The Epidermal Growth Factor Ligand Spitz Modulates Macrophage Efferocytosis, Wound Responses and Migration Dynamics During Drosophila Embryogenesis

Abstract

How multifunctional cells such as macrophages interpret the different cues within their environment and undertake an appropriate response is a key question in developmental biology. Understanding how cues are prioritized is critical to answering this – both the clearance of apoptotic cells (efferocytosis) and the migration toward damaged tissue is dependent on macrophages being able to interpret and prioritize multiple chemoattractants, polarize, and then undertake an appropriate migratory response. Here, we investigate the role of Spitz, the cardinal Drosophila epidermal growth factor (EGF) ligand, in regulation of macrophage behavior in the developing fly embryo, using activated variants with differential diffusion properties. Our results show that misexpression of activated Spitz can impact macrophage polarity and lead to clustering of cells in a variant-specific manner, when expressed either in macrophages or the developing fly heart. Spitz can also alter macrophage distribution and perturb apoptotic cell clearance undertaken by these phagocytic cells without affecting the overall levels of apoptosis within the embryo. Expression of active Spitz, but not a membrane-bound variant, can also increase macrophage migration speeds and impair their inflammatory responses to injury. The fact that the presence of Spitz specifically undermines the recruitment of more distal cells to wound sites suggests that Spitz desensitizes macrophages to wounds or is able to compete for their attention where wound signals are weaker. Taken together these results suggest this molecule regulates macrophage migration and their ability to dispose of apoptotic cells. This work identifies a novel regulator of Drosophila macrophage function and provides insights into signal prioritization and integration in vivo. Given the importance of apoptotic cell clearance and inflammation in human disease, this work may help us to understand the role EGF ligands play in immune cell recruitment during development and at sites of disease pathology.

The EGFR/ErbB inhibitor neratinib modifies the neutrophil phosphoproteome and promotes apoptosis and clearance by airway macrophages

“…This is particularly important since other studies show that alveolar macrophages ingest apoptotic alveolar epithelial cells as well as apoptotic neutrophils in the lungs and airways ( 33 , 34 ). There is very little literature suggesting that ErbB signaling has a role in efferocytosis, although a recent study in Drosophila from our group shows that overexpression of the cardinal EGF ligand, Spitz, impairs macrophage-mediated apoptotic cell clearance ( 35 ). While this supports our current findings, there are likely to be a number of mechanisms at play, including EGF acting as a chemoattractant to “distract” the macrophages from apoptotic cell clearance, or EGFR signaling from other tissues polarizing the macrophages toward a phenotype less efficient at efferocytosis ( 35 ).…”

The EGFR/ErbB inhibitor neratinib modifies the neutrophil phosphoproteome and promotes apoptosis and clearance by airway macrophages

“…It is unclear in our studies whether neratinib is directly regulating macrophage efferocytosis, or upregulating apoptosis and thereby increasing the amount of material available to engulf. There is very little literature suggesting that ErbB signalling has a role in efferocytosis, although a recent study in Drosophila from our group shows that overexpression of the cardinal EGF ligand, Spitz, impairs macrophage-mediated apoptotic cell clearance (Tardy et al, 2021). While this supports our current findings, there are likely to be a number of mechanisms at play, including EGF acting as a chemoattractant to "distract" the macrophages from apoptotic cell clearance, or EGFR signalling from other tissues polarising the macrophages towards a phenotype less efficient at efferocytosis (Tardy et al, 2021).…”