Background: One of the main criteria of successful application of tissue engineered vascular grafts based on decellularized extracellular matrix (dECM) is adequate and healthy tissue remodeling without triggering an immune response in vivo. As already known macrophages play a crucial role on cardiovascular implants integration, remodeling and rejection. We have been observed macrophages arrive at the biomaterials in the very early-stage after implantation and set up a microenvironment for the subsequent tissue regeneration. The aim of this investigation is to characterize the early recellularization of dECM in vivo, to elucidate on the early innate immune response.
Method:
U-shaped rat aortic conduits (RACs) were isolated from adult male Sprague-Dawley rats and decellularized over 9 days with detergent-based decellularization protocol. Afterwards the RACs were implanted into Sprague-Dawley rats in an abdominal aorta position and harvested after 48 hours. The obtained samples were embedded and frozen in liquid nitrogen. To estimate the early cell repopulation of decellularized extracellular matrix of RACs immunofluorescence stainings with specific antibodies for macrophages, endothelial cells, mesenchymal and smooth muscle cells were used. For negative control native aorta and decellularized RACs before implantation were used.
Results: DECM after 48 hours in vivo incubation demonstrated infiltration with immune cells (CD45+) located in both sides of the RACs. On luminal side, the base of immune cell repopulation is CD68+ macrophage. On top of the CD68+ macrophages, an endothelial layer is formed together with the appearance of mesenchymal cells. Smooth muscle cells are not found on the RACs till 48 hours.
Conclusion: Decellularized extracellular matrix of RACs induces the early innate immune response via macrophages and other immune competent cells in vivo. Repopulation with endothelial and mesenchymal cells is the next step of vascular implants remodeling. Further investigations are needed to define subsequence of recellularization and determine the balance between “healthy” and “pathological” innate immune response for tissue engineered grafts. We assume that macrophages arrive first to the dECM and attract other cells for recellularization.
