Senescence in cell oxidative status in two bird species with contrasting life expectancy.

Oxidative stress occurs when the production of reactive oxygen species (ROS) by an organism exceeds its capacity to mitigate the damaging effects of the ROS. Consequently, oxidative stress hypotheses of ageing argue that a decline in fecundity and an increase in the likelihood of death with advancing age reported at the organism level are driven by gradual disruption of the oxidative balance at the cellular level. Here, we measured erythrocyte resistance to oxidative stress in the same individuals over several years in two free-living bird species with contrasting life expectancy, the great tit (known maximum life expectancy is 15.4 years) and the Alpine swift (26 years). In both species, we found evidence for senescence in cell resistance to oxidative stress, with patterns of senescence becoming apparent as subjects get older. In the Alpine swift, there was also evidence for positive selection on cell resistance to oxidative stress, the more resistant subjects being longer lived. The present findings of inter-individual selection and intra-individual deterioration in cell oxidative status at old age in free-living animals support a role for oxidative stress in the ageing of wild animals

ZFP36L2 is required for self-renewal of early burst-forming unit erythroid progenitors

Stem cells and progenitors in many lineages undergo self-renewing divisions, but the extracellular and intracellular proteins that regulate this process are largely unknown. Glucocorticoids stimulate red blood cell formation by promoting self-renewal of early burst-forming unit–erythroid (BFU–E) progenitors. Here we show that the RNA-binding protein ZFP36L2 is a transcriptional target of the glucocorticoid receptor (GR) in BFU–Es and is required for BFU–E self-renewal. ZFP36L2 is normally downregulated during erythroid differentiation from the BFU–E stage, but its expression is maintained by all tested GR agonists that stimulate BFU–E self-renewal, and the GR binds to several potential enhancer regions of ZFP36L2. Knockdown of ZFP36L2 in cultured BFU–E cells did not affect the rate of cell division but disrupted glucocorticoid-induced BFU–E self-renewal, and knockdown of ZFP36L2 in transplanted erythroid progenitors prevented expansion of erythroid lineage progenitors normally seen following induction of anaemia by phenylhydrazine treatment. ZFP36L2 preferentially binds to messenger RNAs that are induced or maintained at high expression levels during terminal erythroid differentiation and negatively regulates their expression levels. ZFP36L2 therefore functions as part of a molecular switch promoting BFU–E self-renewal and a subsequent increase in the total numbers of colony-forming unit–erythroid (CFU–E) progenitors and erythroid cells that are generated.National Institutes of Health (U.S.) (Grant P01 HL 32262

ASXL1 plays an important role in erythropoiesis

ASXL1 mutations are found in a spectrum of myeloid malignancies with poor prognosis. Recently, we reported that Asxl1(+/−) mice develop myelodysplastic syndrome (MDS) or MDS and myeloproliferative neoplasms (MPN) overlapping diseases (MDS/MPN). Although defective erythroid maturation and anemia are associated with the prognosis of patients with MDS or MDS/MPN, the role of ASXL1 in erythropoiesis remains unclear. Here, we showed that chronic myelomonocytic leukemia (CMML) patients with ASXL1 mutations exhibited more severe anemia with a significantly increased proportion of bone marrow (BM) early stage erythroblasts and reduced enucleated erythrocytes compared to CMML patients with WT ASXL1. Knockdown of ASXL1 in cord blood CD34(+) cells reduced erythropoiesis and impaired erythrocyte enucleation. Consistently, the BM and spleens of VavCre(+);Asxl1(f/f) (Asxl1(∆/∆)) mice had less numbers of erythroid progenitors than Asxl1(f/f) controls. Asxl1(∆/∆) mice also had an increased percentage of erythroblasts and a reduced erythrocyte enucleation in their BM compared to littermate controls. Furthermore, Asxl1(∆/∆) erythroblasts revealed altered expression of genes involved in erythroid development and homeostasis, which was associated with lower levels of H3K27me3 and H3K4me3. Our study unveils a key role for ASXL1 in erythropoiesis and indicates that ASXL1 loss hinders erythroid development/maturation, which could be of prognostic value for MDS/MPN patients