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Genetic mechanisms regulating the host response during mastitis

ABSTRACT: Mastitis is a very costly and common disease in the dairy industry. The study of the transcriptome from healthy and mastitic milk somatic cell samples using RNA-Sequencing technology (RNA-Seq) can provide measurements of transcript levels associated with the immune response to the infection. The objective of this study was to characterize the Holstein milk somatic cells transcriptome from 6 cows to determine host response to intramammary infections. RNA-Sequencing was performed on two samples from each cow from two separate quarters, one classified as healthy (n = 6) and one as mastitic (n = 6). In total, 449 genes were differentially expressed between the healthy and mastitic quarters (P-value < 0.01, FDR < 0.05, FC > ±2). Among the differentially expressed genes, the most expressed genes based on Reads Per Kilo base per Million mapped reads (RPKM) in the healthy group were associated with milk components (CSN2 and CSN3), and in the mastitic group they were associated with immunity (B2M and CD74). In-silico functional analysis was performed using the list of 449 differentially expressed genes, which identified 36 significantly enriched metabolic pathways (FDR < 0.01), some of which were associated with the immune system, such as cytokine-cytokine interaction and cell adhesion molecules. Seven functional candidate genes were selected, based on the criteria of being highly expressed and present in significant pathways that are relevant to the inflammatory process (GLYCAM1, B2M, CD74, BoLA DR-Alpha, FCER1G, SDS and NFKBIA). Lastly, we identified the differentially expressed genes that are located in QTL regions previously known to be associated with mastitis, specifically clinical mastitis, somatic cell count and somatic cell score. It was concluded that there are multiple genes within QTL regions that could potentially impact host response to mastitis causing agents, making some cows more susceptible to intramammary infections. The identification of key genes with functional, statistical, biological and positional relevance associated with host defense to infection, will contribute to a better understanding of the underlying genetic architecture associated with mastitis. This in turn will improve the sustainability of agricultural practices, by facilitating the selection of cows with improved host defense leading to increased resistance to mastitis.

ORGANISM(S): Bos taurus

PROVIDER: GSE131607 | GEO | 2019/10/22

REPOSITORIES: GEO

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Project description:Bovine mastitis, the infection of the mammary gland which leads to great health and economic challenges for dairy farmers is accompanied by dramatic changes in the milk proteome. In this study of naturally occurring mastitis not only have the changes in the milk proteome been quantified in subclinical and clinical mastitis but simultaneous changes in the serum proteome have also been characterised and quantified. Milk and serum samples from healthy dairy cows (n=12) were compared to those of cows with subclinical (n=10) and clinical mastitis (n=112) using TMT label-based proteomic approach. The study included the milk and serum samples taken from thirty-two dairy cows ( kept on private farms located in Croatia. All cows were checked by physical examination. Somatic cells count (SCC) and mastitis test in milk samples were performed. According to the results, cows were assigned into three groups: Group I (control, n=10) consisted of healthy cows with SCC below 400,000 cells/ml on the monthly check-up and a negative mastitis test and without any clinical sign of mastitis. Group II (subclinical mastitis, n=12) comprised cows without clinical signs of mastitis but with SCC above 400,000 cells/ml on the monthly basis and a positive mastitis test at the time of sampling. Group III (clinical mastitis, n=10) consisted of cows with clinical signs of mastitis which include changes in milk appearance (flakes and clots in milk), different stages of udder inflammation (hyperemia, edema, pain, udder enlargement and elevated udder temperature) and disturbance of general health (depression, relaxed cold ears, dehydration, elevated body temperature, increased heart and respiratory rate, decreased ruminal contraction and decreased appetite). Blood samples were taken from v. coccygea and centrifuged at 3000 g for 15 min after clotting for two hours at room temperature. Serum samples were stored at -80°C until analysis. Milk samples were taken aseptically before the morning milking. First few streams were discarded. Teat ends were disinfected with cotton swabs soaked with 70% ethanol. Samples were taken into sterile tubes and transported to laboratory on ice within a few hours.

Project description:Background Our objective was to compare mammary tissue gene expression profiles during a Streptococcus uberis (S. uberis) mastitis challenge between lactating cows subjected to dietary-induced negative energy balance (NEB; n = 5) and cows fed ad libitum to maintain positive energy balance (PEB; n = 5). The NEB cows were feed-restricted to 60% of calculated net energy for lactation requirements for 7 d, and cows assigned to PEB were fed the same diet for ad libitum intake. Five days after feed restriction, one rear mammary quarter of each cow was inoculated with 5,000 cfu of S. uberis (O140J). At 20 h post-inoculation, both the S. uberis-infected mammary quarters (i.e., YES) and non-infected rear quarters (i.e., NO) from all cows were biopsied for RNA extraction. Effect of S. uberis Intramammary Infection (IMI; YES vs NO) S. uberis IMI resulted in 2,102 oligos (1,939 annotated genes) differentially expressed genes (DEG; YES versus NO). Of these, 1,082 genes were up-regulated during IMI and were primarily involved with the immune response, e.g., IL6, TNF, IL8, IL10, SELL, LYZ, and SAA1. Genes down-regulated (1,020) included those associated with milk fat synthesis, e.g., LPIN1, LPL, CD36, and BTN1A1. Pathway analysis of all DEG indicated that IL-10 Signaling, IL-6 Signaling, and Glucocorticoid Receptor Signaling were among the top canonical pathways affected by infection. Interestingly, LXR/RXR Signaling was also a primary affected pathway, indicating a relationship between immune system response and metabolism during an IMI. Network analysis indicated that TNF had positive relationships (i.e. up-regulation) with genes involved with immune system function (e.g., CD14, IL8, IL1B, and TLR2) and negative relationships (i.e., down-regulation) with genes involved with lipid metabolism (e.g., GPAM, SCD, FABP4, CD36, and LPL) and antioxidant activity (SOD1). Results provided information into the early response factors associated with the innate immune response to S. uberis infection. Our study indicated that IMI challenge with S. uberis (strain O140J) elicited a strong transcriptomic response, leading to an overall up-regulation of genes involved in the innate immune response and a down-regulation of genes involved with lipid metabolism. Effect of NEB Within Infected Quarters (YES) Energy balance (NEB vs. PEB) resulted in 285 DEG (FDR ≤ 0.05), with 85 DEG up-regulated and 200 DEG down-regulated. Canonical pathways most affected by NEB were IL-8 Signaling (10 genes), Glucocorticoid Receptor Signaling (13), and NRF2-mediated Oxidative Stress Response (10). Among genes differentially expressed by NEB, Cell Growth and Proliferation (48) and Cellular Development (36) were the most enriched functions. Up-regulated genes included ANXA1, HMOX1, and HLAA; down-regulated genes included NOTCH1 and CCND1. Regarding immune response, HLAA was up-regulated due to NEB, whereas the majority of genes involved in immune response were down-regulated (e.g., AKT1, IRAK1, MAPK9, and TRAF6). Results helped identify mechanisms affected by dietary-induced NEB that may be associated with the impairment of immune function and increased risk of mastitis in cows experiencing postpartal NEB. Effect of NEB Within Non-Infected Quarters (NO) Energy balance (NEB vs. PEB) resulted in 278 DEG within non-infected rear mammary quarters. Up-regulated DEG most affected by NEB (genes = 180) included genes involved in lipid metabolism and amino acid metabolism. The down-regulated DEG most affected by NEB (n = 98) included genes involved in carbohydrate metabolism, anti-inflammatory response, and apoptosis. Among genes up-regulated, Ingenuity Pathway Analysis® identified Lipid Metabolism (8), Molecular Transport (14), and Small Molecule Biochemistry (15) as some of the most enriched molecular functions. Genes down-regulated by NEB were associated with Cell Growth and Proliferation (21) and Cell Death (18). Results indicate that dietary induced-NEB alters genes primarily associated with cellular metabolism, proliferation, and tumorigenesis but no candidate genes were identified as being associated with risk of disease.

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Genetic mechanisms regulating the host response during mastitis

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