Study On The Transcriptomics Of The Early Vascular Remodeling Of Vein Grafts In Rabbit Model

Background: Coronary artery bypass grafting is employed for the treatment of multiple-vessel lesions. Studies have shown that continued maladaptive remodeling expedites atherosclerosis and that excessive remodeling leads to graft restenosis. However, few studies have focused on the target genes and special regulatory pathways involved during early remodeling of transplanted veins.Methods: We chose 42 New Zealand white rabbits randomly to create models of vein-graft restenosis. At 1, 3, 7, 14, 28 and 90 days after surgery, we removed bypassed grafts and placed them in groups named T1, T2, T3, T4, T5 and T6, respectively. Group T0 denoted the control group(in which sham surgery was carried out). After killing, we analyzed vessel thickness, electron microscope data, TUNEL staining, and expression of the proliferation-associated gene proliferating cell nuclear antigen(PCNA). We chose specific time-points of gene expression, and then observed changes in mechanistic target of rapamycin(mTOR) signaling.Results: The early stage of vein grafting(1–3 days after surgery) led to apoptosis and degradation of the extracellular matrix. Seven days after surgery, cells began to proliferate, the composition of collagen fiber increased, and the vascular wall became thickened. Electron microscopy and TUNEL analysis showed that apoptosis is the most obvious in T1. Western blot and immunohistochemistry showed that T3 is the high peak of cell proliferation. Therefore, the peak of apoptosis(first days after operation) and the peak of PCNA proliferation(seventh days after operation) were studied. We found that the two complexes in the mTOR signaling pathway had different changes in their function when apoptosis changes to cell proliferation. RICTOR expression in mTOR complex 2(mTORC2) and that of its downstream substrate protein kinase C was enhanced in the early stage after grafting(T1 and T3), and was higher in T1. mTORC1 was stimulated by several environmental aspects and growth factors, so its upstream gene regulation decreased in T1 and increased in T3. Its downstream genes e IF4 b and 4E-BP showed similar changes. 4E-BP expression in T3 was lower than that in T0, but e IF4 e expression was high. At this time, expression of e IF4 e and e IF4 b increased, and led to an increase in protein composition.Conclusions: After transplantation(when apoptosis changes to cell proliferation), the two complexes in the mTOR signaling pathway had different changes in their function. mTORC1 function and its upstream and downstream genes were inhibited on the first day after grafting, but mTORC2 function was enhanced. One week after surgery, mTORC2 was still overexpressed when mTORC1 function had recovered and become enhanced. Hence, excessive expression of mTORC2 may be an important cause of graft restenosis.