Using iPSC Models to Probe Regulation of Cardiac Ion Channel Function

Ion channel trafficking implications in heart failure

Heart failure (HF) is recognized as an epidemic in the contemporary world, impacting around 1%-2% of the adult population and affecting around 6 million Americans. HF remains a major cause of mortality, morbidity, and poor quality of life. Several therapies are used to treat HF and improve the survival of patients; however, despite these substantial improvements in treating HF, the incidence of HF is increasing rapidly, posing a significant burden to human health. The total cost of care for HF is USD 69.8 billion in 2023, warranting a better understanding of the mechanisms involved in HF. Among the most serious manifestations associated with HF is arrhythmia due to the electrophysiological changes within the cardiomyocyte. Among these electrophysiological changes, disruptions in sodium and potassium currents' function and trafficking, as well as calcium handling, all of which impact arrhythmia in HF. The mechanisms responsible for the trafficking, anchoring, organization, and recycling of ion channels at the plasma membrane seem to be significant contributors to ion channels dysfunction in HF. Variants, microtubule alterations, or disturbances of anchoring proteins lead to ion channel trafficking defects and the alteration of the cardiomyocyte's electrophysiology. Understanding the mechanisms of ion channels trafficking could provide new therapeutic approaches for the treatment of HF. This review provides an overview of the recent advances in ion channel trafficking in HF.

Drug Repurposing: Claiming the Full Benefit from Drug Development

PURPOSE OF REVIEW

Drug development has evolved over the years from being one-at-a-time to be massive screens in an industrial manner. Bringing a new therapeutic agent from concept to bedside can take a decade and cost billions of dollars-with most concepts failing along the way. Of the few compounds that make it to clinical testing, less than one out of eight make it to approval. This traditional drug development pipeline is challenging for prevalent diseases and makes the development of new therapeutics for rare diseases financially intractable.

RECENT FINDINGS

Repurposing of drugs is an alternative to identify new applications for the thousands of compounds that have already been approved for clinical use. There is now a range of strategies for such efforts that leverage clinical data, pharmacologic data, and/or genomic or transcriptomic data. These strategies, together with examples, are detailed in this review. Drug repurposing bypasses the pre-clinical work and thereby opens up the opportunity to provide targeted treatment at a fraction of the cost that is accompanied with the development from ideation to full approval. Such an approach makes drug discovery for any disease process more efficient but holds particular promise for rare diseases for which there is little to no other viable drug development channel.

Metabolic Maturation Media Improve Physiological Function of Human iPSC-Derived Cardiomyocytes

Induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) have enormous potential for the study of human cardiac disorders. However, their physiological immaturity severely limits their utility as a model system and their adoption for drug discovery. Here, we describe maturation media designed to provide oxidative substrates adapted to the metabolic needs of human iPSC (hiPSC)-CMs. Compared with conventionally cultured hiPSC-CMs, metabolically matured hiPSC-CMs contract with greater force and show an increased reliance on cardiac sodium (Na⁺) channels and sarcoplasmic reticulum calcium (Ca²⁺) cycling. The media enhance the function, long-term survival, and sarcomere structures in engineered heart tissues. Use of the maturation media made it possible to reliably model two genetic cardiac diseases: long QT syndrome type 3 due to a mutation in the cardiac Na⁺ channel SCN5A and dilated cardiomyopathy due to a mutation in the RNA splicing factor RBM20. The maturation media should increase the fidelity of hiPSC-CMs as disease models.

Physiological immaturity of iPSC-derived cardiomyocytes limits their fidelity as disease models. Feyen et al. developed a low glucose, high oxidative substrate media that increase maturation of ventricular-like hiPSC-CMs in 2D and 3D cultures relative to standard protocols. Improved characteristics include a low resting V_m, rapid depolarization, and increased Ca²⁺ dependence and force generation.

Unveiling a sudden unexplained death case by whole exome sequencing and bioinformatic analysis

BACKGROUND

Sudden unexplained death (SUD) refers to cases of sudden death where autopsy fails to identify any cardiac or extracardiac underlying cause. Guideline-directed standard genetic testing identifies a disease-causing mutation in less than one-third of cases of SUD. Conversely, whole exome sequencing (WES) may provide the key to solve most cases of SUD even after several years from the subject's death.

METHODS

We report on a case of sudden unexpected death of a 37-year-old male, with inconclusive autopsy conducted 14 years ago. A recent reevaluation through WES was performed on DNA extracted from left ventricular samples. A multiple step process including several "in silico" tools was applied to identify potentially pathogenic variants. Data analysis was based on a 562 gene panel, including 234 candidate genes associated with sudden cardiac death or heart diseases, with the addition of 328 genes highly expressed in the heart. WebGestalt algorithms were used for association enrichment analysis of all genes with detected putative pathogenic variants.

RESULTS

WES analysis identified four potentially pathogenic variants: RYR2:c.12168G>T, TTN:c.11821C>T (rs397517804), MYBPC3:c.1255C>T (rs368770848), and ACADVL:c.848T>C (rs113994167). WebGestalt algorithms indicated that their combination holds an unfavorable arrhythmic susceptibility which conceivably caused the occurrence of the events leading to our subject's sudden death.

CONCLUSION

Associating WES technique with online prediction algorithms may allow the recognition of genetic mutations potentially responsible for otherwise unexplained deaths.

Antiarrhythmic Mechanisms of Chinese Herbal Medicine Dingji Fumai Decoction

Background

Dingji Fumai decoction (DFD) is used to treat ventricular arrhythmia, and it has provided a very good curative effect. However, its cellular electrophysiological mechanism is unknown.

Methods

Electrocardiogram was recorded, and oxidative stress response and ion-channel-related molecules were detected in rats with barium chloride- and aconitine-induced ventricular arrhythmia. Moreover, whole-cell patch-clamp assay was used to investigate the inhibitory effect of DFD on Nav_1.5 in Chinese hamster ovary cells.

Results

DFD prolonged the occurrence time and shortened the duration of ventricular arrhythmia, decreased the malondialdehyde and increased the superoxide dismutase, and alleviated the activation of Na⁺-K⁺-ATPase and connexin-43. DFD suppressed Nav_1.5dose-dependently with an IC₅₀ of 24.0 ± 2.4 mg/mL.

Conclusions

The clinical antiarrhythmic mechanisms of DFD are based on its antioxidant potential, alleviation of Na⁺-K⁺-ATPase and connexin-43, and class I antiarrhythmic properties by suppressing Nav_1.5dose-dependently with an IC₅₀ of 24.0 ± 2.4 mg/mL.