Neointimal Hyperplasia after Carotid Transection and Anastomosis Surgery is Associated with Degradation of Decorin and Platelet Derived Growth Factor Signaling.

Objective: Intimal hyperplasia (IH) is the expansion of the vascular intimal region after intervention, which can lead to stenosis and eventual failure of vascular grafts or interventional procedures such as angioplasty or stent placement. Our goals were to investigate the development of IH in a rabbit open surgical model and to evaluate the associated pathophysiological processes involving decorin and the platelet derived growth factor-BB / platelet derived growth factor receptor-β / mitogen activated protein kinase (PDGF/PDGFR-β/MAPK) pathway.
Methods: We conducted carotid transection and primary anastomosis on five New Zealand White rabbits to induce IH and examined the associated pathophysiological changes. Tissue was obtained for histological and protein analysis on post-operative day 21 using the contralateral vessel as a control. Intimal medial thickness (IMT) was calculated to measure IH and compared with the unoperated side. Western blot analysis was performed on tissue lysates to determine the expression of decorin core protein, PDGF-BB, PDGFR-β, and phosphorylated-MAPK (ph-MAPK). Immunofluorescence microscopy was used to assess tissue distribution of matrix metalloproteinase-2 (MMP-2) and phosphorylated-PDGFR-β (ph-PDGFR-β).
Results: Bilateral carotid arteries were harvested on postoperative day 21. We compared the IMT in operated with unoperated specimens. IMT was significantly elevated in operated arteries vs. unoperated arteries in all 5 animals (148.6 μm +/- 9.09 vs. 103.40 μm +/- 7.08; 135.2 μm +/- 8.30 vs. 92.40 μm +/- 2.35; 203.1 μm +/- 30.23 vs.104.00 μm +/- 4.52; 236.2 μm +/- 27.22 vs. 141.50 μm +/- 9.95; 226.9 μm +/- 11.12 vs. 98.8 μm +/- 3.78). Western blot analysis revealed degradation of decorin protein in the operated tissue, including loss of a 50 kDa band and the appearance of a cleaved fragment at 10 kDa. Decorin and MMP-2 were observed, via immunofluorescence microscopy, in the neointima of the operated vessels. Western blot analysis also revealed increased PDGF-BB, PDGFR-β, and ph-MAPK levels in operated tissue. Immunofluorescent staining for ph-PDGFR-β primarily localized to the neointima, indicating increased signaling through PDGF in this region.
Conclusion: Carotid transection and primary reanastomosis in rabbits induced IH that was associated with MMP-2 activation, degradation of decorin, and activation of the PDGF/PDGFR-β /MAPK pathway. The findings in this study should lead to further mechanistic evaluation of these pathways to better understand the potential to modify the intimal hyperplastic response to surgery.