OBJECTIVETo investigate whether apoptosis induced by low-dose radiation (LDR) is regulated by mitochondrial pathways in testicular cells.

METHODSMale mice were exposed to whole-body LDR, and changes in mitochondrial function and in expression of apoptotic factors were analyzed in the testicular cells as follows. Total nitric-oxide synthase (T-NOS) and Na+/K+ ATPase activities were biochemically assayed. Reactive oxygen species (ROS) and mitochondrial membrane potential (Δψm) were determined by flow cytometry using fluorescent probes. Levels of mRNAs encoding cytochrome c (Cyt c) and apoptosis-inducing factor (AIF) were quantified by real-time reverse-transcription PCR (RT-PCR). Expression of Cyt c, AIF, caspase-9, and caspase-3 at the protein level was assessed by western blotting and immunohistochemistry.

RESULTSLDR induced an increase in T-NOS activity and ROS levels, and a decrease in Na+/K+ ATPase activity and mitochondrial Δψm, in the testicular cells. The intensity of these effects increased with time after irradiation and with dose. The cells showed remarkable swelling and vacuolization of mitochondria, and displayed a time- and dose-dependent increase in the expression of Cyt c, AIF, procaspase-9, and procaspase-3. Activation of the two procaspases was confirmed by detection of the cleaved caspases. The changes in expression of the four apoptotic factors were mostly limited to spermatogonia and spermatocytes.

CONCLUSIONLDR can induce testicular cell apoptosis through mitochondrial signaling pathways.