Antisense Oligonucleotide Therapy for Calmodulinopathy.

Background: Calmodulinopathies are rare inherited arrhythmia syndromes caused by dominant heterozygous variants in , , or , which each encode the identical CaM (calmodulin) protein. We hypothesized that antisense oligonucleotide (ASO)-mediated depletion of an affected calmodulin gene would ameliorate disease manifestations, whereas the other 2 calmodulin genes would preserve CaM level and function.

Methods: We tested this hypothesis using human induced pluripotent stem cell-derived cardiomyocyte and mouse models of pathogenic variants.

Therapeutic inhibition of RBM20 improves diastolic function in a murine heart failure model and human engineered heart tissue.

Heart failure with preserved ejection fraction (HFpEF) is prevalent and deadly, but so far, there is no targeted therapy. A main contributor to the disease is impaired ventricular filling, which we improved with antisense oligonucleotides (ASOs) targeting the cardiac splice factor RBM20. In adult mice with increased wall stiffness, weekly application of ASOs over 2 months increased expression of compliant titin isoforms and improved cardiac function as determined by echocardiography and conductance catheter.

Cardiac interstitial tetraploid cells can escape replicative senescence in rodents but not large mammals.

Cardiomyocyte ploidy has been described but remains obscure in cardiac interstitial cells. Ploidy of c-kit+ cardiac interstitial cells was assessed using confocal, karyotypic, and flow cytometric technique. Notable differences were found between rodent (rat, mouse) c-kit+ cardiac interstitial cells possessing mononuclear tetraploid (4n) content, compared to large mammals (human, swine) with mononuclear diploid (2n) content.

Hypoxia Prevents Mitochondrial Dysfunction and Senescence in Human c-Kit Cardiac Progenitor Cells.

Senescence-associated dysfunction deleteriously affects biological activities of human c-Kit cardiac progenitor cells (hCPCs), particularly under conditions of in vitro culture. In comparison, preservation of self-renewal and decreases in mitochondrial reactive oxygen species (ROS) are characteristics of murine CPCs in vivo that reside within hypoxic niches. Recapitulating hypoxic niche oxygen tension conditions of ∼1% O in vitro for expansion of hCPCs rather than typical normoxic cell culture conditions (21% O ) could provide significant improvement of functional and biological activities of hCPCs.

Eat, breathe, ROS: controlling stem cell fate through metabolism.

Research reveals cardiac regeneration exists at levels previously deemed unattainable. Clinical trials using stem cells demonstrate promising cardiomyogenic and regenerative potential but insufficient contractile recovery. Incomplete understanding of the biology of administered cells likely contributes to inconsistent patient outcomes.

Accumulation of Mitochondrial DNA Mutations Disrupts Cardiac Progenitor Cell Function and Reduces Survival.

Transfer of cardiac progenitor cells (CPCs) improves cardiac function in heart failure patients. However, CPC function is reduced with age, limiting their regenerative potential. Aging is associated with numerous changes in cells including accumulation of mitochondrial DNA (mtDNA) mutations, but it is unknown how this impacts CPC function.

PINK1 Is Dispensable for Mitochondrial Recruitment of Parkin and Activation of Mitophagy in Cardiac Myocytes.

Myocyte function and survival relies on the maintenance of a healthy population of mitochondria. The PINK1/Parkin pathway plays an important role in clearing defective mitochondria via autophagy in cells. However, how the PINK1/Parkin pathway regulates mitochondrial quality control and whether it coordinates with other mitophagy pathways are still unclear.

Cellular redox status determines sensitivity to BNIP3-mediated cell death in cardiac myocytes.

The atypical BH3-only protein Bcl-2/adenovirus E1B 19-kDa interacting protein 3 (BNIP3) is an important regulator of hypoxia-mediated cell death. Interestingly, the susceptibility to BNIP3-mediated cell death differs between cells. In this study we examined whether there are mechanistic differences in BNIP3-mediated cell death between neonatal and adult cardiac myocytes.

Unbreak my heart: targeting mitochondrial autophagy in diabetic cardiomyopathy.

Significance: Diabetes is strongly associated with increased incidence of heart disease and mortality due to development of diabetic cardiomyopathy. Even in the absence of cardiovascular disease, cardiomyopathy frequently arises in diabetic patients. Current treatment options for cardiomyopathy in diabetic patients are the same as for nondiabetic patients and do not address the causes underlying the loss of contractility.

Cardiomyocyte health: adapting to metabolic changes through autophagy.

Autophagy is important in the heart for maintaining homeostasis when changes in nutrient levels occur. Autophagy is involved in the turnover of cellular components, and is rapidly upregulated during stress. Studies have found that autophagy is reduced in metabolic disorders including obesity and diabetes.

Autophagy and mitophagy in the myocardium: therapeutic potential and concerns.

The autophagic-lysosomal degradation pathway is critical for cardiac homeostasis, and defects in this pathway are associated with development of cardiomyopathy. Autophagy is responsible for the normal turnover of organelles and long-lived proteins. Autophagy is also rapidly up-regulated in response to stress, where it rapidly clears dysfunctional organelles and cytotoxic protein aggregates in the cell.

Parkin deficiency results in accumulation of abnormal mitochondria in aging myocytes.

Autophagy plays a critical role in cellular quality control and is involved in removing damaged or excess organelles. Dysfunctional mitochondria are quickly cleared from the cell by autophagosomes before they can cause damage to the cell. Parkin is an E3 ubiquitin ligase that selectively ubiquitinates proteins on dysfunctional mitochondria, thereby marking those mitochondria for degradation by autophagosomes.

Loss of MCL-1 leads to impaired autophagy and rapid development of heart failure.

Myeloid cell leukemia-1 (MCL-1) is an anti-apoptotic BCL-2 protein that is up-regulated in several human cancers. MCL-1 is also highly expressed in myocardium, but its function in myocytes has not been investigated. We generated inducible, cardiomyocyte-specific Mcl-1 knockout mice and found that ablation of Mcl-1 in the adult heart led to rapid cardiomyopathy and death.

Parkin protein deficiency exacerbates cardiac injury and reduces survival following myocardial infarction.

It is known that loss-of-function mutations in the gene encoding Parkin lead to development of Parkinson disease. Recently, Parkin was found to play an important role in the removal of dysfunctional mitochondria via autophagy in neurons. Although Parkin is expressed in the heart, its functional role in this tissue is largely unexplored.

Mitochondria and mitophagy: the yin and yang of cell death control.

Mitochondria are primarily responsible for providing the contracting cardiac myocyte with a continuous supply of ATP. However, mitochondria can rapidly change into death-promoting organelles. In response to changes in the intracellular environment, mitochondria become producers of excessive reactive oxygen species and release prodeath proteins, resulting in disrupted ATP synthesis and activation of cell death pathways.

Bnip3-mediated defects in oxidative phosphorylation promote mitophagy.

The Bcl-2 proteins are best known as regulators of the intrinsic mitochondrial pathway of apoptosis. However, recent studies have demonstrated that they can also regulate autophagy. For many years, autophagy was considered to be a nonselective process where the autophagosomes randomly sequestered contents in the cytosol to supply the cells with amino acids and fatty acids during nutrient deprivation.

Bnip3 functions as a mitochondrial sensor of oxidative stress during myocardial ischemia and reperfusion.

Bcl-2/adenovirus E1B 19-kDa protein-interacting protein 3 (Bnip3) is a member of the Bcl-2 homology domain 3-only subfamily of proapoptotic Bcl-2 proteins and is associated with cell death in the myocardium. In this study, we investigated the potential mechanism(s) by which Bnip3 activity is regulated. We found that Bnip3 forms a DTT-sensitive homodimer that increased after myocardial ischemia-reperfusion (I/R).

Bnip3 mediates mitochondrial dysfunction and cell death through Bax and Bak.

Bnip3 is a pro-apoptotic member of the Bcl-2 family that is down-regulated in pancreatic cancers, which correlates with resistance to chemotherapy and a worsened prognosis. In contrast, Bnip3 is up-regulated in heart failure and contributes to loss of myocardial cells during I/R (ischaemia/reperfusion). Bnip3 exerts its action at the mitochondria, but the mechanism by which Bnip3 mediates mitochondrial dysfunction is not clear.