The role of autophagy in hematopoiesis and hematopoietic disease

Autophagy is a cellular process essential for the maintenance of cytoplasm and clearance of expired proteins and organelles through a highly regulated lysosomal pathway. While it is widely believed that autophagy is a two-edged sword during oncogenesis, controversial results were also reported in leukemia, suggesting that autophagy also plays a complex role in leukemogenesis, depending on cell context and stages of leukemogenesis. Nevertheless, a single in vivo model to prove the hypothesis is lacking and the role of autophagy in normal hematopoiesis remains largely unknown. Here we make use of the zebrafish model to investigate the role of autophagy in hematopoiesis under normal and pathological conditions.

We targeted ulk1b in both wild-type and FLT3-ITD overexpressing (FLT3ITD) zebrafish embryos by TALEN-mediated mutagenesis. Zebrafish ulklb mutant embryos in both WT or FLT3ITD background displayed defective autophagy as shown by the immunostaining and western blot of Lc3-I/II as well as in vivo LysoTracker and LysoSensor staining. Defective autophagy associates with increased myelopoiesis in wild-type embryos and more importantly, the further enhanced early pre-leukemic myeloproliferation in zebrafish FLT3ITD model. Interestingly, ulk1b knock-out ameliorated the persistent myeloproliferation observed in FLT3ITD model, demonstrated the complex role of autophagy during leukemogenesis. In both wild-type and FLT3ITD embryos, ulk1b knock-out also resulted in decreased p53 and increased mTOR protein, which provided a direct mechanistic explanation on the observed myeloproliferation and suggested a previously undescribed bi-directional regulatory role between autophagy and mTOR or p53.

In summary, we make use of the strength of zebrafish model to demonstrate the complex role of autophagy in normal and malignant myelopoiesis. Further studies are warrant to examine the undefined role of autophagy in leukemogenesis, which is important for the development of effective autophagy-related therapeutic strategies against AML.