Regional Mucosa-Associated Microbiota Determine Physiological Expression of TLR2 and TLR4 in Murine Colon

Abstract

Many colonic mucosal genes that are highly regulated by microbial signals are differentially expressed along the rostral-caudal axis. This would suggest that differences in regional microbiota exist, particularly mucosa-associated microbes that are less likely to be transient. We therefore explored this possibility by examining the bacterial populations associated with the normal proximal and distal colonic mucosa in context of host Toll-like receptors (TLR) expression in C57BL/6J mice housed in specific pathogen-free (SPF) and germ-free (GF) environments. 16S rRNA gene-based terminal restriction fragment length polymorphism (T-RFLP) and clone library analysis revealed significant differences in the community structure and diversity of the mucosa-associated microbiota located in the distal colon compared to proximal colon and stool, the latter two clustering closely. Differential expression of colonic TLR2 and TLR4 along the proximal-distal axis was also found in SPF mice, but not in GF mice, suggesting that enteric microbes are essential in maintaining the regional expression of these TLRs. TLR2 is more highly expressed in proximal colon and decreases in a gradient to distal while TLR4 expression is highest in distal colon and a gradient of decreased expression to proximal colon is observed. After transfaunation in GF mice, both regional colonization of mucosa-associated microbes and expression of TLRs in the mouse colon were reestablished. In addition, exposure of the distal colon to cecal (proximal) microbiota induced TLR2 expression. These results demonstrate that regional colonic mucosa-associated microbiota determine the region-specific expression of TLR2 and TLR4. Conversely, region-specific host assembly rules are essential in determining the structure and function of mucosa-associated microbial populations. We believe this type of host-microbial mutualism is pivotal to the maintenance of intestinal and immune homeostasis.

Comparative analyses of foregut and hindgut bacterial communities in hoatzins and cows

“…Previous results have shown differences in composition of the microbiota along the length of the gut, in the mouse (Wang et al, 2010), chicken (Rehman et al, 2007) and humans (Costello et al, 2009). Both host diet and phylogeny influence fecal bacterial diversity, as shown by Ley et al (2008) who based on the composition of the feces, showed that herbivores generally clustered into two groups corresponding to foregut and hindgut fermenters.…”

26 Intestinal Dysbiosis Contributes to the Delayed Gastrointestinal Transit in High Fat Diet Fed Mice

“…21,22 The endotoxemia associated with a high-fat diet could initiate myenteric inducible NOS activation, known to increase in neurons after the systemic administration of LPS, 56 and can induce an overproduction of NO in nitrergic neurons, leading to oxidative stress and apoptosis. 42,57 This will be the focus of our future studies as we continue to understand the mechanisms of a HFDinduced nitrergic enteric neuronal degeneration and delayed colonic transit.…”

“…19,20 Gut microbial products signal through the pathogen recognition Toll-like receptor (TLR) family. In the murine enteric nervous system, TLR4 expression is maximal in the distal colon 21 and TLR3, 4, and 7 have been shown to be expressed in myenteric neurons and glia cells. 22 TLRs have been implicated in neuronal apoptosis, 23 and excess TLR4 activation by lipopolysaccharide (LPS) activates proinflammatory pathways and cytokine release within enteric neurons.…”

The Primary Research on the Gut Microbes in KKAy Mice

“…The type strain (ATCC 29148) of Bacteroides thetaiotaomicron only has 6.3 Mb genome sequence, but these genes can code 226 predicted glycoside hydrolases, 163 digesting starch proteins and 15 polysaccharide lyases [6]. Band B from KKAy, is similar with a series of uncultured bacteria which are beneficial for mice to express TLR4 on intestinal mucosa [8]. TLR4 triggers the activation of kinase cascades and stimulates signaling pathways of inflammation in cells for prompted insulin resistance [17].…”