title: Stem cell factor and c-kit are expressed by and may affect vascular SMCs through an autocrine pathway.
abstract: BACKGROUND
  Stem cell factor (SCF) is a membrane-bound and soluble growth factor that activates the c-kit tyrosine kinase receptor. Given the similarities between c-kit and platelet-derived growth factor (PDGF) receptors, we hypothesized that similar to PDGF, SCF/c-kit signaling may play a role in smooth muscle cell (SMC) function and thus the development of intimal hyperplasia.
  
  
  METHODS
  Human saphenous vein SMCs were harvested from veins procured at the time of bypass grafting. Carotid arteries from rats that were balloon injured (n = 12) at variable time points were compared to sham-operated controls (n = 3). Expression of SCF and c-kit was measured by immunohistochemistry (IHC) and Western blotting.
  
  
  RESULTS
  Western blotting revealed that human SMCs express membrane-bound SCF. In separate experiments, we found that this growth factor undergoes proteolytic cleavage to its soluble form following exposure to matrix metalloproteinase-9 (MMP-9), a ubiquitous MMP released at the time of arterial injury. We next evaluated in human SMCs, expression of the SCF receptor, c-kit. Western blotting of human SMC lysates revealed minor but consistent expression of c-kit. IHC demonstrated c-kit expression to be localized to the media. To determine if c-kit is up-regulated during the development of intimal hyperplasia, we evaluated expression of this receptor in a rat carotid balloon injury model. Quantification of IHC staining on injured vessels revealed that c-kit expression within the media was significantly increased at 3, 7, 14, and 28 days following injury (28.1, 30.8, 16, and 10.4% increase over sham controls, respectively, P < 0.05). Furthermore, c-kit expression was prominent within the neointima and maximal at 7 days (53.4 +/- 7.8% of area c-kit positive).
  
  
  CONCLUSIONS
  Human vascular SMCs express the growth factor SCF and its receptor, c-kit. SCF is released from its membrane-bound form via MMP-9. This finding and the dramatic increase in c-kit expression observed in the rat carotid artery after balloon injury suggests SCF/c-kit signaling may affect SMC function via an autocrine pathway.
authors.affiliation: Department of Surgery, Division of Vascular Surgery, Weill Medical College of Cornell University, 525 East 68th Street, Payson 707, New York, NY 1002, USA. kckent@med.cornell.edu
authors.forename: Scott T
authors.initials: ST
authors.lastname: Hollenbeck
authors.forename: Kenji
authors.initials: K
authors.lastname: Sakakibara
authors.forename: Peter L
authors.initials: PL
authors.lastname: Faries
authors.forename: Berhane
authors.initials: B
authors.lastname: Workhu
authors.forename: Bo
authors.initials: B
authors.lastname: Liu
authors.forename: K Craig
authors.initials: KC
authors.lastname: Kent
mesh_terms: D000818:Animals; D019898:Autocrine Communication; D020212:Carotid Artery Injuries / Q000378:metabolism* / Q000473:pathology; D002478:Cells, Cultured; D006801:Humans; D006965:Hyperplasia; D008297:Male; D020780:Matrix Metalloproteinase 9 / Q000494:pharmacology; D009131:Muscle, Smooth, Vascular / Q000166:cytology*; D032389:Myocytes, Smooth Muscle / Q000187:drug effects / Q000378:metabolism*; D019009:Proto-Oncogene Proteins c-kit / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012501:Saphenous Vein; D019089:Stem Cell Factor / Q000378:metabolism*; D017539:Tunica Intima / Q000378:metabolism / Q000473:pathology
chemical_list: D019089:Stem Cell Factor; D019009:Proto-Oncogene Proteins c-kit; D020780:Matrix Metalloproteinase 9