Gastroenterology

Gastroenterology

Volume 137, Issue 6, December 2009, Pages 2041-2051
Gastroenterology

Basic—Alimentary Tract
Regulation of Colonic Epithelial Repair in Mice by Toll-Like Receptors and Hyaluronic Acid

https://doi.org/10.1053/j.gastro.2009.08.055Get rights and content

Background & Aims

The protective component of the host response to dextran sodium sulfate (DSS)-induced colitis in the mouse is mediated through the activation of Toll-like receptor (TLR) 4, the induction of cyclooxygenase (COX)-2, and prostaglandin E2 production. TLR4 ligands include bacterial lipopolysaccharide and hyaluronic acid, a component of the extracellular matrix. Our hypothesis is that hyaluronic acid, through TLRs, plays a protective role in the host response to DSS-induced colitis.

Methods

DSS (2.5%) was administered for 7 days in wild-type and MyD88−/− mice. The mice also received intraperitoneal hyaluronic acid. The expression of hyaluronic acid, COX-2, and macrophage inflammatory protein (MIP)-2 was evaluated by immunohistochemistry.

Results

DSS induced a marked increase in hyaluronic acid in the lamina propria of wild-type but not MyD88−/− mice. Treatment with DSS also induced the MyD88-dependent expression of hyaluronic acid synthases 2 and 3, enzymes involved in hyaluronic acid synthesis, in lamina propria macrophages. Exogenous hyaluronic acid induced the expression of tumor necrosis factor α, MIP-2, and COX-2 in the colon in a MyD88-dependent manner. In wild-type but not MyD88−/−, TLR4−/−, COX-2−/− mice, hyaluronic acid was protective against DSS-induced colitis. In wild-type mice, hyaluronic acid was therapeutic in established DSS-induced colitis.

Conclusions

Endogenous hyaluronic acid expression is markedly increased in DSS-induced colitis and preserves the epithelium through TLR activation and COX-2 expression. Furthermore, exogenous hyaluronic acid, through the activation of TLRs and the production of prostaglandin E2 through COX-2, has protective effects in DSS-induced colitis.

Section snippets

Chemicals and Reagents

DSS was purchased from TdB Consultancy AB (Uppsala, Sweden). This product was tested for endotoxin by Associates of Cape Cod, Inc (East Falmouth, MA); it was found to be endotoxin free. HA (mol wt, 750 kilodaltons) was from Sigma (St. Louis, MO). High-molecular-weight HA (Healon; mol wt, 2 × 103 kilodaltons) was from Physician Sales and Services (St. Louis, MO). PEP-1 (GAHWQFNALTVR) and scrambled control peptide (WRHGEALTAVNQ) were from Sigma-Genosys (St. Louis, MO).20

Animals

Adult (6–8 weeks old)

DSS Induces the Expression of HAS-2 and HAS-3 and the Synthesis of HA in a MyD88-Dependent Manner

In the normal mouse colon, HA is distributed in the lamina propria (Figure 1A). After treatment with DSS, there was a progressive increase in HA in the lamina propria of wild-type (WT) mice. The increased HA expression is extracellular and located between the crypts. At baseline, the distribution of HA in the colons of MyD88−/− mice was similar to that seen in WT mice; however, there was no increase in HA expression with DSS treatment in MyD88−/− mice. DSS induced an increase in plasma HA level

Discussion

DSS-induced colitis is more severe in mice deficient in TLR4 or MyD88, a TLR adaptor molecule; this suggests that TLR4 plays an important role in the host defense response to DSS-induced colitis.17, 18, 19 It has been assumed that LPS is the TLR ligand that mediates the host defense response in DSS-induced colitis. However, HA also binds to TLR4, and HA binding to TLR4 promotes the protective component of the host response in sterile skin and lung injury models where LPS is not involved.13, 14

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    Conflicts of interest The authors disclose no conflicts.

    Funding Supported by National Institutes of Health grants R01DK33165 and R01DK55753.

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