Page 102 - Haematologica April 2020

S. Altamura et al.
poiesis by forming erythropoietic islands in the BM,44 it was important to discriminate whether erythropenia is brought about by a cell-autonomous effect of GPX4 on the erythroid lineage or by a cell-non-autonomous effect of GPX4 on macrophages. Liao et al. recently described that loss of all selenoproteins in hematopoietic cells by deletion of selenocysteine-specific t-RNA impairs stress erythropoiesis and have attributed this to the loss of
selenoprotein W in macrophages.13 Despite the high posi- tion of GPX4 in the hierarchy of selenoproteins, a cell- autonomous contribution of GPX4 to stress erythropoiesis was not considered by the authors.
To address a potential contribution of GPX4 in macrophages on stress erythropoiesis, we used Gpx4fl/fl;LysM-Cre mice that delete Gpx4 in macrophages and neutrophils45 and analyzed BM erythroblastic island
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Figure 6. Iron overload in the liver and simultaneous iron demand for erythropoiesis in mice with a Gpx4-deficient hematopoietic system. In the liver of mice with Gpx4-proficient and Gpx4-deficient hematopoiesis only the wild-type (wt) allele of Gpx4 is detected (A), and the same levels of Gpx4 mRNA (B) and protein (C) are expressed. (D-K, V) Parameters of iron metabolism in the liver: Non-heme hepatic iron (D), ferroportin mRNA (E), heme oxygenase-1 mRNA (F), thiobarbituric acid reactive substances (TBARS)(G), hepcidin mRNA (H), Smad6 mRNA (I), Smad7 mRNA (J), and ID1 mRNA (K). The proteins ferroportin (FPN), heme oxygenase (HO-1), and ferritine light chain (FTL) are expressed at higher level in mice with a Gpx4-deficient hematopoietic system (V). Parameters of splenic and peripheral iron metab- olism: non-heme splenic iron (L), splenic Erfe mRNA (M), plasma iron (N), plasma ferritine (O), plasma EPO (P), plasma ERFE (Q), plasma hepcidin (R), plasma bilirubin total (S), plasma bilirubin direct (T), plasma bilirubin indirect (U). Increased hepatic non-heme iron and TBARS as well as elevated ferroportin and heme oxygenase- 1 expression point to hepatic iron overload, whereas highly increased EPO and ERFE levels in the plasma and elevated Erfe mRNA expression levels are strong indi- cators of severe iron demand in the erythropoietic system. Note that hepcidin expression is not down regulated despite the strong erythropoietic iron demand. For HO-1/actin ratio in the liver and duodenal ferroportin expression, see Online Supplementary Figure S7A-B.
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haematologica | 2020; 105(4)