Pre-epithelial mucus layer in the colon of conventional and germ-free rats

Abstract

The pre-epithelial mucus layer (PML) and epithelial mucins were studied by mucin histochemistry in 10 microns-thick celloidinstabilized cryostat sections in the proximal and distal colon of conventional and germ-free rats aged 120 and 350 days. No continuous PML was found in the proximal colon. A continuous mucus blanket, of fairly homogenous thickness, was observed in the distal colon, where the PML-thickness was 40 +/- 24 microns at 120 days of age and 44 +/- 22 microns at 350 days of age in conventional rats, and 25 +/- 17 microns (120 days) and 22 +/- 10 microns (350 days) in germ-free rats. The stainability of the PML by periodic acid-Schiff and Alcian Blue at pH 2.5 and 1.0 was stronger in conventional rats than in germ-free rats, indicating higher concentrations of mucosubstances and of acid and sulphated mucins, respectively. The PML of the conventional rat distal colon showed a stratified structure of up to eight sublayers. In the distal colon of germ-free rats, the whole gut wall thickness was reduced 47% compared to the conventional rat (germ-free; 185 +/- 73 microns, conventional: 350 +/- 115 microns). No stratification of the PML was observed. The presence of intestinal microflora obviously had a strong influence on the thickness, compactness, mucin content, mucin composition and structure of the pre-epithelial mucus layer.

New Role of Nod Proteins in Regulation of Intestinal Goblet Cell Response in the Context of Innate Host Defense in an Enteric Parasite Infection

“…Bacterial products such as lipopolysaccharides (LPS) and flagellin A from Gram-negative bacteria and lipoteichoic acids (LTA) from Gram-positive bacteria are the most common modulators of mucin production, affecting mainly Muc2 and Muc5AC. Altered goblet cell response is also observed in germfree animals (18,19). Due to the strategic location of goblet cells in the intestinal mucosa, it is very likely that the gut microbiota-Nod axis plays an important role in goblet cell response and that infections with enteric parasites utilize this axis to modulate mucin production in the gut.…”

“…Bacterial products such as LPS and flagellin A from Gramnegative bacteria and lipoteichoic acids (LTA) from Gram-positive bacteria are the most common modulators of mucin production by affecting mainly Muc2 and Muc5AC. In addition to evidence of enhanced mucus secretion in response to intestinal microbes, studies have shown altered goblet cell responses in germfree animals (18,19,41). In our recent study, we observed that treatment with beneficial bacteria L. rhamnosus (JB-1) promotes T. muris expulsion in association with upregulation of goblet cells (42).…”

Roles and regulation of the mucus barrier in the gut

“…18,19 Accordingly, the mucus layer in germ-free mice is relatively thinner than in conventional mice. 20,21 Furthermore, mucins in the small and large intestines of germ-free mice had a higher percentage of neutral and sulphated mucins than those that were conventionally raised. 21,22 When germ-free mice were stimulated with bacterial products [lipopolysaccharide (LPS) and peptidoglycan], the properties of the mucus layer became similar to those of conventional mice.…”

Mucin-bacterial interactions in the human oral cavity and digestive tract

“…The epithelium of germ-free mice differs morphologically from that of conventionally raised animals: non-degraded mucin is found in feces, their goblet cells are smaller and less abundant, the colonic mucus layer is approximately two times thicker and the weight of the cecum can reach up to eight times that of conventional animals. [81][82][83][84] The swelling of the cecum in germ-free animals is due to the accumulation of mucus, and the resulting retention of water, due to the absence of mucin-degrading bacteria. 85 In addition, when fecal suspensions or pure cultures of Clostridium, Bacteroides or Peptococcus were introduced into germ-free rodents, the cecum showed a striking reduction to its normal weight, 86,87 suggesting the beneficial workings of mucin-degrading bacteria.…”