HMGB1 acts as an agent of host defense at the gut mucosal barrier.

Mucosal barriers provide the first line of defense between internal body surfaces and microbial threats from the outside world. 1 In the colon, the barrier consists of two layers of mucus and a single layer of tightly interconnected epithelial cells supported by connective tissue and immune cells. 2 Microbes colonize the loose, outer layer of colonic mucus, but are essentially excluded from the tight, epithelial-associated layer by host defenses. 3 The amount and composition of the mucus is calibrated based on microbial signals and loss of even a single component of this mixture can destabilize microbial biogeography and increase the risk of disease. 4-7 However, the specific components of mucus, their molecular microbial targets, and how they work to contain the gut microbiota are still largely unknown. Here we show that high mobility group box 1 (HMGB1), the prototypical damage-associated molecular pattern molecule (DAMP), acts as an agent of host mucosal defense in the colon. HMGB1 in colonic mucus targets an evolutionarily conserved amino acid sequence found in bacterial adhesins, including the well-characterized Enterobacteriaceae adhesin FimH. HMGB1 aggregates bacteria and blocks adhesin-carbohydrate interactions, inhibiting invasion through colonic mucus and adhesion to host cells. Exposure to HMGB1 also suppresses bacterial expression of FimH. In ulcerative colitis, HMGB1 mucosal defense is compromised, leading to tissue-adherent bacteria expressing FimH. Our results demonstrate a new, physiologic role for extracellular HMGB1 that refines its functions as a DAMP to include direct, virulence limiting effects on bacteria. The amino acid sequence targeted by HMGB1 appears to be broadly utilized by bacterial adhesins, critical for virulence, and differentially expressed by bacteria in commensal versus pathogenic states. These characteristics suggest that this amino acid sequence is a novel microbial virulence determinant and could be used to develop new approaches to diagnosis and treatment of bacterial disease that precisely identify and target virulent microbes.

Evidence that maternal conjugated linoleic acid negatively affects lipid uptake in late-stage chick embryos resulting in increased embryonic mortality.

An experiment was performed to determine the effect of maternal dietary conjugated linoleic acid (CLA) on growth and composition of surviving chick embryos and residual yolk sacs during the last week of development when lipid utilization becomes prevalent. After 14 d on experimental diets, hatchability of non-cooled eggs obtained from CLA-fed hens (0.5% of the diet) was 10%, where 20% of surviving CLA embryos died after d 13 of incubation. Hatchability was 93% for controls and only 4.36% of mortality occurred after d 13 of incubation. Decline in yolk sac weight in control embryos (0.75 g/d) was significantly greater than that from viable CLA embryos (0.51 g/d). Growth rate (2.6 g/d) of surviving embryos from d 13 to 20 was reduced in CLA embryos in comparison to growth rate of controls (3.0 g/d). Relative proportion of lipid in residual yolk sacs in embryos from control-fed hens decreased from 26.72% (d 13) to 15.94% (d 19) during incubation, whereas little change was evident in residual yolk sac from CLA embryos on d 13 (21.52%) to d 19 (20.39%). Fatty acid analysis of residual yolk sac contents suggested that transport of fatty acids from the contents (liquid yolk) to the yolk sac membrane was not impaired in CLA embryos, as shown by a similar pattern in reduction of total fatty acids in residual yolk sac contents between treatment groups. Apart from 18:1n-9 (d 17), there were no consistent differences in the fatty acid content between embryos from hens fed the control diet or the CLA diet at any time point. Maternal CLA led to increased 18:0 and decreased 18:1n-9 in yolk lipid and embryonic tissues compared with controls across time. These findings could possibly suggest that CLA embryos had less capacity to use yolk lipids from the residual yolk sac during the last week of incubation.

Evidence for conjugated linoleic acid-induced embryonic mortality that is independent of egg storage conditions and changes in egg relative fatty acids.

Three experiments were performed to determine the effect of conjugated linoleic acid (CLA) on embryonic development in the absence of vitelline membrane disruption. In experiment 1, when eggs from control and CLA (0.5%)-fed hens were stored at 21 or 15 degrees C for 48 h, mineral movement between the yolk and albumen was not observed (with the exception of Mg and Na). Also, it was found that CLA-induced changes in yolk fatty acid content (e.g., increased saturated fatty acids and CLA) had begun to change after 5 d of feeding hens CLA, and no differences were detected in fatty acid composition after 14 d. In experiment 2, the hatchability of eggs incubated directly after oviposition or stored 24 h at 21 or 15 degrees C was determined from hens fed control or 0.5% CLA diets. Regardless of storage conditions, CLA reduced hatchability. These data showed that CLA elicits negative effects on hatchability independent of vitelline membrane disruption or egg storage condition. In experiment 3, eggs were collected from hens fed 0 or 1% CLA daily for 3 wk, stored at 21 degrees C for 24 h, and incubated. Not only did CLA decrease hatchability, the data showed as the days of CLA feeding increased, the days of survival during incubation decreased. Average days of embryonic survival during incubation for the CLA group diminished to 18.0, 13.4, and 6.3 d for wk 1, 2, and 3 of CLA feeding, respectively, and control remained at 20.6, 20.8, and 19.8 for the 3 wk. These studies suggested that without the disruption of the vitelline membrane, hatchability and embryonic days of survival were significantly reduced by maternal CLA feeding in comparison to control-fed hens. Evidence that embryos die earlier the longer the hens are fed CLA, even though no additional changes in the fatty acid content of eggs were found, suggested that factors other than storage and egg yolk fatty acid composition played a role in CLA-induced embryonic mortality.