Hepatocytes retain apical polarity during proliferation in liver regeneration

In vivo hepatocytes polarity is characterized by apical domain (bile canaliculi) and basolateral domain which faces liver sinusoidal cells. Hepatocyte polarity is highly important physiologically in order to maintain liver functions, and is also in pathological conditions through limiting or preventing harmful agents and micro-organisms to invade hepatocytes such as Hepatitis C virus. In liver regeneration, the architecture of the organ is severely altered. However, there are no available in vivo studies concerning hepatocyte polarity during different stages of cell cycle, therefore in this study we have investigated hepatocytes polarity during cell division in regenerating liver. Mouse (male C57/6-B6 N) liver regeneration was induced using a toxic model by a single injection of 1.6g/kg CCl₄. Then livers were harvested 2, 4, and 6 days after treatment. BrdU was injected 6, 4, and 2h before harvesting liver tissue. Apical hepatocyte membrane was identified by immunostaining of Dipeptidyl peptidase-4 (DPP4), S-phase hepatocytes with anti-BrdU, and alpha-tubulin for mitotic spindle. Polarized hepatocytes were identified in two dimensional images taken in 5µM sections and in 3D images reconstructed from 0,5µM z-stack sections in 50µM thick slices with confocal laser microscopy. Surprisingly, hepatocyte polarity was preserved in all proliferating stages in regenerating liver. Neither cells in S-phase nor mitotic hepatocytes lose apical domains as assessed by immunostaining of DPP4 and BrdU or mitotic spindle. This is remarkable, since in vitro, hepatocyte proliferation is only effectively induced in depolarized cells in subconfluent cultures on 2D supports. These data show that, in both stages of cell cycle (S-phase and Mitosis), the hepatocyte retains apical membrane domains, indicating that polarity is a very robust feature in liver microarchitecture. Our observations indicate that loss of polarity is not a precondition or a consequence of proliferation in vivo.

Bile Canaliculi - Cell division - Hepatocyte - Mitosis - Polarity