Exploring the impact of healthy aging and myeloid malignancies on human hematopoietic progenitors

Despoina Barmpari


Bone marrow (BM) aging and the resulting increase in mutational burden are among the factors
that contribute to the pathogenesis of malignant hematological conditions including
Myelodysplastic Syndrome (MDS), Chronic Myelomonocytic Leukemia (CMML) and Acute Myeloid
Leukemia (AML). These are highly disabling disorders mainly affecting the elderly.
MDS is an heterogenous group of myeloid malignancies, originating from hematopoietic stem cells
(HSCs) with genetic abnormalities, resulting in ineffective hematopoiesis causing several types of
cytopenia. CMML originates from the stem cell compartment as well and is defined by persistent
peripheral monocytosis and the presence of dysplastic cells in the BM. Allogeneic hematopoietic
stem cell transplantation (HSCT) is currently the only curative treatment for MDS and CMML,
however, it is only applicable to younger patients due to the relatively high risk of treatment
associated complications. Nevertheless, a high percentage of MDS and CMML patients eventually
progress to AML, an aggressive form of cancer, which, if left untreated, will kill the patient in a
matter of weeks. The cells responsible for disease maintenance are dysregulated HSCs that carry
mutations and like normal HSCs retain self-renewal ability but are resistant to therapy, leading to
relapse and/or progression to AML. As these aberrant HSC populations are intermingled with
normal HSCs without specific markers to distinguish them, it is not possible to physically isolate
and further study them. Single-cell RNA sequencing (scRNA-seq) has significantly contributed to
solving this, and has enabled the characterization of highly heterogenous tissues, like the BM, by
elucidating transcriptional differences. While several scRNA-seq studies have contributed to the
understanding of MDS over the past years, our knowledge about CMML is highly limited. A
continuous lack of therapies highlights the need for gaining a better understanding of these
In this study, we employed single cell cellular indexing of transcriptomes and epitopes by
sequencing (CITE-seq) of CD34+ BM cells from healthy young and old individuals to evaluate the
BM aging effect. We observed that old HSCs are more quiescent than young HSCs. By studying the
differential expression (DE) of genes between old and young healthy donors in the most immature
CD34+ populations, we identified inflammation as one of the main aging-related changes. We
furthermore investigated the differences in BM cells from two MDS and two CMML patient
samples. Looking for MDS-specific genes and altered pathways in order to decipher the
pathogenesis of the disease, we compared MDS cells with age-matched controls (old BM cells).
We reported an upregulation of the mitochondrial and ribosomal machinery in all MDS
populations and identified DE genes in both MDS samples that have never been correlated with
the disease before, like MAFF, SRGN and FTL. These results indicate a deregulated iron metabolism
causing Reactive Oxygen Species (ROS) accumulation and changes in mitochondrial metabolism.
MDS CD34+ cells had several dysregulated pathways, like immune and inflammatory, and the cells
appeared to be in a stem-like protective state with no evidence of cell cycle activation. In contrast,
CMML patients exhibited higher heterogeneity; we reported DE genes in both CMML patients
including SRGN, which was also found in MDS, indicating that this proteoglycan might have a
general role in myeloid malignancies especially in the most immature compartment. Several
pathways were found dysregulated, including immune response and extracellular matrix related
processes, however, no specific pattern of regulation was identified.
Lastly, we used a newly established single cell proteomics method on the same samples to
decipher alterations related to BM aging and to myeloid malignancies at the protein level. Based
on the direct comparison between transcriptome and proteome at single cell level in all samples,
we verified a correlation between the methods and detected three proteome signatures for HSCs:
one for healthy and one for each of the two MDS diseased samples.
In conclusion, this study serves as a scRNA-seq roadmap, starting from the BM aging effect leading
to the extensive study of two myeloid malignancies, complemented with first-time data on single
cell proteome of the same patients. This comprehensive study increases our understanding of
MDS and CMML and creates many exciting prospects for future research.
ForlagEget Forlag
Antal sider107
StatusUdgivet - 14 jun. 2022


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