Hepatitis C virus is the leading cause of liver disease in the Western hemisphere. The current HCV therapy is inadequate, as it is associated with severe side effects and often not effective. The majority of HCV infections are persistent, life-long chronic infections that slowly induce pathogenesis. Furthermore, HCV does not appear to directly induce liver disease, rather it does so indirectly by stimulating cytokine production and inflammation, which suggests that its impairment of innate immune pathways is not absolute. The virus-host interactions and molecular mechanisms that support persistent HCV replication and chronic infection, and those that eventually induce liver disease are not understood. We hypothesize that innate intracellular immune defenses play an essential role in regulating HCV replication and that viral persistence is linked to HCV control of innate defense processes. Nearly all the studies of this topic have been conducted in Huh-7 cells or derivatives, which exhibit severely impaired innate immune responses. We recently showed that hepatoma-derived HepG2 cells efficiently support the entire HCV life cycle if the liver-specific microRNA miR-122 is expressed along with the missing entry factor CD-81 (HepG2-HFL cells). While HepG2 cells containing these two factors can replicate the entire life cycle of HCV, we found that there was a striking difference in these cells'ability to support infection and spread when compared to the previously established Huh-7.5 cell line. At the same time, we found that the innate immune response in these cells was more active in response to HCV infection. Therefore, we hypothesize that HepG2-HFL cells will faithfully recapitulate the innate immune responses present in hepatocytes, and thus provide a better model through which to understand the interactions between HCV and the innate immune system. Our ultimate goal is to better understand how HCV can subvert the antiviral response while allowing for activation of inflammatory pathways. We propose experiments to compare innate immune pathways in HepG2-HFL cells with those of primary human hepatocytes and Huh-7 cells, with a particular focus on the responses induced by the cellular viral RNA sensors RIG-I, MDA5, and TLR3. We will next examine the interaction between HCV and innate immune pathways in HepG2-HFL cells to determine whether HCV activates innate immune responses that can effectively combat infection as well as inhibit such responses through the action of viral proteins. We anticipate tha the results of these studies will provide novel insights into the interaction between HCV and the innate immune system, which remains poorly understood due to a lack of robust model systems, despite its importance in the pathogenesis of associated disease.
Close to 3% of the world's population is infected with Hepatitis C virus, and it is responsible for the majority of liver transplants and liver cancers in the westen world, with current therapeutic regimes being poorly tolerated and ineffective. The particular challenge with HCV is that it can avoid long-term elimination by the immune system, while provoking sufficient immune response to cause continual liver damage which sets the stage for the development of cirrhosis and liver cancer. We will study how this virus is so efficient at avoiding immune response so that we can better develop novel therapeutics tailored to this viral host interaction.
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