Intestinal
ischemia after
trauma-
hemorrhagic shock (T/HS) results in gut barrier dysfunction and the production/release of biologically active and tissue injurious factors in the mesenteric lymph, which, in turn, causes
acute lung injury and a systemic inflammatory state. Since T/HS-induced
lung injury is associated with pulmonary endothelial and epithelial cell programmed cell death (PCD) and was abrogated by mesenteric lymph duct
ligation, we sought to investigate the cellular pathways involved. Compared with
trauma-
sham shock (T/SS) rats, a significant increase in
caspase-3 and M30 expression was detected in the pulmonary epithelial cells undergoing PCD, whereas
apoptosis-inducing factor (AIF), but not
caspase-3, was detected in endothelial cells undergoing PCD. This AIF-mediated pulmonary endothelial PCD response was validated in an in situ femoral vein assay where endothelial cells were found to express AIF but not
caspase-3. To
complement these studies, human umbilical vein endothelial cell (HUVEC), human lung microvascular endothelial cell (HLMEC), and human alveolar type II epithelial cell (A549) lines were used as in vitro models. T/HS lymph induced the nuclear translocation of AIF in HUVEC and HLMEC, and
caspase inhibition in these cells did not afford any cytoprotection. For proof of principle, AIF silencing in HUVEC reversed the cytotoxic effects of T/HS on cell viability and DNA fragmentation. In A549 cells, T/HS lymph activated caspase-3-mediated apoptosis, which was partially abrogated by N-
benzyloxycarbonyl-Val-Ala-Asp (zVAD). Additionally, T/HS lymph did not cause the nuclear translocation of AIF in A549 cells. Collectively, T/HS-induced pulmonary endothelial PCD occurs via an AIF-dependent
caspase-independent pathway, whereas epithelial cells undergo apoptosis by a
caspase-dependent pathway.