Krug, L. | bioRxiv Science

bioRxiv2019

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

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.

cancer biology↗

bioRxiv2016

Retrotransposon Activation Contributes to Neurodegeneration in a DrosophilaTDP-43 Model of ALS.

Amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD) are two incurable neurodegenerative disorders that exist on a symptomological spectrum and share both genetic underpinnings and pathophysiological hallmarks. Functional abnormality of TAR DNA-binding protein 43 (TDP-43), an aggregation-prone RNA and DNA binding protein, is observed in the vast majority of both familial and sporadic ALS cases and in [~]40% of FTLD cases, but the cascade of events leading to cell death are not understood. We have expressed human TDP-43 (hTDP-43) in Drosophila neurons and glia, a model that recapitulates many of the characteristics of TDP-43-linked human disease including protein aggregation pathology, locomotor impairment, and premature death. We report that such expression of hTDP-43 impairs small interfering RNA (siRNA) silencing, which is the major post-transcriptional mechanism of retrotransposable element (RTE) control in somatic tissue. This is accompanied by de-repression of a panel of both LINE and LTR families of RTEs, with somewhat different elements being active in response to hTDP-43 expression in glia versus neurons. hTDP-43 expression in glia causes an early and severe loss of control of a specific RTE, the endogenous retrovirus (ERV) gypsy. We demonstrate that gypsy causes the degenerative phenotypes in these flies because we are able to rescue the toxicity of glial hTDP-43 either by genetically blocking expression of this RTE or by pharmacologically inhibiting RTE reverse transcriptase activity. Moreover, we provide evidence that activation of DNA damage-mediated programmed cell death underlies both neuronal and glial hTDP-43 toxicity, consistent with RTE-mediated effects in both cell types. Our findings suggest a novel mechanism in which RTE activity contributes to neurodegeneration in TDP-43-mediated diseases such as ALS and FTLD.\n\nAUTHOR SUMMARYFunctional abnormality of TAR DNA-binding protein 43 (TDP-43), an aggregation-prone RNA and DNA binding protein, is observed in the vast majority of both familial and sporadic ALS cases and in [~]40% of FTLD cases, and mutations in TDP-43 are causal in a subset of familial ALS cases. Although cytoplasmic inclusions of this mostly nuclear protein are a hallmark of the disease, the cascade of events leading to cell death are not understood. We demonstrate that expression of human TDP-43 (hTDP-43) in Drosophila neurons or glial cells, which results in toxic cytoplasmic accumulation of TDP-43, causes broad expression of retrotransposons. In the case of glial hTDP-43 expression, the endogenous retrovirus (ERV) gypsy causally contributes to degeneration because inhibiting gypsy genetically or pharmacologically is sufficient to rescue the phenotypic effects. Moreover, we demonstrate that activation of DNA damage-mediated programmed cell death underlies hTDP-43 and gypsy mediated toxicity. Finally, we find that hTDP-43 pathology impairs small interfering RNA silencing, which is an essential system that normally protects the genome from RTEs. These findings suggest a novel mechanism in which a storm of retrotransposon activation drives neurodegeneration in TDP-43 mediated diseases such as ALS and FTLD.

neuroscience↗