Effect of hypoxia on the expression of procaspase-9 and procaspase-3 in neuronal nuclear, mitochondrial and cytosolic fractions of the cerebral cortex of newborn piglets

Previous studies have shown that cerebral hypoxia results in increased activity of caspase-9, a key initiator of programmed cell death, in the cytosolic fractions of the cerebral cortex of newborn piglets. The present study tests the hypothesis that hypoxia results in increased expression of procaspase-9 and procaspase-3 in neuronal nuclear, mitochondrial and cytosolic fractions of the cerebral cortex of newborn piglets. To test this hypothesis, expression of procaspase-9 and procaspase-3 was determined in 10 newborn piglets divided into two groups: normoxic (Nx, n = 5) and hypoxic (Hx, n = 5). The hypoxic piglets were exposed to an FiO2 of 0.06 for 1 h. Tissue hypoxia was documented by ATP and phosphocreatinine (PCr) levels. Neuronal nuclear, mitochondrial and cytosolic fractions were isolated and the expression of procaspase-9 and procaspase-3 was determined by immunoblotting using specific anti-procaspase-9 and anti-procaspase-3 antibodies. ATP levels (μmol/g brain) were 4.34 ± 0.36 in the Nx and 1.43 ± 0.28 in the Hx (p < 0.001 vs. Nx) groups. PCr levels (μmol/g brain) were 3.75 ± 0.27 in the Nx and 0.69 ± 0.26 in the Hx (p < 0.001 vs. Nx) group. Cytosolic procaspase-9 density (OD × mm2) was 88.82 ± 17.55 in the Nx and 215.54 ± 22.77 in the Hx (p < 0.001 vs. Nx). Mitochondrial procaspase-9 density (OD × mm2) was 104.67 ± 12.75 in the Nx and 183.44 ± 16.69 in the Hx (p < 0.001 vs. Nx). Nuclear procaspase-9 density (OD × mm2) was 135.56 ± 15.36 in the Nx and 190.66 ± 29.35 in the Hx (p < 0.001 vs. Nx). Cytosolic procaspase-3 density (OD × mm2) was 23.72 ± 3.71 in the Nx and 92.44 ± 8.46 in the Hx (p < 0.001 vs. Nx). Mitochondrial procaspase-3 density (OD × mm2) was 22.12 ± 2.97 in the Nx and 51.22 ± 10.67 in the Hx (p < 0.001 vs. Nx). Nuclear procaspase-3 density (OD × mm2) was 53.80 ± 7.18 in the Nx and 84.67 ± 5.63 in the Hx (p < 0.001 vs. Nx). We conclude that procaspase-9 and procaspase-3 proteins increased in all cell compartments including cytosolic, mitochondrial and nuclear during hypoxia, indicating increased expression of procaspase-9 during hypoxia. We propose that following increased expression of procaspase-9 and procaspase-3, these molecules traffic among the various cell compartments and become available for their activation resulting in increased caspase-9 and caspase-3 activity.