Radiation-Induced Innate Neutrophil Response in Tumor Is Mediated by the CXCLs/CXCR2 Axis.

The early events that lead to the inflammatory and immune-modulatory effects of radiation therapy (RT) in the tumor microenvironment (TME) after its DNA damage response activating the innate DNA-sensing pathways are largely unknown. Neutrophilic infiltration into the TME in response to RT is an early innate inflammatory response that occurs within 24-48 h. Using two different syngeneic murine tumor models (RM-9 and MC-38), we demonstrated that CXCR2 blockade significantly reduced RT-induced neutrophilic infiltration. CXCR2 blockade showed the same effects on RT-induced tumor inhibition and host survival as direct neutrophil depletion. Neutrophils highly and preferentially expressed CXCR2 compared to other immune cells. Importantly, RT induced both gene and protein expression of CXCLs in the TME within 24 h, attracting neutrophils into the tumor. Expectedly, RT also upregulated the gene expression of both cGAS and AIM2 DNA-sensing pathways in cGAS-positive MC-38 tumors but not in cGAS-negative RM-9 tumors. Activation of these pathways resulted in increased IL-1ß, which is known to activate the CXCLs/CXCR2 axis. Gene ontology analysis of mRNA-Seq supported these findings. Taken together, the findings suggest that the CXCLs/CXCR2 axis mediates the RT-induced innate inflammatory response in the TME, likely translating the effects of innate DNA-sensing pathways that are activated in response to RT-induced DNA damage.

Myeloid-derived growth factor regulates neutrophil motility in interstitial tissue damage.

Neutrophil recruitment to tissue damage is essential for host defense but can also impede tissue repair. The cues that differentially regulate neutrophil responses to tissue damage and infection remain unclear. Here, we report that the paracrine factor myeloid-derived growth factor (MYDGF) is induced by tissue damage and regulates neutrophil motility to damaged, but not infected, tissues in zebrafish larvae. Depletion of MYDGF impairs wound healing, and this phenotype is rescued by depleting neutrophils. Live imaging and photoconversion reveal impaired neutrophil reverse migration and inflammation resolution in mydgf mutants. We found that persistent neutrophil inflammation in tissues of mydgf mutants was dependent on the HIF-1α pathway. Taken together, our data suggest that MYDGF is a damage signal that regulates neutrophil interstitial motility and inflammation through a HIF-1α pathway in response to tissue damage.

Cell type specific gene expression profiling reveals a role for complement component C3 in neutrophil responses to tissue damage.

Tissue damage induces rapid recruitment of leukocytes and changes in the transcriptional landscape that influence wound healing. However, the cell-type specific transcriptional changes that influence leukocyte function and tissue repair have not been well characterized. Here, we employed translating ribosome affinity purification (TRAP) and RNA sequencing, TRAP-seq, in larval zebrafish to identify genes differentially expressed in neutrophils, macrophages, and epithelial cells in response to wounding. We identified the complement pathway and c3a.1, homologous to the C3 component of human complement, as significantly increased in neutrophils in response to wounds. c3a.1-/- zebrafish larvae have impaired neutrophil directed migration to tail wounds with an initial lag in recruitment early after wounding. Moreover, c3a.1-/- zebrafish larvae have impaired recruitment to localized bacterial infections and reduced survival that is, at least in part, neutrophil mediated. Together, our findings support the power of TRAP-seq to identify cell type specific changes in gene expression that influence neutrophil behavior in response to tissue damage.