Restoration of hepatic mast cells and expression of a different mast cell protease phenotype in regenerating rat liver after 70%-hepatectomy

Mast cells (MC) can undergo significant changes in number and phenotype; these alterations result in the differential expression of growth factors and cytokines. Kit ligand (KL; stem cell factor) is produced by mesenchymal cells, and in the liver by biliary epithelial cells. Recent studies suggest that KL, and its receptor c-kit, may be involved in liver regeneration after loss of liver mass. However, KL is also the major growth, differentiating, chemotactic, and activating factor for MC. The aim of our study was to elucidate the dynamics and phenotype of hepatic MC and KL/c-kit expression during liver regeneration after partial (70%) hepatectomy in the rat. Regenerating livers were harvested after 1, 3, 7, and 14 days, respectively (n = 6 each day). MC were stained for naphthol-AS/D-chloroacetate esterase and counted as MC per bile ductule. MC phenotype was assessed by rat MC protease (RMCP)-1 and -2 immunofluorescence staining, in order to distinguish RMCP-1 positive connective tissue MC (CTMC) from RMCP-2 positive mucosa MC (MMC). mRNA expression of RMCP, c-kit, and the differentially spliced variants of KL was quantified by RT-PCR. MC counts per bile ductule decreased in regenerating rat liver tissue at day 3, compared with native livers, and became normal thereafter. Hepatic MC were predominantly of a CTMC phenotype expressing RMCP-1, as previously published; after hepatectomy, between 76 and 99% of all MC double-expressed RMCP-1 and -2, compatible with an MMC phenotype. The ratio of the two alternatively spliced mRNAs for KL (KL-1 : KL-2), and c-kit mRNA expression did not differ significantly between regenerating livers and the livers of sham operated animals. These results suggest that hepatic mast cells are restored during liver regeneration after partial hepatectomy in the rat. Restored MC express an MMC phenotype, suggesting migration from outside into the regenerating liver. Alternative splicing of KL is affected by the surgical procedure in general, and, together with its receptor c-kit, doesn't seem to be involved in liver regeneration after partial hepatectomy in the rat. Further functional studies, and studies in regenerating human livers might offer the possibility of elucidating the role of the hepatic mast cell, and its different protease phenotypes during liver regeneration after surgical loss of liver mass.