Draper/CED-1 Mediates an Ancient Damage Response to Control Inflammatory Blood Cell Migration In Vivo

Abstract

SummaryTissue damage leads to a robust and rapid inflammatory response whereby leukocytes are actively drawn toward the wound. Hydrogen peroxide (H2O2) has been shown to be an immediate damage signal essential for the recruitment of these inflammatory blood cells to wound sites in both Drosophila and vertebrates [1, 2]. Recent studies in zebrafish have shown that wound-induced H2O2 is detected by the redox-sensitive Src family kinase (SFK) Lyn within the responding blood cells [3]. Here, we show the same signaling occurs in Drosophila inflammatory cells in response to wound-induced H2O2 with mutants for the Lyn homolog Src42A displaying impaired inflammatory migration to wounds. We go on to show that activation of Src42A is necessary to trigger a signaling cascade within the inflammatory cells involving the ITAM domain-containing protein Draper-I (a member of the CED-1 family of apoptotic cell clearance receptors) and a downstream kinase, Shark, that is required for migration to wounds. The Src42A-Draper-Shark-mediated signaling axis is homologous to the well-established SFK-ITAM-Syk-signaling pathway used in vertebrate adaptive immune responses. Consequently, our results suggest that adaptive immunoreceptor-signaling pathways important in distinguishing self from non-self appear to have evolved from a more-ancient damage response. Furthermore, this changes the role of H2O2 from an inflammatory chemoattractant to an activator signal that primes immune cells to respond to damage cues via the activation of damage receptors such as Draper.

Toll pathway is required for wound-induced expression of barrier repair genes in the Drosophila epidermis

“…Relevant to the model in Fig. 5, a recent study showed that Src42A can be directly activated by a wound-induced peroxide burst, leading to the recruitment of hemocytes to a wound site (37). Our results show that peroxide injected into spz mutant embryos fails to activate wound reporter genes.…”

Actin is an evolutionarily-conserved damage-associated molecular pattern that signals tissue injury in Drosophila melanogaster

“…This result was confirmed using a different driver (r4-Gal4) that led to constitutively reduced Shark levels in the fat body (Figure 6c). Shark activation occurs downstream of Src family kinase activity (Ziegenfuss et al, 2008; Evans et al, 2015). Silencing of the Src family kinase Src42A using a ubiquitous temperature-sensitive driver also led to a striking reduction in actin-induced TotM levels (Figure 6d).…”

“…Uptake of axonal debris by glial cells and responses to wound healing in Drosophila both require Src42A phosphorylation of the ITAM-bearing receptor Draper ( drpr ), which serves as a platform for Shark recruitment (Ziegenfuss et al, 2008; Evans et al, 2015). We found that drpr null mutants displayed a reduced TotM response to actin injection (Figure 6—figure supplement 1a).…”

Image-Based Measurement of H 2 O 2 Reaction-Diffusion in Wounded Zebrafish Larvae

“…In zebrafish and Drosophila, H 2 O 2 -mediated wound attraction of leukocytes requires oxidation of a redox-sensitive cysteine within the tyrosine kinase Lyn in leukocytes (10,11). Redox-sensitive cysteines may exhibit evolutionary conservation and functional relevance, although not all conserved and functionally relevant cysteines are necessarily redox-regulated.…”