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Bone Marrow Failure
A zebrafish model for HAX1-associated congenital neutropenia
Ferrata Storti Foundation
Haematologica 2021 Volume 106(5):1311-1320
Larissa Doll,1 Narges Aghaallaei,1 Advaita M. Dick,1 Karl Welte,2 Julia Skokowa1 and Baubak Bajoghli1
1Department of Oncology, Hematology, Immunology and Rheumatology, University Hospital, University of Tübingen and 2University Children’s Hospital Tübingen, Tübingen, Germany
ABSTRACT
Severe congenital neutropenia is a rare heterogeneous group of diseases, characterized by an arrest of granulocyte maturation. Autosomal reces- sive mutations in the HAX1 gene are frequently detected in affected individuals. However, the precise role of HAX1 during neutrophil differen- tiation is poorly understood. To date, no reliable animal model has been established to study HAX1-associated congenital neutropenia. Here we show that knockdown of zebrafish hax1 impairs neutrophil development without affecting other myeloid cells and erythrocytes. Furthermore, we found that interference with Hax1 function decreases the expression level of key target genes of the granulocyte colony-stimulating factor signaling path- way. The reduced neutrophil numbers in the morphants could be reversed by granulocyte colony-stimulating factor, which is also the main therapeutic intervention for patients who have congenital neutropenia. Our results demonstrate that the zebrafish is a suitable model for HAX1-associated neu- tropenia. We anticipate that this model will serve as an in vivo platform to identify new avenues for developing tailored therapeutic strategies for patients with congenital neutropenia, particularly for those individuals who do not respond to granulocyte colony-stimulating factor treatment.
Introduction
Severe congenital neutropenia (CN) is a rare hematologic disorder, which is char- acterized by impaired maturation of neutrophil granulocytes.1-6 Mutations in vari- ous genes, including ELANE, HAX1, G6PC3, CXCR4 and G-CSFR are associated with CN.1 Affected individuals are prone to life-threatening infections that begin in their first months of life unless treated by human granulocyte colony-stimulating factor (G-CSF, encoded by the CSF3 gene) or bone marrow transplantation.1,2 CN is also a preleukemic syndrome and patients are predisposed to develop myelodyspla- sia or acute myeloid leukemia after a long period of time.7,8 However, the severity of neutropenia and the risk of leukemia vary between individuals with distinct genetic aberrations, and a group of CN patients do not respond to the G-CSF ther- apy. The cumulative incidence of leukemia in less responsive patients is 40% after 15 years, in comparison to 20% in responsive patients,9 although, the underlying mechanisms are poorly understood.
HAX1 is ubiquitously expressed among human tissues.10,11 It acts as a binding part- ner of multiple proteins and is involved in various signaling pathways and cellular processes.12-14 For example, HAX1 interacts with the mitochondrial proteases PARL and HTRA2 and is involved in anti-apoptotic signaling.15 It interacts with PKD2 pro- tein and is associated with the actin cytoskeleton.16 HAX1 plays a role in BCR-medi- ated internalization through binding to the cytoplasmic domain of B-cell receptors.17 In hematopoietic progenitors, upon activation of the G-CSF receptor (G-CSFR), the cytoplasmic HAX1 binds to the HCSL1 and LEF-1 proteins, transporting LEF-1 into the nucleus. This transcription factor then activates target genes of the G-CSF signal- ing pathway including CEBPA and HCLS1.18 Taking into account that HAX1 is involved in diverse subcellular processes, it remains unclear why patients who lack functional HAX1 display predominantly impaired neutrophil differentiation.
Our current knowledge on the role of HAX1 in granulopoiesis is predominantly derived from in vitro studies and clinical observations.1,2 To date, no faithful animal
Correspondence:
BAUBAK BAJOGHLI
baubak.bajoghli@med.uni-tuebingen.de
Received: October 11, 2019. Accepted: April 9, 2020. Pre-published: April 23, 2020.
https://doi.org/10.3324/haematol.2019.240200
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