Interplay of neuropilin-1 and semaphorin 3A after partial hepatectomy in rats

AIM:To elucidate the role of neuropilin-1(Nrp-1) and semaphorin 3A(Sema3A) in sinusoidal remodeling during liver regeneration in rats.METHODS:Male Wistar/ST rats at 7 wk of age,weighing about 200 g,were used for all animal experiments.In vivo,at 24,48,72,96,144 and 192 h after twothirds partial hepatectomy(PHx),the remnant livers were removed.Liver tissues were immunohistochemically stained for Nrp-1,Sema3A and SE-1,a liver sinusoidal endothelial cell(SEC) marker.Total RNA of the liver tissue was extracted and reversely transcribed into cDNA.The mRNA expression of Sema3A was analyzed by quantitative real-time polymerase chain reaction and normalized to that of ribosomal protein S18.In vitro,SECs were isolated from rat liver and cultured in endothelial growth medium containing 20 ng/mL vascular endothelial cell growth factor.Migration of SECs in primary culture was assessed by cell transwell assay with or without recombinant Sema3A.Apoptotic cells were determined by a terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labeling method.RESULTS:In vitro,immunohistochemistry study revealed that Sema3A and Nrp-1 were constitutively expressed in hepatocytes and SECs,respectively,in normal rat liver tissues.Nrp-1 expression in SECs was quantified by the percentage of immunostained area with antiNrp-1 antibody in relation to the area stained with SE-1.Between 24 h and 96 h following resection of liver,Nrp-1 expression in SECs was transiently increased.Compared with the baseline(5.2% ± 0.1%),Nrp-1 expression in SECs significantly increased at 24 h(17.3% ± 0.7%,P < 0.05),48 h(39.1% ± 0.6%,P < 0.01),72 h(46.9% ± 4.5%,P < 0.01) and 96 h(29.9% ± 3.8%,P < 0.01) after PHx,then returned to the basal level at termination of liver regeneration.Interestingly,the expression of Sema3A was inversely associated with that of Nrp-1 in liver after PHx.Sema3A mRNA expression was significantly reduced by about 75% over the period 24-144 h after PHx(P < 0.05),and returned to basal levels at 192 h after PHx.In vitro,SECs isolated from rats after PHx(PHx-SECs) were observed to migrate to the lower chamber of the cell transwell system after incubation for 24 h,but not cells from normal rats(CONT-SECs),indicating that mobility of PHx-SECs increases as compared with that of CONT-SECs.Moreover,recombinant Sema3A significantly attenuated migration in PHx-SECs in primary culture(vehicle-treated 100% ± 7.9% vs Sema3A-treated 42.6% ± 5.4%,P < 0.01),but not in CONT-SECs.Compared with CONTSECs,the apoptotic rate of PHx-SECs decreased by 78.3%(P < 0.05).There was no difference in apoptosis between CONT-SECs that were treated with vehicle and Sema3A.However,in PHx-SECs,apoptosis was induced by the presence of 5 nmol Sema3A for 24 h(vehicle-treated 21.7% ± 7.6% vs Sema3A-treated 104.3% ± 8.9%,P < 0.05).In addition,immunohistochemistry confirmed the increased expression of Nrp-1 in PHx-SECs,while it was noted to a lesser extent in CONT-SECs.CONCLUSION:The interplay of Nrp-1 and Sema3A shown in our results may lead to a better understanding of interaction between sinusoidal remodeling and SECs during liver regeneration.