Co-transplantation of Liver Sinusoidal Endothelial Cells Promotes Repopulation of Transplanted Hepatocytes Following Hepatic Irradiation

Abstract

Preparative hepatic irradiation enhances engraftment of transplanted hepatocytes. In this study, we sought to investigate the effect of hepatic irradiation on liver sinusoidal endothelial cells (LSECs) and whether co-transplantation of LSECs with hepatocytes can promote the proliferation of transplanted hepatocytes. Male F344 rats received HIR (10, 25 and 50 Gy) using a 320 kVP Philips orthovoltage unit and were sacrificed at various time points from 0 to 1 week post-HIR. Liver tissues were analyzed by H&E, TUNEL apoptosis assay, and electron microscopy. In the transplantation studies, 5 x 105 DPPIV-positive LSEC’s and/or 5 x 105 DPPIV-positive hepatocytes isolated from C57Bl/6 mice were injected intrasplenically to anesthetized DPPIV-deficient mice twenty-four hours after partial liver irradiation using HIR (20 and 40 Gy). The recipient mice were then sacrificed 60 days post transplantation. There was a dose-dependent increase in the number of apoptotic LSECs, as early as 2 h post-HIR, which peaked at 6 h. Electron microscopy demonstrated significant LSEC dehiscence at 24 h. Co-transplantation of liver sinusoidal endothelial cells and hepatocytes resulted in a dose dependent repopulation of the transplanted cells in the irradiated lobes. Interestingly, transplanted hepatocyte colonies formed only next to newly repopulated LSECs and there were no isolated DPPIV positive hepatocyte colonies (>10 cells) in areas where there was no DPPIV positive liver sinusoidal endothelial proliferation. This data suggests a dose-dependent hepatic LSEC injury. Transplantation of LSECs not only replaced injured liver endothelial cells but also promoted repopulation of the newly transplanted hepatocytes. This is consistent with recent reports demonstrating that newly recruited liver sinusoidal endothelial cells played a crucial role in liver regeneration and restoration of liver mass following partial hepatectomy and toxic liver injury and provide a rationale for promoting LSEC recruitment from progenitor cells in the liver and bone marrow to ameliorate liver function after radiation injury.