Defective Expression of LEF-1 Transcription Factor mRNA and - Protein in Patients with Severe Congenital Neutropenia (Kostmann’S Syndrome).

Severe congenital neutropenia (SCN) is characterized by “maturation arrest” of myeloid progenitor cells at the promyelocytic/myelocytic stage with the absence or only few mature neutrophils in the bone marrow and peripheral blood. Significant progress in the treatment of SCN patients has been achieved in the last 15 years by administration of granulocyte colony-stimulating factor (G-CSF), which significantly increases the number of neutrophils leading to an improvement of the quality of life. To date, the pathophysiology and underlying genetic defect in patients with congenital neutropenia is still under investigation. Wnt signalling pathway orchestrates a number of cellular programs such as proliferation, differentiation and cell fate determination in many tissues. In the present study we investigated the mRNA and protein expression patterns of Wnt signalling peptides, such as the High Mobility Group (HMG) box containing transcription factors such as lymphoid enhancer factor-1 (LEF-1) and T cell factors (TCFs), as well as β-catenin in CD33⁺ bone marrow myeloid progenitor cells from SCN patients (n = 6) in comparison to those of patients with cyclic neutropenia (n = 4) and G-CSF-treated healthy controls (n = 3). All SCN and cyclic neutropenia patients are under G-CSF therapy. mRNA expression of genes of interest was measured by quantitative real-time PCR. Protein expression was assessed by immunofluorescence staining, visualized and recorded by confocal microscopy. We found that CD33⁺ cells from patients with SCN exhibited 20 times lower or even absent expression of LEF-1 mRNA and protein, as compared to healthy G-CSF treated controls (mRNA expression ratio: SCN patients 0.83 ± 0.38 AU vs. healthy controls: 15.1 ± 0.4 AU; p < 0.0001). Intriguingly, LEF-1 mRNA expression levels on CD33⁺ cells from cyclic neutropenia patients were comparable to those of healthy controls. Immunostaining with anti-LEF-1 polyclonal antibody (kindly provided by Dr. R. Grosschedl) and confocal microscopy analysis revealed that LEF-1 protein was detectable at the expected level in CD33⁺ cells from healthy G-CSF treated controls. In patients with cyclic neutropenia LEF-1 protein expression in myeloid progenitor cells was comparable to healthy individuals. In contrast, in CD33⁺ cells from patients with SCN, LEF-1 protein was not detectable. mRNA expression of other TCFs: TCF-1, TCF-3, TCF-4 in SCN was not significantly different from healthy individuals. However, the expression level of LEF-1 binding partner in the Wnt pathway, β-catenin, was increased in SCN patients (SCN patients: 224.7 ± 42.4 AU vs. healthy controls: 107.2 ± 7.3 AU, p = 0.052). The defect in LEF-1 expression in SCN patients was further substantiated by the fact that mRNA expression of LEF-1 target genes such as c-myc, cyclin D1, survivin and neutrophil elastase were also significantly downregulated. In conclusion, our results suggest that defective LEF-1 expression might have an impact on the pathogenesis of SCN. In addition, it may help to distinguish SCN from cyclic neutropenia patients.