奶山羊瘤胃上皮外泌体miRNA调控亚急性瘤胃酸中毒发生的宿主-微生物互作机制

Excessively fermentable diets can reduce ruminal pH and increased the risk of subacute ruminal acidosis (SARA), which affects rumen function and health. Our previous studies have proved that the increase of rumen degradable starch (RDS) could significantly change the rumen fermentation, PH, and further induce the inflammatory response. Meanwhile, we also found that the dairy goats could have different subacute ruminal acidosis risk with the same RDS feeds. We assume that the dairy goats with a lower or greater subacute ruminal acidosis risk shape the ruminal microbiota via the rumen epithelium secreted exosome microRNA. The present study aims to select out the dairy goats with a lower or greater subacute ruminal acidosis risk by using the diet with high RDS. Then the key microbes which are related to the rumen fermentation, PH, and the inflammatory response of goat during SARA will be selected out by using the 16SrRNA gene sequencing and the mRNA sequencing. Following, the co-differential miRNAs from rumen epithelium which could regulate the rumen microbiota were screened out by using miRNA sequencing. At last, the rumen microbiome transplantation, the preparation of artificial exosome miRNA, and the germ-free mice were used to test the role of miRNAs in regulating the rumen microbiota and the role of key rumen microbes in regulating rumen fermentation, PH, and the inflammatory response of goat during SARA. Our results could illuminate the relationship among RDS, microbes, and host during the generating process of SARA.

亚急性瘤胃酸中毒（SARA）不利于瘤胃发酵及健康。团队研究发现，提高饲粮瘤胃降解淀粉（RDS）影响瘤胃微生物区系而导致奶山羊SARA，饲喂相同高RDS饲粮不同奶山羊SARA发生风险不同。本项目假设低SARA风险奶山羊瘤胃上皮外泌体miRNA可调控瘤胃微生物区系，稳定瘤胃pH，减少炎症反应。本项目拟通过逐步增加小麦替代玉米比例构建高RDS饲粮并筛选高低SARA风险奶山羊，结合上皮转录组及瘤胃细菌16SrRNA基因测序，筛选出调控SARA发生的差异菌群。运用外泌体miRNA测序分析瘤胃上皮及瘤胃内容物中的共差异miRNA，结合差异菌群筛选宿主调控瘤胃微生物区系的潜在miRNA。运用瘤胃菌群移植、人工外泌体miRNA制备及无菌小鼠平台，验证miRNA对关键细菌定植及菌群改变后对SARA的调控作用。预期结果可阐明奶山羊瘤胃上皮外泌体miRNA调控SARA发生的宿主-微生物互作机制。

为满足高产反刍动物的营养需要，生产中常配制高能饲粮，即高精料饲粮。但其易造成瘤胃代谢异常，引发亚急性瘤胃酸中毒（SARA）等代谢疾病，本试验利用多组学联合分析等技术探究高精料诱导奶山羊SARA发生的机理及耐受性的差异，以期为反刍动物SARA的防治提供理论依据。研究表明：1）通过实时监测SARA发生过程中瘤胃内环境及菌群变化模式以及瘤胃菌群移植抗生素预处理小鼠试验，筛选出可调控SARA发生的核心菌群，证明瘤胃微生物是导致SARA的直接因素；2）采用先增加精料饲喂量，再使用粉碎玉米替代整粒玉米的方式逐步增加饲粮RDS含量，对瘘管奶山羊瘤胃pH连续监测，筛选SARA耐受和易感奶山羊。利用多组学联合分析进一步解析SARA发生的微生物机制，宏基因组研究发现，与健康组相比，SARA易感奶山羊瘤胃微生物中溶菌酶及LPS合成酶的基因显著增加，（半）纤维素降解基因显著减少。瘤胃液代谢组及瘤胃发酵模式显示SARA发生时瘤胃内环境发生显著改变。但瘤胃上皮转录组数据显示两组SARA易感羊表现出相反的炎症状态，进一步采用单细胞核测序分析发现，Th17细胞数量增加及分化在奶山羊SARA的瘤胃上皮炎症发生中发挥着重要调控作用，是SARA发生的潜在分子机制。3）利用多组学联合分析解析奶山羊SARA耐受性差异的宿主-微生物互作机制，通过宏基因组分析发现，耐受奶山羊微生物区系接近健康个体，表现为诱导炎症发生相关微生物减少，粗纤维降解相关微生物增多。转录组结合单细胞核转录组结果发现，耐受奶山羊负责VFAs吸收的瘤胃上皮基底层和棘皮层细胞比例增多，吸收VFAs能力增强可能是耐受奶山羊维持瘤胃内环境稳态，减少炎症发生的关键机制。耐受组与易感组瘤胃内容物交叉移植试验结果显示，易感羊移植耐受羊瘤胃内容物后，可缓解SARA症状，而耐受羊移植易感羊内容物后，仍然耐受SARA。miRNA测序发现，在瘤胃液中鉴定出来自瘤胃上皮的miRNA，且miRNA的靶基因富集到与炎症相关的代谢通路，表明SARA耐受组可能通过外泌体miRNA调控自身微生物区系，保证瘤胃健康。