*Purpose: The objective of this study is to investigate the role of Chemokine (C-X-C motif) ligand 16 (CXCL16) and its unique receptor C-X-C chemokine receptor type 6 (CXCR6) in murine renal ischemia reperfusion injury (IRI). In addition, another objective is to investigate the relationship between CXCL16/CXCR6 and macrophages and the possible underlying mechanism in this situation.

*Methods: In vivo, the model of murine renal ischemia reperfusion injury was used to induce the acute kidney injury. CXCR6 knockout mice were also included in this study. Serum creatinine (Scr) and blood urea nitrogen (BUN) were used to detect the kidney function. Enzyme-linked immunosorbent assay (ELISA) was used to detect the concentration of serum CXCL16. Quantitative Real-time PCR (qPCR) was used to detect the mRNA expression of CXCL16, CXCR6 and inflammatory factors in kidneys. Immunohistochemistry (IHC) was used to detect the histological expression of CXCL16 and CXCR6 and immunoluorescence (IF) was used to identify the expression of F4/80 (the marker of murine macrophage), iNOS (the marker of M1 macrophage) and CD206 (the marker of M2 macrophage) in kidneys. In vitro, chemotaxis assay was used to test the chemotaxis of CXCL16 on RAW264.7 cells (a cell line of macrophage) and LPS was used to induce the polarization of M1 macrophages in RAW264.7 cells. ELISA was used to identify the concentration of inflammatory factors in the supernatants from the cells. RNA sequencing (RNA-seq) was used to investigate the possible underlying the regulation of CXCL16 on macrophages.

*Results: In vivo, after IRI, the serum CXCL16 concentration, the mRNA expression and the histological expression of renal CXCL16/CXCR6 were increased, which was consistent with the increase of Scr and BUN, and all of them peaked at 24h after IRI. At 24h after IRI, the CXCR6 knockout mice showed improved kidney function, less infiltration of macrophage, less ratio of M1 macrophage and less expression of inflammatory factors in kidneys than the wild type ones. However, there was no significant change in the number of M2 macrophages between the CXCR6 knockout and the wild type mice. In vitro, CXCL16 directly increased the chemotaxis of RAW264.7 cells. In addition, CXCL16 promoted pro-inflammatory responses of M1 macrophage with the existence of LPS. RNA-seq highly indicated that the CXCL16 increased the innate immune response of macrophages. Several up and down differential genes have been identified by RNA-seq.

*Conclusions: CXCL16/CXCR6 plays an important role in mediating the chemotaxis of macrophages to the kidney. In addition, CXCL16/CXCR6 promotes the polarization of M1 macrophages as well as the pro-inflammatory responses of M1 macrophages. The underlying mechanism needs to be further investigated.

« Back to 2020 American Transplant Congress