Abstract 2085: Tissue Engineered Vascular Graft Remodelling in a Growing Lamb Model: Expression of Matrix Metalloproteinases (MMPS) and Collagen Content in vitro and in vivo
Objectives: MMPs are a key family of proteases that contribute to matrix remodelling. In this study we aimed to assess whether expression and activity of MMP-2 and MMP-9 and collagen content are regulated in preimplant in vitro samples (under both static and biomimetic (dynamic) culture conditions) as compared to in vivo native and tissue engineered pulmonary artery grafts.
Methods: Autologous vascular derived smooth muscle cells (VSMCs) were seeded onto a biodegradable polymer (PGA/P4HB) and subjected to static as well as dynamic culture conditions. Following conditioning in a bioreactor, tissue engineered pulmonary artery grafts were implanted into young lambs (N=5) replacing their native pulmonary artery for 20, 50 and 80 weeks. Gelatin gel zymography to detect MMP-2 and -9 was performed and collagen content quantified.
Results: Latent (pro) and active MMP-2 and 9 were detected. Comparable levels of active MMP-9 and pro-MMP-2 were detected in VSMCs in static and dynamic culture. Interestingly, higher levels of active MMP-2 were detected in VSMCs in dynamic cultures. Expression of MMP-2 and -9 was minimal in native grafts but was increased in implanted grafts. Pro-MMP 9 expression is expressed as early as 20 weeks post implantation and persists up to 80 weeks post-implantation. The hydroxyproline content of in vitro samples under static versus dynamic conditions increased four-fold to 4.098mcg/mg dry weight. Hydroxyproline content in native tissue was 19.77 and 21.80 mcg/mg dried tissue weight compared to 29.03 and 42.30 mcg/mg in tissue engineered pulmonary artery, at 20 and 80 weeks post-implantation.
Conclusions: This study demonstrates that dynamic culture increases the activation of MMP-2. Similarly, activation of MMP-2 and -9 is increased in implanted grafts as well as expression of pro-MMP-9. This suggests that these MMPs upregulated by the flow conditions may contribute to increased matrix remodelling in the graft and correlate with the increased collagen content of dynamically stressed tissue engineered samples both in vitro and in vivo.