Caspase-3–Dependent Organ Apoptosis Early After Burn Injury

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Abstract
To examine the role played by endotoxin, tumor necrosis factor-alpha (TNF-α), and caspase-3 in the increased apoptosis seen in solid organs in the early period after a burn injury. Burn injury is often associated with immune suppression. Bacterial translocation and systemic endotoxemia have been reported after a burn injury, and caspase-3 activation due to TNF-α and Fas ligand (FasL) are presumed to initiate apoptosis. We hypothesized that endotoxin-induced TNF-α expression and caspase-3 activation could be the stimulus for the apoptosis after burn injury. A 20% full-thickness scald burn was used in C57BL/6 mice. Three hours after burn injury, tissue samples were obtained from the thymus, lung, liver, and spleen. Lipopolysaccharide-nonresponsive (C3H/HeJ) and TNFα null B6x129tnf−/− mice were also used. To detect apoptosis, hematoxylin and eosin stain, in situTUNEL, DNA extraction, and gel electrophoresis were all performed. Caspase-3 activity and TNF-α and FasL mRNA were also measured. Increased apoptosis and caspase-3 activity were observed in the thymus and spleen 3 hours after burn injury but were not seen in liver or lung. In the thymus and spleen, increased expression of FasL mRNA was also observed, whereas increased TNF-α mRNA was not. Increased apoptosis in thymus and spleen were also observed in C3H/HeJ and B6x129tnf−/− mice after burn injury. An inhibitor of the caspase-3 (Z-VAD-fmk) reduced apoptosis in both thymus and spleen. In the early period after a burn injury, increased apoptosis is observed primarily in the lymphoid organs and is independent of endotoxin or TNF-α. The increased caspase-3 activity in thymus and spleen contributes to apoptosis in these organs.