Loss of Ezh2 precipitates lethal disease progression in a mouse model of Calr-mutated myeloproliferative neoplasms.

Patients with CALR-mutant essential thrombocythemia (ET), the myeloproliferative neoplasm (MPN) subtype with the most favorable long-term prognosis, remain at risk of developing secondary myelofibrosis (sMF) or acute myeloid leukemia (AML). Outcomes after such progression are poor. Loss-of-function mutations in the epigenetic regulator EZH2 are frequently acquired during disease evolution, but their causal contribution to CALR-driven MPN has remained uncertain. To investigate this question, we used a knock-in mouse that constitutively expresses a Calr frameshift allele and introduced conditional Ezh2 deletion triggered by tamoxifen. Ezh2 loss in Calr-mutant MPN resulted in lethal disease progression. These mice developed two terminal outcomes that mirror human disease: fibrotic MPN (sMF-like) and blast-phase MPN (AML-like). Transplantation experiments demonstrated that only the AML-like phenotype was transplantable, whereas the sMF-like phenotype did not confer lethal condition in recipients. These findings provide direct in vivo evidence that EZH2 loss drives malignant evolution of CALR-mutant MPN. Transcriptomic profiling of leukemic stem cells from AML-like mice revealed enrichment of fatty acid oxidation (FAO) pathways. Short-term colony assays showed that inhibition of peroxisome proliferator-activated receptor-γ (PPARγ) modestly increased the antiproliferative effect of cytarabine on AML-derived stem and progenitor cells, suggesting a possible reliance on FAO. Reanalysis of public single-cell RNA-sequencing data from patients with MPN progressing to AML also demonstrated elevated FAO signatures in leukemic stem cells. Together, these results identify EZH2 loss as a key determinant of CALR-mutant MPN progression and point to altered metabolic wiring as a potential vulnerability in post-MPN AML.