Mucus Barriers to Microparticles and Microbes are Altered in Hirschsprung's Disease

Abstract

Mucus forms a protective hydrogel layer over the intestinal epithelium, presenting a selective and robust barrier to the uptake of particulates and microbe invasion. Disease can alter mucus production and composition, thus potentially modifying mucosal barrier properties. Hirschsprung's disease (HD) is a developmental abnormality of the nervous system often complicated by intestinal infection. An investigation of colonic mucus barrier properties in an HD animal model, endothelin receptor B mutant mice, revealed significantly reduced microsphere (passive) and microbe (active) transport rates (7-fold and 3.6-fold, respectively, in proximal colonic mucus) relative to wild-type. Transport differences were evident in both the ganglionic and aganglionic colon segments, in agreement with the risk of HD-associated enterocolitis after surgery to remove aganglionic colon segments. The development of therapies aimed at altering colonic mucus barrier properties could be explored towards preventing the onset of enterocolitis in HD.

Keywords: Hirschsprung's disease; intestine; microbe transport; mucus; nanoparticle diffusion.

Figure 1

Schematic representation of colonic tissue preparation with undisturbed mucus layer for video microscopy.

Figure 2

Transport behaviors of carboxylate-modified microspheres in excised colonic tissue. A) Representative 20 s trajectories of carboxylate-modified particles in WT proximal, Ednrb^−/− proximal, WT distal, and Ednrb^−/− distal tissue. B) Ensemble averaged mean-squared displacement (<MSD>) in WT and Ednrb^−/− mucus over 10 s. C) Ensemble <MSD> averages at τ = 1 s & 10 s. Error bars denote standard errors based on three independent experiments, with n ≥ 100 microspheres for each experiment. * p<0.05, ** p<0.01

Figure 3

Predicted percentage of particle penetration across mucus thickness after 1 hr.

Figure 4

Transport of E. Coli ASV in mouse colonic mucus. Representative 20 s trajectories in proximal (A–B) and distal (D–E) colonic mucus of WT (A, D) and Ednrb^−/− (B, E) mice. Average speed of individual microbes in mucus of proximal (C) and distal (F) colon.

Figure 5

Transport of E. Coli ASV in mouse colonic mucus. Average speeds were compared in WT and Ednrb^−/− mutants in both proximal and distal colonic mucus. Data represent the ensemble average, and error bars denote standard errors based on three independent experiments, with n ≥ 90 microbes for each experiment. *p < 0.05, **p < 0.01

Figure 6

Schematic representation of particle (Left side) and bacteria (Right side) interactions with mucus gel in WT and Ednrb^−/− colon. The higher density of negatively charged groups in WT vs. Ednrb^−/− mucus could reduce interactions between particles and mucins, resulting in less hindered motion. Microbes may have increased adherence in mutant colon due to increased sialomucin binding.