Intrinsic immune sensing of retroviral infections in SAMHD1 knockout mice

• Applicant: Professor Dr. Thomas Gramberg
• Subject Area: Virology ; Immunology
• Term: from 2014 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 263025006

Mutations in the dNTP hydrolase SAMHD1 have been associated with the autoimmune disease Aicardi-Goutières syndrome, a hallmark of which is the spontaneous upregulation of type I interferon (IFN). In addition, SAMHD1 acts as an antiviral restriction factor that blocks the infection of HIV-1 and other retroviruses in myeloid cells and quiescent CD4+ T cells. In the absence of SAMHD1, HIV-1 induces a type I IFN response upon infection of human dendritic cells (DC). Newly produced HIV protein or the sensing of viral DNA have both been suggested to trigger this immune response to infection. It is still unclear how the virus-induced and the endogenous response in the absence of SAMHD1 are triggered and whether both responses are initiated by the same or different immune sensors. We will therefore use our recently described SAMHD1 knockout mouse model as a tool to compare the endogenous and the virus-induced immune response in the absence of SAMHD1. Mice deficient for SAMHD1 and a functional type I interferon receptor (IFNAR-/-) do not show an endogenous immune response. Therefore, we will infect mice or bone marrow-derived dendritic cells (BMDC) from SAMHD1-/- mice that are proficient or deficient for IFNAR to determine whether the endogenous immune activation acts antiviral and reveal the full antiviral potency of SAMHD1 in vitro and in vivo. Comparing the transcriptome of BMDCs from these mice upon infection will reveal whether individual transcripts are specifically upregulated in response to infection. Thus, this analysis will determine whether the endogenous and the virus-induced innate response are due to stimulation of the same pathway. Within the second aim of the study, we will further elucidate the nature of the retroviral sensor. We will clarify the role of the DNA sensor cGAS in sensing retroviral infection the absence of SAMHD1. Thus, we will analyze the endogenous and the retrovirus-induced immune response in SAMHD1/cGAS and SAMHD1/STING double knockout mice, which are deficient for the cGAS adaptor molecule STING. We will use BMDCs from these mice in HIV reporter virus infection assays to determine whether both proteins play a role in antiretroviral signaling in mice. Adding retroviral inhibitors and mutated viruses to the infection assays will determine which viral entities are sensed by the immune receptor in mice. The analysis of cGAS and STING in our SAMHD1 mouse model will show whether the newly discovered sensor cGAS can be linked to the induction of autoimmunity and an antiretroviral immune response in the absence of SAMHD1. Together, we will take advantage of our already established SAMHD1 knockout mouse model to analyze how retroviral infections are sensed by intrinsic immunity.

• DFG Programme: Research Grants