Kvβ1.1 (AKR6A8) senses pyridine nucleotide changes in the mouse heart and modulates cardiac electrical activity

Development and testing of nanoparticles delivery for P7C3 small molecule using injury models

The use of nanoparticles (NPs) has emerged as a potential tool for safe and effective drug delivery. In the present study, we developed small molecule P7C3-based NPs and tested its efficacy and toxicity along with the tissue specific aptamer-modified P7C3 NPs. The P7C3 NPs were prepared using poly (D, L-lactic-co-glycolic acid) carboxylic acid (PLGA-COOH) polymer, were conjugated with skeletal muscle-specific RNA aptamer (A01B P7C3 NPs) and characterized for its cytotoxicity, cellular uptake, and wound healing in vitro. The A01B P7C3 NPs demonstrated an encapsulation efficiency of 30.2 ± 2.6%, with the particle size 255.9 ± 4.3 nm, polydispersity index of 0.335 ± 0.05 and zeta potential of + 10.4 ± 1.8mV. The FTIR spectrum of P7C3 NPs displayed complete encapsulation of the drug in the NPs. The P7C3 NPs and A01B P7C3 NPs displayed sustained drug release in vitro for up to 6 days and qPCR analysis confirmed A01B aptamer binding to P7C3 NPs. The C2C12 cells viability assay displayed no cytotoxic effects of all 3 formulations at 48 and 72 h. In addition, the cellular uptake of A01B P7C3 NPs in C2C12 myoblasts demonstrated higher uptake. In vitro assay mimicking wound healing showed improved wound closure with P7C3 NPs. In addition, P7C3 NPs significantly decreased TNF-α induced NF-κB activity in the C2C12/NF-κB reporter cells after 24-hour treatment. The P7C3 NPs showed 3-4-fold higher efficacy compared to P7C3 solutions in both wound-closure and inflammation assays in C2C12 cells. Furthermore, the P7C3 NPs showed 3-4-fold higher efficacy in reducing the infarct size and protected mouse hearts from ex vivo ischemia-reperfusion injury. Overall, this study demonstrates the safe and effective delivery of P7C3 NPs.

Diversification of Potassium Currents in Excitable Cells via Kvβ Proteins

Excitable cells of the nervous and cardiovascular systems depend on an assortment of plasmalemmal potassium channels to control diverse cellular functions. Voltage-gated potassium (Kv) channels are central to the feedback control of membrane excitability in these processes due to their activation by depolarized membrane potentials permitting K⁺ efflux. Accordingly, Kv currents are differentially controlled not only by numerous cellular signaling paradigms that influence channel abundance and shape voltage sensitivity, but also by heteromeric configurations of channel complexes. In this context, we discuss the current knowledge related to how intracellular Kvβ proteins interacting with pore complexes of Shaker-related Kv1 channels may establish a modifiable link between excitability and metabolic state. Past studies in heterologous systems have indicated roles for Kvβ proteins in regulating channel stability, trafficking, subcellular targeting, and gating. More recent works identifying potential in vivo physiologic roles are considered in light of these earlier studies and key gaps in knowledge to be addressed by future research are described.

NAD+ centric mechanisms and molecular determinants of skeletal muscle disease and aging

The nicotinamide adenine dinucleotide (NAD+) is an essential redox cofactor, involved in various physiological and molecular processes, including energy metabolism, epigenetics, aging, and metabolic diseases. NAD+ repletion ameliorates muscular dystrophy and improves the mitochondrial and muscle stem cell function and thereby increase lifespan in mice. Accordingly, NAD+ is considered as an anti-oxidant and anti-aging molecule. NAD+ plays a central role in energy metabolism and the energy produced is used for movements, thermoregulation, and defense against foreign bodies. The dietary precursors of NAD+ synthesis is targeted to improve NAD+ biosynthesis; however, studies have revealed conflicting results regarding skeletal muscle-specific effects. Recent advances in the activation of nicotinamide phosphoribosyltransferase in the NAD+ salvage pathway and supplementation of NAD+ precursors have led to beneficial effects in skeletal muscle pathophysiology and function during aging and associated metabolic diseases. NAD+ is also involved in the epigenetic regulation and post-translational modifications of proteins that are involved in various cellular processes to maintain tissue homeostasis. This review provides detailed insights into the roles of NAD+ along with molecular mechanisms during aging and disease conditions, such as the impacts of age-related NAD+ deficiencies on NAD+-dependent enzymes, including poly (ADP-ribose) polymerase (PARPs), CD38, and sirtuins within skeletal muscle, and the most recent studies on the potential of nutritional supplementation and distinct modes of exercise to replenish the NAD+ pool.

Deletion of Kvβ2 (AKR6) Attenuates Isoproterenol Induced Cardiac Injury with Links to Solute Carrier Transporter SLC41a3 and Circadian Clock Genes

Kvβ subunits belong to the aldo-keto reductase superfamily, which plays a significant role in ion channel regulation and modulates the physiological responses. However, the role of Kvβ2 in cardiac pathophysiology was not studied, and therefore, in the present study, we hypothesized that Kvβ2 plays a significant role in cardiovascular pathophysiology by modulating the cardiac excitability and gene responses. We utilized an isoproterenol-infused mouse model to investigate the role of Kvβ2 and the cardiac function, biochemical changes, and molecular responses. The deletion of Kvβ2 attenuated the QTc (corrected QT interval) prolongation at the electrocardiographic (ECG) level after a 14-day isoproterenol infusion, whereas the QTc was significantly prolonged in the littermate wildtype group. Monophasic action potentials verified the ECG changes, suggesting that cardiac changes and responses due to isoproterenol infusion are mediated similarly at both the in vivo and ex vivo levels. Moreover, the echocardiographic function showed no further decrease in the ejection fraction in the isoproterenol-stimulated Kvβ2 knockout (KO) group, whereas the wildtype mice showed significantly decreased function. These experiments revealed that Kvβ2 plays a significant role in cardiovascular pathophysiology. Furthermore, the present study revealed SLC41a3, a major solute carrier transporter affected with a significantly decreased expression in KO vs. wildtype hearts. The electrical function showed that the decreased expression of SLC41a3 in Kvβ2 KO hearts led to decreased Mg²⁺ responses, whereas, in the wildtype hearts, Mg²⁺ caused action potential duration (APD) shortening. Based on the in vivo, ex vivo, and molecular evaluations, we identified that the deletion of Kvβ2 altered the cardiac pathophysiology mediated by SLC41a3 and altered the NAD (nicotinamide adenine dinucleotide)-dependent gene responses.

NAD+ Metabolism as an Emerging Therapeutic Target for Cardiovascular Diseases Associated With Sudden Cardiac Death

In addition to its central role in mediating oxidation reduction in fuel metabolism and bioenergetics, nicotinamide adenine dinucleotide (NAD+) has emerged as a vital co-substrate for a number of proteins involved in diverse cellular processes, including sirtuins, poly(ADP-ribose) polymerases and cyclic ADP-ribose synthetases. The connection with aging and age-associated diseases has led to a new wave of research in the cardiovascular field. Here, we review the basics of NAD+ homeostasis, the molecular physiology and new advances in ischemic-reperfusion injury, heart failure, and arrhythmias, all of which are associated with increased risks for sudden cardiac death. Finally, we summarize the progress of NAD+-boosting therapy in human cardiovascular diseases and the challenges for future studies.

Metabolic regulation of endothelial SK channels and human coronary microvascular function

BACKGROUND

Diabetic (DM) inactivation of small conductance calcium-activated potassium (SK) channels contributes to coronary endothelial dysfunction. However, the mechanisms responsible for this down-regulation of endothelial SK channels are poorly understood. Thus, we hypothesized that the altered metabolic signaling in diabetes regulates endothelial SK channels and human coronary microvascular function.

METHODS

Human atrial tissue, coronary arterioles and coronary artery endothelial cells (HCAECs) obtained from DM and non-diabetic (ND) patients (n = 12/group) undergoing cardiac surgery were used to analyze metabolic alterations, endothelial SK channel function, coronary microvascular reactivity and SK gene/protein expression/localization.

RESULTS

The relaxation response of DM coronary arterioles to the selective SK channel activator SKA-31 and calcium ionophore A23187 was significantly decreased compared to that of ND arterioles (p < 0.05). Diabetes increases the level of NADH and the NADH/NAD+ ratio in human myocardium and HCAECs (p < 0.05). Increase in intracellular NADH (100 μM) in the HCAECs caused a significant decrease in endothelial SK channel currents (p < 0.05), whereas, intracellular application of NAD+ (500 μM) increased the endothelial SK channel currents (p < 0.05). Mitochondrial reactive oxygen species (mROS) of HCAECs and NADPH oxidase (NOX) and PKC protein expression in the human myocardium and coronary microvasculature were increased respectively (p < 0.05).

CONCLUSIONS

Diabetes is associated with metabolic changes in the human myocardium, coronary microvasculature and HCAECs. Endothelial SK channel function is regulated by the metabolite pyridine nucleotides, NADH and NAD+, suggesting that metabolic regulation of endothelial SK channels may contribute to coronary endothelial dysfunction in the DM patients with diabetes.

Metabolic regulation of Kv channels and cardiac repolarization by Kvβ2 subunits

Voltage-gated potassium (Kv) channels control myocardial repolarization. Pore-forming Kvα proteins associate with intracellular Kvβ subunits, which bind pyridine nucleotides with high affinity and differentially regulate channel trafficking, plasmalemmal localization and gating properties. Nevertheless, it is unclear how Kvβ subunits regulate myocardial K⁺ currents and repolarization. Here, we tested the hypothesis that Kvβ2 subunits regulate the expression of myocardial Kv channels and confer redox sensitivity to Kv current and cardiac repolarization. Co-immunoprecipitation and in situ proximity ligation showed that in cardiac myocytes, Kvβ2 interacts with Kv1.4, Kv1.5, Kv4.2, and Kv4.3. Cardiac myocytes from mice lacking Kcnab2 (Kvβ2^-/-) had smaller cross sectional areas, reduced sarcolemmal abundance of Kvα binding partners, reduced I_to, I_K,slow1, and I_K,slow2 densities, and prolonged action potential duration compared with myocytes from wild type mice. These differences in Kvβ2^-/- mice were associated with greater P wave duration and QT interval in electrocardiograms, and lower ejection fraction, fractional shortening, and left ventricular mass in echocardiographic and morphological assessments. Direct intracellular dialysis with a high NAD(P)H:NAD(P)⁺ accelerated Kv inactivation in wild type, but not Kvβ2^-/- myocytes. Furthermore, elevated extracellular levels of lactate increased [NADH]_i and prolonged action potential duration in wild type cardiac myocytes and perfused wild type, but not Kvβ2^-/-, hearts. Taken together, these results suggest that Kvβ2 regulates myocardial electrical activity by supporting the functional expression of proteins that generate I_to and I_K,slow, and imparting redox and metabolic sensitivity to Kv channels, thereby coupling cardiac repolarization to myocyte metabolism.

Nanoparticle drug delivery characterization for fluticasone propionate and in vitro testing 1

Glucocorticoids, such as fluticasone propionate (FP), are used for the treatment of inflammation and alleviation of nasal symptoms and allergies, and as an antipruritic. However, both short- and long-term therapeutic use of glucocorticoids can lead to muscle weakness and atrophy. In the present study, we evaluated the feasibility of the nanodelivery of FP with poly(dl-lactide-co-glycolide) (PLGA) and tested in vitro function. FP-loaded PLGA nanoparticles were prepared via nanoprecipitation and morphological characteristics were studied via scanning electron microscopy. FP-loaded nanoparticles demonstrated an encapsulation efficiency of 68.6% ± 0.5% with a drug loading capacity of 4.6% ± 0.04%, were 128.8 ± 0.6 nm in diameter with a polydispersity index of 0.07 ± 0.008, and displayed a zeta potential of -19.4 ± 0.7. A sustained in vitro drug release pattern was observed for up to 7 days. The use of fluticasone nanoparticle decreased lipopolysaccharide (LPS)-induced lactate dehydrogenase release compared with LPS alone in C2C12 treated cells. FP also decreased expression of LPS-induced inflammatory genes in C2C12 treated cells as compared with LPS alone. Taken together, the present study demonstrates in vitro feasibility of PLGA-FP nanoparticle delivery to the skeletal muscle cells, which may be beneficial for treating inflammation.

Biochemical and physiological properties of K+ channel-associated AKR6A (Kvβ) proteins

Voltage-gated potassium (Kv) channels play an essential role in the regulation of membrane excitability and thereby control physiological processes such as cardiac excitability, neural communication, muscle contraction, and hormone secretion. Members of the Kv1 and Kv4 families are known to associate with auxiliary intracellular Kvβ subunits, which belong to the aldo-keto reductase superfamily. Electrophysiological studies have shown that these proteins regulate the gating properties of Kv channels. Although the three gene products encoding Kvβ proteins are functional enzymes in that they catalyze the nicotinamide adenine dinucleotide phosphate (NAD[P]H)-dependent reduction of a wide range of aldehyde and ketone substrates, the physiological role for these proteins and how each subtype may perform unique roles in coupling membrane excitability with cellular metabolic processes remains unclear. Here, we discuss current knowledge of the enzymatic properties of Kvβ proteins from biochemical studies with their described and purported physiological and pathophysiological influences.

Physiological role of Kvβ2 (AKR6) in murine skeletal muscle growth and regulation

AIM

Potassium channel accessory subunits (Kvβ) play a key role in cardiac electrical activity through ion channel modulation. In this study, we hypothesize that Kvβ2 regulates skeletal muscle growth and fibre phenotype via protein-protein interactions.

METHODS

Kvβ2 knockout mouse model was used for morphometric, immunohistochemical and biochemical analysis to evaluate the role of Kvβ2 in skeletal muscle physiology.

RESULTS

Deletion of Kvβ2 gene in mice (Kvβ2 knockout, KO) leads to significant decrease in body weight along with skeletal muscle size. Key hindlimb muscles such as biceps, soleus and gastrocnemius were significantly smaller in size in KO mice compared to that of wild type. Morphometric measurements and histological analysis clearly point that the fibre size is decreased in each of the muscle type in KO compared with wild-type mice. In addition, Kvβ2 deletion contributes to fibre-type switching from fast to slow fibre as indicated by more abundant MHCI-expressing fibres in gastrocnemius and soleus muscles, which may underscore the smaller muscle size alongside increase in U3 ubiquitin ligase; NEDD4 expression. Using targeted siRNA knockdown approach, we identified that Kvβ2 knockdown does not affect the myoblasts proliferation. However, Pax7 expression was significantly decreased in 4-week-old gastrocnemius muscle, suggesting that cellular reserve for growth may be deficient in KO mice. This is further supported by decreased migratory capacity of C2C12 cells upon siRNA-targeted Kvβ2 knockdown.

CONCLUSION

Overall, this is the first report identifying that genetic deletion of Kvβ2 leads to decreased skeletal muscle size along with isotype switching.

Statistical considerations in reporting cardiovascular research

The problem of inadequate statistical reporting is long standing and widespread in the biomedical literature, including in cardiovascular physiology. Although guidelines for reporting statistics have been available in clinical medicine for some time, there are currently no guidelines specific to cardiovascular physiology. To assess the need for guidelines, we determined the type and frequency of statistical tests and procedures currently used in the American Journal of Physiology-Heart and Circulatory Physiology. A PubMed search for articles published in the American Journal of Physiology-Heart and Circulatory Physiology between January 1, 2017, and October 6, 2017, provided a final sample of 146 articles evaluated for methods used and 38 articles for indepth analysis. The t-test and ANOVA accounted for 71% (212 of 300 articles) of the statistical tests performed. Of six categories of post hoc tests, Bonferroni and Tukey tests were used in 63% (62 of 98 articles). There was an overall lack in details provided by authors publishing in the American Journal of Physiology-Heart and Circulatory Physiology, and we compiled a list of recommended minimum reporting guidelines to aid authors in preparing manuscripts. Following these guidelines could substantially improve the quality of statistical reports and enhance data rigor and reproducibility.

Nanodrug delivery platform for glucocorticoid use in skeletal muscle injury

Glucocorticoids are utilized for their anti-inflammatory properties in the skeletal muscle and arthritis. However, the major drawback of use of glucocorticoids is that it leads to senescence and toxicity. Therefore, based on the idea that decreasing particle size allows for increased surface area and bioavailability of the drug, in the present study, we hypothesized that nanodelivery of dexamethasone will offer increased efficacy and decreased toxicity. The dexamethasone-loaded poly(lactic-co-glycolic acid) (PLGA) nanoparticles were prepared using nanoprecipitation method. The morphological characteristics of the nanoparticles were studied under scanning electron microscope. The particle size of nanoparticles was 217.5 ± 19.99 nm with polydispersity index of 0.14 ± 0.07. The nanoparticles encapsulation efficiency was 34.57% ± 1.99% with in vitro drug release profile exhibiting a sustained release pattern over 10 days. We identified improved skeletal muscle myoblast performance with improved closure of the wound along with increased cell viability at 10 nmol/L nano-dexamethasone-PLGA. However, dexamethasone solution (1 μmol/L) was injurious to cells because the migration efficiency was decreased. In addition, the use of dexamethasone nanoparticles decreased lipopolysaccharide-induced lactate dehydrogenase release compared with dexamethasone solution. Taken together, the present study clearly demonstrates that delivery of PLGA-dexamethasone nanoparticles to the skeletal muscle cells is beneficial for treating inflammation and skeletal muscle function.

Emerging potential benefits of modulating NAD+ metabolism in cardiovascular disease

Nicotinamide adenine dinucleotide (NAD⁺) and related metabolites are central mediators of fuel oxidation and bioenergetics within cardiomyocytes. Additionally, NAD⁺ is required for the activity of multifunctional enzymes, including sirtuins and poly(ADP-ribose) polymerases that regulate posttranslational modifications, DNA damage responses, and Ca²⁺ signaling. Recent research has indicated that NAD⁺ participates in a multitude of processes dysregulated in cardiovascular diseases. Therefore, supplementation of NAD⁺ precursors, including nicotinamide riboside that boosts or repletes the NAD⁺ metabolome, may be cardioprotective. This review examines the molecular physiology and preclinical data with respect to NAD⁺ precursors in heart failure-related cardiac remodeling, ischemic-reperfusion injury, and arrhythmias. In addition, alternative NAD⁺-boosting strategies and potential systemic effects of NAD⁺ supplementation with implications on cardiovascular health and disease are surveyed.

Corticosteroids and aldose reductase inhibitor Epalrestat modulates cardiac action potential via Kvβ1.1 (AKR6A8) subunit of voltage-gated potassium channel

We previously demonstrated the role of Kvβ1.1 subunit of voltage-activated potassium channel in heart for its sensory roles in detecting changes in NADH/NAD and modulation of ion channel. However, the pharmacological role for the association of Kvβ1 via its binding to ligands such as cortisone and its analogs remains unknown. Therefore, we investigated the significance of Kvβ1.1 binding to cortisone analogs and AR inhibitor epalrestat. In addition, the aldose reductase (AR) inhibitor epalrestat was identified as a pharmacological target and modulator of cardiac activity via binding to the Kvβ1 subunit. Using a combination of ex vivo cardiac electrophysiology and in silico binding, we identified that Kvβ1 subunit binds and interacts with epalrestat. To identify the specificity of the action potential changes, we studied the sensitivity of the action potential prolongation by probing the electrical changes in the presence of 4-aminopyridine and evaluated the specificity of pharmacological effects in the hearts from Kvβ1.1 knock out mouse. Our results show that pharmacological modulation of cardiac electrical activity by cortisone analogs and epalrestat is mediated by Kvβ1.1.