Project description:Here, we characterize RIPK3-dependent transcriptional responses in cortical neurons following infection with neurotropic flaviviruses. Neurons were infected with either Zika virus (ZIKV) strain MR766 at an MOI of 0.1, West Nile virus (WNV) strain TX 2002-HC at an MOI of 0.001, or a saline mock solution. Neurons were derived from mice lacking RIPK3 expression (Ripk3-/-) or wildtype controls. These studies revealed a number of antiviral genes whose upregulation following viral infection is absent in neurons lacking RIPK3, a subset of which were validated using qRT-PCR.
Project description:The transcriptional potential of RIPK3 in a non-infectious system in neurons is unclear. Here we found that RIPK3 activation, independent of any upstream signals is sufficient to induce anti-viral transcription in neurons.
Project description:Flaviviruses pose a significant threat to public health due to their ability to infect the central nervous system (CNS) and cause severe neurologic disease. Astrocytes play a crucial role in the pathogenesis of flavivirus encephalitis through their maintenance of blood-brain barrier (BBB) integrity and their modulation of immune cell recruitment and activation within the CNS. We have previously shown that receptor interacting protein kinase-3 (RIPK3) is a central coordinator of neuroinflammation during CNS viral infection, a function that occurs independently of its canonical function in inducing necroptotic cell death. To date, however, roles for necroptosis-independent RIPK3 signaling in astrocytes are poorly understood. Here, we use mouse genetic tools to induce astrocyte-specific deletion, overexpression, and chemogenetic activation of RIPK3 to demonstrate an unexpected anti-inflammatory function for astrocytic RIPK3. RIPK3 activation in astrocytes was required for host survival in multiple models of flavivirus encephalitis, where it restricted neuropathogenesis by limiting immune cell recruitment to the CNS. Transcriptomic analysis revealed that, despite inducing a traditional pro-inflammatory transcriptional program, astrocytic RIPK3 paradoxically promoted neuroprotection through the upregulation of serpins, endogenous protease inhibitors with broad immunomodulatory activity. Notably, intracerebroventricular administration of SerpinA3N in infected mice preserved BBB integrity, reduced leukocyte infiltration, and improved survival outcomes in mice lacking astrocytic RIPK3. These findings highlight a previously unappreciated role for astrocytic RIPK3 in suppressing pathologic neuroinflammation and suggests new therapeutic targets for the treatment of flavivirus encephalitis.
Project description:The full transcriptional RIPK3-dependent transcriptional potential is unknown. Here, we found that RIPK3 is a dominant driver of anti-viral transcription in neurons following Zika virus infection.
Project description:While recent work has identified roles for cytokines and inflammation in the regulation of neural activity, the capacity for cell intrinsic innate immune signaling within neurons to influence neurotransmission remains poorly understood. However, the existing evidence linking immune signaling with neuronal activity suggests that modulation of neurotransmission may serve previously undefined roles in host protection and pathogen control within the central nervous system. Here, we identify a specialized function for RIPK3, a kinase traditionally associated with necroptotic cell death, in preserving neuronal survival during neurotropic flavivirus infection through the suppression of excitatory neurotransmission. We show that RIPK3 coordinates transcriptomic changes in neurons that suppress neuronal glutamate signaling, thereby desensitizing neurons to excitotoxic cell death. These effects occur independently of the traditional functions of RIPK3 in promoting MLKL-dependent necroptosis and NFκB-mediated inflammatory transcription. Instead, RIPK3 promotes phosphorylation of the key neural regulatory kinase CAMKII, which in turn activates the transcription factor CREB to drive a neuroprotective transcriptional program and suppress deleterious glutamatergic signaling. These findings identify an unexpected function for a canonical cell death protein in promoting neuronal survival during viral infection through the modulation of neuronal activity, highlighting new mechanisms of neuroimmune crosstalk.
Project description:This purpose of this experiment was to investigate the transcriptional differences between C57BL6, RIPK3 knock-out mice infected with influenza strain A/CA/04/2009 (H1N1) virus. Overview of Experiment: Groups of 6-8 week-old C57BL6 and RIPK3 knock-out mice were infected with influenza A/CA/04/2009 virus. Infections were done at 10^5 PFU or time-matched mock infected. Time points were 2 and 4 d.p.i. There were 2-3 animals/dose/time point. Lung samples were collected for virus load and transcriptional analysis. Weight loss and animal survival were also monitored.
Project description:Astrocyte activation is a common feature of neurodegenerative diseases. However, the ways in which dying neurons influence the activity of astrocytes is poorly understood. RIPK3 signaling has recently been described as a key regulator of neuroinflammation, but whether this kinase mediates astrocytic responsiveness to neuronal death has not yet been studied. Here, we used the MPTP model of Parkinson’s disease to show that activation of astrocytic RIPK3 drives dopaminergic cell death and axon damage. Transcriptomic profiling revealed that astrocytic RIPK3 promoted gene expression associated with neuroinflammation and movement disorders, and this coincided with significant engagement of DAMP signaling. Using human cell culture systems, we show that factors released from dying neurons signal through RAGE to induce RIPK3-dependent astrocyte activation. These findings highlight a mechanism of neuron-glia crosstalk in which neuronal death perpetuates further neurodegeneration by engaging inflammatory astrocyte activation via RIPK3.
Project description:Flaviviruses pose a constant threat to human health. These RNA viruses are transmitted by the bite of infected mosquitoes and ticks and regularly cause outbreaks. To identify host factors required for flavivirus infection we performed full-genome loss of function CRISPR-Cas9 screens. Based on these results we focused our efforts on characterizing the roles that TMEM41B and VMP1 play in the virus replication cycle. Our mechanistic studies on TMEM41B revealed that all members of the Flaviviridae family that we tested require TMEM41B. We tested 12 additional virus families and found that SARS-CoV-2 of the Coronaviridae also required TMEM41B for infection. Remarkably, single nucleotide polymorphisms (SNPs) present at nearly twenty percent in East Asian populations reduce flavivirus infection. Based on our mechanistic studies we propose that TMEM41B is recruited to flavivirus RNA replication complexes to facilitate membrane curvature, which creates a protected environment for viral genome replication.