Cotransplantation of Adipose-Derived Mesenchymal Stromal Cells and Endothelial Cells in a Modular Construct Drives Vascularization in SCID/bg Mice

Abstract

A modular approach to adipose tissue engineering was explored by embedding adipose-derived mesenchymal stromal cells (adMSC) in sub-mm-sized collagen rods or ''modules'' and coating with human microvascular endothelial cells (HMEC). After subcutaneous injection into a SCID/Bg mouse, HMEC on modules containing embedded adMSC appeared to detach from the modules to form vessels as early as day 3, as confirmed by the human EC-specific UEA-1 lectin stain, and these vessels persisted for up to 90 days. Vessel numbers decreased over 14 days, but vessel size increased suggesting a maturing of the vasculature. Vessel perfusion with the host was confirmed at 21 days by microCT. HMEC on modules without embedded adMSC remained attached to the module surface at day 3 and UEA-1 staining disappeared over 14 days suggesting cell death. It appeared that cotransplantation with adMSC had an anti-apoptotic and proangiogenic effect on HMEC. The early revascularization strategy may be successful in supporting adMSC viability and differentiation, as a preliminary study suggests progressive fat accumulation in the HMEC + adMSC implants: *60% of the implant area stained positive for Oil Red O by day 90. adMSC-embedded modules without HMEC surface coating did not show similar levels of Oil Red O staining. All implant volumes decreased over the time course of the experiment, yet HMEC + adMSC module implants were larger than adMSC-only implants at day 90. Collagen gel is mechanically weak and contracts in vivo making it unsuitable as a biomaterial for adipose tissue engineering where volume maintenance is critical. When combined with an appropriate biomaterial, the modular approach to adipose tissue engineering may represent a successful strategy to engineer soft tissue substitutes of clinical relevance.

Adipose Stromal Cells Differentiate Along a Smooth Muscle Lineage Pathway Upon Endothelial Cell Contact via Induction of Activin A

“…These vessels develop in several days after injection and stably integrate into host vasculature. 9,23,24 The formation of stable vessels is a complex process requiring finely orchestrated interactions between 2 cell types, EC and mural/pericyte cells, and the surrounding environment. Previously, to facilitate mechanistic analysis of EC-ASC interactions, we introduced an in vitro model of cocultivation of human EC and ASC in a system containing serum but no additional exogenous cytokines or extracellular matrix.…”

In Vivo Remodelling of Vascularizing Engineered Tissues

“…In the SCID/bg mouse, blood vessels did not form without the co-implantation of MSC, which become pericyte support cells and there was little ECM deposited as the implanted tissue remodeled. 12,22 However, in a immunosuppressed rat model, implantation of EC alone formed blood vessels which persisted for long periods of time but were leaky, and there was more granulation tissue that formed as the tissue remodeled. 15 The addition of MSC to the implanted tissue decreased the leakiness of the newly formed vessels.…”

“…21,33 Both top-down and bottom-up approaches have been exploited, using various combinations of cells, growth factors and biomaterials. We have focused on modular tissue engineering, 12,15,16,22 in which several thousand (for rodents) individual microtissues are injected in a space filling manner. In this method the EC form a network after implantation.…”

Application of Modular Therapy for Renoprotection in Experimental Chronic Kidney Disease

“…16 As a consequence of collagen's strong cell adhesive properties, the surface of collagen modules can be seeded with endothelial cells (ECs) to enhance vascularization. 17 Previous reports in rats 17,18 and SCID/bg mice 19 have demonstrated that this EC coverage leads to the formation of vessel-like structures which can integrate into the host's vascular system. This vasculature is expected not only to ensure the adequate oxygenation of the cells within the tissue construct but in this context to also facilitate the entry of the EOC-derived anti-fibrotic factors into the host's circulation.…”