Hyaluronan regulation of microbial host defense of the intestine

描述(申请人提供)：人类婴儿的母乳喂养已被证明对许多致病和病理情况提供保护，而这种保护很大程度上是由牛奶中自然产生的多糖介导的。我们最近在母乳中发现了一种新的葡聚糖，透明质酸(HA)，它在人类哺乳早期浓度最高，并随着时间的推移逐渐下降。母乳中的透明质酸含量明显高于商用婴儿配方奶粉。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，特定大小的HA片段通过肠道上皮细胞驱动抗微生物反应。与其他牛奶多糖不同，HA的一个特殊属性是作为细菌识别Toll样受体4和2的内源配体，这两个受体被认为是触发固有宿主防御系统的重要传感器。因此，HA可能是一种刺激未定植的婴儿肠道以保护其免受病原体侵袭的方法。因此，我们假设，牛奶中的HA以一种大小依赖的方式，对免疫未成熟的婴儿和儿童的肠道内的病原体提供了天然的宿主保护。我们实验室的初步研究表明，在细胞培养和小鼠模型中，HA大小特异性上调了肠上皮细胞的抗微生物反应。在病毒反应蛋白中，我们的数据显示Ifit1显著地由HA诱导，特别是35 kDa的大小范围，而TLR4和TLR2的抗体组合完全阻断了这一作用。重要的是，我们可以从牛奶中分离出的HA也具有同样的刺激能力。HA 35 kDa片段还特异性地诱导人2-防御素2，这是抗菌肽家族中的一个成员，在排除病原体和维持适当的肠道细菌定植方面具有重要作用。同样，从母乳中分离出的HA也具有同样的能力。我们设想，我们拟议的调查最终可能导致确定明确的膳食HA补充剂，这些补充剂将对患有NEC的婴儿、配方奶喂养的婴儿和易患胃肠道感染的儿童具有治疗作用。HA将是一种有吸引力的治疗方法，因为它：1)由于其简单的未经修饰的碳水化合物结构而无毒或无免疫原性；2)易于服用；3)已作为保健食品补充剂和医疗应用大规模商业生产。根据我们的初步数据和先前报道的HA的生物学效应，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(S)。

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.