The proprotein convertase subtilisin/kexin type 9, PCSK9, belongs to the proprotein convertase (PC) family. Human mutations in the gene encoding PCSK9 lead to either familial hyper- or hypocholesterolemia, resulting from a gain or loss of function, respectively. Mice lacking PCSK9 are viable and show a 42% decrease in plasma cholesterol levels. The enzyme triggers the degradation of the low density lipoprotein receptor (LDLR) through a partially unknown mechanism. / PCSK9 is very abundant in the liver and intestine during development and adulthood. Hepatocytes have a capacity to reproduce themselves and, upon injury, can repopulate the liver. For a better understanding of the role of PCSK9 in the liver, partial hepatectomy was performed on Pcsk9 +/+, Pcsk9+/- and Pcsk9-/- mice. The absence of PCSK9 resulted in defective liver regeneration, while wild type (WT) and heterozygous mice had no phenotype. Regeneration defects could be prevented by a high cholesterol diet. PCSK9 deficiency, by contributing to maintaining low circulating cholesterol levels may thus hamper liver regeneration. This knowledge is critical for the analysis of future PCSK9 inhibitors expected to be developed in the near future. / Key words. Proprotein convertase subtilisin/kexin 9 (PCSK9), a familial hyper- or hypocholesterolemia, low density lipoprotein receptor, knockout mouse model, partial hepatectomy.

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