Expression of PCV2 antigen in the ovarian tissues of gilts

Interference of pseudorabies virus infection on functions of porcine granulosa cells via apoptosis modulated by MAPK signaling pathways

BACKGROUND

Pseudorabies virus (PRV) is one of the major viral pathogens leading to reproductive disorders in swine. However, little is known about the effects of PRV infection on porcine reproductive system. Ovarian granulosa cells are somatic cells surrounding oocytes in ovary and required for folliculogenesis. The present study aimed to investigate the interference of PRV on functions of porcine ovarian granulosa cells in vitro.

METHODS

Primary granulosa cells were isolated from porcine ovaries. To investigate the PRV infectivity, transmission electron microscopy (TEM) was used to check the presence of viral particles, and the expression of viral gE gene was detected by quantitative real-time PCR (qPCR) in PRV-inoculated cells. After PRV infection, cell viability was detected by MTS assay, Ki67 for proliferative status was determined by immunofluorescence assay (IFA), cell cycle and apoptosis were detected by flow cytometry, and progesterone (P4) and estradiol (E2) were determined by radioimmunoassay. The checkpoint genes of cell cycle and apoptosis-related proteins were studied by qPCR and western blotting.

RESULTS

Virus particles were observed in the nucleus and cytoplasm of PRV-infected granulosa cells by TEM imaging, and the expression of viral gE gene increased in a time-dependent manner post infection. PRV infection inhibited cell viability and blocked cell cycle at S phase in porcine granulosa cells, accompanied by decreases in expression of Ki67 protein and checkpoint genes related to S phase. Radioimmunoassay revealed decreased levels in P4 and E2, and the expressions of key steroidogenic enzymes were also down-regulated post PRV-infection. In addition, PRV induced apoptosis with an increase in Bax expression and activation of caspase 9, and the phosphorylation of JNK, ERK and p38 MAPKs were significantly up-regulated in porcine ovarian granulosa cells post PRV infection.

CONCLUSIONS

The data indicate that PRV causes infection on porcine ovarian granulosa cells and interferes the cell functions through apoptosis, and the MAPK signaling pathway is involved in the viral pathogenesis.

Risk of pathogenic virus transmission by somatic cell nuclear transfer (SCNT): implications for xenotransplantation

Using somatic cell nuclear transfer (SCNT) for the generation of cloned and transgenic animals bears the risk of transmission of viruses, either by the oocyte or by the introduced donor cell. There is evidence that the zona pellucida (ZP) surrounding the oocyte prevents virus infection, however, virus infections despite intact ZP were reported. Furthermore, the protective ZP has to be penetrated in order to place the somatic cell in the oocyte's perivitelline space during SCNT. Transmission of viruses represents also a severe problem during in vitro fertilization (IVF). Genetically modified and IVF-produced pigs serve as an important biomedical model for numerous diseases and it is important to evaluate whether infections of the model animals can falsify the research data. Of special significance is this topic in the case of xenotransplantation using genetically modified pigs as donor animals, because transmission of porcine viruses may be harmful for the human recipient. This was repeatedly demonstrated in preclinical pig to non-human primate trials. Therefore, donor pigs, oocytes used for SCNT and genetically modified donor cells should be screened for potentially zoonotic viruses when creating genetically modified pigs designed for xenotransplantation.

Prevalence of porcine circovirus 2 throughout China in 2015-2019: A systematic review and meta-analysis

Porcine circovirus type 2 (PCV2) causes infectious diseases in pigs leading to considerable economic losses in the pig industry. To prevent and control PCV2 infections, is important to understand the prevalence and geographical distribution of the virus. We performed the first systematic review and meta-analysis to estimate the prevalence of PCV2 in China. From PubMed, ScienceDirect, Chinese Web of Knowledge, Wanfang, and VIP Chinese Journal, we extracted 53 studies published in China between 2015 and 2019. There were 29,051 samples, 14,230 of which were positive for PCV2. The pooled prevalence of PCV2 was 46.0%, with the highest in Northeastern China (58.1%). The highest prevalence was 86.3% in Xinjiang province. Nursery pigs had the highest prevalence of PCV2 (50.9%), and the serological test detected the highest number of cases (58.5%). PCV2 prevalence was 50.1% in intensive farms and 37.5% in extensive farms. Our findings showed that PCV2 is common throughout China. Effective control measures are necessary to reduce PCV2 infections.

Evaluation of porcine circovirus type 2 infection in in vitro embryo production using naturally infected oocytes

In vitro fertilization (IVF) and somatic cell nuclear transfer (SCNT) are important breeding techniques for livestock. High-quality MII oocytes produced from in vitro maturation (IVM) are required for the two techniques listed above. The ovaries used for IVM operations are primarily acquired from commercial abattoirs, and the pathogen status of slaughtered animals becomes an unavoidable issue. Our previous monitoring data showed that porcine circovirus type 2 (PCV-2) is the main pathogen present in ovaries from abattoirs. However, the characteristics and effects of PCV-2 infection in oocyte maturation and in vitro production (IVP) of embryos are unclear, and currently there are no relevant studies. Therefore, the aim of this study was to determine the PCV-2 infection pattern and determine whether it affects oocyte in vitro maturation and IVP embryo development. More than five hundred ovaries and five thousand oocytes were utilized in the present study. Polymerase chain reaction (PCR) was used to detect PCV-2 DNA in ovaries, follicular fluid (FF), oocytes, cumulus cells and IVP embryos. The effects of viral infections on the rate of oocyte maturation and IVP embryo development were evaluated. We also analyzed the number of copies of the virus in the IVM and IVP process by absolute quantitative fluorescence PCR. Our study showed that the prevalent virus subgenotype in ovaries was PCV-2a. PCV-2a infection did not significantly affect ovarian/oocyte morphology and maturation. Moreover, virus infection did not have a significant effect on the development of the IVP embryos except for a reduction in IVF blastocyst cell numbers. Further tests showed that the viral copy numbers fluctuated at different stages between the IVP embryos and culture medium. For the first time, this study identified the infection pattern of naturally sourced PCV-2 in the course of oocyte maturation and embryo development.

Germocyte lesions caused by porcine circovirus type 2b in Kunming mice

Porcine circovirus type 2 (PCV2) has been known as a causative agent of reproductive failure in the sow. In the present study mouse model was used to investigate PCV2 infection. In order to investigate whether PCV2 can induce lesions of spermatocytes and oocytes, 6 male and 6 female mice were each inoculated intraperitoneally with PCV2b, and 3 male and 3 female mice mock-infected with cell culture supernatant served as controls. Samples of testes and ovaries from PCV2b-inoculated and mock-infected mice were investigated using PCR, histopathological, ultrastructural and immunofluorescent histochemical methods at 14 and 21 day post infection (dpi). The study revealed that in the virus-inoculated mice leydig cells in testes and granulosa cells in ovaries were degenerated, and a small number of spermatocytes and oocytes showed apoptosis. Positive PCV2b antigen signals were also observed in these apoptotic cells. It can be suggested that PCV2 can cause lesions of spermatocyte and oocyte prior to zygotes formation in its host.