Cerebral cavernous malformations (CCMs) are a common type of vascular malformation in the brain that are a major cause of hemorrhagic stroke. This condition has been independently linked to 3 separate genes: Krev1 interaction trapped (KRIT1), Cerebral cavernous malformation 2 (CCM2), and Programmed cell death 10 (PDCD10). Despite the commonality in disease pathology caused by mutations in these 3 genes, we found that the loss of Pdcd10 results in significantly different developmental, cell biological, and signaling phenotypes from those seen in the absence of Ccm2 and Krit1. PDCD10 bound to germinal center kinase III (GCKIII) family members, a subset of serine-threonine kinases, and facilitated lumen formation by endothelial cells both in vivo and in vitro. These findings suggest that CCM may be a common tissue manifestation of distinct mechanistic pathways. Nevertheless, loss of heterozygosity (LOH) for either Pdcd10 or Ccm2 resulted in CCMs in mice. The murine phenotype induced by loss of either protein reproduced all of the key clinical features observed in human patients with CCM, as determined by direct comparison with genotype-specific human surgical specimens. These results suggest that CCM may be more effectively treated by directing therapies based on the underlying genetic mutation rather than treating the condition as a single clinical entity.

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Background Cardiac recovery in response to mechanical unloading by left ventricular assist devices (LVADs) has been demonstrated in subgroups of chronic heart failure (HF) patients. Hallmarks of HF are depletion and disorganization of the transverse tubular system (t-system) in cardiomyocytes. Here, we investigated remodeling of the t-system in human end-stage HF and its role in cardiac recovery. Methods Left ventricular biopsies were obtained from 5 donors (CTRL) and 26 chronic HF patients undergoing implantation of LVADs. Three-dimensional confocal microscopy and computational image analysis were applied to assess t-system structure, density, and distance of ryanodine receptor (RyR) clusters to the sarcolemma, including the t-system. Recovery of cardiac function in response to mechanical unloading was assessed by echocardiography during turn-down of the LVAD. Results The majority of HF myocytes showed remarkable t-system remodeling, particularly sheet-like invaginations of the sarcolemma. Circularity of t-system components was decreased in HF vs CTRL (0.37±0.01 vs 0.46±0.02, p<0.01), and the volume/length ratio was increased in HF (0.36±0.01μm2 vs 0.25±0.02μm2, p<0.0001). T-system density was reduced in HF, leading to increased RyR-sarcolemma distances (0.96±0.05μm vs 0.64±0.1μm, p<0.01). Low RyR-sarcolemma distances at time of LVAD implantation predicted high post-LVAD left-ventricular ejection fractions (EF, p<0.01) and EF increase during unloading (p<0.01). EF in patients with pre-LVAD RyR-sarcolemma distances larger than 1μm did not improve following mechanical unloading. Additionally, calcium transients were recorded in field-stimulated isolated human cardiomyocytes and analyzed with respect to local t-system density. Calcium release in HF myocytes was restricted to regions proximal to the sarcolemma. Local calcium upstroke was delayed (23.9±4.9ms vs 10.3±1.7ms, p<0.05) and more asynchronous (18.1ms±1.5ms vs 8.9±2.2ms, p<0.01) in HF cells with low t-system density versus cells with high t-system density. Conclusions The t-system in end-stage human HF presents a characteristic novel phenotype consisting of sheet-like invaginations of the sarcolemma. Our results suggest that the remodeled t-system impairs excitation-contraction coupling and functional recovery during chronic LVAD unloading. An intact t-system at time of LVAD implantation may constitute a precondition and predictor for functional cardiac recovery following mechanical unloading.

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Objective To prospectively investigate the longitudinal effects of continuous-flow left ventricular assist device (LVAD) unloading on myocardial structure and systolic and diastolic function. Background The magnitude, timeline and sustainability of changes induced by continuous-flow LVAD on the structure and function of the failing human heart are unknown. Methods Eighty consecutive patients with clinical characteristics consistent with chronic heart failure requiring implantation of a continuous-flow LVAD were prospectively enrolled. Serial echocardiograms (1, 2, 3, 4, 6, 9 and 12 months) and right heart catheterizations were performed after LVAD implant. Cardiac recovery was assessed on the basis of improvement in systolic and diastolic function indices on echocardiography that were sustained during LVAD turn-down studies. Results After 6 months of LVAD unloading, 34% of patients had a relative LVEF increase above 50% and 19% of patients, both ischemic and nonischemic, achieved an LVEF≥40%. LV systolic function improved as early as 30 days, the greatest degree of improvement was achieved by 6 months of mechanical unloading and persisted over the 1- year follow up. LV diastolic function parameters also improved as early as 30 days post LVAD unloading and this improvement persisted over time. LV end-diastolic and end-systolic volumes decreased as early as 30 days post LVAD unloading (113 vs. 77ml/m2, p<0.01 and 92 vs. 60ml/m2, p<0.01, respectively). LV mass decreased as early as 30 days post LVAD unloading (114 vs. 95g/m2, p<0.05) and continued to do so over the 1-year follow-up but did not reach values below the normal reference range suggesting no atrophic remodeling after prolonged LVAD unloading. Conclusion Continuous-flow LVAD unloading induced in a subset of patients, both ischemic and nonischemic, early improvement in myocardial structure and systolic and diastolic function that was largely completed within 6 months, with no evidence of subsequent regression.

Ischemic cardiomyopathy (ICM) is the clinical endpoint of coronary heart disease and a leading cause of heart failure. Despite growing demands to develop personalized approaches to treat ICM, progress is limited by inadequate knowledge of its pathogenesis. Since epigenetics has been implicated in the development of other chronic diseases, the current study was designed to determine whether transcriptional and/or epigenetic changes are sufficient to distinguish ICM from other etiologies of heart failure. Specifically, we hypothesize that genome-wide DNA methylation encodes transcriptional reprogramming in ICM. RNA-sequencing analysis was performed on human ischemic left ventricular tissue obtained from patients with end-stage heart failure, which enriched known targets of the polycomb methyltransferase EZH2 compared to non-ischemic hearts. Combined RNA sequencing and genome-wide DNA methylation analysis revealed a robust gene expression pattern consistent with suppression of oxidative metabolism, induced anaerobic glycolysis, and altered cellular remodeling. Lastly, KLF15 was identified as a putative upstream regulator of metabolic gene expression that was itself regulated by EZH2 in a SET domain-dependent manner. Our observations therefore define a novel role of DNA methylation in the metabolic reprogramming of ICM. Furthermore, we identify EZH2 as an epigenetic regulator of KLF15 along with DNA hypermethylation, and we propose a novel mechanism through which coronary heart disease reprograms the expression of both intermediate enzymes and upstream regulators of cardiac metabolism such as KLF15.

SUMMARY This study sought to investigate the effects of mechanical unloading on myocardial energetics and the metabolic perturbation of heart failure (HF) in an effort to identify potential new therapeutic targets that could enhance the unloading-induced cardiac recovery. The authors prospectively examined paired human myocardial tissue procured from 31 advanced HF patients at left ventricular assist device (LVAD) implant and at heart transplant plus tissue from 11 normal donors. They identified increased post-LVAD glycolytic metabolites without a coordinate increase in early, tricarboxylic acid (TCA) cycle intermediates. The increased pyruvate was not directed toward the mitochondria and the TCA cycle for complete oxidation, but instead, was mainly converted to cytosolic lactate. Increased nucleotide concentrations were present, potentially indicating increased flux through the pentose phosphate pathway. Evaluation of mitochondrial function and structure revealed a lack of post-LVAD improvement in mitochondrial oxidative functional capacity, mitochondrial volume density, and deoxyribonucleic acid content. Finally, post-LVAD unloading, amino acid levels were found to be increased and could represent a compensatory mechanism and an alternative energy source that could fuel the TCA cycle by anaplerosis. In summary, the authors report evidence that LVAD unloading induces glycolysis in concert with pyruvate mitochondrial oxidation mismatch, most likely as a result of persistent mitochondrial dysfunction. These findings suggest that interventions known to improve mitochondrial biogenesis, structure, and function, such as controlled cardiac reloading and conditioning, warrant further investigation to enhance unloading-induced reverse remodeling and cardiac recovery.

Ventricular unloading caused clinical, functional, and hemodynamic improvements accompanied by improvements in sympathetic innervation in the failing heart.