Carbonic anhydrase XIV deficiency produces a functional defect in the retinal light response

Synthesis, molecular docking and molecular dynamics simulations, drug-likeness studies, ADMET prediction and biological evaluation of novel pyrazole-carboxamides bearing sulfonamide moiety as potent carbonic anhydrase inhibitors

Pyrazoles are unique bioactive molecules with a versatile biological profile and they have gained an important place on pharmaceutical chemistry. Pyrazole compounds containing sulfonamide nuclei also attract attention as carbonic anhydrase (CA) inhibitors. In this study, a library of pyrazole-carboxamides were synthesized and the structures of the synthesized molecules were characterized using FT-IR, 1H-NMR, 13C-NMR and HRMS. Then the inhibition effects of newly synthesized molecules on human erythrocyte hCA I and hCA II isoenzymes were investigated. Ki values of the compounds were in the range of 0.063-3.368 µM for hCA I and 0.007-4.235 µM for hCA II. Molecular docking studies were performed between the most active compounds 6a, 6b and the reference inhibitor, acetazolamide (AAZ) and the hCA I and hCA II receptors to investigate the binding mechanisms between the compounds and the receptors. These compounds showed better interactions than the AAZ. ADMET analyzes were performed for the compounds and it was seen that the compounds did not show AMES toxicity. The stability of the molecular docking results over time was analysed by 50 ns molecular dynamics simulations. Molecular dynamics simulations revealed that 6a and 6b exhibited good stability after docking to the binding sites of hCA I and hCA II receptors, with minor conformational changes and fluctuations.

Fluconazole-Induced Protein Changes in Osteogenic and Immune Metabolic Pathways of Dental Pulp Mesenchymal Stem Cells of Osteopetrosis Patients

Osteopetrosis is a rare inherited disease caused by osteoclast failure, resulting in increasing bone density in humans. Patients with osteopetrosis possess several dental and cranial complications. Since carbonic anhydrase II (CA-II) deficiency is a major cause of osteopetrosis, CA-II activators might be an attractive potential treatment option for osteopetrosis patients. We conducted comprehensive label-free quantitative proteomics analysis on Fluconazole-treated Dental Pulp Mesenchymal Stem/Stromal Cells from CA-II-Deficient Osteopetrosis Patients. We identified 251 distinct differentially expressed proteins between healthy subjects, as well as untreated and azole-treated derived cells from osteopetrosis patients. Twenty-six (26) of these proteins were closely associated with osteogenesis and osteopetrosis disease. Among them are ATP1A2, CPOX, Ap2 alpha, RAP1B and some members of the RAB protein family. Others include AnnexinA1, 5, PYGL, OSTF1 and PGAM4, all interacting with OSTM1 in the catalytic reactions of HCO3 and the Cl- channel via CAII regulation. In addition, the pro-inflammatory/osteoclast regulatory proteins RACK1, MTSE, STING1, S100A13, ECE1 and TRIM10 are involved. We have identified proteins involved in osteogenic and immune metabolic pathways, including ERK 1/2, phosphatase and ATPase, which opens the door for some CA activators to be used as an alternative drug therapy for osteopetrosis patients. These findings propose that fluconazole might be a potential treatment agent for CAII- deficient OP patients. Altogether, our findings provide a basis for further work to elucidate the clinical utility of azole, a CA activator, as a therapeutic for OP.

Bicarbonate boosts flash response amplitude to augment absolute sensitivity and extend dynamic range in murine retinal rods

Rod photoreceptors in the retina adjust their responsiveness and sensitivity so that they can continue to provide meaningful information over a wide range of light intensities. By stimulating membrane guanylate cyclases in the outer segment to synthesize cGMP at a faster rate in a Ca²⁺-dependent fashion, bicarbonate increases the circulating "dark" current and accelerates flash response kinetics in amphibian rods. Compared to amphibian rods, mammalian rods are smaller in size, operate at a higher temperature, and express visual cascade proteins with somewhat different biochemical properties. Here, we evaluated the role of bicarbonate in rods of cpfl3 mice. These mice are deficient in their expression of functional cone transducin, Gnat2, making cones very insensitive to light, so the rod response to light could be observed in isolation in electroretinogram recordings. Bicarbonate increased the dark current and absolute sensitivity and quickened flash response recovery in mouse rods to a greater extent than in amphibian rods. In addition, bicarbonate enabled mouse rods to respond over a range that extended to dimmer flashes. Larger flash responses may have resulted in part from a bicarbonate-induced elevation in intracellular pH. However, high pH alone had little effect on flash response recovery kinetics and even suppressed the accelerating effect of bicarbonate, consistent with a direct, modulatory action of bicarbonate on Ca²⁺- dependent, membrane guanylate cyclase activity.

Roles of Carbonic Anhydrases and Carbonic Anhydrase Related Proteins in Zebrafish

During recent decades, zebrafish (Danio rerio) have become one of the most important model organisms in which to study different physiological and biological phenomena. The research field of carbonic anhydrases (CAs) and carbonic anhydrase related proteins (CARPs) is not an exception to this. The best-known function of CAs is the regulation of acid–base balance. However, studies performed with zebrafish, among others, have revealed important roles for these proteins in many other physiological processes, some of which had not yet been predicted in the light of previous studies and suggestions. Examples include roles in zebrafish pigmentation as well as motor coordination. Disruption of the function of these proteins may generate lethal outcomes. In this review, we summarize the current knowledge of CA-related studies performed in zebrafish from 1993–2021 that was obtained from PubMed search.

Potential neurotoxicity, immunotoxicity, and carcinogenicity induced by metribuzin and tebuconazole exposure in earthworms (Eisenia fetida) revealed by transcriptome analysis

Metribuzin and tebuconazole have been widely used in agriculture for several decades. Apart from endocrine disruption, little is known about their toxicological effects on organisms without thyroid organs, at the transcriptional level. To explore this toxicity, model earthworm species Eisenia fetida, hatched from the same cocoon and cultured under identical environmental conditions, were independently exposed to the two chemicals at non-lethal concentrations in OECD artificial soil for 48 h after exposure. RNA-seq technology was used to analyze and compare the gene expression profiles of earthworms exposed to metribuzin and tebuconazole. The functions of differentially expressed genes and their standard response patterns of upregulated and downregulated expression for both pesticides were verified. The findings demonstrated that metribuzin and tebuconazole are both potentially toxic to earthworms. Toxicological effects mainly involved the nervous system, immune system, and tumors, at the transcriptional level, as well as the induction of cytochrome P450-dependent detoxification and oxidative stress. In addition, the mitogen-activated protein kinase kinase kinase gene was identified as a biomarker, and the mitogen-activated protein kinase signaling pathway was verified to be a part of the adverse outcome pathway of metribuzin and tebuconazole and their structural analogs.

New Histamine-Related Five-Membered N-Heterocycle Derivatives as Carbonic Anhydrase I Activators

A series of histamine (HST)-related compounds were synthesized and tested for their activating properties on five physiologically relevant human Carbonic Anhydrase (hCA) isoforms (I, II, Va, VII and XIII). The imidazole ring of HST was replaced with different 5-membered heterocycles and the length of the aliphatic chain was varied. For the most interesting compounds some modifications on the terminal amino group were also performed. The most sensitive isoform to activation was hCA I (K_A values in the low micromolar range), but surprisingly none of the new compounds displayed activity on hCA II. Some derivatives (1, 3a and 22) displayed an interesting selectivity for activating hCA I over hCA II, Va, VII and XIII.

Synthesis and Human Carbonic Anhydrase I, II, IX, and XII Inhibition Studies of Sulphonamides Incorporating Mono-, Bi- and Tricyclic Imide Moieties

New derivatives were synthesised by reaction of amino-containing aromatic sulphonamides with mono-, bi-, and tricyclic anhydrides. These sulphonamides were investigated as human carbonic anhydrases (hCAs, EC 4.2.1.1) I, II, IX, and XII inhibitors. hCA I was inhibited with inhibition constants (Kis) ranging from 49 to >10,000 nM. The physiologically dominant hCA II was significantly inhibited by most of the sulphonamide with the Kis ranging between 2.4 and 4515 nM. hCA IX and hCA XII were inhibited by these sulphonamides in the range of 9.7 to 7766 nM and 14 to 316 nM, respectively. The structure-activity relationships (SAR) are rationalised with the help of molecular docking studies.

Activation of carbonic anhydrases from human brain by amino alcohol oxime ethers: towards human carbonic anhydrase VII selective activators

The synthesis and carbonic anhydrase (CA; EC 4.2.1.1) activating effects of a series of oxime ether-based amino alcohols towards four human (h) CA isoforms expressed in human brain, hCA I, II, IV and VII, are described. Most investigated amino alcohol derivatives induced a consistent activation of the tested CAs, with K_As spanning from a low micromolar to a medium nanomolar range. Specifically, hCA II and VII, putative main CA targets when central nervous system (CNS) diseases are concerned, were most efficiently activated by these oxime ether derivatives. Furthermore, a multitude of selective hCA VII activators were identified. As hCA VII is one of the key isoforms involved in brain metabolism and other brain functions, the identified potent and selective hCA VII activators may be considered of interest for investigations of various therapeutic applications or as lead compounds in search of even more potent and selective CA activators.

Recent advances in the medicinal chemistry of carbonic anhydrase inhibitors

Carbonic anhydrase (CA, EC 4.2.1.1) is an enzyme and a very omnipresent zinc metalloenzyme which catalyzed the reversible hydration and dehydration of carbon dioxide and bicarbonate; a reaction which plays a crucial role in many physiological and pathological processes. Carbonic anhydrase is present in human (h) with sixteen different isoforms ranging from hCA I-hCA XV. All these isoforms are widely distributed in different tissues/organs and are associated with a range of pivotal physiological activities. Due to their involvement in various physiological roles, inhibitors of different human isoforms of carbonic anhydrase have found clinical applications for the treatment of various diseases including glaucoma, retinopathy, hemolytic anemia, epilepsy, obesity, and cancer. However, clinically used inhibitors of CA (acetazolamide, brinzolamide, dorzolamide, etc.) are not selective causing the undesirable side effects. One of the major hurdles in the design and development of carbonic anhydrase inhibitors is the lack of balanced isoform selectivity which thrived to new chemotypes. In this review, we have compiled the recent strategies of various researchers related to the development of carbonic anhydrase inhibitors belonging to different structural classes like pyrimidine, pyrazoline, selenourea, isatin, indole, etc. This review also summarizes the structure-activity relationships, analysis of isoform selectivity including mechanistic and in silico studies to afford ideas and to provide focused direction for the design and development of novel isoform-selective carbonic anhydrase inhibitors with therapeutic implications.

Assessment of databases to determine the validity of β- and γ-carbonic anhydrase sequences from vertebrates

BACKGROUND

The inaccuracy of DNA sequence data is becoming a serious problem, as the amount of molecular data is multiplying rapidly and expectations are high for big data to revolutionize life sciences and health care. In this study, we investigated the accuracy of DNA sequence data from commonly used databases using carbonic anhydrase (CA) gene sequences as generic targets. CAs are ancient metalloenzymes that are present in all unicellular and multicellular living organisms. Among the eight distinct families of CAs, including α, β, γ, δ, ζ, η, θ, and ι, only α-CAs have been reported in vertebrates.

RESULTS

By an in silico analysis performed on the NCBI and Ensembl databases, we identified several β- and γ-CA sequences in vertebrates, including Homo sapiens, Mus musculus, Felis catus, Lipotes vexillifer, Pantholops hodgsonii, Hippocampus comes, Hucho hucho, Oncorhynchus tshawytscha, Xenopus tropicalis, and Rhinolophus sinicus. Polymerase chain reaction (PCR) analysis of genomic DNA persistently failed to amplify positive β- or γ-CA gene sequences when Mus musculus and Felis catus DNA samples were used as templates. Further BLAST homology searches of the database-derived "vertebrate" β- and γ-CA sequences revealed that the identified sequences were presumably derived from gut microbiota, environmental microbiomes, or grassland ecosystems.

CONCLUSIONS

Our results highlight the need for more accurate and fast curation systems for DNA databases. The mined data must be carefully reconciled with our best knowledge of sequences to improve the accuracy of DNA data for publication.

pH-controlled histone acetylation amplifies melanocyte differentiation downstream of MITF

Tanning response and melanocyte differentiation are mediated by the central transcription factor MITF. This involves the rapid and selective induction of melanocyte maturation genes, while concomitantly the expression of other effector genes is maintained. In this study, using cell-based and zebrafish model systems, we report on a pH-mediated feed-forward mechanism of epigenetic regulation that enables selective amplification of the melanocyte maturation program. We demonstrate that MITF activation directly elevates the expression of the enzyme carbonic anhydrase 14 (CA14). Nuclear localization of CA14 leads to an increase of the intracellular pH, resulting in the activation of the histone acetyl transferase p300/CBP. In turn, enhanced H3K27 histone acetylation at selected differentiation genes facilitates their amplified expression via MITF. CRISPR-mediated targeted missense mutation of CA14 in zebrafish results in the formation of immature acidic melanocytes with decreased pigmentation, establishing a central role for this mechanism during melanocyte differentiation in vivo. Thus, we describe an epigenetic control system via pH modulation that reinforces cell fate determination by altering chromatin dynamics.

Photoreceptors in a mouse model of Leigh syndrome are capable of normal light-evoked signaling

Mitochondrial dysfunction is an important cause of heritable vision loss. Mutations affecting mitochondrial bioenergetics may lead to isolated vision loss or life-threatening systemic disease, depending on a mutation's severity. Primary optic nerve atrophy resulting from death of retinal ganglion cells is the most prominent ocular manifestation of mitochondrial disease. However, dysfunction of other retinal cell types has also been described, sometimes leading to a loss of photoreceptors and retinal pigment epithelium that manifests clinically as pigmentary retinopathy. A popular mouse model of mitochondrial disease that lacks NADH:ubiquinone oxidoreductase subunit S4 (NDUFS4), a subunit of mitochondrial complex I, phenocopies many traits of the human disease Leigh syndrome, including the development of optic atrophy. It has also been reported that ndufs4 ^-/- mice display diminished light responses at the level of photoreceptors or bipolar cells. By conducting electroretinography (ERG) recordings in live ndufs4 ^-/- mice, we now demonstrate that this defect occurs at the level of retinal photoreceptors. We found that this deficit does not arise from retinal developmental anomalies, photoreceptor degeneration, or impaired regeneration of visual pigment. Strikingly, the impairment of ndufs4 ^-/- photoreceptor function was not observed in ex vivo ERG recordings from isolated retinas, indicating that photoreceptors with complex I deficiency are intrinsically capable of normal signaling. The difference in electrophysiological phenotypes in vivo and ex vivo suggests that the energy deprivation associated with severe mitochondrial impairment in the outer retina renders ndufs4 ^-/- photoreceptors unable to maintain the homeostatic conditions required to operate at their normal capacity.

Carbonic anhydrases as disease markers

INTRODUCTION

The physiologic importance of fast CO₂/HCO₃^- interconversion in various tissues requires the presence of carbonic anhydrase (CA, EC 4.2.1.1). Fourteen CA isozymes are present in humans, all of them being used as biomarkers.

AREAS COVERED

A great number of patents and articles were focused on the use of CA isozymes as biomarkers for various diseases and syndromes in the recent years, in an ascending trend over the last decade. The review highlights the most important studies related with each isozyme and covers the most recent patent literature.

EXPERT OPINION

The CAs biomarker research area expanded significantly in recent years, shifting from the predominant use of CA IX and CA XII in cancer diagnostic, staging, and prognosis towards a wider use of CA isozymes as disease biomarkers. CA isozymes are currently used either alone, in tandem with other CA isozymes and/or in combination with other proteins for the detection, staging, and prognosis of a huge repertoire of human dysfunctions and diseases, ranging from mild transformation of the normal tissues to extreme shifts in tissue organization and function. The techniques used for their detection/quantitation and the state-of-the-art in each clinical application are presented through relevant clinical examples and corresponding statistical data.

Retinal pH and Acid Regulation During Metabolic Acidosis

PURPOSE

Changes in retinal pH may contribute to a variety of eye diseases. To study the effect of acidosis alone, we induced systemic metabolic acidosis and hypothesized that the retina would respond with altered expression of genes involved in acid/base regulation.

METHODS

Systemic metabolic acidosis was induced in Long-Evans rats for up to 2 weeks by adding NH4Cl to the drinking water. After 2 weeks, venous pH was 7.25 ± 0.08 (SD) and [HCO3-] was 21.4 ± 4.6 mM in acidotic animals; pH was 7.41 ± 0.03 and [HCO3-] was 30.5 ± 1.0 mM in controls. Retinal mRNAs were quantified by quantitative reverse transcription polymerase chain reaction. Protein was quantified with Western blots and localized by confocal microscopy. Retinal [H+]o was measured in vivo with pH microelectrodes in animals subjected to metabolic acidosis and in controls.

RESULTS

NH4Cl in drinking water or given intravenous was effective in acidifying the retina. Cariporide, a blocker of Na+/H+ exchange, further acidified the retina. Metabolic acidosis for 2 weeks led to increases of 40-100% in mRNA for carbonic anhydrase isoforms II (CA-II) and XIV (CA-XIV) and acid-sensing ion channels 1 and 4 (ASIC1 and ASIC4) (all p < 0.005). Expression of anion exchange protein 3 (AEP-3) and Na+/H+ exchanger (NHE)-1 also increased by ≥50% (both p < 0.0001). Changes were similar after 1 week of acidosis. Protein for AEP-3 doubled. NHE-1 co-localized with vascular markers, particularly in the outer plexiform layer. CA-II was located in the neural parenchyma of the ganglion cell layer and diffusely in the rest of the inner retina.

CONCLUSIONS

The retina responds to systemic acidosis with increased expression of proton and bicarbonate exchangers, carbonic anhydrase, and ASICs. While responses to acidosis are usually associated with renal regulation, these studies suggest that the retina responds to changes in local pH presumably to control its acid/base environment in response to systemic acidosis.

Synthesis and Biological Evaluation of 4-Sulfamoylphenyl/Sulfocoumarin Carboxamides as Selective Inhibitors of Carbonic Anhydrase Isoforms hCA II, IX, and XII

With the aim to develop potent and selective human carbonic anhydrase inhibitors (hCAIs), we synthesized 4-sulfamoylphenyl/sulfocoumarin benzamides (series 5 a-r and series 7 a-q) and evaluated their inhibition profiles against five isoforms of the zinc-containing human carbonic anhydrase (hCA, EC 4.2.1.1): cytosolic hCA I and II, and the transmembrane isozymes hCA IV, IX, and XII. Compounds 5 a-r were found to selectively inhibit hCA II in the nanomolar range, while being less effective against the other hCA isoforms. As noted from the literature, sulfocoumarin (1,2-benzoxathiine 2,2-dioxide) acts as a "prodrug" inhibitor and is hydrolyzed by the esterase activity of hCA to form 2-hydroxyphenylvinylsulfonic acid, which thereafter binds to the enzyme in a manner similar to that of coumarins and sulfoxocoumarins. All these sulfocoumarins (compounds 7 a-q) were found to be very weak or ineffective as inhibitors of the housekeeping off-target hCA isoforms I and II, and effectively inhibited the transmembrane tumor-associated isoforms IX and XII in the high nanomolar to micromolar ranges. Further structural modifications of these molecules could be useful for the development of effective hCA inhibitors used for the treatment of glaucoma, epilepsy, and cancer.

Optical coherence tomography angiography

Optical coherence tomography (OCT) was one of the biggest advances in ophthalmic imaging. Building on that platform, OCT angiography (OCTA) provides depth resolved images of blood flow in the retina and choroid with levels of detail far exceeding that obtained with older forms of imaging. This new modality is challenging because of the need for new equipment and processing techniques, current limitations of imaging capability, and rapid advancements in both imaging and in our understanding of the imaging and applicable pathophysiology of the retina and choroid. These factors lead to a steep learning curve, even for those with a working understanding dye-based ocular angiography. All for a method of imaging that is a little more than 10 years old. This review begins with a historical account of the development of OCTA, and the methods used in OCTA, including signal processing, image generation, and display techniques. This forms the basis to understand what OCTA images show as well as how image artifacts arise. The anatomy and imaging of specific vascular layers of the eye are reviewed. The integration of OCTA in multimodal imaging in the evaluation of retinal vascular occlusive diseases, diabetic retinopathy, uveitis, inherited diseases, age-related macular degeneration, and disorders of the optic nerve is presented. OCTA is an exciting, disruptive technology. Its use is rapidly expanding in clinical practice as well as for research into the pathophysiology of diseases of the posterior pole.

Carbonic anhydrase activators

Mammalian carbonic anhydrases (CAs; EC 4.2.1.1) of which 16 isoforms are known, are involved in important physiological functions. Their inhibition is exploited pharmacologically for the treatment of many diseases (glaucoma, edema, epilepsy, obesity, hypoxic tumors, neuropathic pain, etc.) but the activators were less investigated till recently. A review on the CA activation is presented, with the activation mechanism, drug design approaches of activators and comparison of the various isoforms activation profiles being discussed. Some CAs, which are abundant in the brain, were recently demonstrated to be activatable by drug-like compounds, affording the possibility to design agents that enhance cognition, with potential therapeutic applications in aging and neurodegenerative diseases as well as tissue engineering.

Carbonic anhydrase XII functions in health and disease

Human CAXII was initially identified as a cancer marker in different cancers and tumors. Expression of CAXII is regulated by hypoxia and estrogen receptors. CAXII expression has been also detected in several tissues, whereas in cancer and tumor tissues its expression is several fold higher. In brain tumors, an alternatively spliced form of CAXII is expressed. Higher expression of CAXII in breast cancer is indicative of lower grade disease. CAXII plays a key role in several physiological functions. Mutation in the CAXII gene causes cystic fibrosis-like syndrome and salt wasting disease. CAXII is also seen in nuclear pulposus cells of the vertebrae. Aging dependent stiffness or degeneration of backbone correlates with CAXII expression level. This finding suggests a possible implication of CAXII as a biomarker for chronic back pain and a pharmacological target for possible treatment of chronic back pain.

RETINAL VASCULAR CYSTOID MACULAR EDEMA: Review and New Theory

: Retinal vascular disease has the potential to affect hundreds of millions of people, with the inherent risk of vision loss related to cystoid macular edema. Although there have been histologic evaluation of eyes having cystoid macular edema, the most recent paper was published more than 30 years ago. In retinal vascular cystoid macular edema fluorescein angiography, a modality that images the superficial vascular plexus, shows increased leakage. Optical coherence tomography angiography has provided unprecedented resolution of retinal vascular flow in a depth resolved manner and demonstrates areas of decreased or absent flow in the deep vascular plexus colocalizing with the cystoid spaces. There has been a large amount of research on fluid management and edema in the brain, much of which may have analogues in the eye. Interstitial flow of fluid as managed by Müller cells may occur in the retina, comparable in some ways to the bulk flow in brain parenchyma, which is managed by astrocytes. Absent blood flow in the deep retinal plexus may restrict fluid management strategies in the retina, to include transport of excess fluid out of the retina into the blood by Müller cells. Application of this theory may help in increasing understanding of the pathophysiology of retinal vascular cystoid macular edema and may lead to new therapeutic approaches.

Deficient glucose and glutamine metabolism in Aralar/AGC1/Slc25a12 knockout mice contributes to altered visual function

PURPOSE

To characterize the vision phenotype of mice lacking Aralar/AGC1/Slc25a12, the mitochondrial aspartate-glutamate carrier mutated in global cerebral hypomyelination (OMIM 612949).

METHODS

We tested overnight dark-adapted control and aralar-deficient mice for the standard full electroretinogram (ERG) response. The metabolic stress of dark-adaptation was reduced by 5 min illumination after which the ERG response was monitored in darkness. We used the electrical response to two identical saturating light flashes (paired-flash stimulation) to isolate the inner retina and photoreceptor responses. Retinal morphology was examined with hematoxylin and eosin staining, immunohistochemistry of antibodies against retinal cells, and 4',6-diamidino-2-phenylindole (DAPI) labeling.

RESULTS

Aralar plays a pivotal role in retina metabolism as aralar provides de novo synthesis pathway for glutamine, protects glutamate from oxidation, and is required for efficient glucose oxidative metabolism. Aralar-deficient mice are not blind as their retinas have light-evoked activity. However, we report an approximate 50% decrease in the ERG amplitude response in the light-evoked activity of dark-adapted retinas from aralar-deficient mice, in spite of normal retina histology. The defective response is partly reversed by exposure to a brief illumination period, which lowers the metabolic stress of dark-adaptation. The metabolic stress and ERG alteration takes place primarily in photoreceptors, but the response to two flashes applied in fast succession also revealed an alteration in synaptic transmission consistent with an imbalance of glutamate and an energy deficit in the inner retina neurons.

CONCLUSIONS

We propose that compromised glucose oxidation and altered glutamine and glutamate metabolism in the absence of aralar are responsible for the phenotype reported.

Acetylcholinesterase and carbonic anhydrase isoenzymes I and II inhibition profiles of taxifolin

Taxifolin, also known as dihydroquercetin, is a flavonoid commonly found in plants. Carbonic anhydrase (CA, EC 4.2.1.1) plays an important role in many critical physiological events including carbon dioxide (CO2)/bicarbonate (HCO3(-)) respiration and pH regulation. There are 16 known CA isoforms in humans, of which human hCA isoenzymes I and II (hCA I and II) are ubiquitous cytosolic isoforms. In this study, the inhibition properties of taxifolin against the slow cytosolic isoenzyme hCA I, and the ubiquitous and dominant rapid cytosolic isoenzyme hCA II were studied. Taxifolin, as a naturally bioactive flavonoid, has a K(i) of 29.2 nM against hCA I, and 24.2 nM against hCA II. For acetylcholinesterase enzyme (AChE) inhibition, K(i) parameter of taxifolin was determined to be 16.7 nM. These results clearly show that taxifolin inhibited both CA isoenzymes and AChE at the nM levels.

Bicarbonate Modulates Photoreceptor Guanylate Cyclase (ROS-GC) Catalytic Activity

By generating the second messenger cGMP in retinal rods and cones, ROS-GC plays a central role in visual transduction. Guanylate cyclase-activating proteins (GCAPs) link cGMP synthesis to the light-induced fall in [Ca(2+)]i to help set absolute sensitivity and assure prompt recovery of the response to light. The present report discloses a surprising feature of this system: ROS-GC is a sensor of bicarbonate. Recombinant ROS-GCs synthesized cGMP from GTP at faster rates in the presence of bicarbonate with an ED50 of 27 mM for ROS-GC1 and 39 mM for ROS-GC2. The effect required neither Ca(2+) nor use of the GCAPs domains; however, stimulation of ROS-GC1 was more powerful in the presence of GCAP1 or GCAP2 at low [Ca(2+)]. When applied to retinal photoreceptors, bicarbonate enhanced the circulating current, decreased sensitivity to flashes, and accelerated flash response kinetics. Bicarbonate was effective when applied either to the outer or inner segment of red-sensitive cones. In contrast, bicarbonate exerted an effect when applied to the inner segment of rods but had little efficacy when applied to the outer segment. The findings define a new regulatory mechanism of the ROS-GC system that affects visual transduction and is likely to affect the course of retinal diseases caused by cGMP toxicity.

Capsaicin: a potent inhibitor of carbonic anhydrase isoenzymes

Carbonic anhydrase (CA, EC 4.2.1.1) is a zinc containing metalloenzyme that catalyzes the rapid and reversible conversion of carbon dioxide (CO₂) and water (H₂O) into a proton (H⁺) and bicarbonate (HCO₃^–) ion. On the other hand, capsaicin is the main component in hot chili peppers and is used extensively used in spices, food additives and drugs; it is responsible for their spicy flavor and pungent taste. There are sixteen known CA isoforms in humans. Human CA isoenzymes I, and II (hCA I and hCA II) are ubiquitous cytosolic isoforms. In this study, the inhibition properties of capsaicin against the slow cytosolic isoform hCA I, and the ubiquitous and dominant rapid cytosolic isozymes hCA II were studied. Both CA isozymes were inhibited by capsaicin in the micromolar range. This naturally bioactive compound has a Ki of 696.15 µM against hCA I, and of 208.37 µM against hCA II.

Expression patterns and subcellular localization of carbonic anhydrases are developmentally regulated during tooth formation

Carbonic anhydrases (CAs) play fundamental roles in several physiological events, and emerging evidence points at their involvement in an array of disorders, including cancer. The expression of CAs in the different cells of teeth is unknown, let alone their expression patterns during odontogenesis. As a first step towards understanding the role of CAs during odontogenesis, we used immunohistochemistry, histochemistry and in situ hybridization to reveal hitherto unknown dynamic distribution patterns of eight CAs in mice. The most salient findings include expression of CAII/Car2 not only in maturation-stage ameloblasts (MA) but also in the papillary layer, dental papilla mesenchyme, odontoblasts and the epithelial rests of Malassez. We uncovered that the latter form lace-like networks around incisors; hitherto these have been known to occur only in molars. All CAs studied were produced by MA, however CAIV, CAIX and CARPXI proteins were distinctly enriched in the ruffled membrane of the ruffled MA but exhibited a homogeneous distribution in smooth-ended MA. While CAIV, CAVI/Car6, CAIX, CARPXI and CAXIV were produced by all odontoblasts, CAIII distribution displayed a striking asymmetry, in that it was virtually confined to odontoblasts in the root of molars and root analog of incisors. Remarkably, from initiation until near completion of odontogenesis and in several other tissues, CAXIII localized mainly in intracellular punctae/vesicles that we show to overlap with LAMP-1- and LAMP-2-positive vesicles, suggesting that CAXIII localizes within lysosomes. We showed that expression of CAs in developing teeth is not confined to cells involved in biomineralization, pointing at their participation in other biological events. Finally, we uncovered novel sites of CA expression, including the developing brain and eye, the olfactory epithelium, melanoblasts, tongue, notochord, nucleus pulposus and sebaceous glands. Our study provides important information for future single or multiple gene targeting strategies aiming at deciphering the function of CAs during odontogenesis.

Carbonic anhydrase inhibitors: synthesis and inhibition of the human carbonic anhydrase isoforms I, II, IX and XII with benzene sulfonamides incorporating 4- and 3-nitrophthalimide moieties

A series of 4 and 5 nitro-1,3-dioxoisoindolin-2-yl benzenesulfonamide derivatives (compounds 1-8) was synthesized by reaction of benzenesulfonamide derivatives with 4 and 3-nitrophthalic anhydrides. These new sulfonamides were investigated as inhibitors of the zinc metalloenzyme carbonic anhydrase (CA, EC 4.2.1.1) and more specifically against the human (h) cytosolic isoforms hCA I and II and the transmembrane, tumor-associated hCA IX and XII. Most of the novel compounds were medium potency-weak hCA I inhibitors (Kis in the range of 295-10,000 nM), but were more effective hCA II inhibitors (Kis of 1.7-887 nM). The tumor-associated hCA IX was also inhibited, with Kis in the micromolar range, whereas against hCA XII the inhibition constants were in the range of 90-3,746 nM. The structure-activity relationship (SAR) with this series of sulfonamides is straightforward, with the main features leading to good activity for each isoforms being established. The high sequence hCA alignment homology and molecular docking studies was performed in order to rationalize the activities reported and binding mode to different hCA as inhibitors.

Membrane associated carbonic anhydrase IV (CA IV): a personal and historical perspective

Carbonic anhydrase IV is one of 12 active human isozymes and one of four expressed on the extracellular surfaces of certain endothelial and epithelial cells. It is unique in being attached to the plasma membrane by a glycosyl-phosphatiydyl-inositol (GPI) anchor rather than by a membrane-spanning domain. It is also uniquely resistant to high concentrations of sodium dodecyl sulfate (SDS), which allows purification from tissues by inhibitor affinity chromatography without contamination by other isozymes. This unique resistance to SDS and recovery following denaturation is explained by the two disulfide bonds. The 35-kDa human CA IV is a "high activity" isozyme in CO2 hydration activity, like CA II, and has higher activity than other isozymes in catalyzing the dehydration of HCO3 (-). Human CA IV is also unique in that it contains no oligosaccharide chains, where all other mammalian CA IVs are glycoproteins with one to several oligosaccharide side chains.Although CA IV has been shown to be active in mediating CO2 and HCO3 (-) transport in many important tissues like kidney and lung, and in isolated cells from brain and muscle, the gene for CA IV appears not to be essential. The CA IV knockout mouse produced by targeted mutagenesis, though slightly smaller and produced in lower than expected numbers, is viable and has no obvious mutant phenotype. Conversely, several dominant negative mutations in humans are associated with one form of reitinitis pigmentosa (RP-17), which we attribute to unfolded protein accumulation in the choreocapillaris, leading to apoptosis of cells in the overlying retina.

NMDA receptor-dependent afterdepolarizations are curtailed by carbonic anhydrase 14: regulation of a short-term postsynaptic potentiation

In the hippocampus, extracellular carbonic anhydrase (Car) speeds the buffering of an activity-generated rise in extracellular pH that impacts H(+)-sensitive NMDA receptors (NMDARs). We studied the role of Car14 in this brain structure, in which it is expressed solely on neurons. Current-clamp responses were recorded from CA1 pyramidal neurons in wild-type (WT) versus Car14 knock-out (KO) mice 2 s before (control) and after (test) a 10 pulse, 100 Hz afferent train. In both WT and KO, the half-width (HW) of the test response, and its number of spikes, were augmented relative to the control. An increase in presynaptic release was not involved, because AMPAR-mediated EPSCs were depressed after a train. The increases in HW and spike number were both greater in the Car14 KO. In 0 Mg(2+) saline with picrotoxin (using a 20 Hz train), the HW measures were still greater in the KO. The Car inhibitor benzolamide (BZ) enhanced the test response HW in the WT but had no effect on the already-prolonged HW in the KO. With intracellular MK-801 [(+)-5-methyl-10,11-dihydro-5H-dibenzo [a,d]-cyclohepten-5,10-imine maleate], the curtailed WT and KO responses were indistinguishable, and BZ caused no change. In contrast, the extracellular alkaline changes evoked by the train were not different between WT and KO, and BZ amplified these alkalinizations similarly. These data suggest that Car14 regulates pH transients in the perisynaptic microenvironment and govern their impact on NMDARs but plays little role in buffering pH shifts in the broader, macroscopic, extracellular space.

Structure, function and applications of carbonic anhydrase isozymes

The carbonic anhydrases enzymes (CAs, EC 4.2.1.1) are zinc containing metalloproteins, which efficiently catalyse the reversible conversion of carbon dioxide to bicarbonate and release proton. These enzymes are essentially important for biological system and play several important physiological and patho-physiological functions. There are 16 different alpha-carbonic anhydrase isoforms studied, differing widely in their cellular localization and biophysical properties. The catalytic domains of all CAs possess a conserved tertiary structure fold, with predominately β-strands. We performed an extensive analysis of all 16 mammalian CAs for its structure and function in order to establish a structure-function relationship. CAs have been a potential therapeutic target for many diseases. Sulfonamides are considered as a strong and specific inhibitor of CA, and are being used as diuretics, anti-glaucoma, anti-epileptic, anti-ulcer agents. Currently CA inhibitors are widely used as a drug for the treatment of neurological disorders, anti-glaucoma drugs, anti-cancer, or anti-obesity agents. Here we tried to emphasize how CAs can be used for drug discovery, design and screening. Furthermore, we discussed the role of CA in carbon capture, carbon sensor and metabolon. We hope this review provide many useful information on structure, function, mechanism, and applications of CAs in various discipline.

Loss of caveolin-1 impairs retinal function due to disturbance of subretinal microenvironment

Caveolin-1 (Cav-1), an integral component of caveolar membrane domains, is expressed in several retinal cell types, including photoreceptors, retinal vascular endothelial cells, Müller glia, and retinal pigment epithelium (RPE) cells. Recent evidence links Cav-1 to ocular diseases, including autoimmune uveitis, diabetic retinopathy, and primary open angle glaucoma, but its role in normal vision is largely undetermined. In this report, we show that ablation of Cav-1 results in reduced inner and outer retinal function as measured, in vivo, by electroretinography and manganese-enhanced MRI. Somewhat surprisingly, dark current and light sensitivity were normal in individual rods (recorded with suction electrode methods) from Cav-1 knock-out (KO) mice. Although photoreceptor function was largely normal, in vitro, the apparent K(+) affinity of the RPE-expressed α1-Na(+)/K(+)-ATPase was decreased in Cav-1 KO mice. Cav-1 KO retinas also displayed unusually tight adhesion with the RPE, which could be resolved by brief treatment with hyperosmotic medium, suggesting alterations in outer retinal fluid homeostasis. Collectively, these findings demonstrate that reduced retinal function resulting from Cav-1 ablation is not photoreceptor-intrinsic but rather involves impaired subretinal and/or RPE ion/fluid homeostasis.

Design and synthesis of thiourea compounds that inhibit transmembrane anchored carbonic anhydrases

A library of 32 novel glycoconjugate thiourea-bridged benzene sulfonamides have been synthesized from the reaction of glycosyl isothiocyanates with a panel of simple benzene sulfonamides comprising either a free amine or hydrazide. All compounds were investigated for their ability to inhibit the enzymatic activity of five human carbonic anhydrase (hCA) isozymes: hCA I, II and membrane-associated isozymes IX, XII and XIV. A physicochemical feature of the free sugar thioureido glycoconjugates was high water solubility (> 20 mg/mL), as well many of these compounds exhibited a desirable potency and CA isozyme selectivity profile. From this library several inhibitors displayed excellent potency-selectivity profiles for transmembrane anchored CAs over off-target CA I and II. These molecules provide potential dual-acting candidates for the development of inhibitors that target the extracellular CAs (IX, XII and XIV)-either directly as free sugars (membrane impermeable) or indirectly as acetylated prodrugs, becoming free sugars upon esterase hydrolysis.

Postnatal weight gain modifies severity and functional outcome of oxygen-induced proliferative retinopathy

In clinical studies, postnatal weight gain is strongly associated with retinopathy of prematurity (ROP). However, animal studies are needed to investigate the pathophysiological mechanisms of how postnatal weight gain affects the severity of ROP. In the present study, we identify nutritional supply as one potent parameter that affects the extent of retinopathy in mice with identical birth weights and the same genetic background. Wild-type pups with poor postnatal nutrition and poor weight gain (PWG) exhibit a remarkably prolonged phase of retinopathy compared to medium weight gain or extensive weight gain pups. A high (r(2) = 0.83) parabolic association between postnatal weight gain and oxygen-induced retinopathy severity is observed, as is a significantly prolonged phase of proliferative retinopathy in PWG pups (20 days) compared with extensive weight gain pups (6 days). The extended retinopathy is concomitant with prolonged overexpression of retinal vascular endothelial growth factor in PWG pups. Importantly, PWG pups show low serum levels of nonfasting glucose, insulin, and insulin-like growth factor-1 as well as high levels of ghrelin in the early postoxygen-induced retinopathy phase, a combination indicative of poor metabolic supply. These differences translate into visual deficits in adult PWG mice, as demonstrated by impaired bipolar and proximal neuronal function. Together, these results provide evidence for a pathophysiological correlation between poor postnatal nutritional supply, slow weight gain, prolonged retinal vascular endothelial growth factor overexpression, protracted retinopathy, and reduced final visual outcome.

Gene expression profiling in the submandibular gland, stomach, and duodenum of CAVI-deficient mice

Carbonic anhydrase VI (CAVI) is the only secreted isozyme of the α-carbonic anhydrase family, which catalyzes the reversible reaction [Formula in text]. It appears that CAVI protects teeth and gastrointestinal mucosa by neutralizing excess acidity. However, the evidence for this physiological function is limited, and CAVI may have additional functions that have yet to be discovered. To explore the functions of CAVI more fully, we generated Car6 (-/-) mice and analyzed Car6 (-/-) mutant phenotypes. We also examined transcriptomic responses to CAVI deficiency in the submandibular gland, stomach, and duodenum of Car6 (-/-) mice. Car6 (-/-) mice were viable and fertile and had a normal life span. Histological analyses indicated a greater number of lymphoid follicles in the small intestinal Peyer's patches. A total of 94, 56, and 127 genes were up- or down-regulated in the submandibular gland, stomach, and duodenum of Car6 (-/-) mice, respectively. The functional clustering of differentially expressed genes revealed a number of altered biological processes. In the duodenum, the significantly affected biological pathways included the immune system process and retinol metabolic processes. The response to oxidative stress and brown fat cell differentiation changed remarkably in the submandibular gland. Notably, the submandibular gland, stomach, and duodenum shared one important transcriptional susceptibility pathway: catabolic process. Real-time PCR confirmed an altered expression in 14 of the 16 selected genes. The generation and of Car6 (-/-) mice and examination of the effects of CAVI deficiency on gene transcription have revealed several affected clusters of biological processes, which implicate CAVI in catabolic processes and the immune system response.

Progressive renal injury from transgenic expression of human carbonic anhydrase IV folding mutants is enhanced by deficiency of p58IPK

Mutations in the human carbonic anhydrase IV (hCAIV) have been associated with retinal degeneration in an autosomal-dominant form of retinitis pigmentosa (RP17). Prior in vitro cell culture studies confirmed that all of the RP17-associated hCAIV mutations cause protein misfolding, leading to endoplasmic reticulum (ER) stress-induced apoptosis in cells expressing the mutant proteins. To evaluate the physiological impacts of these folding mutants in other carbonic anhydrase IV-producing tissues, we generated two transgenic mouse lines expressing R219S or R14W hCAIV under control of the endogenous hCAIV promoter. Expression of either of these mutant proteins in kidneys caused progressive renal injury in male transgenic mice as evidenced by an age-dependent increase in the tubule cell apoptosis starting at approximately 20 weeks of age and vacuolization throughout the renal cortex in older mice. Up-regulation of the ER chaperone, BiP, was observed in the cells of the renal cortex of the male transgenic mice, suggesting ER stress as a causal factor for the renal injury. The renal injury inflicted by expression of the folding mutants was markedly enhanced by haploinsufficiency of the ER cochaperone p58(IPK). The transgenic mice expressing the hCAIV folding mutants on a p58(IPK) heterozygous background showed extensive renal tubular apoptosis by approximately 10 weeks of age in both male and female mice. These data indicate that expression of the RP17-associated folding mutants of hCAIV can adversely affect tissues beyond the retina and their in vivo proteotoxicity is sensitive to modulation of the protein folding environment of the ER.

Bicarbonate homeostasis in excitable tissues: role of AE3 Cl-/HCO3- exchanger and carbonic anhydrase XIV interaction

Bicarbonate transport and metabolism are key elements of normal cellular function. Two alternate transcripts of anion exchanger 3 (AE3), full-length (AE3fl) and cardiac (AE3c), are expressed in central nervous system (CNS), where AE3 catalyzes electroneutral Cl(-)/HCO(3)(-) exchange across the plasma membrane of neuronal and glial cells of CNS. Anion exchanger isoforms, AE3fl and AE3c, associate with the carbonic anhydrases (CA) CAII and CAIV, forming a HCO(3)(-) transport metabolon, to maximize HCO(3)(-) flux across the plasma membrane. CAXIV, with catalytic domain anchored to the extracellular surface, is also expressed in CNS. Here physical association of AE3 and CAXIV was examined by coimmunoprecipitation experiments, using mouse brain and retinal lysates. CAXIV immunoprecipitated with anti-AE3 antibody, and both AE3 isoforms were immunoprecipitated using anti-CAXIV antibody, indicating CAXIV and AE3 interaction in the CNS. Confocal images revealed colocalization of CAXIV and AE3 in Müller and horizontal cells, in the mouse retina. Cl(-)/HCO(3)(-) exchange activity of AE3fl was investigated in transiently transfected human embryonic kidney 293 cells, using intracellular fluorescence measurements of BCECF, to monitor intracellular pH. CAXIV increased the rate of AE3fl-mediated HCO(3)(-) transport by up to 120%, which was suppressed by the CA inhibitor acetazolamide. Association of AE3 and CAXIV may represent a mechanism to enhance disposal of waste CO(2) and to balance pH in excitable tissues.

Carbonic anhydrases CA4 and CA14 both enhance AE3-mediated Cl--HCO3- exchange in hippocampal neurons

Carbonic anhydrase (CA) activity in the brain extracellular space is attributable mainly to isoforms CA4 and CA14. In brain, these enzymes have been studied mostly in the context of buffering activity-dependent extracellular pH transients. Yet evidence from others has suggested that CA4 acts in a complex with anion exchangers (AEs) to facilitate Cl(-)-HCO(3)(-) exchange in cotransfected cells. To investigate whether CA4 or CA14 plays such a role in hippocampal neurons, we studied NH(4)(+)-induced alkalinization of the cytosol, which is mitigated by Cl(-) entry and HCO(3)(-) exit. The NH(4)(+)-induced alkalinization was enhanced when the extracellular CAs were inhibited by the poorly permeant CA blocker, benzolamide, or by inhibitory antibodies specific for either CA4 or CA14. The NH(4)(+)-induced alkalinization was also increased with inhibition of anion exchange by 4,4*-diisothiocyanostilbene-2,2*-disulfonic acid, or by eliminating Cl(-) from the medium. No effect of benzolamide was seen under these conditions, in which no Cl(-)-HCO(3)(-) exchange was possible. Quantitative PCR on RNA from the neuronal cultures indicated that AE3 was the predominant AE isoform. Single-cell PCR also showed that Slc4a3 (AE3) transcripts were abundant in isolated neurons. In hippocampal neurons dissociated from AE3-null mice, the NH(4)(+)-induced alkalinization was much larger than that seen in neurons from wild-type mice, suggesting little or no Cl(-)-HCO(3)(-) exchange in the absence of AE3. Benzolamide had no effect on the NH(4)(+)-induced alkalinization in the AE3 knock-out neurons. Our results indicate that CA4 and CA14 both play important roles in the regulation of intracellular pH in hippocampal neurons, by facilitating AE3-mediated Cl(-)-HCO(3)(-) exchange.

Pathogenesis of retinitis pigmentosa associated with apoptosis-inducing mutations in carbonic anhydrase IV

Missense mutations in the carbonic anhydrase IV (CA IV) gene have been identified in patients with an autosomal dominant form of retinitis pigmentosa (RP17). We used two transient expression systems to investigate the molecular mechanism by which the newly identified CA IV mutations, R69H and R219S, contribute to retinal pathogenesis. Although the R219S mutation drastically reduced the activity of the enzyme, the R69H mutation had a minimal effect, suggesting that loss of CA activity is not the molecular basis for their pathogenesis. Defective processing was apparent for both mutant proteins. Cell surface-labeling techniques showed that the R69H and R219S mutations both impaired the trafficking of CA IV to the cell surface, resulting in their abnormal intracellular retention. Expression of both CA IV mutants induced elevated levels of the endoplasmic reticulum (ER) stress markers, BiP and CHOP, and led to cell death by apoptosis. They also had a dominant-negative effect on the secretory function of the ER. These properties are similar to those of R14W CA IV, the signal sequence variant found in the original patients with RP17. These findings suggest that toxic gain of function involving ER stress-induced apoptosis is the common mechanism for pathogenesis of this autosomal-dominant disease. Apoptosis induced by the CA IV mutants could be prevented, at least partially, by treating the cells with dorzolamide, a CA inhibitor. Thus, the use of a CA inhibitor as a chemical chaperone to reduce ER stress may delay or prevent the onset of blindness in RP17.

Altered visual function in monocarboxylate transporter 3 (Slc16a8) knockout mice

To meet the high-energy demands of photoreceptor cells, the outer retina metabolizes glucose through glycolytic and oxidative pathways, resulting in large-scale production of lactate and CO(2). Mct3, a proton-coupled monocarboxylate transporter, is critically positioned to facilitate transport of lactate and H(+) out of the retina and could therefore play a role in pH and ion homeostasis of the outer retina. Mct3 is preferentially expressed in the basolateral membrane of the retinal pigment epithelium and forms a heteromeric complex with the accessory protein CD147. To examine the physiological role of Mct3 in the retina, we generated mice with a targeted deletion in Mct3 (slc16A8). The overall retinal histology of 4- to 36-wk-old Mct3(-/-) mice appeared normal. In the absence of Mct3, expression of CD147 was lost from the basolateral but not apical RPE. The saturated a-wave amplitude (a(max)) of the scotopic electroretinogram (ERG) was reduced by approximately twofold in Mct3(-/-) mice relative to wild-type mice. A fourfold increase in lactate in the retina suggested a decrease in outer-retinal pH. In single-cell recordings from superfused retinal slices, saturating amplitudes of single rod photocurrents (J(max)) were comparable indicating that Mct3(-/-) mouse photoreceptor cells were inherently healthy. Based on these data, we hypothesize that disruption of Mct3 leads to a potentially reversible decrease in subretinal space pH, thereby reducing the magnitude of the light suppressible photoreceptor current.

Blindness caused by deficiency in AE3 chloride/bicarbonate exchanger

Background

Vision is initiated by phototransduction in the outer retina by photoreceptors, whose high metabolic rate generates large CO₂ loads. Inner retina cells then process the visual signal and CO₂. The anion exchanger 3 gene (AE3/Slc4a3) encodes full-length AE3 (AE3fl) and cardiac AE3 (AE3c) isoforms, catalyzing plasma membrane Cl⁻/HCO₃⁻ exchange in Müller (AE3fl) and horizontal (AE3c) cells. AE3 thus maintains acid-balance by removing photoreceptor-generated CO₂ waste.

Methodology/Principal Findings

We report that Slc4a3^−/− null mice have inner retina defects (electroretinogram b-wave reduction, optic nerve and retinal vessel anomalies). These pathologic features are common to most human vitreoretinal degenerations. Immunobloting analysis revealed that Na⁺/HCO₃⁻ co-transporter (NBC1), and carbonic anhydrase II and CAXIV, protein expression were elevated in Slc4a3^−/− mouse retinas, suggesting compensation for loss of AE3. TUNEL staining showed increased numbers of apoptotic nuclei from 4–6 months of age, in Slc4a3^−/− mice, indicating late onset photoreceptor death.

Conclusions/Significance

Identification of Slc4a3 as underlying a previously unrecognized cause of blindness suggests this gene as a new candidate for a subset of hereditary vitreoretinal retinal degeneration.