Autoantibodies targeting LINE-1-encoded ORF1p are associated with systemic lupus erythematosus diagnosis but not disease activity.

OBJECTIVES: Long Interspersed Element 1 (LINE-1) is an endogenous retroelement that constitutes a significant portion of the human genome and has been implicated in the pathogenesis of systemic lupus erythematosus (SLE). The LINE-1 RNA chaperone protein ORF1p was recently identified as an SLE autoantigen. Here we analyse ORF1p for qualities underlying SLE autoantigen status, compared anti-ORF1p antibodies to markers of SLE disease activity, and performed screening for antibodies against LINE-1 reverse transcriptase ORF2p. METHODS: ORF1p was examined in epithelial cell lines treated with cytotoxic lymphocyte granules and UV irradiation. Anti-ORF1p and anti-ORF2p antibodies were assayed by ELISA and analysed in two SLE cohorts. RESULTS: We found that ORF1p localises to cytoplasmic RNA-containing blebs in apoptotic cells, and is a substrate of the cytotoxic protease granzyme B (GrB). Anti-ORF1p antibodies were present in 4.2% of healthy controls, compared to 15.8% (p=0.0157) and 15.5% (p=0.036) of subjects in the two SLE cohorts. Anti-ORF1p antibodies were not associated with SLE disease activity nor peripheral blood markers of interferon (IFN) activation. Anti-ORF1p titres demonstrated stability over serial time points. Anti-ORF1p antibodies were not associated with anti-DNA, anti-RNP, or other SLE autoantibodies. There was no difference in anti-ORF2p ELISA results in controls versus SLE patients. CONCLUSIONS: LINE-1 ORF1p is a component of apoptotic blebs and a substrate for GrB. Anti-ORF1p antibodies are enriched in SLE subjects but are not associated with dynamic markers of disease activity. These data support a potential role for LINE-1 dysregulation in SLE pathogenesis.

Cell fitness screens reveal a conflict between LINE-1 retrotransposition and DNA replication.

LINE-1 retrotransposon overexpression is a hallmark of human cancers. We identified a colorectal cancer wherein a fast-growing tumor subclone downregulated LINE-1, prompting us to examine how LINE-1 expression affects cell growth. We find that nontransformed cells undergo a TP53-dependent growth arrest and activate interferon signaling in response to LINE-1. TP53 inhibition allows LINE-1+ cells to grow, and genome-wide-knockout screens show that these cells require replication-coupled DNA-repair pathways, replication-stress signaling and replication-fork restart factors. Our findings demonstrate that LINE-1 expression creates specific molecular vulnerabilities and reveal a retrotransposition-replication conflict that may be an important determinant of cancer growth.

Pan-cancer analysis of whole genomes identifies driver rearrangements promoted by LINE-1 retrotransposition.

About half of all cancers have somatic integrations of retrotransposons. Here, to characterize their role in oncogenesis, we analyzed the patterns and mechanisms of somatic retrotransposition in 2,954 cancer genomes from 38 histological cancer subtypes within the framework of the Pan-Cancer Analysis of Whole Genomes (PCAWG) project. We identified 19,166 somatically acquired retrotransposition events, which affected 35% of samples and spanned a range of event types. Long interspersed nuclear element (LINE-1; L1 hereafter) insertions emerged as the first most frequent type of somatic structural variation in esophageal adenocarcinoma, and the second most frequent in head-and-neck and colorectal cancers. Aberrant L1 integrations can delete megabase-scale regions of a chromosome, which sometimes leads to the removal of tumor-suppressor genes, and can induce complex translocations and large-scale duplications. Somatic retrotranspositions can also initiate breakage-fusion-bridge cycles, leading to high-level amplification of oncogenes. These observations illuminate a relevant role of L1 retrotransposition in remodeling the cancer genome, with potential implications for the development of human tumors.

LINE-1 ORF2p expression is nearly imperceptible in human cancers.

BACKGROUND: Long interspersed element-1 (LINE-1, L1) is the major driver of mobile DNA activity in modern humans. When expressed, LINE-1 loci produce bicistronic transcripts encoding two proteins essential for retrotransposition, ORF1p and ORF2p. Many types of human cancers are characterized by L1 promoter hypomethylation, L1 transcription, L1 ORF1p protein expression, and somatic L1 retrotransposition. ORF2p encodes the endonuclease and reverse transcriptase activities required for L1 retrotransposition. Its expression is poorly characterized in human tissues and cell lines. RESULTS: We report mass spectrometry-based tumor proteome profiling studies wherein ORF2p eludes detection. To test whether ORF2p could be detected with specific reagents, we developed and validated five rabbit monoclonal antibodies with immunoreactivity for specific epitopes on the protein. These reagents readily detect ectopic ORF2p expressed from bicistronic L1 constructs. However, endogenous ORF2p is not detected in human tumor samples or cell lines by western blot, immunoprecipitation, or immunohistochemistry despite high levels of ORF1p expression. Moreover, we report endogenous ORF1p-associated interactomes, affinity isolated from colorectal cancers, wherein we similarly fail to detect ORF2p. These samples include primary tumors harboring hundreds of somatically acquired L1 insertions. The new data are available via ProteomeXchange with identifier PXD013743. CONCLUSIONS: Although somatic retrotransposition provides unequivocal genetic evidence for the expression of ORF2p in human cancers, we are unable to directly measure its presence using several standard methods. Experimental systems have previously indicated an unequal stoichiometry between ORF1p and ORF2p, but in vivo, the expression of these two proteins may be more strikingly uncoupled. These findings are consistent with observations that ORF2p is not tolerable for cell growth.

SQuIRE reveals locus-specific regulation of interspersed repeat expression.

Transposable elements (TEs) are interspersed repeat sequences that make up much of the human genome. Their expression has been implicated in development and disease. However, TE-derived RNA-seq reads are difficult to quantify. Past approaches have excluded these reads or aggregated RNA expression to subfamilies shared by similar TE copies, sacrificing quantitative accuracy or the genomic context necessary to understand the basis of TE transcription. As a result, the effects of TEs on gene expression and associated phenotypes are not well understood. Here, we present Software for Quantifying Interspersed Repeat Expression (SQuIRE), the first RNA-seq analysis pipeline that provides a quantitative and locus-specific picture of TE expression (https://github.com/wyang17/SQuIRE). SQuIRE is an accurate and user-friendly tool that can be used for a variety of species. We applied SQuIRE to RNA-seq from normal mouse tissues and a Drosophila model of amyotrophic lateral sclerosis. In both model organisms, we recapitulated previously reported TE subfamily expression levels and revealed locus-specific TE expression. We also identified differences in TE transcription patterns relating to transcript type, gene expression and RNA splicing that would be lost with other approaches using subfamily-level analyses. Altogether, our findings illustrate the importance of studying TE transcription with locus-level resolution.

Alu insertion variants alter mRNA splicing.

RNA splicing is a highly regulated process dependent on sequences near splice sites. Insertions of Alu retrotransposons can disrupt splice sites or bind splicing regulators. We hypothesized that some common inherited polymorphic Alu insertions are responsible for splicing QTLs (sQTL). We focused on intronic Alu variants mapping within 100 bp of an alternatively used exon and screened for those that alter splicing. We identify five loci, 21.7% of those assayed, where the polymorphic Alu alters splicing. While in most cases the Alu promotes exon skipping, at one locus the Alu increases exon inclusion. Of particular interest is an Alu polymorphism in the CD58 gene. Reduced CD58 expression is associated with risk for developing multiple sclerosis. We show that the Alu insertion promotes skipping of CD58 exon 3 and results in a frameshifted transcript, indicating that the Alu may be the causative variant for increased MS risk at this locus. Using RT-PCR analysis at the endogenous locus, we confirm that the Alu variant is a sQTL for CD58. In summary, altered splicing efficiency is a common functional consequence of Alu polymorphisms including at least one instance where the variant is implicated in disease risk. This work broadens our understanding of splicing regulatory sequences around exons.

Structural variants caused by Alu insertions are associated with risks for many human diseases.

Interspersed repeat sequences comprise much of our DNA, although their functional effects are poorly understood. The most commonly occurring repeat is the Alu short interspersed element. New Alu insertions occur in human populations, and have been responsible for several instances of genetic disease. In this study, we sought to determine if there are instances of polymorphic Alu insertion variants that function in a common variant, common disease paradigm. We cataloged 809 polymorphic Alu elements mapping to 1,159 loci implicated in disease risk by genome-wide association study (GWAS) (P < 10-8). We found that Alu insertion variants occur disproportionately at GWAS loci (P = 0.013). Moreover, we identified 44 of these Alu elements in linkage disequilibrium (r2 > 0.7) with the trait-associated SNP. This figure represents a >20-fold increase in the number of polymorphic Alu elements associated with human phenotypes. This work provides a broader perspective on how structural variants in repetitive DNAs may contribute to human disease.

The Human Long Interspersed Element-1 Retrotransposon: An Emerging Biomarker of Neoplasia.

BACKGROUND: A large portion of intronic and intergenic space in our genome consists of repeated sequences. One of the most prevalent is the long interspersed element-1 (LINE-1, L1) mobile DNA. LINE-1 is rightly receiving increasing interest as a cancer biomarker. CONTENT: Intact LINE-1 elements are self-propagating. They code for RNA and proteins that function to make more copies of the genomic element. Our current understanding is that this process is repressed in most normal cells, but that LINE-1 expression is a hallmark of many types of malignancy. Here, we will consider features of cancer cells when cellular defense mechanisms repressing LINE-1 go awry. We will review evidence that genomic LINE-1 methylation, LINE-1-encoded RNAs, and LINE-1 ORF1p (open reading frame 1 protein) may be useful in cancer diagnosis. SUMMARY: The repetitive and variable nature of LINE-1 DNA sequences poses unique challenges to studying them, but recent advances in reagents and next generation sequencing present opportunities to characterize LINE-1 expression and activity in cancers and to identify clinical applications.

Meeting Report: The Role of the Mobilome in Cancer.

Approximately half of the human genome consists of repetitive sequence attributed to the activities of mobile DNAs, including DNA transposons, RNA transposons, and endogenous retroviruses. Of these, only long interspersed elements (LINE-1 or L1) and sequences copied by LINE-1 remain mobile in our species today. Although cells restrict L1 activity by both transcriptional and posttranscriptional mechanisms, L1 derepression occurs in developmental and pathologic contexts, including many types of cancers. However, we have limited knowledge of the extent and consequences of L1 expression in premalignancies and cancer. Participants in this NIH strategic workshop considered key questions to enhance our understanding of mechanisms and roles the mobilome may play in cancer biology. Cancer Res; 76(15); 4316-9. ©2016 AACR.

Interleukin-17 retinotoxicity is prevented by gene transfer of a soluble interleukin-17 receptor acting as a cytokine blocker: implications for age-related macular degeneration.

Age-related macular degeneration (AMD) is a common yet complex retinal degeneration that causes irreversible central blindness in the elderly. Pathology is widely believed to follow loss of retinal pigment epithelium (RPE) and photoreceptor degeneration. Here we report aberrant expression of interleukin-17A (IL17A) and the receptor IL17RC in the macula of AMD patients. In vitro, IL17A induces RPE cell death characterized by the accumulation of cytoplasmic lipids and autophagosomes with subsequent activation of pro-apoptotic Caspase-3 and Caspase-9. This pathology is reduced by siRNA knockdown of IL17RC. IL17-dependent retinal degeneration in a mouse model of focal retinal degeneration can be prevented by gene therapy with adeno-associated virus vector encoding soluble IL17 receptor. This intervention rescues RPE and photoreceptors in a MAPK-dependent process. The IL17 pathway plays a key role in RPE and photoreceptor degeneration and could hold therapeutic potential in AMD.

Molecular pathology of macrophages and interleukin-17 in age-related macular degeneration.

The pathology of age-related macular degeneration (AMD) is characterized by degeneration of photoreceptors and retinal pigment epithelial cells as well as by changes of choroidal capillaries in the macula. Although AMD is not a typical uveitis, there is a consistence and an imbalance of ocular para-inflammation. Ocular inflammation, particularly in the macula, plays a critical role in AMD pathogenesis. The inflammatory and immune-related elements involved in AMD include inflammatory and related cells as well as the secreted molecules and factors from these cells. Innate immune system elements such as macrophages and cytokines play an important role in AMD pathology and pathogenesis. This chapter reviews the observed deviation in macrophage plasticity and the elevated expression of interleukin-17 in AMD eyes while discussing potential contributions to AMD pathogenesis. Targeting of these specific inflammatory pathways and molecules at appropriate times should be explored and may become promising novel adjunct agents to AMD therapy.

Inflammation and Cell Death in Age-Related Macular Degeneration: An Immunopathological and Ultrastructural Model.

The etiology of Age-related Macular Degeneration (AMD) remains elusive despite the characterization of many factors contributing to the disease in its late-stage phenotypes. AMD features an immune system in flux, as shown by changes in macrophage polarization with age, expression of cytokines and complement, microglial accumulation with age, etc. These point to an allostatic overload, possibly due to a breakdown in self vs. non-self when endogenous compounds and structures acquire the appearance of non-self over time. The result is inflammation and inflammation-mediated cell death. While it is clear that these processes ultimately result in degeneration of retinal pigment epithelium and photoreceptor, the prevalent type of cell death contributing to the various phenotypes is unknown. Both molecular studies as well as ultrastructural pathology suggest pyroptosis, and perhaps necroptosis, are the predominant mechanisms of cell death at play, with only minimal evidence for apoptosis. Herein, we attempt to reconcile those factors identified by experimental AMD models and integrate these data with pathology observed under the electron microscope-particularly observations of mitochondrial dysfunction, DNA leakage, autophagy, and cell death.

Aging is not a disease: distinguishing age-related macular degeneration from aging.

Age-related macular degeneration (AMD) is a disease of the outer retina, characterized most significantly by atrophy of photoreceptors and retinal pigment epithelium accompanied with or without choroidal neovascularization. Development of AMD has been recognized as contingent on environmental and genetic risk factors, the strongest being advanced age. In this review, we highlight pathogenic changes that destabilize ocular homeostasis and promote AMD development. With normal aging, photoreceptors are steadily lost, Bruch's membrane thickens, the choroid thins, and hard drusen may form in the periphery. In AMD, many of these changes are exacerbated in addition to the development of disease-specific factors such as soft macular drusen. Para-inflammation, which can be thought of as an intermediate between basal and robust levels of inflammation, develops within the retina in an attempt to maintain ocular homeostasis, reflected by increased expression of the anti-inflammatory cytokine IL-10 coupled with shifts in macrophage plasticity from the pro-inflammatory M1 to the anti-inflammatory M2 polarization. In AMD, imbalances in the M1 and M2 populations together with activation of retinal microglia are observed and potentially contribute to tissue degeneration. Nonetheless, the retina persists in a state of chronic inflammation and increased expression of certain cytokines and inflammasomes is observed. Since not everyone develops AMD, the vital question to ask is how the body establishes a balance between normal age-related changes and the pathological phenotypes in AMD.

Influence of TIMP3/SYN3 polymorphisms on the phenotypic presentation of age-related macular degeneration.

Age-related macular degeneration (AMD) is a leading cause of irreversible central visual loss in the elderly. A recent genome-wide association studies (GWAS) reported that rs9621532 near the tissue inhibitor of metalloproteinase 3 (TIMP3)/synapsin III (SYN3) region of 22q12.3 is associated with AMD. In this study, we characterize its phenotypic influence on AMD using three independent study cohorts: case-control studies from the National Eye Institute Clinical Center (NEI, n=397) and the Age-Related Eye Disease Study (n=523) as well as a nested case-control study from Blue Mountains Eye Study (BMES, n=852). Comparisons between cases and controls show no association between rs9621532 and AMD in the three sample sets. However, stratifying NEI cases uncovers a moderate protective role of rs9621532 in neovascular AMD (nAMD) and the association adhered to a dominant model (odds ratios=0.32; 95% CI: 0.11-0.89; P=0.02). The BMES data followed the same pattern of association with nAMD as that seen in the NEI sample but did not reach statistical significance. Polychotomous logistic regression showed a trend that rs9621532 correlates with less severe disease, for example, with the majority of carriers having intermediate AMD rather than nAMD/geographic atrophy AMD. Functionally, rs9621532 influences TIMP3 mRNA expression in cultured primary human fetal retinal pigment epithelium (hfRPE) cells. In hfRPE donors carrying the protective rs9625132 allele, we measured a reduction in TIMP3 mRNA by quantitative RT-PCR. Our data suggest that rs9621532 carriers have a lower risk of developing nAMD, potentially because of decreased transcription of TIMP3.

Ten Chairpersons of the Ophthalmology Department at Peking Union Medical College.

With the full academic and financial support of the China Medical Board of the Rockefeller Foundation, Peking Union Medical College (PUMC) was officially inaugurated in 1921. Since then, PUMC has been one of the most prestigious medical schools in China and the only one that is connected to the Chinese Academy of Medical Science. From its founding, there have been 10 chairpersons at the PUMC Department of Ophthalmology. The first 4 chairpersons, Howard, Pillat, Von Sallmann, and Kronfeld, were trained in Vienna and established the program's Western system. The latter 6 chairpersons, Luo, Hu, Zhang, Li, Zhao, and Dong, who were educated mainly in China, have maintained the program's excellence and made significant contributions to ophthalmology and medicine in China and the world. Under the strong leadership still in place today, PUMC will continue to provide generations of leaders for academic modern medicine and health care in China. Accordingly, the Department of Ophthalmology, one of the oldest ophthalmology departments in China, will continue making significant contributions to the global realm of eye and vision research and health care.

Controversial view of a genetically altered mouse model of focal retinal degeneration.

Tuo et al. (2012) demonstrated tumor necrosis factor-inducible gene 6 recombinant protein (TSG-6) arrest of focal retinal lesions on a Ccl2 and Cx3cr1 double deficient mouse (DKO) on rd8 background (hereon referred to as DKO rd8). DKO rd8, a model of focal retinal degeneration with earlier onset and higher penetrance than Ccl2 and Cx3cr1 single knockout strains, demonstrates characteristic features of AMD such as focal photoreceptor atrophy, retinal pigmented epithelium (RPE) degeneration, elevated ocular A2E levels and complement deposition in addition to retinal dystrophy. The discovery of the accidently introduced Crb1 mutation (rd8) in the C57BL/6N strain has led to the recent opinion that DKO rd8 is not a model of AMD but solely a model of Crb1­associated retinal degeneration. Differences between DKO rd8 and Crb1 (rd8) photoreceptor and RPE pathology, as well as increased A2E and immune dysfunction, show that DKO rd8 recapitulates some AMD­like features in addition to rd8 retinal dystrophy. The appearance of rd8 lesions and Ccl2/Cx3cr1 lesions and the amelioration of most Ccl2/Cx3cr1 lesions in intervention studies show DKO rd8 to be a useful and appropriate model for therapeutic compound screening, such as the case with anti-inflammatory TSG­6.

Suggestive association between PLA2G12A single nucleotide polymorphism rs2285714 and response to anti-vascular endothelial growth factor therapy in patients with exudative age-related macular degeneration.

PURPOSE: The use of anti-vascular endothelial growth factor (anti-VEGF) therapy, with drugs such as ranibizumab and bevacizumab, to treat neovascular age-related macular degeneration (nAMD) produces an effective but widely variable response. Identifying markers that predict differentiated response could serve as a valuable assay in developing more personalized medicine. This study aimed to identify single nucleotide polymorphisms (SNPs) that influence the outcome of treatment with anti-VEGF therapy for AMD. METHODS: One hundred six patients with nAMD were treated with either ranibizumab or bevacizumab as needed over a period of 12 months. Visual acuity and the presence of macular fluid were measured with optical coherence tomography at baseline, six months, and 12 months. Patients were then classified as good or poor responders based on change in visual acuity and macular fluid on follow-up visits. DNA extracted from blood was genotyped with a TaqMan-based allelic discrimination SNP assay for 21 SNPs in six candidate genes (PLAG12A, IL23R, STAT3, VEGFA, KDR, and HIF1A). The SNPs were primarily selected based on previously reported associations with AMD and functional involvement in angiogenesis pathways. SNPs shown to be promising for association with anti-VEGF therapy were then assessed in an independent AMD case-control cohort. RESULTS: Of the 106 patients with nAMD, 77 were classified as good responders and 29 as poor responders. For rs2285714 (PLA2G12A), the frequency of minor allele T was 40.1% for good responders compared to 51.7% for poor responders (odds ratio: 1.60, 95% confidence interval of odds ratio: 0.87-2.94, p=0.13). Genetic model analysis of rs2285714 (PLA2G12A) demonstrated an association between rs2285714 (PLA2G12A) and therapy response in a dominant genotypic model. Patients carrying at least one T allele of rs2285714 were 2.79 times (95% confidence interval=1.02-7.69, p<0.05) more likely to be poor responders (79.3% of poor responders) than good responders (57.3% of good responders). However, after adjusting for multiple testing by the false discovery rate or Bonferroni correction, the initially observed association was no longer statistically significant. No association was identified between the remaining SNPs and response status. The SNP rs2285714 of PLA2G12A was not significantly associated with AMD in an independent AMD case-control cohort. CONCLUSIONS: Data suggest a possible weak association between rs2285714 (PLA2G12A) and response to anti-VEGF therapy, but the association must be confirmed in additional cohorts with larger patient samples. Identifying factors that predict the differentiated response could provide a valuable assay for developing approaches in personalized medicine.

Carboxyethylpyrrole plasma biomarkers in age-related macular degeneration.

Age-related macular degeneration causes irreversible central blindness in people over the age of 50 and is increasing in prevalence among elderly populations. There are currently limited treatment options available for the exudative form of the disease and no formal treatments for the geographic atrophy form aside from lifestyle change and incorporation of antioxidant supplements in the diet. As such, it is important to be able to assess high-risk AMD patients as early as possible in order to prescribe preventative measures. Carboxyethylpyrrole (CEP) is a promising plasma biomarker suited to this purpose. Both CEP immunoreactivity levels as well as anti-CEP autoantibody titers are significantly elevated in AMD patients and thus provide the potential to assess AMD susceptibility with approximately 80% accuracy when evaluated alongside genomic AMD markers. Moreover, strong evidence implicates CEP as functionally related to AMD pathogenesis, a role which must be explored further. This avenue of research will foster improved understanding of the disease itself and perhaps reveal better therapeutic targets and options. Further research into the role of CEP in AMD pathogenesis and the application of CEP as an AMD biomarker is merited.