Severe congenital neutropenia (CN) is a heterogeneous disorder of myelopoiesis with two major types of inheritance:

  1. autosomal dominant CN defined by mutations in ELA2 gene encoding neutrophil elastase (NE) (

    Horwitz M., et al., Nat Genet. 1999;23:433
    ) and

  2. autosomal recessive CN (including Kostmann syndrome) carrying HAX-1 mutations (

    Klein C., et al., Nat Genet. 2007;39:86
    ), both characterized by a maturation arrest of granulopoiesis at the level of promyelocytes.

In the present study we aimed to evaluate the expression profile of genes specifically expressed in the CD33+ bone marrow promyelocytes of both patient groups harbouring ELA2 or HAX1 mutations. In healthy individuals mRNA expression levels of neutrophil serine proteases (neutrophil elastase (ELA2), cathepsin G, cathepsin D, proteinase 3 and azurocidin) as well as of myeloperoxidase (MPO) and defensins reached highest levels in the azurophil granules at the promyelocytic stage of neutrophil differentiation (

Borregaard N., et al., Curr Opin Hematol. 2001;8:23
). We found downregulation of mRNA expression levels of ELA2 (8.9 fold), cathepsin G (7.6 fold), cathepsin D (11.2 fold), proteinase 3 (9.2 fold) and defensin B1 (6.5 fold) in both groups of CN patients (with ELA2 or HAX1 mutations), in comparison to G-CSF-treated patients with idiopathic neutropenia (IN) and G-CSF-treated healthy controls. In contrast, there were no difference in mRNA expression levels of azurocidin and only slight decrease in the expression of MPO mRNA in CN patients. Additionally, we found significantly reduced protein levels of neutrophil elastase (NE) in plasma of CN patients irrespective of “ELA2 or HAX1” inheritance, in comparison to cyclic neutropenia (CyN) patients, IN patients and G-CSF-treated healthy controls. Taken together, both ELA2 and HAX1 mutations are associated with defective expression of neutrophil serine proteases such as NE, cathepsin G, cathepsin D, proteinase 3 as well as of defensin B1 in CD33+ myeloid progenitor cells of CN patients, suggesting a common pathway for both patient groups. Intriguingly, ELA2 expression is directly regulated by LEF-1, suggesting that abrogated LEF-1 expression in CN promyelocytes (
Skokowa J., et al., Nat. Med. 2006;12:1191
) may be responsible for defective serine proteases expression in both groups, since all are regulated by a similar mechanism.

Topics:
carrying, congenital neutropenia, mutation, neutrophils, serine proteases, granules, rna, messenger, cathepsin d, cathepsins, colony-stimulating factors

Author notes

Disclosure: No relevant conflicts of interest to declare.

2007, The American Society of Hematology
2007
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