Project description:Leptin receptor (LEPR) identifies a subpopulation of hematopoietic stem cells (HSCs) with high repopulating potential. In this study, we demonstrated that LEPR-expressing HSCs while exhibiting significantly higher engrafting potential and self-renewing capacity in young mice showed early age-associated decline in these functions as compared to the LEPR- HSCs. LEPR+ HSCs have transcriptomic profiles significantly different from LEPR- HSCs in young mouse bone marrow, but middle-aged HSCs do not have distinct transcriptomic profiles based on LEPR status. The age-related phenotypes were associated with a proinflammatory transcriptomic profile at baseline in young LEPR+ HSCs, which was further exacerbated by age. In contrast, LEPR- HSCs did not show age-associated functional impairment at the ages tested. This suggested that subsets of HSCs are susceptible to age-related decline in function at varying ages and that LEPR+ HSCs are a potential target for early cellular therapeutic interventions in delaying the detrimental effects of aging in hematopoiesis.
Project description:Decline in hematopoietic function in aged individuals is associated with expansion of phenotypic hematopoietic stem cells (HSCs) and a shift in their lineage potential toward production of myeloid cells. Both HSC-intrinsic changes, and extrinsic changes in the bone marrow (BM) microenvironment, have been identified in old mice and humans. However, to extend healthy and robust hematopoietic function from youth into older age, we need to understand and effectively target the processes that initiate functional hematopoietic decline. We recently identified decline in Insulin-Like Growth Factor 1 (IGF1) in the BM microenvironment as early as middle age to be an HSC-extrinsic initiating driver of HSC aging (Young et al., Cell Stem Cell 2021). As systemic IGF1 administration has significant undesirable side effects, we sought to comprehensively interrogate the cell population(s) in the BM microenvironment that are responsible for IGF1 decline, towards the goal of cell type-specific targeted therapy. We performed single cell RNA-seq to comprehensively profile hematopoietic and non-hematopoietic fractions of the BM in young (2-4mo; n = 5 biological replicates) and middle-aged (12-14mo; n = 10) mice. In young mice, we find Igf1 to be nearly entirely detected in the mesenchymal stromal cell populations Adipo-CAR and Osteo-CAR, and Igf1 is significantly reduced in expression in both populations in middle-aged mice. Using two independent mesenchymal stromal cell Cre mouse lines, Lepr-Cre and Prx1-CreERT2, we found that knockout of Igf1 resulted in myeloid-biased hematopoiesis that replicated aging phenotypes. This result was similar to our published work showing that knockout of Igf1 using Nestin-CreER causes myeloid-biased hematopoiesis. While these Cre models generally do not mark similar cell types, it has been shown that Lepr-Cre-expressing perisinusoidal stromal cells include cells that express certain Nestin transgenes. Using fluorescent reporters, we find that all three lines (Lepr-Cre, Prx1-CreERT2, and Nestin-CreER) overlap in expression in the CAR populations that abundantly express Igf1 in young mice. Taken together, our work identifies a new role for Cxcl12-abundant reticular cells in sustaining hematopoietic function through local IGF1 production and suggests that specifically targeting CAR cells to maintain or restore Igf1 expression during aging will have beneficial effects on lymphoid cell production and adaptive immunity.
Project description:The decline of hematopoietic stem cell (HSC) function upon aging contributes to senescent immune remodeling and to leukemia pathogenesis. Aged HSCs show epigenetic alterations affecting DNA methylation, histone modifications, and show a reduction in the polar distribution of histone 4 lysine 16 acetylation (H4K16ac). Here, we determined the deposition patterns of H4K16ac in young, aged and re-juvenated HSCs using ChIP-seq.
Project description:The decline of endothelial autophagy is closely related to vascular senescence and disease, although the molecular mechanisms connecting these outcomes in vascular endothelial cells (VECs) remain unclear. Here, we identify a crucial role for CD44, a multifunctional adhesion molecule, in controlling autophagy and aging in VECs. The CD44 intercellular domain (CD44ICD) negatively regulates autophagy by reducing PIK3R4 and PIK3C3 levels and disrupting STAT3-dependent PtdIns3K complexes. CD44 and its homologue clec-31 are increased in aging vascular endothelium and Caenorhabditis elegans, respectively, suggesting that an age-dependent increase in CD44 induces autophagy decline and aging phenotypes. Accordingly, CD44 knockdown ameliorates age-associated phenotypes in VECs. The endothelium-specific CD44ICD knock-in mouse is shorter-lived, with VECs exhibiting obvious premature aging characteristics associated with decreased basal autophagy. Autophagy activation suppresses the premature aging of human and mouse VECs overexpressing CD44ICD, function conserved in the CD44 homologue clec-31 in C. elegans. Our work describes a mechanism coordinated by CD44 function bridging autophagy decline and 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:Aging is the progressive decline in organismal function that leads to an increased risk of multiple diseases and mortality. The molecular basis of this decline is unknown. Using quantitative PCR for mitochondrial mRNA from multiple tissues from the same animals, we found that the rate of change in mouse mitochondrial expression is tissue-specific, with cardiac expression declining early (8-10 months), adipose expression declining late (25-30 months), and no change in kidney or skin. In cardiac tissue, mitochondria-derived mRNA levels declined more slowly than nuclear encoded mRNAs, suggesting a potential dysregulation. These changes were independent of alteration in mitochondrial number, as measured by quantitative PCR of mitochondrial DNA and citrate synthase activity. We found no change in the variability between mitochondrial mRNA levels with age, suggesting that the changes are not due to random dysregulation at the level of gene expression. Caloric restriction (CR), a lifespan-extending intervention proposed to act through mitochondrial biogenesis, delayed the decline in both cardiac and adipose mitochondrial mRNA levels of F344 rats. CR caused an increase in citrate synthase activity but did not alter mitochondrial DNA content, indicating increased translation or reduced turnover of mitochondrial proteins. These results demonstrate that mitochondrial gene expression changes with age are not coupled to mitochondrial number, are likely to be regulated, and are governed by tissue-specific processes. These findings indicate that aging is neither a programmed organism-wide change orchestrated in a top-down fashion nor a product of random dysregulation of gene expression but that tissue-specific factors may independently control aging in different organ compartments. Keywords: aging Cardiac ventricle total RNA from 10 young (4-6 month) and 10 young (25-28 month) mice were compared.
Project description:Leptin receptors (Lepr) are expressed by various types of stem cells including mesenchymal stem cells, hematopoietic stem cells, embryonic stem cells, and induced pluripotent stem cells. Leptin/lepr signaling is also a central regulator of metabolism. However, the role of Lepr in pluripotency, metabolic disease progression and growth development is still controversial and poorly understood. In the present study, we explored the Lepr function in disease progression, pluripotency and metabolism using day 14.5 mouse embryonic fibroblasts (MEFs) and their reprogrammed induced pluripotent stem cells (iPSCs) as model system. We successfully reprogrammed mouse embryonic fibroblasts into iPSCs from control and db/db (Lepr deficient) mice. Using a global quantitative proteomic approach, we identified key pathways regulating pluripotency, metabolic homeostasis and protein synthesis during fetal growth and development. The Lepr MEFs show abnormal metabolic abnormalities and mitochondrial dysfunction as compared to control MEFs, while Lepr iPSCs show upregulated elongated factor 4 e (eIF4e) protein synthesis pathway and altered Oct4 and Stat3 pathways which are involved in normal fetal growth development. Furthermore, chip analysis revealed that higher Stat3 binding on the promoter of eIF4e in Lepr iPSCs leads to higher protein synthesis in these cell types as compared to control iPSCs. Finally, point mutation corrected Lepr iPSCs using CRISPR/Cas9 gene editing method showed recovered pluripotency, metabolic and protein synthesis pathways. In conclusion, we have shown that Lepr signaling is involved in the regulation of the metabolic properties and key developmental pathways in MEFs and stemness of pluripotent stem cells. Disruption of Lepr signaling has been shown to involve in the pathophysiology of various diseases including obesity and diabetes. The generated MEFs and iPSCs in this present study provide valuable tools to explore the role of Lepr in the progression of obesity, diabetes and metabolic abnormalities, and to find the putative targets of Lepr signaling during the development of these diseases.
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:To study the regulation of Lepr on transcriptome in WT and Lepr KO AMs under resting state and after LPS stimulation, Lepr-sufficient (Lepr+/+, Lyz2-Cre) and Lepr-deficient (Leprfl/fl, Lyz2-Cre) alveolar macrophages (AMs) were isolated by collecting BALF. Lipopolysaccharide (LPS) was added in vitro for 1h or cells were left untreated. Total RNA was extracted for deep sequencing. Gene expression in WT and Lepr KO cells were analyzed.