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Blocking cholesterol synthesis in the liver promotes hepatocarcinogenesis in the mouse model HCyp51-/-

Kaja Blagotinšek1,Martina Perše2,Jera Jeruc3,Gregor Lorbek1,Žiga Urlep1,Damjana Rozman1

1Centre for Functional Genomics and Bio-Chips, Institute of Biochemistry, Faculty of Medicine, University of Ljubljana, Ljubljana, Slovenia,2Medical Experimental Centre, Institute of Pathology, Faculty of Medicine, University of Ljubljana, Ljubljana, Slovenia,3Institute of Pathology, Faculty of Medicine, University of Ljubljana, Ljubljana, Slovenia

Cholesterol represents a major sterol of mammalian cells and is required for cell proliferation and viability. Lack of cholesterol leads to a strong response of endoplasmic reticulum (ER) sensing mechanism and inflammation progress that is resulting in non-alcoholic (fatty) liver disease (NA(F)LD) development. NA(F)LD, the hepatic manifestation of the metabolic syndrome, can progress to fibrosis, cirrhosis and even further to hepatocellular carcinoma (HCC). HCC is the most common malignant liver tumor worldwide and has been frequently linked with NA(F)LD as one of the important etiological cause of it´s development. The male to female ratio average between 7:1 in NA(F)LD related HCCs. Interestingly, the frequency of HCC in females become 1.5-fold higher after 50 years, potentially due to reduced estrogens which leads to the increase of liver inflammation and hepatocellular demage.
For evaluation of the age-related changes due to cholesterol synthesis block in the liver and it´s potential connection to hepatocarcinogenesis we applied the first hepatocyte specific knock-out mouse model of lanosterol 14α-demethylase (HCyp51-/-) [2]. The second mouse model HCyp51‍ doxy+/doxy+  which allows time-dependent control of Cyp51 knock-out with the doxycycline application, was used for detailed  biochemical studies of carcinogenesis on the primary hepatocyte level. The liver is composed of the non- and parenchymal cells. Hepatocytes as parenchymal cells represent approximately 50% of total cells in mouse liver while the rest are non-parenchymal cells. Analysis of hepatic gene expression was evaluated by qPCR. Histopathology was performed on liver sections.
Our results shows sexual dimorphism of HCC development in HCyp51-‍/- mouse model with male to female ratio of 1:2. Appearance of HCC is age-dependent and the first tumor cases were observed at year 1 with a rising number at later age. Special focus is paid to hepatocyte cholesterol synthesis in the liver, where fundamentally up-regulated cholesterogenic genes (Sqle, Lss, Nsdhl, Tm7sf2) in 1.5 year old males were observed. Lipid plasma parameters were mostly unchanged, however, elevated ALT and AST ratio in KO mice pointed to liver injury that could be the first announcement for the HCC development.
Our data show that mechanisms involved in HCC development in HCyp51-/-  mice include a combination of chronic complementary effects. To identify which of those pathways play essential roles in NA(F)LD induced HCC progression on a global scale, the expression profiling by microarrays is in progress. The future perspective is to deepen our knowledge of biochemical pathways involved in NA(F)LD induced carcinogenesis by applying described mouse models and immortalizated hepatocytes with knocked-out Cyp51 with CRISPR technology.
Acknowledgements: This work was supported by the Slovenian Research Agency (ARRS) program grant P1-0390. K. Blagotinsek, Z. Urlep and G. Lorbek is/were supported by the graduate fellowship of ARRS.
Blagotinšek K (2017). Curr Pharm Des 23, pp 1-6.
Keber R et al. (2011). J Biol Chem 286 (33), pp 29086-97.
Rozman D (2014). Dig Dis Sci 59(2), pp 238-41.

2006 - University of Ljubljana, Faculty of Medicine, Center for Functional Genomics and Bio-chips.