Risk of single low dose irradiation for developing retina and contribution of bone marrow cells to injured retinal tissue

Abstract

Abstract: : Purpose: Bone marrow (BM) stem cells have been demonstrated to regenerate into various kinds of cells by differentiation or cell fusion. Recent in vivo studies have also demonstrated that transplanted or endogenous stem cells are capable of migrating and differentiating into only damaged site. Until now, the influence of irradiation has been ignored in the experiment such as regeneration and transplantation. At first we examined the particular influence of the immature and mature retina by irradiation. As a second step, we investigated whether BM cells was migrated into those retinas and had specific antigens as retinal cells. Methods: The retinas irradiated gradually were investigated on time course pathologically. Moreover, to examine its cell death, we used the method of TUNEL and Brd–U labeling assay on time course. Next, we examined which BM cells prepared from GFP transgenic mice differentiate into neural retina by transplantation into the circulatory system of irradiated adult or newborn mice. We examined which BM cells prepared from GFP transgenic mice differentiate into neural retina by transplantation into the circulatory system of irradiated adult or newborn mice. Results: Pathologically, the retinal layer structure was destroyed completely and retinal cells decreased till about 20% in newborn mice at the lethal dose. After that, the retina had not been recovered and almost did not changed at post 1year. Adult retina was not observed any change histologically. In newborn mice, its cell death was caused by the apoptosis using TUNEL and DNA fragmentation. Retinal cells incorporated Brd–U intensely appeared after 24 hr. In adult mice, BM cells almost did not differentiate, but in newborn, approximately 4% of retinal cells became GFP+ cells at 1 year of age. Our experiments confirmed that the injury by irradiation leads BM cells into neural retina. Fluorescence microscopy showed that the GFP+ population contained various cells expressing specific protein, such as MAP2, GFAP, nestin, CD11b/Mac–1 and Pax6. But HPC–1 and CD45 almost were not stained. Examination of flat mounts of the retina showed that GFP+ cells also contributed to vascularization. However, rhodopsin and calcindin were not expressed by the influence of irradiation. Conclusions: In the future, we have to take careful for the retinal injury due to the irradiation, when postnatal BM transplantaion for genetic deficiency of the immune system and over dose examination for very low birth weight (VLBW).

Keywords: plasticity • regeneration • transplantation