EV71 infection induces neurodegeneration via activating TLR7 signaling and IL-6 production

PLoS Pathog. 2019 Nov 15;15(11):e1008142. doi: 10.1371/journal.ppat.1008142. eCollection 2019 Nov.

Abstract

As a neurotropic virus, human Enterovirus 71 (EV71) infection causes hand-foot-and-mouth disease (HFMD) and may develop severe neurological disorders in infants. Toll-like receptor 7 (TLR7) acts as an innate immune receptor and is also a death receptor in the central nervous system (CNS). However, the mechanisms underlying the regulation of TLR7-mediated brain pathogenesis upon EV71 infection remain largely elusive. Here we reveal a novel mechanism by which EV71 infects astrocytes in the brain and induces neural pathogenesis via TLR7 and interleukin-6 (IL-6) in C57BL/6 mice and in human astroglioma U251 cells. Upon EV71 infection, wild-type (WT) mice displayed more significant body weight loss, higher clinical scores, and lower survival rates as compared with TLR7-/- mice. In the cerebral cortex of EV71-infected mice, neurofilament integrity was disrupted, and inflammatory cell infiltration and neurodegeneration were induced in WT mice, whereas these were largely absent in TLR7-/- mice. Similarly, IL-6 production, Caspase-3 cleavage, and cell apoptosis were significantly higher in EV71-infected WT mice as compared with TLR7-/- mice. Moreover, EV71 preferentially infected and induced IL-6 in astrocytes of mice brain. In U251 cells, EV71-induced IL-6 production and cell apoptosis were suppressed by shRNA-mediated knockdown of TLR7 (shTLR7). Moreover, in the cerebral cortex of EV71-infected mice, the blockade of IL-6 with anti-IL-6 antibody (IL-6-Ab) restored the body weight loss, attenuated clinical scores, improved survival rates, reduced the disruption of neurofilament integrity, decreased cell apoptotic induction, and lowered levels of Caspase-3 cleavage. Similarly, in EV71-infected U251 cells, IL-6-Ab blocked EV71-induced IL-6 production and cell apoptosis in response to viral infection. Collectively, it's exhibited TLR7 upregulation, IL-6 induction and astrocytic cell apoptosis in EV71-infected human brain. Taken together, we propose that EV71 infects astrocytes of the cerebral cortex in mice and human and triggers TLR7 signaling and IL-6 release, subsequently inducing neural pathogenesis in the brain.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Apoptosis*
  • Astrocytes / metabolism
  • Astrocytes / pathology
  • Astrocytes / virology
  • Brain / metabolism
  • Brain / pathology
  • Brain / virology
  • Child, Preschool
  • Enterovirus A, Human / isolation & purification*
  • Enterovirus Infections / complications*
  • Enterovirus Infections / virology
  • Female
  • Humans
  • Infant
  • Interleukin-6 / metabolism*
  • Male
  • Mice
  • Mice, Inbred C57BL
  • Mice, Knockout
  • Neurodegenerative Diseases / epidemiology*
  • Neurodegenerative Diseases / metabolism
  • Neurodegenerative Diseases / virology
  • Toll-Like Receptor 7 / genetics
  • Toll-Like Receptor 7 / metabolism*

Substances

  • Interleukin-6
  • Toll-Like Receptor 7

Grants and funding

This work was supported by National Natural Science Foundation of China (81730061 and 31800147), National Health and Family Planning Commission of China (National Mega Project on Major Infectious Disease Prevention) (2017ZX10103005 and 2017ZX10202201), Guangdong Province “Pearl River Talent Plan” Innovation and Entrepreneurship Team Project (2017ZT07Y580), and Open Research Fund Program of the State Key Laboratory of Virology of China (2019KF001). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.