Cytopenias and Functional Defects in a Novel Murine Model of VPS45 Severe Congenital Neutropenia

Mutations in the VPS45 gene are associated with a rare form of severe congenital neutropenia (SCN5), a life-threatening inherited error of immunity. We developed and characterized a novel mouse model of SCN5 by CRISPR/Cas9-mediated knock-in of pathogenic VPS45 E238K and T224N mutations. Both Vps45 mutations led to decreased protein expression in bone marrow cells. In vivo phenotyping demonstrated a non-Mendelian genetic distribution with reduced numbers of knock-in homozygotes Vps45 ^E238K . Vps45 ^E238K knock-in homozygous mice showed reduced body weight, reduced body condition with age, and increased mortality. As in human SCN5, Vps45 ^E238K knock-in homozygotes demonstrated neutropenia and lymphopenia. Functionally, Vps45 ^E238K knock-in homozygote neutrophils exhibited increased lipopolysaccharide-induced apoptosis and decreased peroxide production, phagocytic capacity and in vivo cell migration, phenocopying the functional defects reported in patients. Vps45 ^T224N knock-in homozygous mice showed a milder phenotype or no abnormalities. In conclusion, this mouse model phenocopies, in part, human SCN5. It provides a novel platform for future studies of the pathophysiology of defects in neutrophil number and function in human SCN5, potential therapies for the disease, and the biochemistry and cell biology of VPS45.

We report a mouse model of severe congenital neutropenia due to VPS45 missense mutations. It represents the first animal model of human neutropenia due to a defect in intracellular trafficking.