Tfr2-mediated erythropoiesis expansion controls systemic glucose homeostasis by modulating erythroid metabolic demand Free

Introduction: Erythropoiesis is a highly energy-demanding and tightly regulated process. It involves cell proliferation, massive hemoglobin synthesis, and extensive cellular remodelling to produce red blood cells (RBCs) optimized for oxygen transport. The iron-sensor Transferrin Receptor 2 (TFR2) is a negative regulator of erythropoietin (EPO) signalling in erythroid cells, and its inactivation in hematopoietic cells boosts RBC production in wild-type (wt) mice,and ameliorates anemia and ineffective erythropoiesis (IE) in β-thalassemia models. Interestingly, erythroid differentiation is paralleled by a metabolic shift toward oxidative phosphorylation (OXPHOS), likely driven by EPO. Indeed, overactivation of EPO signalling in polycythemia vera mice causes a massive augment in the metabolic activity of erythroid cells, leading to systemic hypoglycemia and weight loss.

Aim: To determine whether hematopoietic Tfr2 deletion enhances erythroid metabolic activity via increased EPO sensitivity, thereby impacting systemic glucose homeostasis.

Methods: Wt and thalassemic mice with or without hematopoietic Tfr2 (Tfr2^BMKO) were generated through bone marrow transplantation (BMT). A cohort was sacrificed 8 weeks after BMT for RNA-seq analysis of sorted erythroid precursors at different stages of differentiation. A second cohort underwent complete hematological and metabolic characterization 8-11 weeks after BMT.

Separately, 8-week-old wt mice were treated with a single injection of EPO (200 UI) or 2 injections of Phenylhydrazine (PHZ, 50 mg/kg, days 0 and 2). PHZ-treated mice received either regular or 20% glucose-supplemented drinking water. Complete blood count, glycemia and body weight were monitored at days 0,2,3,5,7,9 and 14.

Results: As expected, non-thalassemic Tfr2^BMKO animals exhibit enhanced erythropoiesis and elevated RBC count. These mice develop systemic insulin-independent hypoglycemia, with blood glucose levels inversely correlating with RBC count, and improved glucose tolerance as compared to controls. RNA-seq analysis reveals upregulation of genes involved in glucose transport, glycolysis, pentose phosphate pathway, TCA cycle and OXPHOS in Tfr2 deficient erythroblasts. This increased metabolic activity is likely driven by EPO signalling overactivation.

Consistently, in wt mice, EPO-induced erythropoietic expansion, resulting in increased RBC count and Hb levels, causes a ~10% decline in blood glucose, without affecting body mass, supporting the notion of an erythropoiesis-dependent modulation of systemic glucose homeostasis.

Similarly, PHZ-induced hemolytic anemia in wt mice elicits a rapid erythropoietic response accompanied by a ~25% glycemia reduction and ~10% body weight loss, underscoring the substantial energetic demand of massive RBC production. Moreover , PHZ-driven erythropoietic expansion also prevents hyperglycemia in mice receiving glucose supplementation, suggesting that the modulation of erythropoiesis may serve as a novel tool for systemic glycemic control. Interestingly, while glucose is essential to sustain erythropoiesis-related metabolic needs, its supplementation does not improve anemia recovery, but mitigates weight loss during erythropoietic stress.

Notably, the hypoglycemic effect of expanded erythropoiesis is contingent on its effectiveness, and on erythroblasts proper management of glucose. Indeed, β-thalassemia mice, characterized by anemia, IE and impaired erythroid metabolism, show early-onset insulin-independent hyperglycemia and glucose intolerance. Remarkably, hematopoieticTfr2 deletion, restoring erythroid differentiation and metabolic activity, corrects the dysregulated glucose phenotype of these mice.

Conclusions: Our results highlight a critical reciprocal dependence between erythropoiesis and glucose homeostasis, identify TFR2 as a modulator of erythroid bioenergetics, and suggest that IE may directly contribute to diabetes development in β-thalassemia because of an inefficient glucose utilization by erythroid cells. Although glucose supplementation does not improve anemia-recovery, it prevents massive body weight loss due to energy request to sustain enhanced erythropoiesis, offering a potential supportive strategy during erythropoietic stress. Overall, these findings identify a unique and previously unexplored role for erythropoiesis in the regulation of systemic glucose homeostasis, positioning the bone marrow as a novel metabolic organ.