Enterocyte proliferation and apoptosis in the distal small intestine is influenced by the composition of colonizing commensal bacteria in the neonatal gnotobiotic pig

¹ Department of Animal and Poultry Science, University of Saskatchewan, 51 Campus Drive, Saskatoon, Saskatchewan, Canada S7N 5A8

^* To whom correspondence should be addressed. E-mail: andrew.vankessel{at}usask.ca.

	Abstract

We previously reported marked differences in small intestinal morphology, including changes in crypt depth and villus height, after inoculation of germfree pigs with different bacterial species. In an attempt to identify the mechanisms governing changes in villus morphology associated with bacterial colonization, 2 gnotobiotic experiments were performed. In each experiment, 16 piglets were allocated to 4 treatment groups including germfree (GF), mono-association with Lactobacillus fermentum (LF) or Escherichia coli (EC), or conventionalized with sow feces (SF). Piglets were reared under gnotobiotic conditions until 14 d of age at which time whole intestinal tissue and enterocytes were collected for histological, gene expression, and protein analysis. Proliferating cell nuclear antigen (PCNA), tumor necrosis factor (TNF), Fas ligand (FasL), CD3, caspase 3 (casp3), and toll-like receptors (TLR) 2, 4, and 9 expression were measured by quantitative PCR (qPCR). Activated casp3 was measured by Western-blot. Increased abundance of activated casp3 and transcripts encoding PCNA, TNF, CD3, and FasL was observed in SF and EC treatment groups compared with GF and LF. Expression of TLR2 was increased (P < 0.05) in the SF treatment and tended to be greater (P < 0.08) in EC relative to LF and GF. Results indicate that conventional bacteria and E. coli but not L. fermentum increase overall cell turnover by stimulating increased apoptosis through the expression of FasL and TNF and by increasing cell proliferation. The differential regulation of TLR expression indicates microbially induced changes may be mediated in part by these receptors. Induction of inflammatory responses and activation of apoptosis through death receptors appears to play a significant role in enterocyte turnover mediated by commensal bacteria.

Key Words: commensal bacteria, enterocyte turnover, gnotobiotic pig

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