Epidemiology of Diagnosed Age-related Macular Degeneration in Germany: An Evaluation of the Prevalence Using AOK PLUS Claims Data.

INTRODUCTION: Epidemiologic data on age-related macular degeneration (AMD) are mainly based on cohort studies, including both diagnosed and undiagnosed cases. Using health claims data allows estimating epidemiological data of diagnosed subjects with AMD within the health care system using diagnosis codes from a regional claims database (AOK PLUS) to estimate the prevalence and incidence of non-exudative and exudative AMD in Germany. METHODS: Patients with AMD were identified among AOK PLUS insured patients based on at least two outpatient, ophthalmologic or one inpatient H35.3 diagnoses for the years 2012 to 2021. Patients without continuous observation in a calendar year were excluded. Prevalence was assessed, and 1-year cumulative incidence was determined by the number of newly diagnosed patients divided by the number of individuals at risk. For 2020 and 2021, the AMD stage was assessed by diagnostic subcodes for non-exudative and exudative AMD, respectively. For 2012 to 2019, patient numbers were estimated based on the average proportions of non-exudative AMD and exudative AMD, respectively, in 2020 and 2021. Incidence and prevalence numbers were then extrapolated to Germany. RESULTS: Between 2012 to 2021, the prevalence of diagnosed AMD cases remained relatively stable among approximately 3.27 million AOK PLUS insured persons, ranging from 0.96% (minimum in 2021) to 1.31% (maximum in 2014) for non-exudative AMD, about twice as high as for exudative AMD (min-max: 0.53-0.72%). The age- and sex-adjusted projections amounted to 644,153 diagnosed non-exudative and 367,086 diagnosed German patients with exudative AMDs in 2021. The 1-year cumulative incidence for non-exudative and exudative AMD, respectively, ranged from 122,427-142,932 to 46,092-86,785 newly diagnosed cases. CONCLUSION: The number of diagnosed cases with AMD in Germany has increased slightly over the past decade. For the first time, patient counts with non-exudative and exudative AMD were approximated for Germany based on a representative, large-scale database study.

Backbone amides are determinants of Cl- selectivity in CLC ion channels.

Chloride homeostasis is regulated in all cellular compartments. CLC-type channels selectively transport Cl- across biological membranes. It is proposed that side-chains of pore-lining residues determine Cl- selectivity in CLC-type channels, but their spatial orientation and contributions to selectivity are not conserved. This suggests a possible role for mainchain amides in selectivity. We use nonsense suppression to insert α-hydroxy acids at pore-lining positions in two CLC-type channels, CLC-0 and bCLC-k, thus exchanging peptide-bond amides with ester-bond oxygens which are incapable of hydrogen-bonding. Backbone substitutions functionally degrade inter-anion discrimination in a site-specific manner. The presence of a pore-occupying glutamate side chain modulates these effects. Molecular dynamics simulations show backbone amides determine ion energetics within the bCLC-k pore and how insertion of an α-hydroxy acid alters selectivity. We propose that backbone-ion interactions are determinants of Cl- specificity in CLC channels in a mechanism reminiscent of that described for K+ channels.

Dynorphin Neuropeptides Decrease Apparent Proton Affinity of ASIC1a by Occluding the Acidic Pocket.

Prolonged acidosis, as it occurs during ischemic stroke, induces neuronal death via acid-sensing ion channel 1a (ASIC1a). Concomitantly, it desensitizes ASIC1a, highlighting the pathophysiological significance of modulators of ASIC1a acid sensitivity. One such modulator is the opioid neuropeptide big dynorphin (Big Dyn) which binds to ASIC1a and enhances its activity during prolonged acidosis. The molecular determinants and dynamics of this interaction remain unclear, however. Here, we present a molecular interaction model showing a dynorphin peptide inserting deep into the acidic pocket of ASIC1a. We confirmed experimentally that the interaction is predominantly driven by electrostatic forces, and using noncanonical amino acids as photo-cross-linkers, we identified 16 residues in ASIC1a contributing to Big Dyn binding. Covalently tethering Big Dyn to its ASIC1a binding site dramatically decreased the proton sensitivity of channel activation, suggesting that Big Dyn stabilizes a resting conformation of ASIC1a and dissociates from its binding site during channel opening.

Efficient expression of a cnidarian peptide-gated ion channel in mammalian cells.

Hydra Na+ channels (HyNaCs) are peptide-gated ion channels of the DEG/ENaC gene family that are directly activated by neuropeptides of the Hydra nervous system. They have previously been successfully characterized in Xenopus oocytes. To establish their expression in mammalian cells, we transiently expressed heteromeric HyNaC2/3/5 in human HEK 293 and monkey COS-7 cells. We found that the expression of HyNaC2/3/5 using native cDNAs was inefficient and that codon optimization strongly increased protein expression and current amplitude in patch-clamp experiments. We used the improved expression of codon-optimized channel subunits to perform Ca2+ imaging and to demonstrate their glycosylation pattern. In summary, we established efficient expression of a cnidarian ion channel in mammalian cell lines.

Divergent Cl- and H+ pathways underlie transport coupling and gating in CLC exchangers and channels.

The CLC family comprises H+-coupled exchangers and Cl- channels, and mutations causing their dysfunction lead to genetic disorders. The CLC exchangers, unlike canonical 'ping-pong' antiporters, simultaneously bind and translocate substrates through partially congruent pathways. How ions of opposite charge bypass each other while moving through a shared pathway remains unknown. Here, we use MD simulations, biochemical and electrophysiological measurements to identify two conserved phenylalanine residues that form an aromatic pathway whose dynamic rearrangements enable H+ movement outside the Cl- pore. These residues are important for H+ transport and voltage-dependent gating in the CLC exchangers. The aromatic pathway residues are evolutionarily conserved in CLC channels where their electrostatic properties and conformational flexibility determine gating. We propose that Cl- and H+ move through physically distinct and evolutionarily conserved routes through the CLC channels and transporters and suggest a unifying mechanism that describes the gating mechanism of both CLC subtypes.

Cross-kingdom auxiliary subunit modulation of a voltage-gated sodium channel.

Voltage-gated, sodium ion-selective channels (NaV) generate electrical signals contributing to the upstroke of the action potential in animals. NaVs are also found in bacteria and are members of a larger family of tetrameric voltage-gated channels that includes CaVs, KVs, and NaVs. Prokaryotic NaVs likely emerged from a homotetrameric Ca2+-selective voltage-gated progenerator, and later developed Na+ selectivity independently. The NaV signaling complex in eukaryotes contains auxiliary proteins, termed beta (ß) subunits, which are potent modulators of the expression profiles and voltage-gated properties of the NaV pore, but it is unknown whether they can functionally interact with prokaryotic NaV channels. Herein, we report that the eukaryotic NaVß1-subunit isoform interacts with and enhances the surface expression as well as the voltage-dependent gating properties of the bacterial NaV, NaChBac in Xenopus oocytes. A phylogenetic analysis of the ß-subunit gene family proteins confirms that these proteins appeared roughly 420 million years ago and that they have no clear homologues in bacterial phyla. However, a comparison between eukaryotic and bacterial NaV structures highlighted the presence of a conserved fold, which could support interactions with the ß-subunit. Our electrophysiological, biochemical, structural, and bioinformatics results suggests that the prerequisites for ß-subunit regulation are an evolutionarily stable and intrinsic property of some voltage-gated channels.

Probing the conformation of a conserved glutamic acid within the Cl- pathway of a CLC H+/Cl- exchanger.

The CLC proteins form a broad family of anion-selective transport proteins that includes both channels and exchangers. Despite extensive structural, functional, and computational studies, the transport mechanism of the CLC exchangers remains poorly understood. Several transport models have been proposed but have failed to capture all the key features of these transporters. Multiple CLC crystal structures have suggested that a conserved glutamic acid, Gluex, can adopt three conformations and that the interconversion of its side chain between these states underlies H+/Cl- exchange. One of these states, in which Gluex occupies the central binding site (Scen) while Cl- ions fill the internal and external sites (Sint and Sext), has only been observed in one homologue, the eukaryotic cmCLC. The existence of such a state in other CLCs has not been demonstrated. In this study, we find that during transport, the prototypical prokaryotic CLC exchanger, CLC-ec1, adopts a conformation with functional characteristics that match those predicted for a cmCLC-like state, with Gluex trapped in Scen between two Cl- ions. Transport by CLC-ec1 is reduced when [Cl-] is symmetrically increased on both sides of the membrane and mutations that disrupt the hydrogen bonds stabilizing Gluex in Scen destabilize this trapped state. Furthermore, inhibition of transport by high [Cl-] is abolished in the E148A mutant, in which the Gluex side chain is removed. Collectively, our results suggest that, during the CLC transport cycle, Gluex can occupy Scen as well as the Sext position in which it has been captured crystallographically and that hydrogen bonds with the side chains of residues that coordinate ion binding to Scen play a role in determining the equilibrium between these two conformations.

Cellular encoding of Cy dyes for single-molecule imaging.

A general method is described for the site-specific genetic encoding of cyanine dyes as non-canonical amino acids (Cy-ncAAs) into proteins. The approach relies on an improved technique for nonsense suppression with in vitro misacylated orthogonal tRNA. The data show that Cy-ncAAs (based on Cy3 and Cy5) are tolerated by the eukaryotic ribosome in cell-free and whole-cell environments and can be incorporated into soluble and membrane proteins. In the context of the Xenopus laevis oocyte expression system, this technique yields ion channels with encoded Cy-ncAAs that are trafficked to the plasma membrane where they display robust function and distinct fluorescent signals as detected by TIRF microscopy. This is the first demonstration of an encoded cyanine dye as a ncAA in a eukaryotic expression system and opens the door for the analysis of proteins with single-molecule resolution in a cellular environment.

Atomic determinants of BK channel activation by polyunsaturated fatty acids.

Docosahexaenoic acid (DHA), a polyunsaturated ω-3 fatty acid enriched in oily fish, contributes to better health by affecting multiple targets. Large-conductance Ca2+- and voltage-gated Slo1 BK channels are directly activated by nanomolar levels of DHA. We investigated DHA-channel interaction by manipulating both the fatty acid structure and the channel composition through the site-directed incorporation of unnatural amino acids. Electrophysiological measurements show that the para-group of a Tyr residue near the ion conduction pathway has a critical role. To robustly activate the channel, ionization must occur readily by a fatty acid for a good efficacy, and a long nonpolar acyl tail with a Z double bond present at the halfway position for a high affinity. The results suggest that DHA and the channel form an ion-dipole bond to promote opening and demonstrate the channel druggability. DHA, a marine-derived nutraceutical, represents a promising lead compound for rational drug design and discovery.

Incorporation of Non-Canonical Amino Acids.

In this chapter we discuss the strengths, caveats and technical considerations of three approaches for reprogramming the chemical composition of selected amino acids within a membrane protein. In vivo nonsense suppression in the Xenopus laevis oocyte, evolved orthogonal tRNA and aminoacyl-tRNA synthetase pairs and protein ligation for biochemical production of semisynthetic proteins have been used successfully for ion channel and receptor studies. The level of difficulty for the application of each approach ranges from trivial to technically demanding, yet all have untapped potential in their application to membrane proteins.

Common gating of both CLC transporter subunits underlies voltage-dependent activation of the 2Cl-/1H+ exchanger ClC-7/Ostm1.

CLC anion transporters form dimers that function either as Cl(-) channels or as electrogenic Cl(-)/H(+) exchangers. CLC channels display two different types of "gates," "protopore" gates that open and close the two pores of a CLC dimer independently of each other and common gates that act on both pores simultaneously. ClC-7/Ostm1 is a lysosomal 2Cl(-)/1H(+) exchanger that is slowly activated by depolarization. This gating process is drastically accelerated by many CLCN7 mutations underlying human osteopetrosis. Making use of some of these mutants, we now investigate whether slow voltage activation of plasma membrane-targeted ClC-7/Ostm1 involves protopore or common gates. Voltage activation of wild-type ClC-7 subunits was accelerated by co-expressing an excess of ClC-7 subunits carrying an accelerating mutation together with a point mutation rendering these subunits transport-deficient. Conversely, voltage activation of a fast ClC-7 mutant could be slowed by co-expressing an excess of a transport-deficient mutant. These effects did not depend on whether the accelerating mutation localized to the transmembrane part or to cytoplasmic cystathionine-ß-synthase (CBS) domains of ClC-7. Combining accelerating mutations in the same subunit did not speed up gating further. No currents were observed when ClC-7 was truncated after the last intramembrane helix. Currents and slow gating were restored when the C terminus was co-expressed by itself or fused to the C terminus of the ß-subunit Ostm1. We conclude that common gating underlies the slow voltage activation of ClC-7. It depends on the CBS domain-containing C terminus that does not require covalent binding to the membrane domain of ClC-7.

ClC-7 is a slowly voltage-gated 2Cl(-)/1H(+)-exchanger and requires Ostm1 for transport activity.

Mutations in the ClC-7/Ostm1 ion transporter lead to osteopetrosis and lysosomal storage disease. Its lysosomal localization hitherto precluded detailed functional characterization. Using a mutated ClC-7 that reaches the plasma membrane, we now show that both the aminoterminus and transmembrane span of the Ostm1 ß-subunit are required for ClC-7 Cl(-)/H(+)-exchange, whereas the Ostm1 transmembrane domain suffices for its ClC-7-dependent trafficking to lysosomes. ClC-7/Ostm1 currents were strongly outwardly rectifying owing to slow gating of ion exchange, which itself displays an intrinsically almost linear voltage dependence. Reversal potentials of tail currents revealed a 2Cl(-)/1H(+)-exchange stoichiometry. Several disease-causing CLCN7 mutations accelerated gating. Such mutations cluster to the second cytosolic cystathionine-ß-synthase domain and potential contact sites at the transmembrane segment. Our work suggests that gating underlies the rectification of all endosomal/lysosomal CLCs and extends the concept of voltage gating beyond channels to ion exchangers.

Recurrent stroke due to a novel voltage sensor mutation in Cav2.1 responds to verapamil.

BACKGROUND AND PURPOSE: Familial hemiplegic migraine is characterized by recurrent migraine, hemiparesis, and ataxia. Causes may be mutations in calcium and sodium channels or in a subunit of the Na/K-ATPse. Migraine treatment with calcium channel blockers was only successful in some patients. Summary of Case- We describe a 6-year-old girl with recurrent ischemic strokes after minor head trauma associated with seizures, hemiparesis, fever, and altered consciousness. Genetic analysis revealed a spontaneous, novel dominant CACNA1A mutation (c.4046G→A, p.R1349Q) that removed a highly conserved arginine of the voltage sensing region of the P/Q-type Ca(v)2.1 channel. Because a homologous mutation in the tottering-5J mouse increased open probability of the channel as well as calcium influx, we treated the patient with the calcium channel blocker verapamil during characteristic prodromi after head trauma. Treatment was instantly effective and prevented a new stroke. CONCLUSIONS: CACNA1A mutations should be considered in the diagnostic workup of childhood stroke, especially if associated with ataxia and migraine.

Analysis of CLCN2 as candidate gene for megalencephalic leukoencephalopathy with subcortical cysts.

Mutations in the gene MLC1 are found in approximately 80% of the patients with the inherited childhood white matter disorder megalencephalic leukoencephalopathy with subcortical cysts (MLC). Genetic linkage studies have not led to the identification of another disease gene. We questioned whether mutations in CLCN2, coding for the chloride channel protein 2 (ClC-2), are involved in MLC. Mice lacking this protein develop white matter abnormalities, which are characterized by vacuole formation in the myelin sheaths, strikingly similar to the intramyelinic vacuoles in MLC. Sequence analysis of CLCN2 at genomic DNA and cDNA levels in 18 MLC patients without MLC1 mutations revealed some nucleotide changes, but they were predicted to be nonpathogenic. Further, in electrophysiological experiments, one of the observed amino acid changes was shown to have no effect on the ClC-2-mediated currents. In conclusion, we found no evidence suggesting that the CLCN2 gene is involved in MLC.

Differential effects of N-glycans on surface expression suggest structural differences between the acid-sensing ion channel (ASIC) 1a and ASIC1b.

ASICs (acid-sensing ion channels) are H(+)-gated Na(+) channels with a widespread expression pattern in the central and the peripheral nervous system. ASICs have a simple topology with two transmembrane domains, cytoplasmic termini and a large ectodomain between the transmembrane domains; this topology has been confirmed by the crystal structure of chicken ASIC1. ASIC1a and ASIC1b are two variants encoded by the asic1 gene. The variable part of the protein includes the cytoplasmic N-terminus, the first transmembrane domain and approximately the first third of the ectodomain. Both variants contain two consensus sequences for N-linked glycosylation in the common, distal part of the ectodomain. In contrast with ASIC1a, ASIC1b contains two additional consensus sequences in the variable, proximal part of the ectodomain. Here we show that all the extracellular asparagine residues within the putative consensus sequences for N-glycosylation carry glycans. The two common distal glycans increase surface expression of the channels, but are no absolute requirement for channel activity. In sharp contrast, the presence of at least one of the two proximal glycans, which are specific to ASIC1b, is an absolute requirement for surface expression of ASIC1b. This result suggests substantial differences in the structure of the proximal ectodomain between the two ASIC1 variants.