Differences across cyclophilin A orthologs contribute to the host range restriction of hepatitis C virus

Hepatitis C is a life-long disease that begins when a virus infects the cells of the liver. Although the infection is curable, it is expensive to treat, and there is not yet a vaccine to prevent the disease. This is largely because the virus that causes hepatitis C, also known as HCV, naturally only infects humans and chimpanzees, which has made it difficult to generate an effective animal model for developing a vaccine. Mice are frequently used as a model for studying disease and can be genetically altered to allow HCV to enter their liver cells. However, once HCV enters mouse cells, it struggles to replicate. As a result, an infection does not develop, and the immune system’s response to the virus cannot be fully explored. Replication of HCV in humans relies on a protein called cyclophilin A, or CypA for short. Now, Gaska et al. have set out to improve current animal models for HCV by investigating whether HCV can also use CypA from other species, including mice, to replicate. Gaska et al. showed that the mouse form of CypA could help HCV replicate in human liver cells with lower than normal levels of CypA, but only very poorly. Editing the mouse gene for CypA to be more like the human version resulted in higher HCV replication. Putting variants of CypA into the liver cells of mice, which do not normally replicate HCV at high levels, led to an increase in HCV replication. However, replication of HCV in mice was still far lower than in human liver cells, suggesting that the mouse model system could be improved by learning more about which proteins interact with CypA. Injection drug use – one of the main ways hepatitis C spreads – is becoming increasingly common because of the growing opioid epidemic in many countries. A clinically relevant animal model that supports hepatitis C virus infection would be an important milestone towards a vaccine that could prevent the continued spread of this disease.