Hepatocytes lacking thioredoxin reductase 1 have normal replicative potential during development and regeneration

Area of Science:

• Cellular biology
• Molecular biology
• Biochemistry

Background:

• Ribonucleotide reductase (RNR) is essential for DNA replication.
• In bacteria, RNR electron supply uses thioredoxin reductase or glutathione reductase pathways.
• Thioredoxin reductase deficiency in yeast/plants impairs growth, suggesting pathway redundancy is organism-dependent.

Purpose of the Study:

• To investigate the role of thioredoxin reductase 1 (Txnrd1) in mouse hepatocyte proliferation.
• To determine if Txnrd1-independent pathways can support DNA replication and liver growth.

Main Methods:

• Studied Txnrd1-deficient hepatocytes in mice during development and regeneration.
• Assessed hepatocyte proliferation using markers like PCNA, phosphohistone H3, and BrdU incorporation.
• Utilized genetic chimeras to compare Txnrd1-deficient and normal hepatocytes.
• Confirmed RNR dependency using hydroxyurea and measured DNA synthesis via thymidine incorporation.

Main Results:

• Txnrd1-deficient hepatocytes showed normal liver growth rates and proliferation levels compared to controls.
• DNA replication and S/M phase progression were unaffected in Txnrd1-deficient hepatocytes.
• Both Txnrd1-deficient and normal hepatocytes contributed equally to liver development and regeneration in chimeras.
• Hydroxyurea blocked replication, confirming RNR's essential role.

Conclusions:

• Mouse hepatocytes possess a functional Txnrd1-independent pathway for supplying electrons to RNR.
• This alternative pathway fully supports DNA replication and normal proliferative growth in hepatocytes.
• Findings challenge the presumed necessity of thioredoxin reductases for RNR function in all eukaryotes.