Introduction: Enterocytes at the tips of microvilli are more sensitive to an ischemic insult than those cells residing in the crypts, an effect thought to be due to a relative lack of collateral flow. We speculated that this increased cellular sensitivity to ischemia may be an intrinsic feature of the cells related to their differentiated phenotype.
Methods: In vivo: Sprague-Dawley rats underwent laparotomy and small intestinal ischemia was induced by clamping of the superior mesenteric artery (SMA) for 30 minutes or 1 hour, after which reperfusion was allowed for various time points up to 4 days. Injury was assessed histologically as well as with Northern blots probing for the differentiation markers, intestinal alkaline phosphatase (IAP) and lactase. In vitro: Butyrate treated HT-29 cells, a model of enterocyte differentiation, were subjected to treatment with 2-deoxyglucose and oligomycin-A (in-vitro model of ischemia) and apoptosis assayed by FACS analysis.
Results: In vivo: The mucosal changes consistent with ischemia/reperfusion injury were evident: a rapid inflammatory response followed by progressive villus cell loss beginning at the tips and progressing to the crypts, depending on the degree of insult, with an eventual return to normal microanatomy. IAP and lactase were lost immediately after ischemia and returned with reperfusion, confirming that the differentiated cells are particularly sensitive to ischemic injury. In vitro: A significant increase in apoptosis was seen beginning after 2.5 hours of ischemic time compared to non-ischemic controls (13.3% vs. 0.59%, p<0.005). The differentiated cells were significantly more sensitive to ischemia-induced apoptosis compared to the undifferentiated cells (14.6 vs. 2.6 fold increases respectively, p<0.005).
Conclusions: We conclude that differentiated enterocytes may be inherently more sensitive to ischemia-induced injury than their undifferentiated counterparts. These findings call into question the popularly-held belief that villus tip cells are more susceptible to ischemia because of the microvascular anatomy.
