Reticulon-1 and reduced migration towards chemoattractants by macrophages differentiated from the bone marrow of UV-irradiated and UV-chimeric mice

The ability of macrophages to respond to chemoattractants and inflammatory signals is important for their migration to sites of inflammation and immune activity and for host responses to infection. Macrophages differentiated from the bone marrow of UV-irradiated mice, even after activation with LPS, migrated inefficiently towards CSF-1 and CCL2. When bone marrow cells were harvested from UV-irradiated mice, and transplanted into naïve mice, the recipient mice (UV-chimeric) had reduced accumulation of elicited macrophages in the peritoneal cavity in response to inflammatory thioglycollate or alum. Macrophages differentiating from the bone marrow of UV-chimeric mice also had an inherent reduced ability to migrate towards chemoattractants in vitro, even after LPS activation. Microarray analysis identified reduced reticulon-1 mRNA in macrophages differentiated from the bone marrow of UV-chimeric mice. By using an anti-reticulon-1 antibody, a role for reticulon-1 in macrophage migration was confirmed. The proposal that reduced reticulon-1 is responsible for the poor inherent ability of macrophages to respond to chemokine gradients was supported by Western blotting. In summary, skin exposure to erythemal UV radiation can modulate macrophage progenitors in the bone marrow such that the properties of their differentiated progeny respond inefficiently to signals to accumulate at sites of inflammation and immunity. Donor BM cells were isolated from congenic B6.SJL-Ptprca (CD45.1 alloantigen) mice that had been administered 8 kJ/m2 UVR to their shaved backs three days previously. BM cells from tibias and femurs were disaggregated and passed through sterile cotton wool to remove bone debris. Red blood cells were lysed with ammonium chloride. The recipient mice were 8-week-old C57BL/6J mice (CD45.2 alloantigen) that were gamma-irradiated (2 x 550 rad) using a 137Cs source (Gammacell 3000 Elan, MDS Nordion, Ottawa, Canada) prior to injection of 2 x 10e6 donor BM cells. Control chimeric mice were gamma-irradiated and injected with 2 x 10e6 BM cells from naïve congenic B6.SJL-Ptprca mice (shaved but not UV-irradiated).