An Unsuspected Dyserythropoiesis in Gaucher Disease

Introduction: Gaucher disease (GD) is a lysosomal storage disorder, impairing glucosylceramide catabolism. GlcCer-laden macrophages transform into Gaucher cells and are responsible for the major GD symptoms (tissue infiltration, organomegaly, bone lesion). However, other signs of the disease such as anemia, spleen and bone infarcts might involve red blood cells (RBC). Despite the lysosomal characteristic of GD and the evidence of the central rdole of macrophages, our recent findings pointed out unexpected RBC abnormalities (Franco et al, Blood. 2013;121:546-555). These findings uncovered an overlooked aspect in GD showing that GD RBC exhibit abnormal rheological, morphological and membrane adhesion properties. Thus, RBC could be considered as culprit for ischemic events in GD. In this study, we analyzed the erythroid differentiation in GD to address the etiology of red cell abnormal behavior. We induced in vitro erythropoiesis from circulating GD patient progenitors.

Methods: After purification of CD34⁺ cells from peripheral blood of Gaucher patients (n=20) or controls (CTL), erythroid progenitors were expanded in the absence of erythropoietin (EPO) and differentiated in a second step with erythropoietin. GD and CTL CD34^- cells were differentiated into macrophages by addition of M-CSF in the culture medium. To determine the effect of CTL and GD macrophages on normal erythropoiesis, in vitro generated macrophages were co-cultured with CTL erythroid progenitors in the presence of EPO. Proliferation of progenitors as well as erythroid differentiation were examined by flow cytometry and cytology.

Results: Our preliminary results showed: (i) a dramatic decrease in proliferation of progenitors in the first step of expansion (**p <0.005), (ii) an accelerated erythroid maturation as evaluated by the percentage of cells expressing and non-expressing Glycophorin A and C-Kit, respectively (**p <0.005), (iii) an absence of effect of Gaucher macrophages co-culture on normal erythroid terminal maturation, and (iv) a correlation between the acceleration level of maturation and the degree of anemia in GD patients as determined by hemoglobin level (**p<0.005).

Conclusion: We evidenced an unexpected dyserythropoiesis characterized by accelerated erythroid differentiation in GD. The observed dyserythropoiesis is independent of macrophage defects and is intrinsic to the GD erythroid lineage. These studies by helping to understand the role of erythroid cells in the pathophysiology of GD as well as the mechanism of anemia should prove useful for the development of additive therapies to alleviate debilitating clinical complications of this morbid disease such as osteonecrosis and splenomegaly.