Real-time functional analysis of Hv1 channel in neutrophils: a new approach from zebrafish model

Voltage-gated proton channel (Hv1) has been studied in various immune cells, including neutrophils. However, most studies have taken an in vitro approach using isolated cells or primary cultured cells of mammals; therefore, limited evidence is available on the function of Hv1 in a physiological context. In this study, we have developed the in vivo system that enables real-time functional analysis of Hv1 using zebrafish embryos (Danio rerio). Hvcn1-deficiency (hvcn1(-/-)) in zebrafish completely abolished voltage-gated proton current, which is typically observed in wild-type neutrophils. Importantly, hvcn1-deficiency significantly reduced reactive oxygen species production and calcium response of zebrafish neutrophils, comparable to the results observed in mammalian models. These findings verify zebrafish Hv1 (DrHv1) as the primary contributor for native Hv1-derived proton current in neutrophils and suggest the conserved function of Hv1 in the immune cells across vertebrate animals. Taking advantage of Hv1 zebrafish model, we compared real-time behaviors of neutrophils between wild-type and hvcn1(-/-) zebrafish in response to tissue injury and acute bacterial infection. Notably, we observed a significant increase in the number of phagosomes in hvcn1(-/-) neutrophils, raising a possible link between Hv1 and phagosomal maturation. Furthermore, survival analysis of zebrafish larvae potentially supports a protective role of Hv1 in the innate immune response against systemic bacterial infection. This study represents the influence of Hv1 on neutrophil behaviors and highlights the benefits of in vivo approach toward the understanding of Hv1 in a physiological context.