Molecular mechanism of programmed cell death in the gut epithelium of neonatal piglets.

In the intestinal mucosa of pig, calf and rat neonates, we observed the cells die in the packets which suggests involvement of some paracrine factors. The death signal was transferred via tissue continuum as well as across the gut lumen, and the involvement of TGF-beta1 and TNFalpha was demonstrated. Present study aimed to clarify the molecular mechanisms of programmed cell death in the mucosa of the small intestine of pig neonates. Groups (packets) of cells and the neighboring cells underwent apoptosis, and expressed an enhanced TGF-RII. In the dying cells the death signal promoted via TGF-RII was associated with enhanced expression of active caspase 8, TGF-beta1, TNFalpha and Bid. Quantitative study showed that high expression of TGF-beta1 was positively correlated with expression of BID and negatively with BCL-2, illustrating the transmission of signal from TGF-RII through SMAD cascade and RunX protein. We hypothesize that TGF-beta1 sensitizes the enterocytes for TNFalpha signaling and both cytokines control the apoptosis process in the gut epithelium. Intensive mitosis triggers many errors in DNA replication, and the role of p53 is to detect them and promote either repair or apoptosis. During first days of live all damaged cells were directed towards apoptosis while at day 7 at least some of them were repaired. Autophagy, the second form of programmed cell death, was recognized by its key marker MAP I LC3. Our data showed the colocalization of MAP I LC3 with active caspase 3 thus suggesting a coexistence between these two forms of cell death, at least in the early postnatal life.