Expression of endogenous retroviruses in blood mononuclear cells and brain tissue from multiple sclerosis patients

The association between human endogenous retroviruses and multiple sclerosis: A systematic review and meta-analysis

BACKGROUND

The interaction between genetic and environmental factors is crucial to multiple sclerosis (MS) pathogenesis. Human Endogenous Retroviruses (HERVs) are endogenous viral elements of the human genome whose expression is associated with MS.

OBJECTIVE

To perform a systematic review and meta-analysis and to assess qualitative and quantitative evidence on the expression of HERV families in MS patients.

METHODS

Medline, Embase and the Cochrane Library were searched for published studies on the association of HERVs and MS. Meta-analysis was performed on the HERV-W family. Odds Ratio (OR) and 95% confidence interval (CI) were calculated for association.

RESULTS

43 reports were extracted (25 related to HERV-W, 13 to HERV-H, 9 to HERV-K, 5 to HRES-1 and 1 to HER-15 family). The analysis showed an association between expression of all HERV families and MS. For HERV-W, adequate data was available for meta-analysis. Results from meta-analyses of HERV-W were OR = 22.66 (95%CI 6.32 to 81.20) from 4 studies investigating MSRV/HERV-W (MS-associated retrovirus) envelope mRNA in peripheral blood mononuclear cells, OR = 44.11 (95%CI 12.95 to 150.30) from 6 studies of MSRV/HERV-W polymerase mRNA in serum/plasma and OR = 6.00 (95%CI 3.35 to 10.74) from 4 studies of MSRV/HERV-W polymerase mRNA in CSF.

CONCLUSIONS

This systematic review and meta-analysis shows an association between expression of HERVs, and in particular the HERV-W family, and MS.

[New therapeutic strategies for remyelination in multiple sclerosis]

Multiple sclerosis (MS) is characterized by oligodendrocyte death and myelin sheath destruction of the central nervous system (CNS) in response to autoinflammatory processes. Besides demyelination axonal degeneration constitutes the second histopathological hallmark of this disease. A large number of immunomodulatory and targeted immunosuppression treatments have been approved for relapsing remitting (RR) MS where they effectively reduce relapse rates; however, currently no treatment options exist to repair injured axonal tracts or myelin damage that accumulates over time particularly in progressive MS. In light of the growing available therapeutic repertoire of highly potent immunomodulatory medications there is an increasing interest in the development of therapies aimed at neutralizing neurodegenerative damage. Endogenous remyelination processes occur mainly as a result of oligodendrocyte precursor cell (OPC) activation, recruitment and maturation; however, this repair activity appears to be limited and increasingly fails during disease progression. Based on these observations OPCs are considered as promising targets for the regenerative treatment of all stages of MS. This article presents an overview of approved medications with a suggested role in regeneration, regenerative treatments that are currently being tested in clinical trials, as well as promising future therapeutic approaches derived from basic glial cell research aiming at the promotion of the endogenous repair activity of the brain.

Promoting remyelination in multiple sclerosis: current drugs and future prospects

Myelin destruction due to inflammatory oligodendrocyte cell damage or death in conjunction with axonal degeneration are among the major histopathological hallmarks of multiple sclerosis (MS). The majority of available immunomodulatory medications for MS are approved for relapsing-remitting (RR) MS, for which they reduce relapse rate, MRI measures of inflammation, and the accumulation of disability. These medications are, however, of little benefit during progressive MS where axonal degeneration following demyelination outweighs inflammation. This has sparked great interest in the development of new remyelination therapies aimed at reversing the neurodegenerative damage observed in this disease. Remyelination as a result of oligodendrocyte production from oligodendrocyte precursor cells (OPCs) is considered a promising potential target for the treatment of all stages of MS. In this review we present an overview of a) approved medications (some of them FDA-and EMA-approved for other diseases) with a proposed role in regeneration, b) regenerative treatments under investigation in clinical trials, and c) promising future therapeutic approaches aiming specifically at facilitating endogenous repair.

Tracing environmental markers of autoimmunity: introducing the infectome

We recently introduced the concept of the infectome as a means of studying all infectious factors which contribute to the development of autoimmune disease. It forms the infectious part of the exposome, which collates all environmental factors contributing to the development of disease and studies the sum total of burden which leads to the loss of adaptive mechanisms in the body. These studies complement genome-wide association studies, which establish the genetic predisposition to disease. The infectome is a component which spans the whole life and may begin at the earliest stages right up to the time when the first symptoms manifest, and may thus contribute to the understanding of the pathogenesis of autoimmunity at the prodromal/asymptomatic stages. We provide practical examples and research tools as to how we can investigate disease-specific infectomes, using laboratory approaches employed from projects studying the “immunome” and “microbiome”. It is envisioned that an understanding of the infectome and the environmental factors that affect it will allow for earlier patient-specific intervention by clinicians, through the possible treatment of infectious agents as well as other compounding factors, and hence slowing or preventing disease development.

Infectome: a platform to trace infectious triggers of autoimmunity

The "exposome" is a term recently used to describe all environmental factors, both exogenous and endogenous, which we are exposed to in a lifetime. It represents an important tool in the study of autoimmunity, complementing classical immunological research tools and cutting-edge genome wide association studies (GWAS). Recently, environmental wide association studies (EWAS) investigated the effect of environment in the development of diseases. Environmental triggers are largely subdivided into infectious and non-infectious agents. In this review, we introduce the concept of the "infectome", which is the part of the exposome referring to the collection of an individual's exposures to infectious agents. The infectome directly relates to geoepidemiological, serological and molecular evidence of the co-occurrence of several infectious agents associated with autoimmune diseases that may provide hints for the triggering factors responsible for the pathogenesis of autoimmunity. We discuss the implications that the investigation of the infectome may have for the understanding of microbial/host interactions in autoimmune diseases with long, pre-clinical phases. It may also contribute to the concept of the human body as a superorganism where the microbiome is part of the whole organism, as can be seen with mitochondria which existed as microbes prior to becoming organelles in eukaryotic cells of multicellular organisms over time. A similar argument can now be made in regard to normal intestinal flora, living in symbiosis within the host. We also provide practical examples as to how we can characterise and measure the totality of a disease-specific infectome, based on the experimental approaches employed from the "immunome" and "microbiome" projects.

Infectious causes of multiple sclerosis

Multiple sclerosis (MS) is a serious chronic neurological disorder in which demyelination and inflammation occur in the white matter of the CNS. The findings of many epidemiological studies and a discordance of MS in monozygotic twins suggest that the disorder is acquired. The most likely cause is a virus because more than 90% of patients with MS have high concentrations of IgG, manifest as oligoclonal bands, in the brain and CSF. Most chronic inflammatory CNS disorders are infectious. More indirect evidence that MS is caused by a virus is the association of several viruses with demyelinating encephalomyelitis in human beings, and the induction of demyelination in animals infected with viruses in research. Nevertheless, no virus has been isolated from the brains of patients who had MS. Molecular analysis of IgG gene specificity in the brain and CSF of those with MS has shown features of an antigen-driven response: clonal amplification and extensive somatic mutations. A viral antigen against which the IgG in MS brain and CSF is directed might be identified.

Association of human endogenous retroviruses with multiple sclerosis and possible interactions with herpes viruses

The hypothesis that human endogenous retroviruses (HERVs) play a role in autoimmune diseases is subject to increasing attention. HERVs represent both putative susceptibility genes and putative pathogenic viruses in the immune-mediated neurological disease multiple sclerosis (MS). Gammaretroviral HERV sequences are found in reverse transcriptase-positive virions produced by cultured mononuclear cells from MS patients, and they have been isolated from MS samples of plasma, serum and CSF, and characterised to some extent at the nucleotide, protein/enzyme, virion and immunogenic level. Two types of sequences, HERV-H and HERV-W, have been reported. No known HERV-H or HERV-W copy contains complete ORFs in all prerequisite genes, although several copies have coding potential, and several such sequences are specifically activated in MS, apparently resulting in the production of complete, competent virions. Increased antibody reactivity to specific Gammaretroviral HERV epitopes is found in MS serum and CSF, and cell-mediated immune responses have also been reported. Further, HERV-encoded proteins can have neuropathogenic effects. The activating factor(s) in the process resulting in protein or virion production may be members of the Herpesviridae. Several herpes viruses, such as HSV-1, VZV, EBV and HHV-6, have been associated with MS pathogenesis, and retroviruses and herpes viruses have complex interactions. The current understanding of HERVs, and specifically the investigations of HERV activation and expression in MS are the major subjects of this review, which also proposes to synergise the herpes and HERV findings, and presents several possible pathogenic mechanisms for HERVs in MS.

Demystified. Human endogenous retroviruses

Human endogenous retroviruses (HERVs) are a family of viruses within our genome with similarities to present day exogenous retroviruses. HERVs have been inherited by successive generations and it is possible that some have conferred biological benefits. However, several HERVs have been implicated in certain cancers and autoimmune diseases. This article demystifies these retroviruses by providing an insight into HERVs, their means of classification, and a synopsis of HERVs implicated in cancer and autoimmunity. Furthermore, the biological roles of HERVs are explored.

Molecular characterization of a MSRV-like sequence identified by RDA from monozygotic twin pairs discordant for schizophrenia

Retroviral-related amplicons were used in modified RDA to identify four sequences from affected members of three pairs of monozygotic twins discordant for schizophrenia. One sequence (schizophrenia associated retrovirus, SZRV-1, GenBank Accession No. AF135487) is characterized here. It is similar to two known sequences of retroviral origin: multiple sclerosis-associated retrovirus, MSRV (GenBank Accession No. AF009668), and ERV-9 (GenBank Accession No. S77575). It is present in multiple copies in the human genome and has been localized to six different chromosomal sites. A zooblot shows that this multicopy sequence is predominant in the primate lineage and present in rhesus monkeys and humans. SZRV-1 is expressed as a 9-kb RNA band in the placenta. This could offer support to the hypothesis that retroviral sequences transposing during fetal growth may alter neurodevelopmental genes and cause diseases, although its direct involvement in the causation of schizophrenia remains to be established.

[Endogenous retroviral sequences analogous to that of the new retrovirus MSRV associated with multiple sclerosis (part 1)]

Multiple sclerosis (MS) is still of unknown origin and may involve autoimmune, genetic and viral components in a pathogenic sequence whose relative importance is yet to be determined. A peptide, isolated from the cerebrospinal fluid of MS patients, is similar to a fragment of the pol protein reverse transcriptase (RT) of the newly reported MSRV retrovirus. The 700 amino acid sequence of MSRV-RT is closely related to a novel human retroviral-like sequences. We also identified a gag-like sequence upstream of this human genomic RT-like sequence, which allowed us to identify altogether 4,000 nucleotides, possibly coding for an endogenous retroviruses. Homologous sequences found in other locations in the human genome seem to characterize a new family of retroviral endogenous sequences, which may be of relevance to multiple sclerosis.