A role of hypoxia inducible factor 1 alpha in Mouse Gammaherpesvirus 68 (MHV68) lytic replication and reactivation from latency

Abstract

The hypoxia inducible factor 1 alpha (HIFI) protein and the hypoxic microenvironment are critical for infection and pathogenesis by the oncogenic gammaherpesviruses ({gamma}HV) such as Kaposi Sarcoma-associated Herpes Virus (KSHV) and Epstein-Barr virus (EBV). However, understanding the role of HIFI during the virus life cycle and its biological relevance in the context of host pathogenesis has been challenging due to the lack of animal models for human {gamma}HV. To study the role of HIFI we employed the murine gammaherpesvirus 68 (MHV68), a rodent pathogen that readily infects laboratory mice. We show that MHV68 infection induces HIFI protein and HIFI-responsive gene expression in permissive cells. Deletion of HIFI reduces virus production due to a global downregulation of viral gene expression. Most notable was the marked decrease in many viral genes bearing hypoxia regulatory element (HRE) such as viral G-Protein Coupled Receptor (vGPCR), which is known to activate HIF1 transcriptional activity during KSHV infection. Intranasal infection of HIF1LoxP/LoxP mice with MHV68 expressing Cre-recombinase impaired virus expansion during early acute infection and affected lytic reactivation in the splenocytes explanted from mice. Moreover, low oxygen conditions accelerated lytic reactivation and enhanced virus production in MHV68 infected splenocytes. Thus, we conclude that HIFI plays a critical role to promote virus replication. Our results highlight the importance of the mutual interactions of the oxygen-sensing machinery and gammaherpesviruses in viral replication and pathogenesis.\n\nAUTHOR SUMMARYThe host oxygen sensing machinery including the HIF1 pathway is important during the viral life cycle of oncogenic gammaherpesviruses such as KSHV and EBV. However, due to the host specificity, the effects of HIF1 in herpes biology is limited to studies with in vitro systems. Here, we study the role of HIF1 using the mouse gammaherpesvirus 68 (MHV68) that readily infects laboratory mice. We demonstrate that MHV68 infection upregulates HIF1 during replication and inactivation of HIF1 transcriptional activity significantly decreased viral genes expression which results in impaired virus production in vitro. In vivo deletion of HIF1 impaired viral expansion during acute infection and affected reactivation from latency. These results show the importance of the interplay with the oxygen-sensing machinery in gammaherpesvirus infection and pathogenesis, placing the MHV68 mouse model as a unique platform to gain insight into this important aspect of oncogenic gamma-herpesviruses biology and to test HIF1 targeted therapeutics.