Abstract
Mycobacterium avium subspecies paratuberculosis (MAP) is the aetiological agent of Johne’s disease (JD), a chronic enteritis in ruminants that causes substantial economic loses to agriculture worldwide. Current diagnostic assays are hampered by low sensitivity and specificity that seriously complicate disease control; a new generation of diagnostic and prognostic assays are therefore urgently needed. Circulating microRNAs (miRNAs) have been shown to have significant potential as novel biomarkers for a range of human diseases, but their potential application in the veterinary sphere has been less well characterised. The aim of this study was therefore to apply RNA-sequencing approaches to serum from an experimental JD infection model as a route to identify novel diagnostic and prognostic miRNA biomarkers. Sera from experimental MAP-challenged calves (n = 6) and age-matched controls (n = 6) were used. We identified a subset of known miRNAs from bovine serum across all samples, with approximately 90 being at potentially functional abundance levels. The majority of known bovine miRNAs displayed multiple isomiRs that differed from the canonical sequences. Thirty novel miRNAs were identified after filtering and were found within sera from all animals tested. No significant differential miRNA expression was detected when comparing sera from MAP-challenged animals to their age-matched controls at six-month’s post-infection. However, comparing sera from pre-infection bleeds to six-month’s post-infection across all 12 animals did identify increased miR-205 (2-fold) and decreased miR-432 (2-fold) within both challenged and control groups, which suggests changes in circulating miRNA profiles due to ageing or development (P<0.00001). In conclusion our study has identified a range of novel miRNA in bovine serum, and shown the utility of small RNA sequencing approaches to explore the potential of miRNA as novel biomarkers for infectious disease in cattle.
Highlights
Johne’s disease is a chronic enteritis of ruminants that is caused by Mycobacterium avium subspecies paratuberculosis (MAP) infection [1]
We show here that it is possible to describe circulating miRNA repertoires in bovine serum from low serum volumes, opening up the application of this approach to bovine sera samples and existing biobanks
It has been reported that large percentages of small RNA reads derived from mammalian sera typically either align to non-miRNA sequences or else cannot be reliably mapped [44,45,46]
Summary
Johne’s disease is a chronic enteritis of ruminants that is caused by Mycobacterium avium subspecies paratuberculosis (MAP) infection [1] Clinical features such as prolonged diarrhoea, progressive wasting and reduced milk yields have obvious implications for animal health and welfare and translate into substantial economic losses, with the dairy industry being vulnerable [2]. The TH2 humoral response offers little protection against disease progression and faecal shedding of MAP commences [6] At this point, transmission within herds through the faecaloral route is enabled and becomes more established as shedding increases in line with the onset and progression of the clinical disease. The ability to accurately identify animals at an early stage of infection that are progressing towards shedding is critical to the success of such a disease control approach and requires a robust prognostic biomarker
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