Dynamic Changes of Smooth Muscle and Endothelial Markers in the Early Healing Process of Dacron Vascular Grafts in the Dog, Using RT-PCR

Abstract

Previous studies of neointima formation on Dacron vascular grafts mainly focused on the late stages using immunohistochemistry staining for von Willebrand factor (vWF) and smooth muscle (SM) α-actin. However, it is impossible to use immunohistochemistry to study the early events of neointima formation, because graft samples lack sufficient cellular material. Therefore, we used reverse transcriptase-polymerase chain reaction (RT-PCR) to demonstrate dynamic changes of SM and endothelial markers during the early stages of neointima formation. Preclotted Dacron grafts were implanted in the descending thoracic aorta of 14 mongrel dogs. Specimens were retrieved at 1–4 weeks. Total RNAs were extracted from mid-portion of graft flow surfaces, and RT-PCR for vWF, SM myosin heavy chain (MHC), and SM α-actin were performed and expressed as a ratio to the ribosome s17 signal. SM MHC and vWF mRNA expression was low at 1–2 weeks but elevated at 3–4 weeks (P < 0.05). However, SM α-actin mRNA levels were expressed consistently throughout the study period. At 3–4 weeks, vWF mRNA expression was inversely correlated to thrombus formation on the graft flow surface. Increased expressions of SM MHC and vWF mRNA corresponded to the formation of neointima and an endothelial layer at the later stages. However, SM α-actin mRNA expression did not vary during the healing process. The application of RT-PCR should permit further studies of gene regulation in the early vascular graft healing process in vivo. This model can also be used to study the molecular events that are involved in SM cell differentiation.