Using Disease-Specific Induced Pluripotent Stem Cells to Understand the Etiology of the Hematopoietic Defects in Gaucher Disease

Abstract

Gaucher disease (GD) is the most common lysosomal storage disease, resulting from mutations in the gene encoding the lysosomal enzyme, glucocerebrosidase (GCase). GCase deficiency results in the lysosomal accumulation of sphingolipids, primarily in macrophages and neurons leading to multi-organ pathology including hepatosplenomegaly, bone disease, neurological symptoms, and cytopenias. It is currently unclear whether the hematopoietic abnormalities of GD are due to an inherent defect in the hematopoietic stem cell population or are a consequence of the other pathological manifestations. To investigate the potential effects of GCase deficiency on hematopoietic progenitor cells (HPCs), we generated GD-HPCs from induced pluripotent stem cells (GD-iPSCs) representing all 3 clinical subtypes of GD. We found no differences in the efficiency of GD-HPC generation or the kinetics of hematopoietic marker expression compared to controls, suggesting that the consequences of enzyme deficiency lie downstream of the generation of the HPC pool. We assessed the multipotency of GD-HPCs through colony formation assays, liquid differentiation protocols, and flow cytometry. Examination of the lineage potential of GD-HPCs by these methods revealed skewed commitment to the myelo-erythroid lineage with increased myeloid differentiation and decreased erythroid differentiation. This decreased erythroid differentiation could account for the anemia present in patients. The increased myeloid differentiation may represent a mechanism to compensate for the accumulation of dysfunctional lipid-laden macrophages. Supplementation of the mutant HPCs with recombinant enzyme restored GD-HPC myelo-erythroid multipotency, demonstrating the direct role of GCase enzyme activity in HPC lineage specification. Enzyme deficiency also impaired megakaryocytepoiesis, reflecting the thrombocytopenia found in patients. Interestingly, GD-HPCs also gave rise to conspicuous lipid-laden macrophage cells. These cells are reminiscent of hallmark Gaucher cells found infiltrating patient tissues, for the first time suggesting the direct derivation of Gaucher cells from HPCs. Together, these findings offer unique insights into the importance of GCase enzymatic activity in HPC multipotency and suggest that enzyme deficiency within this population could account for the cytopenias present in GD patients. Additionally, they suggest a unique origin for the lipid-laden Gaucher cells central to GD pathology.