Researchers use skin cells from pediatric patients and program them into stem cells to investigate molecular mechanisms for rare form of childhood leukemia
Juvenile myelomonocytic leukemia (JMML) is diagnosed in children whose average age at diagnosis is two. Hematopoietic stem cell transplantation can cure some patients but not all. On the other end, minimal treatment -- or none at all -- can also result in remission. How does one decide how to treat JMML patients?
To begin characterizing JMML, practitioners consider that not all patients have mutations in the same gene, but 85% of JMML patients can have a mutation in NF1, NRAS, KRAS, PTPN11, or CBL genes. A mutation could affect a single enzyme by up-regulating it, or it could down-regulate a regulatory molecule. Effects that culminate into cell proliferation lead to cancer.
It is known that 35% of JMML patients carry gain-of-function PTPN11 mutations that alter an enzyme, Src-homology 2 domain-containing phosphatase 2 (SHP2). However, progress in treatment for JMML has been hindered by lack of a model in which to study the disease.
To build upon our knowledge base, a research group explored modeling JMML at the molecular level using stem cells. Skin fibroblast cells were collected from patients known to harbor PTPN11 mutations. The skin fibroblasts were converted into human induced pluripotent stem cells (hiPSC) using established protocols for reprogramming. These stem cells and those obtained from healthy controls were differentiated into blood cells and analyzed.
It was found that the expression of several genes was dysregulated in blood cells generated from PTPN11 mutant stem cells. At the protein level, STAT5, a critical component of signaling and proliferation in JMML, was vastly higher in comparison to control. Furthermore, extracellular-signal-regulated kinases (ERKs) were also higher. While apoptosis (cell death) was similar in mutant and control cells, cell proliferation was eight-fold higher among mutant cells.
The research group investigated micro-RNA (mi-R) molecules that reduce protein levels via targeted degradation of mRNA. They found miR-223 and miR-15a levels increased by 50-fold and 10-fold, respectively, in PTPN11 mutant vs. control cells. To validate their observations, they also compared bone marrow samples from JMML patients and healthy controls, and found miR-223 and miR-15a RNA molecules significantly increased among patients.
The research team investigated 13 known targets of miR-223 and miR-15a, and found the expression of mRNA for nine genes to be significantly reduced in PTPN11 mutant stem cells and patient samples.
The up-regulation of miR-223 and miR-15a is observed in 60% of patients harboring the PTPN11 mutation, which may be a reason for further sub-classification of this disease. This work has illuminated molecular mechanisms in JMLL using stem cells, and provides targets for developing therapeutic interventions. At HemaCare, we provide stem cells for research and applaud the use of hiPSC for drug discovery and disease mechanism.
- Mulero-Navarro S, et al. Myeloid Dysregulation in a Human Induced Pluripotent Stem Cell Model of PTPN11-Associated Juvenile Myelomonocytic Leukemia. Cell Rep. 2015 Oct 20;13(3):504-15.