Autoantibody against transient receptor potential M1 cation channels of retinal ON bipolar cells in paraneoplastic vitelliform retinopathy
© Wang et al.; licensee BioMed Central Ltd. 2012
Received: 21 August 2012
Accepted: 7 November 2012
Published: 13 November 2012
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.
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.
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.
KeywordsParaneoplastic vitelliform retinopathy Autoimmune retinopathy Transient receptor potential channel Bipolar cell Melanoma-associated retinopathy Autoantibody
Paraneoplastic retinopathy (PR) is mediated by tumor-associated autoantibodies directed against retinal antigens. PR patients usually develop reduced visual acuity, photopsias, nyctalopia, visual field defects, and reduced a- and/or b-waves in electroretinography (ERG) [1, 2]. The two main types of PR are cancer-associated retinopathy (CAR) and melanoma-associated retinopathy (MAR). CAR is mostly associated with small-cell lung cancer and has specific autoantibodies against photoreceptors [3, 4]. MAR typically develops in patients with metastatic cutaneous or uveal melanoma; autoantibodies against retinal bipolar cells are the hallmark of MAR [5–8]. In MAR, the fundus is unremarkable in 44% cases, although fundus changes such as focal depigmentation, optic nerve pallor, and/or retinal vascular attenuation have been reported [6, 9]. Recently, a MAR-like retinopathy phenotype, termed paraneoplastic vitelliform retinopathy, has been recognized that is also associated with cutaneous or uveal melanoma [10, 11]. Unlike the typical normal-appearing fundus in MAR, paraneoplastic vitelliform retinopathy is characterized by vitelliform retinal lesions at the level of the retinal pigment epithelium (RPE) with associated serous retinal detachment and subretinal accumulation of hyperautofluorescent material in the posterior pole [10, 12].
Similar to CAR and MAR that are immunologically heterogeneous, serum autoantibodies, such as anti-bipolar cell antigens, interphotoreceptor retinoid-binding protein (IRBP), carbonic anhydrase II (CAII), and bestrophin, are reported in patients with paraneoplastic vitelliform retinopathy [10, 13, 14]. Among them, anti-bipolar cell antibody is the most commonly identified autoantibody [15, 16]. As reduced ERG b-wave is indicative of retinal bipolar cell impairment, it is hypothesized that the autoantibodies generated by melanoma patients are directed against retinal bipolar cells in paraneoplastic vitelliform retinopathy.
Recently, a new connection between PR and bipolar cells has been made by the identification of a cation channel named transient receptor potential M1 (TRPM1, also known as melastatin 1). TRPM1 was initially identified in melanocytes and cutaneous melanoma and is a marker for metastasis and prognosis [17–19]. The loss or downregulation of TRPM1 mRNA correlates with an increased risk of metastatic melanoma [17, 18]. The patterns of TRPM1 transcript expression also help differentiate Spitz nevi from nodular melanomas, with higher ubiquitous expression in Spitz nevi and higher incidence of loss in nodular melanomas . TRPM1 is also expressed in retinal bipolar dendritic tips [20–23]. Several studies demonstrated that TRPM1 cation channel is essential for ON bipolar cell signaling [22, 24, 25]. In addition, several groups have found that human TRPM1 mutations are linked to congenital stationary night blindness [26–28]. Furthermore, it has been reported that TRPM1 is the target of autoantibodies in some PR patients [29, 30].
As a subtype of PR, the exact pathogenesis of paraneoplastic vitelliform retinopathy remains elusive. Recently, we reported the clinical manifestations and pathology of a paraneoplastic vitelliform retinopathy case with lesions in inner nuclear layer (INL), outer plexiform layer (OPL), and outer nuclear layer (ONL) of the retina, the loci of which correspond to the clinical fundus lesions . Herein, we re-examine this case including metastatic melanoma cells in the lung with immunohistochemistry and transmission electron microscopy (TEM).
The detailed clinical history and some pathological findings were described previously . Briefly, an 80-year-old male with lung biopsy confirmed metastatic melanoma was suspected of choroidal metastases. One year after diagnosis with metastatic melanoma, he developed nyctalopia and bilateral retinal lesions. The patient was referred to the Department of Ophthalmic Oncology at the Cole Eye Institute. His best corrected visual acuity was 20/30 in the right eye and 20/25 in the left eye. Fundus examination showed bilateral, multiple, deep, yellowish lesions in the posterior pole and mid-periphery. Optical coherence tomography excluded the possibility of choroidal metastases. ERG showed a mild reduction in both a- and b-wave amplitudes for both scotopic and photopic waveforms. His serum was found to have autoantibodies against CAII and an unknown 35-kDa RPE protein. The patient expired approximately one month following ophthalmic examination.
Cellular markers used in the study
Rod bipolar cell, DB4 ON bipolar cell
DB3 OFF bipolar cell
ON bipolar dendrite, melanocyte
Our study provides direct morphological evidence that the retinal bipolar cells are damaged in paraneoplastic vitelliform retinopathy. Importantly, TRPM1 is identified as a target of anti-bipolar antibody produced in this patient with paraneoplastic vitelliform retinopathy. TRPM1 channels on the ON bipolar dendritic tips in the OPL were specifically targeted and TRPM1 antigens were also detected in the metastatic melanoma cells in the lung. Additionally, the ultrastructures of the bipolar nuclei and synapses were damaged.
In addition to previously reported serum autoantibodies, including IRBP, CAII, and bestrophin in patients with paraneoplastic vitelliform retinopathy [10, 13, 14], peroxiredoxin 3 (PRDX3) is identified as a new putative antigen in RPE attacked by autoantibodies in a melanoma patient with paraneoplastic vitelliform maculopathy . It is hypothesized that the paraneoplastic autoimmune reaction against this 26-kDa PRDX3 may be a cause of paraneoplastic vitelliform retinopathy. However, our patient’s serum was only detected two retinal autoantibodies against a 30-kDa protein (CAII) and an unknown 35-kDa RPE protein by Western blot .
Neuron cells in the inner nuclear layer and their functions and markers
Responsible for signals transmitting from photoreceptors to retinal ganglion cells; divided into ON and OFF bipolar cells according to their responses to visual stimuli: light stimuli increase the conductance of ON bipolar cells but decrease that in OFF bipolar cell
Responsible for modulation of signal reaching ganglion cells; affecting orientation selectivity, light–dark effect and color discrimination
Having an integrative role in retinal processing and release inhibitory neurotransmitters; providing feedback for the photoreceptors
Forming architectural support structures in the retina; involved in protein synthesis, intracellular transport and secretion; helping nourish and maintain the outer neuroretina
Glutamine synthetase 
Recently, TRPM1 is identified as a suspected target of the autoantibodies produced in melanoma patients with MAR . Dhingra et al.  demonstrate that sera of melanoma patients with PR specifically recognized TRPM1 in mouse bipolar cells. Up to date, no TRPM1 abnormality has been illustrated in the human retina of paraneoplastic vitelliform retinopathy. Although the clinical findings of PR patients with serum anti-TPRM1 autoantibody have reported in the literature (CAR and MAR patients) [29, 30], the pathological mechanism of all these PR entities is through the common identified TRPM1 channel. Additional unknown mechanisms may play a role in determining the phenotypes of PR patients. In this study, we illustrate that TRPM1 channels are diffusely damaged and TRPM1 antigen is also expressed on the metastatic lung melanoma cells. Although downregulation or loss of TRPM1 expression has been reported in melanoma metastasis , this study cannot compare TRRM1 expression levels between original cutaneous melanoma and lung metastasis in this case due to lack of original melanoma specimens. However, our findings strongly support that anti-TRPM1 autoantibody is involved in the pathogenesis of paraneoplastic vitelliform retinopathy, an atypical MAR. ERG of Trpm1 deficient mice has a normal a-wave, but no b-wave, indicating a loss of bipolar cell response . The damaged TRPM1 channel, either before or after ON bipolar cell damage, could cause abnormal light signal transduction, which consequently affects night vision and ERG b-wave. In this case, lesions were also found from the INL and OPL extending to the ONL that might cause abnormal ERG a-wave. However, whether the ONL changes are primary or secondary events remains to be resolved.
Both immunohistochemistry and TEM showed specific damages in bipolar cells and TRPM1 cation channel on the ON bipolar dendritic tips. The immunohistochemical data provide evidence of autoantibodies against the TRPM1 cation channel on retinal ON bipolar cells and metastatic melanoma cells in paraneoplastic vitelliform retinopathy.
Written informed consent was obtained from the patient’s family for publication of this Case report and any accompanying images. A copy of the written consent is available for review by the Series Editor of this journal.
Retinal pigment epithelium
Interphotoreceptor retinoid-binding protein
Carbonic anhydrase II
Transient receptor potential M1
Inner nuclear layer
Outer plexiform layer
Outer nuclear layer
Transmission electron microscopy
Protein kinase C alpha
The National Eye Institute Intramural Research Program supported the study.
- Heckenlively JR, Ferreyra HA: Autoimmune retinopathy: a review and summary. Semin Immunopathol. 2008, 30 (2): 127-134. 10.1007/s00281-008-0114-7.View ArticlePubMedGoogle Scholar
- Alabduljalil T, Behbehani R: Paraneoplastic syndromes in neuro-ophthalmology. Curr Opin Ophthalmol. 2007, 18 (6): 463-469. 10.1097/ICU.0b013e3282f0b497.View ArticlePubMedGoogle Scholar
- Kobayashi M, Ikezoe T, Uemura Y, Takeuchi T, Ueno H, Ohtsuki Y, Taguchi H: Establishment of a novel small cell lung carcinoma cell line with specific recoverin expression from a patient with cancer-associated retinopathy. Lung Cancer. 2007, 56 (3): 319-326. 10.1016/j.lungcan.2007.01.030.View ArticlePubMedGoogle Scholar
- Khan N, Huang JJ, Foster CS: Cancer associated retinopathy (CAR): An autoimmune-mediated paraneoplastic syndrome. Semin Ophthalmol. 2006, 21 (3): 135-141. 10.1080/08820530500350662.View ArticlePubMedGoogle Scholar
- Honnorat J, Antoine JC: Paraneoplastic neurological syndromes. Orphanet J Rare Dis. 2007, 2: 22-10.1186/1750-1172-2-22.View ArticlePubMedPubMed CentralGoogle Scholar
- Keltner JL, Thirkill CE, Yip PT: Clinical and immunologic characteristics of melanoma-associated retinopathy syndrome: eleven new cases and a review of 51 previously published cases. J Neuroophthalmol. 2001, 21 (3): 173-187. 10.1097/00041327-200109000-00004.View ArticlePubMedGoogle Scholar
- Zacks DN, Pinnolis MK, Berson EL, Gragoudas ES: Melanoma-associated retinopathy and recurrent exudative retinal detachments in a patient with choroidal melanoma. Am J Ophthalmol. 2001, 132 (4): 578-581. 10.1016/S0002-9394(01)01086-8.View ArticlePubMedGoogle Scholar
- Nieuwendijk TJ, Hooymans JM: Paraneoplastic vitelliform retinopathy associated with metastatic choroidal melanoma. Eye (Lond). 2007, 21 (11): 1436-1437. 10.1038/sj.eye.6702949.View ArticleGoogle Scholar
- Lu Y, Jia L, He S, Hurley MC, Leys MJ, Jayasundera T, Heckenlively JR: Melanoma-associated retinopathy: a paraneoplastic autoimmune complication. Arch Ophthalmol. 2009, 127 (12): 1572-1580. 10.1001/archophthalmol.2009.311.View ArticlePubMedPubMed CentralGoogle Scholar
- Sotodeh M, Paridaens D, Keunen J, van Schooneveld M, Adamus G, Baarsma S: Paraneoplastic vitelliform retinopathy associated with cutaneous or uveal melanoma and metastases. Klin Monbl Augenheilkd. 2005, 222 (11): 910-914. 10.1055/s-2005-858840.View ArticlePubMedGoogle Scholar
- Grunwald L, Kligman BE, Shields CL: Acute exudative polymorphous paraneoplastic vitelliform maculopathy in a patient with carcinoma, not melanoma. Arch Ophthalmol. 2011, 129 (8): 1104-1106. 10.1001/archophthalmol.2011.215.View ArticlePubMedGoogle Scholar
- Koreen L, He SX, Johnson MW, Hackel RE, Khan NW, Heckenlively JR: Anti-retinal pigment epithelium antibodies in acute exudative polymorphous vitelliform maculopathy: a new hypothesis about disease pathogenesis. Arch Ophthalmol. 2011, 129 (1): 23-29. 10.1001/archophthalmol.2010.316.View ArticlePubMedGoogle Scholar
- Bianciotto C, Shields CL, Thirkill CE, Materin MA, Shields JA: Paraneoplastic retinopathy with multiple detachments of the neurosensory retina and autoantibodies against interphotoreceptor retinoid binding protein (IRBP) in cutaneous melanoma. Br J Ophthalmol. 2010, 94 (12): 1684-1685. 10.1136/bjo.2008.151480. 1696View ArticlePubMedGoogle Scholar
- Eksandh L, Adamus G, Mosgrove L, Andreasson S: Autoantibodies against bestrophin in a patient with vitelliform paraneoplastic retinopathy and a metastatic choroidal malignant melanoma. Arch Ophthalmol. 2008, 126 (3): 432-435. 10.1001/archopht.126.3.432.View ArticlePubMedGoogle Scholar
- Palmowski AM, Haus AH, Pfohler C, Reinhold U, Allgayer R, Tilgen W, Ruprecht KW, Thirkill CE: Bilateral multifocal chorioretinopathy in a woman with cutaneous malignant melanoma. Arch Ophthalmol. 2002, 120 (12): 1756-1761.PubMedGoogle Scholar
- Aronow ME, Adamus G, Abu-Asab M, Wang Y, Chan CC, Singh AD: Paraneoplastic Vitelliform Retinopathy: Clinicopathologic Correlation and Review of the Literature. Surv Ophthalmol. 2012, 57 (6): 558-564. 10.1016/j.survophthal.2012.02.004.View ArticlePubMedPubMed CentralGoogle Scholar
- Erickson LA, Letts GA, Shah SM, Shackelton JB, Duncan LM: TRPM1 (Melastatin-1/MLSN1) mRNA expression in Spitz nevi and nodular melanomas. Mod Pathol. 2009, 22 (7): 969-976. 10.1038/modpathol.2009.56.View ArticlePubMedGoogle Scholar
- Duncan LM, Deeds J, Cronin FE, Donovan M, Sober AJ, Kauffman M, McCarthy JJ: Melastatin expression and prognosis in cutaneous malignant melanoma. J Clin Oncol. 2001, 19 (2): 568-576.PubMedGoogle Scholar
- Miller AJ, Du J, Rowan S, Hershey CL, Widlund HR, Fisher DE: Transcriptional regulation of the melanoma prognostic marker melastatin (TRPM1) by MITF in melanocytes and melanoma. Cancer Res. 2004, 64 (2): 509-516. 10.1158/0008-5472.CAN-03-2440.View ArticlePubMedGoogle Scholar
- Bellone RR, Brooks SA, Sandmeyer L, Murphy BA, Forsyth G, Archer S, Bailey E, Grahn B: Differential gene expression of TRPM1, the potential cause of congenital stationary night blindness and coat spotting patterns (LP) in the Appaloosa horse (Equus caballus). Genetics. 2008, 179 (4): 1861-1870. 10.1534/genetics.108.088807.View ArticlePubMedPubMed CentralGoogle Scholar
- Kim DS, Ross SE, Trimarchi JM, Aach J, Greenberg ME, Cepko CL: Identification of molecular markers of bipolar cells in the murine retina. J Comp Neurol. 2008, 507 (5): 1795-1810. 10.1002/cne.21639.View ArticlePubMedPubMed CentralGoogle Scholar
- Morgans CW, Zhang J, Jeffrey BG, Nelson SM, Burke NS, Duvoisin RM, Brown RL: TRPM1 is required for the depolarizing light response in retinal ON-bipolar cells. Proc Natl Acad Sci USA. 2009, 106 (45): 19174-19178. 10.1073/pnas.0908711106.View ArticlePubMedPubMed CentralGoogle Scholar
- Klooster J, Blokker J, Ten Brink JB, Unmehopa U, Fluiter K, Bergen AA, Kamermans M: Ultrastructural localization and expression of TRPM1 in the human retina. Invest Ophthalmol Vis Sci. 2011, 52 (11): 8356-8362. 10.1167/iovs.11-7575.View ArticlePubMedGoogle Scholar
- Koike C, Obara T, Uriu Y, Numata T, Sanuki R, Miyata K, Koyasu T, Ueno S, Funabiki K, Tani A, Ueda H, Kondo M, Mori Y, Tachibana M, Furukawa T: TRPM1 is a component of the retinal ON bipolar cell transduction channel in the mGluR6 cascade. Proc Natl Acad Sci USA. 2010, 107 (1): 332-337. 10.1073/pnas.0912730107.View ArticlePubMedGoogle Scholar
- Koike C, Numata T, Ueda H, Mori Y, Furukawa T: TRPM1: a vertebrate TRP channel responsible for retinal ON bipolar function. Cell Calcium. 2010, 48 (2–3): 95-101.View ArticlePubMedGoogle Scholar
- Audo I, Kohl S, Leroy BP, Munier FL, Guillonneau X, Mohand-Said S, Bujakowska K, Nandrot EF, Lorenz B, Preising M, Kellner U, Renner AB, Bernd A, Antonio A, Moskova-Doumanova V, Lancelot ME, Poloschek CM, Drumare I, Defoort-Dhellemmes S, Wissinger B, Leveillard T, Hamel CP, Schorderet DF, De Baere E, Berger W, Jacobson SG, Zrenner E, Sahel JA, Bhattacharya SS, Zeitz C: TRPM1 is mutated in patients with autosomal-recessive complete congenital stationary night blindness. Am J Hum Genet. 2009, 85 (5): 720-729. 10.1016/j.ajhg.2009.10.013.View ArticlePubMedPubMed CentralGoogle Scholar
- van Genderen MM, Bijveld MM, Claassen YB, Florijn RJ, Pearring JN, Meire FM, McCall MA, Riemslag FC, Gregg RG, Bergen AA, Kamermans M: Mutations in TRPM1 are a common cause of complete congenital stationary night blindness. Am J Hum Genet. 2009, 85 (5): 730-736. 10.1016/j.ajhg.2009.10.012.View ArticlePubMedPubMed CentralGoogle Scholar
- Li Z, Sergouniotis PI, Michaelides M, Mackay DS, Wright GA, Devery S, Moore AT, Holder GE, Robson AG, Webster AR: Recessive mutations of the gene TRPM1 abrogate ON bipolar cell function and cause complete congenital stationary night blindness in humans. Am J Hum Genet. 2009, 85 (5): 711-719. 10.1016/j.ajhg.2009.10.003.View ArticlePubMedPubMed CentralGoogle Scholar
- Dhingra A, Fina ME, Neinstein A, Ramsey DJ, Xu Y, Fishman GA, Alexander KR, Qian H, Peachey NS, Gregg RG, Vardi N: Autoantibodies in melanoma-associated retinopathy target TRPM1 cation channels of retinal ON bipolar cells. J Neurosci. 2011, 31 (11): 3962-3967. 10.1523/JNEUROSCI.6007-10.2011.View ArticlePubMedPubMed CentralGoogle Scholar
- Kondo M, Sanuki R, Ueno S, Nishizawa Y, Hashimoto N, Ohguro H, Yamamoto S, Machida S, Terasaki H, Adamus G, Furukawa T: Identification of autoantibodies against TRPM1 in patients with paraneoplastic retinopathy associated with ON bipolar cell dysfunction. PLoS One. 2011, 6 (5): e19911-10.1371/journal.pone.0019911.View ArticlePubMedPubMed CentralGoogle Scholar
- Nomura A, Shigemoto R, Nakamura Y, Okamoto N, Mizuno N, Nakanishi S: Developmentally regulated postsynaptic localization of a metabotropic glutamate receptor in rat rod bipolar cells. Cell. 1994, 77 (3): 361-369. 10.1016/0092-8674(94)90151-1.View ArticlePubMedGoogle Scholar
- Morigiwa K, Vardi N: Differential expression of ionotropic glutamate receptor subunits in the outer retina. J Comp Neurol. 1999, 405 (2): 173-184. 10.1002/(SICI)1096-9861(19990308)405:2<173::AID-CNE3>3.0.CO;2-L.View ArticlePubMedGoogle Scholar
- Morgans CW, Brown RL, Duvoisin RM: TRPM1: the endpoint of the mGluR6 signal transduction cascade in retinal ON-bipolar cells. Bioessays. 2010, 32 (7): 609-614. 10.1002/bies.200900198.View ArticlePubMedPubMed CentralGoogle Scholar
- Haverkamp S, Haeseleer F, Hendrickson A: A comparison of immunocytochemical markers to identify bipolar cell types in human and monkey retina. Vis Neurosci. 2003, 20 (6): 589-600. 10.1017/S0952523803206015.View ArticlePubMedGoogle Scholar
- Kunzevitzky NJ, Almeida MV, Goldberg JL: Amacrine cell gene expression and survival signaling: differences from neighboring retinal ganglion cells. Invest Ophthalmol Vis Sci. 2010, 51 (7): 3800-3812. 10.1167/iovs.09-4540.View ArticlePubMedPubMed CentralGoogle Scholar
- Katyal S, Glubrecht DD, Li L, Gao Z, Godbout R: Disabled-1 alternative splicing in human fetal retina and neural tumors. PLoS One. 2011, 6 (12): e28579-10.1371/journal.pone.0028579.View ArticlePubMedPubMed CentralGoogle Scholar
- Duquette PM, Zhou X, Yap NL, MacLaren EJ, Lu JJ, Wallace VA, Chen HH: Loss of LMO4 in the retina leads to reduction of GABAergic amacrine cells and functional deficits. PLoS One. 2010, 5 (10): e13232-10.1371/journal.pone.0013232.View ArticlePubMedPubMed CentralGoogle Scholar
- Sarthy PV, Fu M: Localization of L-glutamic acid decarboxylase mRNA in cat retinal horizontal cells by in situ hybridization. J Comp Neurol. 1989, 288 (4): 593-600. 10.1002/cne.902880406.View ArticlePubMedGoogle Scholar
- Aartsen WM, van Cleef KW, Pellissier LP, Hoek RM, Vos RM, Blits B, Ehlert EM, Balaggan KS, Ali RR, Verhaagen J, Wijnholds J: GFAP-driven GFP expression in activated mouse Muller glial cells aligning retinal blood vessels following intravitreal injection of AAV2/6 vectors. PLoS One. 2010, 5 (8): e12387-10.1371/journal.pone.0012387.View ArticlePubMedPubMed CentralGoogle Scholar
- The pre-publication history for this paper can be accessed here:http://www.biomedcentral.com/1471-2415/12/56/prepub
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.