AZD8055 Is More Effective Than Rapamycin in Inhibiting Proliferation and Promoting Mitochondrial Clearance in Erythroid Differentiation.

Background: As an important downstream effector of various signaling pathways, mTOR plays critical roles in regulating many physiological processes including erythropoiesis. It is composed of two distinct complexes, mTORC1 and mTORC2, which differ in their components and downstream signaling effects. Our previous study revealed that the inhibition of mTORC1 by rapamycin significantly repressed the erythroid progenitor expansion in the early stage but promoted enucleation and mitochondria clearance in the late stage of erythroid differentiation. However, the particular roles and differences of mTORC1 and mTORC2 in the regulation of erythropoiesis still remain largely unknown. In the present study, we investigated the comparative effects of dual mTORC1/mTORC2 mTOR kinase inhibitor AZD8055 and mTORC1 inhibitor rapamycin on erythroid differentiation in K562 cells induced by hemin and erythropoiesis in β-thalassemia mouse model. Materials and Methods: In vitro erythroid differentiation model of hemin-induced K562 cells and β-thalassemia mouse model were treated with AZD8055 and rapamycin. Cell Counting Kit-8 was used to detect cell viability. The cell proliferation, cell cycle, erythroid surface marker expression, mitochondrial content, and membrane potential were determined and analyzed by flow cytometry and laser scanning confocal microscopy. Globin gene expression during erythroid differentiation was measured by RT-qPCR. The mTORC2/mTORC1 and autophagy pathway was evaluated using western blotting. Results: Both AZD8055 and rapamycin treatments increased the expression levels of the erythroid differentiation-specific markers, CD235a, α-globin, γ-globin, and ε-globin. Notably, AZD8055 suppressed the cell proliferation and promoted the mitochondrial clearance of hemin-induced K562 cells more effectively than rapamycin. In a mouse model of β-thalassemia, both rapamycin and AZD8055 remarkably improve erythroid cell maturation and anemia. Moreover, AZD8055 and rapamycin treatment inhibited the mTORC1 pathway and enhanced autophagy, whereas AZD8055 enhanced autophagy more effectively than rapamycin. Indeed, AZD8055 treatment inhibited both mTORC2 and mTORC1 pathway in hemin-induced K562 cells. Conclusion: AZD8055 is more effective than rapamycin in inhibiting proliferation and promoting mitochondrial clearance in erythroid differentiation, which might provide us one more therapeutic option other than rapamycin for ineffective erythropoiesis treatment in the future. These findings also provide some preliminary information indicating the roles of mTORC1 and mTORC2 in erythropoiesis, and further studies are necessary to dissect the underlying mechanisms.