Elucidation of the host bronchial lymph node miRNA transcriptome response to bovine respiratory syncytial virus
Bovine Respiratory Disease (BRD) is responsible for the majority of calf morbidity and mortality. One of the main causes of BRD is initial infection with Bovine Respiratory Syncytial Virus (BRSV). The objective of this study was to elucidate the changes in the host's bronchial lymph node miRNA transcriptome in response to BRSV in a controlled viral challenge. Holstein-Friesian calves were either inoculated with BRSV (103.5 TCID50/ml x 15 ml) (n=12) or mock challenged with phosphate buffered saline (n=6). Clinical signs were scored daily until euthanasia at day 7 post-challenge. Total RNA was extracted and sequenced (75 bp) from bronchial lymph nodes. Sequences were filtered for contaminant short RNA species, and subsequently read counts for known miRNAS were generated using the miRDeep2 package with the UMD 3.1 version of the genome and the bovine mature miRNA sequences from the miRBase database (release 22). EdgeR was used for differential expression analysis and Targetscan was used to identify target genes for the differentially expressed (DE) miRNAs. Pathway and gene ontology analyses on target genes were carried out using Ingenuity Pathway analysis (Qiagen).  There was a clear separation between BRSV challenged and control calves based on miRNA gene expression changes, despite an observed mild clinical manifestation of the disease. There were 119 DE miRNAs (p<0.05, FDR<0.1, fold change>1.5) between the BRSV challenged and control calves. The DE miRNAs were predicted to target 465 genes which were previously found to be DE in bronchial lymph node tissue, between these BRSV challenged and control calves. Out of the DE predicted target genes, 455 genes had inverse fold changes to that of the DE miRNAs. There were 8 enriched pathways among the DE predicted target genes with inverse fold changes to that of the DE miRNA including: granulocyte and agranulocyte adhesion and diapedesis, interferon signaling and role of pathogen recognition receptors in recognition of bacteria and viruses. Functions predicted to be increased included: T cell response, apoptosis of leukocytes, immune response of cells and stimulation of cells. Pathogen recognition and proliferation of cytotoxic T cells are vital for the recognition and subsequent elimination of the virus. Overall design: Examination of a single tissue type (broncial lymph node) in two different treatment groups, BRSV challenged calves (n=12) and control calves (n=6)