Effect of bcl-2 deficiency on the radiation response of clonogenic cells in small and large intestine, bone marrow and testis

Abstract

Purpose : Overexpression of bcl -2 protects against radiation induced apoptosis in lymphohaematopoietic cell types in vivo, whilst bcl -2 deficiency radiosensitizes murine T-lymphocytes in vitro. However, there are few data regarding the influence of bcl-2 deficiency on the radiosensitivity of non-lymphoid cell types. The purpose of this study was to investigate the role of bcl-2 in the clonogenic radiation response of intestinal crypts, bone marrow progenitor cells and testicular stem cells. Method : Survival curves were obtained for each cell type from bcl -2 null (-/-), heterozygote (+/-) and wild type (+/+) mice. Crypt survival in the small and large intestine was assessed using the crypt microcolony assay. Committed haemopoietic progenitors were assayed using in vitro colony-forming cell (CFC) assays and survival of clonogenic spermatogonia was assessed by scoring regenerative tubules at 35 days post-irradiation. Results : There was no difference in small intestine crypt survival between the three genotypes. In the colon, there was a tendency towards lower clonogen survival in the +/- and -/- animals. Haemopoietic in vitro CFC from -/- animals showed lower survival in comparison to +/+ mice, but spermatogonial stem cells were comparatively more radioresistant. Conclusions : Deficiencies in bcl -2 a ffect the radiation response of different cell populations in small but different ways. This may be due to variations between cells in their innate capacity for apoptosis, their dependence on different members of the bcl -2 family gene and their cell-cycle status and p53 expression.