Bone Marrow-Derived Mesenchymal Stromal Cells Enhance Chimeric Vessel Development Driven by Endothelial Cell-Coated Microtissues

Abstract

Adding bone marrow-derived mesenchymal stromal cells (bmMSCs) to endothelialized collagen gel modules resulted in mature vessel formation, presumably caused in part by the observed display of pericyte-like behavior for the transplanted GFP(+) bmMSCs. A previous study determined that rat aortic endothelial cells (RAECs) delivered on the surface of small (∼0.8 mm long×0.5 mm diameter) collagen gel cylinders (microtissues, modular tissue engineering) formed vessels after transplantation into immunosuppressed Sprague-Dawley (SD) rats. Although the RAECs formed vessels in this allogeneic transplant model, there was a robust inflammatory response and the vessels that formed were leaky as shown by microcomputed tomography (microCT) perfusion studies. In vitro assays showed that SD rat bmMSCs embedded into the collagen gel modules increased the extent of EC proliferation and enhanced EC sprouting. In vivo, although vessel number was not affected, the new vessels formed by the bmMSCs and RAECs were more stable and leaked less in the microCT perfusion analysis than vessels formed by implanted RAECs alone. Addition of the bmMSCs also decreased the total number of CD68(+) macrophages that infiltrated the implant and changed the distribution of CD163(+) (M2) macrophages so that they were found within the newly developed vascularized tissue. Most interestingly, the bmMSCs became smooth muscle actin positive and migrated to surround the EC layer of the vessel, which is the location typical of pericytes. The combination of these two effects was presumed to be the cause of improved vascularity when bmMSCs were embedded in the EC-coated modules. Further exploration of these observations is warranted to exploit modular tissue engineering as a means of forming large vascularized functional tissues using microtissue components.

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

“…The mice were euthanized at various time points (3,7,14,21,30,60, and 90 days) and the implants excised. The dimensions of each implant were carefully measured with calipers and the volume estimated using the volume of an ellipsoid.…”

“…We have used bmMSC to enhance the chimeric vasculature produced when rat aortic endothelial cells were transplanted in an allogenic rat model with immunosuppression. 21 Without the bmMSC, the chimeric vasculature containing both host and donor cells was immature at 21 days and was well (although likely not completely) formed at 60 days; with bmMSC, a mature vasculature was produced by 21 days. 21 We also transplanted Human Umbilical Vein Endothelial Cells (HUVEC) on modules after subcutaneous transplant into severely combined immunodeficient mice (SCID/bg).…”

“…21 Without the bmMSC, the chimeric vasculature containing both host and donor cells was immature at 21 days and was well (although likely not completely) formed at 60 days; with bmMSC, a mature vasculature was produced by 21 days. 21 We also transplanted Human Umbilical Vein Endothelial Cells (HUVEC) on modules after subcutaneous transplant into severely combined immunodeficient mice (SCID/bg). Like others, 22,23 HUVEC rapidly underwent apoptosis and no HUVEC-derived vessels formed.…”

Toward anIn VitroVasculature: Differentiation of Mesenchymal Stromal Cells Within an Endothelial Cell-Seeded Modular Construct in a Microfluidic Flow Chamber

“…11 Embedding MSC within modules accelerated vessel formation and maturation in vivo, with the MSC appearing to differentiate into smooth muscle actin (SMA)-positive pericyte-like cells that integrated with the new vasculature. 12 The objectives of this article were to assess the remodeling of the MSC + EC modular constructs in vitro over 21 days subject to flow in a microfluidic chamber. 2 Others have used similar microfluidic systems to combine threedimensional co-cultures and flow (reviewed in 13 ).…”

In Vivo Remodelling of Vascularizing Engineered Tissues

“…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.…”