PARP-2 sustains erythropoiesis in mice by limiting replicative stress in erythroid progenitors.

Erythropoiesis is a tightly regulated process in which multipotential hematopoietic stem cells produce mature red blood cells. Here we show that deletion of poly(ADP-ribose) polymerase-2 (PARP-2) in mice leads to chronic anemia at steady state, despite increased erythropoietin plasma levels, a phenomenon not observed in mice lacking PARP-1. Loss of PARP-2 causes shortened lifespan of erythrocytes and impaired differentiation of erythroid progenitors. In erythroblasts, PARP-2 deficiency triggers replicative stress, as indicated by the presence of micronuclei, the accumulation of γ-H2AX (phospho-histone H2AX) in S-phase cells and constitutive CHK1 and replication protein A phosphorylation. Transcriptome analyses revealed the activation of the p53-dependent DNA-damage response pathways in PARP-2-deficient cells, culminating in the upregulation of cell-cycle and cell death regulators, concomitant with G2/M arrest and apoptosis. Strikingly, while loss of the proapoptotic p53 target gene Puma restored hematocrit levels in the PARP-2-deficient mice, loss of the cell-cycle regulator and CDK inhibitor p21 leads to perinatal death by exacerbating impaired fetal liver erythropoiesis in PARP-2-deficient embryos. Although the anemia displayed by PARP-2-deficient mice is compatible with life, mice die rapidly when exposed to stress-induced enhanced hemolysis. Our results pinpoint an essential role for PARP-2 in erythropoiesis by limiting replicative stress that becomes essential in the absence of p21 and in the context of enhanced hemolysis, highlighting the potential effect that might arise from the design and use of PARP inhibitors that specifically inactivate PARP proteins.

Transcriptomic analysis of polyamine-related genes and polyamine levels in placenta, yolk sac and fetus during the second half of mouse pregnancy.

In mammals, polyamines are essential for the maintenance of cell growth. Although early studies reported the highest values of mammalian ornithine decarboxylase (ODC) activity, a key enzyme in polyamine biosynthesis, in rodent placenta, the role of this enzyme in the second half of rodent pregnancy is still controversial. In order to get new insights on polyamine metabolism during this period of pregnancy, we studied polyamine levels, ODC expression and activity and transcript profile of different polyamine-related genes in mouse placenta, fetus and yolk sac. Results indicated that ODC activity and protein levels were higher in placenta than in fetus and yolk sac, especially in the labyrinth, although no correlation between ODC activity and polyamine levels were observed. The half-life of placental ODC ( approximately 190 min) was also higher than the fetal one ( approximately 24 min). Messenger RNAs of all biosynthetic and retroconversion enzymes of polyamine metabolism were present in the three gestational compartments analyzed, as well as those of antizymes 1 and 2 and antizyme inhibitor 1. However, no expression of antizyme 3 and antizyme inhibitor 2 was detected. The catabolic enzyme diamine oxidase was expressed only in the maternal part of placenta but not in the fetal part or in the fetus. The expansion of polyamine pools in the fetus was markedly higher than in placenta, in spite of its lower biosynthetic activity. Our results suggest that the elevated polyamine biosynthetic activity of mouse placenta is required to satisfy the high demand of polyamines required by the growing fetus, during the later period of pregnancy.

Influence of dietary arginine on the anabolic effects of androgens.

Feeding mice an arginine-deficient diet decreased plasma concentrations of arginine, citrulline and ornithine in the females and arginine in the males, abolishing the sexual dimorphic pattern of these amino acids found in mice fed the standard diet. In addition, the restriction of dietary arginine produced a marked decrease in body and renal weights as well as in the activity of renal ornithine decarboxylase, decreases that were gender dependent since they were observed exclusively in males. The fact that these changes were not associated with the decrease in the circulating levels of testosterone and that the dietary arginine restriction prevented the body weight gain induced by testosterone treatment of female mice fed the standard diet indicates that dietary arginine is required for the anabolic action of androgens. Moreover, under certain conditions that could compromise the renal synthesis of arginine, as in the compensatory renal hypertrophy that follows unilateral nephrectomy, the myotrophic effect of testosterone was transiently impaired. The results also revealed that arginine deficiency produced an opposite effect in the expression of IGF-I and IGF-binding protein 1 in the liver and kidney. Taken together, our results indicate that dietary arginine may be relevant to the anabolic action of testosterone, and suggest that this effect may be mediated by changes in the insulin-like growth factor system.