Truncated CSF3 receptors induce pro-inflammatory responses in severe congenital neutropenia

Severe congenital neutropenia (SCN) patients are prone to develop myelodysplastic syndrome (MDS) or acute myeloid leukaemia (AML). Leukaemic progression of SCN is associated with the early acquisition of CSF3R mutations in haematopoietic progenitor cells (HPCs), which truncate the colony-stimulating factor 3 receptor (CSF3R). These mutant clones may arise years before MDS/AML becomes overt. Introduction and activation of CSF3R truncation mutants in normal HPCs causes a clonally dominant myeloproliferative state in mice treated with CSF3. Paradoxically, in SCN patients receiving CSF3 therapy, clonal dominance of CSF3R mutant clones usually occurs only after the acquisition of additional mutations shortly before frank MDS or AML is diagnosed. To seek an explanation for this discrepancy, we introduced a patient-derived CSF3R-truncating mutation in ELANE-SCN and HAX1-SCN derived and control induced pluripotent stem cells and compared the CSF3 responses of HPCs generated from these lines. In contrast to CSF3R-mutant control HPCs, CSF3R-mutant HPCs from SCN patients do not show increased proliferation but display elevated levels of inflammatory signalling. Thus, activation of the truncated CSF3R in SCN-HPCs does not evoke clonal outgrowth but causes a sustained pro-inflammatory state, which has ramifications for how these CSF3R mutants contribute to the leukaemic transformation of SCN.

Malignant Transformation Involving CXXC4 Mutations Identified in a Leukemic Progression Model of Severe Congenital Neutropenia

Severe congenital neutropenia (SCN) patients treated with CSF3/G-CSF to alleviate neutropenia frequently develop acute myeloid leukemia (AML). A common pattern of leukemic transformation involves the appearance of hematopoietic clones with CSF3 receptor (CSF3R) mutations in the neutropenic phase, followed by mutations in RUNX1 before AML becomes overt. To investigate how the combination of CSF3 therapy and CSF3R and RUNX1 mutations contributes to AML development, we make use of mouse models, SCN-derived induced pluripotent stem cells (iPSCs), and SCN and SCN-AML patient samples. CSF3 provokes a hyper-proliferative state in CSF3R/RUNX1 mutant hematopoietic progenitors but does not cause overt AML. Intriguingly, an additional acquired driver mutation in Cxxc4 causes elevated CXXC4 and reduced TET2 protein levels in murine AML samples. Expression of multiple pro-inflammatory pathways is elevated in mouse AML and human SCN-AML, suggesting that inflammation driven by downregulation of TET2 activity is a critical step in the malignant transformation of SCN.

Combinatorial CSF3R and RUNX1 mutations seen in SCN-AML do not result in AML in mice

An additional mutation in Cxxc4 causes AML development in CSF3R/RUNX1 mutant mice

Mutant CXXC4 protein is more stable than wild-type and reduces TET2 protein levels

CXXC4 mutations are also found in de novo AML patients

Ectopic miR-125a Expression Induces Long-Term Repopulating Stem Cell Capacity in Mouse and Human Hematopoietic Progenitors

Umbilical cord blood (CB) is a convenient and broadly used source of hematopoietic stem cells (HSCs) for allogeneic stem cell transplantation. However, limiting numbers of HSCs remain a major constraint for its clinical application. Although one feasible option would be to expand HSCs to improve therapeutic outcome, available protocols and the molecular mechanisms governing the self-renewal of HSCs are unclear. Here, we show that ectopic expression of a single microRNA (miRNA), miR-125a, in purified murine and human multipotent progenitors (MPPs) resulted in increased self-renewal and robust long-term multi-lineage repopulation in transplanted recipient mice. Using quantitative proteomics and western blot analysis, we identified a restricted set of miR-125a targets involved in conferring long-term repopulating capacity to MPPs in humans and mice. Our findings offer the innovative potential to use MPPs with enhanced self-renewal activity to augment limited sources of HSCs to improve clinical protocols.

Genetic Variations in MicroRNA-Binding Sites Affect MicroRNA-Mediated Regulation of Several Genes Associated With Cardio-metabolic Phenotypes

BACKGROUND

Genome-wide association studies enabled us to discover a large number of variants and genomic loci contributing to cardiovascular and metabolic disorders. However, because the vast majority of the identified variants are thought to merely be proxies for other functional variants, the causal mechanisms remain to be elucidated. We hypothesized that the part of the functional variants involved in deregulating cardiometabolic genes is located in microRNA (miRNA)-binding sites.

METHODS AND RESULTS

Using the largest genome-wide association studies available on glycemic indices, lipid traits, anthropometric measures, blood pressure, coronary artery diseases, and type 2 diabetes mellitus, we identified 11,067 variants that are associated with cardiometabolic phenotypes. Of these, 230 variants are located within miRNA-binding sites in the 3'-untranslated region of 155 cardiometabolic genes. Thirty-seven of 230 variants were found to fulfill our predefined criteria for being functional in their genomic loci. Ten variants were subsequently selected for experimental validation based on genome-wide association studies results, expression quantitative trait loci (eQTL) analyses, and coexpression of their host genes and regulatory miRNAs in relevant tissues. Luciferase reporter assays revealed an allele-specific regulation of genes hosting the variants by miRNAs. These cotransfection experiments showed that rs174545 (FADS1:miR-181a-2), rs1059611 (LPL:miR-136), rs13702 (LPL:miR-410), rs1046875 (FN3KRP:miR-34a), rs7956 (MKRN2:miR-154), rs3217992 (CDKN2B:miR-138-2-3p), and rs11735092 (HSD17B13:miR-375) decrease or abrogate miRNA-dependent regulation of the genes. Conversely, 2 variants, rs6857 (PVRL2:miR-320e) and rs907091 (IKZF3:miR-326), were shown to enhance the activity of miRNAs on their host genes.

CONCLUSIONS

We provide evidence for a model in which polymorphisms in miRNA-binding sites can both positively and negatively affect miRNA-mediated regulation of cardiometabolic genes.

The association of common polymorphisms in miR-196a2 with waist to hip ratio and miR-1908 with serum lipid and glucose

OBJECTIVE

MicroRNAs (miRNAs) have been implicated in the regulation of cardiometabolic disorders. Given the crucial role of miRNAs in gene expression, genetic variation within miRNA genes is expected to affect miRNA function and substantially contribute to disease risk.

METHODS

2,320 variants in miRNA-encoding sequences were systematically retrieved, and their associations with 17 cardiometabolic traits/diseases were investigated, using genome-wide association studies (GWAS) on glycemic indices, anthropometric measures, lipid traits, blood pressure, coronary artery disease, and type 2 diabetes. Next, target genes of the identified miRNAs that may mediate their effect on the phenotypes were examined. Furthermore, trans- expression quantitative trait loci analysis and luciferase reporter assay to provide functional evidence for our findings were performed.

RESULTS

rs11614913:C/T in miR-196a2 was associated with waist to hip ratio (P-value=1.7 × 10(-5) , β = 0.023). Two target genes, SFMBT1 and HOXC8, which may mediate this association were identfied, and they were shown experimentally as direct targets of miR-196a2. Moreover, rs174561:C/T in miR-1908 was found to be associated with total cholesterol (P-value=6.5 × 10(-16) , β=0.044), LDL-cholesterol (P-value=4.3 × 10(-18) , β=0.049), HDL-cholesterol (P-value=1.7 × 10(-6) , β=0.026), triglyceride (P-value=7.8 × 10(-14) , β=0.038), and fasting glucose (P-value=4.3 × 10(-10) , β=0.02). In addition, a number of miR-1908 target genes were highlighted as potential mediators.

CONCLUSIONS

The results indicated miRNA-dependent regulation of fat distribution by miR-196a2 and of lipid metabolism by miR-1908.