Transcriptome profiling of Staphylococci-infected cow mammary gland parenchyma

Abstract

Background: Genome-wide gene expression profiling allows for identification of genes involved in the defense response of the host against pathogens. As presented here, transcriptomic analysis and bioinformatics tools were applied in order to identify genes expressed in the mammary gland parenchyma of cows naturally infected with coagulase-positive and coagulase-negative Staphylococci.

Results: In cows infected with coagulase-positive Staphylococci, being in 1st or 2nd lactation, 1700 differentially expressed genes (DEGs) were identified. However, examination of the 3rd or 4th lactations revealed 2200 DEGs. Gene ontology functional classification showed the molecular functions of the DEGs overrepresented the activity of cytokines, chemokines, and their receptors. In cows infected with coagulase-negative Staphylococci, in the 1st or 2nd lactations 418 DEGs, while in the 3rd or 4th lactations, 1200 DEGs were identified that involved in molecular functions such as protein, calcium ion and lipid binding, chemokine activity, and protein homodimerization. Gene network analysis showed DEGs associated with inflammation, cell migration, and immune response to infection, development of cells and tissues, and humoral responses to infections caused by both types of Staphylococci.

Conclusion: A coagulase-positive Staphylococci infection caused a markedly stronger host response than that of coagulase-negative, resulting in vastly increased DEGs. A significant increase in the expression of the FOS, TNF, and genes encoding the major histocompatibility complex proteins (MHC) was observed. It suggests these genes play a key role in the synchronization of the immune response of the cow's parenchyma against mastitis-causing bacteria. Moreover, the following genes that belong to several physiological pathways (KEGG pathways) were selected for further studies as candidate genes of mammary gland immune response for use in Marker Assisted Selection (MAS): chemokine signaling pathway (CCL2, CXCL5, HCK, CCR1), cell adhesion molecules (CAMs) pathway (BOLA-DQA2, BOLA-DQA1, F11R, ITGAL, CD86), antigen processing and presentation pathway (CD8A, PDIA3, LGMN, IFI30, HSPA1A), and NOD-like receptor signaling pathway (TNF, IL8, IL18, NFKBIA).

Keywords: Chronic mastitis; Dairy cows; Gene expression profiling; Transcriptomics; Udder parenchyma; microarray; qPCR.

Fig. 1

Gene map of the signaling pathways of the Toll-like receptor, activation of complement and interaction of cytokines (shown only partly) derived from the KEGG database. Genes showing significantly different expression in the CoPS-3/4 vs. H groups are marked with red asterisks. The figure shows the dependence of complement activation and cytokine pathways on the Toll-like receptor pathway (red arrows). Differentially expressed genes are located on the paths leading to the complement and cytokine pathways

Fig. 2

Validation of microarray analysis using real-time PCR. The relative levels of mRNA expressed are shown as the mean (with standard error – SE) of six animals. Groups differ from each other significantly at *P < 0.05, **P < 0.01, and ***P < 0.001