Cell size is a determinant of stem cell potential during aging (HSC treatments RNA-seq dataset)
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ABSTRACT: Stem cells are remarkably small in size. Human hematopoietic stem cells (HSCs) measure a mere 7 μm in diameter. Whether small size is important for stem cell function is unknown. We find that murine HSCs enlarge under conditions known to decrease stem cell function. This decreased fitness of large HSCs is due to reduced proliferative potential. We further show that preventing HSC enlargement by inhibiting macromolecule biosynthesis or reducing the size of large HSCs by shortening G1 averts the loss of stem cell potential. Naturally large HSCs also exhibit decreased stem cell potential indicating that large size characterizes exhausted HSCs under physiological conditions. Finally, we show that our findings are relevant to aging. A fraction of murine and human HSCs enlarge during aging. Preventing this age-dependent enlargement improves HSC function. We conclude that small cell size is important for stem cell function and propose that stem cell enlargement contributes to their functional decline during aging.
Project description:Stem cells are remarkably small in size. Human hematopoietic stem cells (HSCs) measure a mere 7 μm in diameter. Whether small size is important for stem cell function is unknown. We find that murine HSCs enlarge under conditions known to decrease stem cell function. This decreased fitness of large HSCs is due to reduced proliferative potential. We further show that preventing HSC enlargement by inhibiting macromolecule biosynthesis or reducing the size of large HSCs by shortening G1 averts the loss of stem cell potential. Naturally large HSCs also exhibit decreased stem cell potential indicating that large size characterizes exhausted HSCs under physiological conditions. Finally, we show that our findings are relevant to aging. A fraction of murine and human HSCs enlarge during aging. Preventing this age-dependent enlargement improves HSC function. We conclude that small cell size is important for stem cell function and propose that stem cell enlargement contributes to their functional decline during aging.
Project description:Increasing evidence links metabolic activity and cell growth to decline in hematopoietic stem cell (HSC) function during aging. The Lin28b/Hmga2 pathway controls tissue development and in the hematopoietic system the postnatal downregulation of this pathway causes a decrease in self renewal of adult HSCs compared to fetal HSCs. Igf2bp2 is an RNA binding protein and a mediator of the Lin28b/Hmga2 pathway, which regulates metabolism and growth signaling by influencing RNA stability and translation of its target genes. It is currently unknown whether Lin28/Hmga2/Igf2bp2 signaling impacts on aging-associated impairments in HSC function and hematopoiesis. Here, we analyzed homozygous Igf2bp2 germline knockout mice and wildtype control animals to address this question. The study shows that Igf2bp2 deletion rescues aging phenotypes of the hematopoietic system, such as the expansion of HSC numbers in bone marrow and the biased increase of myeloid cells in peripheral blood. This rescue of hematopoietic aging coincides with reduced mitochondrial metabolism and glycolysis in Igf2bp2-/- HSCs compared to Igf2bp2+/+ HSCs. Conversely, Igf2bp2 overexpression activates protein synthesis pathways in HSCs and leads to a rapid loss of self renewal by enhancing myeloid skewed differentiation in an mTOR/PI3K-dependent manner. Together, these results show that Igf2bp2 regulates energy metabolism and growth signaling in HSCs and that the activity of this pathways influences self renewal, differentiation, and aging of HSCs.
Project description:During aging, hematopoietic stem cell (HSC) function progressively declines which can lead to reduced blood cell production and regeneration, impaired lymphoid cell production and ineffective erythropoiesis. In this study, we uncovered that during aging the cell surface presentation of the type-1 transmembrane protein P-selectin (CD62P, encoded by Selp) increases in a large fraction of HSCs. Notably, expression of P-selectin molecularly and functionally dichotomized the aging HSC pool; stem cells presenting with high abundance of P-selectin were hallmarked by aging-associated gene expression programs and reduced repopulation upon regenerative stress. Overexpression of Selp in young HSCs was sufficient to impair long-term reconstitution potential and repress erythropoiesis. Moreover, IL-1β, which is chronically elevated in the aged bone marrow, triggered Selp expression in HSCs. The aged transcriptome, including Selp, was largely restored when aged HSCs were transplanted to young mice. Mechanistically, we uncovered that appropriate stimulation of P-selectin by its primary ligand, P-selectin glycoprotein ligand-1 (PSGL-1), suppressed aging-associated gene expression and reversely, lack of P-selectin signaling led to HSC premature aging. Collectively, our study uncovered a novel functional role of P-selectin engagement in regulating HSC regeneration and driving stem cell aging when perturbed.
Project description:Loss of immune function and an increased incidence of myeloid leukemia are two of the most clinically significant consequences of aging of the hematopoietic system. To better understand the mechanisms underlying hematopoietic aging, we evaluated the cell intrinsic functional and molecular properties of highly purified long-term hematopoietic stem cells (LT-HSCs) from young and old mice. We found that LT-HSC aging was accompanied by cell autonomous changes, including increased stem cell self-renewal, differential capacity to generate committed myeloid and lymphoid progenitors, and diminished lymphoid potential. Expression profiling revealed that LT-HSC aging was accompanied by the systemic down-regulation of genes mediating lymphoid specification and function and up-regulation of genes involved in specifying myeloid fate and function. Moreover, LT-HSCs from old mice expressed elevated levels of many genes involved in leukemic transformation. These data support a model in which age-dependent alterations in gene expression at the stem cell level presage downstream developmental potential and thereby contribute to age-dependent immune decline, and perhaps also to the increased incidence of leukemia in the elderly.
Project description:Loss of immune function and an increased incidence of myeloid leukemia are two of the most clinically significant consequences of aging of the hematopoietic system. To better understand the mechanisms underlying hematopoietic aging, we evaluated the cell intrinsic functional and molecular properties of highly purified long-term hematopoietic stem cells (LT-HSCs) from young and old mice. We found that LT-HSC aging was accompanied by cell autonomous changes, including increased stem cell self-renewal, differential capacity to generate committed myeloid and lymphoid progenitors, and diminished lymphoid potential. Expression profiling revealed that LT-HSC aging was accompanied by the systemic down-regulation of genes mediating lymphoid specification and function and up-regulation of genes involved in specifying myeloid fate and function. Moreover, LT-HSCs from old mice expressed elevated levels of many genes involved in leukemic transformation. These data support a model in which age-dependent alterations in gene expression at the stem cell level presage downstream developmental potential and thereby contribute to age-dependent immune decline, and perhaps also to the increased incidence of leukemia in the elderly. 3 old mice and 5 young mice were assayed
Project description:Aging of hematopoietic stem cells (HSCs) leads to several functional changes, including alterations affecting self-renewal and differentiation. While it is well established that many of the age-induced changes are intrinsic to HSCs, less is known about the stability of this state. Here, we entertained the hypothesis that HSC aging is driven by the acquisition of permanent genetic mutations. To examine this issue at a functional level in vivo, we applied induced pluripotent stem (iPS) cell reprogramming of aged hematopoietic progenitors and allowed the resulting aged-derived iPS cells to reform hematopoiesis via blastocyst complementation. Next, we functionally characterized iPS-derived HSCs in primary chimeras and following the transplantation of 're-differentiated' HSCs into new hosts; the gold standard to assess HSC function. Our data demonstrate remarkably similar functional properties of iPS-derived and endogenous blastocyst-derived HSCs, despite the extensive chronological and proliferative age of the former. Our results therefore favor a model in which an underlying, but reversible, epigenetic component is a hallmark of HSC aging rather than being driven by an increased DNA mutation burden. Hematopoietic stem cells (HSC) have been sorted out from young and aged steady-state mice, and from recipients transplanted with young and aged bone marrow. Generated iPS and commercially available ES cells were also sorted and analyzed.
Project description:Maintaining proteostasis is key to resisting stress and to promoting healthy aging. Proteostasis is necessary to preserve stem cell function, but little is known about the mechanisms that regulate proteostasis during stress in stem cells, and whether disruptions in proteostasis contribute stem cell aging is largely unexplored. We determined that ex vivo cultured mouse and human hematopoietic stem cells (HSCs) rapidly increase protein synthesis. This challenge to HSC proteostasis was associated with nuclear accumulation of Hsf1, and deletion of Hsf1 impaired HSC maintenance ex vivo. Strikingly, supplementing cultures with small molecules that enhance Hsf1 activation partially suppressed protein synthesis, rebalanced proteostasis, and supported retention of HSC serial reconstituting activity. Although Hsf1 was dispensable for young adult HSCs in vivo, Hsf1 deficiency increased protein synthesis and impaired the reconstituting activity of middle-aged HSCs. Hsf1 thus promotes proteostasis and the regenerative activity of HSCs in response to culture stress and aging.
Project description:Maintaining proteostasis is key to resisting stress and to promoting healthy aging. Proteostasis is necessary to preserve stem cell function, but little is known about the mechanisms that regulate proteostasis during stress in stem cells, and whether disruptions in proteostasis contribute stem cell aging is largely unexplored. We determined that ex vivo cultured mouse and human hematopoietic stem cells (HSCs) rapidly increase protein synthesis. This challenge to HSC proteostasis was associated with nuclear accumulation of Hsf1, and deletion of Hsf1 impaired HSC maintenance ex vivo. Strikingly, supplementing cultures with small molecules that enhance Hsf1 activation partially suppressed protein synthesis, rebalanced proteostasis, and supported retention of HSC serial reconstituting activity. Although Hsf1 was dispensable for young adult HSCs in vivo, Hsf1 deficiency increased protein synthesis and impaired the reconstituting activity of middle-aged HSCs. Hsf1 thus promotes proteostasis and the regenerative activity of HSCs in response to culture stress and aging.
Project description:Adult and fetal hematopoietic stem cells (HSCs) display a glycolytic phenotype, which is required for maintenance of stemness; however, whether mitochondrial respiration is required to maintain HSC function is not known. Here we report that loss of the mitochondrial complex III subunit Rieske iron sulfur protein (RISP) in fetal mouse HSCs allows them to proliferate but impairs their differentiation, resulting in anemia and prenatal death. RISP null fetal HSCs displayed impaired respiration resulting in a decreased NAD+/NADH ratio. RISP null fetal HSCs and progenitors exhibited an increase in both DNA and histone methylation concomitant with increases in 2-hydroxyglutarate (2-HG), a metabolite known to inhibit DNA and histone demethylases. RISP inactivation in adult HSCs also impaired respiration resulting in loss of quiescence resulting in severe pancytopenia and lethality. Thus, respiration is dispensable for adult or fetal HSC proliferation, but essential for fetal HSC differentiation and maintenance of adult HSC quiescence.
Project description:Hematopoietic stem cells (HSCs) and their progeny sustain lifetime hematopoiesis. Aging alters HSC function, number, and composition and increases risk of hematological malignancies, but how these changes occur in HSCs remains unclear. Signaling via p38MAPK has been proposed as a candidate mechanism underlying induction of HSC aging. Here, using genetic models of both chronological and premature aging, we describe a multimodal role for p38α, the major p38MAPK isozyme in hematopoiesis, in HSC aging. We report that p38α regulates differentiation bias and sustains transplantation capacity of HSCs in the early phase of chronological aging (from young to 1-year-old). However, p38α decreased HSC transplantation capacity in the late progression phase of chronological aging (from 1- to 2-years-old). Furthermore, co-deletion of p38α in mice deficient in Ataxia-telangiectasia mutated (Atm), a model of premature aging, exacerbated aging-related HSC phenotypes seen in Atm single mutant mice. Mechanistically, p38α makes a positive contribution to inflammation during the late phase aging, resulting in defects in 2-year-old HSCs. Overall, we propose multiple functions of p38MAPK, which both promotes and suppresses HSC aging context-dependently.