Kdm6b is Required for Self-Renewal of Normal and Leukemic Mouse Stem Cells Under Proliferative Stress

KDM6B (JMJD3) is one of two known epigenetic modifiers responsible for the removal of the repressive histone mark, histone-3 lysine-27 trimethylation (H3K27me3), and has been shown to play a role in development, differentiation, and inflammatory stress response. Unlike the other H3K27me3 demethylase, UTX (KDM6A), which is frequently mutated in hematopoietic malignancies, KDM6B is upregulated in a myriad of blood disorders. This suggests that it may have important functions in the pathogenesis of hematopoietic cancers. Here, we examined the role of Kdm6b in hematopoietic stem cell (HSC) fate decisions under normal and malignant conditions to evaluate its potential as a therapeutic target. Loss of Kdm6b leads to a significant reduction in phenotypic and functional HSCs in adult mice, which increases with increased age. Loss of Kdm6b results in the inability to maintain the HSC population post-transplantation in a dose-dependent manner. In addition, Kdm6b is necessary for HSC self-renewal in response to inflammatory, genotoxic and oncogenic stress. Kdm6b HSCs have a stress response gene expression signature which overlaps significantly with immediate early response genes, genes associated with aged HSCs and genes involved in quiescence of HSCs. When stimulated with an inflammatory or proliferative agent, Kdm6bФeficient HSCs are not able to efficiently resolve gene expression programs, leading to delayed cell cycle entry and a self-renewal block, forcing them to differentiate once they commit to divide. Thus, Kdm6b is necessary for self-renewal of normal and leukemic stem cells, and KDM6B inhibition combined with proliferative agents may force differentiation and eventual depletion of leukemic stem cells in patients

Rare variant analysis of blood pressure phenotypes in the Genetic Analysis Workshop 18 whole genome sequencing data using sequence kernel association test

Sequence kernel association test (SKAT) has become one of the most commonly used nonburden tests for analyzing rare variants. Performance of burden tests depends on the weighting of rare and common variants when collapsing them in a genomic region. Using the systolic and diastolic blood pressure phenotypes of 142 unrelated individuals in the Genetic Analysis Workshop 18 data, we investigated whether performance of SKAT also depends on the weighting scheme. We analyzed the entire sequencing data for all 200 replications using 3 weighting schemes: equal weighting, Madsen-Browning weighting, and SKAT default linear weighting. We considered two options: all single-nucleotide polymorphisms (SNPs) and only low-frequency SNPs. A SKAT default weighting scheme (which heavily downweights common variants) performed better for the genes in which causal SNPs are mostly rare. This SKAT default weighting scheme behaved similarly to other weighting schemes after eliminating all common SNPs. In contrast, the equal weighting scheme performed the best for MAP4 and FLT3, both of which included a common variant with a large effect. However, SKAT with all 3 weighting schemes performed poorly. Overall power across all causal genes was about 0.05, which was almost identical to the type I error rate. This poor performance is partly due to a small sample size because of the need to analyze only unrelated individuals. Because a half of causal SNPs were not found in the annotation file based on the 1000 Genomes Project, we suspect that performance was also affected by our use of incomplete annotation information

Divergent effects of DNMT3A and TET2 mutations on hematopoietic progenitor cell fitness

The DNA methylation regulators DNMT3A and TET2 are recurrently mutated in hematological disorders. Despite possessing antagonistic biochemical activities, loss-of-function murine models show overlapping phenotypes in terms of increased hematopoietic stem cell (HSC) fitness. Here, we directly compared the effects of these mutations on hematopoietic progenitor function and disease initiation. In contrast to Dnmt3a-null HSCs, which possess limitless self-renewal in vivo, Tet2-null HSCs unexpectedly exhaust at the same rate as control HSCs in serial transplantation assays despite an initial increase in self-renewal. Moreover, loss of Tet2 more acutely sensitizes hematopoietic cells to the addition of a common co-operating mutation (Flt

Dnmt3a Regulates T-cell Development and Suppresses T-ALL Transformation

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematopoietic neoplasm resulting from the malignant transformation of T-cell progenitors, and comprises approximately 15% and 25% of pediatric and adult ALL cases respectively. It is well-established that activating NOTCH1 mutations are the major genetic lesions driving T-ALL in most patients, but efforts to develop targeted therapies against this pathway have produced limited success in decreasing leukemic burden and come with significant clinical side effects. A finer detailed understanding of the genetic and molecular mechanisms underlying T-ALL is required identify patients at increased risk for treatment failure and the development of precision medicine strategies. Generation of genetic models that more accurately reflect the normal developmental history of T-ALL are necessary to identify new avenues for treatment. The DNA methyltransferase enzyme DNMT3A is also recurrently mutated in T-ALL patients, and we show here that inactivation of Dnmt3a combined with Notch1 gain-of-function leads to an aggressive T-ALL in mouse models. Moreover, conditional inactivation of Dnmt3a in mouse hematopoietic cells leads to an accumulation of immature progenitors in the thymus which are less apoptotic. These data demonstrate that Dnmt3a is required for normal T-cell development, and acts as a T-ALL tumor suppressor