Targeting the Microtubule EB1-CLASP2 Complex Modulates NaV1.5 at Intercalated Discs

[Figure: see text].

Toward Biological Pacing by Cellular Delivery of Hcn2/SkM1

Electronic pacemakers still face major shortcomings that are largely intrinsic to their hardware-based design. Radical improvements can potentially be generated by gene or cell therapy-based biological pacemakers. Our previous work identified adenoviral gene transfer of Hcn2 and SkM1, encoding a "funny current" and skeletal fast sodium current, respectively, as a potent combination to induce short-term biological pacing in dogs with atrioventricular block. To achieve long-term biological pacemaker activity, alternative delivery platforms need to be explored and optimized. The aim of the present study was therefore to investigate the functional delivery of Hcn2/SkM1 via human cardiomyocyte progenitor cells (CPCs). Nucleofection of Hcn2 and SkM1 in CPCs was optimized and gene transfer was determined for Hcn2 and SkM1 in vitro. The modified CPCs were analyzed using patch-clamp for validation and characterization of functional transgene expression. In addition, biophysical properties of Hcn2 and SkM1 were further investigated in lentivirally transduced CPCs by patch-clamp analysis. To compare both modification methods in vivo, CPCs were nucleofected or lentivirally transduced with GFP and injected in the left ventricle of male NOD-SCID mice. After 1 week, hearts were collected and analyzed for GFP expression and cell engraftment. Subsequent functional studies were carried out by computational modeling. Both nucleofection and lentiviral transduction of CPCs resulted in functional gene transfer of Hcn2 and SkM1 channels. However, lentiviral transduction was more efficient than nucleofection-mediated gene transfer and the virally transduced cells survived better in vivo. These data support future use of lentiviral transduction over nucleofection, concerning CPC-based cardiac gene delivery. Detailed patch-clamp studies revealed Hcn2 and Skm1 current kinetics within the range of previously reported values of other cell systems. Finally, computational modeling indicated that CPC-mediated delivery of Hcn2/SkM1 can generate stable pacemaker function in human ventricular myocytes. These modeling studies further illustrated that SkM1 plays an essential role in the final stage of diastolic depolarization, thereby enhancing biological pacemaker functioning delivered by Hcn2. Altogether these studies support further development of CPC-mediated delivery of Hcn2/SkM1 and functional testing in bradycardia models.

P1599Sodium channel gene therapy with dual adeno-associated viral vectors

Background

Sodium channel gene therapy carries significant potential for treatment of acquired and inherited arrhythmias. However, delivery is challenging to the length of the transgene that exceeds the packaging capacity of Adeno-Associated Virus (AAV), the most advanced long-term gene therapy vector to date. To overcome this issue, we have developed dual AAV vectors for the delivery of the skeletal muscle sodium channel 1 (SkM1).

Purpose

To achieve cardiac delivery of SkM1 and other large therapeutic genes using dual AAV vectors.

Methods

Dual AAV vectors were constructed, containing SkM1 gene fragments that allow reconstruction in the target cells by trans-splicing and recombination. An oversized single AAV vector containing SkM1 served as a control. HEK293T cells and neonatal rat ventricular cardiomyocytes (NRVMs) were transduced with dual AAV vectors or oversized single AAV vector at an MOI of 50,000 per vector. Etoposide and Teniposide were added 2h before transduction to improve the efficiency. SkM1 mRNA and protein were isolated 3 days post transduction and the expression was detected by RT-qPCR and Western blot.

Results

Robust full-length SkM1 protein expression was detected in both HEK cells and NRVMs transduced by dual AAV vectors while no expression was detected in the control. Transduction with dual AAV vectors also showed significantly higher SkM1 mRNA expression in both cell types (4 to 29-fold) comparing to oversized single AAV vector. Moreover, a relatively high level of SkM1 mRNA expression was achieved in NRVM; 22-fold higher than the native cardiac sodium channel.

Conclusion

Efficient delivery and expression of SkM1 was successfully achieved in vitro by hybrid dual AAV vectors. This approach supports the application of SkM1 and other sodium channel antiarrhythmic gene therapies. In vivo validation and functional testing are currently in on-going.

Supraventricular tachycardias, conduction disease, and cardiomyopathy in 3 families with the same rare variant in TNNI3K (p.Glu768Lys)

BACKGROUND

Rare genetic variants in TNNI3K encoding troponin-I interacting kinase have been linked to a distinct syndrome consisting primarily of supraventricular tachycardias and variably expressed conduction disturbance and dilated cardiomyopathy in 2 families.

OBJECTIVE

The purpose of this study was to identify new genetic variants associated with inherited supraventricular tachycardias, cardiac conduction disease, and cardiomyopathy.

METHODS

We conducted next generation sequencing in 3 independent multigenerational families with atrial/junctional tachycardia with or without conduction disturbance, dilated cardiomyopathy, and sudden death. We also assessed the effect of identified variant on protein autophosphorylation.

RESULTS

In this study, we uncovered the same ultra-rare genetic variant in TNNI3K (c.2302G>A, p.Glu768Lys), which co-segregated with disease features in all affected individuals (n = 23) from all 3 families. TNNI3K harboring the TNNI3K-p.Glu768Lys variant displayed enhanced kinase activity, in line with expectations from previous mouse studies that demonstrated increased conduction indices and procardiomyopathic effects with increased levels of Tnni3k.

CONCLUSION

This study corroborates further the causal link between rare genetic variation in TNNI3K and this distinct complex phenotype, and points to enhanced kinase activity of TNNI3K as the underlying pathobiological mechanism.

Human Cardiomyocyte Progenitor Cells in Co-culture with Rat Cardiomyocytes Form a Pro-arrhythmic Substrate: Evidence for Two Different Arrhythmogenic Mechanisms

Background: Cardiomyocyte progenitor cells (CMPCs) are a promising cell source for regenerative cell therapy to improve cardiac function after myocardial infarction. However, it is unknown whether undifferentiated CMPCs have arrhythmogenic risks. We investigate whether undifferentiated, regionally applied, human fetal CMPCs form a pro-arrhythmic substrate in co-culture with neonatal rat ventricular myocytes (NRVMs).

Method: Unipolar extracellular electrograms, derived from micro-electrode arrays (8 × 8 electrodes) containing monolayers of NRVMs (control), or co-cultures of NRVMs and locally seeded CMPCs were used to determine conduction velocity and the incidence of tachy-arrhythmias. Micro-electrodes were used to record action potentials. Conditioned medium (Cme) of CMPCs was used to distinguish between coupling or paracrine effects.

Results: Co-cultures demonstrated conduction slowing (5.6 ± 0.3 cm/s, n = 50) compared to control monolayers (13.4 ± 0.4 cm/s, n = 26) and monolayers subjected to Cme (13.7 ± 0.6 cm/s, n = 11, all p < 0.001). Furthermore, co-cultures had a more depolarized resting membrane than control monolayers (−47.3 ± 17.4 vs. −64.8 ± 7.7 mV, p < 0.001) and monolayers subjected to Cme (−64.4 ± 8.1 mV, p < 0.001). Upstroke velocity was significantly decreased in co-cultures and action potential duration was prolonged. The CMPC region was characterized by local ST-elevation in the recorded electrograms. The spontaneous rhythm was faster and tachy-arrhythmias occurred more often in co-cultured monolayers than in control monolayers (42.0 vs. 5.4%, p < 0.001).

Conclusion: CMPCs form a pro-arrhythmic substrate when co-cultured with neonatal cardiomyocytes. Electrical coupling between both cell types leads to current flow between a, slowly conducting, depolarized and the normal region leading to local ST-elevations and the occurrence of tachy-arrhythmias originating from the non-depolarized zone.

Fruits and vegetables in the prevention of cancer and cardiovascular disease

OBJECTIVE

We quantified the public health benefit of fruits and vegetables on the prevention of cancer and cardiovascular disease (CVD), using currently available human data.

DESIGN

We reviewed over 250 observational studies on cancer and CVD. Relative risks (RRs) for high versus low intake of fruits and vegetables were obtained. The preventable proportion of chronic diseases, i.e. the per cent of cases attributable to low consumption of fruits and vegetables, was estimated using three scenarios: best guess, optimistic (using stronger RRs) and conservative (using weaker RRs and eliminating the contribution of smoking and/or drinking). The preventable proportion was calculated for increasing average intake from the current 250 g day(-1) to the recommended 400 g day(-1) among the general Dutch population.

RESULTS

It is estimated that in the Netherlands cancer incidence could be reduced by 19% (12,000 cases annually, best guess), ranging from 6% (conservative) to 28% (optimistic). Cardiovascular deaths could be reduced by 16% (8000 deaths annually, best guess), ranging from 6% to 22%. Evidence is most abundant for gastrointestinal cancers, followed by hormone-related cancers, but limited for other sites and CVD.

CONCLUSIONS

Increasing consumption of fruits and vegetables carries a large public health potential. Population trials and biological mechanisms should eventually provide scientific proof of their efficacy. The available evidence is sufficient to justify public health education and promotion aimed at a substantial increase in the consumption of fruits and vegetables.

Comparison of effect of cafetière and filtered coffee on serum concentrations of liver aminotransferases and lipids: six month randomised controlled trial

OBJECTIVE

To study the effects of prolonged intake of cafetière coffee, which is rich in the diterpenes cafestol and kahweol, on serum aminotransferase and lipid concentrations.

DESIGN

Randomised parallel controlled trial.

SUBJECTS

46 healthy men and women aged 19 to 69.

INTERVENTION

Consumption of five to six strong cups (0.9 litres) a day of either cafetière (22 subjects) or filtered coffee (24 subjects) for 24 weeks.

MAIN OUTCOME MEASURES

Mean changes in serum aminotransferase and lipid concentrations.

RESULTS

Cafetière coffee raised alanine aminotransferase concentration by up to 80% above baseline values relative to filtered coffee. After 24 weeks the rise was still 45% (9 U/l (95% confidence interval 3 to 15 U/l), P = 0.007). Alanine aminotransferase concentration exceeded the upper limit of normal in eight of the 22 subjects drinking cafetière coffee, being twice the upper limit of normal in three of them. Cafetière coffee raised low density lipoprotein cholesterol concentrations by 9-14%. After 24 weeks the rise was 0.26 mmol/l (0.04 to 0.47 mmol/l) (P = 0.03) relative to filtered coffee. Triglyceride concentrations initially rose by 26% with cafetière coffee but returned close to baseline values within six months. All increases were reversible after the intervention was stopped.

CONCLUSIONS

Daily consumption of five to six cups of strong cafetière coffee affects the integrity of liver cells as suggested by small increases in serum alanine aminotransferase concentration. The effect does not subside with prolonged intake. High intakes of coffee brews rich in cafestol and kahweol may thus be responsible for unexplained increases in this enzyme activity in apparently healthy subjects. Cafetière coffee also raises low density lipoprotein cholesterol concentration and thus the risk of coronary heart disease.