{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,6,15]],"date-time":"2026-06-15T03:46:01Z","timestamp":1781495161063,"version":"3.54.1"},"reference-count":40,"publisher":"MDPI AG","issue":"4","license":[{"start":{"date-parts":[[2020,2,24]],"date-time":"2020-02-24T00:00:00Z","timestamp":1582502400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100003407","name":"Ministero dell\u2019Istruzione, dell\u2019Universit\u00e0 e della Ricerca","doi-asserted-by":"publisher","award":["RBFR12SJA8"],"award-info":[{"award-number":["RBFR12SJA8"]}],"id":[{"id":"10.13039\/501100003407","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100009886","name":"regione Puglia","doi-asserted-by":"publisher","award":["01_0129"],"award-info":[{"award-number":["01_0129"]}],"id":[{"id":"10.13039\/501100009886","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["IJMS"],"abstract":"<jats:p>Translational readthrough (TRT) of aquaporin-4 (AQP4) has remarkably expanded the importance of this new post-transcriptional mechanism, as well as the regulation potential of AQP4. The TRT isoform of AQP4, named AQP4ex, is central for both AQP4 polarization and water channel activity in the central nervous system (CNS). Here we evaluate the relevance of the TRT mechanism by analyzing whether AQP4ex is also expressed in peripheral tissues and whether the expression of AQP4ex is necessary for its polarized expression as it occurs in perivascular astrocyte processes. To this purpose, AQP4ex null mice were used, and analysis was performed by immunolocalization and immunoblot. The results demonstrate that AQP4ex is expressed in kidney, stomach, trachea and skeletal muscle with the same localization pattern as the canonical AQP4 isoforms. AQP4ex protein levels vary from 6% to about 13% of the total AQP4 protein levels in peripheral tissues. Immunogold electron microscopy experiments demonstrated the localization of AQP4ex at the astrocytic endfeet, and experiments conducted on AQP4ex null mice CNS confirmed that the expression of AQP4ex is necessary for anchoring of the perivascular AQP4. Without the readthrough isoform, AQP4 assemblies are mis-localized, being uniformly distributed on the astrocyte processes facing the neuropile. No alteration of AQP4 polarization was found in AQP4ex null kidney, stomach, trachea or skeletal muscle, suggesting that AQP4ex does not have a role for proper membrane localization of AQP4 in peripheral tissues. We conclude that a dual role for AQP4ex is limited to the CNS.<\/jats:p>","DOI":"10.3390\/ijms21041531","type":"journal-article","created":{"date-parts":[[2020,2,25]],"date-time":"2020-02-25T04:21:26Z","timestamp":1582604486000},"page":"1531","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":29,"title":["Tissue Distribution of the Readthrough Isoform of AQP4 Reveals a Dual Role of AQP4ex Limited to CNS"],"prefix":"10.3390","volume":"21","author":[{"given":"Claudia","family":"Palazzo","sequence":"first","affiliation":[{"name":"Department of Basic Medical Sciences, Neurosciences and Sense Organs, School of Medicine, University of Bari Aldo Moro, 70124 Bari, Italy"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Pasqua","family":"Abbrescia","sequence":"additional","affiliation":[{"name":"Department of Basic Medical Sciences, Neurosciences and Sense Organs, School of Medicine, University of Bari Aldo Moro, 70124 Bari, Italy"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Onofrio","family":"Valente","sequence":"additional","affiliation":[{"name":"Department of Basic Medical Sciences, Neurosciences and Sense Organs, School of Medicine, University of Bari Aldo Moro, 70124 Bari, Italy"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Grazia Paola","family":"Nicchia","sequence":"additional","affiliation":[{"name":"Department of Bioscience, Biotechnology and Biopharmaceutics, University of Bari Aldo Moro, 70125 Bari, Italy"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-5180-2407","authenticated-orcid":false,"given":"Shervin","family":"Banitalebi","sequence":"additional","affiliation":[{"name":"Division of Anatomy, Department of Molecular Medicine, Institute of Basic Medical Sciences, University of Oslo, 0317 Oslo, Norway"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-1071-1247","authenticated-orcid":false,"given":"Mahmood","family":"Amiry-Moghaddam","sequence":"additional","affiliation":[{"name":"Division of Anatomy, Department of Molecular Medicine, Institute of Basic Medical Sciences, University of Oslo, 0317 Oslo, Norway"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Maria","family":"Trojano","sequence":"additional","affiliation":[{"name":"Department of Basic Medical Sciences, Neurosciences and Sense Organs, School of Medicine, University of Bari Aldo Moro, 70124 Bari, Italy"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Antonio","family":"Frigeri","sequence":"additional","affiliation":[{"name":"Department of Basic Medical Sciences, Neurosciences and Sense Organs, School of Medicine, University of Bari Aldo Moro, 70124 Bari, Italy"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2020,2,24]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"259","DOI":"10.1038\/nrd4226","article-title":"Aquaporins: Important but elusive drug targets","volume":"13","author":"Verkman","year":"2014","journal-title":"Nat. Rev. Drug Discov."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"2993","DOI":"10.1242\/jcs.108.9.2993","article-title":"Localization of MIWC and GLIP water channel homologs in neuromuscular, epithelial and glandular tissues","volume":"108","author":"Frigeri","year":"1995","journal-title":"J. Cell Sci."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"171","DOI":"10.1523\/JNEUROSCI.17-01-00171.1997","article-title":"Specialized membrane domains for water transport in glial cells: High-resolution immunogold cytochemistry of aquaporin-4 in rat brain","volume":"17","author":"Nielsen","year":"1997","journal-title":"J. Neurosci."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"13052","DOI":"10.1073\/pnas.91.26.13052","article-title":"Molecular characterization of an aquaporin cDNA from brain: Candidate osmoreceptor and regulator of water balance","volume":"91","author":"Jung","year":"1994","journal-title":"Proc. Natl. Acad. Sci. USA"},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"5497","DOI":"10.1016\/S0021-9258(17)37486-0","article-title":"Molecular cloning of a mercurial-insensitive water channel expressed in selected water-transporting tissues","volume":"269","author":"Hasegawa","year":"1994","journal-title":"J. Biol. Chem."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"2936","DOI":"10.1016\/j.bpj.2011.05.012","article-title":"Model of aquaporin-4 supramolecular assembly in orthogonal arrays based on heterotetrameric association of M1-M23 isoforms","volume":"100","author":"Jin","year":"2011","journal-title":"Biophys. J."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"13609","DOI":"10.1073\/pnas.2235843100","article-title":"Aquaporin-4 square array assembly: Opposing actions of M1 and M23 isoforms","volume":"100","author":"Furman","year":"2003","journal-title":"Proc. Natl. Acad. Sci. USA"},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"903","DOI":"10.1016\/j.neuroscience.2010.02.008","article-title":"Higher order structure of aquaporin-4","volume":"168","author":"Nicchia","year":"2010","journal-title":"Neuroscience"},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"1236","DOI":"10.1111\/jcmm.13401","article-title":"Supramolecular aggregation of aquaporin-4 is different in muscle and brain: Correlation with tissue susceptibility in neuromyelitis optica","volume":"22","author":"Rosito","year":"2018","journal-title":"J. Cell Mol. Med."},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"6001","DOI":"10.1074\/jbc.273.11.6001","article-title":"Regulation of aquaporin-4 water channels by phorbol ester-dependent protein phosphorylation","volume":"273","author":"Han","year":"1998","journal-title":"J. Biol. Chem."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"971","DOI":"10.1016\/j.neuroscience.2009.09.020","article-title":"Water permeability through aquaporin-4 is regulated by protein kinase C and becomes rate-limiting for glioma invasion","volume":"168","author":"McCoy","year":"2010","journal-title":"Neuroscience"},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"1923","DOI":"10.1002\/glia.21234","article-title":"Translational regulation mechanisms of aquaporin-4 supramolecular organization in astrocytes","volume":"59","author":"Pisani","year":"2011","journal-title":"Glia"},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"470","DOI":"10.1091\/mbc.e13-06-0331","article-title":"A novel human aquaporin-4 splice variant exhibits a dominant-negative activity: A new mechanism to regulate water permeability","volume":"25","author":"Pisani","year":"2014","journal-title":"Mol. Biol. Cell"},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"790","DOI":"10.1002\/glia.23126","article-title":"Translational readthrough generates new astrocyte AQP4 isoforms that modulate supramolecular clustering, glial endfeet localization, and water transport","volume":"65","author":"Pisani","year":"2017","journal-title":"Glia"},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"8928","DOI":"10.1093\/nar\/gku608","article-title":"Evidence of efficient stop codon readthrough in four mammalian genes","volume":"42","author":"Loughran","year":"2014","journal-title":"Nucleic Acids Res."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"51","DOI":"10.1186\/s40478-019-0707-5","article-title":"AQP4ex is crucial for the anchoring of AQP4 at the astrocyte end-feet and for neuromyelitis optica antibody binding","volume":"7","author":"Palazzo","year":"2019","journal-title":"Acta Neuropathol. Commun."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"4328","DOI":"10.1073\/pnas.92.10.4328","article-title":"Immunolocalization of the mercurial-insensitive water channel and glycerol intrinsic protein in epithelial cell plasma membranes","volume":"92","author":"Frigeri","year":"1995","journal-title":"Proc. Natl. Acad. Sci. USA"},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"695","DOI":"10.1172\/JCI2545","article-title":"Expression of aquaporin-4 in fast-twitch fibers of mammalian skeletal muscle","volume":"102","author":"Frigeri","year":"1998","journal-title":"J. Clin. Invest."},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"29","DOI":"10.4161\/chan.3735","article-title":"Distribution of the AQP4 water channel in normal human tissues: Protein and tissue microarrays reveal expression in several new anatomical locations, including the prostate gland and seminal vesicles","volume":"1","author":"Mobasheri","year":"2007","journal-title":"Channels (Austin)"},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"1492","DOI":"10.1016\/j.bbagen.2013.09.033","article-title":"Human aquaporins: Regulators of transcellular water flow","volume":"1840","author":"Day","year":"2014","journal-title":"Biochim. Biophys. Acta"},{"key":"ref_21","first-page":"573","article-title":"Mildly abnormal retinal function in transgenic mice without M\u00fcller cell aquaporin-4 water channels","volume":"43","author":"Li","year":"2002","journal-title":"Invest. Ophthalmol. Vis. Sci."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"1057","DOI":"10.1038\/ki.1995.389","article-title":"The aquaporin family of water channels in kidney","volume":"48","author":"Nielsen","year":"1995","journal-title":"Kidney Int."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"305","DOI":"10.1016\/S0014-5793(99)01256-9","article-title":"High-resolution immunogold cytochemistry indicates that AQP4 is concentrated along the basal membrane of parietal cell in rat stomach","volume":"459","author":"Fujita","year":"1999","journal-title":"FEBS Lett."},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"2027","DOI":"10.1023\/A:1026266225912","article-title":"Partitioning of aquaporin-4 water channel mRNA and protein in gastric glands","volume":"48","author":"Huang","year":"2003","journal-title":"Dig. Dis. Sci."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"1282","DOI":"10.1096\/fj.00-0525fje","article-title":"Muscle loading modulates aquaporin-4 expression in skeletal muscle","volume":"15","author":"Frigeri","year":"2001","journal-title":"FASEB J."},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"594","DOI":"10.1016\/j.celrep.2018.12.077","article-title":"Cell-Type-Specific Profiling of Alternative Translation Identifies Regulated Protein Isoform Variation in the Mouse Brain","volume":"26","author":"Sapkota","year":"2019","journal-title":"Cell Rep."},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"201","DOI":"10.1007\/978-981-13-2233-4_8","article-title":"Multiple Localization by Functional Translational Readthrough","volume":"89","author":"Bersch","year":"2018","journal-title":"Subcell Biochem."},{"key":"ref_28","doi-asserted-by":"crossref","unstructured":"Stiebler, A.C., Freitag, J., Schink, K.O., Stehlik, T., Tillmann, B.A., Ast, J., and B\u00f6lker, M. (2014). Ribosomal readthrough at a short UGA stop codon context triggers dual localization of metabolic enzymes in Fungi and animals. Plos Genet., 10.","DOI":"10.1371\/journal.pgen.1004685"},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"e03640","DOI":"10.7554\/eLife.03640","article-title":"Peroxisomal lactate dehydrogenase is generated by translational readthrough in mammals","volume":"3","author":"Schueren","year":"2014","journal-title":"Elife"},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"7008","DOI":"10.1093\/emboj\/20.24.7008","article-title":"Polarized trafficking and surface expression of the AQP4 water channel are coordinated by serial and regulated interactions with different clathrin-adaptor complexes","volume":"20","author":"Madrid","year":"2001","journal-title":"EMBO J."},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"14108","DOI":"10.1073\/pnas.241508198","article-title":"Syntrophin-dependent expression and localization of Aquaporin-4 water channel protein","volume":"98","author":"Neely","year":"2001","journal-title":"Proc. Natl. Acad. Sci. USA"},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"2106","DOI":"10.1073\/pnas.0437946100","article-title":"An alpha-syntrophin-dependent pool of AQP4 in astroglial end-feet confers bidirectional water flow between blood and brain","volume":"100","author":"Otsuka","year":"2003","journal-title":"Proc. Natl. Acad Sci. USA"},{"key":"ref_33","doi-asserted-by":"crossref","first-page":"879","DOI":"10.1002\/glia.20347","article-title":"Assembly of a perivascular astrocyte protein scaffold at the mammalian blood-brain barrier is dependent on alpha-syntrophin","volume":"53","author":"Bragg","year":"2006","journal-title":"Glia"},{"key":"ref_34","doi-asserted-by":"crossref","first-page":"1674","DOI":"10.1096\/fj.04-3281fje","article-title":"New possible roles for aquaporin-4 in astrocytes: Cell cytoskeleton and functional relationship with connexin43","volume":"19","author":"Nicchia","year":"2005","journal-title":"FASEB J."},{"key":"ref_35","doi-asserted-by":"crossref","first-page":"2156","DOI":"10.1111\/j.1471-4159.2008.05302.x","article-title":"Expression of multiple AQP4 pools in the plasma membrane and their association with the dystrophin complex","volume":"105","author":"Nicchia","year":"2008","journal-title":"J. Neurochem."},{"key":"ref_36","doi-asserted-by":"crossref","first-page":"869","DOI":"10.1002\/glia.20661","article-title":"Dystrophin-dependent and -independent AQP4 pools are expressed in the mouse brain","volume":"56","author":"Nicchia","year":"2008","journal-title":"Glia"},{"key":"ref_37","doi-asserted-by":"crossref","first-page":"1363","DOI":"10.1002\/glia.20855","article-title":"Aquaporin-4 orthogonal arrays of particles are the target for neuromyelitis optica autoantibodies","volume":"57","author":"Nicchia","year":"2009","journal-title":"Glia"},{"key":"ref_38","doi-asserted-by":"crossref","first-page":"1755","DOI":"10.1002\/glia.20724","article-title":"Actin cytoskeleton remodeling governs aquaporin-4 localization in astrocytes","volume":"56","author":"Nicchia","year":"2008","journal-title":"Glia"},{"key":"ref_39","doi-asserted-by":"crossref","first-page":"2087","DOI":"10.1007\/s00429-014-0775-z","article-title":"Postnatal development of the molecular complex underlying astrocyte polarization","volume":"220","author":"Lunde","year":"2015","journal-title":"Brain Struct Funct."},{"key":"ref_40","doi-asserted-by":"crossref","first-page":"1753","DOI":"10.1007\/s00429-016-1305-y","article-title":"Factors determining the density of AQP4 water channel molecules at the brain-blood interface","volume":"222","author":"Hoddevik","year":"2017","journal-title":"Brain Struct Funct."}],"container-title":["International Journal of Molecular Sciences"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1422-0067\/21\/4\/1531\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T09:01:11Z","timestamp":1760173271000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1422-0067\/21\/4\/1531"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2020,2,24]]},"references-count":40,"journal-issue":{"issue":"4","published-online":{"date-parts":[[2020,2]]}},"alternative-id":["ijms21041531"],"URL":"https:\/\/doi.org\/10.3390\/ijms21041531","relation":{},"ISSN":["1422-0067"],"issn-type":[{"value":"1422-0067","type":"electronic"}],"subject":[],"published":{"date-parts":[[2020,2,24]]}}}