We surveyed 16 published and unpublished data sets to determine whether a consistent pattern of transcriptional deregulation in aging murine hematopoietic stem cells (HSC) exists. Despite substantial ...heterogeneity between individual studies, we uncovered a core and robust HSC aging signature. We detected increased transcriptional activation in aged HSCs, further confirmed by chromatin accessibility analysis. Unexpectedly, using 2 independent computational approaches, we established that deregulated aging genes consist largely of membrane-associated transcripts, including many cell surface molecules previously not associated with HSC biology. We show that Selp (P-selectin), the most consistent deregulated gene, is not merely a marker for aged HSCs but is associated with HSC functional decline. Additionally, single-cell transcriptomics analysis revealed increased heterogeneity of the aged HSC pool. We identify the presence of transcriptionally “young-like” HSCs in aged bone marrow. We share our results as an online resource and demonstrate its utility by confirming that exposure to sympathomimetics or deletion of Dnmt3a/b molecularly resembles HSC rejuvenation or aging, respectively.
•A comprehensive transcriptome analysis of aged murine HSC identifies an aging signature.•The HSC aging signature is highly enriched for cell membrane–related transcripts and identifies age-associated heterogeneity.
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ABSTRACT
The complement system, and specifically C5a, is involved in renal ischemia‐reperfusion (IR) injury. The 2 receptors for complement anaphylatoxin C5a (C5aR1 and C5aR2) are expressed on ...leukocytes as well as on renal epithelium. Extensive evidence shows that C5aR1 inhibition protects kidneys from IR injury; however, the role of C5aR2 in IR injury is less clear as initial studies proposed the hypothesis that C5aR2 functions as a decoy receptor. By Using wild‐type, C5aR1‐/‐, and C5aR2‐/‐ mice in a model of renal IR injury, we found that a deficiency of either of these receptors protected mice from renal IR injury. Surprisingly, C5aR2‐/‐ mice were most protected and had lower creatinine levels and reduced acute tubular necrosis. Next, an in vivo migration study demonstrated that leukocyte chemotaxis was unaffected in C5aR2‐/‐ mice, whereas neutrophil activation was reduced by C5aR2 deficiency. To further investigate the contribution of renal cell‐expressed C5aR2 vs. leukocyte‐expressed C5aR2 to renal IR injury, bone marrow chimeras were created. Our data show that both renal cell‐expressed C5aR2 and leukocyte‐expressed C5aR2 mediate IR‐induced renal dysfunction. These studies reveal the importance of C5aR2 in renal IR injury. They further show that C5aR2 is a functional receptor, rather than a decoy receptor, and may provide a new target for intervention.—Poppelaars, F., van Werkhoven, M. B., Kotimaa, J., Veldhuis, Z. J., Ausema, A., Broeren, S. G. M., Damman, J., Hempel, J. C., Leuvenink, H. G. D., Daha, M. R., van Son, W. J., van Kooten, C., van Os, R. P., Hillebrands, J.‐L., Seelen, M. A. Critical role for complement receptor C5aR2 in the pathogenesis of renal ischemia‐reperfusion injury. FASEB J. 31, 3193–3204 (2017). www.fasebj.org
Niemann-Pick type C1 (NPC1) disease is a progressive lysosomal storage disorder caused by mutations of the NPC1 gene. While neurodegeneration is the most severe symptom, a large proportion of NPC1 ...patients also present with splenomegaly, which has been attributed to cholesterol and glycosphingolipid accumulation in late endosomes and lysosomes. However, recent data also reveal an increase in the inflammatory monocyte subset in the Npc1nih mouse model expressing an Npc1 null allele. We evaluated the contribution of hematopoietic cells to splenomegaly in NPC1 disease under conditions of hypercholesterolemia. We transplanted Npc1nih (Npc1 null mutation) or Npc1wt bone marrow (BM) into Ldlr−/− mice and fed these mice a cholesterol-rich Western-type diet. At 9 weeks after BM transplant, on a chow diet, the Npc1 null mutation increased plasma granulocyte-colony stimulating factor (G-CSF) by 2-fold and caused mild neutrophilia. At 18 weeks after BM transplant, including 9 weeks of Western-type diet feeding, the Npc1 mutation increased G-csf mRNA levels by ∼5-fold in splenic monocytes/macrophages accompanied by a ∼4-fold increase in splenic neutrophils compared with controls. We also observed ∼5-fold increased long-term and short-term hematopoietic stem cells (HSCs) in the spleen, and a ∼30–75% decrease of these populations in BM, reflecting HSC mobilization, presumably downstream of elevated G-CSF. In line with these data, four patients with NPC1 disease showed higher plasma G-CSF compared with age-matched and gender-matched healthy controls. In conclusion, we show elevated G-CSF levels and HSC mobilization in the setting of an Npc1 null mutation and propose that this contributes to splenomegaly in patients with NPC1 disease.
Expansion of hematopoietic stem cells (HSCs) is a 'holy grail' of regenerative medicine, as successful stem cell transplantations depend on the number and quality of infused HSCs. Although many ...attempts have been pursued to either chemically or genetically increase HSC numbers, neither clonal analysis of these expanded cells nor their ability to support mature blood lineages has been demonstrated. Here we show that miR-125a, at the single cell level, can expand murine long-term repopulating HSCs. In addition, miR-125a increases clone longevity, clone size and clonal contribution to hematopoiesis. Unexpectedly, we found that miR-125a expanded HSCs clones were highly homogenously distributed across multiple anatomical sites. Interestingly, these miR-125a overexpressing cells had enhanced mobility and were more frequently detected in the spleen. Our study reveals a novel, cell-intrinsically controlled mechanism by which HSC migration is regulated.
Genetical genomics is a strategy for mapping gene expression variation to expression quantitative trait loci (eQTLs). We performed a genetical genomics experiment in four functionally distinct but ...developmentally closely related hematopoietic cell populations isolated from the BXD panel of recombinant inbred mouse strains. This analysis allowed us to analyze eQTL robustness/sensitivity across different cellular differentiation states. Although we identified a large number (365) of "static" eQTLs that were consistently active in all four cell types, we found a much larger number (1,283) of "dynamic" eQTLs showing cell-type-dependence. Of these, 140, 45, 531, and 295 were preferentially active in stem, progenitor, erythroid, and myeloid cells, respectively. A detailed investigation of those dynamic eQTLs showed that in many cases the eQTL specificity was associated with expression changes in the target gene. We found no evidence for target genes that were regulated by distinct eQTLs in different cell types, suggesting that large-scale changes within functional regulatory networks are uncommon. Our results demonstrate that heritable differences in gene expression are highly sensitive to the developmental stage of the cell population under study. Therefore, future genetical genomics studies should aim at studying multiple well-defined and highly purified cell types in order to construct as comprehensive a picture of the changing functional regulatory relationships as possible.
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.
•Tolerance of oxidative DNA lesions ensures the genomic and functional integrity of hematopoietic stem and precursor cells.•Endogenous DNA damage–induced replication stress is associated with mitochondrial dysfunction.
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Adult somatic stem cells possess extensive self‐renewal capacity, as their primary role is to replenish aged and functionally impaired tissues. We have previously shown that the stem cell pool in ...short‐lived DBA/2 (D2) mice is reduced during aging, in contrast to long‐lived C57BL/6 (B6) mice. This suggests the existence of a genetically determined mitotic clock operating in stem cells, which possibly limits organismal aging. In the study reported here, unfractionated bone marrow (BM) cells or highly purified Lin−Sca‐1+c‐kit+ (LSK) cells were serially transplanted in lethally irradiated D2 and B6 mice. In both strains, serial transplantation resulted in a substantial loss of stem cell activity. However, as we estimate that in B6 mice, the maximum number of population doublings of primitive cells is approximately 30, in D2 mice this is only approximately 20, resulting in a 1,000–fold difference in expansion potential, irrespective of whether whole bone marrow or purified hematopoietic stem cells (HSCs) were transplanted. Interestingly, recipients reconstituted with serially transplanted BM cells were able to accept a freshly isolated graft without any further conditioning. Finally, we show that whereas transplantation of BM cells into healthy, nonconditioned, young B6 recipients does not lead to engraftment, young BM cells do engraft and provide multilineage reconstitution in nonirradiated aged mice. Our data clearly establish the relevance of an intrinsic, genetically controlled program associated with impaired stem cell functioning during aging.
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