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TLR4 governs strain-specific transcriptional responses of bovine mammary epithelial cells challenged by Staphylococcus aureus and its small colony variant

ABSTRACT: Staphylococcus aureus small colony variants (SCVs) are metabolically adapted, slow-growing subpopulations responsible for chronic, recurrent bovine mastitis through enhanced intracellular persistence and immune evasion. The role of Toll-like receptor 4 (TLR4) in regulating bovine mammary epithelial transcriptional responses to S. aureus SCV challenge remains poorly understood. Using CRISPR-Cas9-generated TLR4-knockout (TLR4-KO) MAC-T cells combined with RNA sequencing, global transcriptional responses of wild-type (WT) and TLR4-KO MAC-T cells infected with S. aureus SCV Heba3231 and its isogenic parental strain (PS) were compared. The WT cells mounted highly divergent S. aureus strain-specific responses, with only 0.5% overlap in differentially expressed genes between PS and SCV conditions. The PS infection induced apoptotic and HIF-1 signalling pathways, whereas SCV infection promoted lipid metabolic reprogramming, accompanied by suppression of epithelial barrier integrity genes. TLR4 disruption dramatically amplified transcriptional dysregulation, with a 192-fold increase for the PS (1,921 DEGs) and a 6.6-fold increase for SCV (2,279 DEGs) relative to WT infected controls. This revealed a large core set of TLR4-regulated genes with approximately 57% shared across S. aureus strains that govern innate immunity, structural homeostasis, and apoptotic coordination. WFDC2, ITGB3, SH3BGRL, and HKDC1 emerged as novel TLR4-dependent candidate genes. Collectively, these findings identify TLR4 as a key determinant of strain-specific transcriptional discrimination and epithelial homeostasis during S. aureus infection, with particular relevance to SCV-mediated persistence in bovine mastitis.

ORGANISM(S): Bos taurus

PROVIDER: GSE334132 | GEO | 2026/06/08

REPOSITORIES: GEO

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Project description:Purpose: The goal of this study is to explore the role of miRNAs in dairy cow response to E. coli and S. aureus, mastitis causing pathogens, is not well understood. Results: The global expression of miRNAs in bovine mammary epithelial cells (MAC-T cells) challenged with heat-inactivated Staphylococcus aureus (S. aureus) or Escherichia coli (E. coli) bacteria (treatments: 6, 12, 24 and 48 hr) and without challenge (control: 0, 6, 12, 24 and 48 hr) was profiled using next-generation-sequencing. A total of 231 known bovine miRNAs were identified with more than 10 counts per million (CPM) in at least one of 13 libraries and 5 miRNAs including bta-miR-21-5p, miR-27b, miR-22-3p, miR-184 and let-7f represented more than 50% of the total reads of known bovine miRNAs. One hundred and fifty novel miRNAs were identified and half of them belong to the bta-miR-2284 family. Seventeen miRNAs were significantly (P<0.05) differentially regulated by the presence of pathogens. E. coli initiated an earlier regulation of miRNAs (6 miRNAs differentially regulated within the first 6 hrs post challenge as compared to one for S. aureus) while S. aureus presented a delayed response. Five differentially expressed miRNAs (Bta-miR184, miR-24-3p, miR-148, miR-486 and bta-let-7a-5p) were unique to E. coli while four (bta-miR-2339, miR-499, miR-23a and miR-99b) were unique to S. aureus. In addition, our study revealed a temporal differential regulation of five miRNAs (bta-miR-193a-3p, miR-423-5p, miR-30b-5p, miR-29c and miR-un116) in unchallenged cells. Target gene predictions of pathogen differentially expressed miRNAs indicate a significant enrichment in gene ontology functional categories in development/cellular processes, biological regulation as well as cell growth and death. Furthermore, target genes were significantly enriched in several KEGG (Kyoto encyclopedia of genes and genomes) pathways of the immune system, signal transduction, cellular process, nervous system, development and pathways in human diseases, especially cancer. Conclusion: Using next-generation sequencing, our study identified 150 novel bovine miRNAs and revealed a pathogen directed differential regulation of miRNAs in MAC-T cells with roles in immunity and development. E. coli elicited an earlier differential regulation of miRNAs as opposed to a delayed regulation by S. aureus. Furthermore, target gene prediction showed significant enrichments for functions in different biological and cellular processes as well as KEGG pathways in immunity, development and human diseases. Our study provides a further confirmation of the involvement of mammary epithelia cells in contributing to the immune response to infecting pathogens and suggests the potential of miRNAs to serve as biomarkers for diagnosis of mastitis and development of control measures. Bovine mammary epithelial cells (MAC-T cells) challenged with heat-inactivated Staphylococcus aureus (S. aureus) or Escherichia coli (E. coli) bacteria (treatments: 6, 12, 24 and 48 hr) and without challenge (control: 0, 6, 12, 24 and 48 hr) was profiled using next-generation-sequencing, no replicates, using illumina HiScanSQ platform.

Project description:Mastitis is a common disease that hinders the development of dairy industry and animal husbandry. It leads to the abuse of antibiotics, the emergence of super drug-resistant bacteria, and poses a great threat to human food health and safety. Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) are the most common pathogens of mastitis in dairy cows and usually cause subclinical or clinical mastitis. CircRNAs and N6-methyladenosine (m6A) play important roles in immunological diseases. However, the mechanisms by which m6A modifies circRNA in bovine mammary epithelial cells remain poorly understood. The aim of our study was to investigate m6A-modified circRNAs in bovine mammary epithelial cells (MAC-T cells) injured by S. aureus and E. coli. The profile of m6A-modified circRNA showed a total of 1599 m6A peaks within 1035 circRNAs in the control group, 35 peaks within 32 circRNAs in the S. aureus group, and 1016 peaks within 728 circRNAs in the E. coli group. Compared with the control group, 67 peaks within 63 circRNAs were significantly different in the S. aureus group, and 192 peaks within 137 circRNAs were significantly different in the E. coli group. Furthermore, we found the source genes of these differentially m6A-modified circRNAs in the S. aureus and E. coli groups with similar functions according to GO and KEGG analyses, which were mainly associated with cells injury, such as inflammation, apoptosis, and autophagy. CircRNA-miRNA-mRNA interaction networks predicted the potential circRNA regulation mechanism in S. aureus- and E. coli-induced cell injury. We found that the mRNAs in the networks, such as BCL2, MIF and TNFAIP8L2, greatly participated in the MAPK, WNT, and inflammation pathways. This is the first report on m6A-modified circRNA regulation of cells under S. aureus and E. coli treatment, and sheds new light on potential mechanisms and targets from the perspective of epigenetic modification in mastitis and other inflammatory diseases.

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TLR4 governs strain-specific transcriptional responses of bovine mammary epithelial cells challenged by Staphylococcus aureus and its small colony variant

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