Modulation of apoptosis by starvation: morphological and biochemical study of rat intestinal mucosa

Morphology at light and electron microscopic levels, expression and activation of transglutaminase and DNA fragmentation at internucleosomal sites were used as markers to study the effect of starvation on the apoptosis of small intestinal epithelial cells. The cells entering apoptotic programme in well-fed animals undergo many morphological changes in apical cytoplasm involving alterations in actin cytoskeleton organisation which may cause a discharge of microvilli. Some free floating cells in the intestinal lumen show characteristics of apoptotic cell death, e.g. shrinkage of cell and peripheral condensation of chromatin, while mitochondria and lysosomes remain unchanged. Apoptotic bodies are also seen in scanning electron micrographs. During progressive starvation, epithelial cells do not enter the apoptotic cell death programme. Biochemical markers for apoptosis such as increased transglutaminase activity and DNA fragmentation are clearly discernible in normally fed animals. The percentage of cells labelled immunohistochemically by antibody against transglutaminase decreased during starvation while DNA fragmentation was absent. The exact mechanism for suppressing apoptosis in intestinal cells under starvation is not known. However, the data presented here support the existence of such a regulatory process.