Responses of Bovine Innate Immunity to Mycobacterium avium subsp. paratuberculosis Infection Revealed by Changes in Gene Expression and Levels of MicroRNA

Abstract

Paratuberculosis in cattle is a chronic granulomatous gastroenteritis caused by Mycobacterium avium subsp. paratubercolosis (MAP) which is endemic worldwide. In dairy herds, it is responsible for huge economic losses. However, current diagnostic methods do not detect subclinical infection making control of the disease difficult. The identification of MAP infected animals during the sub-clinical phase of infection would play a key role in preventing the dissemination of the pathogen and in reducing transmission. Gene expression and circulating microRNA (miRNA) signatures have been proposed as biomarkers of disease both in the human and veterinary medicine. In this paper, gene expression and related miRNA levels were investigated in cows positive for MAP, by ELISA and culture, in order to identify potential biomarkers to improve diagnosis of MAP infection. Three groups, each of 5 animals, were used to compare the results of gene expression from positive, exposed and negative cows. Overall 258 differentially expressed genes were identified between unexposed, exposed, but ELISA negative and positive groups which were involved in biological functions related to inflammatory response, lipid metabolism and small molecule biochemistry. Differentially expressed miRNA was also found among the three groups: 7 miRNAs were at a lower level and 2 at a higher level in positive animals vs unexposed animals, while 5 and 3 miRNAs were respectively reduced and increased in the exposed group compared to the unexposed group. Among the differentially expressed miRNAs 6 have been previously described as immune-response related and two were novel miRNAs. Analysis of the miRNA levels showed correlation with expression of their target genes, known to be involved in the immune process. This study suggests that miRNA expression is affected by MAP infection and play a key role in tuning the host response to infection. The miRNA and gene expression profiles may be biomarkers of infection and potential diagnostic of MAP infection earlier than the current ELISA based diagnostic tests.

Identification of microRNAs in bovine faeces and their potential as biomarkers of Johne’s Disease

“…A number of groups have previously described the differential expression of miRNA between MAP infected and control groups of cattle across a range of biological samples. Using miRNA-seq of RNA from whole blood of infected, exposed and negative cattle, Malvisi et al 9 identified 9 DE miRNA between negative and infected groups. Using an ileal loop model in neonate calves, Liang et al 10 identified 9 miRNAs that showed differential expression between infected and control tissues.…”

“…Previous studies in MAP infected cattle have measured miRNA expression in serum 8 , whole blood 9 and ileal tissues 10 . We have previously investigated circulating miRNA expression in peripheral blood at silent and subclinical MAP infection stages but detected minimal changes that did not provide diagnostic benefit 11,12 .…”

Establishment a real-time reverse transcription PCR based on host biomarkers for the detection of the subclinical cases of Mycobacterium avium subsp. paratuberculosis

“…Recently, several studies have attempted to diagnose subclinical stages of JD by analyzing hostpathogen interactions, including gene expression, miRNA, protein, and metabolites to MAP infection [17][18][19][20]27]. Some of the studies have been conducted to identify prognostic biomarkers of JD by understanding host response to infection during the progression of JD [21,[28][29][30][31].…”

<i>Mycobacterium avium subspecies paratuberculosis</i>: A possible causative agent in human morbidity and risk to public health safety

“…Infection with MAP has an incubation period which can last from 2 to 6 years (Malvisi et al, 2016) where no signs of infection are seen, progression from this subclinical form to the symptomatic clinical form results in the disease state JD. After infection has occurred, mycobacteria remain hidden in the intestine or associated lymph nodes, predominately in macrophages and payers patches (Tiwari et al, 2006).…”

“…Mycobacterium avium subspecies paratuberculosis (MAP) is the causative agent of paratuberculosis (paraTB) (Malvisi et al, 2016) or Johne's disease (JD) in cattle, a chronic granulomatous gastroenteritis. MAP is an obligate intracellular parasite of animals (Grant, 2005); where it can only reproduce within a host cell (in this case a macrophage) of a susceptible species and is unable to reproduce outside of this cellular environment.…”