Abstract
Hepatitis B virus (HBV) is a blood-borne pathogen responsible for chronic hepatitis, cirrhosis, and liver cancer. The mechanism of HBV entry into hepatocytes remains to be investigated. Recently, sodium taurocholate cotransporting polypeptide (NTCP) was discovered as a major HBV receptor based on an in vitro infection system using NTCP-reconstituted HepG2 cells. However, this infection system relies on the compound polyethylene glycol (4% PEG), which is not physiologically relevant to human infection. High concentration of heparin has been commonly used as an inhibitor control for in vitro infection in the field. Surprisingly, we found that heparin at physiological concentration can enhance HBV infection in a PreS1-peptide sensitive, NTCP-dependent manner in both HepaRG and HepG2-NTCP-AS cells. O-sulfation of heparin is more important for the infection enhancement than N-sulfation. This system based on the HepG2-NTCP-AS cells can support in vitro infection with HBV genotypes B and C, as well as using serum samples from HBeAg positive and negative chronic carriers. In summary, our study provides a PEG-free infection system closely resembling human natural infection. In addition, it points to a future research direction for heparin and heparin-binding host factor(s) in the blood, which are potentially involved in viral entry. To our knowledge, this is the first soluble and circulatory host factor which can enhance HBV in vitro infection.
Highlights
Hepatitis B virus (HBV) is an enveloped and partially double-stranded DNA virus which established chronic infection in around 240 million carriers worldwide
To look for any soluble host factors which might facilitate HBV infection of hepatocytes, we examined the plasma from a healthy individual for its potential effect on HBV in vitro infection
We established a similar HepG2-NTCP-AS system to search for potential host factors in the plasma involved in viral entry
Summary
HBV is an enveloped and partially double-stranded DNA virus which established chronic infection in around 240 million carriers worldwide. In the presence of PEG, the efficiency of HBV infection on PHH was elevated up to 20 times, mainly due to the enhanced adsorption between virus and hepatocytes[4]. PEG is a non-biological chemical not found in human body It remains a concern whether the current PEG-containing infection protocol could faithfully mimic the viral entry event in vivo. To our surprise, at its physiological concentration (1 to 5 μg/ml), heparin could enhance HBV infection efficiency in both HepaRG and NTCP-reconstituted hepatocytes. This phenomenon was most pronounced when without PEG or with a reduced amount of PEG (1.2%). One implication from our studies here is that heparin-binding host factors may deserve further attention in future studies of viral entry
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