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Bioinformatics analysis of mammary gland and liver transcriptome in response to an intra-mammary E. coli lipopolysaccharide challenge in early-lactation dairy cattle
During mastitis, pathogens are detected by the receptors on the epithelial cells of the mammary tissue and an acute phase response activates the immune system to eliminate the pathogens. The liver is a central organ during inflammation and synthesizes the necessary components for immediate defense at the site of tissue damage. The objective of this study was to determine gene expression patterns in mammary and liver tissue in response to an intra-mammary E. coli lipopolysaccharide (LPS) challenge in early-lactating dairy cattle. Fourteen Holstein cows were used. At ~7 DIM, 7 cows served as controls (CTR) and 7 cows (LPS) received an intra-mammary E. coli LPS challenge (200 µg in sterile saline). For transcript profiling the mammary and liver tissue were sampled by biopsy 2 h after the challenge. A bovine oligonucleotide (70-mers) microarray with >13,000 annotated sequences was used for profiling. Data were analyzed using the MIXED procedure of SAS (SAS Inst. Inc., Cary, NC) and a threshold of 1.5-fold change and a P value of 0.05 were considered to define differentially expressed genes (DEG). Bioinformatics analyses was conducted using the Dynamic Impact Approach (DIA) and Ingenuity Pathway Analysis (IPA) (Ingenuity Systems, Inc.). In mammary tissue, a total of 189 DEG (20 downregulated, 169 upregulated) were observed in LPS vs. CTR cows. The most-impacted and activated KEGG pathways highlighted by the DIA analysis were NOD-like receptor signaling, RIG-I-like receptor signaling, Apoptosis, Cytosolic DNA-sensing and Chemokine signaling. The IPA analysis underscored the presence of 13 transcription regulators (2 downregulated, 11 upregulated) of which 4 upregulated (NF-kB, MYC, STAT3 and HIF1A) are key components of inflammatory response processes and are involved in cell apoptosis. In liver tissue, a total of 107 DEG (42 downregulated, 65 upregulated) were observed due to LPS. The DIA analysis highlighted the inhibition of Fatty acid elongation in mitochondria and activation of p53 signaling pathway. From IPA analysis the most important upregulated transcription regulators (ZFP36, CEBPD, MYC and CREM) are involved in the immune and inflammatory responses and are necessary to maintaining homeostasis of the organism during infection. Results suggest that within 2 h from intra-mammary LPS challenge the liver responds to stimuli and alters its transcriptome as a way to maintain homeostasis.
Keywords:
system biology, mammary, liver, LPS