Functional Role of Caspases in Heat-Induced Testicular Germ Cell Apoptosis

In the present study, we determined whether a pan caspase inhibitor could prevent or attenuate heat-induced germ cell apoptosis. Groups of five adult (8 wk old) C57BL/6 mice pretreated with vehicle (DMSO) or Quinoline-Val-Asp (Ome)-CH2-O-Ph (Q-VD-OPH), a new generation broad-spectrum caspase inhibitor, were exposed once to local testicular heating (43°C for 15 min) and killed 6 h later. The inhibitor (40 mg/kg body weight) or vehicle was administered intraperitoneally (i.p.) 1 h before local testicular heating. Germ cell apoptosis was detected by TUNEL assay and quantitated as number of apoptotic germ cells per 100 Sertoli cells at stages XI–XII. Compared with controls (16.8 (plus-minus) 3.1), mild testicular hyperthermia within 6 h resulted in a marked activation (277.3 (plus-minus) 21.6) of germ cell apoptosis, as previously reported by us. Q-VD-OPH at this dose markedly inhibited caspase 3 activation and significantly prevented (by 67.0%) heatinduced germ cell apoptosis. Q-VD-OPH-mediated rescue of germ cells was independent of cytosolic translocation of mitochondrial cytochrome c and DIABLO. Electron microscopy further revealed normal appearance of these rescued cells. Similar protection from heat-induced germ cell apoptosis was also noted after pretreatment with minocycline, a second-generation tetracycline that effectively inhibits cytochrome c release and, in turn, caspase activation. Collectively, the present study emphasizes the role of caspases in heatinduced germ cell apoptosis.