Time-course for in vitro development of basement membrane, gap junctions, and repair by adult endothelial cells seeded on precoated ePTFE

Endothelium properties of a tissue-engineered blood vessel for small-diameter vascular reconstruction

PURPOSE

A tissue-engineered blood vessel (TEBV) produced in vitro by the self-assembly method was developed in our laboratory for the replacement of small-diameter blood vessels. The interior of this vessel is covered by an endothelium. The aim of the present study was to evaluate whether the endothelial layer would make a favorable contribution at the time of implantation of the TEBV by investigating in vitro the hemocompatible properties of the endothelial cells covering its interior.

METHODS

The secretion of the von Willebrand factor (vWF) and expression of thrombomodulin by the endothelium were assessed, and the adhesive molecules E-selectin and intercellular adhesion molecule-1 (ICAM-1) were quantified as a function of maturation time. To evaluate the functional response of the endothelium on injury, the cellular response to physiological stimulatory factors (thrombin and lipopolysaccharide [LPS]) was analyzed.

RESULTS

The endothelial cells formed a confluent monolayer displaying favorable hemocompatible properties (78% +/- 10% of cells expressing thrombomodulin with only 12 +/- 3 mU/10(6) cells of vWF secreted over a 2-hour period), which acquired their full expression after a culture period of 4 days. Moreover, pro-adhesive properties toward inflammatory cells were not observed. The cells were also able to respond to physiological-stimulating agents (thrombin and LPS) and demonstrated a statistically significant overexpression of the corresponding molecules under the conditions tested.

CONCLUSIONS

These results indicate that the endothelium of the tissue-engineered blood vessel produced by the self-assembly approach displays advantageous qualities with regard to the vessel's future implantation as a small-diameter vascular prosthesis.

Recombinant human laminin-10 (alpha5beta1gamma1). Production, purification, and migration-promoting activity on vascular endothelial cells

The laminin (LN) family of large heterotrimeric extracellular matrix glycoproteins has multiple functions: LNs take part in the regulation of processes such as cell migration, differentiation, and proliferation, in addition to contributing to the structure of basement membranes. LN-10, composed of alpha5, beta1, and gamma1 chains, is widely distributed in most basement membranes of both epithelia and endothelia. We determined the complete human cDNA sequence for the LN alpha5 chain and produced recombinant human LN-10 (rLN-10) in HEK293 cells by triple transfection of full-length cDNAs encoding the human LN alpha5, beta1, and gamma1 chains. The rLN-10 was purified using affinity chromatography and had an apparent molecular mass of approximately 800 kDa in SDS-PAGE and a native domain structure in rotary shadowing electron microscopy. By using function-blocking monoclonal antibodies, integrin alpha(3)beta(1) was found to be a major mediator of adhesion of HT-1080 and human saphenous vein endothelial cells. Human saphenous vein endothelial cells adhered more strongly to rLN-10 than to LN-1 and LN-8 and showed better migration on rLN-10, compared with several other matrices. Considering the cell adhesive and migration-promoting properties of rLN-10 on endothelial cells, this molecule could be useful in improving the biocompatibility and endothelialization of vascular grafts.

Effect of HUVEC on human osteoprogenitor cell differentiation needs heterotypic gap junction communication

Bone development and remodeling depend on complex interactions between bone-forming osteoblasts and other cells present within the bone microenvironment, particularly vascular endothelial cells that may be pivotal members of a complex interactive communication network in bone. Our aim was to investigate the interaction between human umbilical vein endothelial cells (HUVEC) and human bone marrow stromal cells (HBMSC). Cell differentiation analysis performed with different cell culture models revealed that alkaline phosphatase activity and type I collagen synthesis were increased only by the direct contact of HUVEC with HBMSC. This "juxtacrine signaling" could involve a number of different heterotypic connexions that require adhesion molecules or gap junctions. A dye coupling assay with Lucifer yellow demonstrated a functional coupling between HUVEC and HBMSC. Immunocytochemistry revealed that connexin43 (Cx43), a specific gap junction protein, is expressed not only in HBMSC but also in the endothelial cell network and that these two cell types can communicate via a gap junctional channel constituted at least by Cx43. Moreover, functional inhibition of the gap junction by 18alpha-glycyrrhetinic acid treatment or inhibition of Cx43 synthesis with oligodeoxyribonucleotide antisense decreased the effect of HUVEC cocultures on HBMSC differentiation. This stimulation could be mediated by the intercellular diffusion of signaling molecules that permeate the junctional channel.

In vitro endothelialization of bioprosthetic heart valves provides a cell monolayer with proliferative capacities and resistance to pulsatile flow

OBJECTIVES

Degeneration of bioprosthetic heart valves has been suggested to be at least partly an immunogenic reaction toward the xenogeneic tissue. An autologous endothelial lining has been proposed to overcome this problem. We examined in vitro endothelialization of such tissue and retention of endothelial cells after exposure to flow resembling the in vivo situation.

METHODS

Cultured human saphenous vein endothelial cells were used to in vitro endothelialize photo-oxidized bioprosthetic heart valves. The endothelialized valves were mounted in a specially designed flow device, creating a pulsatile flow through the valve. Maintenance of a confluent cell layer and deposition of basement membrane markers were determined with immunohistochemical labeling.

RESULTS

Labeling of the main components of the basement membrane, laminin and collagen type IV, was verified within 6 hours after in vitro endothelialization. Under static conditions, 4-mm wide denudations were completely re-endothelialized in 4 days, which was similar to the growth rate on gelatin-coated cell culture plastic, which served as a control material. After exposure of endothelialized valves to pulsatile flows for 24 hours (80 beats/min, 3.4 L/min), there were minimal cell losses from the bioprostheses. The cell layer adapted to the pulsatile flow, as verified by rearrangement of morphology and intracellular stress fibers.

CONCLUSIONS

This study shows the feasibility of in vitro endothelialization of photo-oxidized bioprosthetic heart valves. The cells are able to withstand a pulsatile flow in vitro, to develop basement membrane-like structures, and to re-endothelialize denuded areas. This technology may be used to enhance the performance of bioprosthetic heart valve prostheses.