INDUCIBLE AND ENDOTHELIAL NITRIC OXIDE SYNTHASE (INOS AND ENOS) DIFFERENTIALLY REGULATE LIVER REGENERATION AFTER PARTIAL HEPATECTOMY

Abstract

P1206 Aims: Liver regeneration plays an important role in survival after liver resection and partial liver transplantation. Previous studies showed that liver regeneration is inhibited in iNOS-deficient mice, indicating that nitric oxide production by iNOS is required for regeneration. However, the role of nitric oxide production by eNOS remains unclear. Accordingly, the aim of this study was to investigate if liver regeneration is altered in eNOS-deficient mice after partial hepatectomy. Methods: Seventy-percent partial hepatectomy was performed in the wild-type (C57/BL), iNOS knock-out and eNOS knock-out mice. Liver cell proliferation was detected by 5-bromo-2’-deoxyuridine (BrdU) incorporation, proliferative cell nuclear antigen (PCNA) expression and mitotic figures. Cell apoptosis was detected by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) staining. Results: PCNA is a marker for entry of cells into the G1 phase of the cell cycle. PCNA-positive cells increased from 0.4 cells/high power field (hpf) to 14 cells/hpf 48 h after partial hepatectomy in wild-type animals. In iNOS-deficient mice, PCNA-positive cells were only half as high. Surprisingly, PCNA-positive cells increased 2.3-fold in eNOS knock-out mice compared to wild-type animals. BrdU labeling, an indicator of the S phase of the cell cycle, was 0.4 cells/hpf prior to partial hepatectomy and increased to 56 cells/hpf 48 h after partial hepatectomy in wild-type mice. Peak BrdU labeling decreased to 32% in iNOS-deficient mice. By contrast, Brdu labeling was 2.1-fold higher in the eNOS knock-out mice compared to wild-type. Similar alterations were observed in the number of mitotic figures, an indicator of the M phase of the cell cycle. Apoptotic cells also increased after partial hepatectomy. TUNEL-positive cells were 2-fold higher in the livers from iNOS knock-out mice than the wild-type mice but were only slightly decreased in eNOS-deficient mice. Conclusions: Liver regeneration is inhibited in iNOS-deficient mice but stimulated in eNOS-deficient mice after partial hepatectomy, indicating that iNOS and eNOS play different roles in regulating liver regenration. Suppression of regeneration is associated with increased apoptosis in iNOS-deficient mice. However, the mechanism of stimulated liver regeneration in eNOS knock-out mice remains to be identified. Supported by NIDDK.