The LPA2 receptor agonist Radioprotectin-1 spares Lgr5-positive intestinal stem cells from radiation injury in murine enteroids

Rapidly proliferating cells are highly sensitive to ionizing radiation and can undergo apoptosis if the oxidative and genotoxic injury exceed the defensive and regenerative capacity of the cell. Our earlier work has established the antiapoptotic action of the growth factor-like lipid mediator lysophosphatidic acid (LPA). Activation of the LPA(2) GPCR has been hypothesized to elicit antiapoptotic and regenerative actions of LPA. Based on this hypothesis we developed a novel nonlipid agonist of LPA(2), which we designated Radioprotectin-1 (RP-1). We tested RP-1 at the six murine LPA GPCR subtypes using the transforming growth factor alpha shedding assay and found that it had a 25 nM EC50 that is similar to that of LPA18:1 at 32 nM. RP-1 effectively reduced apoptosis induced by gamma-irradiation and the radiomimetic drug Adriamycin only in cells that expressed LPA 2 either endogenously or after transfection. RP-1 reduced gamma-H2AX levels in irradiated mouse embryonic fibroblasts transduced with the human LPA(2) GPCR but was ineffective in vector transduced MEF control cells and significantly increased clonogenic survival after gamma-irradiation. gamma-Irradiation induced the expression of lpar2 transcripts that was further enhanced by RP-1 exposure within 30 min after irradiation. RP-1 decreased the mortality of C57BL/6 mice in models of the hematopoietic and gastrointestinal acute radiation syndromes. Using Lgr5-EGFPCreER;Tdtomato(flox) transgenic mice, we found that RP-1 increased the survival and growth of intestinal enteroids via the enhanced survival of Lgr5(+) intestinal stem cells. Taken together, our results suggest that the LPA(2)-specific agonist RP-1 exerts its radioprotective and radiomitigative action through specific activation of the upregulated LPA(2) GPCR in Lgr5(+) stem cells.