In this study we further show that expression of
In this study, we further show that Cy3.5 hydrazide of SUV39H1 in HSC is controlled by the highly conserved miR-125 miRNA family. While previously shown to be important regulators of HSC self-renewal and differentiation potential (O\'Connell et al., 2010; Ooi et al., 2010), the contribution of miR-125 members to age-associated changes in the hematopoietic system had not previously been investigated. We found that the expression of miR-125b is increased with age in HSC and that inhibition of miR-125b leads to increased SUV39H1 expression and attenuates the myeloid-biased differentiation potential of HSC from elderly individuals. miRNAs play an important role in the regulation of lifespan and aging in model organisms and a growing body of evidence indicates that they may also act as regulators of aging pathways in mammalian tissues (reviewed in Smith-Vikos and Slack, 2012). Indeed a recent study has shown that the miR-212/132 cluster is upregulated with age in mouse HSC and that this miRNA can affect HSC function with age via the regulation of the transcription factor FOXO3 (Mehta et al., 2015). As well as impacting on expression of SUV39H1, overexpression of the miR-125b-2 tricistron in HSC has been shown to suppress signaling through the transforming growth factor β (TGFβ) pathway (Emmrich et al., 2014). TGFβ signaling is a critical regulator of HSC homeostasis and quiescence (Blank and Karlsson, 2015) and, interestingly, reduced TGFβ signaling is a prominent feature of aging in mouse HSC (Sun et al., 2014). As well as playing an important role during normal hematopoiesis, miR-125 has also been implicated as an oncomir in a number of myeloid and lymphoid leukemias (Shaham et al., 2012). Thus, the age-associated increase in miR-125 observed in this study may also contribute to the enhanced susceptibility to hematological malignancies observed in the elderly (Sant et al., 2010). At present, the mechanism driving upregulation of miR-125 with age in HSC is not known and will require further investigation. Interestingly, HSC aging is associated with increased levels of both homeobox factors (Pang et al., 2011; Sun et al., 2014) and nuclear NF-κB (Chambers et al., 2007), two transcription factors that have been shown to be activators of miR-125b expression (Emmrich et al., 2014; Tan et al., 2012).
Acknowledgments We thank Drs T. Jenuwein and S. Amigorena for Suv39h1null mice, Dr C. Muchardt for iMEFs, and Drs H. Raslova and D. Bluteau for the pRRL-EF1α-MCS-PGK-GFP lentiviral vector. We are grateful to Dr D. Bonnet for critical reading of the manuscript. The authors also wish to thank clinicians of the Service Hématologie-Greffe of Hôpital Saint Louis and Chirurgie Orthopédique of Hôpital Lariboisière as well as the Fondation Générale de Santé and members of the Unité de Thérapie Cellulaire, Hôpital Saint Louis for human samples. We are also grateful to the Pole Cytométrie of the IUH for help with FACS sorting, to A. Biffi for help with analysis of Suv39h1null mice, and to L. Renou for preparation of miR-125b lentiviral vectors. M.G. was supported by grants from INSERM, the Agence de la Biomedecine, and the Fondation de France. D.G. was supported by a Marie-Curie Intra-European Fellowship. F.P. was supported by grants from INSERM and the Ligue Contre le Cancer Comité d’Ile de France. D.D. is recipient of a fellowship from the Fondation de France and D.B. is recipient of a fellowship from the Ligue Nationale Contre le Cancer.
Introduction The development of transgenic and knockout mouse models has permitted an examination of how the gain of or loss of a particular gene affects the fitness of hematopoietic stem and progenitor cells (HSPCs). One commonly used approach is to transplant recipient mice with an equal combination of normal and genetically modified HSPCs. By following the progeny of the transplanted cells in the recipient mice over the course of ≥16 weeks, one can identify genetic modifications that give the HSPC a functional advantage or disadvantage compared with wild-type (WT) cells. This competitive transplant approach is a critical tool for assessing the in vivo functional impact of genetic (knockout, transgenic, knockin) or chemical modifications, and has been extremely useful in advancing HSPC biology (Figure 1A).