Mcl-1 and Bcl-xL Cooperatively Maintain Integrity of Hepatocytes in Developing and Adult Murine Liver†

• DOI: 10.1002/hep.23126
• Publication Date: 2009-06-15T18:32:48Z
• Authors: Hayato Hikita; Tetsuo Takehara; Satoshi Shimizu; Takahiro Kodama; Wei Li; Takuya Miyagi; Atsushi Hosui; Hisashi Ishida; Kazuyoshi Ohkawa; Tatsuya Kanto; Naoki Hiramatsu; Xiao-Ming Yin; Lothar Hennighausen; Tomohide Tatsumi; Norio Hayashi
• Keywords: Mice, Knockout; 0303 health sciences; Caspase 3; Fas-Associated Death Domain Protein; bcl-X Protein; Alanine Transaminase; Apoptosis; 3. Good health; Mice; 03 medical and health sciences; Liver; Proto-Oncogene Proteins c-bcl-2; Hepatocytes; Animals; Myeloid Cell Leukemia Sequence 1 Protein; Genetic Predisposition to Disease; Alleles; BH3 Interacting Domain Death Agonist Protein

Anti-apoptotic members of the Bcl-2 family, including Bcl-2, Bcl-xL, Mcl-1, Bcl-w and Bfl-1, inhibit the mitochondrial pathway of apoptosis. Bcl-xL and Mcl-1 are constitutively expressed in the liver. Although previous research established Bcl-xL as a critical apoptosis antagonist in differentiated hepatocytes, the significance of Mcl-1 in the liver, especially in conjunction with Bcl-xL, has not been clear. To examine this question, we generated hepatocyte-specific Mcl-1–deficient mice by crossing

mcl-1

flox

/

flox

mice and

AlbCre

mice and further crossed them with

bcl-x

flox

/

flox

mice, giving Mcl-1/Bcl-xL–deficient mice. The

mcl-1

flox

/

flox

AlbCre

mice showed spontaneous apoptosis of hepatocytes after birth, as evidenced by elevated levels of serum alanine aminotransferase (ALT) and caspase-3/7 activity and an increased number of terminal deoxynucleotidyl transferase-mediated 2′-deoxyuridine 5′-triphosphate nick-end labeling (TUNEL)-positive cells in the liver; these phenotypes were very close to those previously found in hepatocyte-specific Bcl-xL–deficient mice. Although

mcl-1

flox

/+

AlbCre

mice did not display apoptosis, their susceptibility to Fas-mediated liver injury significantly increased. Further crossing of Mcl-1 mice with Bcl-xL mice showed that

bcl-x

flox

/+

mcl-1

flox

/+

AlbCre

mice also showed spontaneous hepatocyte apoptosis similar to Bcl-xL–deficient or Mcl-1–deficient mice. In contrast,

bcl-x

flox

/

flox

mcl-1

flox

/+

AlbCre

,

bcl-x

flox

/+

mcl-1

flox

/

flox

AlbCre,

and

bcl-x

flox

/

flox

mcl-1

flox

/

flox

AlbCre

mice displayed a decreased number of hepatocytes and a reduced volume of the liver on day 18.5 of embryogenesis and rapidly died within 1 day after birth, developing hepatic failure evidenced by increased levels of blood ammonia and bilirubin.

Conclusion:

Mcl-1 is critical for blocking apoptosis in adult liver and, in the absence of Bcl-xL, is essential for normal liver development. Mcl-1 and Bcl-xL are two major anti-apoptotic Bcl-2 family proteins expressed in the liver and cooperatively control hepatic integrity during liver development and in adult liver homeostasis in a gene dose-dependent manner. (Hepatology 2009.)