Vertical transmission of porcine circovirus-like virus P1 in BALB/c mice.

BACKGROUND: Porcine circovirus-like virus P1 is the animal virus with the smallest genome discovered so far, and it has become widely distributed in the Chinese mainland in recent years. RESULTS: In this study, a BALB/c mouse model was used to reveal P1 infection in female reproductive systems and the vertical transmission of the virus. The female reproductive system, including the ovary and uterus, was harvested on day 14 postinfection and examined for pathological lesions. One-day-old mice without colostrum born from infected or uninfected mothers were collected, and P1 virus distribution in the different organs was investigated. During the trials, all the mice showed no clinical symptoms or gross lesions. However, stillbirth did occur in groups infected with the P1 virus. P1 nucleic acid was detected in the heart, liver, spleen, lung, kidney, and brain tissues of 1-day-old mice born from infected mice. Microscopic lesions in P1-infected female mice were characterized by necrosis of the ovarian follicular granulosa cells and abscission, follicular atresia, necrosis of the endometrial epithelial and uterine glandular epithelial cells, and hyperplasia of the squamous endometrial epithelium. The spermatocytes in the seminiferous tubules of the infected male mice were disorderly arranged, and the germ and Sertoli cells were shed, necrotic, and decreased in number. Immunohistochemical results identified P1-positive particles in the nucleus and cytoplasm of cells from the ovary and uterus of female mice. CONCLUSIONS: This study shows that the P1 virus could cause pathological damage to the reproductive system of female mice and could be transmitted vertically.

First detection and complete genome analysis of porcine circovirus-like virus P1 and porcine circovirus-2 in yak in China.

Porcine circovirus-like virus P1, like porcine circovirus type 2 (PCV2), is a potential pathogen of post-weaning multisystemic wasting syndrome in swine. Yaks are a valuable species and an iconic symbol of the Tibet Plateau which is the highest and largest plateau in the world. In this study, a total of 105 yak diarrheal samples, collected from 13 farms in Linzhi in the Tibet Plateau from January 2019 to December 2021, that were screened for P1 and PCV2 by polymerase chain reaction, 10.48% (n = 11) were positive for P1, 4.76% (n = 5) for PCV2, and 5.71% (n = 6) were positive for coinfection of P1 and PCV2. In addition, the whole genomes of eight P1 strains and eight PCV2 strains were sequenced. Alignment of deduced amino acid sequences of P1 ORF1 and PCV2 ORF2 gene revealed that ON012566 had one unique amino acid mutation at residues 137 (T to P). This mutation has important implication for the study of virus virulence, tissue tropism, and immune response. Phylogenetic analysis shows that the yak-origin P1 strains in this study with cattle-origin P1 reference strains were grouped into one cluster. The yak-origin PCV2 (ON012566) and a buffalo-origin PCV2 (KM116514) reference strain clustered in the same branch in the PCV2b regions. Meanwhile, the remaining PCV2 strains and buffalo-origin PCV2 reference strain (ON012565) clustered in the PCV2d regions. To summarize, to our knowledge, this is the first report on the molecular prevalence and genome characteristics of P1 and PCV2 in yaks in the world and will contribute to further study of the molecular epidemiology, source, and evolution of P1 and PCV2 strains.

Porcine circovirus-like virus P1 activates pancreatic secretion pathway by interacting with CHRM3 protein.

The porcine circovirus-like virus P1, a member of the circovirus family, causes post-weaning multisystemic wasting syndrome (PMWS) in weaned piglets with progressive wasting as the main clinical symptom. The pancreatic secretion pathway induces pancreatic acinar cells to secrete various digestive enzymes and as such is an important signaling pathway for the digestive system and somatic growth. This study examined the effects and mechanism of P1 virus infection on the pancreatic secretion pathway. The experiment was conducted by transfecting double-copy plasmid P1 into PK-15 and 3D4 cells and by infecting cells with the P1 virus. Samples were collected at various times after transfection or infection. The pathway's transcription and translation levels of CHRM3, Gq, PLC-ß2, PRKCA, Rab3D, RhoA, Rac1, and amyA proteins were detected by real-time PCR and Western blots; these analyses confirmed that the P1 virus infection could upregulate the expression level of key pancreatic secretion signaling molecules. Then, we confirmed that the VP1 protein of the P1 virus could interact with the pathway initiation protein CHRM3 using Co-IP, pull-downs, and confocal fluorescence microscopy. Finally, we demonstrated that the VP1 protein activates the pancreatic secretory pathway through the CHRM3 protein. In conclusion, this study demonstrated that the P1 virus can interact with the CHRM3 receptor protein to activate the pancreatic secretion pathway and promote the secretion of various digestive enzymes downstream of the pathway, thereby providing a basis for P1 virus pathogenesis.

Nearly 20 Years of Genetic Diversity and Evolution of Porcine Circovirus-like Virus P1 from China.

Porcine circovirus-like virus P1 can infect many kinds of animals and mainly causes postweaning multisystemic wasting syndrome. In China, the genetic diversity, variation, and evolutionary processes of this virus have not been described yet. To improve our knowledge of its genetic diversity, evolution, and gene flow, we performed a bioinformatics analysis using the available nucleotide sequences of the P1 virus; among them, 12 nucleotide sequences were from ten pig farms in Jiangsu Province in this epidemiological survey, and 84 sequences were downloaded from GenBank. The P1 sequences showed a rich composition of AT nucleotides. Analyses of the complete genomic sequences were polymorphic and revealed high haplotype (gene) diversity and nucleotide diversity. A phylogenetic analysis based on the NJ method showed that all P1 virus sequences formed two distinct groups: A and B. High genetic differentiation was observed between strains from groups A and B. The codon usage pattern of P1 was affected by dinucleotide compositions. Dinucleotide UU/CC was overrepresented, and dinucleotide CG was underrepresented. The mean evolutionary rate of the P1 virus was estimated to be 3.64 × 10-4 nucleotide substitutions per site per year (subs/site/year). The neutrality tests showed negative values. The purifying selection and recombination events may play a major driving role in generating the genetic diversity of the P1 population. The information from this research may be helpful to obtain new insights into the evolution of P1.

Interaction of porcine circovirus-like virus P1 capsid protein with host proteins.

BACKGROUND: Porcine circovirus-like virus P1 is a relatively new kind of virus that is closely related to the post-weaning multisystemic wasting syndrome, congenital tremors, and abortions in swine. The molecular mechanisms of P1 virus infection and pathogenesis are fully unknown. To analyze P1 and its host interactions, we used a yeast two-hybrid (Y2H) assay to identify cellular proteins interacting with the Cap of the P1 virus. In this study, the Cap of the P1 virus exhibited no self-activation and toxicity to yeast cells and was used as bait to screen the Y2H library prepared from the pancreas tissue. RESULTS: Five cellular proteins (EEP, Ral GDS, Bcl-2-L-12, CPS1, and one not identified) were found to interact with P1 Cap. The interaction between Cap and Ral GDS was confirmed by co-immunoprecipitation. CONCLUSIONS: Our data are likely to support the future investigation of the underlying mechanism of P1 infection and pathogenesis.

Characterization of porcine circovirus-like virus P1 replication and lesions in BALB/c mice.

Five-week-old male BALB/c mice were inoculated intraperitoneally with a single (sP1) or multiple doses (mP1) of porcine circovirus-like virus P1 or cell culture medium. None of the mice exhibited clinical signs or gross lesions throughout the study. However, the body weights of the mP1 mice were significantly decreased, and the mice inoculated with P1 exhibited viral replication, seroconversion, and microscopic lesions. P1 nucleic acid was detected in the heart, liver, spleen, lung, bladder, testis, brain, thymus, and pancreatic tissues. Special P1 antibody was found in the P1-inoculated mice. Microscopic lesions in the sP1 and mP1 mice were characterized by interstitial pneumonia, including edema in the connective tissue around the pulmonary vessels, mild inflammatory cell infiltrate, thickened alveolar walls, myocardial necrosis, and dissolution of Purkinje cell nuclei. The results showed that the P1 virus could infect BALB/c mice. Thus, BALB/c mice may serve as models for P1 research.

Genomic Rearrangement and Recombination of Porcine Circovirus Type 2 and Porcine Circovirus-Like Virus P1 in China.

Porcine circovirus type 2 (PCV2) belongs to the genus Circovirus of the family Circoviridae, and it has been associated with porcine circovirus (associated) disease (PCVD or PCVAD) in pigs. PCVAD is the generic term for a series of disease syndromes that have caused economic losses to the pig industry worldwide. Since the discovery of PCV2 in the late 1990s, the virus has continued to evolve, and novel genotypes have continued to appear. Moreover, there has been recombination between different genotypes of PCV2. This review attempts to illustrate some progress concerning PCV2 in genome rearrangement and genomic recombination with non-PCV2-related nucleic acids, particularly focusing on the porcine circovirus-like virus P1 formed by the recombination of PCV2. The presence of rearranged PCV2 genomes can be demonstrated both in vivo and in vitro, and these subviral molecules ranged from 358 to 1,136 bp. Depending on whether it has the ability to encode a protein, the agents formed by PCV2 recombination can be divided into two categories: porcine circovirus-like viruses and porcine circovirus-like mini agents. We mainly discuss the porcine circovirus-like virus P1 regarding genomic characterization, etiology, epidemiology, and pathogenesis. Further research needs to be conducted on the pathogenicity of other porcine circovirus-like viruses and porcine circovirus-like mini agents and the effects of their interactions with PCV2, especially for the porcine circovirus-like mini agents that do not have protein-coding functions in the genome.

Complete genome sequences of porcine circovirus-like virus P1 mutants with 163 amino acids in the capsid protein.

Porcine circovirus-like virus P1 is a novel circovirus that was originally detected in China in 2005. Here, we report the genome sequences of P1 isolates JS02, JS03, and HuN06, each with 163 amino acids in its capsid protein. The complete genome of each of these isolates contains 649 nucleotides and has a T insertion at position 207. Phylogenetic analysis based on complete genome sequences of 18 P1 reference strains grouped 16 P1 sequences from this study into one cluster, with the JS02, JS03, and HuN06 isolates forming an independent clade. However, phylogenetic analysis based on amino acid sequences of the capsid protein showed that the JS02, JS03, and HuN06 strains were on the same large branch with PCV2, distinct from other P1 isolates. These results help us to understand the origin and evolution of P1.

First molecular identification of porcine circovirus-like agents in dogs and cats in China.

Porcine circovirus-like agents comprise two types of viruses: porcine circovirus-like viruses (P1, P2, P3, and P4) and porcine circovirus-like mini agents (PCVL258, PCVL264, PCVL201, and PCVL347). Of these, P1 has been identified in pigs, cattle, goats, and rabbits in China; P2, P3, P4, PCVL258, and PCVL264 have been identified in pigs; and PCVL201 and PCVL347 have been identified in cattle. The purpose of this study was to determine whether dogs and cats have been exposed to porcine circovirus-like agents. We screened 158 serum samples from diseased dogs and 41 from cats in China by PCR and nucleotide sequencing. In dogs, approximately 18% (n = 28) were positive for P1, 17% (n = 26) for PCVL258, and 9% (n = 14) for PCVL264; in cats, 17.1% (n = 7) were positive for P1, 9.8% (n = 4) for P4, and 14.6% (n = 6) for PCVL258. The P1 genomes in this study consisted of 648 nucleotides (nt) and shared 96.8 to 100% nt identity with other P1 genomes in GenBank. The P4 genome shared 98.3 to 100% nt identity with other reported P4 genomes, and PCVL258 and PCVL264 showed 100% nt identity with previously reported genomes. To our knowledge, this is the first report on molecular characterization of porcine circovirus-like agents in dogs and cats. Further studies are needed to clarify the epidemiology, evolution, and pathogenesis of porcine circovirus-like agents in dogs and cats.

Basigin-CyP elevated porcine circovirus type2 replication.

Porcine circovirus type2 (PCV2) is a member of the circoviridae family. PCV2 was identified as the main pathogen of postweaning multisystemic wasting syndrome (PMWS) in weaned piglets and causes massive economic loss. Basigin, is a transmembrane glycoprotein belonging to the immunoglobulin superfamily; which is also a receptor for cyclophilins. CyP belongs to the immunophilin family that has peptidyl-prolyl cis-trans isomerase activity. Basigin-CyP interaction affects the replication stages of several viruses. In this study, we found that Basigin could elevate the replication of PCV2, and the Basigin only affected the replication stage rather than adsorption or endocytosis stages. In addition, the ligands of Basigin, CyPA and CyPB also elevated the replication of PCV2. Basigin-CyP interation was necessary for elevating PCV2 replication; At last, CyPs were proved to promote the replication of PCV2 by activating ERK signaling.

PCV2 inhibits the Wnt signalling pathway in vivo and in vitro.

Porcine circovirus type 2 (PCV2) is an important pathogen of the current pig industry. The Wnt signalling pathway plays an important role in the growth of young animals. In this study, we mainly elucidated the relationship between PCV2 and the Wnt signalling pathway. In an in vivo experiment in mice, we demonstrated the downregulatory effects of PCV2 infection on expression levels of downstream components of the Wnt signalling pathway. Weight loss in mice was reversed by activating the Wnt signalling pathway, and the body weight was still significantly higher than that in mice infected with PCV2. We detected levels of growth hormone (GH) in the liver and sera, which showed that GH was also downregulated in mice challenged with PCV2. Lithium chloride, the activator of Wnt signalling, upregulated GH, albeit to a significantly lesser degree than that in corresponding non-stimulated mock mice. In vitro studies showed that PCV2 infection downregulated protein expression of ß-catenin and mRNA expression of matrix metallopeptidase-2 (Mmp2), downregulated protein expression of ß-catenin in the cytoplasm and nucleus, and reduced the activity of the TCF/LEF promoter, demonstrating that PCV2 inhibited activation of the Wnt signalling pathway in vitro. Finally, we found that Rep protein of PCV2 might be responsible for the inhibitory effect.

Complete genome sequences of porcine-circovirus-like mini agents in pigs and cattle.

Porcine circovirus (PCV) genomes are single-stranded circular DNAs of about 1770 nucleotides (nt). Here, we present for the first time two small PCV-like agents with circular DNA genomes (258 and 264 nt) in pigs and two (201 and 347 nt) in cattle, with no obvious protein-coding capacity. Sequences of the four PCV-like mini agents differed by 1.5%-18.7% from each other and by 4.5%-56.7% from other reference PCV strains and PCV-like viruses.

Porcine Circovirus-Like Virus P1 Inhibits Wnt Signaling Pathway in Vivo and in Vitro.

Porcine circovirus-like virus P1 is an important pathogen of the current pig industry, the infection mechanism is not entirely clear. Wnt signaling pathway plays an important role in the growth of young animals and infection of some viruses. This study was designed to demonstrate the effects of P1 infection on the Wnt signaling pathway. In vivo experiments, we demonstrated the down-regulatory effects of P1 infection in piglets and mice on the downstream components expression levels of Wnt signaling pathway, and the effects of Wnt signaling pathway activation on the pathogenesis of P1. In vitro studies, we found P1 infection down-regulated protein level of ß-catenin and mRNA level of mmp2, prevented the ß-catenin from entering into nucleus, abolished the TCF/LEF promoter activity, proved that P1 could inhibit the activation of Wnt signaling pathway in vitro. Finally, we found that VP1 of P1 virus also had the inhibitory effects on Wnt signaling pathway in vitro, elucidated the mechanism of P1's inhibitory effects on the Wnt signaling pathway and offered the possibility that the suppression of Wnt signaling pathway was involved in the post-weaning multisystemic wasting syndrome (PMWS), laying a foundation for elucidating the pathogenesis of P1.

Protective efficacy of a DNA vaccine encoding capsid protein of porcine circovirus-like virus P1 against porcine circovirus 2 in mice.

The capsid protein is the major immunogenic protein of porcine circovirus 2 (PCV2). The nucleotide sequence of porcine circovirus-like virus P1 shares high homology with open reading frame (ORF) 2 of PCV2, and ORF1 of P1 encodes its structural protein. Mice were vaccinated twice intramuscularly with a plasmid expressing the P1 ORF1 protein (pcDNA3.1(+)-ORF1) at 2-week intervals. All animals vaccinated with pcDNA3.1(+)-ORF1 developed higher specific anti-P1 antibody levels, and had less PCV2 viremia and milder histopathological changes than PCV2-challenged mice in the control group. Our results show that the P1 DNA vaccine elicited immune responses against PCV2 infection in a mouse model.

MicroRNA-30a-5p promotes replication of porcine circovirus type 2 through enhancing autophagy by targeting 14-3-3.

Accumulating evidence demonstrates that autophagy and microRNAs (miRNAs) play key roles in regulating virus-host interactions and can restrict or facilitate viral replication. In the present study we examined whether a functional relationship exists between autophagy, miRNA and porcine circovirus type 2 (PCV2) infection, using several approaches. We demonstrated that there was a positive correlation between PCV2 infection and autophagy in 3D4/21 cells and autophagy induced by PCV2 infection triggered PCV2 replication. Four miRNA were selected by real-time PCR and further studied, but only miR-30a-5p mimic had a significant effect on PCV2 replication. Overexpression of miR-30a-5p significantly enhanced PCV2 infection and autophagy in a dose-dependent manner. Blockage of miR-30a-5p significantly decreased PCV2 replication. We provided further evidence that miR-30a-5p regulate the link between PCV2 infection and host immune system. Furthermore, miR-30a-5p targeted and regulated 14-3-3 gene, which is a regulator of autophagy. Flow cytometry data demonstrated that miR-30a-5p promotes cell cycle arrest at the G2 phase to regulate PCV2 replication and autophagy by interacting directly with 14-3-3, but not with the PCV2 genome. These data not only provide new insights into virus-host interactions during PCV2 infection but also suggest a potential new antiviral therapeutic strategy against PCV2 infection.

Nitric oxide-generating compound GSNO suppresses porcine circovirus type 2 infection in vitro and in vivo.

BACKGROUND: Nitric oxide (NO), an important signaling molecule with biological functions, has antimicrobial activity against a variety of pathogens including viruses. To our knowledge, little information is available about the regulatory effect of NO on porcine circovirus type 2 (PCV2) infection. This study was conducted to investigate the antiviral activity of NO generated from S-nitrosoglutathione (GSNO), during PCV2 infection of PK-15 cells and BALB/c mice. RESULTS: GSNO released considerable NO in the culture medium of PK-15 cells, and NO was scavenged by its scavenger hemoglobin (Hb) in a dose-dependent manner. NO strongly inhibited PCV2 replication in PK-15 cells, and the antiviral effect was reversed by Hb. An in vivo assay indicated that GSNO treatment reduced the progression of PCV2 infection in mice, evident as reductions in the percentages of PCV2-positive sera and tissue samples and in the viral DNA copies in serum samples. GSNO also improved the growth performance and immune organs (spleens and thymuses) of the PCV2-infected mice to some degree. CONCLUSIONS: Our data demonstrate that the NO-generating compound GSNO suppresses PCV2 infection in PK-15 cells and BALB/c mice, indicating that NO and its donor, GSNO, have potential value as antiviral drugs against PCV2 infection.

Genome sequence of a porcine circovirus-like virus P1 mutant in China.

A new porcine circovirus-like virus P1 mutant was isolated and sequenced in China in 2015. This P1 mutant has a mutation in its ORF1-encoded capsid protein that results in its elongation by eight amino acids.

Molecular characterization of porcine circovirus-like virus P1 in eastern China.

A large-scale epidemiological study of porcine circovirus-like virus P1 was carried out from 2007 to 2015 in China, which revealed a high level of P1 infection. Thirty-nine sequences obtained from pigs in eastern China showed remarkable genetic diversity, with the P1 predominant sequences and the mutant P1 with ORF1 or ORF2 containing an additional amino-acid extension at the C-terminus. This information may be useful for understanding the evolution of P1 circovirus-like virus.

Syndecan-4, a PRRSV attachment factor, mediates PRRSV entry through its interaction with EGFR.

The causative agent of porcine reproductive and respiratory syndrome is the PRRS virus (PRRSV), an enveloped, single-stranded and positive-sense RNA virus. The host factors and mechanisms that are involved in PRRSV entry are still largely unknown. In our present studies, we found that syndecan-4, one of the heparan sulfate proteoglycans, plays a critical role in PRRSV entry, especially in PRRSV attachment. Moreover, EGFR interacts with syndecan-4 in MACR-145 cells and disruption of their interaction impaired PRRSV entry. Furthermore, EGFR inhibitor AG1478 or syndecan-4 derived peptide SSTN87-131 inhibited syndecan-4 endocytosis induced by PRRSV entry. Altogether, syndecan-4, a PRRSV attachment factor, mediated PRRSV entry by interacting with EGFR.

Development and application of an indirect enzyme-linked immunosorbent assay using recombinant truncated Cap protein for the diagnosis of porcine circovirus-like virus P1.

BACKGROUND: Porcine circovirus-like virus P1 is a newly discovered virus. To date, there has been no specific serological assay for use in the diagnosis of P1 infection. RESULTS: Because P1 has high homology to porcine circovirus type 2 (PCV2) at the nucleotide level, the C-terminal portion of the capsid protein (amino acids 73-114), a discriminative antigen, was expressed in a prokaryotic expression system. The recombinant product (rctCap), composed of three identical repeated domains, was shown to be strongly immunoreactive to P1-specific serum. This assay was validated by comparison with an indirect immunofluorescence assay (IFA). The diagnostic sensitivity and specificity of the rctCap enzyme-linked immunosorbent assay (ELISA) developed in this study are 93.6% and 98.3%, respectively, compared with the results from IFAs on 450 sera samples from pigs. CONCLUSIONS: The indirect ELISA that we developed with rctCap, the recombinant capsid fragment containing the 217-342 nt repeat domain, was sensitive, specific, and suitable for the large-scale detection of P1 infections in swine.