mTOR inhibitor INK128 attenuates dextran sodium sulfate-induced colitis by promotion of MDSCs on Treg cell expansion

Accumulating evidence has shown that mammalian target of rapamycin (mTOR) pathway and myeloid-derived suppressor cells (MDSCs) are involved in pathogenesis of inflammatory bowel diseases (IBDs). INK128 is a novel mTOR kinase inhibitor in clinical development. However, the exact roles of MDSCs and INK128 in IBD are unclear. Here, we showed that the INK128 treatment enhanced the resistance of mice to dextran sodium sulfate (DSS)–induced colitis and inhibited the differentiation of MDSCs into macrophages. Moreover, interferon (IFN)-α level was elevated in INK128-treated colitis mice. When stimulated with IFN-α in vitro, MDSCs showed a superior immunosuppression activity. Of note, the regulatory T cells (Tregs) increased but Th1 cells decreased in INK128-treated colitis mice. These results indicate that mTOR inhibitor INK128 attenuates DSS-induced colitis via Treg expansion promoted by MDSCs. Our work provides a new evidence that INK128 is potential to be a therapeutic drug on DSS-induced colitis via regulating MDSCs as well as maintaining Treg expansion.     

From growing to secreting: New roles for mTOR in aging cells

Deregulation of the nutrient sensitive mTOR signaling pathway has been recently involved in several age-related diseases, and pharmacological blockade of mTOR extends longevity in model organisms and in mice. Mechanistic studies in vitro have shed light on the role of mTOR-dependent growth signals in promoting senescence and exhaustion of quiescent stem cells, thus linking excess nutrients to tissue ageing. Novel findings add complexity to this theoretical framework, revealing that mTOR cooperates with autophagy to promote the "secretory phenotype" of senescent cells and the release of factors known to contribute to defective renewal and dysfunction of aging tissues. Thus, both cell autonomous and cell non-autonomous mechanisms link unchecked mTOR activity to cell senescence and by extension to the aging process.     

骨髓问充质干细胞移植对VCD所致卵巢损伤的修复研究

目的：探讨小鼠骨髓间充质干细胞（MSCs）移植对去氧乙烯基环己烯（VCD）所致卵巢早衰治疗的可行性。方法：采用VCD（160mgkg^-l,day^-1）连续腹腔注射来诱导小鼠卵巢早衰。每侧卵巢注射转染了绿色荧光基因小鼠骨髓来源的MSCs,于移植后14、28天及45天,取各组血液标本及卵巢组织,同时观察小鼠动情周期的变化;酶联免疫法检测血清FSH、LH水平,显微镜下观察MSC在卵巢的分布。结果：MSCs移植后各组均可见绿色荧光,并且主要分布于卵巢间质区,卵巢泡膜细胞区也可见绿色荧光细胞。MSCs组动情周期较实验对照组缩短,FSH与LH水平较实验对照组低,差异具有显著性。结论：骨髓间充质干细胞可改善卵巢早衰小鼠的卵巢内分泌功能,并且长时间存在于卵巢组织。骨髓间充质干细胞可能成为卵巢早衰治疗的新方法。     

Can ovarian infertility be treated with bone marrow- or ovary-derived germ cells?

A year ago, reproductive biologists and general public were astonished with evidence reported by Johnson et al. in Nature 428:145 that mammalian ovaries possess persisting large germline stem cells, which allegedly enable follicular renewal in adult females. Recently, the same research group declared such view obscure, and reported that mammalian oocytes originate from putative germ cells in bone marrow and are distributed by peripheral blood to the ovaries (Cell 122:303). While neglecting available data on the germ cell origin from the ovarian surface epithelium (OSE) in adult mouse and human females and complexity of follicular renewal in humans, the authors widely extrapolated their observations on formation of allogeneic oocytes after bone marrow (or blood) transplantation in ovaries of adult mice treated with cytostatics to clinical implications in the public media. Yet, the resulting outcome that such allogeneic oocytes may enable the propagation of ovarian cycles is a poor alleviation for the women with ovarian infertility. Women lacking primary follicles, or carrying follicles with low quality eggs persisting in aging ovaries, are not concerned about the lack of menstrual cycles or ovarian steroids, but about virtually no chance of having genetically related children. Johnson et al. also reported that the germ cell formation in bone marrow disappears in ovariectomized mice. Such observation, however, raises solid doubts on the bone marrow origin of oocytes. Since germ cells developing from the OSE cells of adult human ovaries during periodical follicular renewal are known to enter blood vessels in order to enable formation of primary follicles at distant ovarian sites, they also contaminate peripheral blood and hence bone marrow. Better knowledge on the complexity of follicular renewal in humans and exploration of a potential of human OSE cells to produce new oocytes in vitro are essential for novel approaches to the autologous treatment of premature ovarian failure and age induced ovarian infertility.     

Human placenta‐derived mesenchymal stem cells inhibit apoptosis of granulosa cells induced by IRE1α pathway in autoimmune POF mice

Previous studies have shown that the ovarian failure in autoimmune‐induced premature ovarian failure (POF) mice could be improved by the transplantation of human placenta‐derived mesenchymal stem cells (hPMSCs); however, the protective mechanism of hPMSCs transplantation on ovarian dysfunction remains unclear. Ovarian dysfunction is closely related to the apoptosis of granulosa cells (GCs). To determine the effects of hPMSCs transplantation on GCs apoptosis, an autoimmune POF mice model was established with zona pellucida glycoprotein 3 (ZP3) peptide. It is reported that the inositol‐requiring enzyme 1α (IRE1α) and its downstream molecules play a central role in the endoplasmic reticulum (ER) stress‐induced apoptosis pathway. So the aim of this study is to investigate whether hPMSCs transplantation attenuated GCs apoptosis via inhibiting ER stress IRE1α signaling pathway. The ovarian dysfunction, follicular dysplasia, and GCs apoptosis were observed in the POF mice. And the IRE1α pathway was activated in ovaries of POF mice, as demonstrated by, increased X‐box binding protein 1 (XBP1), up‐regulated 78 kDa glucose‐regulated protein (GRP78) and caspase‐12. Following transplantation of hPMSCs, the ovarian structure and function were significantly improved in POF mice. In addition, the GCs apoptosis was obviously attenuated and IRE1α pathway was significantly inhibited. Transplantation of hPMSCs suppressed GCs apoptosis‐induced by ER stress IRE1α signaling pathway in POF mice, which might contribute to the hPMSCs transplantation‐mediating ovarian function recovery.     

Endocrine alterations and signaling changes associated with declining ovarian function and advanced biological aging in follicle-stimulating hormone receptor haploinsufficient mice

Reproductive aging in female mammals is characterized by a progressive decline in fertility due to loss of follicles and reduced ovarian steroidogenesis. In this study we examined some of the endocrine and signaling parameters that might contribute to a decrease in ovulation and reproductive performance of mice with haploinsufficiency of the FSH receptor (FSH-R). For this purpose we compared ovarian changes and hormone levels in FSH-R heterozygous (+/-) and wild-type mice of different ages (3, 7, and 12 mo). Hormone-induced ovulations in immature and 3-mo-old +/- mice were consistently lower. The number of corpora lutea (CL) were lower at 3 and 7 mo, and none were present in 1-yr-old +/- females. The plasma steroid and gonadotropin levels exhibited changes associated with typical ovarian aging. Plasma FSH and LH levels were higher in 7-mo-old +/- mice, but FSH levels continued to rise in both genotypes by 1 yr. Serum estradiol and progesterone were lower in +/- mice at all ages, and testosterone was several-fold higher in 7-mo-old and 1-yr-old +/- mice. Inhibin alpha (Western blot) appeared to be lower in +/- ovaries at all ages. FSH-R (FSH* binding) declined steadily from 3 mo and reaching the lowest point at 1 yr. LH receptor (LH* binding) was high in the 1-yr-old ovary, and expression was localized in the stroma and interstitial cells. Our findings demonstrate that haploinsufficiency of the FSH-R gene could cause premature exhaustion of the gonadal reserves previously noted in these mice. This is accompanied by age-related changes in the hypothalamic-pituitary axis. As these features in our FSH-R +/- mice resemble reproductive failure occurring in middle-age women, further studies in this model might provide useful insights into the mechanisms underlying ovarian aging.     

Current understanding of ovarian aging

The reproductive system of human female exhibits a much faster rate of aging than other body systems. Ovarian aging is thought to be dominated by a gradual decreasing numbers of follicles, coinciding with diminished quality of oocytes. Menopause is the final step in the process of ovarian aging. This review focuses on the mechanisms underlying the ovarian aging involving a poor complement of follicles at birth and a high rate of attrition each month, as well as the alternated endocrine factors. We also discuss the possible causative factors that contribute to ovarian aging, e.g., genetic factors, accumulation of irreparable damage of microenvironment, pathological effect and other factors. The appropriate and reliable methods to assess ovarian aging, such as quantification of follicles, endocrine measurement and genetic testing have also been discussed. Increased knowledge of the ovarian aging mechanisms may improve the prevention of premature ovarian failure.     

Fecal microbiota transplantation from young donor mice improves ovarian function in aged mice

Advanced maternal age is characterized by declines in the quantity and quality of oocytes in the ovaries, and the aging process is accompanied by changes in gut microbiota composition. However, little is known about the relationship between gut microbiota and ovarian aging. By using fecal microbiota transplantation (FMT) to transplant material from young (5-week-old) into aged (42-week-old) mice, we find that the composition of gut microbiota in FMT-treated mice presents a “younger-like phenotype” and an increase of commensal bacteria, such as Bifidobacterium and Ruminococcaceae. Moreover, the FMT-treated mice show increased anti-inflammatory cytokine IL-4 and decreased pro-inflammatory cytokine IFN-γ. Fertility tests for assessing ovarian function reveal that the first litter size of female FMT-treated mice is significantly higher than that of the non-FMT group. Morphology analysis demonstrates a dramatic decrease in follicle atresia and apoptosis as well as an increase in cellular proliferation in the ovaries of the FMT-treated mice. Our results also show that FMT improves the immune microenvironment in aged ovaries, with decreased macrophages and macrophage-derived multinucleated giant cells (MNGCs). These results suggest that FMT from young donors could be a good choice for delaying ovarian aging.     

Smurf2 regulates hematopoietic stem cell self‐renewal and aging

The age‐dependent decline in the self‐renewal capacity of stem cells plays a critical role in aging, but the precise mechanisms underlying this decline are not well understood. By limiting proliferative capacity, senescence is thought to play an important role in age‐dependent decline of stem cell self‐renewal, although direct evidence supporting this hypothesis is largely lacking. We have previously identified the E3 ubiquitin ligase Smurf2 as a critical regulator of senescence. In this study, we found that mice deficient in Smurf2 had an expanded hematopoietic stem cell (HSC) compartment in bone marrow under normal homeostatic conditions, and this expansion was associated with enhanced proliferation and reduced quiescence of HSCs. Surprisingly, increased cycling and reduced quiescence of HSCs in Smurf2‐deficient mice did not lead to premature exhaustion of stem cells. Instead, HSCs in aged Smurf2‐deficient mice had a significantly better repopulating capacity than aged wild‐type HSCs, suggesting that decline in HSC function with age is Smurf2 dependent. Furthermore, Smurf2‐deficient HSCs exhibited elevated long‐term self‐renewal capacity and diminished exhaustion in serial transplantation. As we found that the expression of Smurf2 was increased with age and in response to regenerative stress during serial transplantation, our findings suggest that Smurf2 plays an important role in regulating HSC self‐renewal and aging.     

壳寡糖对病理性卵巢衰退小鼠免疫功能和生殖功能的作用

目的：探讨壳寡糖促进病理性卵巢功能衰退小鼠生殖功能和免疫功能恢复的可能性。方法：选用43只生育旺盛期雌性小鼠,除正常对照组（n=8）外,其它通过白消安/环磷酰胺构建病理性卵巢功能衰退模型模拟卵巢功能早衰,随机选取3只,卵巢切片HE染色观察卵泡情况以判断不孕模型。构建成功后将余下32只随机平均分为4组（n=8）,经不同剂量壳寡糖（0,100,200,300 mg/（kg·d））灌胃后,比较组间卵巢、脾脏、胸腺脏体比的变化,观察卵泡情况、检测腹腔巨噬细胞吞噬能力、外周血雌二醇（E₂）及孕酮（P）水平,检测卵巢生殖上皮细胞中生殖细胞标志物小鼠血管同源物（MVH）、干细胞标志物OCT-4以及卵巢中免疫因子肿瘤坏死因子α（TNF-α）、白介素-2（IL-2）、白介素-6（IL-6）表达量的变化,并分析生殖干细胞标记物表达水平变化与免疫因子表达水平变化的相关关系。结果：随壳寡糖灌胃剂量的增加,卵巢、脾脏和胸腺脏体比同步增高;卵巢中总卵泡数及各级卵泡数都呈递增趋势;外周血E2水平递增,P水平呈递减趋势;腹腔巨噬细胞吞噬功能随剂量增高而增强;生殖干细胞标记物和免疫因子的表达水平均呈显著递增趋势,表明生殖干细胞标记物的表达水平与免疫因子表达水平的变化呈显著的正相关关系（P < 0.05）。结论：壳寡糖可改善病理性卵巢功能早衰小鼠的免疫功能,促进雌性生殖干细胞增殖、分化,从而促进卵巢病理性早衰机体生殖功能在一定程度上的恢复。     

Nicotinamide riboside intervention alleviates hematopoietic system injury of ionizing radiation-induced premature aging mice

Radiotherapy destroys cancer cells and inevitably harms normal human tissues, causing delayed effects of acute radiation exposure (DEARE) and accelerating the aging process in most survivors. However, effective methods for preventing premature aging induced by ionizing radiation are lacking. In this study, the premature aging mice of DEARE model was established after 6 Gy total body irradiation (TBI). Then the therapeutic effects and mechanism of nicotinamide riboside on the premature aging mice were evaluated. The results showed that 6 Gy TBI induced premature aging of the hematopoietic system in mice. Nicotinamide riboside treatment reversed aging spleen phenotypes by inhibiting cellular senescence and ameliorated serum metabolism profiles. Further results demonstrated that nicotinamide riboside supplementation alleviated the myeloid bias of hematopoietic stem cells and temporarily restored the regenerative capacity of hematopoietic stem cells probably by mitigating the reactive oxygen species activated GCN2/eIF2α/ATF4 signaling pathway. The results of this study firstly indicate that nicotinamide riboside shows potential as a DEARE therapeutic agent for radiation-exposed populations and patients who received radiotherapy.     

Adult Sox2+ stem cell exhaustion in mice results in cellular senescence and premature aging

Aging is characterized by a gradual functional decline of tissues with age. Adult stem and progenitor cells are responsible for tissue maintenance, repair, and regeneration, but during aging, this population of cells is decreased or its activity is reduced, compromising tissue integrity and causing pathologies that increase vulnerability, and ultimately lead to death. The causes of stem cell exhaustion during aging are not clear, and whether a reduction in stem cell function is a cause or a consequence of aging remains unresolved. Here, we took advantage of a mouse model of induced adult Sox2+ stem cell depletion to address whether accelerated stem cell depletion can promote premature aging. After a short period of partial repetitive depletion of this adult stem cell population in mice, we observed increased kyphosis and hair graying, and reduced fat mass, all of them signs of premature aging. It is interesting that cellular senescence was identified in kidney after this partial repetitive Sox2+ cell depletion. To confirm these observations, we performed a prolonged protocol of partial repetitive depletion of Sox2+ cells, forcing regeneration from the remaining Sox2+ cells, thereby causing their exhaustion. Senescence specific staining and the analysis of the expression of genetic markers clearly corroborated that adult stem cell exhaustion can lead to cellular senescence induction and premature aging.     

Phosphoglycerate mutase family member 5 maintains oocyte quality via mitochondrial dynamic rearrangement during aging

Decline in ovarian reserve with aging is associated with reduced fertility and the development of metabolic abnormalities. Once mitochondrial homeostasis is imbalanced, it may lead to poor reproductive cell quality and aging. However, Phosphoglycerate translocase 5 (PGAM5), located in the mitochondrial membrane, is associated with necroptosis, apoptosis, and mitophagy, although the underlying mechanisms associated with ovarian aging remain unknown. Therefore, we attempted to uncover whether the high phosphoglycerate mutant enzyme family member 5 (PGAM5) expression is associated with female infertility in cumulus cells, and aims to find out the underlying mechanism of action of PGAM5. We found that PGAM5 is highly expressed and positively associated with aging, and has the potential to help maintain and regulate mitochondrial dynamics and metabolic reprogramming in aging granulosa cells, ovaries of aged female mice, and elderly patients. PGAM5 undergoes activation in the aging group and translocated to the outer membrane of mitochondria, co‐regulating DRP1; thereby increasing mitochondrial fission. A significant reduction in the quality of mitochondria in the aging group, a serious imbalance, and a significant reduction in energy, causing metabolism shift toward glycolysis, were also reported. Since PGAM5 is eliminated, the mitochondrial function and metabolism of aging cells are partially reversed. A total of 70 patients undergoing in vitro fertilization (IVF) treatment were recruited in this clinical study. The high expression of PGAM5 in the cumulus cells is negatively correlated with the pregnancy rate of infertile patients. Hence, PGAM5 has immense potential to be used as a diagnostic marker.     

Postnatal androgenization induces premature aging of rat ovaries

In the present paper, we report that ovaries of adult rats treated with testosterone propionate (TP) on a critical postnatal Day 5 exhibit histologic and immunohistochemical findings which resemble those of the anovulatory ovaries in middle-aged female rats. The sterile rat model has been long known whereas ovarian failure seems to be a reason for anovulation with normal hypothalamo-pituitary-gonadotropin background. Appropriate function of ovarian steroidogenic cells is also regulated by mesenchymal cells. To characterize the ovarian failure, we studied the histology, luteinizing hormone receptor (LHR) expression, and characterized changes of vascular pericytes, T cells, and dendritic cells in ovarian steroidogenic compartments consisting of interstitial cells (ISC) of ovarian interstitial glands, and granulosa and theca interna cells of ovarian follicles. Normal adult ovaries contained 63% of mature interstitial glands. The mature ISC exhibited moderate cytoplasmic and strong surface LHR expression and fine (<5 micrometer) cytoplasmic vacuoles (ISC of 'luteal type'). They originated from young ISC of 'thecal type,' which exhibited strong cytoplasmic LHR expression. Remaining 37% were aged interstitial glands, which consisted of aged ISC (increased cytoplasmic vacuolization, nuclear pyknosis, and reduced surface LHR expression) and regressing ISC (weak cytoplasmic and no surface LHR expression). However, no mature ISC of 'luteal type' were detected in anovulatory ovaries of adult rats (45- and 60-day-old) injected with TP (100 or 500 microgram) on postnatal Day 5 (TP rats). Their ovaries contained 96% of aged interstitial glands with aged and regressing ISC. Remaining 4% were abnormal interstitial glands with direct transition of young ISC of 'thecal type' into aged ISC (young/aged glands). Lack of mature ISC, and similar amount of aged (96%) and young/aged interstitial glands (4%) was also detected in anovulatory ovaries of untreated persistently estrous middle-aged (10-month-old) females (aging PE rats). The aging process in TP and aging PE rats was accompanied by regression of vascular pericytes, T cells, and dendritic cells within the interstitial glands. In addition, anovulatory ovaries of TP rats and aging PE females contained mature follicles exhibiting LHR overexpression by granulosa cells, and aged (cystic) follicles with reduced layers of granulosa cells lacking LHR expression. In contrast, when the rats were injected with 500 microgram of TP later, on postnatal Day 10, the adult females exhibited estrous cycles and normal ovaries with corpora lutea. These results show that injection of TP during the critical postnatal period causes a lack of mature and preponderance of aged ISC in adult ovaries, accompanied by degeneration of mesenchymal cells. We suggest that mesenchymal cells regulate qualitative aspects of tissue-specific cells, and this function of mesenchymal cells is programmed during the critical period of development.     

Female XX sex chromosomes increase survival and extend lifespan in aging mice

Female longevity is observed in humans and much of the animal kingdom, but its causes remain elusive. Using a genetic manipulation that generates XX and XY mice, each with either ovaries or testes, we show that the female XX sex chromosome complement increases survival during aging in male and female mice. In combination with ovaries, it also extends lifespan. Understanding causes of sex‐based differences in aging could lead to new pathways to counter age‐induced decline in both sexes.     

Vasoactive intestinal peptide deficiency promotes ovarian dysfunction associated to a proinflammatory microenvironment reminiscent of premature aging

Complex immune regulation during pregnancy is required to ensure a successful pregnancy outcome. Vasoactive intestinal peptide (VIP) has local immunoregulatory effects on the ovary, uterus and maternal-fetal interface that favor a tolerogenic maternal microenvironment. Since the VIP Knockout (KO) mice are subfertile, we investigated the mechanisms underlying the effects of VIP deficiency on ovarian physiology and immune homeostasis. Therefore, we studied VIP KO, deficient (HT) and wild type (WT) female mice in estrus at 3 or 8 months of age. Young KO mice showed abnormal cycle timing and regularity associated with dysfunctional ovaries. Ovaries presented higher number of atretic follicles and reduced number of corpora lutea leading to a lower ovulation rates. Part of the VIP KO mice (25 %) failed to ovulate or ovulated oocytes incompetent to be fertilized (50 %). In particular, ovaries of young KO mice exhibited features of premature aging accompanied by a pro-inflammatory milieu with increased levels of IL-1β. A unique macrophage subpopulation identified as “foamy macrophages” was found. On the other hand, aged VIP KO females did not gain body weight probably due to the sustained production of E2. Finally, the adoptive transfer of FOXP3+ cells to infertile VIP KO females resulted in their selective recruitment to the ovary. It increased FOXP3/RORγt and TGFβ/IL-6 ratio improving ovarian microenvironment and pregnancy rate. The present results suggest that VIP contributes to ovarian homeostatic mechanisms required for a successful pregnancy.     

Mouse Offspring Derived from Fetal Ovaries or Reaggregates Which were Cultured and Transplanted into Adult Females

Primordial germ cells (PGCs) and gonia could be promising novel targets and vehicles for manipulation of the mammalian germ line. To make such manipulation a practical possibility, PGCs or gonia must be allowed to produce gametes and offspring after they were isolated from embryos and manipulated in culture. As the first step to develop such research strategy, we obtained offspring from mouse oogonia which were isolated from embryonic ovaries and cultured as dispersed cells before transplantation into female mice as reaggregates.     

Skin-Derived Mesenchymal Stem Cells Help Restore Function to Ovaries in a Premature Ovarian Failure Mouse Model

Skin-derived mesenchymal stem cells (SMSCs) can differentiate into the three embryonic germ layers. For this reason, they are considered a powerful tool for therapeutic cloning and offer new possibilities for tissue therapy. Recent studies showed that skin-derived stem cells can differentiate into cells expressing germ-cell specific markers in vitro and form oocytes in vivo. The idea that SMSCs may be suitable for the treatment of intractable diseases or traumatic tissue damage has attracted attention. To determine the ability of SMSCs to reactivate injured ovaries, a mouse model with ovaries damaged by busulfan and cyclophosphamide was developed and is described here. Female skin-derived mesenchymal stem cells (F-SMSCs) and male skin-derived mesenchymal stem cells (M-SMSCs) from red fluorescence protein (RFP) transgenic adult mice were used to investigate the restorative effects of SMSCs on ovarian function. Significant increases in total body weight and the weight of reproductive organs were observed in the treated animals. Both F-SMSCs and M-SMSCs were shown to be capable of partially restoring fertility in chemotherapy-treated females. Immunostaining with RFP and anti-Müllerian hormone (AMH) antibodies demonstrated that the grafted SMSCs survived, migrated to the recipient ovaries. After SMSCs were administered to the treated mice, real-time PCR showed that the expression levels of pro-inflammatory cytokines TNF-α, TGF-β, IL-8, IL-6, IL-1β, and IFNγ were significantly lower in the ovaries than in the untreated controls. Consistent with this observation, expression of oogenesis marker genes Nobox, Nanos3, and Lhx8 increased in ovaries of SMSCs-treated mice. These findings suggest that SMSCs may play a role within the ovarian follicle microenvironment in restoring the function of damaged ovaries and could be useful in reproductive health.     

Accumulating mitochondrial DNA mutations drive premature hematopoietic aging phenotypes distinct from physiological stem cell aging

Somatic stem cells mediate tissue maintenance for the lifetime of an organism. Despite the well-established longevity that is a prerequisite for such function, accumulating data argue for compromised stem cell function with age. Identifying the mechanisms underlying age-dependent stem cell dysfunction is therefore key to understanding the aging process. Here, using a model carrying a proofreading-defective mitochondrial DNA polymerase, we demonstrate hematopoietic defects reminiscent of premature HSC aging, including anemia, lymphopenia, and myeloid lineage skewing. However, in contrast to physiological stem cell aging, rapidly accumulating mitochondrial DNA mutations had little functional effect on the hematopoietic stem cell pool, and instead caused distinct differentiation blocks and/or disappearance of downstream progenitors. These results show that intact mitochondrial function is required for appropriate multilineage stem cell differentiation, but argue against mitochondrial DNA mutations per se being a primary driver of somatic stem cell aging.