Hepatocyte DNA replication in growing liver requires either glutathione or a single allele of txnrd1

Abstract

Ribonucleotide reductase (RNR) activity requires an electron donor, which in bacteria, yeast, and plants is usually either reduced thioredoxin (Trx) or reduced glutaredoxin (Grx). Mice lacking glutathione reductase are viable and, although mice lacking thioredoxin reductase 1 (TrxR1) are embryonic-lethal, several studies have shown that mouse cells lacking the txnrd1 gene, encoding TrxR1, can proliferate normally. To better understand the in vivo electron donor requirements for mammalian RNR, we here investigated whether replication of TrxR1-deficient hepatocytes in mouse livers employed either an alternative source of Trx-reducing activity or, instead, solely relied upon the glutathione (GSH) pathway. Neither normal nor genetically TrxR1-deficient livers expressed substantial levels of mRNA splice-forms encoding cytosolic variants of TrxR2, and the TrxR1-deficient livers showed severely diminished total TrxR activity, making it unlikely that any alternative TrxR enzyme activities complemented the genetic TrxR1 deficiency. To test whether the GSH pathway was required for replication, GSH levels were depleted by administration of buthionine sulfoximine (BSO) to juvenile mice. In controls not receiving BSO, replicative indexes were similar in hepatocytes having either two, one, or no functional alleles of txnrd1. Following BSO treatment, hepatocytes containing either two or one copies of this gene were also normal. However, hepatocytes completely lacking a functional txnrd1 gene exhibited severely reduced replicative indexes after GSH depletion. We conclude that hepatocyte proliferation in vivo requires either GSH or at least one functional allele of txnrd1, demonstrating that either the GSH- or TrxR1-dependent redox pathway can independently support hepatocyte proliferation during liver growth.

Glutathione and Glutaredoxin Act as a Backup of Human Thioredoxin Reductase 1 to Reduce Thioredoxin 1 Preventing Cell Death by Aurothioglucose

“…7C. Also, recent in vivo data show that either glutathione or a single allele of the TrxR-dependent redox pathway can independently support hepatocyte DNA replication and proliferation (29).…”

“…Tan et al (28) found that the Trx system can function as an alternative system to reduce glutathione disulfide in Saccharomyces cerevisiae. It was also found that in mice, normal cell proliferation without TrxR1 occurred both embryonically and during liver regeneration (29).…”

The Thioredoxin Reductase-1 Inhibitor Aurothioglucose Attenuates Lung Injury and Improves Survival in a Murine Model of Acute Respiratory Distress Syndrome

“…Importantly, our data indicate that TrxR1 inhibition is only detrimental in settings of GSH system disruption. Work by ourselves and others suggests that a cross-talk between the Trx and GSH systems most reasonably explains the tolerance of TrxR1 inhibition in vivo and in vitro (2,23,34,38,39,42). Other than dietary riboflavin deficiency that is easily correctable, GSH system deficiencies are virtually unknown in humans supporting the translational potential of ATG or other TrxR1 inhibitors for the treatment of lung injury in human patients (10)(11)(12).…”

Dual targeting of the thioredoxin and glutathione systems in cancer and HIV

“…Conrad and colleagues demonstrated that, although cells from TrxR1-deficient mice have normal proliferative capacity, they exhibit heightened sensitivity to the GSH synthesis inhibitor buthionine sulfoximine (BSO) (8). In addition, Schmidt and colleagues showed that hepatocyte DNA replication requires either GSH or TrxR1 (9). This finding was recently confirmed in primary human T lymphocytes (10), where the two systems are required for optimal activity of ribonucleotide reductase.…”