Streptococcus agalactiae-induced autophagy of bovine mammary epithelial cell via PI3K/AKT/mTOR pathway

Enterogenic Stenotrophomonas maltophilia migrates to the mammary gland to induce mastitis by activating the calcium-ROS-AMPK-mTOR-autophagy pathway

BACKGROUND

Mastitis is an inflammatory disease of the mammary gland that has serious economic impacts on the dairy industry and endangers food safety. Our previous study found that the body has a gut/rumen-mammary gland axis and that disturbance of the gut/rumen microbiota could result in 'gastroenterogenic mastitis'. However, the mechanism has not been fully clarified. Recently, we found that long-term feeding of a high-concentrate diet induced mastitis in dairy cows, and the abundance of Stenotrophomonas maltophilia (S. maltophilia) was significantly increased in both the rumen and milk microbiota. Accordingly, we hypothesized that 'gastroenterogenic mastitis' can be induced by the migration of endogenous gut bacteria to the mammary gland. Therefore, this study investigated the mechanism by which enterogenic S. maltophilia induces mastitis.

RESULTS

First, S. maltophilia was labelled with superfolder GFP and administered to mice via gavage. The results showed that treatment with S. maltophilia promoted the occurrence of mastitis and increased the permeability of the blood-milk barrier, leading to intestinal inflammation and intestinal leakage. Furthermore, tracking of ingested S. maltophilia revealed that S. maltophilia could migrate from the gut to the mammary gland and induce mastitis. Subsequently, mammary gland transcriptome analysis showed that the calcium and AMPK signalling pathways were significantly upregulated in mice treated with S. maltophilia. Then, using mouse mammary epithelial cells (MMECs), we verified that S. maltophilia induces mastitis through activation of the calcium-ROS-AMPK-mTOR-autophagy pathway.

CONCLUSIONS

In conclusion, the results showed that enterogenic S. maltophilia could migrate from the gut to the mammary gland via the gut-mammary axis and activate the calcium-ROS-AMPK-mTOR-autophagy pathway to induce mastitis. Targeting the gut-mammary gland axis may also be an effective method to treat mastitis.

Droplet digital PCR quantification of selected microRNAs in raw mastitic cow's milk from the west of Poland

Introduction

MicroRNAs (miRNAs), a class of noncoding small RNAs, have been recognised as potential biomarkers of mammary gland conditions, including bovine mastitis diagnosis. The aim of this study was to quantify selected miRNAs in the milk of mastitic cows.

Material and Methods

Milk samples (n = 90) were collected from healthy and mastitic dairy cows originating from local dairy cattle farms located in the west of Poland. MicroRNAs of the miR-21a, miR-92a, miR-146a and miR-383 species were quantified using the highly sensitive droplet digital PCR method. Direct measurement of somatic cell count (SCC) was performed using a cell counter. Cows were divided into three groups: those with an SCC below 200,000/mL were designated Low (n = 25), those with an SCC between 200,000 and 999,999 were Medium (n = 34), and those with an SCC of 1,000,000 or higher were High (n = 31). Microbiological analyses were performed using standard culture testing.

Results

The level of miR-383 was very low and this miRNA was excluded from analysis. The miR-92a was used to normalise miR-21a and miR-146a expression levels. The obtained results of expression of miR-21a and miR-146a correlated with somatic cell number (R = 0.53 and 0.79, respectively).

Conclusion

These results show that ddPCR is a useful method for quantifying miRNAs in raw cow milk. It seems that miR-146a is a promising marker for bovine mastitis, although further studies are needed to select a panel of miRNAs that can be used in mastitis monitoring in Poland.

Crosstalk between integrin/FAK and Crk/Vps25 governs invasion of bovine mammary epithelial cells by S. agalactiae

Streptococcus agalactiae (S. agalactiae) is a contagious obligate parasite of the udder in dairy cows. Here, we examined S. agalactiae-host interactions in bovine mammary epithelial cells (BMECs) in vitro. We found that S. agalactiae infected BMECs through laminin β2 and integrin. Crk, Vps25, and RhoA were differentially expressed in S. agalactiae-infected cells. S. agalactiae infection activated FAK and Crk. FAK deficiency decreased the number of intracellular S. agalactiae and Crk activation. Knockdown of Crk or Vps25 increased the level of intracellular S. agalactiae, whereas its overexpression had the opposite effect. RhoA expression and actin cytoskeleton were altered in S. agalactiae-infected BMECs. Crk and Vps25 interact in cells, and invaded S. agalactiae also activates Crk, allowing it to cooperate with Vps25 to defend against intracellular infection by S. agalactiae. This study provides insights into the mechanism by which intracellular infection by S. agalactiae is regulated in BMECs.

CDK5RAP3, a key defender of udder, modulates NLRP3 inflammasome activation by regulating autophagolysosome degradation in S. agalactiae-infected mastitis

Streptococcus agalactiae, as one of the main pathogens of clinical and subclinical mastitis, affects animal welfare and leads to huge economic losses to farms due to the sharp decline in milk yield. However, both the real pathogenic mechanisms of S. agalactiae-induced mastitis and the regulator which controls the inflammation and autophagy are largely unknown. Served as a substrate of ubiquitin-like proteins of E3 ligase, CDK5RAP3 is widely involved in the regulation of multiple signaling pathways. Our findings revealed that CDK5RAP3 was significantly down-regulated in mastitis infected by S. agalactiae. Surprisingly, inflammasome activation was triggered by CDK5RAP3 knockdown: up-regulated NLRP3, IL1β and IL6, and cleaved caspase1 promoting by NF-κB, thereby resulting in pyroptosis. Additionally, the accumulation of autophagy markers (LC3B and p62) after CDK5RAP3 knockdown suggested that the autophagolysosome degradation pathway was inhibited, thereby activating the NF-κB pathway and NLRP3 inflammasome. Hence, our findings suggest that downregulation or ablation of CDK5RAP3 inhibits autophagolysosome degradation, causes inflammation by activating the NF-κB /NLRP3 inflammasome, and triggers cell death. In conclusion, CDK5RAP3 holds the key to understanding the interaction between autophagy and immune responses, its anti-inflammatory role in this study will throw new light on the clinical drug discovery to cure S. agalactiae mastitis.

Effect of NZ2114 against Streptococcus dysgalactiae biofilms and its application in murine mastitis model

Bovine mastitis caused by Streptococcus dysgalactiae (S. dysgalactiae) is usually treated with antibiotics, which may potentially increase drug resistance as the abuse. NZ2114, a variant of fungal defensin plectasin, displayed a potent antibacterial activity against S. dysgalactiae. The inhibition/eradication effect of the antimicrobial peptide NZ2114 on the early/mature biofilm of S. dysgalactiae CVCC 3938 was evaluated, as well as the elimination of bacteria in mature biofilms. In this study, NZ2114 displayed potent antibacterial activity against S. dysgalactiae CVCC 3938 and three clinical isolated S. dysgalactiae strains (0.11-0.45 μM). The early biofilm inhibition of S. dysgalactiae CVCC 3938 was 55.5–85.9% after treatment with NZ2114 at concentrations of 1–16 × MIC, which was better than that of vancomycin at the same concentration. The mature biofilm eradication rate was up to 92.7–97.6% with the increasing concentration (2–16 × MIC) of NZ2114, and the eradication rate did not change significantly with further increase of NZ2114 concentration, while the biofilm eradication rate of vancomycin-treated group at the same concentration remained at 92.5%. NZ2114 reduced the number of persister bacteria in biofilm. Scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM) further demonstrated that NZ2114 could effectively reduce the biofilm thickness and bacterial number of S. dysgalactiae CVCC 3938. In vivo therapeutic effect of NZ2114 on murine mastitis model showed that NZ2114 was better than vancomycin in alleviating mammary gland inflammation by regulating cytokines production, inhibiting bacterial proliferation, and reducing the number of mammary gland bacteria. These data suggested that NZ2114 is a potential peptide candidate for the treatment of mastitis.

Mycoplasma bovis inhibits autophagy in bovine mammary epithelial cells via a PTEN/PI3K-Akt-mTOR-dependent pathway

Although autophagy can eliminate some intracellular pathogens, others, e.g., Staphylococcus aureus, Salmonella, Mycoplasma bovis, can evade it. The phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt)/mammalian target of rapamycin (mTOR) pathway, a key regulator of autophagy, is involved in initiation and promotion of a range of pathological diseases. As the effects of M. bovis on the autophagic pathway are not well documented, our objective was to elucidate the effects of M. bovis infection on the PI3K-Akt-mTOR cellular autophagic pathway in bovine mammary epithelial cells (bMECs). Ultrastructure of bMECs infected with M. bovis was assessed with transmission electron microscopy, co-localization of LC3 puncta with M. bovis was confirmed by laser confocal microscopy, and autophagy-related indicators were quantified with Western blotting and RT-PCR. In M. bovis-infected bMECs, intracellular M. bovis was encapsulated by membrane-like structures, the expression level of LC3-II and Beclin1 protein decreased at the middle stage of infection, degradation of SQSTM1/P62 was blocked, autophagy of bMECs was inhibited, and PI3K-Akt-mTOR protein was activated by phosphorylation. Furthermore, the tumor suppressor PTEN can inhibit the PI3K-Akt signaling pathway through dephosphorylation of phosphatidylinositol 3,4,5-trisphosphate and may be important for cellular resistance to infection. In the present study, the number of intracellular M. bovis was inversely related to the change in the level of autophagy markers (e.g., LC3-II, SQSTM1/P62) within host cells induced by the low knockdown of Akt or PTEN. We concluded that M. bovis-infected bMECs alleviated cellular autophagy through a PI3K-Akt-mTOR pathway, and that PTEN acted as a protective gene regulating autophagy, a key step in controlling infection.