Autoantibodies in melanoma-associated retinopathy target TRPM1 cation channels of retinal ON bipolar cells

Case Report: Longitudinal Evaluation and Treatment of a Melanoma-Associated Retinopathy Patient

Melanoma-associated retinopathy (MAR) is a paraneoplastic syndrome associated with cutaneous metastatic melanoma in which patients develop vision deficits that include reduced night vision, poor contrast sensitivity, and photopsia. MAR is caused by autoantibodies targeting TRPM1, an ion channel found in melanocytes and retinal ON-bipolar cells (ON-BCs). The visual symptoms arise when TRPM1 autoantibodies enter ON-BCs and block the function of TRPM1, thus detection of TRPM1 autoantibodies in patient serum is a key criterion in diagnosing MAR. Electroretinograms are used to measure the impact of TRPM1 autoantibodies on ON-BC function and represent another important diagnostic tool for MAR. To date, MAR case reports have included one or both diagnostic components, but only for a single time point in the course of a patient's disease. Here, we report a case of MAR supported by longitudinal analysis of serum autoantibody detection, visual function, ocular inflammation, vascular integrity, and response to slow-release intraocular corticosteroids. Integrating these data with the patient's oncological and ophthalmological records reveals novel insights regarding MAR pathogenesis, progression, and treatment, which may inform new research and expand our collective understanding of the disease. In brief, we find TRPM1 autoantibodies can disrupt vision even when serum levels are barely detectable by western blot and immunohistochemistry; intraocular dexamethasone treatment alleviates MAR visual symptoms despite high levels of circulating TRPM1 autoantibodies, implicating antibody access to the retina as a key factor in MAR pathogenesis. Elevated inflammatory cytokine levels in the patient's eyes may be responsible for the observed damage to the blood-retinal barrier and subsequent entry of autoantibodies into the retina.

Integrated transcriptomic and immunological profiling reveals new diagnostic and prognostic models for cutaneous melanoma

The mortality rate associated with cutaneous melanoma (SKCM) remains alarmingly high, highlighting the urgent need for a deeper understanding of its molecular underpinnings. In our study, we leveraged bulk transcriptome sequencing data from the SKCM cohort available in public databases such as TCGA and GEO. We utilized distinct datasets for training and validation purposes and also incorporated mutation and clinical data from TCGA, along with single-cell sequencing data from GEO. Through dimensionality reduction, we annotated cell subtypes within the single-cell data and analyzed the expression of tumor-related pathways across these subtypes. We identified differentially expressed genes (DEGs) in the training set, which were further refined using the Least Absolute Shrinkage and Selection Operator (LASSO) machine learning algorithm, employing tenfold cross-validation. This enabled the construction of a prognostic model, whose diagnostic efficacy we subsequently validated. We conducted Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses on the DEGs, and performed immunological profiling on two risk groups to elucidate the relationship between model genes and the immune responses relevant to SKCM diagnosis, treatment, and prognosis. We also knocked down the GMR6 expression level in the melanoma cells and verified its effect on cancer through multiple experiments. The results indicate that the GMR6 gene plays a role in promoting the proliferation, invasion, and migration of cancer cells in human melanoma. Our findings offer novel insights and a theoretical framework that could enhance prognosis, treatment, and drug development strategies for SKCM, potentially leading to more precise therapeutic interventions.

"ThermoTRP" Channel Expression in Cancers: Implications for Diagnosis and Prognosis (Practical Approach by a Pathologist)

Temperature-sensitive transient receptor potential (TRP) channels (so-called "thermoTRPs") are multifunctional signaling molecules with important roles in cell growth and differentiation. Several "thermoTRP" channels show altered expression in cancers, though it is unclear if this is a cause or consequence of the disease. Regardless of the underlying pathology, this altered expression may potentially be used for cancer diagnosis and prognostication. "ThermoTRP" expression may distinguish between benign and malignant lesions. For example, TRPV1 is expressed in benign gastric mucosa, but is absent in gastric adenocarcinoma. TRPV1 is also expressed both in normal urothelia and non-invasive papillary urothelial carcinoma, but no TRPV1 expression has been seen in invasive urothelial carcinoma. "ThermoTRP" expression can also be used to predict clinical outcomes. For instance, in prostate cancer, TRPM8 expression predicts aggressive behavior with early metastatic disease. Furthermore, TRPV1 expression can dissect a subset of pulmonary adenocarcinoma patients with bad prognosis and resistance to a number of commonly used chemotherapeutic agents. This review will explore the current state of this rapidly evolving field with special emphasis on immunostains that can already be added to the armoire of diagnostic pathologists.

Plasma Antiretinal Autoantibody Profiling and Diagnostic Efficacy in Patients With Autoimmune Retinopathy

PURPOSE

To evaluate plasma antiretinal autoantibody (ARA) profiling and diagnostic efficacy for autoimmune retinopathy (AIR).

DESIGN

A multicenter, diagnostic evaluation study.

METHODS

Forty-nine patients with a clinical diagnosis of AIR, disease controls including 20 patients with retinitis pigmentosa (RP), and 30 normal controls were included. Plasma samples from patients were analyzed for the presence of 6 ARAs, including recoverin, α-enolase, carbonic anhydrase II, heat shock protein 60, aldolase C, and cone-rod homeobox/cone-rod retinal dystrophy 2 using western blotting.

RESULTS

Autoantibody detection rates against cone-rod homeobox/cone-rod retinal dystrophy 2, heat shock protein 60, and aldolase C in AIR were 67.3%, 40.8%, and 42.9%, respectively, which were higher than those in RP and normal controls (P < .001, P < .001, and P = .007, respectively), but recoverin, α-enolase, and carbonic anhydrase II were not different from other control groups (P = .117, P = .774, and P = .467, respectively). Among ARAs, antirecoverin antibody was the most specific, as it was found in 3 (6.1%) patients with AIR and none of the control groups. As the number of detected ARAs increased, the probability of AIR increased (odds ratio: 1.913; P < .001; 95% confidence interval: 1.456-2.785). The positive number of ARAs was significantly higher when photoreceptor disruption was observed on optical coherence tomography, or severe dysfunction was observed in electroretinography (P = .022 and P = .029, respectively).

CONCLUSIONS

The profiles of ARAs in the AIR group were different from those in the RP and normal controls. The higher number of positive ARAs suggests a higher possibility of AIR diagnosis. ARAs should be used as adjunct tools for the clinical diagnosis of AIR.

Melanoma-associated retinopathy with anti-TRPM1 autoantibodies showing concomitant Off-bipolar cell dysfunction

BACKGROUND

To report the clinical features of a patient with melanoma-associated retinopathy (MAR) with anti-transient receptor potential cation channel, subfamily M, member 1 (TRPM1) autoantibodies showing concomitant Off-bipolar cell dysfunction.

METHODS

We evaluated a patient with a past history of scalp melanoma presented with sudden-onset shimmering photopsia in both eyes. MAR was confirmed with complete ophthalmic examinations, electronegative electroretinogram (ERG), and the presence of anti-TRPM1 autoantibodies by Western blot analysis. S-cone ERG and photopic On-Off ERG were studied in this patient as well.

RESULTS

The patient's best-corrected visual acuity was 6/30 in the right eye and 6/8.6 in the left eye. Fundus and OCT findings were unremarkable. Visual field test showed severe constriction in both eyes. His full-field ERG was electronegative. S-cone ERG recorded preservation of L/M-cone-mediated response and undetectable S-cone-mediated response. Photopic On-Off ERG disclosed attenuated On- and Off-response. Western blot analysis confirmed immunoreactivity of the patient's serum to a 30 kDa TRPM1 recombinant protein. Whole-body positron emission tomography scan detected lymph node metastases in the neck.

CONCLUSIONS

Anti-TRPM1 autoantibody-positive MAR varies greatly in its presentation and clinical course. We present a case of anti-TRPM1 autoantibody-positive MAR with atypical feature of Off-bipolar cell involvement. A complete electroretinographic study together with identification of the pathogenic antiretinal autoantibodies may help better understand and subclassify the disease in the future.

Broad locations of antigenic regions for anti-TRPM1 autoantibodies in paraneoplastic retinopathy with retinal ON bipolar cell dysfunction

PURPOSE

Cancer-associated retinal ON bipolar cell dysfunction (CARBD), which includes melanoma-associated retinopathy (MAR), has been reported to be caused by autoantibodies against the molecules expressed in ON bipolar cells, including TRPM1. The purpose of this study was to determine the antigenic regions of the autoantibodies against TRPM1 in the sera of CARBD patients, in whom we previously detected anti-TRPM1 autoantibodies.

METHODS

The antigenic regions against TRPM1 in the sera of eight CARBD patients were examined by Western blots using HEK293T cells transfected with the plasmids expressing FLAG-tagged TRPM1 fragments. The clinical course of these patients was also documented.

RESULTS

The clinical course differed among the patients. The electroretinograms (ERGs) and symptoms were improved in three patients, deteriorated in one patient, remained unchanged for a long time in one patient, and were not followable in three patients. Seven of the eight sera possessed multiple antigenic regions: two sera contained at least four antigen recognition regions, and three sera had at least three regions. The antigen regions were spread over the entire TRPM1 protein: five sera in the N-terminal intracellular domain, six sera in the transmembrane-containing region, and six sera in the C-terminal intracellular domain. No significant relationship was observed between the location of the antigen epitope and the patients' clinical course.

CONCLUSIONS

The antigenic regions of anti-TRPM1 autoantibodies in CARBD patients were present not only in the N-terminal intracellular domain, which was reported in an earlier report, but also in the transmembrane-containing region and in the C-terminal intracellular domain. In addition, the antigenic regions for TRPM1 were found to vary among the CARBD patients examined, and most of the sera had multiple antigenic regions.

Negative electroretinograms: genetic and acquired causes, diagnostic approaches and physiological insights

The dark-adapted human electroretinogram (ERG) response to a standard bright flash includes a negative-going a-wave followed by a positive-going b-wave that crosses the baseline. An electronegative waveform (or negative ERG) results when the b-wave is selectively reduced such that the ERG fails to cross the baseline following the a-wave. In the context of a normally sized a-wave, it indicates a site of retinal dysfunction occurring after phototransduction (commonly at the photoreceptor to bipolar cell synapse). This is an important finding. In genetic disease, the pattern of ERG abnormality can point to variants in a small group of genes (frequently those associated with congenital stationary night blindness and X-linked retinoschisis, but negative ERGs can also be seen in other conditions including syndromic disease). In acquired disease, there are numerous causes, but specific features may point to melanoma-associated retinopathy (MAR). In some cases, the visual symptoms precede the diagnosis of the melanoma and so the ERG findings can initiate investigations facilitating early detection and treatment. Negative ERGs can occur in other paraneoplastic conditions, and in a range of other diseases. This review will outline the physiological basis for the negative ERG, report prevalences in the literature from different cohorts, discuss the range of causes, displaying examples of a number of ERG phenotypes, highlight features of a clinical approach to patients, and briefly discuss further insights relating to current flows shaping the a-wave trough and from single-cell transcriptome analysis.

Paraneoplastic ocular syndrome: a pandora's box of underlying malignancies

Paraneoplastic syndromes affecting the visual system are a group of conditions that arise in the systemic malignancy framework. In this review, we have provided a detailed and comprehensive overview of the published literature on the various ophthalmic paraneoplastic manifestations. A systematic review of many databases has been performed to identify ample literature on the paraneoplastic syndromes related to ophthalmology. We have discussed here the clinical features, pathogenesis, and treatment strategies of various ophthalmic paraneoplastic syndromes. It can be challenging to distinguish these disorders from their non-paraneoplastic counterparts and to determine the appropriate systemic assessment for the tumour responsible, to have a proper approach towards the management of the syndrome. METHOD: We searched PubMed, Science Direct and Journal of Ophthalmology for studies published in English between 1995 and April 2020, incorporating the general search term "paraneoplastic ocular syndrome" with connecting terms relevant to subheadings-e.g. Key search terms were cancer-associated retinopathy, (CAR), melanoma-associated retinopathy, (MAR), paraneoplastic retinopathy, autoimmune retinopathy, autoimmune-related retinopathy, and optic neuropathy, (ARRON), acute zonal occult outer retinopathy, (AZOOR), paraneoplastic vitelliform maculopathy, paraneoplastic vitelliform retinopathy, bilateral diffuse uveal melanocytic proliferation, (BDUMP), paraneoplastic optic neuropathy, (PON), polyneuropathy, organomegaly, endocrinopathy, monoclona gammopathy, and skin changes syndrome (POEMS) and various other terms. References from identified studies have been reviewed and included if deemed appropriate, valid, and scientifically important. If referenced in a selected English paper, we contemplated papers in other languages too. We preferentially selected papers that have been published in the last 10 years, but we have included relevant older references.

Prevalence of electronegative electroretinograms in a healthy adult cohort

Objective

An electronegative electroretinogram (ERG) can indicate important ocular or systemic disease. This study explored the prevalence of electronegative responses to dark-adapted stimuli in a largely healthy cohort.

Methods and Analysis

211 participants recruited from the TwinsUK cohort underwent ERG testing incorporating international standard (International Society for Clinical Electrophysiology of Vision (ISCEV)) protocols and additional stimuli. Responses were recorded using conductive fibre electrodes, following pupil dilation and 20 min dark adaptation. Responses analysed were to the ISCEV standard and strong flashes (3.0 and 10 cd/m² s), and to additional white flashes (0.67–67 cd/m² s). A-wave and b-wave amplitudes were extracted; b:a ratios were calculated and proportions of eyes with ratios<1 were noted.

Results

Mean (SD) age was 62.4 (11.4) years (median, 64.3; range 23–86 years). 93% were female. Mean (SD) b:a ratios for right and left eyes, respectively, were 1.86 (0.33) and 1.81 (0.29) for the standard flash, and 1.62 (0.25) and 1.58 (0.23) for the stronger flash; average b:a ratio was lower for the stronger flash (p<0.0001). No waveforms were electronegative. For additional flashes, b:a ratio decreased with increasing flash strength. No electronegative waveforms were seen except in three eyes (0.7%) for the strongest flash; in some cases, drift in the waveform may have artefactually reduced the b:a ratio.

Conclusion

For standard dark-adapted stimuli, no participants had electronegative waveforms. The findings support the notion that electronegative waveforms (in response to standard flash strengths) are unusual, and should prompt further investigation.

An update on autoimmune retinopathy

Autoimmune retinopathy (AIR) refers to a group of rare autoimmune retinal degenerative diseases presumably caused by cross-reactivity of serum autoantibodies against retinal antigens. The pathogenesis of AIR remains largely presumptive and there are a significant number of antiretinal antibodies that have been detected in association with AIR. The diagnosis of AIR is largely based on the demonstration of antiretinal antibodies in the serum along with suggestive clinical features and ancillary investigations. A high index of suspicion along with early diagnosis and treatment may play a critical role to lower the risk of irreversible immunological damage to the retinal cells in these patients. A multi-disciplinary approach for complete management and evaluation is helpful in such conditions. Various therapeutic options have been described for the treatment of AIR, though there is no consensus on standard treatment protocol.

Clinical Correlation between Acute Exudative Polymorphous Paraneoplastic Vitelliform Maculopathy and Metastatic Melanoma Disease Activity: A 48-month Longitudinal Case Report

PURPOSE

Longitudinal evaluation of acute exudative polymorphous paraneoplastic vitelliform maculopathy (AEPPVM) following diagnosis and treatment of metastatic melanoma.

METHODS

Case report of a 47-year-old male with unknown primary metastatic melanoma and AEPPVM monitored before and during melanoma treatment using clinical exam, retinal imaging, and electroretinograms (ERG). Genetic testing and autoantibody panels were performed.

RESULTS

He presented within a month of metastatic melanoma diagnosis with numerous bilateral vitelliform lesions in the posterior pole, consistent with AEPPVM. Metastatic disease was treated with immunotherapy, radiosurgery, and radiation over 48 months. Maculopathy and metastatic disease improved and worsened in parallel. Genetic testing was negative for bestrophin-1. An autoantibody panel was positive for anti-recoverin and transducin-α.

CONCLUSION

AEPPVM is an uncommon paraneoplastic retinopathy found in patients with metastatic malignancy. To our knowledge, this is the first report demonstrating a temporal association between metastatic disease activity and quantifiable changes in retinal imaging over a 4-year period.

Melanoma-associated retinopathy during pembrolizumab treatment probably controlled by intravitreal injections of dexamethasone

PURPOSE

Melanoma-associated retinopathy (MAR) is a rare paraneoplastic syndrome due to antibodies targeting bipolar retinal cells. Its evolution, particularly in patients treated with immune checkpoint inhibitors (ICI), is currently poorly understood. In the few cases published, patients' visual function got worse when these molecules were prescribed. Here, we present a case of a patient with severe MAR treated with an ICI for melanoma progression.

METHODS

A 68-year-old woman with a history of melanoma of the palpebral conjunctiva presented with sudden and gradually worsening visual disturbances. Simultaneously, a metastatic evolution of the melanoma was diagnosed and surgically treated exclusively. Visual acuity assessment, static automated perimetry and ERG results lead to the diagnosis of MAR. Since systemic corticosteroid therapy did not improve her symptoms, repeated intraocular corticosteroid injections were performed with a positive outcome. Later on, metastatic progression of the patient's melanoma led to the introduction of pembrolizumab, an ICI targeting PD-1. Immunotherapy has changed the prognosis of patient affected by metastatic melanoma, but these molecules may induce various immune-related adverse effects. In our case, intraocular corticosteroid injections were still performed simultaneously. Visual acuity assessment, static automated perimetry and ERG were performed during the course of this treatment.

RESULTS

Full-field ERGs results suggested the possibility that the ophthalmologic treatment might restore the patient's retinal function despite the continued immunotherapy.

CONCLUSION

We report the first case of MAR with a positive outcome after 1 year of ICI, possibly thanks to intravitreal corticosteroid therapy.

CLINICAL COURSE OF PARANEOPLASTIC RETINOPATHY WITH ANTI-TRPM1 AUTOANTIBODY IN JAPANESE COHORT

PURPOSE

To report the clinical course of eyes with paraneoplastic retinopathy caused by an autoantibody against transient receptor potential cation channel, subfamily M, member 1 (TRPM1).

METHODS

Ten paraneoplastic retinopathy patients with retinal ON-bipolar cell dysfunction, including six melanoma-associated retinopathy, from eight institutions in Japan were evaluated for the presence of an anti-TRPM1 antibody. The results of ophthalmic examinations and the presence of anti-TRPM1 antibody were analyzed.

RESULTS

Five patients were positive for the anti-TRPM1 antibody. These patients had similar clinical findings in both eyes at the time of diagnosis; relatively preserved best-corrected visual acuity, absence of fundus and optical coherence tomography abnormalities, and specific abnormalities of the electroretinography (ERG); and negative-type ERGs with bright stimulus flashes. One patient whose retinal ON-bipolar cells remained dysfunctional for the entire testing period, although the anti-TRPM1 antibody had disappeared. On the other hand, the ERGs recovered in 2 cases within 2 years after the onset. One case progressed to additional impairment of the photoreceptors with deterioration of ERGs. One case died and the clinical course was unavailable.

CONCLUSION

Paraneoplastic retinopathy patients with retinal ON-bipolar cell dysfunction possess autoantibodies against TRPM1 at the onset of the disease process; however, the clinical course of these eyes can be different.

Identification and characterization of novel TRPM1 autoantibodies from serum of patients with melanoma-associated retinopathy

Melanoma-associated retinopathy (MAR) is a rare paraneoplastic retinal disorder usually occurring in the context of metastatic melanoma. Patients present with night blindness, photopsias and a constriction of the visual field. MAR is an auto-immune disorder characterized by the production of autoantibodies targeting retinal proteins, especially autoantibodies reacting to the cation channel TRPM1 produced in melanocytes and ON-bipolar cells. TRPM1 has at least three different isoforms which vary in the N-terminal region of the protein. In this study, we report the case of three new MAR patients presenting different anti-TRPM1 autoantibodies reacting to the three isoforms of TRPM1 with variable binding affinity. Two sera recognized all isoforms of TRPM1, while one recognized only the two longest isoforms upon immunolocalization studies on overexpressing cells. Similarly, the former two sera reacted with all TRPM1 isoforms on western blot, but an immunoprecipitation enrichment step was necessary to detect all isoforms with the latter serum. In contrast, all sera labelled ON-bipolar cells on Tprm1+/+ but not on Trpm1-/- mouse retina as shown by co-immunolocalization. This confirms that the MAR sera specifically detect TRPM1. Most likely, the anti-TRPM1 autoantibodies of different patients vary in affinity and concentration. In addition, the binding of autoantibodies to TRPM1 may be conformation-dependent, with epitopes being inaccessible in some constructs (truncated polypeptides versus full-length TRPM1) or applications (western blotting versus immunohistochemistry). Therefore, we propose that a combination of different methods should be used to test for the presence of anti-TRPM1 autoantibodies in the sera of MAR patients.

Outcomes Associated With Sustained-Release Intraocular Fluocinolone Implants in a Case of Melanoma-Associated Retinopathy Treated Without Systemic Immunosuppression

Importance

Melanoma-associated retinopathy (MAR) is a paraneoplastic syndrome in which antiretinal antibodies crossreact with retinal ON-bipolar cells, resulting in night blindness and progressive visual field loss. Current therapeutic options include cytoreductive surgery in combination with immunoglobulin, corticosteroids, or plasmapheresis, but their effectiveness is limited and may be contraindicated, given the possible protective role of circulating autoantibodies against metastatic spread. We report 3-year follow-up of the first case (to our knowledge) of MAR treated with intravitreal long-acting steroid implants.

Objective

To report on a patient with MAR who was treated with intravitreal fluocinolone acetonide implants in the absence of systemic immunosuppression.

Design, Setting, and Participants

This is a 3-year follow-up of a 73-year-old woman with a history of surgical excision of a malignant melanoma of the left pinna who presented with visual symptoms of shimmering and nyctalopia. Fundus examination, fundus autofluorescence, and optical coherence tomography were normal, with no evidence of cystoid macular edema. Automated perimetry showed a reduction in visual field and full-field electroretinography (ERG) demonstrated findings consistent with generalized ON-bipolar cell dysfunction, typical of MAR. The patient was treated with bilateral fluocinolone acetonide intravitreal implants.

Main Outcomes and Measures

Visual acuity, visual field, and electroretinography testing for 3 years after treatment.

Results

Visual fields improved in this 73-year-old patient from 20/30 (Snellen measured as 6/9) OD and 20/16 (6/5) OS at baseline to 20/20 OU within 1 week of treatment. Detailed electroretinography monitoring indicated characteristic abnormalities that partly resolved after treatment, consistent with improved inner retinal ON-bipolar cell function. Bilateral cataracts developed approximately 2 years after injection; cataract surgery was performed uneventfully. At 3 years posttreatment, the patient remained visually stable and in systemic disease remission, with best-corrected visual acuity remaining at 20/20 OU.

Conclusions and Relevance

We report what is, to our knowledge, the first case of MAR treated with intravitreal slow-release corticosteroid implants, which shows improvements in visual symptoms, visual fields, and retinal function. Sustained-release intraocular steroid implants may offer an effective and safe alternative to systemic immunosuppression in MAR, although results from 1 case should be generalized with abundant caution.

TRPM1 Autoantibodies in Melanoma Patients Without Self-Reported Visual Symptoms

Purpose

Melanoma-associated retinopathy (MAR) is a paraneoplastic syndrome associated with cutaneous malignant melanoma (CMM). Visual symptoms include night blindness, photopsia, and reduced-contrast sensitivity. An abnormal ERG b-wave and the presence of anti-bipolar cell autoantibodies, including autoantibodies reacting with the ON-bipolar cell TRPM1 channel, help to confirm the diagnosis. The goal of this study was to determine if CMM patients without visual symptoms also express anti-TRPM1 autoantibodies.

Methods

Serum samples from 15 CMM patients were tested using three assays: immunofluorescent labeling of TRPM1-transfected HEK cells, immunofluorescent labeling of retinal sections from wild-type and TRPM1 knockout mice, and immunoblot detection of a bacterially produced recombinant TRPM1 peptide.

Results

Serum specimens from 5 of the 15 CMM patients without declared visual symptoms were positive for anti-TRPM1 autoantibodies in at least one of the three assays. One of 50 control sera from patients not known to have cancer was also weakly reactive with the TRPM1 peptide.

Conclusions

Autoantibodies against TRPM1 are present in CMM patient sera without self-reported visual symptoms. Most patients had advanced (stage III and IV) disease and were undergoing aggressive treatments, including immunotherapy. It is unknown if immunotherapy affects the expression of TRPM1 autoantibodies. The presence of TRPM1 autoantibodies may predispose patients for MAR.

Ion channels as therapeutic antibody targets

It is now well established that antibodies have numerous potential benefits when developed as therapeutics. Here, we evaluate the technical challenges of raising antibodies to membrane-spanning proteins together with enabling technologies that may facilitate the discovery of antibody therapeutics to ion channels. Additionally, we discuss the potential targeting opportunities in the anti-ion channel antibody landscape, along with a number of case studies where functional antibodies that target ion channels have been reported. Antibodies currently in development and progressing towards the clinic are highlighted.

Are Anti-Retinal Autoantibodies a Cause or a Consequence of Retinal Degeneration in Autoimmune Retinopathies?

Autoantibodies (AAbs) against various retinal proteins have been associated with vision loss in paraneoplastic and non-paraneoplastic autoimmune retinopathies (AR). There are two major paraneoplastic syndromes associated anti-retinal AAbs, cancer-associated retinopathy (CAR), and melanoma-associated retinopathy. Some people without a cancer diagnosis may present symptoms of CAR and have anti-retinal AAbs. The etiology and pathogenesis of those entities are not fully understood. In this review, we provide evidence for the role of AAbs in retinal death and degeneration. Studies of epitope mapping for anti-recoverin, anti-enolase, and anti-carbonic anhydrase II revealed that although patients' AAbs may recognize the same retinal protein as normal individuals they bind to different molecular domains, which allows distinguishing between normal and diseased AAbs. Given the great diversity of anti-retinal AAbs, it is likely some antibodies have greater pathogenic potential than others. Pathogenic, but not normal antibodies penetrate the target cell, reach their specific antigen, induce apoptosis, and impact retinal pathophysiology. Photoreceptors, dying by apoptosis, induced by other than immunologic mechanisms produce substantial amounts of metabolic debris, which consequently leads to autoimmunization and enhanced permeability of the blood-retinal barrier. AAbs that were made as a part of anti-cancer response are likely to be the cause of retinal degeneration, whereas others, generated against released antigens from damaged retina, contribute to the progression of retinopathy. Altogether, AAbs may trigger retinal degeneration and may also exacerbate the degenerative process in response to the release of sequestered antigens and influence disease progression.

Seeing is believing: A review of apheresis therapy in the treatment of ophthalmologic disease

Apheresis procedures have a role in treatment of disparate diseases involving many different organ systems. Often the disease processes where apheresis plays a role in treatment are considered "orphan diseases"-relatively rare disease processes that lack specific pharmaceutical agents or established treatment protocols. Many of these disease processes can affect the eye with devastating results for the eyesight of these patients. The unique ability of apheresis to affect disease by modifying blood plasma and modulating disease-causing agents therein renders apheresis procedures valuable tools in the treatment of certain ophthalmologic diseases. This review comprehensively evaluates the role of apheresis in the treatment of ophthalmologic diseases of the eye and surrounding orbit including age-related macular degeneration, bilateral diffuse uveal melanocytic proliferation, paraneoplastic retinopathy, atopic keratoconjunctivitis, sympathetic ophthalmia, and endocrine-associated ophthalmopathy. Apheresis procedure parameters are provided for the apheresis practitioner based on review of the relevant literature.

Autoantibodies in Melanoma-Associated Retinopathy Recognize an Epitope Conserved Between TRPM1 and TRPM3

Purpose

Melanoma-associated retinopathy (MAR) is a paraneoplastic syndrome associated with malignant melanoma and the presence of anti-retinal autoantibodies, including autoantibodies against transient receptor potential melanopsin 1 (TRPM1), a cation channel expressed by both melanocytes and retinal bipolar cells. The goal of this study was to further map the antigenic epitope.

Methods

Patient sera were tested by immunofluorescence and Western blotting on HEK293 cells transfected with enhanced green fluorescent protein (EGFP)-TRPM1 fusion constructs and mouse retina sections.

Results

The epitope recognized by MAR patient sera was mapped to a region encoded by exons 9 and 10 of the human TRPM1 gene. This region of TRPM1 is highly conserved with TRPM3, and indeed MAR sera were found to cross-react with TRPM3, a closely related channel expressed in the retinal pigment epithelium (RPE).

Conclusions

These results indicate that TRPM1 autoantibodies in MAR patient sera recognize a short, intracellular segment of TRPM1. Cross-reactivity with TRPM3 in the RPE may account for other visual symptoms that are experienced by some MAR patients such as retinal and RPE detachments. We propose that TRPM1 autoantibodies are generated in response to abnormal TRPM1 polypeptides encoded by an alternate mRNA splice variant expressed by malignant melanocytes.

The Transduction Cascade in Retinal ON-Bipolar Cells: Signal Processing and Disease

Our robust visual experience is based on the reliable transfer of information from our photoreceptor cells, the rods and cones, to higher brain centers. At the very first synapse of the visual system, information is split into two separate pathways, ON and OFF, which encode increments and decrements in light intensity, respectively. The importance of this segregation is borne out in the fact that receptive fields in higher visual centers maintain a separation between ON and OFF regions. In the past decade, the molecular mechanisms underlying the generation of ON signals have been identified, which are unique in their use of a G-protein signaling cascade. In this review, we consider advances in our understanding of G-protein signaling in ON-bipolar cell (BC) dendrites and how insights about signaling have emerged from visual deficits, mostly night blindness. Studies of G-protein signaling in ON-BCs reveal an intricate mechanism that permits the regulation of visual sensitivity over a wide dynamic range.

Serum Autoantibody Profiling of Patients with Paraneoplastic and Non-Paraneoplastic Autoimmune Retinopathy

PURPOSE

Although multiple serum antiretinal autoantibodies (ARAs) have been reported in patients with paraneoplastic and non-paraneoplastic autoimmune retinopathy ((n)pAIR), not all retinal antigens involved in (n)pAIR are specified. This study aims to serologically identify patients with presumed (n)pAIR through determination of both known and unknown ARAs by autoantibody profiling.

METHODS

An antigen suspension bead array using 188 different antigens representing 97 ocular proteins was performed to detect ARAs in serum samples of patients with presumed (n)pAIR (n = 24), uveitis (n = 151) and cataract (n = 21). Logistic regressions were used to estimate the associations between ocular antigens and diagnosis. Validation of interphotoreceptor matrix proteoglycan 2 (IMPG2) and recoverin antigens was performed by immunohistochemistry and immunoblot, respectively.

RESULTS

Samples of patients with presumed (n)pAIR exhibited a broad spectrum of ARAs. We identified retinal antigens that have already been described previously (e.g. recoverin), but also identified novel ARA targets. Most ARAs were not specific for (n)pAIR since their presence was also observed in patients with cataract or uveitis. High titers of autoantibodies directed against photoreceptor-specific nuclear receptor and retinol-binding protein 3 were more common in patients with presumed (n)pAIR compared to uveitis (p = 0.015 and p = 0.018, respectively). The presence of all other ARAs did not significantly differ between groups. In patients with presumed (n)pAIR, anti-recoverin autoantibodies were the most prevalent ARAs. Validation of bead array results by immunohistochemistry (anti-IMPG2) and immunoblot (anti-recoverin) showed concordant results in (n)pAIR patients.

CONCLUSIONS

Patients with (n)pAIR are characterized by the presence of a broad spectrum of ARAs. The diagnosis of (n)pAIR cannot be based on the mere presence of serum ARAs, as these are also commonly present in uveitis as well as in age-related cataract patients.

The TRPM1 channel in ON-bipolar cells is gated by both the α and the βγ subunits of the G-protein Go

Transmission from photoreceptors to ON bipolar cells in mammalian retina is mediated by a sign-inverting cascade. Upon binding glutamate, the metabotropic glutamate receptor mGluR6 activates the heterotrimeric G-protein Gα_oβ3γ13, and this leads to closure of the TRPM1 channel (melastatin). TRPM1 is thought to be constitutively open, but the mechanism that leads to its closure is unclear. We investigated this question in mouse rod bipolar cells by dialyzing reagents that modify the activity of either Gα_o or Gβγ and then observing their effects on the basal holding current. After opening the TRPM1 channels with light, a constitutively active mutant of Gα_o closed the channel, but wild-type Gα_o did not. After closing the channels by dark adaptation, phosducin or inactive Gα_o (both sequester Gβγ) opened the channel while the active mutant of Gα_o did not. Co-immunoprecipitation showed that TRPM1 interacts with Gβ3 and with the active and inactive forms of Gα_o. Furthermore, bioluminescent energy transfer assays indicated that while Gα_o interacts with both the N- and the C- termini of TRPM1, Gβγ interacts only with the N-terminus. Our physiological and biochemical results suggest that both Gα_o and Gβγ bind TRPM1 channels and cooperate to close them.

Ion Channels in the Eye: Involvement in Ocular Pathologies

The eye is the sensory organ of vision. There, the retina transforms photons into electrical signals that are sent to higher brain areas to produce visual sensations. In the light path to the retina, different types of cells and tissues are involved in maintaining the transparency of avascular structures like the cornea or lens, while others, like the retinal pigment epithelium, have a critical role in the maintenance of photoreceptor function by regenerating the visual pigment. Here, we have reviewed the roles of different ion channels expressed in ocular tissues (cornea, conjunctiva and neurons innervating the ocular surface, lens, retina, retinal pigment epithelium, and the inflow and outflow systems of the aqueous humor) that are involved in ocular disease pathophysiologies and those whose deletion or pharmacological modulation leads to specific diseases of the eye. These include pathologies such as retinitis pigmentosa, macular degeneration, achromatopsia, glaucoma, cataracts, dry eye, or keratoconjunctivitis among others. Several disease-associated ion channels are potential targets for pharmacological intervention or other therapeutic approaches, thus highlighting the importance of these channels in ocular physiology and pathophysiology.

Properties and functions of TRPM1 channels in the dendritic tips of retinal ON-bipolar cells

An increase in light intensity induces a depolarization in retinal ON-bipolar cells via a reduced glutamate release from presynaptic photoreceptor cells. The underlying transduction cascade in the dendritic tips of ON-bipolar cells involves mGluR6 glutamate receptors signaling to TRPM1 proteins that are an indispensable part of the transduction channel. Several other proteins are recognized to participate in the transduction machinery. Deficiency in many of these leads to congenital stationary night blindness, because rod bipolar cells, a subgroup of ON-bipolar cells, constitute the main route for sensory information under scotopic conditions. Here, we review the current knowledge about TRPM1 ion channels and how their activity is regulated within the postsynaptic compartment of ON-bipolar cells. The functional properties of TRPM1 channels in the dendritic compartment are not well understood as they differ substantially from those of recombinant TRPM1 channels. Critical evaluation of possible explanations of these discrepancies indicates that some key components of this transduction pathway might still not be known. The continued exploration of this pathway will yield further clinically useful insights.

Voriconazole, an antifungal triazol that causes visual side effects, is an inhibitor of TRPM1 and TRPM3 channels

PURPOSE

Administration of voriconazole, an antifungal triazole, causes transient visual disturbances in patients and attenuates the b-wave of the ERG. We sought to identify the retinal target of voriconazole underlying the effect on the ERG b-wave.

METHODS

Electroretinograms were recorded from mice before and after intraperitoneal injection of voriconazole. The effect of voriconazole on ON-bipolar cells was tested by patch-clamp recordings of ON-bipolar cells in mouse retinal slices. Effects of voriconazole on mGluR6 and TRPM3 were assessed by patch-clamp recordings of Chinese hamster ovary (CHO) and HEK293 cells transfected with either TRPM3 or mGluR6 plus Kir3.1/Kir3.4.

RESULTS

Voriconazole attenuated the ERG b-wave in mice, and inhibited ON-bipolar cell responses evoked by application of CPPG, an mGluR6 antagonist, onto the ON-bipolar cell dendrites, indicating that voriconazole blocks a step in the mGluR6-TRPM1 signal transduction pathway. Voriconazole almost completely blocked capsaicin-activated currents in ON-bipolar cells, which have been attributed to direct activation of the TRPM1 cation channel. Furthermore, application of voriconazole to CHO cells expressing TRPM3, a closely related channel to TRPM1, showed that voriconazole reversibly blocked pregnenolone sulfate-stimulated TRPM3 currents in transfected cells. In contrast, voriconazole only slightly inhibited mGluR6-mediated activation of G-protein activated inward rectifier potassium (GIRK) currents in cotransfected cells, suggesting that mGluR6 is not the primary target of voriconazole in ON-bipolar cells.

CONCLUSIONS

The visual disturbances associated with voriconazole are likely due to block of TRPM1 channels in retinal ON-bipolar cells. Other neurological effects of voriconazole may be due to block of TRPM3 channels expressed in the brain.

Case of paraneoplastic retinopathy with retinal ON-bipolar cell dysfunction and subsequent resolution of ERGs

PURPOSE

To report a patient with cancer-associated retinopathy and retinal ON-bipolar cell dysfunction who had a resolution of the electroretinograms (ERGs) after a resection of an ovarian cancer and chemotherapy.

CASE REPORT

A 71-year-old Japanese female patient visited us complaining of night blindness and photopsia in both eyes for 6 months. Her visual acuity was 20/20 in both eyes, and fundus examination, fluorescence angiography, and optical coherence tomography showed no abnormalities in both eyes. The rod responses of the ERGs were absent and bright-flash ERGs were electronegative. The ON responses of the focal macular ERGs and full-field long-flash ERGs were absent. These ERG findings indicate an ON-bipolar cell dysfunction. A general physical examination revealed the presence of ovarian cancer. After resection of the ovarian cancer and adjuvant chemotherapy, the ERGs of the left eye completely recovered within 2 years and those of right eye recovered subsequently. The autoantibody against transient receptor potential melastatin 1 (TRPM1) was not detected in the serum.

CONCLUSION

Our case demonstrates that retinal ON-bipolar dysfunction can be caused by ovarian cancer. Our case indicates that some autoantibodies against other than TRPM1 might cause transient dysfunction of retinal ON-bipolar cells.

Oligomeric state of purified transient receptor potential melastatin-1 (TRPM1), a protein essential for dim light vision

Transient receptor potential melastatin-1 (TRPM1) is essential for the light-induced depolarization of retinal ON bipolar cells. TRPM1 likely forms a multimeric channel complex, although almost nothing is known about the structure or subunit composition of channels formed by TRPM1 or any of its close relatives. Recombinant TRPM1 was robustly expressed in insect cells, but only a small fraction was localized to the plasma membrane. Similar intracellular localization was observed when TRPM1 was heterologously expressed in mammalian cells. TRPM1 was affinity-purified from Sf9 cells and complexed with amphipol, followed by detergent removal. In blue native gels and size exclusion chromatography, TRPM1 migrated with a mobility consistent with detergent- or amphipol-bound dimers. Cross-linking experiments were also consistent with a dimeric subunit stoichiometry, and cryoelectron microscopy and single particle analysis without symmetry imposition yielded a model with approximate 2-fold symmetrical features. Finally, electron microscopy of TRPM1-antibody complexes revealed a large particle that can accommodate TRPM1 and two antibody molecules. Taken together, these data indicate that purified TRPM1 is mostly dimeric. The three-dimensional structure of TRPM1 dimers is characterized by a small putative transmembrane domain and a larger domain with a hollow cavity. Blue native gels of solubilized mouse retina indicate that TRPM1 is present in two distinct complexes: one similar in size to the recombinant protein and one much larger. Because dimers are likely not functional ion channels, these results suggest that additional partner subunits participate in forming the transduction channel required for dim light vision and the ON pathway.

Pharmacological analysis of intrinsic neuronal oscillations in rd10 retina

In the widely used mouse model of retinal degeneration, rd1, the loss of photoreceptors leads to rhythmic electrical activity of around 10-16 Hz in the remaining retinal network. Recent studies suggest that this oscillation is formed within the electrically coupled network of AII amacrine cells and ON-bipolar cells. A second mouse model, rd10, displays a delayed onset and slower progression of degeneration, making this mouse strain a better model for human retinitis pigmentosa. In rd10, oscillations occur at a frequency of 3-7 Hz, raising the question whether oscillations have the same origin in the two mouse models. As rd10 is increasingly being used as a model to develop experimental therapies, it is important to understand the mechanisms underlying the spontaneous rhythmic activity. To study the properties of oscillations in rd10 retina we combined multi electrode recordings with pharmacological manipulation of the retinal network. Oscillations were abolished by blockers for ionotropic glutamate receptors and gap junctions. Frequency and amplitude of oscillations were modulated strongly by blockers of inhibitory receptors and to a lesser extent by blockers of HCN channels. In summary, although we found certain differences in the pharmacological modulation of rhythmic activity in rd10 compared to rd1, the overall pattern looked similar. This suggests that the generation of rhythmic activity may underlie similar mechanisms in rd1 and rd10 retina.

Choroidal atrophy in a patient with paraneoplastic retinopathy and anti-TRPM1 antibody

The purpose of this paper is to report choroidal atrophy in a patient with cancer-associated retinopathy who had autoantibodies against the transient receptor potential cation channel, subfamily M, member 1 (TRPM1). A 69-year-old man visited our clinic in July 2010 with complaints of blurred vision and night blindness in both eyes. The full-field electroretinograms were negative type, indicating ON bipolar cell dysfunction. General physical examination revealed small cell carcinoma of the lung, and Western blot of the patient’s serum showed autoantibodies against TRPM1. We diagnosed this patient with cancer-associated retinopathy and retinal ON bipolar dysfunction due to anti-TRPM1 autoantibody. We followed him for more than 2 years from the initial visit and his symptoms have not changed. However, consistent with the choroidal hypopigmentation of the fundus, spectral domain optical coherence tomography showed a decrease in choroidal thickness of about one third over a 2-year follow-up period. We suggest that this case of gradually progressive choroidal atrophy was caused by the autoantibody against TRPM1 directly, because TRPM1 is expressed not only on ON bipolar cells but also on melanocytes. These findings indicate that we should be aware of choroidal thickness in patients with paraneoplastic retinopathy who have retinal ON bipolar dysfunction with the anti-TRPM1 antibody.

Autoantibodies to transient receptor potential cation channel, subfamily M, member 1 in a Japanese patient with melanoma-associated retinopathy

PURPOSE

To report a case of melanoma-associated retinopathy (MAR) in a Japanese patient found to have autoantibodies to transient receptor potential cation channel, subfamily M, member 1 (TRPM1).

CASE

An 82-year-old man presented with blurred vision OS as well as night blindness and photopsia OU. Fundus photography, fluorescein angiography, and spectral domain-optical coherence tomography findings were essentially normal. Goldmann perimetry revealed a relative central scotoma, including the blind spot in the right eye, as well as a relative scotoma around a blind spot OS. The full-field scotopic electroretinograms showed a "negative-type" pattern OU, suggestive of extensive bipolar cell dysfunction. Systemic examination revealed that the patient had malignant melanoma of the anus with lung metastasis. Autoantibodies to TRPM1 were detected in the serum of the patient by immunoblot analysis. Vitreous opacity developed during follow-up. The visual symptoms and vitreous opacity of the patient were markedly improved after oral prednisolone therapy. The patient died as a result of widespread metastasis of the melanoma at 11 months after his first visit.

CONCLUSION

The present case is the first reported instance of MAR positive for autoantibodies to TRPM1 in an Asian patient.

Genetic risk factors for insidious equine recurrent uveitis in Appaloosa horses

Appaloosa horses are predisposed to equine recurrent uveitis (ERU), an immune-mediated disease characterized by recurring inflammation of the uveal tract in the eye, which is the leading cause of blindness in horses. Nine genetic markers from the ECA1 region responsible for the spotted coat color of Appaloosa horses, and 13 microsatellites spanning the equine major histocompatibility complex (ELA) on ECA20, were evaluated for association with ERU in a group of 53 Appaloosa ERU cases and 43 healthy Appaloosa controls. Three markers were significantly associated (corrected P-value <0.05): a SNP within intron 11 of the TRPM1 gene on ECA1, an ELA class I microsatellite located near the boundary of the ELA class III and class II regions and an ELA class II microsatellite located in intron 1 of the DRA gene. Association between these three genetic markers and the ERU phenotype was confirmed in a second population of 24 insidious ERU Appaloosa cases and 16 Appaloosa controls. The relative odds of being an ERU case for each allele of these three markers were estimated by fitting a logistic mixed model with each of the associated markers independently and with all three markers simultaneously. The risk model using these markers classified ~80% of ERU cases and 75% of controls in the second population as moderate or high risk, and low risk respectively. Future studies to refine the associations at ECA1 and ELA loci and identify functional variants could uncover alleles conferring susceptibility to ERU in Appaloosa horses.

Diagnostic features of the autoimmune retinopathies

The term autoimmune retinopathy encompasses a spectrum of rare autoimmune diseases that affect retinal function, often but not exclusively at the level of the photoreceptor. They typically present with painless visual loss, which may be accompanied by normal fundus examination. Some are progressive, often rapidly. They present a diagnostic challenge because there are no standardised clinical or laboratory based diagnostic criteria. Included within the spectrum are cancer-associated retinopathy, melanoma-associated retinopathy and presumed non-paraneoplastic autoimmune retinopathy. Differentiation from other retinopathies can be challenging, with overlap in symptoms, signs, and investigation findings, and an absence of pathognomonic features. However, technological developments in ophthalmic imaging and serological investigation over the past decade are adding novel dimensions to the investigation and classification of patients with these rare diseases. This review addresses the clinical, imaging, and serological features of the autoimmune retinopathies, and discusses the relative strengths and limitations of candidate diagnostic features.

TRPM1

The transient receptor potential (TRP) channels play a wide variety of essential roles in the sensory systems of various species, both invertebrates and vertebrates. The TRP channel was first identified as a molecule required for proper light response in Drosophila melanogaster. We and another group recently revealed that TRPM1, the founding member of the melanoma-related transient receptor potential (TRPM) subfamily, is required for the photoresponse in mouse retinal ON-bipolar cells. We further demonstrated that Trpm1 is a component of the transduction cation channel negatively regulated by the metabotropic glutamate receptor 6 (mGulR6) cascade in ON-bipolar cells through a reconstitution experiment using CHO cells expressing Trpm1, mGluR6, and Goα. Furthermore, human TRPM1 mutations are associated with congenital stationary night blindness (CSNB), whose patients lack rod function and suffer from night blindness starting in early childhood. In addition to the function of transduction cation channel, TRPM1 is one of the retinal autoantigens in some paraneoplastic retinopathy (PR) associated with retinal ON-bipolar cell dysfunction. In this chapter, we describe physiological functions of the TRPM1 channel and its underlying biochemical mechanisms in retinal ON-bipolar cells in association with CSNB and PR.

Autoimmune retinopathy

PURPOSE OF REVIEW

Autoimmune retinopathy (AIR) is an immune-mediated disorder characterized by progressive visual loss, abnormal electroretinographic and visual field findings in the presence of circulating anti-retinal antibodies. This review highlights advances made toward understanding the pathophysiology, clinical manifestations, and trends in the management of AIR.

RECENT FINDINGS

The pathophysiology of AIR is likely antibody-mediated. AIR serum autoantibodies are variable in their size and retinal tissue they target and can also be present in healthy controls and multiple autoimmune diseases. Rarely, AIR may be associated with dysregulated self-tolerance mechanisms in the thymus. Despite progress in research, our understanding of AIR remains incomplete. Lack of standardized methods for anti-retinal antibody testing continues to challenge the interpretation of seropositivity. Conventional immunosuppressives have been further studied, and promising immunomodulatory therapies, such as targeted B-cell therapy, have been introduced. Newer imaging modalities such as fundus autofluorescence and spectral domain optical coherence tomography may be helpful in diagnosis, monitoring progression of disease and response to treatment.

SUMMARY

AIR is a rare but vision-threatening disease whose pathogenesis is poorly defined. Lack of standardized clinical or laboratory criteria further complicates the diagnosis and management. Despite recent progress, further basic science research into the autoimmune process is needed. Prospective controlled clinical trials with immunomodulatory therapy can help define future treatment paradigms.

Degeneration of retinal on bipolar cells induced by serum including autoantibody against TRPM1 in mouse model of paraneoplastic retinopathy

The paraneoplastic retinopathies (PRs) are a group of eye diseases characterized by a sudden and progressive dysfunction of the retina caused by an antibody against a protein in a neoplasm. Evidence has been obtained that the transient receptor potential melastatin 1 (TRPM1) protein was one of the antigens for the autoantibody against the ON bipolar cells in PR patients. However, it has not been determined how the autoantibody causes the dysfunction of the ON bipolar cells. We hypothesized that the antibody against TRPM1 in the serum of patients with PR causes a degeneration of retinal ON bipolar cells. To test this hypothesis, we injected the serum from the PR patient, previously shown to contain anti-TRPM1 antibodies by westerblot, intravitreally into mice and examined the effects on the retina. We found that the electroretinograms (ERGs) of the mice were altered acutely after the injection, and the shape of the ERGs resembled that of the patient with PR. Immunohistochemical analysis of the eyes injected with the serum showed immunoreactivity against bipolar cells only in wild-type animals and not in TRPM1 knockout mice,consistent with the serum containing anti-TRPM1 antibodies. Histology also showed that some of the bipolar cells were apoptotic by 5 hours after the injection in wild type mice, but no bipolar cell death was found in TRPM1 knockout mice, . At 3 months, the inner nuclear layer was thinner and the amplitudes of the ERGs were still reduced. These results indicate that the serum of a patient with PR contained an antibody against TRPM1 caused an acute death of retinal ON bipolar cells of mice.

Diagnosis of occult melanoma using transient receptor potential melastatin 1 (TRPM1) autoantibody testing: a novel approach

PURPOSE

To report the first case of melanoma-associated retinopathy (MAR) and underlying occult melanoma diagnosed based on the presence of serum transient receptor potential melastatin 1 (TRPM1) autoantibodies.

DESIGN

Interventional case report with basic science correlation.

PARTICIPANTS

One patient with MAR.

INTERVENTION

Testing for the presence of serum TRPM1 autoantibodies.

MAIN OUTCOME MEASURES

Diagnosis of an occult melanoma involving the axillary lymph nodes (unknown primary site) and MAR based on the presence of TRPM1 autoantibodies in the patient's serum.

RESULTS

The patient's clinical exam was remarkable for mild intraocular inflammation in both eyes and retinal hemorrhages with an apparent choroidal neovascularization in the left eye, which was confirmed by fluorescein angiography and indocyanine green angiography testing. Humphrey visual field 30-2 SITA-fast (Humphrey Visual Field Analyzer, Carl Zeiss Meditec, Inc, Dublin, CA) demonstrated diffuse depression in both eyes out of proportion to the clinical exams, prompting electroretinography testing that revealed an electronegative response. Dark-adapted thresholds were markedly elevated and mediated by cones. Due to concern for MAR, a systemic work-up for melanoma was performed by the primary care physician that was unrevealing. Given our continued clinical suspicion for MAR, the patient's serum was sent for evaluation for TRPM1 autoantibodies. The patient's serum applied to normal human retina exhibited positivity in the inner nuclear layer. Application of the patient's serum to wild-type and TRPM1 knockout mouse retina revealed strongly labeled bipolar cells in the wild-type retina, but not in the TRPM1 knockout retina, indicating TRPM1-dependent immunoreactivity. The antigen was confirmed as TRPM1 by labeling of TRPM1-transfected human embryonic kidney 293 cells. Additional systemic work-up prompted by this finding resulted in identification of an occult metastatic melanoma involving the axillary lymph nodes with an unknown primary site. The patient underwent surgical excision of the occult melanoma without evidence of other sites of metastases. He also received intravenous immunoglobulin therapy and his vision has stabilized.

CONCLUSIONS

This is the first reported case of a melanoma-associated retinopathy diagnosed utilizing the innovative approach of testing for serum TRPM1 autoantibodies.

Serum TRPM1 autoantibodies from melanoma associated retinopathy patients enter retinal on-bipolar cells and attenuate the electroretinogram in mice

Melanoma-associated retinopathy (MAR) is a paraneoplastic syndrome associated with cutaneous malignant melanoma and the presence of autoantibodies that label neurons in the inner retina. The visual symptoms and electroretinogram (ERG) phenotype characteristic of MAR resemble the congenital visual disease caused by mutations in TRPM1, a cation channel expressed by both melanocytes and retinal bipolar cells. Four serum samples from MAR patients were identified as TRPM1 immunoreactive by 1. Labeling of ON-bipolar cells in TRPM1+/+ but not TRPM1−/− mouse retina, 2. Labeling of TRPM1-transfected CHO cells; and 3. Attenuation of the ERG b-wave following intravitreal injection of TRPM1-positive MAR IgG into wild-type mouse eyes, and the appearance of the IgG in the retinal bipolar cells at the conclusion of the experiment. Furthermore, the epitope targeted by the MAR autoantibodies was localized within the amino-terminal cytoplasmic domain of TRPM1. Incubation of live retinal neurons with TRPM1-positive MAR serum resulted in the selective accumulation of IgG in ON-bipolar cells from TRPM1+/+ mice, but not TRPM1−/− mice, suggesting that the visual deficits in MAR are caused by the uptake of TRPM1 autoantibodies into ON-bipolar cells, where they bind to an intracellular epitope of the channel and reduce the ON-bipolar cell response to light.

The immunological basis of degenerative diseases of the eye

It has become clear that disorders that were once considered "degenerative" have complex mechanisms, with many having been shown to have immune mediation as part of the disease process. These include arteriosclerotic heart disease and Alzheimer's disease. Indeed, several ocular disorders that once fell into the "degenerative" category meet this criterion as well. Immune mediation has been shown to be a part of many of the most common ocular disorders, and not just that of uveitis, or ocular inflammatory disease.

Autoantibody against transient receptor potential M1 cation channels of retinal ON bipolar cells in paraneoplastic vitelliform retinopathy

Background

Paraneoplastic retinopathy is caused by the cross-reaction of neoplasm-directed autoantibodies against retinal antigens and results in retinal damage. Paraneoplastic vitelliform retinopathy, a presumed paraneoplastic retinopathy with features of atypical melanoma-associated retinopathy, has recently been reported in patients with metastatic melanoma. Ocular ultrastructure and its autoantibody localization of paraneoplastic vitelliform retinopathy are still indefinable. This is the first report of anti-transient receptor potential M1 antibody directly against human retinal bipolar dendritic tips in a melanoma patient with paraneoplastic vitelliform retinopathy.

Case presentation

We present a pair of postmortem eyes of an 80-year-old male with metastatic cutaneous melanoma, who developed paraneoplastic vitelliform retinopathy. The autopsied eyes were examined with light microscopy, immunohistochemistry, and transmission electron microscopy. Microscopically, the inner nuclear layer and outer plexiform layer were the most affected retinal structures, with local thinning. The lesions extended to the outer nuclear layer, resulting in focal retinal degeneration, edema, and atrophy. No active inflammation or melanoma cells were observed. Immunohistochemistry showed tightly compact bipolar cell nuclei (protein kinase C alpha/calbindin positive) with blur/loss of ON bipolar cell dendritic tips (transient receptor potential M1 positive) in diffusely condensed outer plexiform layer. The metastatic melanoma cells in his lung also showed immunoreactivity against transient receptor potential M1 antibody. Transmission electron microscopy illustrated degenerated inner nuclear layer with disintegration of cells and loss of cytoplasmic organelles. These cells contained many lysosomal and autophagous bodies and damaged mitochondria. Their nuclei appeared pyknotic and fragmentary. The synapses in the outer plexiform layer were extensively degenerated and replaced with empty vacuoles and disintegrated organelles.

Conclusion

This case provides a convincing histological evidence of melanoma-associated autoantibodies directly against transient receptor potential M1 channels that target the ON bipolar cell structures in the inner nuclear and outer plexiform layers in paraneoplastic vitelliform retinopathy.