The Mucin Muc2 Limits Pathogen Burdens and Epithelial Barrier Dysfunction during Salmonella enterica Serovar Typhimurium Colitis

Abstract

c Salmonella enterica serovar Typhimurium is a model organism used to explore the virulence strategies underlying Salmonella pathogenesis. Although intestinal mucus is the first line of defense in the intestine, its role in protection against Salmonella is still unclear. The intestinal mucus layer is composed primarily of the Muc2 mucin, a heavily O-glycosylated glycoprotein. The core 3-derived O-glycans of Muc2 are synthesized by core 3 ␤1,3-N-acetylglucosaminyltransferase (C3GnT). Mice lacking these glycans still produce Muc2 but display a thinner intestinal mucus barrier. We began our investigations by comparing Salmonella-induced colitis and mucus dynamics in Muc2-deficient (Muc2 ؊/؊ ) mice, C3GnT ؊/؊ mice, and wild-type C57BL/6 (WT) mice. Salmonella infection led to increases in luminal Muc2 secretion in WT and C3GnT ؊/؊ mice. When Muc2 ؊/؊ mice were infected with Salmonella, they showed dramatic susceptibility to infection, carrying significantly higher cecal and liver pathogen burdens, and developing significantly higher barrier disruption and higher mortality rates, than WT mice. We found that the exaggerated barrier disruption in infected Muc2 ؊/؊ mice was invA dependent. We also tested the susceptibility of C3GnT ؊/؊ mice and found that they carried pathogen burdens similar to those of WT mice but developed exaggerated barrier disruption. Moreover, we found that Muc2 ؊/؊ mice were impaired in intestinal alkaline phosphatase (IAP) expression and lipopolysaccharide (LPS) detoxification activity in their ceca, potentially explaining their high mortality rates during infection. Our data suggest that the intestinal mucus layer (Muc2) and core 3 O-glycosylation play critical roles in controlling Salmonella intestinal burdens and intestinal epithelial barrier function, respectively.

The Levels of Brachyspira hyodysenteriae Binding to Porcine Colonic Mucins Differ between Individuals, and Binding Is Increased to Mucins from Infected Pigs with De Novo MUC5AC Synthesis

“…The MUC2 mucin is predominantly secreted in the intestine. There is evidence from Muc2 knockout mice that the lack of Muc2 increases the susceptibility to Salmonella and C. rodentium infections (33,34). Unlike MUC2, MUC5AC does not form part of the normal mucin repertoire in the colon.…”

Antimicrobial peptides and the enteric mucus layer act in concert to protect the intestinal mucosa

“…27,44,45 Similarly, mice deficient in muc13 or core 3 ß1,3-N-acetylglucosaminyl-transferase (C3GnT) with therefore a reduced mucin O-glycosylation exhibit an enhanced susceptibility to inflammation. 46,47 Also, aberrant mucin assembly-associated ER stress in goblet and Paneth cells was reported in 2 strains of muc2 mutant mice leading to spontaneous inflammation and increased mucosal permeability.…”

“…29,30 The finding that IAP could not be detected at the mucosa of mucin (Muc) 2-deficient mice suggests that IAP also needs to bind to the intestinal mucus layer after being secreted by the epithelial cells. 27 Finally, SIgA within the enteric mucus layer provides high affinity protection against enteric pathogens and toxins but additionally provides low affinity binding to commensal bacteria and thereby reinforces the antimicrobial and anti-inflammatory barrier. 31 Epithelial signaling through the interleukin-1 and Toll-like receptor adapter molecule MyD88 as well as the MyD88 adaptor-like (Mal) was shown to promote epithelial integrity in models of enteric inflammation and infection.…”

“…2 Additional molecules with potent antiinflammatory properties such as lipopolysaccharide binding peptide (LBP), intestinal alkaline phosphatase (IAP) or secretory IgA (sIgA) were identified within the mucus layer. [26][27][28] LBP, a potent modulator of lipopolysaccharide recognition, is highly enriched in enteric mucus. 26 IAP, expressed by intestinal epithelial cells, dephosphorylates the bioactive lipid A portion of the endotoxin molecule and renders it less stimulatory, significantly reducing the systemic toxicity of microbiota-derived endotoxin and promoting mucosal wound healing.…”

The Helical Shape of Campylobacter jejuni Promotes In Vivo Pathogenesis by Aiding Transit through Intestinal Mucus and Colonization of Crypts

“…Indeed, this layer is being increasingly appreciated for its functionality as a physical barrier to pathogen infection in the gut (38,39). The large, interconnected mucin glycoproteins that make up the mucus layer create a thick, viscous medium that C. jejuni must move through.…”