Graft smooth muscle cells specifically synthesize increased collagen

Anastomotic intimal hyperplasia is characterized by smooth muscle cell (SMC) proliferation, but its final form is predominantly extracellular matrix. The purpose of this study was to compare collagen synthesis from graft SMC to that from adjacent native arterial SMC.

Thoracoabdominal bypass grafts were excised 20 weeks after implantation into canine models. SMC harvested from six anastomotic graft segments and adjacent native aorta were passaged twice, grown to near-confluence, and then assayed for collagen synthesis and total protein synthesis. In four of these sites type I alpha-1 procollagen mRNA levels were measured and normalized to glyceraldehyde-3-phosphate dehydrogenase. To control for increases in collagen synthesis associated with proliferation, SMC were plated at equal densities and tritium-thymidine incorporation and DNA concentration were determined. Data (mean +/- SE) were analyzed with two-factor ANOVA for repeated measures and paired Student t test and were considered significant if p < 0.05.

There was no difference in thymidine incorporation and total protein synthesis between groups, but collagen synthesis (graft: 52.9 +/- 1.6 disintegrations per minute/ng DNA versus native: 42.6 +/- 1.9 dpm/ng DNA; p = 0.03) and collagen synthesis as a percentage of total protein synthesis (graft: 7.16% +/- 0.11% versus native: 5.8% +/- 0.14%; p = 0.001) increased significantly in graft SMC as compared to native SMC. Type I alpha-1 procollagen mRNA levels were higher in graft SMC, but this difference was not significant.

Graft SMC specifically produce more collagen than SMC from adjacent native artery. This change does not simply reflect increases in either total protein synthesis or proliferation and may, in part, be due to increased collagen gene expression.