| 1. |
- Angelini, Marina, et al.
(författare)
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Suppression of ventricular arrhythmias by targeting late L-type Ca2+ current
- 2021
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Ingår i: The Journal of General Physiology. - : ROCKEFELLER UNIV PRESS. - 0022-1295 .- 1540-7748. ; 153:12
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Tidskriftsartikel (refereegranskat)abstract
- Ventricular arrhythmias, a leading cause of sudden cardiac death, can be triggered by cardiomyocyte early afterdepolarizations (EADs). EADs can result from an abnormal late activation of L-type Ca2+ channels (LTCCs). Current LTCC blockers (class IV antiarrhythmics), while effective at suppressing EADs, block both early and late components of I-Ca,I-L, compromising inotropy. However, computational studies have recently demonstrated that selective reduction of late I-Ca,I-L (Ca2+ influx during late phases of the action potential) is sufficient to potently suppress EADs, suggesting that effective antiarrhythmic action can be achieved without blocking the early peak I-Ca,I-L, which is essential for proper excitation-contraction coupling. We tested this new strategy using a purine analogue, roscovitine, which reduces late I-Ca,I-L with minimal effect on peak current. Scaling our investigation from a human Ca(V)1.2 channel clone to rabbit ventricular myocytes and rat and rabbit perfused hearts, we demonstrate that (1) roscovitine selectively reduces I-Ca,I-L noninactivating component in a human Ca(V)1.2 channel clone and in ventricular myocytes native current, (2) the pharmacological reduction of late I-Ca,I-L suppresses EADs and EATs (early after Ca2+ transients) induced by oxidative stress and hypokalemia in isolated myocytes, largely preserving cell shortening and normal Ca2+ transient, and (3) late I-Ca,I-L reduction prevents/suppresses ventricular tachycardia/fibrillation in ex vivo rabbit and rat hearts subjected to hypokalemia and/or oxidative stress. These results support the value of an antiarrhythmic strategy based on the selective reduction of late I-Ca,I-L to suppress EAD-mediated arrhythmias. Antiarrhythmic therapies based on this idea would modify the gating properties of Ca(V)1.2 channels rather than blocking their pore, largely preserving contractility.
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| 2. |
- Iacomussi, Sofia, et al.
(författare)
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Governance of Access in Biobanking: The Case of Telethon Network of Genetic Biobanks
- 2021
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Ingår i: Biopreservation and Biobanking. - : Mary Ann Liebert. - 1947-5535 .- 1947-5543. ; 19:6, s. 483-492
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Tidskriftsartikel (refereegranskat)abstract
- The discussion concerning the measure of the quality of a biobank should focus not only on the number of stored samples and their quality but also on the assessment of their access arrangements and governance. This article aims at contributing to the ongoing debate on samples and data access governance in biobanking by presenting the case of the Telethon Network of Genetic Biobanks (TNGB). We attempt to contribute to the need for clear and available access criteria and harmonization in access arrangements to maximize the influence of biobanks in the progress of biomedical research. We reviewed all the sample requests submitted to the TNGB from 2008 to 2020, focusing on those rejected by the Access Committee and the reasons behind the rejections. The analysis of the reasons behind the rejected requests allowed us to analyze how those relate to the issues of scientific misconduct, prioritization, and noncompliance with the biobank's mission. We discuss those issues in light of the actions and motivations used by TNGB in the access decision-making process. Based on this analysis, we suggest that a cross-implementation of a checklist for access assessment would improve the whole access process, ensuring a more transparent and smoother governance. Finally, we conclude that the TNGB's Charter and approach toward access governance could contribute as an important reference point to deal with the issues that have emerged in the international discussion on the topic.
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| 3. |
- Madhvani, Roshni V., et al.
(författare)
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Targeting the Late Component of the Cardiac L-type Ca2+ Current to Suppress Early Afterdepolarizations
- 2015
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Ingår i: The Journal of General Physiology. - : Rockefeller University Press. - 0022-1295 .- 1540-7748. ; 145:5, s. 395-404
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Tidskriftsartikel (refereegranskat)abstract
- Early afterdepolarizations (EADs) associated with prolongation of the cardiac action potential (AP) can create heterogeneity of repolarization and premature extrasystoles, triggering focal and reentrant arrhythmias. Because the L-type Ca2+ current (ICa,L) plays a key role in both AP prolongation and EAD formation, L-type Ca2+ channels (LTCCs) represent a promising therapeutic target to normalize AP duration (APD) and suppress EADs and their arrhythmogenic consequences. We used the dynamic-clamp technique to systematically explore how the biophysical properties of LTCCs could be modified to normalize APD and suppress EADs without impairing excitation–contraction coupling. Isolated rabbit ventricular myocytes were first exposed to H2O2 or moderate hypokalemia to induce EADs, after which their endogenous ICa,L was replaced by a virtual ICa,L with tunable parameters, in dynamic-clamp mode. We probed the sensitivity of EADs to changes in the (a) amplitude of the noninactivating pedestal current; (b) slope of voltage-dependent activation; (c) slope of voltage-dependent inactivation; (d) time constant of voltage-dependent activation; and (e) time constant of voltage-dependent inactivation. We found that reducing the amplitude of the noninactivating pedestal component of ICa,L effectively suppressed both H2O2- and hypokalemia-induced EADs and restored APD. These results, together with our previous work, demonstrate the potential of this hybrid experimental–computational approach to guide drug discovery or gene therapy strategies by identifying and targeting selective properties of LTCC.
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| 4. |
- Nilsson, Michelle, et al.
(författare)
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An epilepsy-associated KV1.2 charge-transfer-center mutation impairs KV1.2 and KV1.4 trafficking
- 2022
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 119:17
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Tidskriftsartikel (refereegranskat)abstract
- Significance: A child with epilepsy has a previously unreported, heterozygous mutation in KCNA2, the gene encoding KV1.2 proteins. Four KV1.2 assemble into a potassium-selective channel, a protein complex at the neuronal cell surface regulating electrical signaling. KV1.2 subunits assemble with other KV1-family members to form heterotetrameric channels, contributing to neuronal potassium-channel diversity. The most striking consequence of this mutation is preventing KV1.2-subunit trafficking, i.e., their ability to reach the cell surface. Moreover, the mutation is dominant negative, as mutant subunits can assemble with wild-type KV1.2 and KV1.4, trapping them into nontrafficking heterotetramers and decreasing their functional expression. Thus, KV1-family genes’ ability to form heterotetrameric channels is a double-edged sword, rendering KV1-family members vulnerable to dominant-negative mutations in a single member gene.Abstract: We report on a heterozygous KCNA2 variant in a child with epilepsy. KCNA2 encodes KV1.2 subunits, which form homotetrameric potassium channels and participate in heterotetrameric channel complexes with other KV1-family subunits, regulating neuronal excitability. The mutation causes substitution F233S at the KV1.2 charge transfer center of the voltage-sensing domain. Immunocytochemical trafficking assays showed that KV1.2(F233S) subunits are trafficking deficient and reduce the surface expression of wild-type KV1.2 and KV1.4: a dominant-negative phenotype extending beyond KCNA2, likely profoundly perturbing electrical signaling. Yet some KV1.2(F233S) trafficking was rescued by wild-type KV1.2 and KV1.4 subunits, likely in permissible heterotetrameric stoichiometries: electrophysiological studies utilizing applied transcriptomics and concatemer constructs support that up to one or two KV1.2(F233S) subunits can participate in trafficking-capable heterotetramers with wild-type KV1.2 or KV1.4, respectively, and that both early and late events along the biosynthesis and secretion pathway impair trafficking. These studies suggested that F233S causes a depolarizing shift of ∼48 mV on KV1.2 voltage dependence. Optical tracking of the KV1.2(F233S) voltage-sensing domain (rescued by wild-type KV1.2 or KV1.4) revealed that it operates with modestly perturbed voltage dependence and retains pore coupling, evidenced by off-charge immobilization. The equivalent mutation in the Shaker K+ channel (F290S) was reported to modestly affect trafficking and strongly affect function: an ∼80-mV depolarizing shift, disrupted voltage sensor activation and pore coupling. Our work exposes the multigenic, molecular etiology of a variant associated with epilepsy and reveals that charge-transfer-center disruption has different effects in KV1.2 and Shaker, the archetypes for potassium channel structure and function.
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| 5. |
- Pantazis, Antonios, et al.
(författare)
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Tracking the motion of the K(V)1.2 voltage sensor reveals the molecular perturbations caused by ade novomutation in a case of epilepsy
- 2020
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Ingår i: Journal of Physiology. - : WILEY. - 0022-3751 .- 1469-7793. ; 598:22, s. 5245-5269
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Tidskriftsartikel (refereegranskat)abstract
- Key points K(V)1.2 channels, encoded by theKCNA2gene, regulate neuronal excitability by conducting K(+)upon depolarization. A newKCNA2missense variant was discovered in a patient with epilepsy, causing amino acid substitution F302L at helix S4, in the K(V)1.2 voltage-sensing domain. Immunocytochemistry and flow cytometry showed that F302L does not impair KCNA2 subunit surface trafficking. Molecular dynamics simulations indicated that F302L alters the exposure of S4 residues to membrane lipids. Voltage clamp fluorometry revealed that the voltage-sensing domain of K(V)1.2-F302L channels is more sensitive to depolarization. Accordingly, K(V)1.2-F302L channels opened faster and at more negative potentials; however, they also exhibited enhanced inactivation: that is, F302L causes both gain- and loss-of-function effects. Coexpression of KCNA2-WT and -F302L did not fully rescue these effects. The probands symptoms are more characteristic of patients with loss ofKCNA2function. Enhanced K(V)1.2 inactivation could lead to increased synaptic release in excitatory neurons, steering neuronal circuits towards epilepsy. An exome-based diagnostic panel in an infant with epilepsy revealed a previously unreportedde novomissense variant inKCNA2, which encodes voltage-gated K(+)channel K(V)1.2. This variant causes substitution F302L, in helix S4 of the K(V)1.2 voltage-sensing domain (VSD). F302L does not affect KCNA2 subunit membrane trafficking. However, it does alter channel functional properties, accelerating channel opening at more hyperpolarized membrane potentials, indicating gain of function. F302L also caused loss of K(V)1.2 function via accelerated inactivation onset, decelerated recovery and shifted inactivation voltage dependence to more negative potentials. These effects, which are not fully rescued by coexpression of wild-type and mutant KCNA2 subunits, probably result from the enhancement of VSD function, as demonstrated by optically tracking VSD depolarization-evoked conformational rearrangements. In turn, molecular dynamics simulations suggest altered VSD exposure to membrane lipids. Compared to other encephalopathy patients withKCNA2mutations, the proband exhibits mild neurological impairment, more characteristic of patients withKCNA2loss of function. Based on this information, we propose a mechanism of epileptogenesis based on enhanced K(V)1.2 inactivation leading to increased synaptic release preferentially in excitatory neurons, and hence the perturbation of the excitatory/inhibitory balance of neuronal circuits.
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| 6. |
- Zamora, Juan Carlos, et al.
(författare)
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Considerations and consequences of allowing DNA sequence data as types of fungal taxa
- 2018
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Ingår i: IMA Fungus. - : INT MYCOLOGICAL ASSOC. - 2210-6340 .- 2210-6359. ; 9:1, s. 167-185
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Tidskriftsartikel (refereegranskat)abstract
- Nomenclatural type definitions are one of the most important concepts in biological nomenclature. Being physical objects that can be re-studied by other researchers, types permanently link taxonomy (an artificial agreement to classify biological diversity) with nomenclature (an artificial agreement to name biological diversity). Two proposals to amend the International Code of Nomenclature for algae, fungi, and plants (ICN), allowing DNA sequences alone (of any region and extent) to serve as types of taxon names for voucherless fungi (mainly putative taxa from environmental DNA sequences), have been submitted to be voted on at the 11th International Mycological Congress (Puerto Rico, July 2018). We consider various genetic processes affecting the distribution of alleles among taxa and find that alleles may not consistently and uniquely represent the species within which they are contained. Should the proposals be accepted, the meaning of nomenclatural types would change in a fundamental way from physical objects as sources of data to the data themselves. Such changes are conducive to irreproducible science, the potential typification on artefactual data, and massive creation of names with low information content, ultimately causing nomenclatural instability and unnecessary work for future researchers that would stall future explorations of fungal diversity. We conclude that the acceptance of DNA sequences alone as types of names of taxa, under the terms used in the current proposals, is unnecessary and would not solve the problem of naming putative taxa known only from DNA sequences in a scientifically defensible way. As an alternative, we highlight the use of formulas for naming putative taxa (candidate taxa) that do not require any modification of the ICN.
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