Immuno-senescence and elevated central carbon metabolism in hematopoietic stem cell compartment upon aging.

Abstract

e24030 Background: Aging is associated with decline of hematopoiesis, compromised innate immunity, and propensity for malignancies. Aging of the hematopoietic stem and progenitor cell (HSPC) compartment is caused by accumulation of senescent cells and elimination of the latter rejuvenates innate immunity in animal models. Methods: HSC (CD34+) were isolated from the bone marrow of healthy human subjects (age range 20 – 74 years; n = 18) and separated by FACS in 3 distinct subsets with high, intermediate, and low glucose uptake (GU) capacity (GUhigh, GUinter, GUlow). Single-cell RNA-sequencing (scRNAseq) studies, followed by gene ontology (GO) analysis of biological processes, analysis of cell cycle, and gene set enrichment analysis (GSEA) were performed. Results: While the percentages of GUinter and GUlow subpopulations remain relatively constant with age, the proportion of GUhigh subset increases continuously with age (from 0.2% in adults < 30 years to 6,7% in > 60 years). GO analysis revealed that the GUhigh subset showed a significantly higher expression of genes involved in myeloid development, cell cycle arrest, inflammation and stress response, apoptosis, and significantly lower expressions of genes involved in lymphoid development. GSEA confirmed that the gene sets for cell cycle arrest, senescence associated secretory phenotype (SASP), anti-apoptosis/survival and P53 pathways are significantly up-regulated in the GUhigh subset. The latter shows therefore all deregulations that are inherent hallmarks of senescence. Most of the molecular deregulations are similar to those found in murine models of aging, but there are significant differences. In addition, cell cycle analysis revealed that the proportion of cells in the G1 phase was significantly reduced in the GUhigh subset. Comparing the frequencies of old to young GUhigh, GUlow cells along the cell cycle progression ranks showed a significant depletion of cells in late G1 phase among GUhigh cells but not in the other subsets. The frequencies of non-cycling cells in the GUlowsubset have remained high (> 70%) irrespective of age, thus providing evidence for the quiescence status of the GUlow subset, as well as for persistence of HSPC with “young phenotype”. Conclusions: Our series of proteome and single cell transcriptome analyses have shown that the GUhigh subpopulation is highly enriched in senescent HSPCs. This property may be exploited to enrich, visualize, and trace senescence in human bone marrow. Cell cycle analysis has revealed a significantly shortened G1 phase that is linked to dedifferentiated state in the senescent HSPC. Our results indicate a dependency of senescent HSPCs on elevated glucose metabolism as well as on anti-apoptotic factors for survival. These may represent ideal targets for elimination of senescent HSPC to restore innate immunity as demonstrated in murine models.