Essential role for Nix in autophagic maturation of erythroid cells

Abstract

Erythroid cells undergo enucleation and the removal of organelles during terminal differentiation1,2,3. Although autophagy has been suggested to mediate the elimination of organelles for erythroid maturation2,3,4,5,6, the molecular mechanisms underlying this process remain undefined. Here we report a role for a Bcl-2 family member, Nix (also called Bnip3L)7,8,9, in the regulation of erythroid maturation through mitochondrial autophagy. Nix-/- mice developed anaemia with reduced mature erythrocytes and compensatory expansion of erythroid precursors. Erythrocytes in the peripheral blood of Nix-/- mice exhibited mitochondrial retention and reduced lifespan in vivo. Although the clearance of ribosomes proceeded normally in the absence of Nix, the entry of mitochondria into autophagosomes for clearance was defective. Deficiency in Nix inhibited the loss of mitochondrial membrane potential (ΔΨm), and treatment with uncoupling chemicals or a BH3 mimetic induced the loss of ΔΨm and restored the sequestration of mitochondria into autophagosomes in Nix-/- erythroid cells. These results suggest that Nix-dependent loss of ΔΨm is important for targeting the mitochondria into autophagosomes for clearance during erythroid maturation, and interference with this function impairs erythroid maturation and results in anaemia. Our study may also provide insights into molecular mechanisms underlying mitochondrial quality control involving mitochondrial autophagy.

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Figure 1: Reticulocytosis and retention of mitochondria in Nix -/- RBCs.
Figure 2: Decreased survival of RBCs in Nix -/- mice.
Figure 3: Defective clearance of mitochondria by autophagy in Nix -/- reticulocytes.
Figure 4: Removal of mitochondria by autophagy in FCCP-treated or ABT-737-treated Nix -/- reticulocytes.

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Acknowledgements

We thank L. Huang, D. Yoon, A. Syed and D. Townley for technical assistance, and M. Andreeff for ABT-737. This work was supported by grants from the American Society of Hematology (M.C.), the American Heart Association (M.C.) and the NIH (J.W. and J.T.P.), a VA Merit grant (P.T.) and by a Ruth L. Kirschstein National Research Service Award (H.S.).

Author Contributions H.S. conducted the majority of the experiments, supervised by J.W. and M.C.; P.T. stained spleen sections and blood smears; S.K.D. measured osmotic fragility and assisted with biotin and CMFDA labelling; A.S. performed RT–PCR for Epo; J.T.P. and P.T. provided experimental advice; M.C. and J.W. generated the Nix-/- mice, designed experiments and prepared the manuscript; and all authors edited the manuscript.

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Correspondence to Min Chen or Jin Wang.

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Sandoval, H., Thiagarajan, P., Dasgupta, S. et al. Essential role for Nix in autophagic maturation of erythroid cells. Nature 454, 232–235 (2008) doi:10.1038/nature07006

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