Cathepsin L-deficiency enhances liver regeneration after partial hepatectomy

Cathepsin L (Ctsl) plays a pivotal role in lysosomal and autophagic proteolysis. Previous investigations revealed that partial hepatectomy (PH) decreases biosynthesis of cathepsins in liver, followed by suppression of lysosomal and autophagic proteolysis during liver regeneration. Conversely, it was reported that autophagy-deficiency suppressed liver regeneration. Thus, the purpose of this study is to determine if Ctsl deficiency affects liver regeneration after PH.

70% of PH was performed in male Ctsl-deficient mice (Ctsl-/-) and wild-type littermates (Ctsl +/+) after PH. Mice were sacrificed and wet weight of the whole remaining liver was measured. Bromodeoxyuridine (BrdU)-immunostaining of liver sections was performed. Expression of cyclin D1, p62, LC-3, Nrf2, cleaved-Notch1, Hes1 was evaluated by western blot analysis. NQO1 mRNA expression was measured by realtime-PCR.

After a 70% of PH, the liver mass was significantly restored within 5 days in Ctsl-/- mice compared to wild-type. Ctsl-deficiency enhanced the increases in both the rate of BrdU-positive cells and cyclin D1 expression after PH more than wild-type mice. On the other hand, Ctsl-deficiency upregulated p62, cleaved-Notch1 and Hes1 expression after PH. Moreover, the protein level of Nrf2 in the nucleus and mRNA expression of NQO1 in the liver after PH was also up-regulated in Ctsl-/- mice.

These findings suggest that accumulation of p62 due to loss of Ctsl plays an important role in liver regeneration through activation of Nrf2-Notch1 signaling. Taken together, Ctsl might be a new therapeutic target on disorder of liver regeneration.