Increased susceptibility of radiation-induced intestinal apoptosis in SMP30 KO mice

Abstract

Recently, senescence marker protein-30 (SMP30) knockout (KO) mice have been reported to be susceptible to apoptosis, however, the role of SMP30 has not been characterized in the small intestine. The aim of the present study is to investigate the role of SMP30 in the process of spontaneous and γ-radiation-induced apoptosis in mouse small intestine. Eight-week-old male wild-type (WT) mice and SMP30 KO mice were examined after exposure to 0, 1, 3, 5, and 9 Gy of γ-radiation. Apoptosis in the crypts of the small intestine increased in the 0 to 5 Gy radiated SMP30 KO and WT mice. Radiation-induced apoptosis and the BAX/Bcl-2 ratio in the SMP30 KO mice were significantly increased in comparison to each identically treated group of WT mice (p < 0.05). The levels of spontaneous apoptosis in both WT and KO mice were similar (p > 0.05), indicating that increased apoptosis of crypt cells of SMP30 KO by irradiation can be associated with SMP30 depletion. These results suggested that SMP30 might be involved in overriding the apoptotic homeostatic mechanism in response to DNA damage.

Figure 1

(A) Representative photomicrographs of intestines stained with hematoxylin and eosin (H & E) from WT mice. N, normal control; VC, vitamin C; Gy, Gray; Original magnification 1000×, Bars = 20 μm; (B) Representative photomicrographs of intestines stained with H & E from SMP30 KO mice. N, normal control; VC, vitamin C; Gy, Gray; Original magnification × 1000, Bars = 20 μm; (C) Apoptotic cells in the H & E stained sections were quantified. Values represent the mean ± SD in each group. WT, wild type; KO, knock out. * Statistically significant difference (p < 0.05).

Figure 1

(A) Representative photomicrographs of intestines stained with hematoxylin and eosin (H & E) from WT mice. N, normal control; VC, vitamin C; Gy, Gray; Original magnification 1000×, Bars = 20 μm; (B) Representative photomicrographs of intestines stained with H & E from SMP30 KO mice. N, normal control; VC, vitamin C; Gy, Gray; Original magnification × 1000, Bars = 20 μm; (C) Apoptotic cells in the H & E stained sections were quantified. Values represent the mean ± SD in each group. WT, wild type; KO, knock out. * Statistically significant difference (p < 0.05).

Figure 2

(A) Detection of apoptosis in the crypts of the intestine by terminal deoxynucleotide transferase labelling of DNA strand breaks (TUNEL) in the WT mice. N, normal control; VC, vitamin C; Gy, Gray; Original magnification 1000×, Bars = 20 μm; (B) Detection of apoptosis in the crypts of the intestine by terminal deoxynucleotide transferase labelling of DNA strand breaks (TUNEL) in SMP30 KO mice. N, normal control; VC, vitamin C; Gy, Gray; Original magnification × 1000, Bars = 20 μm; (C) Positive cells were quantified in the sections stained with the TUNEL method. Values represent the mean ± SD in each group. WT, wild type; KO, knock out. * Statistically significant difference (p < 0.05).

Figure 3

(A) BAX expression detected by immunohistochemistry in the crypts of the intestine in the WT mice: N, normal control; VC, vitamin C; Gy, Gray. Original magnification × 1000, Bars = 20 μm. (B) BAX expression detected by immunohistochemistry in the crypts of the intestine in SMP30 KO mice. N, normal control; VC, vitamin C; Gy, Gray. Original magnification 1000×, Bars = 20 μm. (C) Positive cells were quantified from immunohistochemically stained sections with BAX. Values represent the mean ± SD in each group. WT; wild type, KO; knock out. *, **, and †, Statistically significant difference (p < 0.05).

Figure 4

Bcl-2 expression detected by immunohistochemistry in the crypts of the intestine in WT mice (A) and SMP30 KO mice (B). N, normal control; VC, vitamin C; Gy, Gray. Original magnification × 1000, Bars = 20 μm. (C) Positive cells were quantified from the immunohistochemically stained sections with Bcl2. Values represent the mean ± SD in each group. WT, wild type; KO, knock out; * and †, Statistically significant difference (p < 0.05).

Figure 5

Comparison of apoptotic cells and the BAX/Bcl-2 ratio in the WT and SMP30 KO mice. The BAX/Bcl2 ratio significantly increased only in the 1 Gy and 3 Gy groups, while apoptosis increased in the 1 Gy, 3 Gy, and 5 Gy groups.