TNF-TNFR2/p75 Signaling Inhibits Early and Increases Delayed Nontargeted Effects in Bone Marrow-derived Endothelial Progenitor Cells

Background: Ionizing radiation can induce DNA damage in nonirradiated (N-IR) cells via nontargeted effects (NTE). Results: TNF- and IL-1 mediate NTE in N-IR bone marrow-derived EPCs, and neutralizing TNF- diminishes NTE in WT and p55 knock-out BM-EPCs. Conclusion: TNF-TNFR2/p75 signaling alters accumulation of inflammatory cytokines that attenuate NTE in N-IR EPCs. Significance: TNFR2/p75 may represent a gene target for mitigation of delayed RBR in BM-EPCs. TNF-, a pro-inflammatory cytokine, is highly expressed after being irradiated (IR) and is implicated in mediating radiobiological bystander responses (RBRs). Little is known about specific TNF receptors in regulating TNF-induced RBR in bone marrow-derived endothelial progenitor cells (BM-EPCs). Full body -IR WT BM-EPCs showed a biphasic response: slow decay of p-H2AX foci during the initial 24 h and increase between 24 h and 7 days post-IR, indicating a significant RBR in BM-EPCs in vivo. Individual TNF receptor (TNFR) signaling in RBR was evaluated in BM-EPCs from WT, TNFR1/p55KO, and TNFR2/p75KO mice, in vitro. Compared with WT, early RBR (1-5 h) were inhibited in p55KO and p75KO EPCs, whereas delayed RBR (3-5 days) were amplified in p55KO EPCs, suggesting a possible role for TNFR2/p75 signaling in delayed RBR. Neutralizing TNF in -IR conditioned media (CM) of WT and p55KO BM-EPCs largely abolished RBR in both cell types. ELISA protein profiling of WT and p55KO EPC -IR-CM over 5 days showed significant increases in several pro-inflammatory cytokines, including TNF-, IL-1 (Interleukin-1 alpha), RANTES (regulated on activation, normal T cell expressed and secreted), and MCP-1. In vitro treatments with murine recombinant (rm) TNF- and rmIL-1, but not rmMCP-1 or rmRANTES, increased the formation of p-H2AX foci in nonirradiated p55KO EPCs. We conclude that TNF-TNFR2 signaling may induce RBR in naive BM-EPCs and that blocking TNF-TNFR2 signaling may prevent delayed RBR in BM-EPCs, conceivably, in bone marrow milieu in general.