Somatic cell nuclear transfer and transcription-factor-based reprogramming revert adult cells to an embryonic state, and yield pluripotent stem cells that can generate all tissues. Through different ...mechanisms and kinetics, these two reprogramming methods reset genomic methylation, an epigenetic modification of DNA that influences gene expression, leading us to hypothesize that the resulting pluripotent stem cells might have different properties. Here we observe that low-passage induced pluripotent stem cells (iPSCs) derived by factor-based reprogramming of adult murine tissues harbour residual DNA methylation signatures characteristic of their somatic tissue of origin, which favours their differentiation along lineages related to the donor cell, while restricting alternative cell fates. Such an 'epigenetic memory' of the donor tissue could be reset by differentiation and serial reprogramming, or by treatment of iPSCs with chromatin-modifying drugs. In contrast, the differentiation and methylation of nuclear-transfer-derived pluripotent stem cells were more similar to classical embryonic stem cells than were iPSCs. Our data indicate that nuclear transfer is more effective at establishing the ground state of pluripotency than factor-based reprogramming, which can leave an epigenetic memory of the tissue of origin that may influence efforts at directed differentiation for applications in disease modelling or treatment.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Embryonic stem cells provide an in vitro model for developmental biologists to study cell fate decisions during ontogenesis, while somatic stem cells allow physiologists to understand tissue ...homeostasis in the adult. The behavior of stem cells is dependent on an intimate relationship with a supportive niche. This brief review highlights some of the most important recent trends in stem cell biology, focusing in particular on the supportive microenvironments for both embryonic and adult stem cells. Known intrinsic and extrinsic molecular players from the best-characterized stem cell types are summarized, illuminating a number of shared environmental cues among tissues originating from all three embryonic germ layers.
Despite two decades of studies documenting the in vitro blood-forming potential of murine embryonic stem cells (ESCs), achieving stable long-term blood engraftment of ESC-derived hematopoietic stem ...cells in irradiated mice has proven difficult. We have exploited the Cdx-Hox pathway, a genetic program important for blood development, to enhance the differentiation of ESCs along the hematopoietic lineage. Using an embryonic stem cell line engineered with tetracycline-inducible Cdx4, we demonstrate that ectopic Cdx4 expression promotes hematopoietic mesoderm specification, increases hematopoietic progenitor formation, and, together with HoxB4, enhances multilineage hematopoietic engraftment of lethally irradiated adult mice. Clonal analysis of retroviral integration sites confirms a common stem cell origin of lymphoid and myeloid populations in engrafted primary and secondary mice. These data document the cardinal stem cell features of self-renewal and multilineage differentiation of ESC-derived hematopoietic stem cells.
Background:
The hematopoietic stem cell (HSC) niche constitutes a complex bone marrow (BM) microenvironment critical to tightly control HSC proliferation. Several stromal components have been ...associated to the HSC niche, including osteoblasts, mesenchymal stromal and progenitor cells, perivascular cells and adipocytes. Perturbation of the BM stromal compartment is capable of driving hematopoietic dysplasia and even leukemic transformation. Recently, the effect of reduced bone mineral density (BMD) on hematopoiesis was investigated in several cohorts, with conflicting results. Osteoporosis is characterized by both reduced BMD and microarchitectural deterioration, which constitute the most frequent alteration of the BM microenvironment. It still remains unclear to which extent modification of the BM microenvironment, in particular in the context of osteoporosis, influences blood cell production.
Aims:
To describe the association between lumbar spine BMD and microarchitecture (measured by the trabecular bone score ‐ TBS), and complete blood counts.
Methods:
We analyzed the complete peripheral blood counts and bone parameters of 1475 postmenopausal women taking part of the CoLaus/OsteoLaus cohort, a Caucasian population‐based sample in Lausanne, Switzerland. BMD and TBS were measured by two different Dual X‐rays Absorptiometry (DXA) machines (Hologic and GE Lunar) at 5‐year interval. For this study, we focused on patients with homeostatic hematopoiesis. Exclusion criteria were thus any active treatment or disease that could influence haematopoiesis and any active treatment for osteoporosis (excepted vitamin D, calcium and menopausal hormone replacement therapy ‐ HRT ‐). Bivariate and multivariate associations between each peripheral blood cell count and BMD or TBS were performed. Multivariable analyses were adjusted for age, body mass index (BMI), C‐reactive protein and HRT.
Results:
Our study included 803 (16.9% osteoporotic) and 901 (13.2% osteoporotic) women, respectively for the two timepoints. At the first timepoint of analysis, participants were on average 63‐year‐old, with a BMI of 25.6 kg/m^2; 15 (1.9%) had anemia, 29 (3.6%) leukopenia, and 5 (0.6%) thrombocytopenia.
No consistent significant associations between blood counts and BMD or TBS were found across bone markers or timepoints.
In order to investigate an effect of extreme values reflecting the highest and the lowest bone quality, we compared participants in the highest BMD and TBS tertiles and participants in the lowest BMD and TBS tertiles. Neutrophils were significantly different in the lowest BMD and TBS tertile (3.18 ± 0.09 vs. 3.47 ± 0.08 G/l, p = 0.028) at the first assessment. At the second assessment, significant differences were found for leucocytes (5.90 ± 0.11 vs. 5.56 ± 0.10 G/l, p = 0.033), lymphocytes (1.87 ± 0.04 vs. 1.72 ± 0.04 G/l p = 0.033) and monocytes (0.49 ± 0.01 vs. 0.46 ± 0.1 G/l, p = 0.033). No significant association was therefore reproducible between timepoints.
Summary/Conclusion:
In this cohort of postmenopausal women assessed at two separate timepoints and with two different DXA instruments, BM microenvironment changes related to bone condition did not have a reproductible impact on blood cell production in homeostasis. This study underlines the complexity of understanding the clinical relevance of changes in the BM, and prompt further research given disparate results obtained in other clinical scenarios, namely in the context of stress hematopoiesis.
Background:
Hematopoietic stem cells (HSCs) are a small group of cells that ensure a steady production of all mature blood cells throughout an organism's lifetime. HSCs mediate this process by giving ...rise to progenitors that in turn produce terminally differentiated mature blood cell lineages via several rounds of cell division and well‐orchestrated differentiation steps. Cellular metabolism has emerged as a crucial regulator guiding this complex process. Especially, HSCs differ from their committed progeny by relying primarily on anaerobic glycolysis rather than mitochondrial oxidative phosphorylation for energy production. This distinct metabolic state protects the HSCs from cellular damage inflicted by reactive oxygen species (ROS) in active mitochondria. However, whether this change in the metabolic program is the cause or a consequence of the unique function of HSCs remains unknown.
Aims:
Having previously shown that mitochondrial activity can be used as a reliable readout for HSC fate, here we asked if modulation of mitochondrial activity results in enhancement of HSC function.
Methods:
We used in vitro mitochondrial activity and in vivo long‐term blood reconstitution assays as readouts of murine and human HSC functionality.
Results:
We previously demonstrated that modulation of mitochondrial metabolism in murine and human HSCs, by chemical uncouplers of the electron transport chain or via NAD+ boosting agent Nicotinamide Riboside (NR), results in better long‐term blood production in serially transplanted mice (Vannini N∗, Girotra M∗. et al., Nature Communication 2016 and, Vannini et al., Cell Stem Cell, in press).
Here we proceeded to carry out a screen, using mitochondrial activity as readout, to identify metabolic modulators that enhance HSC function. We found two novel candidates, a natural compound and a vitamin precursor, that modulate mitochondrial activity in both mouse and human HSCs, and resulted in enhanced HSC function post bone‐marrow transplantation. Interestingly, we found that these candidates mediate their effects partially by inducing mitophagy, supporting recent studies highlighting the role of mitophagy as a key driver of HSC function. Moreover, our preliminary analysis reveals that they mediate similar effects in aged human HSCs, making them ideal candidates to revert age‐associated myeloid bias in human patients.
Summary/Conclusion:
Our data establishes a causal relationship between mitochondrial metabolism and HSC function via mitophagy. It also provides a valuable tool to identify optimal ex vivo conditions for HSC expansion, to improve the outcome for patients suffering from bone marrow insufficiency and to restore the functionality of the immune system in aged individuals.
Endothelial cells and leptin receptor
(LepR
) stromal cells are critical sources of haematopoietic stem cell (HSC) niche factors, including stem cell factor (SCF), in bone marrow. After irradiation ...or chemotherapy, these cells are depleted while adipocytes become abundant. We discovered that bone marrow adipocytes synthesize SCF. They arise from Adipoq-Cre/ER
progenitors, which represent ∼5% of LepR
cells, and proliferate after irradiation. Scf deletion using Adipoq-Cre/ER inhibited haematopoietic regeneration after irradiation or 5-fluorouracil treatment, depleting HSCs and reducing mouse survival. Scf from LepR
cells, but not endothelial, haematopoietic or osteoblastic cells, also promoted regeneration. In non-irradiated mice, Scf deletion using Adipoq-Cre/ER did not affect HSC frequency in long bones, which have few adipocytes, but depleted HSCs in tail vertebrae, which have abundant adipocytes. A-ZIP/F1 'fatless' mice exhibited delayed haematopoietic regeneration in long bones but not in tail vertebrae, where adipocytes inhibited vascularization. Adipocytes are a niche component that promotes haematopoietic regeneration.