Influence of the site of small bowel resection on intestinal epithelial cell apoptosis

Abstract

Massive small bowel resection (SBR) results in a significant increase in intestinal epithelial cell (EC) proliferation as well as apoptosis. Because the site of SBR (proximal (P) vs. distal (D)) affects the degree of intestinal adaptation, we hypothesized that different rates of EC apoptosis would also be found between P-SBR and D-SBR models. Wild-type C57BL/6J mice underwent: (1) 60% P-SBR, (2) 60% D-SBR, or (3) SHAM-operation (transaction-reanastomosis) at the mid-gut point. Mice were sacrificed after 7 days. EC apoptosis was measured by TUNEL staining. EC-related apoptotic gene expression including intrinsic and extrinsic pathways was measured with reverse transcriptase-polymerase chain reaction. Bcl-2 and bax protein expression were analyzed by Western immunoblotting. Both models of SBR led to significant increases in villus height and crypt depth; however, the morphologic adaptation was significantly higher after P-SBR compared to D-SBR (P<0.01). Both models of SBR led to significant increases in enterocyte apoptotic rates compared to respective sham levels; however, apoptotic rates were 2.5-fold higher in ileal compared to jejunal segments (P<0.01). P-SBR led to significant increases in bax (pro-apoptotic) and Fas expression, whereas D-SBR resulted in a significant increase in TNF-alpha expression (P<0.01). EC apoptosis seems to be an important component of intestinal adaptation. The significant difference in EC apoptotic rates between proximal and distal intestinal segments appeared to be due to utilization of different mechanisms of action.

Figure 1

Changes in the overall epithelial cell apoptosis rates (number of apoptotic cells per crypt-villus complex) at 7 days after SBR compared to sham transection are shown. Note the 2.5-fold higher enterocyte apoptotic rates in ileal compared to jejunal segments. Values represent means ± SD. N=7 in each group. * P<0.05, # P<0.01.

Figure 2

mRNA expression of bcl-2 and bax at 7 days after distal and proximal SBR compared to respective segments of sham-transected mice. Note the significant increase in bcl-2 in both D-SBR and P-SBR groups, as well as the significantly higher levels of bcl-2 expression after D-SBR compared to P-SBR. Values represent means ± SD. * P<0.05, § P<0.001

Figure 3

Protein expression of bcl-2 and bax at 7 days after distal and proximal SBR compared to respective segments of sham-transected mice. Note significantly higher bcl-2 levels after D-SBR compared to P-SBR and a significant increase in bax protein expression only after P-SBR. Values represent means ± SD. * P<0.05, § P<0.001

Figure 4

Alterations in mRNA expression of Fas and TNF-alpha at 7 days after distal and proximal SBR compared to respective segments of sham-transected mice. Note the differential expression of TNF-alpha and Fas between the different sites of resection. Values represent means ± SD. * P<0.05, # P<0.01