Subclinical mastitis regulation by extracellular vesicles miRNAs in dairy cows

International audience

Inglés. Mastitis is a severe inflammation of the mammary gland of dairy cows. Typically, mastitis monitoring is based on measuring the somatic cell count (SCC) level on milk samples. However, diagnosis of subclinical infection is problematic since the milk and the udder appear normal, reducing the possibilities of early treatments [1]. Recently, several studies revealed that miRNAs vehiculated by extracellular vesicles (EVs) have a fine-tuned role in the regulation of bovine mastitis [2]. The main aim of this study was to investigate the milk EVs miRNome profile during subclinical mastitis. Milk samples were collected from a total of 170 dairy cows during routine monitoring tests. EVs were isolated from milk by size exclusion chromatography (SEC) columns and their characterization was done by western blot using TSG101 and CD9 markers. Then, miRNAs were extracted from EVs using an automated extractor and a smallRNA-sequencing protocol was performed on selected samples. The differential analysis was conducted using an SCC threshold value of 200,000 cells/ml to allocate samples in each group. Finally, the functional analysis to predict miRNAs role was performed using miRWalk, OmicsNet and Cytoscape. A total of 1997 differentially expressed microRNAs were identified, and the majority of them were downregulated. A total of 68 miRNAs was obtained by false discovery rate (FDR) value < 0.05. Finally, the functional analysis highlighted miR-455-5p, miR-1301-3p, miR-503-5p and miR-361-5p, which were the main downregulated microRNAs These miRNAs are related to innate immunity and inflammation processes. In particular, miR-1301-3p has already been reported as regulating mastitis in bovine experimentally infected with Staphylococcus aureus [3], but no studies investigating the role of miRNAs in spontaneous bovine mastitis are present in literature. Intriguingly, miR-455-5p seems to have anti-inflammatory activity in humans and its downregulation in our samples could be explained by the onset of subclinical mastitis [4]. In conclusion, investigating miRNAs role in subclinical mastitis could allow a better understanding of the disease and an improvement in its diagnosis and management.[1] Ruegg PL. 2017. A 100-Year Review: Mastitis detection, management, and prevention. Journal of Dairy Science, 100:10381–10397.[2] Ji Z-H et al. 2022. Exosomes in mastitis - research Status, opportunities, and challenges. Animals, 12:2881.[3] Luoreng ZM et al. 2021. Expression profiling of microRNA from peripheral blood of dairy cows in response to Staphylococcus aureus-infected Mastitis. Frontiers in Veterinary Science 8:691196.[4] Torabi S et al. 2019. miR-455-5p downregulation promotes inflammation pathways in the relapse phase of relapsing-remitting multiple sclerosis disease. Immunogenetics 71:87–95.