Sun Woo Sophie Kang, Dong Fu, David G. Le Couteur and Victoria C. Cogger
Centre for Education and Research on Ageing, Concord Repatriation General Hospital, Australia
Ageing is associated with increased susceptibility to liver diseases and impaired hepatic function. One important factor in normal liver function is functionally sound hepatocytes, the major metabolic cells of the liver. Hepatocytes are polarized cells and loss of polarization results in accumulation of bile, toxins and metabolites leading to hepatocellular damage. Here we examined whether there were changes in hepatocyte polarization that may contribute to age related susceptibility to liver disease. Hepatocytes were freshly isolated from C57BL6 male mice aged 3 mths and 24 mths. Cells were cultured in a collagen sandwich configuration and were observed for 72 hours. Lipid droplets were quantified with lipidtox neutral red staining (Invitrogen) and polarization was determined by immunofluorescence of tight junctional protein Zonula occludens-1. In addition, ATP levels were quantified, and expression of mitochondrial proteins were measured by western blot. We found that hepatocytes from 24 mth mice polarized significantly faster rate than 3 mth mice with more and larger lipid droplets present from the beginning of polarization, which persisted after 60 hours and the formation of the bile canalicular network. Whereas, a reduction of lipid droplet number was evident after 24 hours in 3 mth hepatocytes. Despite the increase in polarization rate in 24 mth hepatocytes, cellular ATP levels were lower and peaked earlier in the time-course with protein expression of mitochondrial fusion proteins lower than in 3 mth hepatocytes. Our findings suggest there are changes in re-establishment of hepatocyte polarization with age, which may impact susceptibility to liver diseases.