Submitted to: Frontiers in Veterinary Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/17/2020
Publication Date: 9/22/2020
Citation: Casas, E., Ma, H., Lippolis, J.D. 2020. Expression of viral microRNAs in serum and white blood cells of cows exposed to bovine leukemia virus. Frontiers in Veterinary Science. 7. https://doi.org/10.3389/fvets.2020.536390.
Interpretive Summary: Bovine leukemia virus (BLV) produces leucosis, which can lead to leukemia in cattle. This virus causes economic losses to the cattle industry due to loss of milk production and condemnation at slaughter. Small pieces of RNA, called microRNAs that are produced and circulate in cattle, are known to regulate gene expression such as immune responses to viral infections and disease. It is known that the BLV produces its own microRNAs. Establishing the difference in quantity (expression) of BLV microRNAs between animals exposed (seropositive group) or not (seronegative) to the virus, will produce information needed to understand how genes in cattle are turned on or off, and how the animal’s immune system responds to BLV. The goal of this study was to establish if the expression of BLV microRNAs was different when compared between seropositive and seronegative Holstein cows to BLV. Seropositive animals had a higher expression of BLV microRNAs than seronegative animals. Most microRNAs had a consistent expression with an average of 7 fold difference between seropositive and seronegative groups, with the exception of two BLV microRNAs, which had a differential expression averaging 27 fold. Two BLV microRNAs targeted genes in cattle that are associated with response to stress and immunity. One of the microRNAs produced by the BLV targets several genes related with development of leukemia in humans. Viral microRNAs involved in the development of leukemia in humans could also be responsible for the development of the condition in cattle.
Technical Abstract: Bovine leukemia virus (BLV) affects cattle health and productivity, causing abnormal immune function and immunosuppression. MicroRNAs (miRNAs) are known to be involved in gene expression and have been associated with stress and immune response, tumor growth, and viral infection. The objective of this study was to determine the expression of circulating miRNAs produced by BLV in animals exposed to the virus. Sera from 14 animals were collected to establish IgG reactivity to BLV by ELISA, where seven animals were seropositive and seven were seronegative for BLV exposure. White blood cells (WBC) from each animal were also collected and miRNAs were identified by sequencing from sera and WBC. The seropositive group had higher counts of BLV miRNAs when compared to seronegative group in sera and WBC. Blv-miR-1-3p, blv-miR-B2-5p, blv-miR-B4-3p, and blv-miR-B5-5p were statistically significant (P< 0.00001) in serum with an average of 7 log2 fold difference between seropositive and seronegative groups. Blv-miR-B1-3p, blv-miR-B1-5p, blv-miR-B3, blv-miR-B4-3p, blv-miR-B4-5p, blv-miR-B5-5p were statistically significant (P< 1.08e-9) in WBC with an average of 7 log2 fold difference between the seropositive and the seronegative groups. Blv-miR-B2-3p and blv-miR-B2-5p were also statistically significant in WBC (P< 2.79e-17), with an average of 27 log2 fold difference between the seropositive and the seronegative groups. There were 18 genes identified as being potential targets for blv-miR-B1-5p, and 3 genes for blv-miR-B4-5p. Gene ontology analysis indicated that the target genes are mainly involved in the response to stress and in the immune system process. Several of the identified genes have been associated with leukemia development in humans and cattle. Differential expression of genes targeted by BLV miRNAs should be evaluated to determine their effect in BLV replication.