levels in SMC located in the center as compared to the peripheral region. However, inhibition of PKA (with 10 microM Rp-cAMP) or PKC (with 5-20 ng/ml staurosporine) failed to alter either the strain-induced increase in SMC proliferation or alignment. These data characterize the strain 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-induced alignment and proliferation, suggesting either their lack of involvement or the multifactorial nature of these responses.
authors.affiliation: Department of Surgery, Yale University School of Medicine, New Haven, Connecticut 06510, USA.
authors.forename: I
authors.initials: I
authors.lastname: Mills
authors.forename: C R
authors.initials: CR
authors.lastname: Cohen
authors.forename: K
authors.initials: K
authors.lastname: Kamal
authors.forename: G
authors.initials: G
authors.lastname: Li
authors.forename: T
authors.initials: T
authors.lastname: Shin
authors.forename: W
authors.initials: W
authors.lastname: Du
authors.forename: B E
authors.initials: BE
authors.lastname: Sumpio
mesh_terms: D051698:Activating Transcription Factor 2; D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D001011:Aorta / Q000166:cytology; D002417:Cattle; D002455:Cell Division / Q000502:physiology; D002478:Cells, Cultured / Q000201:enzymology; D000242:Cyclic AMP / Q000378:metabolism; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000502:physiology*; D004730:Endothelium, Vascular / Q000166:cytology / Q000201:enzymology; D016350:Leucine Zippers / Q000502:physiology; D009131:Muscle, Smooth, Vascular / Q000737:chemistry / Q000166:cytology* / Q000201:enzymology; D011493:Protein Kinase C / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology*; D013314:Stress, Mechanical; D014157:Transcription Factors / Q000378:metabolism
chemical_list: D051698:Activating Transcription Factor 2; D017362:Cyclic AMP Response Element-Binding Protein; D014157:Transcription Factors; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D000262:Adenylyl Cyclases