Hydropericardium syndrome in Japanese quail (Coturnix coturnix japonica)

An efficient double-fluorescence approach for generating fiber-2-edited recombinant serotype 4 fowl adenovirus expressing foreign gene

Recently, the infection of serotype 4 fowl adenovirus (FAdV-4) in chicken flocks has become endemic in China, which greatly threatens the sustainable development of poultry industry. The development of recombinant FAdV-4 expressing foreign genes is an efficient strategy for controlling both FAdV-4 and other important poultry pathogens. Previous reverse genetic technique for generating the recombinant fowl adenovirus is generally inefficient. In this study, a recombinant FAdV-4 expressing enhanced green fluorescence protein (EGFP), FA4-EGFP, was used as a template virus and directly edited fiber-2 gene to develop an efficient double-fluorescence approach to generate recombinant FAdV-4 through CRISPR/Cas9 and Cre-Loxp system. Moreover, using this strategy, a recombinant virus FAdV4-HA(H9) stably expressing the HA gene of H9N2 influenza virus was generated. Chicken infection study revealed that the recombinant virus FAdV4-HA(H9) was attenuated, and could induce haemagglutination inhibition (HI) titer against H9N2 influenza virus at early time points and inhibit the viral replication in oropharynx. All these demonstrate that the novel strategy for constructing recombinant FAdV-4 expressing foreign genes developed here paves the way for rapidly developing attenuated FAdV-4-based recombinant vaccines for fighting the diseases caused by both FAdV-4 and other pathogens.

Hsp70 Inhibits the Replication of Fowl Adenovirus Serotype 4 by Suppressing Viral Hexon with the Assistance of DnaJC7

Fowl adenovirus serotype 4 (FAdV-4) infection results in serious hepatitis-hydropericardium syndrome (HHS) in broilers, which has caused great economic losses to the poultry industry; however, the specific host responses to FAdV-4 remain unknown. In this study, we identified 141 high-confidence protein-protein interactions (PPIs) between the main viral proteins (Hexon, Fiber 1, Fiber 2, and Penton bases) and host proteins via a liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay. We found that heat shock protein 70 (Hsp70), the protein with the highest score, and its cofactor DnaJ heat shock protein 40 family member C7 (DnaJC7) could negatively regulate the replication of FAdV-4. Furthermore, the nucleotide binding domain (NBD) of Hsp70 and the J domain of DnaJC7 were necessary for inhibiting FAdV-4 replication. We verified that DnaJC7 as a bridge could bind to Hsp70 and Hexon, assisting the indirect interaction between Hsp70 and Hexon. In addition, we found that FAdV-4 infection strongly induced the expression of autophagy proteins and cellular Hsp70 in a dose-dependent manner. Blockage of Hexon by Hsp70 overexpression was significantly reduced when the autophagy pathway was blocked by the specific inhibitor chloroquine (CQ). Our results showed that Hsp70 was co-opted by DnaJC7 to interact with viral Hexon and inhibited Hexon through the autophagy pathway, leading to a considerable restriction of FAdV-4 replication. IMPORTANCE FAdV-4, as the main cause of HHS, has quickly spread all over the world in recent years, seriously threatening the poultry industry. The aim of this study was to identify the important host proteins that have the potential to regulate the life cycle of FAdV-4. We found that Hsp70 and DnaJC7 played crucial roles in regulating the amount of viral Hexon and extracellular viral titers. Moreover, we demonstrated that Hsp70 interacted with viral Hexon with the assistance of DnaJC7, followed by suppressing Hexon protein through the autophagy pathway. These results provide new insight into the role of the molecular chaperone complex Hsp70-DnaJC7 in FAdV-4 infection and suggest a novel strategy for anti-FAdV-4 drug development by targeting the specific interactions among Hsp70, DnaJC7 and Hexon.

Isolation, identification and genetic characterization analysis of a fowl aviadenovirus serotype 4 strain from Tianjin, China

A fowl aviadenovirus serotype 4 (FAdV-4), Y17215-1, was isolated from the liver of chickens with Hydropericardium-hepatitissyndrome(HHS) in a chicken farm of Tianjin, China. Obvious cytopathic effects were observed in the infected chicken liver hepatocellular carcinoma cell line (LMH cells) at 24 h post infection (hpi), which consisted of enlarger and rounder shape of cells. The typical and specific green fluorescence was observed by indirect immunofluorescence assay (IFA). Tissue Culture Infectious Dose50 (TCID₅₀) of it measured after five stable passage in LMH cells reached 10^6.5TCID₅₀/0.1 mL. The strain was inoculated through allantoic membrane of 10-day specific pathogen free(SPF) Chick embryos, the thicker allantoic membranes were observed at 120 hpi. 7-day-old SPF chickens were inoculated with the strain via intramuscular (i.m.) or intranasal (i.n.) injection which resulted in 100% mortality of test chickens. Additionally, the sickness and death of cohabitation chickens in the test group were observed which indicated that the virus can infect healthy chickens by horizontal transmission. The sick chickens showed depression, anorexia and diarrhea with green watery feces. Y17215-1-inoculated chickens mainly presented swollen liver with blood spot, and the enhancement of effusion or yellow gel like effusion that were observed in the pericardium through necropsy. Histopathological examination showed focal necrosis of hepatocytes and characteristic eosinophilic inclusion bodies in the cytoplasm. The results showed that the Y17215-1 isolate had high pathogenicity to SPF chickens. The phylogenetic analysis of the major structural proteins including hexon, fiber-1 and fiber-2 revealed that Y17215-1 strain belongs to C species of fowl aviadenovirus of aviadenovirus family, and has high homology with other Chinese strains isolated in recent years, but was distinct from ON1、MX-SHP95、KR5 and other foreign isolates. This study laid a foundation for further study of epidemiological investigation, pathogenic mechanism as well as the diagnosis and control technology of FAdV-4.

Transcriptome Analysis Reveals the Potential Role of Long Noncoding RNAs in Regulating Fowl Adenovirus Serotype 4-Induced Apoptosis in Leghorn Male Hepatocellular Cells

Hepatitis-hydropericardium syndrome (HHS) is caused by fowl adenovirus serotype 4 (FAdV-4) and has resulted in considerable economic losses to the poultry industry globally. FAdV-4 elicits apoptosis in host cells. Long noncoding RNAs (lncRNAs) have emerged as important regulatory RNAs with profound effects on various biological processes, including apoptosis. However, it remains unknown whether lncRNAs participate in FAdV-4-induced apoptosis. In this study, RNA sequencing was applied to determine the transcription of cellular lncRNA in leghorn male hepatocellular (LMH) cells infected with FAdV-4. Cellular RNA transcription analysis demonstrated that FAdV-4 infection elicited 1798 significantly differentially expressed (DE) lncRNAs in infected LMH cells at 24 h post-infection (hpi) compared to mock control infection. In addition, 2873 DE mRNAs were also found. Target prediction and analyses revealed that 775 DE lncRNAs whose 671 target mRNAs were among the DE mRNAs were involved in several signaling pathways, including the AMPK signaling pathway, p53 signaling pathway and insulin signaling pathway. From these 775 DE lncRNAs, we identified 71 DE lncRNAs related to apoptosis based on their target gene functions. Subsequently, lncRNA 54128 was selected from the 71 identified DE lncRNAs, and its role in FAdV-4-induced apoptosis was verified. LncRNA 54128 interference significantly suppressed the rate of apoptosis, which was accompanied by reduced BMP4 transcription levels. To the best of our knowledge, this is the first study to analyze host lncRNA transcription during FAdV-4 infection. Our findings provide a better understanding of host responses to FAdV-4 infection and provide new directions for understanding the potential association between lncRNAs and FAdV-4 pathogenesis.

Fowl Adenovirus Serotype 4 Induces Hepatic Steatosis via Activation of Liver X Receptor-α

Fowl adenovirus serotype 4 (FAdV-4) is a hepatotropic virus that causes severe hepatic damage characterized by basophilic intranuclear inclusion bodies, vacuolar degeneration, and multifocal necrosis in hepatocytes. Many aspects of FAdV-4 infection and pathogenesis, however, remain unknown. Here, we found that FAdV-4-induced hepatic injury is accompanied by the accumulation of oil droplets (triglycerides) in the cytoplasm of hepatocytes, a typical indicator of steatosis, in FAdV-4-infected chickens. Significant upregulation of adipose synthesis-related genes, such as liver X receptor-α (LXR-α), peroxisome proliferator-activated receptor gamma (PPAR-γ), and sterol regulatory element-binding protein-1c (SREBP-1c), and significant downregulation of low-density lipoprotein secretion-related genes and lipid oxidation- and lipid decomposition-related genes were observed in the infected chickens. FAdV-4 infection in cultured leghorn male hepatoma (LMH) cells caused similar signs of steatosis, with alterations in various lipogenesis-related genes. We eliminated the effect of LXR-α activation on FAdV-4-induced steatosis and found that treatment with an LXR-α antagonist (SR9243) and RNA interference (small interfering RNA targeting LXR-α [Si-LXR-α]) decreased the number of oil droplets and the accumulation of lipogenic genes, but treatment with an LXR-α agonist (T0901317) increased the number of oil droplets and the accumulation of lipogenic genes in the cells. Additionally, SR9243 treatment or Si-LXR-α transfection led to significant reductions in viral DNA level, protein expression, and virus production, whereas T0901317 treatment caused significant increases in viral DNA level, protein expression, and virus production. However, inhibition of SREBP-1c activity had no significant effect on virus production. Collectively, these results indicated that FAdV-4-induced steatosis involves activation of the LXR-α signaling pathway, which might be a molecular mechanism underlying the hepatic injury associated with FAdV-4 infection.IMPORTANCE Fowl adenovirus serotype 4 (FAdV-4) is an important hepatotropic adenovirus in chicken, but the underlying mechanism of FAdV-4-induced hepatic injury remains unclear. We report here that infection with FAdV-4 induced the accumulation of oil droplets (triglycerides) in the cytoplasm of hepatocytes, a typical indicator of steatosis, in the livers of chickens. FAdV-4-induced steatosis might be caused by a disrupted balance of fat metabolism, as evidenced by differential regulation of various lipase genes. The significant upregulation of liver X receptor-α (LXR-α) prompted us to investigate the interplay between LXR-α activation and FAdV-4-induced steatosis. Treatment with an agonist, an antagonist, or RNA interference targeting LXR-α in cultured leghorn male hepatoma (LMH) cells indicated that FAdV-4-induced steatosis was dependent upon LXR-α activation, which contributed to virus replication. These results provide important mechanistic insights, revealing that FAdV-4 induces hepatic steatosis by activating the LXR-α signaling pathway and highlighting the therapeutic potential of strategies targeting the LXR-α pathway for the treatment of FAdV-4 infection.

Pathogenesis of Hypervirulent Fowl Adenovirus Serotype 4: The Contributions of Viral and Host Factors

Since 2015, severe outbreaks of hepatitis-hydropericardium syndrome (HHS), caused by hypervirulent fowl adenovirus serotype 4 (FAdV-4), have emerged in several provinces in China, posing a great threat to poultry industry. So far, factors contributing to the pathogenesis of hypervirulent FAdV-4 have not been fully uncovered. Elucidation of the pathogenesis of FAdV-4 will facilitate the development of effective FAdV-4 vaccine candidates for the control of HHS and vaccine vector. The interaction between pathogen and host defense system determines the pathogenicity of the pathogen. Therefore, the present review highlights the knowledge of both viral and host factors contributing to the pathogenesis of hypervirulent FAdV-4 strains to facilitate the related further studies.

Fowl adenovirus serotype 4-induced apoptosis, autophagy, and a severe inflammatory response in liver

Fowl adenovirus serotype 4 (FAdV-4) is a hepatotrophic virus that causes severe liver diseases. Upon histological examination, the most remarkable findings in the liver are small multifocal areas of necrosis and mononuclear cell infiltration, including basophilic intranuclear inclusion bodies in hepatocytes surrounded by a clear halo or which fill the entire nucleus. Here, we examined the mechanism responsible for FAdV-4-mediated hepatocyte damage in vivo and in vitro. The results showed that FAdV-4 impaired liver integrity and function, which decreased albumin and blood glucose concentrations and increased the plasma activity of aspartate aminotransferase and lactate dehydrogenase, compared with a non-infected control group (P<0.05). FAdV-4 induced hepatocyte apoptosis in a time-dependent manner in vivo and in vitro. Additionally, we found that FAdV-4 also induced the autophagy of hepatocytes, which promoted the conversion of microtubule-associated protein light chain 3 (LC3-I) to LC3-II, which is a hallmarks of autophagy. Furthermore, the mRNA expressions of interleukin (IL)-1β, IL-6, IL-8, and tumor necrosis factor (TNF)-α in vivo and in vitro showed a statistically significant increase (P<0.05) compared to that of the control group. However, the molecular mechanisms underlying the FAdV-4-induced apoptotic and autophagic cell death remain unclear. In summation, our observations suggested that FAdV-4 induced liver injury via apoptosis, autophagy, and a severe inflammatory response.