Background and Purpose: Small-for-size syndrome following partial hepatectomy and living donor liver transplantation is characterized with compromised liver regeneration. Liver macrophage accounts for priming liver regeneration through release of interleukin-6 (IL-6), and mediating immunosuppression through programmed cell death protein ligand 1 (PD-L1). Breakdown of intrahepatic immune microenvironment through modulation of PD-L1 may accelerate liver regeneration. The current study was to explore the innate immunity of small-for-size liver remnant after extended hepatectomy, and to investigate the effect of blocking PD-L1 on hepatocyte proliferation in vitro and in vivo.
Methods: Liver samples were obtained from rats following extended partial hepatectomy for RNA-sequencing, RT-PCR, and IHC. After major hepatectomy and minor hepatectomy in humans and rats, serum PD-L1 was detected. Liver regeneration in rats was evaluated with liver-to-body weight (LBW) ratio and kinetic growth rate (KGR), Ki67 and PCNA, and macrophage polarization was accessed by iNOS and CD163 expression by WB and IHC. BRL or LO2 hepatocytes co-cultured with rat bone marrow derived macrophages (BMDMs) or human THP-1 macrophages were compared with cell survival by CCK-8. PD-1/PD-L1 inhibitor, BMS-1 and Nivolumab, were employed to test the effect of blocking PD-L1 on proliferation of hepatocytes cocultured with M2 macrophages and the regeneration parameters after 80% PH in rats.
Results: Liver/serum PD-L1 levels were significantly higher after major hepatectomy in both humans and rats by RNA-sequencing, RT-PCR, and IHC (P<0.05); compromised liver regeneration after extended hepatectomy in rats was associated with intrahepatic and serum PD-L1 upregulation and M2 macrophage polarization (P<0.05). blocking PD-L1 reversed the effect of M2 macrophages on in vitro hepatocytes survival, and promoted liver growth in rats through M1 macrophage polarization (P<0.05).
Conclusion: Comprised hepatic regeneration following extended hepatectomy is characterized upregulated PD-L1 and blocking PD-L1 promotes small-for-size liver restoration.