Genetic variation of toll-like receptor genes and infection by Mycobacterium avium ssp. paratuberculosis in Holstein-Friesian cattle.

Toll-like receptors (TLR) are membrane proteins that play a key role in innate immunity, by recognizing pathogens and subsequently activating appropriate responses. Mutations in TLR genes are associated with susceptibility to inflammatory and infectious diseases in humans. In cattle, 3 members of the TLR family, TLR1, TLR2, and TLR4, are associated with Mycobacterium avium ssp. paratuberculosis infection, although the extent of this association for the TLR1 and TLR4 receptors has not yet been determined. Moreover, the causal variant in the TLR2 gene has not yet been unequivocally established. In this study, 24 single nucleotide polymorphisms (SNP) in the bovine TLR1, TLR2, and TLR4 genes were selected from the literature, databases, and in silico searches, for a population-based genetic association study of a Spanish Holstein-Friesian sample. Whereas previous results regarding the TLR1 gene were not corroborated, a risk haplotype was detected in TLR2; however, its low frequency indicates that this detected association should be interpreted with caution. In the case of the TLR4 gene, 3 tightly linked SNP were found to be associated with susceptibility to M. avium ssp. paratuberculosis infection. Moreover, one of these SNP, the SNP c.-226G>C, which is localized in the 5'UTR region of the TLR4 gene, has been reported to be able to alter TLR4 expression, raising the possibility that this mutation may contribute to the response of the individual to infection.

SP110 as a novel susceptibility gene for Mycobacterium avium subspecies paratuberculosis infection in cattle.

The intracellular pathogen resistance 1 (Ipr1) gene has been reported to play a role in mediating innate immunity in a mouse model of Mycobacterium tuberculosis infection, and polymorphisms of its human ortholog, SP110 nuclear body protein, have been suggested to be associated with tuberculosis. Thus, the bovine SP110 gene was considered to be a promising candidate for a genetic association study of bovine paratuberculosis, or Johne's disease, a chronic granulomatous enteritis caused by Mycobacterium avium ssp. paratuberculosis (MAP). Initially, single nucleotide polymorphisms (SNP) within the bovine SP110 gene were identified, and subsequently a population-based genetic association study was carried out. Seventeen new SNP along the SP110 gene were identified in Holstein-Friesian cattle, and 6 more were compiled from public databases. A total of 14 SNP were included in the association study of 2 independent populations. The SNP c.587A>G was found to be significantly associated with MAP infection, with the major allele A appearing to confer greater disease susceptibility in one of the analyzed populations. In addition, 2 haplotypes containing this SNP were also found to be associated with infection in the same population. The SNP c.587A>G is a nonsynonymous mutation that causes an amino acid change in codon 196 from asparagine to serine. In silico analyses point to SNP c.587A>G as a putative causal variant for susceptibility to MAP infection. The elucidation of the precise mechanism by which this SNP can exert its effect in the protein and, as a result, in the risk of infection, requires future functional analyses. Likewise, the absence of genetic association in one of the analyzed populations renders it necessary to carry out this study in other independent populations, with the aim of substantiating the repeatability of the present results. Nevertheless, the present results deepen our understanding of the genetic basis of susceptibility and resistance mechanisms related to MAP infection in cattle and, in turn, constitute a step forward toward the implementation of marker-assisted selection in breeding programs aimed at controlling paratuberculosis.

Genetic association between bovine NOD2 polymorphisms and infection by Mycobacterium avium subsp. paratuberculosis in Holstein-Friesian cattle.

Nucleotide-Binding Oligomerization Domain 2 (NOD2) has been reported to be a candidate gene for Mycobacterium avium subsp. paratuberculosis (MAP) infection in a Bos taurus × Bos indicus mixed breed based on a genetic association with the c.2197T>C single nucleotide polymorphism (SNP). Nevertheless, this SNP has also been reported to be monomorphic in the B. taurus species. In the present work, 18 SNPs spanning the bovine NOD2 gene have been analysed in a genetic association study of two independent populations of Holstein-Friesian cattle. We found that the C allele of SNP c.*1908C>T, located in the 3'-UTR region of the gene, is significantly more frequent in infected animals than in healthy ones, which supports the idea that the bovine NOD2 gene plays a role in susceptibility to MAP infection. However, in silico analyses of the NOD2 nucleotide sequence did not yield definitive data about a possible direct effect of SNP c.*1908C>T on susceptibility to infection and led us to consider its linkage disequilibrium with the causative variant. A more exhaustive genetic association study including all putative, functional SNPs from this gene and subsequent functional analyses needs to be conducted to achieve a more complete understanding of how different variants of NOD2 may affect susceptibility to MAP infection in cattle.

Identification of single nucleotide polymorphisms in the bovine solute carrier family 11 member 1 (SLC11A1) gene and their association with infection by Mycobacterium avium subspecies paratuberculosis.

Johne's disease is a chronic enteritis caused by Mycobacterium avium ssp. paratuberculosis (MAP) that causes substantial financial losses for the cattle industry. Susceptibility to MAP infection is reported to be determined in part by genetic factors, so marker-assisted selection could help to obtain bovine populations that are increasingly resistant to MAP infection. Solute carrier family 11 member 1 (SLC11A1) was adjudged to be a potential candidate gene because of its role in innate immunity, its involvement in susceptibility to numerous intracellular infections, and its previous association with bovine MAP infection. The objectives of this study were to carry out an exhaustive process of discovery and compilation of polymorphisms in SLC11A1 gene, and to perform a population-based genetic association study to test its implication in susceptibility to MAP infection in cattle. In all, 57 single nucleotide polymorphisms (SNP) were detected, 25 of which are newly described in Bos taurus. Twenty-four SNP and two 3'-untranslated region polymorphisms, previously analyzed, were selected for a subsequent association study in 558 European Holstein-Friesian animals. The SNP c.1067C>G and c.1157-91A>T and a haplotype formed by these 2 SNP yielded significant association with susceptibility to MAP infection. The c.1067C>G is a nonsynonymous SNP that causes an amino acid change in codon 356 from proline to alanine (P356A) that could alter SLC11A1 protein function. This association study supports the involvement of SLC11A1 gene in susceptibility to MAP infection in cattle. Our results suggest that SNP c.1067C>G may be a potential causal variant, although functional studies are needed to assure this point.