背景:乳腺炎是人类和动物中最严重的疾病之一,尤其是在奶牛场。越来越多的证据表明,高谷物饮食和低膳食纤维诱导亚急性瘤胃酸中毒(SARA)引起的胃肠道菌群失调与乳腺炎的发生和发展有关。然而,潜在的机制仍然未知。
结果:在本研究中,我们发现患有SARA相关乳腺炎的奶牛在瘤胃中的代谢谱发生了改变,特别是唾液酸水平增加。在抗生素处理的小鼠中消耗唾液酸(SA),但不是健康的老鼠,诱发明显的乳腺炎。SA治疗的抗生素处理的小鼠也诱导粘膜和全身炎症反应,如结肠和肝损伤增加和一些炎症标志物所证明的。此外,抗生素损害肠道屏障完整性引起的肠道菌群失调,SA治疗加重。SA增强了抗生素治疗引起的血清LPS水平,导致乳腺和结肠中TLR4-NF-κB/NLRP3途径的激活增加。此外,SA促进抗生素引起的肠道菌群失调,特别是增强的肠杆菌科和阿克曼纳科,与乳腺炎参数相关。来自SA-抗生素处理的小鼠的粪便微生物群移植模拟受体小鼠的乳腺炎。体外实验表明,SA促进大肠杆菌生长和毒力基因表达,导致巨噬细胞产生更高的促炎细胞因子。通过钨酸钠靶向抑制肠杆菌科或用共生罗伊氏乳杆菌治疗可缓解SA促进的乳腺炎。此外,SARA奶牛通过富集利用SA的机会致病性莫拉草科和利用SA的共生Prevotellaceae的消耗而具有独特的瘤胃微生物结构。用特异性唾液酸酶抑制剂扎那米韦治疗小鼠降低了SA的产生和Moraxellaceae的丰度,并改善了由患有SARA相关乳腺炎的奶牛的瘤胃微生物群移植引起的小鼠乳腺炎。
结论:这项研究,第一次,表明SA通过促进肠道微生物群紊乱加重肠道菌群失调引起的乳腺炎,并受共生细菌调节,表明微生物群-肠-乳轴在乳腺炎发病机制中的重要作用,并提出基于肠道代谢调节的乳腺炎干预的潜在策略。视频摘要。
Mastitis is one of the most severe diseases in humans and animals, especially on dairy farms. Mounting evidence indicates that gastrointestinal dysbiosis caused by induction of subacute ruminal acidosis (SARA) by high-grain diet consumption and low in dietary fiber is associated with mastitis initiation and development, however, the underlying mechanism remains unknown.
In the present study, we found that cows with SARA-associated mastitis have altered metabolic profiles in the rumen, with increased sialic acids level in particular. Consumption of sialic acid (SA) in antibiotic-treated mice, but not healthy mice, induced marked mastitis. SA treatment of antibiotic-treated mice also induced mucosal and systemic inflammatory responses, as evidenced by increased colon and liver injuries and several inflammatory markers. In addition, gut dysbiosis caused by antibiotic impaired gut barrier integrity, which was aggravated by SA treatment. SA potentiated serum LPS level caused by antibiotic treatment, leading to increased activation of the TLR4-NF-κB/NLRP3 pathways in the mammary gland and colon. Moreover, SA facilitated gut dysbiosis caused by antibiotic, and especially enhanced Enterobacteriaceae and Akkermansiaceae, which correlated with mastitis parameters. Fecal microbiota transplantation from SA-antibiotic-treated mice mimicked mastitis in recipient mice. In vitro experiments showed that SA prompted Escherichia coli growth and virulence gene expression, leading to higher proinflammatory cytokine production in macrophages. Targeting the inhibition of Enterobacteriaceae by sodium tungstate or treating with the commensal Lactobacillus reuteri alleviated SA-facilitated mastitis. In addition, SARA cows had distinct ruminal microbial structure by the enrichment of SA-utilizing opportunistic pathogenic
Moraxellaceae and the depletion of SA-utilizing commensal Prevotellaceae. Treating mice with the specific sialidase inhibitor zanamivir reduced SA production and
Moraxellaceae abundance, and improved mastitis in mice caused by ruminal microbiota transplantation from cows with SARA-associated mastitis.
This study, for the first time, indicates that SA aggravates gut dysbiosis-induced mastitis by promoting gut microbiota disturbance and is regulated by commensal bacteria, indicating the important role of the microbiota-gut-mammary axis in mastitis pathogenesis and suggesting a potential strategy for mastitis intervention based on gut metabolism regulation. Video Abstract.