Loss of miR-144/451 alleviates β-thalassemia by stimulating ULK1-mediated autophagy of free α-globin.

Most cells can eliminate unstable or misfolded proteins through quality control mechanisms. In the inherited red blood cell disorder β-thalassemia, mutations in the β-globin gene (HBB) lead to a reduction of the corresponding protein and the accumulation of cytotoxic free α-globin, which causes maturation arrest and apoptosis of erythroid precursors and reductions in the lifespan of circulating red blood cells. We showed previously that excess α-globin is eliminated by ULK1-dependent autophagy and that stimulation of this pathway by systemic mTORC1 inhibition alleviates β-thalassemia pathologies. We show here that disruption of the bi-cistronic microRNA locus miR-144/451 alleviates β-thalassemia by reducing mTORC1 activity and stimulating ULK1-mediated autophagy of free α-globin through two mechanisms. Loss of miR-451 upregulated its target mRNA, Cab39, which encodes a cofactor for LKB1, a serine-threonine kinase that phosphorylates and activates the central metabolic sensor, AMPK. The resultant enhancement of LKB1 activity stimulated AMPK and its downstream effects, including repression of mTORC1 and direct activation of ULK1. Additionally, loss of miR-144/451 inhibited the expression of erythroblast transferrin receptor 1 (TfR1), causing intracellular iron restriction, which has been shown to inhibit mTORC1, reduce free α-globin precipitates and improve hematological indices in β-thalassemia. The beneficial effects of miR-144/451 loss in β-thalassemia were inhibited by disruption of the Cab39 or Ulk1 genes. Our findings link the severity of a common hemoglobinopathy to a highly expressed erythroid microRNA locus and to a fundamental, metabolically regulated protein quality control pathway that is amenable to therapeutic manipulation.