Perspectives on the role of endogenous human retroviruses in autoimmune diseases

The Roles of Human Endogenous Retroviruses (HERVs) in Inflammation

Human endogenous retroviruses (HERVs) are ancient, currently inactive, and non-infectious due to recombination, deletions, and mutations in the host genome. However, HERV-derived elements are involved in physiological phenomena including inflammatory response. In recent studies, HERV-derived elements were involved directly in various inflammatory diseases including autoimmune diseases such as rheumatoid arthritis (RA), multiple sclerosis, amyotrophic lateral sclerosis (ALS), and Sjogren’s syndrome. Regarding the involvement of HERV-derived elements in inflammation, two possible mechanisms have been proposed. First, HERV-derived elements cause nonspecific innate immune processes. Second, HERV-derived RNA or proteins might stimulate selective signaling mechanisms. However, it is unknown how silent HERV elements are activated in the inflammatory response and what factors and signaling mechanisms are involved with HERV-derived elements. In this review, we introduce HERV-related autoimmune diseases and propose the possible action mechanisms of HERV-derived elements in the inflammatory response at the molecular level.

Human Endogenous Retroviruses: Residues of Ancient Times Are Differentially Expressed in Crohn's Disease

Background

Eight percent of the human genome consists of human endogenous retroviruses (HERV). These genetic elements are remnants of ancient retroviral germ-line infections. Altered HERV expression is associated with several chronic inflammatory diseases. A physiological role of the HERV-derived proteins syncytin-1 and -2 has been described for the integrity of the human placental cell layer in terms of maintaining feto-maternal tolerance. The aim of this project was to investigate HERV expression in Crohn's disease (CD) with a further focus on syncytins in the gut.

Material and Methods

Seventy-four ileal and colonic tissue samples of CD patients and healthy controls have been investigated for mRNA expression of major HERV groups by a comprehensive microarray screening. The most prominent differences have been validated by qRT-PCR. Immunohistochemistry (IHC), Western Blot (WB) and qRT-PCR were performed for syncytin-1 and -2.

Results

HERV microarray screening revealed a distinct expression profile in ileal and colonic tissue, as well as differential expression in CD compared to healthy controls. qRT-PCR validated differential expression of at least 3 HERV-groups in CD. qRT-PCR, IHC and WB showed a tissue-dependent diminished epithelial expression of syncytins in inflamed CD.

Conclusion

For the first time, HERV expression has been comprehensively studied in the gut. Between CD and healthy controls we could show a tissue dependent differential HERV expression profile. Notably, we could show that syncytin-1 and -2 are expressed in the epithelial layer in ileal and colonic tissue samples, whereas their diminished tissue-dependent expression in inflamed CD might modulate inflammatory processes at the gut barrier.

Impact of sex disparities on the clinical manifestations in patients with systemic lupus erythematosus: A systematic review and meta-analysis

BACKGROUND

Systemic lupus erythematosus (SLE) is a chronic autoimmune multiorgan disorder of unknown etiology. It affects both men and women, but with different disease manifestations of differing disease severity and in varying proportion, with a female predominance of approximately 90%. There have been numerous studies addressing this issue, especially its implications in relation to optimal sex-tailored treatment and improvement of survival rate; however, further research is warranted. A meta-analysis of studies was performed to compare the impact of sex on the clinical outcomes of SLE in different populations.

METHODS

A literature search of the MEDLINE/PubMed and EMBASE databases (until January 2016) was conducted to identify relevant articles. Clinical manifestations reported in these patients were considered as endpoints for this meta-analysis. Two independent reviewers determined eligibility criteria. A fixed-effect model has been used where a small heterogeneity was observed, or else, a random-effect model has been used among the studies. Odd ratio (OR) with 95% confidence interval (CI) was used to express the pooled effect on dichotomous variables, and the pooled analyses were performed with RevMan 5.3.

RESULTS

Sixteen studies consisting of a total of 11,934 SLE patients (10,331 females and 1603 males) have been included in this meta-analysis. The average female-to-male ratio of all the included studies is around 9.3:1. Several statistically significant differences were found: alopecia, photosensitivity, and oral ulcers were significantly higher in female patients (OR 0.36, 95% CI 0.29-0.46, P < 0.00001; OR 0.72, 95% CI 0.63-0.83, P < 0.00001; and OR 0.70, 95% CI 0.60-0.82, P < 0.00001, respectively). Malar rash was significantly higher in female patients (OR 0.68, 95% CI 0.53-0.88, P = 0.003), and arthritis was significantly lower in male patients (OR 0.72, 95% CI 1.25-1.84, P < 0.00001). However, serositis and pleurisies were significantly higher in female patients (OR 1.52, 95% CI 1.25-1.84 P < 0.0001; and OR 1.26, 95% CI 1.07-1.48, P = 0.006, respectively). Renal involvement was higher in male patients (OR 1.51, 95% CI 1.31-1.75, P < 0.00001).

CONCLUSION

The results of this meta-analysis suggest that alopecia, photosensitivity, oral ulcers, arthritis, malar rash, lupus anticoagulant level, and low level of C3 were significantly higher in female lupus patients, whereas renal involvement, serositis and pleurisies, thrombocytopenia, and anti-double stranded deoxyribonucleic acid level were predominant in male patients.

Role of the human endogenous retrovirus HERV-K18 in autoimmune disease susceptibility: study in the Spanish population and meta-analysis

Background

Human endogenous retroviruses (HERVs) are genomic sequences that resulted from ancestral germ-line infections by exogenous retroviruses and therefore are transmitted in a Mendelian fashion. Increased HERV expression and antibodies to HERV antigens have been found in various autoimmune diseases. HERV-K18 in chromosome 1 was previously associated with type one diabetes and multiple sclerosis (MS). The etiology of these complex conditions has not been completely elucidated even after the powerful genome wide association studies (GWAS) performed. Nonetheless, this approach does not scrutinize the repetitive sequences within the genome, and part of the missing heritability could lie behind these sequences. We aimed at evaluating the role of HERV-K18 in chromosome 1 on autoimmune disease susceptibility.

Methods

Two HERV-K18 SNPs (97Y/C and 154W/Stop substitutions) conforming three haplotypes were genotyped in Spanish cohorts of multiple sclerosis (n = 942), rheumatoid arthritis (n = 462) and ethnically matched controls (n = 601). Our findings were pooled in a meta-analysis including 5312 autoimmune patients and 4032 controls.

Results

Significant associations of both HERV-K18 polymorphisms in chromosome 1 with MS patients stratified by HLA-DRB1*15∶01 were observed [97Y/C p = 0.02; OR (95% CI) = 1.5 (1.04–2.17) and 154W/Stop: p = 0.001; OR (95% CI) = 1.6 (1.19–2.16)]. Combined meta-analysis of the previously published association studies of HERV-K18 with different autoimmune diseases, together with data derived from Spanish cohorts, yielded a significant association of the HERV-K18.3 haplotype [97Y–154W: p_M-H = 0.0008; OR_M-H (95% CI) = 1.22 (1.09–1.38)].

Conclusion

Association of the HERV-K18.3 haplotype in chromosome 1 with autoimmune-disease susceptibility was confirmed through meta-analysis.

The distribution of human endogenous retrovirus K-113 in health and autoimmune diseases in Poland

OBJECTIVE

During the evolution of the human genome, a number of retroviral integrations have occurred creating a group of human endogenous retroviruses (HERVs). As of now several studies have pointed to the association of HERVs with certain autoimmune diseases such as RA, SLE, multiple sclerosis (MS) and SS as well as various neoplasms. In this study, we investigated the prevalence of HERV-K113 in patients with RA, SLE and in healthy subjects in the Polish population.

METHODS

Genomic DNA samples from 155 RA patients, 139 SLE patients and 261 newborns (as controls) were tested for the presence of the HERV-K113 allele using PCR. Each individual's DNA was genotyped for null, homozygous or heterozygous insertion of HERV-K113.

RESULTS

Our data revealed statistically significant differences in the insertion frequencies of HERV-K113 between the groups of RA and SLE patients vs healthy controls (provirus DNA was found in 14.19, 15.11 and 8.05% of individuals, respectively). No homozygous individuals for the K113 allele were found in each of the groups. There was no evidence for HERV-K113 association with clinical features in either group.

CONCLUSION

Our study-the first such performed for the Polish population-provides a consistent observation with previous reports on the genetic association of HERV-K113 integrations in autoimmune disorders. Here, we found that the prevalence of insertionally polymorphic HERV-K113 was significantly increased in Polish patients with SLE and RA.

The human microbiome in multiple sclerosis: pathogenic or protective constituents?

The human microbiome is comprised of commensal and pathogenic microorganisms, which exert diverse effects in close proximity to the site of intection as well as in remote tissues through immune-mediated mechanisms. Multiple infectious agents have been implicated in the pathogenesis of multiple sclerosis (MS) with variable findings depending on the agent, techniques, and disease phenotype. Herein, the contributions of individual infectious agents to MS and their effects on the immune and nervous systems are reviewed, focusing on herpes viruses, coronaviruses, retroviruses, and synchronic infections. While infectious agents are often assumed to be pathogenic, their effects might also be beneficial to the host in the long-term, depending on age and the type of immunogen/pathogen exposure, as proposed by the hygiene hypothesis. The human microbiome has potential impact on future diagnostic and therapeutic issues in MS.

Human endogenous retroviruses and multiple sclerosis: innocent bystanders or disease determinants?

Human endogenous retroviruses (HERVs) constitute 5–8% of human genomic DNA and are replication incompetent despite expression of individual HERV genes from different chromosomal loci depending on the specific tissue. Several HERV genes have been detected as transcripts and proteins in the central nervous system, frequently in the context of neuroinflammation. The HERV-W family has received substantial attention in large part because of associations with diverse syndromes including multiple sclerosis (MS) and several psychiatric disorders. A HERV-W-related retroelement, multiple sclerosis retrovirus (MSRV), has been reported in MS patients to be both a biomarker as well as an effector of aberrant immune responses. HERV-H and HERV-K have also been implicated in MS and other neurological diseases but await delineation of their contributions to disease. The HERV-W envelope-encoded glycosylated protein, syncytin-1, is encoded by chromosome 7q21 and exhibits increased glial expression within MS lesions. Overexpression of syncytin-1 in glia induces endoplasmic reticulum stress leading to neuroinflammation and the induction of free radicals, which damage proximate cells. Syncytin-1's receptor, ASCT1 is a neutral amino acid transporter expressed on glia and is suppressed in white matter of MS patients. Of interest, antioxidants ameliorate syncytin-1's neuropathogenic effects raising the possibility of using these agents as therapeutics for neuroinflammatory diseases. Given the multiple insertion sites of HERV genes as complete and incomplete open reading frames, together with their differing capacity to be expressed and the complexities of individual HERVs as both disease markers and bioactive effectors, HERV biology is a compelling area for understanding neuropathogenic mechanisms and developing new therapeutic strategies.

Expression of syncytin in leukemia and lymphoma cells

Syncytin is a placenta-specific protein and generally believed to play a pivotal role in syncytiotrophoblast morphogenesis. In this study, transcripts of this gene were quantified by real-time RT-PCR and the translated products were measured by an indirect immunofluorescence assay. Results showed that syncytin was found to be expressed in all nine leukemia and lymphoma cell lines studied albeit at different levels and in 43 peripheral blood samples of 57 leukemia or lymphoma patients. Neither the transcripts nor the translated syncytin was detected in blood samples of normal individuals. In conclusion, peripheral blood syncytin may serve as a marker for leukemia and lymphoma.

Increase in human endogenous retrovirus HERV-K (HML-2) viral load in active rheumatoid arthritis

To study the viral loads of human endogenous retrovirus HERV-K (HML-2) type 1 and type 2 in rheumatoid arthritis (RA), we measured the viral loads of HERV-K (HML-2) type 1 and type 2 using nucleic acid sequence-based amplification (NASBA) technology. We analyzed plasma samples from RA patients (n = 79) and healthy volunteers (HV, n = 46) and synovial fluid samples from RA (n = 10) and osteoarthritis (OA, n = 10) patients. HERV-K type 1 and type 2 viruses were detected and quantified for the majority of plasma and synovial fluid samples from RA patients. HERV-K type 1 and type 2 viral loads were significantly elevated in RA patients compared with HV in plasma (P < 0.0001) and from RA patients compared with OA patients in synovial fluid (type 1: P = 0.0007; type 2: P = 0.023). Moreover, an association was observed between the HERV-K type 1 viral load in plasma and the disease activity in RA patients (RA patients with low activity versus high activity P = 0.0129; RA patients with intermediate activity versus high activity P = 0.037). Our findings showed that HERV-K (HML-2) viral load can be detected in plasma samples from RA patients, with higher levels observed for those with active disease. There was an association of HERV-K type 1 levels with the disease activity.

Human RNA "rumor" viruses: the search for novel human retroviruses in chronic disease

Retroviruses are an important group of pathogens that cause a variety of diseases in humans and animals. Four human retroviruses are currently known, including human immunodeficiency virus type 1, which causes AIDS, and human T-lymphotropic virus type 1, which causes cancer and inflammatory disease. For many years, there have been sporadic reports of additional human retroviral infections, particularly in cancer and other chronic diseases. Unfortunately, many of these putative viruses remain unproven and controversial, and some retrovirologists have dismissed them as merely "human rumor viruses." Work in this field was last reviewed in depth in 1984, and since then, the molecular techniques available for identifying and characterizing retroviruses have improved enormously in sensitivity. The advent of PCR in particular has dramatically enhanced our ability to detect novel viral sequences in human tissues. However, DNA amplification techniques have also increased the potential for false-positive detection due to contamination. In addition, the presence of many families of human endogenous retroviruses (HERVs) within our DNA can obstruct attempts to identify and validate novel human retroviruses. Here, we aim to bring together the data on "novel" retroviral infections in humans by critically examining the evidence for those putative viruses that have been linked with disease and the likelihood that they represent genuine human infections. We provide a background to the field and a discussion of potential confounding factors along with some technical guidelines. In addition, some of the difficulties associated with obtaining formal proof of causation for common or ubiquitous agents such as HERVs are discussed.

Role of endogenous retroviruses in autoimmune diseases

Molecular epidemiologic proof that HERVs and other retroelements are involved in autoimmunity or other disorders is complicated by their large numbers in the human genome. As discussed, most HERVs are no longer functional or active because of the accumulation of mutations, frameshifts, and deletions. Detection or quantification of HERV transcripts that may be pathologically involved in a particular autoimmune disease thus is often compromised by the presence in great excess of related, but nonfunctional, RNA. This phenomenon should not deter active work in the field, although it will require development of improved methods to discriminate accurately between closely related RNA transcripts. Development of improved immunologic methods to precisely identify epitopes on autoantigens or rare self-reactive T-cell clones may further implicate HERVs and the other repetitive elements in regulation of the immune system in health and disease.

Expression of DNMT-1 in patients with atopic dermatitis

DNA methylation is known to play an important role in gene transcription and alterations of methylation that contribute to the development of certain disorders such as cancer, immunodeficiency, and autoimmune diseases. We investigated the DNA methylation profiles in patients with atopic dermatitis (AD). Messenger RNA (mRNA) levels for DNA methyltransferase-1 (DNMT-1) in peripheral blood mononuclear cells (PBMC) were examined using a real-time quantitative polymerase chain reaction method. The levels of DNMT-1 mRNA were significantly lower in PBMC from the AD patients who had higher serum IgE levels compared with normal controls. Our observations suggest that suppression of DNMT-1 might be related to the pathogenesis of AD, especially in whom serum IgE level is high. This is the first report of DNMT-1 expression in AD patients.

Endogenous superantigens shape response to exogenous superantigens

Endogenous superantigen-mediated thymic negative selection resulted in a paucity of mature T cells bearing T-cell receptor (TCR) Vbeta8 in the periphery. Consequently, the magnitude of immune response to exogenous superantigen staphylococcal enterotoxin B, which activates TCR Vbeta8(+) T cells, was significantly reduced and conferred protection from superantigen-induced mortality.

Human endogenous retrovirus expression profiles in samples from brains of patients with schizophrenia and bipolar disorders

The detection and identification of retroviral transcripts in brain samples, cerebrospinal fluid, and plasma of individuals with recent-onset schizophrenia and schizoaffective disorders suggest that activation or upregulation of distinct human endogenous retroviruses (HERVs) may play a role in the etiopathogenesis of neuropsychiatric diseases. To test this hypothesis, we performed a comprehensive microarray-based analysis of HERV transcriptional activity in human brains. We investigated 50 representative members of 20 HERV families in a total of 215 brain samples derived from individuals with schizophrenia or bipolar disorders and matched controls. A characteristic brain-specific retroviral activity profile was found that consists of members of the class I families HERV-E, HERV-F, and ERV9 and members of HERV-K taxa. In addition to these constitutively expressed HERVs, a number of differentially active HERV elements were identified in all brain samples independent of the disease pattern that may reflect differences in the genetic background of the tested individuals. Only a subgroup of the HML-2 family (HERV-K10) was significantly overrepresented in both bipolar-disorder- and schizophrenia-associated samples compared to healthy brains, suggesting a potential association with disease. Real-time PCR analysis of HERV env transcripts with coding capacity potentially involved in neuroinflammatory conditions revealed that env expression of HERV-W, HERV-FRD, and HML-2 remains unaffected regardless of the clinical picture. Our data suggest that HERV transcription in brains is weakly correlated with schizophrenia and related diseases but may be influenced by the individual genetic background, brain-infiltrating immune cells, or medical treatment.

The role of human endogenous retroviruses in trophoblast differentiation and placental development

A major portion of the human genome appears to be of retroviral origin. These endogenous retroviral elements are expressed in a variety of normal tissues and during disease states, such as autoimmune and malignant conditions. Recently, potential roles have been described for endogenous retroviral envelope proteins in normal differentiation of human villous cytotrophoblast into syncytiotrophoblast. This article provides a brief critical review of the current state of knowledge concerning the expression of the env regions of three endogenous retroviral elements: ERV-3, HERV-W, and HERV-FRD. A testable model of villous cytotrophoblast differentiation is constructed, in which a complementary expression of endogenous retroviral envelope proteins initiates hCG production, decreased cell proliferation, and intercellular fusion.

Expression and functions of human endogenous retroviruses in the placenta: an update

The placenta is unique amongst normal tissues in transcribing many different human endogenous retrovirus (HERV) families at high levels and this has led to the suggestion that HERVs may fulfil important functions in reproduction. This review discusses our current knowledge of the placental expression of HERVs, in particular the envelope proteins of ERV3 and HERV-W which may have critical roles in placental function.

[Envelope capture by retroviruses]

Retroelement transposition is a major source of diversity in genome evolution. Among the retrotransposable elements, the retroviruses are distinct in that their "transposition" extends from their initial host cells to neighboring cells and organisms. A determining step in the conversion of a retrotransposable element into an infectious retrovirus is the acquisition of an envelope glycoprotein, designated Env. Here, we review some examples of envelope "capture" by mammal retroviruses and provide evidence for such a mechanism by HTLV. This phenomenon may explain the notable conservation of env genes observed between phylogenetically distant retroviruses. Elucidation of these recombination processes should help to clarify retroviral phylogeny, better understand retroviral pathogenesis, and may lead to the identification of new retroelements.

Possible mechanisms of gender bias in SLE: a new hypothesis involving a comparison of SLE with atopy

The prevalence of systemic lupus erythematosus (SLE) is far higher in females than in males, and numerous investigations of this gender bias have been performed from several perspectives. Sex hormones, particularly estrogens, may be significant in causing the gender discrepancy. This article discusses the possible importance of estrogens in regulating the expression of and responsivity to autoantigens in SLE and in atopic disorders, which are associated with hyperreactivity to exogenous antigens. Estrogens seem to play an important role in the overexpression of endogenous autoantigens, such as human endogenous retroviruses (HERV), and this may be related to the existence of a gender bias in the incidence of SLE but not atopy.

Immune abnormalities induced by human endogenous retroviral peptides: with reference to the pathogenesis of systemic lupus erythematosus

P15E is a specific sequence among the envelope gene (env)-encoded transmembrane proteins of exogenous and endogenous retroviruses. A synthetic peptide (CKS- 17) that shows homology to this p15E region in several species of retrovirus is known to induce immune abnormalities. In this study, we examined the effect of a synthetic peptide derived from a region of human endogenous retrovirus (HERV) clone 4-1 (lambda4 - 1) similar to sequences of CKS-17 on the induction of systemic lupus erythematosus (SLE)-related immune abnormalities. Our results indicated that this peptide could induce T-cell activation and anergy in normal peripheral blood mononuclear cells, and the peptide could also promote the production of interleukins IL-6 and IL-16. These phenomena are representative immune abnormalities observed in SLE patients. Thus, our findings support the possibility that HERV acts as a pathogen in human SLE.

Endocrine aspects of cancer gene therapy

The field of cancer gene therapy is in continuous expansion, and technology is quickly moving ahead as far as gene targeting and regulation of gene expression are concerned. This review focuses on the endocrine aspects of gene therapy, including the possibility to exploit hormone and hormone receptor functions for regulating therapeutic gene expression, the use of endocrine-specific genes as new therapeutic tools, the effects of viral vector delivery and transgene expression on the endocrine system, and the endocrine response to viral vector delivery. Present ethical concerns of gene therapy and the risk of germ cell transduction are also discussed, along with potential lines of innovation to improve cell and gene targeting.

Emergence of vertebrate retroviruses and envelope capture

Retroviruses are members of the superfamily of retroelements, mobile genetic elements that transpose via an RNA intermediate. However, retroviruses are distinct from other retroelements in that their "transposition" is not confined to single cells but extends to neighboring cells and organisms. As such, the "transposition" of these elements is defined as infection. It appears that a key step in the conversion of a retrotransposon into a retrovirus is the modular acquisition or capture of an envelope glycoprotein (Env) which facilitates dissemination from its initial host cell. Here we present several examples of retroviruses for which envelope capture has been identified. Indeed, capture may explain the notable conservation of env sequences among otherwise phylogenetically distant retroviruses. In a recent example, sequence homologies reported between the env of the phylogenetically distant murine leukemia viruses (MLV) and human T cell leukemia viruses (HTLV) argue in favor of an env capture by the latter. Env acquisition can provide new adaptive properties to replication-competent viruses in addition to altering their host range. Also, the captured env can alter the spectrum of physiological affects of infection in new host cells and organisms. The elucidation of such envelope exchanges and properties thereof should contribute significantly to the clarification of retroviral phylogeny, insight into retroviral pathogenesis, and to the discovery of new retroviruses.

Characterization of endogenous retroviruses in sheep

Endogenous retrovirus (ERV) sequences have been found in all mammals. In vitro and in vivo experiments revealed ERV activation and cross-species infection in several species. Sheep (Ovis aries) are used for various biotechnological purposes; however, they have not yet been comprehensively screened for ERV sequences. Therefore, the aim of the study was to classify the ERV sequences in the ovine genome (OERV) by analyzing the retroviral pro-pol sequences. Three OERV beta families and nine OERV gamma families were revealed. Novel open reading frames (ORF) in the amplified proviral fragment were found in one OERV beta family and two OERV gamma families. Hybrid OERV produced by putative recombination events were not detected. Quantitative analysis of the OERV sequences in the ovine genome revealed no relevant variations in the endogenous retroviral loads of different breeds. Expression analysis of different tissues from fetal and pregnant sheep detected mRNA from both gammaretrovirus families, showing ORF fragments. Thus, the release of retroviruses from sheep cells cannot be excluded.