Urinary bladder tissue engineering using natural scaffolds in a porcine model: role of Toll-like receptors and impact of biomimetic molecules.

Natural scaffolds have been shown to induce T helper 2 (TH2)-specific immune responses in host tissues; however, the precise mechanisms that underlie this immune response are unknown. Using a porcine animal model, we evaluated the role of Toll-like receptors (TLRs) and matrix remodelling in the implantation of bladder acellular matrix (ACM) grafts and ACMs fortified with biomimetic materials. Bladders were decellularized with detergent and treated in 3 different ways prior to implantation: ACM alone, hyaluronic acid (HA)-ACM and HA-vascular endothelial growth factor (VEGF)-ACM. Animals were sacrificed at 4 or 10 weeks post-implantation and total gene expressions for TH2 (IL-4), TH1 (IFN-γ), TLR2, TLR4, and TGF-β1 were analyzed using real-time RT-PCR. Using histology (H&E and Masson's trichrome) and immunohistochemistry (uroplakin, α-smooth muscle actin, CD31 and factor VIII) the regenerative capacity was correlated with the gene expression of different proteins. IL-4, TLR2, and TLR4 gene expression were markedly decreased at 4 and 10 weeks in both the HA-ACM group and the HA-VEGF-ACM group compared to ACM alone. IFN-γ expression was negligible in all groups and time periods. TGF-β1 expression was highest in the HA- and VEGF-treated grafts. Recellularization was inversely proportional to TLR and TH2 expression but proportional to TGF-β1. ACM alone grafts demonstrated stronger TLR4 expression which may promote a distinct TH2 immune response and a reduced regenerative capacity in grafts. Treatment of grafts with HA and VEGF may help regulate host immune responses by reducing TLR4 and IL-4 and increasing TGF-β1.