IDH1(R132H) mutation increases murine haematopoietic progenitors and alters epigenetics

Abstract

Mutations in the IDH1 and IDH2 genes encoding isocitrate dehydrogenases are frequently found in human glioblastomas1 and cytogenetically normal acute myeloid leukaemias (AML)2. These alterations are gain-of-function mutations in that they drive the synthesis of the ‘oncometabolite’ R-2-hydroxyglutarate (2HG)3. It remains unclear how IDH1 and IDH2 mutations modify myeloid cell development and promote leukaemogenesis. Here we report the characterization of conditional knock-in (KI) mice in which the most common IDH1 mutation, IDH1(R132H), is inserted into the endogenous murine Idh1 locus and is expressed in all haematopoietic cells (Vav-KI mice) or specifically in cells of the myeloid lineage (LysM-KI mice). These mutants show increased numbers of early haematopoietic progenitors and develop splenomegaly and anaemia with extramedullary haematopoiesis, suggesting a dysfunctional bone marrow niche. Furthermore, LysM-KI cells have hypermethylated histones and changes to DNA methylation similar to those observed in human IDH1- or IDH2-mutant AML. To our knowledge, our study is the first to describe the generation and characterization of conditional IDH1(R132H)-KI mice, and also the first report to demonstrate the induction of a leukaemic DNA methylation signature in a mouse model. Our report thus sheds light on the mechanistic links between IDH1 mutation and human AML.

Fighting Fire with Fire in Cancer

“…Mutant IDH1 enzyme expressed solely in the myeloid compartment (LysM promoter) resulted in splenomegaly, decreased bone marrow cellularity, and extramedullary hematopoiesis by age 6 months [48]. LysM IDH1 knock-in LSK cells showed an increase in highly methylated CpG sites and histone hypermethylation [48], consistent with the DNA methylation changes observed in human IDH1-or IDH2-mutant gliomas [49] and AML [50].…”

“…In the absence of Cre recombinase (Cre), neither the LSL IDH1 R132 mutant allele nor the wild type IDH allele is expressed, but when Cre is present, a stop codon is excised and the mutant IDH1 protein is expressed from the endogenous locus [48]. Initial characterization of various mouse strains revealed that IDH1 knockout mice were viable and fertile but that expression of the mutant IDH1 enzyme and its consequent D2HG production were embryonic lethal [36].…”

“…Initial characterization of various mouse strains revealed that IDH1 knockout mice were viable and fertile but that expression of the mutant IDH1 enzyme and its consequent D2HG production were embryonic lethal [36]. Mutant IDH1 enzyme expressed solely in the myeloid compartment (LysM promoter) resulted in splenomegaly, decreased bone marrow cellularity, and extramedullary hematopoiesis by age 6 months [48]. LysM IDH1 knock-in LSK cells showed an increase in highly methylated CpG sites and histone hypermethylation [48], consistent with the DNA methylation changes observed in human IDH1-or IDH2-mutant gliomas [49] and AML [50].…”

L-2-Hydroxyglutarate production arises from noncanonical enzyme function at acidic pH

“…D-2HG inhibits a large family of >70 different αKG-dependent enzymes that regulate chromatin-modifications, stability of hypoxia-inducible factors, extracellular matrix maturation, and DNA repair 1 . In particular, D-2HG-mediated inhibition of chromatin-modifying enzymes impairs induction of gene expression programs required for normal cell differentiation and ‘locks’ malignant cells in an undifferentiated stem cell-like state 5–7 . The relative contributions of different D-2HG targets to oncogenesis likely varies depending on the cellular context 8,9 .…”

Mitochondrial metabolic remodeling in response to genetic and environmental perturbations

“…A single hit, which is both loss of function and gain of function, is only ever observed in these genes. In both gliomas and AML, mutations in IDH genes have been suggested as a very early, and perhaps founder mutations, although in neither disease does IDH mutation appear to be able to induce transformation on its own 55, 56, 57, 58. What is common to all three genes is that they are either situated directly within the mitochondrial matrix ( SDH , FH , and IDH2 ) or their metabolic activity directly affects that of the mitochondrion ( IDH1 ).…”