The GNASR201C mutation associated with clonal hematopoiesis supports transplantable hematopoietic stem cell activity

Spatial Mapping of Hematopoietic Clones in Human Bone Marrow

Clonal hematopoiesis (CH) is the expansion of somatically mutated cells in the hematopoietic compartment of individuals without hematopoietic dysfunction. Large CH clones (i.e., >2% variant allele fraction) predispose to hematologic malignancy, but CH is detected at lower levels in nearly all middle-aged individuals. Prior work has extensively characterized CH in peripheral blood, but the spatial distribution of hematopoietic clones in human bone marrow is largely undescribed. To understand CH at this level, we developed a method for spatially aware somatic mutation profiling and characterized the bone marrow of a patient with polycythemia vera. We identified the complex clonal distribution of somatic mutations in the hematopoietic compartment, the restriction of somatic mutations to specific subpopulations of hematopoietic cells, and spatial constraints of these clones in the bone marrow. This proof of principle paves the way to answering fundamental questions regarding CH spatial organization and factors driving CH expansion and malignant transformation in the bone marrow.

SIGNIFICANCE

CH occurs commonly in humans and can predispose to hematologic malignancy. Although well characterized in blood, it is poorly understood how clones are spatially distributed in the bone marrow. To answer this, we developed methods for spatially aware somatic mutation profiling to describe clonal heterogeneity in human bone marrow. See related commentary by Austin and Aifantis, p. 139.

Quantitative association between gene expression and blood cell production of individual hematopoietic stem cells in mice

Individual hematopoietic stem cells (HSCs) produce different amounts of blood cells upon transplantation. Taking advantage of the intercellular variation, we developed an experimental and bioinformatic approach to evaluating the quantitative association between gene expression and blood cell production across individual HSCs. We found that most genes associated with blood production exhibit the association only at some levels of blood production. By mapping gene expression with blood production, we identified four distinct patterns of their quantitative association. Some genes consistently correlate with blood production over a range of levels or across all levels, and these genes are found to regulate lymphoid but not myeloid production. Other genes exhibit one or more clear peaks of association. Genes with overlapping peaks are found to be coexpressed in other tissues and share similar molecular functions and regulatory motifs. By dissecting intercellular variations, our findings revealed four quantitative association patterns that reflect distinct dose-response molecular mechanisms modulating the blood cell production of HSCs.

Genome-wide analyses of 200,453 individuals yield new insights into the causes and consequences of clonal hematopoiesis

Clonal hematopoiesis (CH), the clonal expansion of a blood stem cell and its progeny driven by somatic driver mutations, affects over a third of people, yet remains poorly understood. Here we analyze genetic data from 200,453 UK Biobank participants to map the landscape of inherited predisposition to CH, increasing the number of germline associations with CH in European-ancestry populations from 4 to 14. Genes at new loci implicate DNA damage repair (PARP1, ATM, CHEK2), hematopoietic stem cell migration/homing (CD164) and myeloid oncogenesis (SETBP1). Several associations were CH-subtype-specific including variants at TCL1A and CD164 that had opposite associations with DNMT3A- versus TET2-mutant CH, the two most common CH subtypes, proposing key roles for these two loci in CH development. Mendelian randomization analyses showed that smoking and longer leukocyte telomere length are causal risk factors for CH and that genetic predisposition to CH increases risks of myeloproliferative neoplasia, nonhematological malignancies, atrial fibrillation and blood epigenetic ageing.

Proteomic Profiling Change and Its Implies in the Early Mycosis Fungoides (MF) Using Isobaric Tags for Relative and Absolute Quantification (iTRAQ)

Purpose

Mycosis fungoides (MF) is the most common T-cell lymphoma, with indolent biologic behavior in the early stage and features of invasive in the tumor stage. The diagnosis of MF is still ambiguous and difficult. We focused on the proteomic profiling change in the pathogenesis of early MF and identified candidate biomarkers for early diagnosis.

Methods

We collected peripheral blood samples of MF patients and healthy individuals (HI) performed proteomic profiling analysis using isobaric tags for relative and absolute quantification (iTRAQ) platform. Differently expressed proteins (DEPs) were filtered, and involved biological functions were analyzed through Gene Ontology (GO) and Ingenuity Pathway Analysis (IPA) software.

Results

We identified 78 DEPs including fifty proteins were upregulated and 28 proteins were downregulated in the MF group with HI as a control. Total DEPs were analyzed according to the biological regulation and metabolic process through GO analysis. The pathways of LXR/RXR activation and FXR/RXR activation were significantly activated, in which APOH, CLU, and ITIH4 were involved. The top annotated disease and function network was (Cancer, Organismal Injury and Abnormalities, Reproductive System Disease), with a key node CLU. These DEPs were involved in cancer, including thyroid carcinoma, head and neck carcinoma, and cancer of secretory structure, in which CLU, GNAS, and PKM played an indirect role in the occurrence and development of cancer. Relevant causal network was IL12 (family), which is related to GNAS, PKM, and other DEPs.

Conclusion

Proteomic profiling of early-stage MF provided candidate protein biomarkers such as CLU, GNAS, and PKM, which benefit the early diagnosis and understanding of the mechanism of MF development. Besides, lipid metabolism may be one of the pathogenesis of MF, and IL12 was a potential marker for the diagnosis and treatment of early MF.

Transcriptional regulators CITED2 and PU.1 cooperate in maintaining hematopoietic stem cells

Reduced expression of the transcription factor PU.1 is frequently associated with development of acute myeloid leukemia (AML), whereas elevated levels of CITED2 (CBP/p300-interacting-transactivator-with-an-ED-rich-tail 2) enhance maintenance of both normal and leukemic hematopoietic stem and progenitor cells (HSPCs). Recent findings indicate that PU.1 and CITED2 act in the same gene regulatory network. We therefore examined a potential synergistic effect of simultaneous PU.1 downregulation and CITED2 upregulation on stem cell biology and AML pathogenesis. We found that simultaneous PU.1/CITED2 deregulation in human CD34⁺ cord blood (CB) cells, as well as CITED2 upregulation in preleukemic murine PU.1-knockdown (PU.1^KD/KD) bone marrow cells, significantly increased the maintenance of HSPCs compared with the respective deregulation of either factor alone. Increased replating capacity of PU.1^KD/KD/CITED2 cells in in vitro assays eventually resulted in outgrowth of transformed cells, while upregulation of CITED2 in PU.1^KD/KD cells enhanced their engraftment in in vivo transplantation studies without affecting leukemic transformation. Transcriptional analysis of CD34⁺ CB cells with combined PU.1/CITED2 alterations revealed a set of differentially expressed genes that highly correlated with gene signatures found in various AML subtypes. These findings illustrate that combined PU.1/CITED2 deregulation induces a transcriptional program that promotes HSPC maintenance, which might be a prerequisite for malignant transformation.