Sporadic ALS/MND: a global neurodegeneration with retroviral involvement?

HERV-W ENV transcription in B cells predicting symptomatic COVID-19 and risk for long COVID can express a full-length protein despite stop codon in mRNA from chromosome X via a ribosome readthrough

The human genome comprises 8% of endogenous retroviruses (HERVs). Though HERVS contribute to physiological functions, copies retained pathogenic potential. The HERV-W ENV protein was shown expressed in patients with worse COVID-19 symptoms and post-COVID syndrome. A significant detection of the mRNA encoding HERV-W ENV from patients with COVID-19 in B cells from RNAseq reads obtained from peripheral blond mononuclear cells. This data stratified with increased COVID-19 symptoms or with post-acute sequelae of COVID-19 (long COVID) after 3 months. The HERV-W ENV-U3R RNA was confirmed to display the best alignment with chromosome X ERVWE2 locus. However, a stop codon precluding its translation was re-addressed after recent understandings of ribosome readthrough mechanisms. Experimental results evidenced that this HERV gene can effectively express a full-length protein in the presence of molecules allowing translation via a readthrough mechanism at the ribosome level. Results not only confirm HERV-W ENV RNA origin in these patients but show for the first time how a defective HERV copy can be translated into a complete protein when specific factors make it possible at the ribosome level. The present proof of concept now requires further studies to identify the factors involved in this newly understood mechanism, following SARS-CoV-2 exposure.

Neuromuscular Complications of SARS-CoV-2 and Other Viral Infections

In this article we review complications to the peripheral nervous system that occur as a consequence of viral infections, with a special focus on complications of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). We discuss neuromuscular complications in three broad categories; the direct consequences of viral infection, autoimmune neuromuscular disorders provoked by viral infections, and chronic neurodegenerative conditions which have been associated with viral infections. We also include discussion of neuromuscular disorders that are treated by immunomodulatory therapies, and how this affects patient susceptibility in the current context of the coronavirus disease 2019 (COVID-19) pandemic. COVID-19 is associated with direct consequences to the peripheral nervous system via presumed direct viral injury (dysgeusia/anosmia, myalgias/rhabdomyolysis, and potentially mononeuritis multiplex) and autoimmunity (Guillain Barré syndrome and variants). It has important implications for people receiving immunomodulatory therapies who may be at greater risk of severe outcomes from COVID-19. Thus far, chronic post-COVID syndromes (a.k.a: long COVID) also include possible involvement of the neuromuscular system. Whether we may observe neuromuscular degenerative conditions in the longer term will be an important question to monitor in future studies.

A comparative study of motor neuron disease in HIV-infected and HIV-uninfected patients

BACKGROUND

This study is a descriptive review of the clinical and treatment outcome differences in HIV-infected patients with motor neuron syndrome (MNS) and HIV-uninfected patients with motor neuron disease (MND).

METHODS

A retrospective analysis of patients with MND/S was performed at Inkosi Albert Luthuli Central Hospital (IALCH), Durban, South Africa between 2003 and 2017.

RESULTS

One hundred and thirty six patients were included in the study, 101 (76%) were HIV-uninfected and 35 (26%) were HIV-infected. Ninety four percent of the HIV-infected cohort were <50 years, median 41, IQR (33-45), p < 0.001, had median ALS functional rating scale revised (ALSFRS-R) score of 28, IQR [24-30] and 40% of these patients on anti-retroviral therapy (ART) survived longer than 10 years. Ninety one percent of the HIV-uninfected cohort were >50 years, median 66, IQR(57-74), P < 0.001, had median ALSFRS-R score of 44 (IQR 42-45) and 93% died within 5 years of their illness.

CONCLUSION

HIV-infected MNS patients were younger, had more severe disease at presentation and survived longer if treated with ART with possible reversal of the disease process, compared to patients with MND.

Infectious agents and amyotrophic lateral sclerosis: another piece of the puzzle of motor neuron degeneration

Amyotrophic lateral sclerosis (ALS) is the most common neurodegenerative disease affecting motor neurons (MN). This fatal disease is characterized by progressive muscle wasting and lacks an effective treatment. ALS pathogenesis has not been elucidated yet. In a small proportion of ALS patients, the disease has a familial origin, related to mutations in specific genes, which directly result in MN degeneration. By contrast, the vast majority of cases are though to be sporadic, in which genes and environment interact leading to disease in genetically predisposed individuals. Lately, the role of the environment has gained relevance in this field and an extensive list of environmental conditions have been postulated to be involved in ALS. Among them, infectious agents, particularly viruses, have been suggested to play an important role in the pathogenesis of the disease. These agents could act by interacting with some crucial pathways in MN degeneration, such as gene processing, oxidative stress or neuroinflammation. In this article, we will review the main studies about the involvement of microorganisms in ALS, subsequently discussing their potential pathogenic effect and integrating them as another piece in the puzzle of ALS pathogenesis.

Cooccurrences of Putative Endogenous Retrovirus-Associated Diseases

At least 8% of the human genome is composed of endogenous retrovirus (ERV) sequences. ERVs play a role in placental morphogenesis and can sometimes protect the host against exogenous viruses. On the other hand, ERV reactivation has been found to be associated with different diseases, for example, multiple sclerosis (MS), schizophrenia, type 1 diabetes mellitus (T1D), or amyotrophic lateral sclerosis (ALS). Little is known about the cooccurrence of these diseases. If all these diseases are caused by ERV, antiretroviral therapy should perhaps also show some effects in the other diseases. Here, we summarize literature demonstrating that some ERV-associated diseases seem to appear together more often than expected, for example, MS and ALS, MS and T1D, MS and schizophrenia, or ALS and T1D. In contrast, some ERV-associated diseases seem to appear together less frequently than expected, for example, schizophrenia and T1D. Besides, some reports demonstrate amelioration of MS, ALS, or schizophrenia under antiretroviral therapy in human immunodeficiency virus-infected patients. If such results could be confirmed in larger studies, alternative therapy strategies for ERV-associated diseases like MS and schizophrenia might be possible.

Redox Imbalance and Viral Infections in Neurodegenerative Diseases

Reactive oxygen species (ROS) are essential molecules for many physiological functions and act as second messengers in a large variety of tissues. An imbalance in the production and elimination of ROS is associated with human diseases including neurodegenerative disorders. In the last years the notion that neurodegenerative diseases are accompanied by chronic viral infections, which may result in an increase of neurodegenerative diseases progression, emerged. It is known in literature that enhanced viral infection risk, observed during neurodegeneration, is partly due to the increase of ROS accumulation in brain cells. However, the molecular mechanisms of viral infection, occurring during the progression of neurodegeneration, remain unclear. In this review, we discuss the recent knowledge regarding the role of influenza, herpes simplex virus type-1, and retroviruses infection in ROS/RNS-mediated Parkinson's disease (PD), Alzheimer's disease (AD), and amyotrophic lateral sclerosis (ALS).

Amyotrophic lateral sclerosis presentation of a human T-lymphotropic virus type-1 myelopathy--insight into pathogenesis

A 41-year-old human T-lymphotropic virus type 1-positive woman developed a syndrome with upper and lower motor neuron signs sometime after bilateral vertebral artery dissections. Over 2 years, she developed a progressive myelopathy affecting predominantly the motor system. She had the picture of a 'person in a barrel' and died from complications. At autopsy, spinal cord revealed inflammatory infiltrates and extensive gliosis involving mainly the anterior horns. The vertebral arterial dissections may have permitted the entry of infected lymphocytes and macrophages, secreting cytokines and metalloproteinases, into the medulla progressing to the spinal cord. Few cases with pathological correlation have been reported.

Transient Reversal of HIV-Associated Motor Neuron Disease Following the Introduction of Highly Active Antiretroviral Therapy

Neurological diseases occur frequently in patients with human immunodeficiency virus (HIV) infection, and include a variety of neuromuscular disorders. On the other hand, only a few cases of motor neuron disease (MND) have been reported to date in HIV-positive patients, even though this neurological complication occurs with a 27-fold greater frequency in these subjects compared with the general population. A retroviral etiology for MND has long been hypothesized, and epidemiological and experimental data suggest a pathogenetic link between HIV infection and MND, because retroviral infections may cause motor neuron damage in both laboratory animals and humans, as a result of various pathways. Furthermore, the introduction of potent, protease inhibitor-based antiretroviral combinations has had a great impact on the natural history of HIV disease and produced a dramatic improvement in some patients with HIV-associated MND, but optimal treatment for this progressive neurological complication has not been well defined. A case of MND in a male HIV-infected patient with significant but transient reversal of neurological symptoms after the use of protease inhibitor-containing antiretroviral regimen is described.

Viruses and neurodegeneration

Neurodegenerative diseases (NDs) are chronic degenerative diseases of the central nervous system (CNS), which affect 37 million people worldwide. As the lifespan increases, the NDs are the fourth leading cause of death in the developed countries and becoming increasingly prevalent in developing countries. Despite considerable research, the underlying mechanisms remain poorly understood. Although the large majority of studies do not show support for the involvement of pathogenic aetiology in classical NDs, a number of emerging studies show support for possible association of viruses with classical neurodegenerative diseases in humans. Space does not permit for extensive details to be discussed here on non-viral-induced neurodegenerative diseases in humans, as they are well described in literature.Viruses induce alterations and degenerations of neurons both directly and indirectly. Their ability to attack the host immune system, regions of nervous tissue implies that they can interfere with the same pathways involved in classical NDs in humans. Supporting this, many similarities between classical NDs and virus-mediated neurodegeneration (non-classical) have been shown at the anatomic, sub-cellular, genomic and proteomic levels suggesting that viruses can explain neurodegenerative disorders mechanistically. The main objective of this review is to provide readers a detailed snapshot of similarities viral and non-viral neurodegenerative diseases share, so that mechanistic pathways of neurodegeneration in human NDs can be clearly understood. Viruses can guide us to unveil these pathways in human NDs. This will further stimulate the birth of new concepts in the biological research, which is needed for gaining deeper insights into the treatment of human NDs and delineate mechanisms underlying neurodegeneration.

No evidence of HIV pol gene in spinal cord tissues in sporadic ALS by real-time RT-PCR

An association of retroviruses and especially HIV has been reported in SALS, but CNS tissues have not been directly tested. To be valid, direct testing should be performed in light of the highly variable distribution of neuropathology from one patient to another and the degradable nature of RNA viruses. We aimed to seek direct evidence of retrovirus and especially HIV in SALS by real-time RT-PCR. We tested 20 SALS spinal cords in our repository specifically created for RNA preservation. We extracted RNA from anterior horns and surrounding tissue scrape from each sample and validated RNA quality. We indexed our search to neuropathologic degeneration and tested multiple areas in many of the nervous systems. We used real-time RT-PCR to a highly conserved region in the highly conserved pol gene and established the lowest limit of detection using a positive control. HIV-1 pol gene sequence was not detected in any of the 20 SALS nervous systems. Our assay was able to detect down to 60 viral copy numbers. In conclusion, we could not find direct evidence of retroviral/HIV activity in SALS CNS to support a relationship. However, our method could miss novel retroviruses with non-homology in the pol gene.

Detection of reverse transcriptase activity in the serum of patients with motor neurone disease

The recognition that both human and murine retroviruses can cause motor neurone disease-like syndromes has raised the possibility that a retrovirus may be involved in the aetiology of motor neurone disease. This possibility was explored by looking for evidence of reverse transcriptase in the serum of motor neurone disease patients. Sera from 56 patients with motor neurone disease and 58 controls were tested by the product-enhanced reverse transcriptase assay, a technique that is approximately a million fold more sensitive than conventional reverse transcriptase assays and capable of detecting very low numbers of retroviral particles. Cell-free reverse transcriptase activity was detected in the serum of 33 of the 56 motor neurone disease patients (59%) but in only 3 of the controls (P < 0.00001). The reverse transcriptase activity was detectable in the presence of a large excess of an effective inhibitor of human cellular DNA polymerases and was therefore tentatively considered to be compatible with a retroviral origin. The reverse transcriptase activity, however, was not found to be due to the presence of known human exogenous retroviruses including HIV-1, HIV-2, HTLV-I, HTLV-II, HRV-5 or human foamy virus, as assessed by PCR-based assays. Further investigations will be required to determine the source of the reverse transcriptase activity observed in these motor neurone disease patient sera.

Lack of evidence for HTLV tax-rex DNA in motor neurone disease

It has recently been claimed (Ferrante et al., 1995. HTLV tax-rex DNA and antibodies in idiopathic amyotrophic lateral sclerosis. J. Neurol. Sci. 129 (Suppl.) 140-144) that human T-lymphotropic virus (HTLV) tax-rex sequences are detectable in the peripheral blood mononuclear cells (PBMCs) of 40% of patients with motor neurone disease (MND). In an attempt to confirm this we employed a highly sensitive 'nested' polymerase chain reaction (PCR) assay, capable of detecting single molecules of HTLV proviral DNA, to look for tax-rex sequences in the PBMCs of 43 patients with MND. We were unable to detect the presence of HTLV tax-rex in any of 43 MND patients tested, using three different PCR primer sets under both high and low stringency conditions. Using the same DNA samples we were able to detect the presence of the single-copy pyruvate dehydrogenase gene, thus demonstrating that the extracted DNA was indeed amplifiable by PCR. To further exclude the possibility that the extracted DNA samples contained unrecognised inhibitory factors we conducted spiking experiments with trace amounts (approximately 10 copies) of HTLV proviral DNA. Spiked samples yielded PCR products of the expected size. We are therefore unable to confirm the presence of HTLV tax-rex sequences in this disease.