On the molecular mechanisms of hematopoietic stem cell aging

In dit proefschrift hebben we de veroudering van hematopoëtische stamcellen (HSC’s) met verschillende methoden onderzocht, met als doel de onderliggende mechanismen bloot te leggen. We hebben hierbij de focus gelegd op het vinden van factoren die geassocieerd zijn met de veroudering van HSC’s, de zogenaamde gemeenschappelijkheden van veroudering.In this thesis, we have investigated hematopoietic stem cell aging using varied methodologies in an effort to further the understanding of its development and underlying mechanisms. We focused on what we term the commonalities of aging, seeking factors that are most frequently associated with HSC aging

On the molecular mechanisms of hematopoietic stem cell aging

In dit proefschrift hebben we de veroudering van hematopoëtische stamcellen (HSC’s) met verschillende methoden onderzocht, met als doel de onderliggende mechanismen bloot te leggen. We hebben hierbij de focus gelegd op het vinden van factoren die geassocieerd zijn met de veroudering van HSC’s, de zogenaamde gemeenschappelijkheden van veroudering

Eosinophil Morphology Eosinophil granules and degranulation

Endogenous DNA damage is causally associated with the functional decline and transformation of stem cells that characterize aging. DNA lesions that have escaped DNA repair can induce replication stress and genomic breaks that induce senescence and apoptosis. It is not clear how stem and proliferating cells cope with accumulating endogenous DNA lesions and how these ultimately affect the physiology of cells and tissues. Here we have addressed these questions by investigating the hematopoietic system of mice deficient for Rev1, a core factor in DNA translesion synthesis (TLS), the postreplicative bypass of damaged nucleotides. Rev1 hematopoietic stem and progenitor cells displayed compromised proliferation, and replication stress that could be rescued with an antioxidant. The additional disruption of Xpc, essential for global-genome nucleotide excision repair (ggNER) of helix-distorting nucleotide lesions, resulted in the perinatal loss of hematopoietic stem cells, progressive loss of bone marrow, and fatal aplastic anemia between 3 and 4 months of age. This was associated with replication stress, genomic breaks, DNA damage signaling, senescence, and apoptosis in bone marrow. Surprisingly, the collapse of the Rev1Xpc bone marrow was associated with progressive mitochondrial dysfunction and consequent exacerbation of oxidative stress. These data reveal that, to protect its genomic and functional integrity, the hematopoietic system critically depends on the combined activities of repair and replication of helix-distorting oxidative nucleotide lesions by ggNER and Rev1-dependent TLS, respectively. The error-prone nature of TLS may provide mechanistic understanding of the accumulation of mutations in the hematopoietic system upon aging

CBX7 Induces Self-Renewal of Human Normal and Malignant Hematopoietic Stem and Progenitor Cells by Canonical and Non-canonical Interactions

In this study, we demonstrate that, among all five CBX Polycomb proteins, only CBX7 possesses the ability to control self-renewal of human hematopoietic stem and progenitor cells (HSPCs). Xenotransplantation of CBX7-overexpressing HSPCs resulted in increased multi-lineage long-term engraftment and myelopoiesis. Gene expression and chromatin analyses revealed perturbations in genes involved in differentiation, DNA and chromatin maintenance, and cell cycle control. CBX7 is upregulated in acute myeloid leukemia (AML), and its genetic or pharmacological repression in AML cells inhibited proliferation and induced differentiation. Mass spectrometry analysis revealed several non-histone protein interactions between CBX7 and the H3K9 methyltransferases SETDB1, EHMT1, and EHMT2. These CBX7- binding proteins possess a trimethylated lysine peptide motif highly similar to the canonical CBX7 target H3K27me3. Depletion of SETDB1 in AML cells phenocopied repression of CBX7. We identify CBX7 as an important regulator of self-renewal and uncover non-canonical crosstalk between distinct pathways, revealing therapeutic opportunities for leukemia

Niche derived netrin-1 regulates hematopoietic stem cell dormancy via its receptor neogenin-1

Funder: Studienstiftung des Deutschen Volkes (German National Academic Foundation); doi: https://doi.org/10.13039/501100004350Funder: Heinrich F.C. Behr StiftungFunder: Dietmar Hopp Stiftung; doi: https://doi.org/10.13039/501100005941Abstract: Haematopoietic stem cells (HSCs) are characterized by their self-renewal potential associated to dormancy. Here we identify the cell surface receptor neogenin-1 as specifically expressed in dormant HSCs. Loss of neogenin-1 initially leads to increased HSC expansion but subsequently to loss of self-renewal and premature exhaustion in vivo. Its ligand netrin-1 induces Egr1 expression and maintains quiescence and function of cultured HSCs in a Neo1 dependent manner. Produced by arteriolar endothelial and periarteriolar stromal cells, conditional netrin-1 deletion in the bone marrow niche reduces HSC numbers, quiescence and self-renewal, while overexpression increases quiescence in vivo. Ageing associated bone marrow remodelling leads to the decline of netrin-1 expression in niches and a compensatory but reversible upregulation of neogenin-1 on HSCs. Our study suggests that niche produced netrin-1 preserves HSC quiescence and self-renewal via neogenin-1 function. Decline of netrin-1 production during ageing leads to the gradual decrease of Neo1 mediated HSC self-renewal

Niche derived netrin-1 regulates hematopoietic stem cell dormancy via its receptor neogenin-1

Funder: Studienstiftung des Deutschen Volkes (German National Academic Foundation); doi: https://doi.org/10.13039/501100004350Funder: Heinrich F.C. Behr StiftungFunder: Dietmar Hopp Stiftung; doi: https://doi.org/10.13039/501100005941Abstract: Haematopoietic stem cells (HSCs) are characterized by their self-renewal potential associated to dormancy. Here we identify the cell surface receptor neogenin-1 as specifically expressed in dormant HSCs. Loss of neogenin-1 initially leads to increased HSC expansion but subsequently to loss of self-renewal and premature exhaustion in vivo. Its ligand netrin-1 induces Egr1 expression and maintains quiescence and function of cultured HSCs in a Neo1 dependent manner. Produced by arteriolar endothelial and periarteriolar stromal cells, conditional netrin-1 deletion in the bone marrow niche reduces HSC numbers, quiescence and self-renewal, while overexpression increases quiescence in vivo. Ageing associated bone marrow remodelling leads to the decline of netrin-1 expression in niches and a compensatory but reversible upregulation of neogenin-1 on HSCs. Our study suggests that niche produced netrin-1 preserves HSC quiescence and self-renewal via neogenin-1 function. Decline of netrin-1 production during ageing leads to the gradual decrease of Neo1 mediated HSC self-renewal

Aging of hematopoietic stem cells

Hematopoietic stem cells (HSCs) ensure a balanced production of all blood cells throughout life. As they age, HSCs gradually lose their self-renewal and regenerative potential, while the occurrence of cellular derailment strongly increases. Here we review our current understanding of the molecular mechanisms that contribute to HSC aging. We argue that most of the causes that underlie HSC aging result from cell-intrinsic pathways, and reflect on which aspects of the aging process may be reversible. As many hematological pathologies are strongly age-associated, strategies to intervene in aspects of the stem cell aging process may have significant clinical relevance

microRNAs in hematopoiesis

miRNAs have been implicated in all stages of hematopoiesis including maintenance of self-renewal of hematopoietic stem cells (HSCs) and differentiation into mature blood cells. Regulation by miRNAs is markedly intertwined with transcription factors. In this review, we highlight miRNAs shown to be important for HSC maintenance and lineage differentiation with focus on their interaction with transcription factors. We also pay attention to the diverse modes of miRNA regulation. (C) 2014 Elsevier Inc. All rights reserved