Decrease in α-Globin and Increase in the Autophagy-Activating Kinase ULK1 mRNA in Erythroid Precursors from β-Thalassemia Patients Treated with Sirolimus

Abstract

The β-thalassemias are hereditary monogenic diseases characterized by a low or absent production of adult hemoglobin and excess in the content of α-globin. This excess is cytotoxic for the erythroid cells and responsible for the β-thalassemia-associated ineffective erythropoiesis. Therefore, the decrease in excess α-globin is a relevant clinical effect for these patients and can be realized through the induction of fetal hemoglobin, autophagy, or both. The in vivo effects of sirolimus (rapamycin) and analogs on the induction of fetal hemoglobin (HbF) are of key importance for therapeutic protocols in a variety of hemoglobinopathies, including β-thalassemias. In this research communication, we report data showing that a decrease in autophagy-associated p62 protein, increased expression of ULK-1, and reduction in excess α-globin are occurring in erythroid precursors (ErPCs) stimulated in vitro with low dosages of sirolimus. In addition, increased ULK-1 mRNA content and a decrease in α-globin content were found in ErPCs isolated from β-thalassemia patients recruited for the NCT03877809 clinical trial and treated with 0.5–2 mg/day sirolimus. Our data support the concept that autophagy, ULK1 expression, and α-globin chain reduction should be considered important endpoints in sirolimus-based clinical trials for β-thalassemias.

Therapeutic Relevance of Inducing Autophagy in β-Thalassemia

“…Evidently, γ-globin gene activation and fetal hemoglobin (HbF) induction can be obtained either by CRISPR-Cas9 gene editing, targeting γ-globin gene repressors or the binding sequences presenting the γ-globin gene promoter (Figure 3, approach "B") [37][38][39], or by exposure of β-thalassemic erythroid cells to a variety of HbF inducers, (Figure 3C) as reviewed elsewhere [40][41][42] (Figure 3, approach "C"). Finally, a decrease in the excess free α-globin chains can be achieved in erythroid cells by the activation (or potentiation) of autophagy (as outlined in Figure 3, approach "D"), and is reported in several studies [43][44][45][46][47][48].…”

“…Zurlo et al, 2023 [47] Two clinical trials on β-thalassemia have been proposed, useful to further clarify this issue (NCT03877809 and NCT04247750). Rapamycin (sirolimus) has been proposed as an in vivo fetal hemoglobin inducer for the treatment of β-thalassemia.…”

“…Autophagy pathways are essential for eukaryotic tissue development, cellular homeostasis and protection against metabolic and proteotoxic Interestingly, Khandros et al, using the heterozygous thalassemic (Th3/+) mouse model system, found an accumulation of insoluble α-globin chains in erythroid precursors that further accumulates in proteasome-inhibited β-thalassemic reticulocytes [43]. In addition, as shown in Figure 4, a key biological process leading to a reduction in excess free α-globin in erythroid cells is the autophagy process, which is dependent on the Unc-51-like autophagy-activating kinase 1 (Ulk1) [45,47,48].…”

Impact of α-Globin Gene Expression and α-Globin Modifiers on the Phenotype of β-Thalassemia and Other Hemoglobinopathies: Implications for Patient Management

“…In addition, clinical parameters related to hemolysis and ineffective erythropoiesis (such as soluble transferrin receptor, ferritin, and bilirubin levels) were significantly reduced during sirolimus administration in these patients, suggesting that autophagy and α-globin clearance are important and effective processes to be considered during clinical trials involving thalassemia patients. Notably, a reduction in free α-globin and the upregulation of ULK1 gene expression was also found in erythroid cells isolated from rapamycin-treated β-thalassemia patients during the NCT03877809 clinical trial [109,110]. In addition, clinical parameters related to hemolysis and ineffective erythropoiesis (such as soluble transferrin receptor, ferritin, and bilirubin levels) were significantly reduced during sirolimus administration in these patients, suggesting that autophagy and α-globin clearance are important and effective processes to be considered during clinical trials involving thalassemia patients.…”

“…Notably, a reduction in free α-globin and the upregulation of ULK1 gene expression was also found in erythroid cells isolated from rapamycin-treated β-thalassemia patients during the NCT03877809 clinical trial [ 109 , 110 ]. In addition, clinical parameters related to hemolysis and ineffective erythropoiesis (such as soluble transferrin receptor, ferritin, and bilirubin levels) were significantly reduced during sirolimus administration in these patients, suggesting that autophagy and α-globin clearance are important and effective processes to be considered during clinical trials involving thalassemia patients.…”