Hepatitis B virus activates expression of the RIG-like receptor pathway in murine intrahepatic cells in humanized mice

Question:

A number of studies has shown that RIG-I-like receptors (RLR) play an important role in innate immunity. While studies on host recognition of HBV have focused on HBV infected cells, less is known about the distinct role of non-parenchymal cells in sensing HBV by RLRs in vivo. Aim of the study was to investigate the influence of HBV infection both on human hepatocytes and murine cells, in particular non-parenchymal cells (NPCs: Kupffer cells, stellate cells, dendritic cells) using human liver chimeric USB mice and by comparing transcriptional levels of murine and human RLR specific molecules in the setting of HBV or HCV chronic infection.

Methods:

Analyses were performed by measuring gene expression levels of different key signaling molecules of the RLR pathway using either human-specific or murine-specific RT-qPCR assays.

Results:

We found significant up-regulation of key regulators of RLR signalling, like mRIG-I (median 2.0-fold, p = 0.0002), mMDA5 (2.3-fold, p < 0.0001), mMAVS (2.9-fold, p = 0.0003), mTRAF3 (1.9-fold, p = 0.017) and mIRF3 (1.4-fold, p = 0.016) in murine liver cells within HBV infected mice. Nevertheless, interferons (mIFN-β, mIFN-λ, mIFN-γ), inflammatory cytokines (mTNFα, mIL-6, mIL1b, mIL12) and chemokines (mCXCL10) were not induced. On the other hand, the induction of human RLRs (hRIG-I: 1.9-fold, p = 0.012; hMDA5: 1.7-fold, p = 0.005) determined in human HBV-infected hepatocytes correlated with the induction of specific human chemokines (CXCL-8, -9, -10), although the indicated interferons and cytokines were also not induced in human hepatocytes. Of note, murine and human cells showed different patterns of negative/positive regulators of RIG-like receptor signalling. While NLRC5 (p = 0.0002, 4.1-fold) and NLRX1 (p = 0.007, 2-fold) appeared to be stronger up-regulated in murine NPCs, TRIM13 was higher expressed (2.4-fold, p = 0.0036) in human hepatocytes, indicating distinct modulations of RIG-I-signaling in different cell compartments during HBV infection. Interestingly, induction of the non-parenchymal cell compartment appeared HBV-specific, since expression of the same murine RLR genes measured in humanized mice infected with HCV was not up-regulated, although these genes appeared clearly enhanced in HCV infected human hepatocytes.

Conclusions:

These results indicate that intrahepatic sensing of HBV infection occurs both in murine and human cells. However, while upregulation of RLR signalling results in chemokine induction in human hepatocytes, the lack of IFN/chemokine induction and enhancement of negative regulators of RIG-I-signaling in murine cells suggest a role of NPCs in viral tolerance during chronic HBV infection.