Signaling pathway for radiation-induced apoptosis in the lymphoblasts from neuronopathic (type A) and non-neuronopathic (type B) forms of Niemann-Pick disease.

Deficient activity of human lysosomal hydrolase, acid sphingomyelinase (ASM), results in the neuronopathic (type A) and non-neuronopathic (type B) forms of Niemann-Pick disease (NPD). A deficiency of ASM is known to deprive lymphoblasts of their response to apoptotic induction by X-ray irradiation. To elucidate the genetic heterogeneity of apoptotic induction in NPD cells, we investigated radiation-induced apoptosis of lymphoblasts in patients with type A (genotype: IVS3-2A-G/IVS3-2A-G) and type B (genotype: S436R/S436R) NPD. Epstein-Barr virus (EBV)-transformed lymphoblasts established from a patient with type A NPD, a patient with type B NPD and a normal control were irradiated with 20 Gy and incubated for 24 h. The cells were harvested and the morphological features of apoptosis were observed with DNA-specific fluorochrome bis-benzimide. Exposure of lymphoblasts to 20 Gy of radiation resulted in 25-30% apoptosis of total cells in normal lymphoblasts, 8-9% apoptosis in type A NPD and 20-27% apoptosis in type B NPD. The radiation-induced apoptotic response in the lymphoblasts of type A NPD was significantly different from that of the normal lymphoblasts (P<0.0005). On the other hand, the radiation-induced apoptotic response in type B NPD was not markedly different from that in normal lymphoblasts (P=0.624). In the patient with type B NPD, the signaling pathway for radiation-induced apoptosis was preserved in lymphoblasts, which suggests that the extent of cell signaling system disturbance due to ASM deficiency may be related to the phenotypes in types A and B NPD.