Research ArticleALS

Human endogenous retrovirus-K contributes to motor neuron disease

Science Translational Medicine  30 Sep 2015:
Vol. 7, Issue 307, pp. 307ra153
DOI: 10.1126/scitranslmed.aac8201

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A viral endgame

A large number of viral sequences are present in the human genome but remain silent. However, under pathological conditions, these viruses can get expressed. Li et al. now report that one such virus, human endogenous retrovirus-K, is expressed in neurons of a subpopulation of patients with amyotrophic lateral sclerosis (ALS), a progressive neurodegenerative disease. The envelope protein of this virus causes degeneration of neurons, and transgenic animals expressing this protein develop an ALS-like syndrome caused by nucleolar dysfunction in motor neurons. Reactivation of the virus is regulated by the transcription factor TDP-43. Thus, therapeutic approaches against this virus could potentially alter the course of the disease.

Abstract

The role of human endogenous retroviruses (HERVs) in disease pathogenesis is unclear. We show that HERV-K is activated in a subpopulation of patients with sporadic amyotrophic lateral sclerosis (ALS) and that its envelope (env) protein may contribute to neurodegeneration. The virus was expressed in cortical and spinal neurons of ALS patients, but not in neurons from control healthy individuals. Expression of HERV-K or its env protein in human neurons caused retraction and beading of neurites. Transgenic animals expressing the env gene developed progressive motor dysfunction accompanied by selective loss of volume of the motor cortex, decreased synaptic activity in pyramidal neurons, dendritic spine abnormalities, nucleolar dysfunction, and DNA damage. Injury to anterior horn cells in the spinal cord was manifested by muscle atrophy and pathological changes consistent with nerve fiber denervation and reinnervation. Expression of HERV-K was regulated by TAR (trans-activation responsive) DNA binding protein 43, which binds to the long terminal repeat region of the virus. Thus, HERV-K expression within neurons of patients with ALS may contribute to neurodegeneration and disease pathogenesis.

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