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 2

Extracellular HERV-K RNA induces neurotoxicity through Tlr7.

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Extracellular HERV-K RNA induces neurotoxicity through Tlr7. (A) Neurons...
(A) Neurons and SH-SY5Y cells were analyzed for TLR7/TLR8 expression by FACS. (B) Neurons were incubated with 5 μg/mL biotinylated HERV-K or PBS (control) for 12 hours and stained with streptavidin–Alexa Fluor 488 and DAPI. Scale bar: 10 μm. (C) WT and Tlr7-KO neurons were incubated with 5 μg/mL HERV-K for 7 days or left untreated (control). Cells were immunostained with NeuN, MAP-2, and DAPI. Scale bar: 10 μm. (D) WT, Tlr7-KO, and Myd88-KO neurons were incubated with various HERV-K doses for 7 days (left) or with 5 μg/mL HERV-K for various durations (right) (P = 0.0001 over dose and time, WT groups; P < 0.0001, P = 0.0006 over dose and time, respectively, Myd88-KO groups; n.s. over Tlr7-KO, all groups). *P < 0.05, and ***P < 0.001 (n = 4–11). (E) WT and Tlr7-KO neurons were incubated with various HERV-K doses for 5 days and immunostained for active caspase-3, NeuN, and DAPI. Caspase-3–positive cells were quantified (P = 0.0005 over WT groups; n.s. over Tlr7-KO groups). **P < 0.01 (n = 5–6). (F) WT and Sarm1-KO neurons were incubated with HERV-K for 7 days (P = 0.0006 over WT groups; n.s. over Sarm1-KO groups). *P < 0.05, and **P < 0.01 (n = 4–10). (G) SH-SY5Y cells were incubated with HERV-K for 3 days (P = 0.0015 over all groups). *P < 0.05, and **P < 0.01 (n = 6). (H) WT neurons and neuron/microglia (+WT MG or +Tlr7-KO MG) cocultures were incubated with HERV-K for 3 days (P = 0.009 over neurons + WT MG groups; n.s. over neurons + Tlr7-KO MG groups; n.s. over neurons all groups). *P < 0.05, and **P < 0.01 (n = 5–6). (I) WT and Tlr7-KO neurons were incubated with nonphosphorothioated HERV-K oligoribonucleotide for 7 days (P < 0.0001 over WT groups, n.s. over Tlr7-KO groups). **P < 0.01, and ***P < 0.001 (n = 3–12). (J) WT and Tlr7-KO neurons were incubated with 50-nucleotide HERV-K oligoribonucleotide (HERV-K long) or with scrambled 50-nucleotide HERV-K (HERV-K long mut.) for 7 days (P < 0.0001 over WT groups and n.s. over Tlr7-KO). **P < 0.01, and ***P < 0.001 (n = 4–11). (D–J) Unless stated otherwise, relative neuronal viability was assessed. Controls were 10 μg/mL HERV-K (-GU) oligoribonucleotide, 1 mM loxoribine, 1 mg/mL LPS, or 10 ng/mL TL8-506. Results are presented as mean ± SEM. P values for all groups: Kruskal-Wallis test; P values for indicated relevant groups compared with control: Kruskal-Wallis test with Dunn’s post-hoc analysis.