The role of vacuolar protein sorting-associated protein 18 homolog (VPS18) in neutrophil biology

Gao, Jincheng (2025): The role of vacuolar protein sorting-associated protein 18 homolog (VPS18) in neutrophil biology. Dissertation, LMU München: Faculty of Medicine

Abstract

Neutrophils are the first responders to inflammation and an adequate number of neutrophils in the circulation is essential to maintain immune homeostasis. Congenital neutropenia is a group of rare genetic disorders of hematopoiesis characterized by diminished neutrophil counts in the circulation from birth. It is a life-threatening condition that can lead to recurrent infections. The mechanisms underlying congenital neutropenia are diverse, complex and remain incompletely understood. However, impaired intracellular vesicle trafficking has been linked to this disorder. Vacuolar protein sorting-associated protein 18 homolog (VPS18) is a core subunit of the HOPS and COVERT complexes and regulates intracellular vesicle trafficking through the endolysosomal and autophagosomal pathways. A patient with a heterozygous mutation in the VPS18 gene showed congenital neutropenia and recurrent infections. The underlying mechanisms of the symptoms of this patient and the role of VPS18 in neutrophil biology remained exclusive. Thus, the aim of this study was to elucidate the role of VPS18 in neutrophil biology in vitro and in vivo using the hematopoietic Hoxb8 cell system and a transgenic zebrafish model. Analysis of Hoxb8 cells as a model system for neutrophils revealed impaired maturation during differentiation in Vps18 mutants as studied by May-Grünwald-Giemsa staining. This finding was further confirmed by quantifying different myeloid maturation stages in these cells based on stage-specific markers on the cell surface. Upon differentiation, Vps18 mutants exhibited an increase in early and late apoptotic cells compared to CTRL Hoxb8 cells. Subsequently, an essential rescue experiment elucidated that the premature apoptosis in Vps18 mutants was specifically caused by VPS18 deficiency. In the zebrafish model, a reduced number of neutrophils was observed in vps18+/- zebrafish larvae which resembles the patient's situation, compared to vps18+/+ zebrafish larvae. The migration behavior of the residual neutrophils was analyzed in vivo using a spinning disk confocal microscope. Here, no differences in neutrophil migration were detectable under steady state conditions or during acute inflammation between vps18+/+ and vps18+/- zebrafish larvae. In summary, the neutrophil maturation defects in vitro and in vivo upon reduction of VPS18 expression provide evidence that VPS18 plays a fundamental role in neutrophil development.

• Item Type: Theses (Dissertation, LMU Munich)
• Keywords: VPS18, neutrophil biology, neutropenia
• Subjects: 600 Technology, Medicine; 600 Technology, Medicine > 610 Medical sciences and medicine
• Faculties: Faculty of Medicine
• Language: English
• Date of oral examination: 26. February 2025
• 1. Referee: Walzog, Barbara
• Signature of the printed copy: 0700/UMD 22678