A Mouse Model of SARS-CoV-2 Infection and Pathogenesis.

Since December 2019, a novel coronavirus SARS-CoV-2 has emerged and rapidly spread throughout the world, resulting in a global public health emergency. The lack of vaccine and antivirals has brought an urgent need for an animal model. Human angiotensin-converting enzyme II (ACE2) has been identified as a functional receptor for SARS-CoV-2. In this study, we generated a mouse model expressing human ACE2 (hACE2) by using CRISPR/Cas9 knockin technology. In comparison with wild-type C57BL/6 mice, both young and aged hACE2 mice sustained high viral loads in lung, trachea, and brain upon intranasal infection. Although fatalities were not observed, interstitial pneumonia and elevated cytokines were seen in SARS-CoV-2 infected-aged hACE2 mice. Interestingly, intragastric inoculation of SARS-CoV-2 was seen to cause productive infection and lead to pulmonary pathological changes in hACE2 mice. Overall, this animal model described here provides a useful tool for studying SARS-CoV-2 transmission and pathogenesis and evaluating COVID-19 vaccines and therapeutics.

Upregulation of microRNA-146a by hepatitis B virus X protein contributes to hepatitis development by downregulating complement factor H.

UNLABELLED: Hepatic injuries in hepatitis B virus (HBV) patients are caused by immune responses of the host. In our previous study, microRNA-146a (miR-146a), an innate immunity-related miRNA, and complement factor H (CFH), an important negative regulator of the alternative pathway of complement activation, were differentially expressed in HBV-expressing and HBV-free hepatocytes. Here, the roles of these factors in HBV-related liver inflammation were analyzed in detail. The expression levels of miR-146a and CFH in HBV-expressing hepatocytes were assessed via analyses of hepatocyte cell lines, transgenic mice, adenovirus-infected mice, and HBV-positive human liver samples. The expression level of miR-146a was upregulated in HBV-expressing Huh-7 hepatocytes, HBV-expressing mice, and patients with HBV infection. Further results demonstrated that the HBV X protein (HBx) was responsible for its effects on miR-146a expression through NF-κB-mediated enhancement of miR-146a promoter activity. HBV/HBx also downregulated the expression of CFH mRNA in hepatocyte cell lines and the livers of humans and transgenic mice. Furthermore, overexpression and inhibition of miR-146a in Huh-7 cells downregulated and upregulated CFH mRNA levels, respectively. Luciferase reporter assays demonstrated that miR-146a downregulated CFH mRNA expression in hepatocytes via 3'-untranslated-region (UTR) pairing. The overall effect of this process in vivo is to promote liver inflammation. These results demonstrate that the HBx-miR-146a-CFH-complement activation regulation pathway might play an important role in the immunopathogenesis of chronic HBV infection. These findings have important implications for understanding the immunopathogenesis of chronic hepatitis B and developing effective therapeutic interventions. IMPORTANCE: Hepatitis B virus (HBV) remains an important pathogen and can cause severe liver diseases, including hepatitis, liver cirrhosis, and hepatocellular carcinoma. Although HBV was found in 1966, the molecular mechanisms of pathogenesis are still poorly understood. In the present study, we found that the HBV X protein (HBx) promoted the expression of miR-146a, an innate immunity-related miRNA, through the NF-κB signal pathway and that increasingly expressed miR-146a downregulated its target complement factor H (CFH), an important negative regulator of the complement alternative pathway, leading to the promotion of liver inflammation. We demonstrated that the HBx-miR-146a-CFH-complement activation regulation pathway is potentially an important mechanism of immunopathogenesis caused by chronic HBV infection. Our data provide a novel molecular mechanism of HBV pathogenesis and thus help to understand the correlations between the complement system, an important part of innate immunity, and HBV-associated disease. These findings will also be important to identify potential therapeutic targets for HBV infection.

[Study on the differences of two mouse models of hepatitis B virus infection by transduction with rAAV8-1. 3HBV].

We recently developed a mouse model of hepatitis B virus (HBV) chronic infection by intravenous (i.v.) injection with rAAV8-1. 3HBV to C57BL/6 mice. To define the responses of different mouse strains after injection with rAAV8-1. 3HBV, we intravenously injected rAAV8-1. 3HBV at doses of 4 x10(9) (Viral genome,vg), 4 x 10(10) vg and 4 x 10(11) vg to C57BL/6 and BALB/c mice,respectively, and determined the levels of serum HBV antigen and antibody by ELISA,serum viral DNA by real-time PCR,and HBcAg expression in liver by immunohistochemical staining. For C57BL/6 mouse strain with injection of rAAV8-1. 3HBV at three doses, 100% of the mice carried HBV for more than 8 months. The levels of serum HBsAg and HBeAg, serum viral DNA and HBcAg-positive hepatocytes increased in a rAAV8-1. 3HBV dose-dependent manner. For C57BL/6 mice injected with rAAV8-1. 3HBV at the dose of 4 x 10(11) vg,over 40% of hepatocytes expressed HBcAg and serum viral DNA reached over 10(5) IU/mL. No HBV antibody was detected in sera of C57BL/6 mice. For BALB/c mice with injection of rAAV8-1. 3HBV at three doses, serum HBeAg, serum viral DNA and HBcAg-positive hepatocytes persisted for more than 8 months, but serum HBsAg declined remarkably at 2 weeks after injection. The levels of serum HBeAg and HBcAg-positive hepatocytes in BALB/c mice increased in a rAAV8-1. 3HBV dose-dependent manner. Injection with rAAV8-1. 3HBV at the dose of 4 x 10(11) vg resulted in over 50% of BALB/c mice hepatocytes expressing HBcAg. Serum anti-HBsAg were detected in BALB/c mice with rAAV8-1. 3HBV injection at the dose of 4 x10 (10) vg. In conclusion, both C57BL/6 and BALB/c strains can be developed to chronic HBV infection mouse models by i. v. injection with rAAV8-1. 3HBV at doses of 4 x10(9) - 4 x 10(11) vg and the levels of HBV replication increase in a rAAV8-1. 3HBV dose-dependent manner. In contrast to C57BL/6 strain, the BALB/c mice carry out humoral immunity to HBsAg, but fail to mediate HBV clearance.

Over-expression of uPA increases risk of liver injury in pAAV-HBV transfected mice.

AIM: To investigate the relationship between over-expression of urokinase plasminogen activator (uPA) and hepatitis B virus (HBV) related liver diseases in a transgenic mouse model. METHODS: Albumin-tetracycline reverse transcriptional activator and tetO-uPA transgenic mice were generated respectively through pronuclear injection and crossed to produce the double transgenic in-alb-uPA mice, for which doxycycline (Dox)-inducible and liver-specific over-expression of uPA can be achieved. Hydrodynamic transfection of plasmid adeno-associated virus (AAV)-1.3 HBV was performed through the tail veins of the Dox-induced in-alb-uPA mice. Expression of uPA and HBV antigens were analyzed through double-staining immunohistochemical assay. Cytokine production was detected by enzyme linked immunosorbent assay and α-fetoprotein (AFP) mRNA level was evaluated through real-time quantitative polymerase chain reaction. RESULTS: Plasmid AAV-1.3 HBV hydrodynamic transfection in Dox-induced transgenic mice not only resulted in severe liver injury with hepatocarcinoma-like histological changes and hepatic AFP production, but also showed an increased serum level of HBV antigens and cytokines like interleukin-6 and tumor necrosis factor-α, compared with the control group. CONCLUSION: Over-expression of uPA plays a synergistic role in the development of liver injury, inflammation and regeneration during acute HBV infection.

[Construction of HCV-producing cell model based on self-cleaving ribozyme].

OBJECTIVES: To construct a stable HCV-producing cell model for anti-HCV drug research. METHODS: The HCV-ribozyme recombinant plasmid pJFH1-Rbz was constructed to generate the exact 5' and 3' ends of HCV genomic RNA by placing two self-cleaving ribozymes at both ends of the HCV JFH-1 cDNA. The plasmid was then transfected into HepG2 cells and the resultant clones were screened with G418. Subsequently, immunofluorescence and Western blot were performed to detect the expression of HCV core protein, HCV RNA level was quantitated by TaqMan real-time PCR method and HCV particles was detected by electron microscopy. RESULTS: HCV core protein was detected in the screened cell clone, and the level of HCV RNA was up to 1000,0000 copies/ml in the culture medium. Electron microscopy showed the viral particles in the culture suspension were approximately 55 nm in diameter. IFN-treating experiment demonstrated that the HCV RNA level decreased with the increasing concentration of IFN alpha. CONCLUSION: We constructed a stable HCV-producing cell model which can be used for anti-HCV drug research.

[Immunosuppressant dexamethasone can significantly extend the expression of hepatitis B virus antigens in the HBV mouse model by hydrodynamic transfection method].

To develop a HBV infection mouse model by hydrodynamic-based transfection and further to optimize the method of development of HBV infection mouse model. We first developed a construct which contained inverted terminal repeat elements (ITR) of adeno-associated virus (AAV) and 1. 3 copies of HBV genome (ayw subtype). The pAAV-HBV1. 3 DNA was then injected hydrodynamically into the tail veins of C57BL/6 mice in 5 seconds. The virus load in serum and liver was assayed by ELISA and Real-time PCR. The expression of virus antigen and the pathologic changes of liver were analyzed by HE and immunohistochemical staining. Meanwhile, to develop HBV transfected immunosuppressied mouse, mice were injected intraperitoneally triple with 0.2 ml dexamethason (50 mg/kg) every two days before HBV transfection. The levels of HBsAg and HBeAg were assayed by ELISA. Our data showed: (1) HBsAg and HBeAg were positive (100%) in serum and liver of experimental normal mouse at day 10 after HBV transfection, and became negative at day 30 and day 60. Meanwhile the viral load in serum and liver in experimental group was significantly higher than that in control group at day 10, 30 and 60 after HBV transfection (P < 0.01, P < 0.05, respectively). (2) HBsAg and HBeAg in serum in immunosuppressed mouse model were positive until 60 days. In conclusion, a HBV infection mouse model was developed successfully by hydrodynamic-based transfection. By suppressing the immune status of mice injected with dexamethasone, the expression of HBV antigens was extended longer than that in normal adult mice. These models pave a way for HBV research and evaluation of HBV vaccine and drug development.

An easy-to-use site-directed mutagenesis method with a designed restriction site for convenient and reliable mutant screening.

Site-directed mutagenesis (SDM) has been a very important method to probe the function-structure relationship of proteins. In this study, we introduced an easy-to-use, polymerase chain reaction (PCR)-based SDM method for double-stranded plasmid DNA, with a designed restriction site to ensure simple and efficient mutant screening. The DNA sequence to be mutated was first translated into amino acid sequence and then the amino acid sequence was reversely translated into DNA sequence with degenerate codons, resulting in a large number of sequences with silent mutations, which contained various restriction endonuclease (RE) sites. Certain mutated sequence with an appropriate RE site was selected as the target DNA sequence for designing a pair of mutation primers to amplify the full-length plasmid via inverse PCR. The amplified product was 5'-phosphorylated, circularized, and transformed into an Escherichia coli host. The transformants were screened by digesting with the designed RE. This protocol uses only one pair of primers and only one PCR is conducted, without the need for hybridization with hazardous isotope for mutant screening or subcloning step.

[Expression and purification of TAT-HBX-EGFP fusion protein and its transmembrane distribution in mouse].

OBJECTIVE: To highly express TAT-HBX-EGFP fusion protein and study its distribution in mouse liver. METHODS: TAT-HBX-EGFP recombinant vector was constructed and fusion protein was induced by IPTG and expression in BL21; fusion protein was purified by Ni-NTA argarose, then injected into the peritoneal cavity of the mice. Distribution of fusion protein was observed by immunofluorescence. RESULTS: TAT-HBX-EGFP was highly expression in E. coli; HBX could be induced into mouse liver by TAT. CONCLUSION: HBX protein could be induced into mouse liver by TAT induced peptide.

[Expression of K18, Ser-33 and Ser-52 phosphorylated K18 in HBV infected human liver disease and its significance].

OBJECTIVE: To investigate the expression of K18, Ser-33 and Ser-52 phosphorylated K18 in HBV infected human liver disease and its significance. METHODS: The expression and localization of K18 and Ser-33, Ser-52 phosphorylated K18 in healthy liver tissue, in liver tissues of patients with post-HBV infection cirrhosis and severe chronic hepatitis were detected by histochemistry. RESULTS: K18, Ser-33 and Ser-52 phosphorylated K18 were expressed in normal liver cells, in liver tissues of cirrhosis patients and severe chronic hepatitis cases. The expression of K18 in the liver cells from the 3 different sources had no significant difference in levels. Ser-33 and Ser-52 phosphorylated K18 were expressed in normal liver cells, in liver tissues of cirrhosis patients chronicity HBV hepatitis and severe chronic hepatitis cases. Ser-33 and Ser-52 located around cytoplasmic membrane, diffused into cytoplasm and expressed at a higher levels in cirrhosis and severe chronic hepatitis. CONCLUSION: The expression levels of Ser-33 and Ser-52 phosphorylated K18 increased along with the progression of HBV infected human liver disease. The phosphorylation of K18 could be a marker of progression of HBV infected human liver disease.

[A follow up study of total IgM, IgG, nucleoprotein and spike protein antibodies against severe acute respiratory syndrome (SARS) coronavirus in patients with SARS].

OBJECTIVE: To survey the dynamic changing and persistence of the special antibodies, including total IgM, IgG, nucleocapsid protein and spike protein antibodies, against severe acute respiratory syndrome coronavirus (SARS-CoV) in patients with SARS. METHODS: 146 cases, all clinically diagnosed as SARS with positive SARS-CoV IgG, were followed up. 362 serum samples were collected from the onset of the disease to 660 days afterward. Total IgM and IgG against SARS-CoV were tested with commercial ELISA kits. For recombinant nucleoprotein and spike protein, we developed an ELISA to test these two antibodies. RESULTS: Within 20 days of the onset, the positive rate of anti-SARS-CoV IgM was 46.5% (20/43); it reached a peak after 21 - 40 days (80.6%, 25/31). Then, the positive rate of IgM went down gradually to 8.2% (6/73) until 550 days after the onset. The patient's IgG positive rate was lower (34.9%, 15/43) than that of IgM within 20 days of the onset. Then it went up rapidly to 100%. It remained positive (98.6%, 70/71) until 600 - 660 days after the onset. When N-IgG and S-IgG were tested 40 days after the onset of the disease at three different times, the positive rate of N-IgG (92.5%, 37/40) was higher than that of S-IgG (67.5%, 27/40), but the two structure protein antibodies were always lower than the total IgG. CONCLUSIONS: In SARS patients with definite clinical and etiological diagnosis, the highest positive rate of the antibodies against SARS-CoV was found at 21 - 40 days after the onset. IgM disappeared almost 500 days (91.8%) after the onset. Total IgG positive rate could reach 100% and 98.6% and the positivity might persist nearly two years. So it is speculated that the total IgG antibody may be positive 3 to 5 years after infection, but it seems that N-IgG and S-IgG keep positive shorter in time than total IgG antibody.

[Molecular cloning and expression of the severe acute respiratory syndrome-associated coronavirus nucleocapsid protein and its clinical application].

OBJECTIVE: To clone and express nucleocapsid (N) protein of the severe acute respiratory syndrome (SARS)-associated coronavirus, and to evaluate its antigenicity and application value in the development of serological diagnostic test for SARS. METHODS: SARS-associated coronavirus N protein gene was amplified from its genomic RNA by reverse transcript nested polymerase chain reaction (RT-nested-PCR) and cloned into pBAD/Thio-TOPO prokaryotic expression vector. The recombinant N fusion protein was expressed and purified, and its antigenicity and specificity was analyzed by Western Blot, to establish the recombinant N protein-based ELISA for detection of IgG antibodies to SARS-associated coronavirus, and SARS-associated coronavirus lysates-based ELISA was compared parallelly. RESULTS: The recombinant expression vector produced high level of the N fusion protein after induction, and that protein was purified successfully by affinity chromatography and displayed higher antigenicity and specificity as compared with whole virus lysates. CONCLUSION: The recombinant SARS-associated coronavirus N protein possessed better antigenicity and specificity and could be employed to establish a new, sensitive, and specific ELISA for SARS diagnosis.

A clinicopathological study of three cases of severe acute respiratory syndrome (SARS).

AIMS: The severe acute respiratory syndrome (SARS) caused a large outbreak of atypical pneumonia in Beijing, China from early March 2003. We report the pathological features from three patients who died of SARS. METHODS: Autopsies were performed on three patients who died 9-15 days after the onset of the illness, and the clinical and laboratory features reviewed. Tissue sections were stained with haematoxylin and eosin (H&E), and in situ reverse transcriptase polymerase chain reaction (RT-PCR) on lung sections was performed using SARS coronavirus-specific primers. RESULTS: The typical gross pathological change in the lungs was diffuse haemorrhage on the lung surface. Histopathological examination revealed serous, fibrinous and haemorrhagic inflammation in most pulmonary alveoli, with capillary engorgement and some capillary microthrombosis. The pulmonary alveoli were thickened with interstitial mononuclear inflammatory infiltrates, diffuse alveolar damage, desquamation of pneumocytes and hyaline-membrane formation; fibrinoid material and erythrocytes were present in alveolar spaces. There were thromboemboli in some bronchial arterioles. Haemorrhagic necrosis and reduced numbers of lymphocytes were observed in lymph nodes and spleen. In situ RT-PCR detected SARS coronavirus RNA in type II alveolar cells, interstitial cells and bronchiolar epithelial cells from all three patients. CONCLUSIONS: Severe immunological damage in lung tissue is responsible for the clinical features of SARS.

[A clinicopathological study on 3 cases of severe acute respiratory syndrome].

OBJECTIVE: To study the pathological characteristics of severe acute respiratory syndrome (SARS) and its relationship to clinical manifestation. METHODS: Tissue specimens from 3 autopsy cases of diagnosed SARS were studied under microscopy and the clinical data were reviewed. RESULTS: The typical pathological changes of lungs were diffuse hemorrhage on surface. A mixture features of serous, fibrinous and hemorrhagic inflammation were seen in most pulmonary alveoli with engorgement of capillary and there were microthrombosis in some capillary. Pulmonary alveoli became thick with interstitial mononuclear inflammatory infiltration, diffused alveoli damage, desquamation of pneumocytes and hyaline-membrane formation. Fibrinoid materials and erythrocytes could be found in alveolar spaces. There were thrombo-embolisms in some bronchial artery. Meanwhile, haemorrhagic necrosis was showed in lymph nodes and spleen with attenuation of lymphocytes. Other atypical pathological changes, such as hydropic degeneration, fatty degeneration, interstitial cell proliferation and some lesions observed in liver, heart, kidney, pancreas may have existed before the hospitalization. CONCLUSION: Severe damages of pulmonary and immunological system damage are responsible for clinical features of SARS and may lead to death of patients.

Clinicopathological study on TTV infection in hepatitis of unknown etiology.

AIM: To investigate the state of infection, replication site, pathogenicity and clinical significance of transfusion transmitted virus (TTV) in patients with hepatitis, especially in patients of unknown etiology. METHODS: Liver tissues taken from 136 cases of non-A non-G hepatitis were tested for TT virus antigen and nucleic acid by in situ hybridization (ISH) and nested-polymerase chain reaction (PCR). Among them, TT virus genome and its complemental strand were also detected in 24 cases of autopsy liver and extrahepatic tissues with ISH. Meanwhile, TTV DNA was detected in the sera of 187 hepatitis patients by nested-PCR. The pathological and clinical data of the cases infected with TTV only were analyzed. RESULTS: In liver, the total positive rate of TTV DNA was 32.4% and the positive signals were located in the nuclei of hepatocytes. In serus, TTV DNA was detected in 21.4% cases of hepatitis A-G, 34.4% of non-A non-G hepatitis and 15% of healthy donors. The correspondence rate of TTV DNA detection between liver tissue with ISH and sera with PCR was 63.2% and 89.3% in the same liver tissues by ISH and by PCR, respectively. Using double-strand probes and single-strand probes designed to detect TTV genome, the correspondence rate of TTV DNA detected in liver and extrahepatic tissues was 85.7%. Using single-strand probes, TTV genome could be detected in liver and extrahepatic tissues by PCR, but its complemental strands (replication strands) could be observed only in livers. The liver function of most cases infected with TTV alone was abnormal and the liver tissues had different pathological damage such as ballooning, acidophilia degeneration, formation of apoptosis bodies and focus of necrosis, but the inflammation in the lobule and portal area was mild. CONCLUSION: The positive rate of TTV DNA among cases of hepatitis was higher than that of donors, especially in patients with non-A non-G hepatitis, but most of them were coinfected with other hepatitis viruses. TTV can infect not only hepatocytes, but also extrahepatic tissues. However, the chief replication place may be liver. The infection of TTV may have some pathogenicity. Although the pathogenicity is comparatively weak, it can still damage the liver tissues. The lesions in acute hepatitis (AH) and chronic hepatitis (CH) are mild, but in severe hepatitis (SH), it can be very serious and cause liver function failure, therefore, we should pay more attention to TTV when studying the possible pathogens of so-called "liver hepatitis of unknown etiology".