Characterization of the Natural History of Extracellular Matrix Production in Tissue-Engineered Vascular Grafts during Neovessel Formation

Abstract

Background: The extracellular matrix (ECM) is a critical determinant of neovessel integrity. Materials and Methods: Thirty-six (polyglycolic acid + polycaprolactone and poly lactic acid) tissue-engineered vascular grafts seeded with syngeneic bone marrow mononuclear cells were implanted as inferior vena cava interposition grafts in C57BL/6 mice. Specimens were characterized using immunohistochemical staining and qPCR for representative ECM components in addition to matrix metalloproteinases (MMPs). Total collagen, elastin, and glycosaminoglycan (GAG) contents were determined. MMP activity was measured using zymography. Results: Collagen production on histology demonstrated an initial increase in type III at 1 week followed by type I production at 2 weeks and type IV at 4 weeks. Gene expression of both type I and type III peaked at 2 weeks, whereas type IV continued to increase over the 4-week period. Histology demonstrated fibrillin-1 deposition at 1 week followed by elastin production at 4 weeks. Elastin gene expression significantly increased at 4 weeks, whereas fibrillin-1 decreased at 4 weeks. GAG demonstrated abundant production at each time point on histology. Gene expression of decorin significantly increased at 4 weeks, whereas versican decreased over time. Biochemical analysis showed that total collagen production was greatest at 2 weeks, and there was a significant increase in elastin and GAG production at 4 weeks. Histological characterization of MMPs showed abundant production of MMP-2 at each time point, while MMP-9 decreased over the 4-week period. Gene expression of MMP-2 significantly increased at 4 weeks, whereas MMP-9 significantly decreased at 4 weeks. Conclusions: ECM production during neovessel formation is characterized by early ECM deposition followed by extensive remodeling.

Beyond Burst Pressure: Initial Evaluation of the Natural History of the Biaxial Mechanical Properties of Tissue-Engineered Vascular Grafts in the Venous Circulation Using a Murine Model

“…In particular, we quantified in vitro pressure-diameter responses of the TEVGs at their evolving in vivo axial stretches and found a progressive biaxial development and remodeling of neotissue that tended to yield a behavior similar to that of the native IVC by 24 weeks. When considered in combination with our earlier results, 23 early development of neotissue appears to parallel the rapid degradation of polymer (over the first 2 weeks) and to initiate in part because of a marked early increase in MMP-9 activity (presumably due to invading macrophages), followed by increased activity of MMP-2 at 6 weeks (presumably due to SMCs and myofibroblasts), as well as production of fibrillin-1, versican, and collagens III and I. As it can be seen in Figure 4, there was an associated decrease in stiffness (which is the inverse of compliance, cf.…”

“…We previously showed that the associated scaffold, consisting of a PGA-based copolymer, largely degrades within 4 weeks of implantation and is replaced during this period primarily by fibrillar collagens (types I and III), with some type IV collagen, elastin, and glycosaminoglycans. 23 Yet, total polymer degradation requires *26 weeks and there is continued neotissue formation and remodeling during this extended period. Earlier data collected at 1, 2, and 4 weeks revealed further that deposition of type III collagen preceded that of type I, not unlike in wound healing, and similarly that deposition of fibrillin-1 preceded that of elastin, not unlike that in development.…”

Comparison of the Biological Equivalence of Two Methods for Isolating Bone Marrow Mononuclear Cells for Fabricating Tissue-Engineered Vascular Grafts

“…MMP-2 is integral to the remodeling process in TEVG and peaks at 2 weeks after implantation in mice. 9 In the present study, MMP 2 was positive and similar between the two groups at 2 weeks after implantation (Fig. 5, right).…”

The Role of Myeloid Cell-Derived PDGF-B in Neotissue Formation in a Tissue-Engineered Vascular Graft

“…These data provide novel insight into one potential molecular mediator of neotissue formation in TEVGs. Degradation of the biodegradable polyglycolic acid/(P[CL/LA]) scaffold used in this study occurs by hydrolysis [18]. Monocytes and macrophages are among the earliest cell types to infiltrate the scaffold upon implantation, and are understood to be critical to the process of scaffold degradation and neotissue formation.…”