Biology subjects

Poelzing, S.

Publications and source records attributed to Poelzing, S..

14 recordsLinked to original sources

bioRxiv2026

Concealed Conduction Vulnerability in Scn1b Haploinsufficiency Emerges with Osmotic Stress

RationaleSCN1B encodes the {beta}-subunits of the main cardiac voltage-gated sodium channel, NaV1.5. Variants are linked to cardiac conduction disease, often with concealed phenotypes. Whether {beta}1-subunits regulate conduction through nanoscale intercalated disc (ID) structures, e.g. perinexi, and ephaptic coupling remains unresolved. ObjectiveTest whether Scn1b haploinsufficiency induces latent conduction abnormalities that are unmasked by perturbations in extracellular nanodomains. Methods and ResultsAdult Scn1b+/- mice and wild-type (WT) littermates underwent multiscale phenotyping (qRT-PCR, Western blot, patch clamp, transmission electron microscopy (TEM), ex vivo optical mapping, in vivo ECG). Scn1b+/- hearts showed [~]50% reductions in Scn1b mRNA and {beta}1 protein without changes in canonical conduction proteins. Peak sodium current, baseline conduction velocity ex vivo, and baseline QRS duration in vivo were unchanged. However, TEM revealed increased baseline perinexal width in Scn1b+/- hearts. Osmotic expansion of the perinexus with mannitol slowed conduction to a greater extent in Scn1b+/- hearts and prolonged QRS duration in vivo. In contrast, perinexal narrowing with dextran 2MDa selectively increased conduction velocity in Scn1b+/- hearts. ConclusionsScn1b haploinsufficiency preserves baseline excitability and conduction but structurally remodels the ID at the nanoscale, increasing sensitivity to extracellular nanodomain perturbations. These data support a structural role for {beta}1-subunits in ephaptic coupling, and that conduction is maintained over a range of perinexal widths with pathological conduction slowing occurring beyond a critical width. Importantly, osmotic stress unmasks a concealed conduction phenotype, identifying extracellular nanodomain stability as a potential therapeutic target to mitigate arrhythmia risk in SCN1B-associated disease.

biophysics↗

bioRxiv2026

Dissecting Gap Junctional and Ephaptic Contributions to Electrical Conduction in a Novel Cardiomyocyte Pair Model

Electrical communication between excitable cells depends on both direct gap junction (GJ) currents and field-mediated ephaptic interactions, but their relative contributions have remained difficult to quantify experimentally, limiting mechanistic insight into arrhythmia and other disorders of bioelectric signaling in excitable tissues. Building on the concept of a nanoscale, sodium channel-rich perinexus at the cardiac intercalated disc, we developed a Single-on-Paired (SoP) preparation in which whole-cell sodium current is recorded from one adult ventricular myocyte that remains end-to-end coupled to an intact partner. This configuration revealed a composite two-cell sodium current characterized by a unique pre-peak waveform which exhibits two slopes in the rising phase, and a pronounced activation jump in sodium current amplitude between closely spaced voltage steps. This feature was absent in isolated single myocytes and interpretable as an Intercalated Disc Signature of intercellular activation. By combining graded GJ inhibition, perinexal widening via a Scn1b-derived competitive adhesion peptide, and controlled modulation of extracellular sodium, we show that low sodium conditions favor GJ-dominated activation, whereas at higher, more physiological sodium levels, perinexus-centered ephaptic mechanisms provide substantial support for intercellular activation. A complementary two-cell computational model, simulating our SoP model and incorporating lateral and junctional sodium channels, reproduces the two-cell Intercalated Disc Signature and predicts a shift from GJ-dominated activation at low sodium to ephaptic-dominated support at higher, more physiological sodium concentrations when GJ conductance is reduced. Together, these results provide direct experimental evidence for a specific structural and molecular substrate of ephaptic coupling in the heart and establish a framework for dissecting how nanoscale extracellular cleft geometry, channel organization, sodium level, and GJ conductance jointly tune electric-field-based mechanisms of activation in excitable tissues, with implications for paradoxical clinical responses to anti-arrhythmic interventions.

biophysics↗

bioRxiv2025

Hypernatremia Enhances Transient Outward Potassium and Late Sodium Currents in a Mouse Model of Long QT Syndrome Type 3

Cardiac voltage-gated sodium channel gain-of-function (NavGOF) is characterized by action potential duration (APD) prolongation. Hypernatremia and perinexal widening synergistically prolong cardiac APD in guinea pig. However, guinea pig lack the transient outward potassium current (Ito), which could be increased by hypernatremia and thereby shorten APD. ObjectiveDetermine whether hypernatremia and perinexal expansion synergistically prolong APD in an animal model functionally expressing Ito. MethodsWhole-cell Ito was measured in isolated genetically-modified NavGOF ({Delta}KPQ) mouse ventricular myocytes. Ventricular APD at 30 (APD30) and 90 (APD90) percent repolarization were measured from optically mapped, Langendorff-perfused wild-type (WT) and {Delta}KPQ mouse hearts at different perfusate sodium concentrations (145 or 160mM), without and with the perinexal adhesion antagonist {beta}adp1. ResultsIn isolated myocytes, hypernatremia (160mM sodium) increased Ito. In whole-heart, hypernatremia significantly decreased both APD30 and APD90 in WT but only APD30 in {Delta}KPQ preparations. Perinexal disruption with {beta}adp1 did not change APD30 or APD90 in WT hearts, however it decreased APD30 and increased APD90 in {Delta}KPQ hearts. Combination of hypernatremia and {beta}adp1 did not synergistically change APD in {Delta}KPQ hearts. Computational models predict that Ito activation can prevent synergistic APD prolongation in mouse during hypernatremia and perinexal expansion that was observed previously in a guinea pig NavGOF model lacking Ito. ConclusionsHypernatremia during NavGOF prevents early ventricular repolarization due to Ito activation (mouse) and prolongs repolarization in the absence of Ito (guinea pig). Future studies in animal models electrophysiologically similar to humans are needed to determine if hypernatremia and perinexal expansion are proarrhythmic during NavGOF.

physiology↗

bioRxiv2025

Age-dependent remodeling of the sciatic proteome in 5xFAD mice can be attenuated by exercise or donepezil treatment to maintain neuromuscular function

Background: Alzheimers disease (AD) progresses along a continuum for years to possibly decades prior to cognitive decline and clinical diagnosis. Preclinical AD is associated with neuromuscular dysfunction. We previously characterized early neuromuscular impairment prior to cognitive decline at 4 months of age in the 5xFAD mouse model of AD. However, the underlying cause(s) for peripheral nerve dysfunction leading to impaired skeletal muscle torque production are not understood, therefore limiting interventional capacity. We hypothesized that either voluntary wheel running or donepezil treatment, begun prior to neuromuscular decline, would delay manifestation of neuromuscular impairment in 5xFAD mice. Methods: Sciatic nerves from 5xFAD and wild-type (WT) mice were analyzed by tandem mass tag (TMT)-labeled proteomics at 3, 4, and 7 months to investigate proteome remodeling. Separate cohorts, using 3-month-old 5xFAD mice and WT littermates given voluntary wheel access for 4 weeks or treated with the acetylcholinesterase inhibitor donepezil to test if neuromuscular dysfunction could be attenuated. Afterwards, we assessed tibial nerve stimulated plantar flexion torque and sciatic nerve compound (motor) neuron action potential (CNAP) in-vivo at 4 months. Additionally, we performed TMT-labeled proteomics to ascertain the effect of exercise and donepezil treatments on sciatic proteome. Results: Sciatic nerves in 5xFAD mice exhibited proteomic remodeling from 3 to 4 months, particularly in pathways linked to mitochondrial turnover, calcium handling, lipid metabolism, and inflammation, coinciding with onset of neuromuscular dysfunction. Both exercise and donepezil attenuated in nerve-stimulated muscle torque and CNAP dysfunction. Both exercise and donepezil attenuated proteomic remodeling of the sciatic nerve involving mitochondrial-centric processes through both shared and independent mechanisms. Conclusions: Declines in neuromuscular function may be pre-clinical identifiers for AD that share pathway similarities with noted central effects of the pathology on the brain. Our findings highlight the importance of a systemic approach to AD pathology and importance of disease state in interventional efficacy. Graphical abstract.Created in Biorender. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=137 SRC="FIGDIR/small/662603v1_ufig1.gif" ALT="Figure 1"> View larger version (40K): org.highwire.dtl.DTLVardef@c41009org.highwire.dtl.DTLVardef@1f8d8e8org.highwire.dtl.DTLVardef@689ba5org.highwire.dtl.DTLVardef@1c28884_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗

bioRxiv2024

Ephaptic coupling enables action potential conduction

BackgroundCardiac action potentials are believed to propagate solely by electrotonic transmission via gap junctions. In the alternative theory of ephaptic transmission, changes in extracellular electrical fields and ion concentrations may enable a cardiomyocyte to activate its neighbors. The involvement of ephaptic mechanisms remain highly disputed and has been discounted due to the reported inability of an isolated cardiomyocyte to activate another. MethodsIsolated rat cardiomyocytes were subjected to whole cell patch clamp. Transmission of action potentials was tested in current clamp in isolated cardiomyocytes pushed together and in native cardiomyocyte pairs. Sodium channel activation and inactivation was tested in voltage clamp. ResultsIsolated cardiomyocytes were pushed together end-to-end and one stimulated to fire an action potential. In 10 attempts, 2 pairs showed successful transmission of action potentials, showing that ephaptic transmission is possible. In native pairs, subthreshold depolarization was transferred between cardiomyocytes of native electrically coupled pairs, however, only after a delay, which is not be explained from electrotonic theory. Once action potentials were elicited in one cardiomyocyte of a native pair, the neighbor was activated with delays under 2 msec. The activation delay did not correlate with gap junctional coupling, again suggesting the presence of an alternative mechanism. In voltage clamp of native cardiomyocyte pairs, one cardiomyocyte was held at -90 mV while depolarizing pulses were applied to its neighbor. Consistently, activation of sodium channels in the depolarized cell led to activation of sodium channels in the hyperpolarized cell, which fits well with ephaptic but not electrotonic theory. Ephaptic transmission requires a shielded local domain. To separate this, we measured steady state inactivation in native pairs. As expected, all channels inactivated at -40 mV. However, when maintaining a potential of - 40 mV for an extended period, sodium current elicited at 0 mV re-emerged by de-inactivation. The de-inactivation at -40 mV support that a shielded domain exists where potassium currents can hyperpolarize the local potential. ConclusionsWe show for the first time that ephaptic transmission is possible, that it is most likely in operation, also in the presence of gap junctional coupling, and finally our study suggests that data obtained in single cells may fail to reproduce key features of the electrophysiology of cardiomyocytes that interact with neighboring cardiomyocytes.

physiology↗

bioRxiv2024

Detection, Isolation and Quantification of Myocardial Infarct with Four Different Histological Staining Techniques

Precise quantification of myocardial infarction is crucial for evaluating the therapeutic strategies. We developed a robust, color-based semi-automatic algorithm capable of infarct region detection, isolation and quantification with four different histological staining techniques, and the isolation and quantification of diffuse fibrosis in the heart. Our method is developed based on the color difference in the infarct and non-infarct regions after histological staining. Mouse cardiac tissues stained with Massons trichrome (MTS), hematoxylin and eosin (H&E), 2,3,5-Triphenyltetrazolium chloride and picrosirius red were included to demonstrate the performance of our method. We demonstrate that our algorithm can effectively identify and produce a clear visualization of infarct tissue for the four staining techniques. Notably, the infarct region on a H&E-stained tissue section can be clearly visualized after processing. The MATLAB-based program we developed holds promise in the infarct quantification. Additionally, our program can isolate and quantify the diffuse fibrotic elements from an MTS-stained cardiac section, which suggested the algorithms potential for evaluating pathological cardiac fibrosis in diseased cardiac tissues. In conclusion, we demonstrate that this color-based algorithm is capable of accurately identifying, isolating and quantifying cardiac infarct regions with different staining techniques, as well as the diffuse and patchy fibrosis in MTS-stained cardiac tissues.

pathology↗

bioRxiv2023

Development and Characterization of the Mode-of-Action of Inhibitory and Agonist Peptides Targeting the Voltage-Gated Sodium Channel SCN1B/β1 Subunit

Treatment of cardiac arrhythmias by targeting ion channels is challenging, with safe and effective therapies remaining an unmet clinical need. Modeling and experimental studies have shown that a voltage-gated sodium channel (VGSC)-rich nanodomain at edge of the gap junction (GJ) called the perinexus could provide new mechanistic insights into normal and abnormal conduction of action potentials in the heart. We have reported that a 19 amino acid SCN1B ({beta}1/{beta}1B) mimetic peptide derived from the immunoglobulin domain of the VGSC subunit called {beta}adp1 acutely disrupts {beta}1-mediated adhesive interactions at cardiac perinexii, prompting arrhythmogenic changes during time courses of up to an hour. In the present study, we sought to gain further insight on {beta}adp1 mode-of-action, as well as identifying new SCN1B ({beta}1/{beta}1B) mimetic peptides, with potential for inhibiting and/or promoting {beta}1-mediated adhesion. This included studies of the effect of {beta}adp1 and related peptides on SCN1B ({beta}1/{beta}1B) Regulated Intramembrane Proteolysis (RIP) - a signaling pathway that has been shown to effect gene transcription, including that of VGSC subunits. Using patch clamp to assay cell-cell contact-associated VGSC activity in cardiomyocytes, and electric cell substrate impedance sensing (ECIS) to assess intercellular adhesion in cells heterologously expressing {beta}1, we find that inhibitory effects of {beta}adp1 can persist for up to 5 hours. However, this acute inhibition is not sustained, with {beta}adp1 effects on {beta}1-mediated adhesion lost after 24 hours. We also determined that a short peptide (LQLEED) near the carboxyl-terminal portion of {beta}adp1 inhibited adhesion in {beta}1-expressing cells in a manner similar to {beta}adp1. Paradoxically, dimeric peptides incorporating a repeat of the LQLEED sequence promoted intercellular adhesion at all time points studied over a 2-day time course. Inhibitory and agonistic peptides were found to effect {beta}1 RIP, with {beta}adp1increasing RIP continuously over 48 hours, whilst dimeric agonists acutely increased RIP at 6 hours post-treatment, but not thereafter. In the presence of DAPT, an inhibitor of RIP, the effects of {beta}adp1 on ECIS-measured intercellular adhesion were lost, suggesting a relationship between RIP and inhibitory effects of the peptide. In sum, we identify novel SCN1B ({beta}1/{beta}1B) mimetic peptides with potential to inhibit and promote intercellular {beta}1-mediated adhesion, possibly including by effects on {beta}1 RIP, suggesting paths to development of anti-arrhythmic drugs targeting the perinexus.

cell biology↗

bioRxiv2023

EXTRACELLULAR PERINEXAL SEPARATION IS A PRINCIPAL DETERMINANT OF CARDIAC CONDUCTION

RationaleCardiac conduction is understood to occur through gap junctions. Recent evidence supports ephaptic coupling as another mechanism of electrical communication in heart. Conduction via gap junctions predicts a direct relationship between conduction velocity (CV) and bulk extracellular volume. Ephaptic theory is premised on the existence of a biphasic relationship between CV and the volume of specialized extracellular clefts within intercalated discs. ObjectiveDetermine the relationship between ventricular CV and structural changes to micro and nano-scale extracellular spaces. MethodsConduction and connexin43 (Cx43) gap junction protein expression were quantified from optically mapped guinea pig whole-heart preparations perfused with albumin, mannitol, dextran 70kDa, or dextran 2MDa. Peak sodium current was quantified from isolated guinea pig ventricular myocytes. Extracellular resistance (Re) was quantified by impedance spectroscopy. Intercellular communication was assessed in a heterologous expression system with fluorescence recovery after photobleaching. Perinexal width was quantified from transmission electron micrographs. ResultsCV was significantly reduced by mannitol, and increased by albumin, dextran 70kDa and 2MDa. The combination of albumin and dextran 70kDa decreased CV relative to albumin alone. Re was reduced by mannitol, not significantly changed by albumin, and increased by both dextran 70kDa and dextran 2MDa. Cx43 gap junction expression and conductance, and peak sodium current were not significantly altered by the osmotic agents. The perinexal width in response to osmotic agents, in order of narrowest to widest, was: albumin with dextran 70kDa, albumin or dextran 2MDa alone, dextran 70kDa or no osmotic agent, and mannitol. When compared in the same order, CV was biphasically related to perinexal width. ConclusionsCardiac conduction does not correlate with bulk tissue impedance, but is biphasically related to perinexal separation, providing evidence that the relationship between CV and extracellular volume in ventricular myocardium is determined by ephaptic mechanisms under conditions of normal gap junctional coupling.

biophysics↗

bioRxiv2023

The Calcium Transient Coupled to the L-Type Calcium Current Attenuates Action Potential Alternans

BackgroundAction potential (AP) alternans are linked to increased arrhythmogenesis. It is suggested that calcium (Ca2+) transient (CaT) alternans cause AP alternans through bi-directional coupling feedback mechanisms because CaT alternans can precede AP alternans and develop in AP alternans free conditions. However, the CaT is an emergent response to intracellular Ca2+ handling, and the mechanisms linking AP and CaT alternans are still a topic of investigation. This study investigated the development of AP alternans in the absence of CaT. MethodsAP (patch clamp) and intracellular Ca2+ (Fluo-4 epifluorescence) were recorded simultaneously from isolated rabbit ventricle myocytes perfused with the intracellular Ca2+ buffer BAPTA (10-20 mM) to abolish CaT and/or the L-type Ca2+ channel activator Bay K 8644 (25 nM). ResultsAfter a rate change, alternans were critically damped and stable, overdamped and ceased over seconds, underdamped with longer scale harmonics, or unstably underdamped progressing to 2:1 capture. Alternans in control cells were predominantly critically damped, but after CaT ablation with 10 or 20 mM BAPTA, exhibited respectively increased overdamping or increased underdamping. Alternans were easier to induce in CaT free cells as evidenced by a higher alternans threshold (ALT-TH: at least 7 pairs of alternating beats) relative to control cells. Alternans in Bay K 8644 treated cells were often underdamped, but the ALT-TH was similar to control. In CaT ablated cells, Bay K 8644 prolonged AP duration (APD) leading predominantly to unstably underdamped alternans. ConclusionsAP alternans occur more readily in the absence of CaT suggesting that the CaT dampens the development of AP alternans. The data further demonstrate that agonizing the L-type calcium current without the negative feedback of the CaT leads to unstable alternans. This negative feedback mechanism may be important for understanding treatments aimed at reducing CaT or its dynamic response to prevent arrhythmias.

physiology↗

bioRxiv2023

Multifunctional ferromagnetic fiber robots for navigation, sensing, and treatment in minimally invasive surgery

Small-scale robots capable of remote active steering and navigation offer great potential for biomedical applications. However, the current design and manufacturing procedure impede their miniaturization and integration of various diagnostic and therapeutic functionalities. Here, we present a robotic fiber platform for integrating navigation, sensing, and therapeutic functions at a submillimeter scale. These fiber robots consist of ferromagnetic, electrical, optical, and microfluidic components, fabricated with a thermal drawing process. Under magnetic actuation, they can navigate through complex and constrained environments, such as artificial vessels and brain phantoms. Moreover, we utilize Langendorff mouse hearts model, glioblastoma microplatforms, and in vivo mouse models to demonstrate the capabilities of sensing electrophysiology signals and performing localized treatment. Additionally, we demonstrate that the fiber robots can serve as endoscopes with embedded waveguides. These fiber robots provide a versatile platform for targeted multimodal detection and treatment at hard-to-reach locations in a minimally invasive and remotely controllable manner.

bioengineering↗

bioRxiv2022

Acute adenoviral cardiac infection elicits an arrhythmogenic substrate prior to inflammatory myocardial remodeling and myocarditis

BackgroundViral cardiac infection represents a significant clinical challenge encompassing several etiological agents, disease stages, complex presentation, and a resulting lack of mechanistic understanding. Myocarditis is a major cause of sudden cardiac death in young adults, where current knowledge in the field is dominated by later disease phases, and pathological immune responses. However, little is known regarding how infection can acutely induce an arrhythmogenic substrate prior to significant immune responses. Adenovirus is a leading cause of myocarditis, but due to species-specificity, models of infection are lacking and it is not understood how adenoviral infection may underlie sudden cardiac arrest. Mouse Adenovirus Type-3 (MAdV-3) was previously reported as cardiotropic, yet has not been utilized to understand mechanisms of cardiac infection and pathology. MethodsWe have developed MAdV-3 infection as a model to investigate acute cardiac infection and molecular alterations to the infected heart prior to an appreciable immune response or gross cardiomyopathy. ResultsOptical mapping of infected hearts exposes decreases in conduction velocity concomitant with increased Cx43Ser368 phosphorylation, a residue known to regulate gap junction function. Hearts from animals harboring a phospho-null mutation at Cx43Ser368 are protected against MAdV-3 induced conduction velocity slowing. Additional to gap junction alterations, patch clamping of MAdV-3-infected adult mouse ventricular cardiomyocytes reveals prolonged action potential duration as a result of decreased IK1 and IKs current density. Turning to human systems, we find human adenovirus type-5 (HAdV-5) increases phosphorylation of Cx43Ser368 and disrupts synchrony in human induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs), indicating common mechanisms with our mouse whole heart and adult cardiomyocyte data. ConclusionsTogether, these findings demonstrate that adenoviral infection creates an arrhythmogenic substrate through direct targeting of gap junction and ion channel function in the heart. Such alterations are known to precipitate arrhythmias and likely contribute to sudden cardiac death in acutely infected patients.

pathology↗

bioRxiv2020

Electrical Automaticity and Intercellular Synchronization via Shared Extracellular Compartments

Electrically excitable cells often spontaneously and synchronously depolarize in vitro and in vivo. It remains unknown how cells synchronize and autorhythmically activate above the intrinsic mean activation frequency of isolated cells without pacemaking mechanisms. Recent insights into ephaptic coupling (non-gap junction or synaptic coupling) suggest that cyclic ion accumulation and depletion in diffusion limited extracellular volumes densely expressing ion channels modifies action potentials. This report explores how potassium accumulation and depletion in a restricted extracellular domain promotes spontaneous oscillations in the Hodgkin Huxley action potential model, which does not spontaneously activate on its own without external stimulus. Simulations demonstrate cells sharing a diffusion limited extracellular compartment can become autorhythmic and synchronous despite intercellular electrical heterogeneity. Autorhythmic frequency can be determined by net potassium flux into the cleft and the cleft volume. Additionally, inexcitable cells can induce autorhythmic activity in an excitable cell via a shared cleft and sufficient potassium fluxes contributed by each cell. Importantly, the synchronization and autorhythmic activity conferred by shared cleft with reduced potassium efflux can occur in the absence of gap junctions. Lastly, not only can potassium oscillations in shared restricted clefts initiate, support, and suppress autorhythmic depolarizations, the same mechanism can homogenize repolarization. The work has implications for understanding how automaticity is coordinated among excitable cells and suggests a new role for non-excitable cells such as fibroblasts, macrophages, or astrocytes with sarcolemmal potassium handling proteins facing shared and restricted intercellular clefts. SIGNIFICANCEA mechanism of cyclic ion accumulation and depletion in diffusion limited extracellular compartments can suppress, initiate, and support autorhythmic activity. Additionally, autorhythmicity can emerge from electrophysiologically heterogeneous cell pairs sharing a diffusion limited extracellular compartment, even if the individual cells will not spontaneously depolarize on their own. Sustained and synchronous autorhythmic activity can occur in the absence of gap junction coupling. Lastly, the shared diffusion limited extracellular compartment can also reduce action potential duration gradients by synchronizing repolarization.

biophysics↗

bioRxiv2020

No Relationship Between Perceived Health Anomalies and Perceived Experimental Success in Retired Breeder Male Hartley Albino Guinea Pigs

Guinea pigs used in our laboratory for cardiac research sometimes exhibit physical abnormalities. These issues may abate or intensify during the time they are housed in our facility. After using a guinea pig for research, experimentalists note the apparent health of an animal based on visible features and/or abnormal electrophysiology of the heart. There was an existing anecdotal observation that the health of the Guinea Pigs, and subsequently the experimental success rate, had a seasonal variation; therefore we sought to determine if there is a time of year in which our guinea pigs are more likely to be perceived as unhealthy, and whether any determined monthly pattern correlates with an experimentalists ability to complete an experimental protocol. An electronic log was created to record the perceived health of the animal and the ability to complete the experiment successfully. Irregular symptoms included, but were not limited to, severe weight or hair loss and irregularities with the heart found post thoracotomy or during baseline electrophysiological recordings of whole-heart preparations. Animals that did not exhibit significant weight or hair loss, or other ailments were considered "healthy". Overall, our results indicate that there are no monthly variations in perceived Hartley Albino guinea pig health or correlations with experimental completion rates, suggesting mild hair or weight loss that is common when shipping animals may not significantly affect the ability to conduct ex vivo whole-heart electrophysiological studies.

scientific communication and education↗

bioRxiv2019

Targeting the Cx43 Carboxyl Terminal H2 Domain Preserves Left Ventricular Function Following Ischemia-Reperfusion Injury

BackgroundCT1 is a 25 amino acid therapeutic peptide incorporating the Zonula Occludens-1 (ZO-1)-binding domain of connexin43 (Cx43) that is currently in Phase III clinical testing for healing chronic skin wounds. In preclinical studies in mice, we reported that CT1 reduces arrhythmias and improves ventricular function following cardiac injury, effects that were accompanied by increases in PKC{varepsilon} phosphorylation of Cx43 at serine 368 (pS368). In this study, we undertake a systematic characterization of the molecular mode-of-action of CT1 in mitigating the effects of ischemia reperfusion injury on ventricular contractile function.\n\nMethods and ResultsTo determine the basis of CT1-mediated increases in pS368 we undertook tandem mass spectrometry of reactants in an in vitro assay of PKC{varepsilon} phosphorylation, identifying an interaction between negatively charged amino acids in the CT1 Asp-Asp-Leu-Glu-Iso sequence and positively charged lysines (Lys345, Lys346) in a short -helical sequence (H2) within the Cx43 CT domain. In silico modeling provided further support of the specificity of this interaction, leading us to conclude that CT1 has potential to directly interact with both Cx43 and ZO-1. Using surface plasmon resonance, thermal shift and phosphorylation assays, we characterized a series of CT1 variant peptides, identifying sequences competent to interact with either ZO-1 PDZ2 or the Cx43 CT, but with limited or no ability to bind both polypeptides. Based on this analysis, it was found that only those peptides competent to interact with Cx43, but not ZO-1 alone, resulted in increased pS368 phosphorylation in vitro and in vivo. Moreover, in a mouse model of global ischemia reperfusion injury we determined that pre-ischemic infusion only with those peptides competent to bind Cx43 preserved left ventricular (LV) contractile function following injury. Interestingly, a short 9 amino acid (MW=1110) Cx43-binding variant of the original 25 amino acid CT1 sequence demonstrated potent LV-protecting effects when infused either before or after ischemic injury.\n\nConclusionsInteraction of CT1 with the Cx43 CT, but not ZO-1 PDZ2, explains cardioprotection mediated by this therapeutic peptide. Pharmacophores targeting the Cx43 carboxyl terminus could provide a novel translational approach to preservation of ventricular function following ischemic injury.

cell biology↗