HBV-driven host chromatin accessibility changes affect liver metabolic pathways, iron homeostasis and promote a preneoplastic phenotype.

BACKROUND AND AIMS: Complex host-virus interactions account for adaptive and innate immunity dysfunctions and viral cccDNA mini-chromosome persistence, key features of HBV chronicity and challenges for HBV cure. The extent of HBV direct impact on liver transcriptome remains controversial. Transcriptional activation in eukaryotic cells is tightly linked with disruption of nucleosome organization at accessible genomic sites of remodeled chromatin. We sought to investigate the impact of HBV on chromatin accessibility and transcription.

METHODS

We used ATAC-seq (Assay for Transposase Accessible Chromatin followed by high throughput sequencing) to detect early changes in chromatin accessibility coupled with RNA-seq in HBV-infected Primary Human Hepatocytes (PHHs).

RESULTS

An increasing number of genomic sites change their nucleosome organization over time after HBV infection, with a prevalent, but not exclusive, reduction of chromatin accessibility at specific sites that is partially prevented by inhibiting HBV transcription and replication. ATAC-seq and RNA-seq integration showed that HBV infection impacts on liver fatty acids, bile acids, iron metabolism and liver cancer pathways. The upregulation of iron uptake genes leads to a significant increase of iron content in HBV-infected PHHs whereas iron chelation inhibits cccDNA transcription and viral replication. The chromatin accessibility and transcriptional changes imposed by HBV early after infection persist, as an epigenetic scar, in chronic HBV (CHB) patients and in HBV-related HCCs. These changes are to a large extent independent from viral replication levels and disease activity.

CONCLUSIONS

Altogether our results show that HBV infection impacts on host cell chromatin landscape and specific transcriptional programs including liver metabolism and liver cancer pathways. Re-wiring of iron metabolism boosts viral replication early after infection. The modulation of genes involved in cancer-related pathways may favor the development or the selection of a pro-neoplastic phenotype and persists in HBV-related HCCs.