Hyaluronan regulation of microbial host defense of the intestine

描述（由申请人提供）：已证明母乳喂养人类婴儿可保护婴儿免受许多病原性和病理性疾病的侵害，其中大部分保护作用由乳汁中天然存在的聚糖介导。我们最近在人乳中发现了一种新的聚糖，透明质酸（HA），在人类哺乳的早期阶段出现最高浓度，并随着时间的推移逐渐减少。人乳HA水平明显高于商业婴儿配方。重要的是，我们还发现，给小鼠喂食特定大小范围的纯化HA在上皮损伤/细菌诱导的结肠炎模型中具有保护作用。此外，我们的数据表明肠上皮产生了大小特异性的HA片段驱动的抗微生物反应。与其他乳聚糖不同，HA的一个特殊属性是其作为细菌识别Toll样受体（TLR）4和2的内源性配体的功能，已知Toll样受体4和2是触发先天宿主防御系统的重要传感器。因此，HA可能是一种刺激未定殖的婴儿肠道以保护免受病原体侵害的方法。因此，我们假设牛奶中的HA以大小依赖的方式提供了先天性宿主保护，以对抗免疫初始婴儿和儿童肠道中的病原体。我们实验室的初步研究表明，在细胞培养物和小鼠模型中，HA大小特异性上调肠上皮细胞中的抗菌反应。在病毒应答蛋白中，我们的数据显示IFIT 1被HA显著诱导，特别是35 kDa大小范围的HA，并且TLR 4和TLR 2的抗体的组合完全阻断这种作用。重要的是，我们可以从牛奶中分离出的HA也具有相同的刺激能力。HA 35 kDa片段还特异性诱导人2-防御素2，其是抗微生物肽家族的一个成员，其在排除病原体和维持适当的肠道细菌定植中是重要的。同样，从人乳中分离的HA具有相同的能力。我们设想，我们提出的研究可能最终导致确定明确的膳食HA补充剂，这将是治疗NEC的婴儿，婴儿谁是配方奶粉喂养和儿童容易患胃肠道传染病。HA将是一种有吸引力的治疗剂，因为它：1）由于其简单的未修饰的碳水化合物结构而无毒或无免疫原性; 2）易于施用; 3）已经作为健康食品补充剂以及用于医学应用而大规模商业生产。根据我们的初步数据和之前报道的HA生物学效应，我们认为其保护效力的关键将取决于介导个体宿主反应所需的HA多糖大小。

DESCRIPTION (provided by applicant): Breastfeeding of human infants has been shown to provide protection against many pathogenic and pathologic conditions, and much of that protection is mediated by naturally occurring glycans in milk. We have recently identified a new glycan, hyaluronan (HA), in human milk, which occurs at the highest concentration during the early stage of human lactation and decreases gradually over time. Human milk HA levels are markedly higher than in commercial infant formulas. Importantly, we have also discovered that feeding purified HA of a specific size range to mice is protective in an epithelial damage/ bacteria-induced colitis model. Additionally our data indicate size-specific, HA fragment driven anti-microbial responses by intestinal epithelium. A special attribute of HA, different from other milk glycans, is its function as an endogenous ligand of the bacterial recognition Toll-like receptors (TLRs) 4 and 2, which are known to be important sensors that trigger the innate host defense system. Thus HA may be a way to stimulate the uncolonized infant gut to protect against pathogens. Therefore we hypothesize that HA in milk, in a size dependent manner, provides innate host protection against pathogens in the gut of immune-naive infants and children. Preliminary studies from our lab show HA size-specific upregulation of antimicrobial responses in intestinal epithelial cells in cell cultures and mouse models. Among the virus response proteins, our data show IFIT1 is markedly induced by HA, specifically of the 35kDa size range, and a combination of antibodies to TLR4 and TLR2 completely blocks this effect. Importantly, the HA we can isolate from milk also has the same stimulatory ability. The HA 35kDa fragments also specifically induce human 2-defensin 2, one member of the antimicrobial peptide family that is important in excluding pathogens and maintaining proper intestinal bacterial colonization. Again, the HA isolated from human milk has the same ability. We envision that our proposed investigation could ultimately lead to identifying defined dietary HA supplements that would be therapeutic to infants with NEC, infants who are formula fed and children prone to gastrointestinal infectious disease. HA would be an attractive therapeutic because it is: 1) not toxic or immunogenic due to its simple unmodified carbohydrate structure; 2) easily administered; 3) already being produced commercially on a large scale as a health food supplement as well as for medical applications. Based on our preliminary data and the previously reported biological effects of HA, we think the key to its protective potency will depend on the HA polysaccharide size(s) needed to mediate individual host responses.