Effect of heat shock and endotoxin stress on enterocyte viability apoptosis and function varies based on whether the cells are exposed to heat shock or endotoxin first
D. Z. Xu, Q. Lu, G. M. Swank and E. A. Deitch
Department of Surgery, UMDNJ-New Jersey Medical School, Newark, USA.
BACKGROUND: Stress-gene responses, including the heat shock (HS) response
and the acute phase response, are protective mechanisms for cells after
exposure to stress. Both responses cannot occur simultaneously, and, in
endothelial cells, the sequence of stress-gene expression seems to be a
critical factor in whether cellular protection or injury occurs. OBJECTIVE:
To determine if the sequence of stress-gene expression affects cellular
protection or injury in epithelial cells. DESIGN: Randomized controlled in
vitro study. SETTING: University research laboratory. SUBJECTS: Rat
intestinal epithelial cell-6 (IEC-6) cells were grown on 35-mm culture
dishes, chamber slides, or in a bicameral system to confluence or until
tight junction integrity was established. INTERVENTIONS: Rat IEC-6 cells
were examined for viability, apoptosis, and bacterial translocation (BT)
after exposure to 25-micrograms/mL lipopolysaccharide (LPS) for 18 hours to
HS (43 degrees C) for 90 minutes, to LPS followed by HS, or to HS followed
by LPS. MAIN OUTCOME MEASURES: The IEC-6 cells were stained for viability
and apoptosis using trypan blue and a direct immunoperoxidase detection of
digoxigenin-labeled genomic DNA (Apop Tag Plus In Situ Apoptosis Detection
Kit, Oncor, Gaithersburg, Md), respectively. Bacterial translocation was
measured by culturing the bacteria (ie, Escherichia coli) that crossed the
IEC-6 cell monolayer in the bicameral system. RESULTS: Control cells
(medium only) and cells exposed to LPS alone, HS alone, or HS followed by
LPS had a viability from 92% to 98%, and the percentage of apoptotic cells
ranged from 2.2% to 5.7%. In contrast, IEC-6 cells exposed to LPS followed
by HS had a significantly lower viability (83%, P < .05 vs all other
groups) and a higher percentage of apoptotic cells (12.2%, P < .01). At
3 hours after challenge with E coli, the LPS-exposed IEC-6 cell monolayers
had significantly increased BT vs control monolayers (P < .05), while
the IEC-6 cell monolayers exposed to HS followed by LPS had decreased BT (P
< .05). Conversely, cells exposed to LPS followed by HS had the highest
magnitude of BT (P < .01 vs all other groups). CONCLUSIONS: These
results indicate that preinduction of HS response can diminish LPS-induced
cell injury, while induction of HS response after the LPS challenge (ie,
the acute phase response) may lead to decreased enterocyte viability,
increased apoptosis, and cellular dysfunction as manifested by BT.
