Human endogenous retrovirus HERV-K(HML-2) RNA causes neurodegeneration through Toll-like receptors
Paul Dembny, Andrew G. Newman, Manvendra Singh, Michael Hinz, Michal Szczepek, Christina Krüger, Robert Adalbert, Omar Dzaye, Thorsten Trimbuch, Thomas Wallach, Gunnar Kleinau, Katja Derkow, Bernhard C. Richard, Carola Schipke, Claus Scheidereit, Harald Stachelscheid, Douglas Golenbock, Oliver Peters, Michael Coleman, Frank L. Heppner, Patrick Scheerer, Victor Tarabykin, Klemens Ruprecht, Zsuzsanna Izsvák, Jens Mayer, Seija Lehnardt
Paul Dembny, Andrew G. Newman, Manvendra Singh, Michael Hinz, Michal Szczepek, Christina Krüger, Robert Adalbert, Omar Dzaye, Thorsten Trimbuch, Thomas Wallach, Gunnar Kleinau, Katja Derkow, Bernhard C. Richard, Carola Schipke, Claus Scheidereit, Harald Stachelscheid, Douglas Golenbock, Oliver Peters, Michael Coleman, Frank L. Heppner, Patrick Scheerer, Victor Tarabykin, Klemens Ruprecht, Zsuzsanna Izsvák, Jens Mayer, Seija Lehnardt
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Research Article Immunology Neuroscience

Human endogenous retrovirus HERV-K(HML-2) RNA causes neurodegeneration through Toll-like receptors

Abstract

Although human endogenous retroviruses (HERVs) represent a substantial proportion of the human genome and some HERVs, such as HERV-K(HML-2), are reported to be involved in neurological disorders, little is known about their biological function. We report that RNA from an HERV-K(HML-2) envelope gene region binds to and activates human Toll-like receptor (TLR) 8, as well as murine Tlr7, expressed in neurons and microglia, thereby causing neurodegeneration. HERV-K(HML-2) RNA introduced into the cerebrospinal fluid (CSF) of either C57BL/6 wild-type mice or APPPS1 mice, a mouse model for Alzheimer’s disease (AD), resulted in neurodegeneration and microglia accumulation. Tlr7-deficient mice were protected against neurodegenerative effects but were resensitized toward HERV-K(HML-2) RNA when neurons ectopically expressed murine Tlr7 or human TLR8. Transcriptome data sets of human AD brain samples revealed a distinct correlation of upregulated HERV-K(HML-2) and TLR8 RNA expression. HERV-K(HML-2) RNA was detectable more frequently in CSF from individuals with AD compared with controls. Our data establish HERV-K(HML-2) RNA as an endogenous ligand for species-specific TLRs 7/8 and imply a functional contribution of human endogenous retroviral transcripts to neurodegenerative processes, such as AD.

Authors

Paul Dembny, Andrew G. Newman, Manvendra Singh, Michael Hinz, Michal Szczepek, Christina Krüger, Robert Adalbert, Omar Dzaye, Thorsten Trimbuch, Thomas Wallach, Gunnar Kleinau, Katja Derkow, Bernhard C. Richard, Carola Schipke, Claus Scheidereit, Harald Stachelscheid, Douglas Golenbock, Oliver Peters, Michael Coleman, Frank L. Heppner, Patrick Scheerer, Victor Tarabykin, Klemens Ruprecht, Zsuzsanna Izsvák, Jens Mayer, Seija Lehnardt

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Figure 1

HERV-K(HML-2)–derived oligoribonucleotides activate microglia and macrophages via Tlr7 and TLR8.

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HERV-K(HML-2)–derived oligoribonucleotides activate microglia and macrop...
(A) Microglia from C57BL/6 (wild-type, WT), Tlr7-KO, or MyD88-KO mice and (B) THP-1 macrophages were incubated for 12 hours with various doses of HERV-K(HML-2) oligoribonucleotide containing a GUUGUGU motif present in the env region (HERV-K, left) or with 5 μg/mL of HERV-K for various durations (right). Untreated cells (control) and control oligoribonucleotide, HERV-K (-GU), 10 μg/mL, served as negative controls. LPS (100 ng/mL), loxoribine (1 mM), poly(I:C) (100 ng/mL), and LyoVec served as further controls. TNF-α amounts in culture supernatants were determined by immuno multiplex assay. Data are pooled from 3 independent experiments. (C) Microglia and (D) THP-1 macrophages were incubated for 2 hours with 5 μg/mL HERV-K, HERV-K (-GU), or mutant oligoribonucleotide or 1 μg/mL LPS. Protein lysates were assayed for NF-κB activation by electrophoretic mobility shift assay (EMSA), while a parallel Western blot probed with p65 antibody confirmed equal loading of probes. One representative experiment of 3 independent experiments is shown. HEK-Blue cells coexpressing murine (E) or human (F) TLR7 or TLR8 and an NF-κB/AP1-inducible secreted embryonic alkaline phosphatase (SEAP) reporter gene were incubated for 48 hours with various HERV-K doses, HERV-K (-GU) (20 μg/mL), R848 (100 ng/mL, TLR7/8 agonist), or TNF-α (100 ng/mL, SEAP induction). HEK-Blue–null cells served as negative controls. Data are pooled from 3–7 independent experiments. Results are presented as mean ± SEM. *P < 0.05, and **P < 0.01 over HERV-K dose compared with control (1-way ANOVA, Bonferroni’s post hoc analysis). (G) Binding affinity measurements of TLR8 protein and oligoribonucleotides using microscale thermophoresis. TLR8-RNA interaction was monitored by titrating RNA from 500 μM to 30 nM [HERV-K, HERV-K (-GU), control oligoribonucleotide 1] and 62.5 μM to 3.8 nM (control oligoribonucleotide 2) against 50 nM RED-Tris-NTA–labeled TLR8 measured with NanoTemper Monolith NT.115 (left). KD values were calculated from dose response curves, which were calculated from titration experiments (right). Results are presented as mean ± SD. n = 3.