Dysregulated Autophagy and Sarcomere Dysfunction in Patients With Heart Failure With Co-Occurrence of P63A and P380S BAG3 Variants

BACKGROUND

Mutations to the co-chaperone protein BAG3 (B-cell lymphoma-2-associated athanogene-3) are a leading cause of dilated cardiomyopathy (DCM). These mutations often impact the C-terminal BAG domain (residues 420-499), which regulates heat shock protein 70-dependent protein turnover via autophagy. While mutations in other regions are less common, previous studies in patients with DCM found that co-occurrence of 2 BAG3 variants (P63A, P380S) led to worse prognosis. However, the underlying mechanism for dysfunction is not fully understood.

METHODS AND RESULTS

In this study, we used proteomics, Western blots, and myofilament functional assays on left ventricular tissue from patients with nonfailing, DCM, and DCM with BAG363/380 to determine how these mutations impact protein quality control and cardiomyocyte contractile function. We found dysregulated autophagy and increased protein ubiquitination in patients with BAG363/380 compared with nonfailing and DCM, suggesting impaired protein turnover. Expression and myofilament localization of BAG3-binding proteins were also uniquely altered in the BAG3,63/380 including abolished localization of the small heat shock protein CRYAB (alpha-crystallin B chain) to the sarcomere. To determine whether these variants impacted sarcomere function, we used cardiomyocyte force-calcium assays and found reduced maximal calcium-activated force in DCM and BAG363/380. Interestingly, myofilament calcium sensitivity was increased in DCM but not with BAG363/380, which was not explained by differences in troponin I phosphorylation.

CONCLUSIONS

Together, our data support that the disease-enhancing mechanism for BAG3 variants outside of the BAG domain is through disrupted protein turnover leading to compromised sarcomere function. These findings suggest a shared mechanism of disease among pathogenic BAG3 variants, regardless of location.

Does Stereotactic Online Adaptive MRgRT to the Prostate Preclude the Need for Rectal Spacer

PURPOSE/OBJECTIVE(S)

Historical prospective trials have shown that hydrogel rectal spacers can be very effective at decreasing rectal wall dose, and in turn rectal toxicity, in patients undergoing curative intent fractionated courses of radiotherapy for prostate cancer. However, in the modern era of stereotactic online adaptive MR guided radiation (MRgRT), it's not yet determined if rectal spacers improve the potential daily need for plan adaptation.

MATERIALS/METHODS

A prospective database of MRgRT patients were queried for intact prostate cancer patients who received stereotactic online adaptive MR guided radiation. Patients were reviewed for the presence of a hydrogel rectal spacer present on the planning images. The number of adaptive fractions as well as the organs at risk out of tolerance were noted for each patient. Comparisons between number of fractions adapted as well as the number of fractions adapted for rectal constraints, were noted. For each case within this patient group that required plan adaptation, pre-specified dose constraints were finally met prior to treatment delivery.

RESULTS

A total of 27 patients were treated with stereotactic online adaptive MRgRT from 2020 to 2022. 8 patients had a hydrogel rectal spacer placed prior to treatment. Out of the 95 fractions delivered to non-hydrogel patients, 78 were adapted, with 52 for urethra, 31 for bladder, 5 for bladder neck, and 35 for rectum. Of the 40 fractions delivered to patients with a hydrogel spacer, 20 were adapted. The corresponding reasons for adaptation in this group were 14 times for the urethra, 19 times for the bladder, 8 times for the bladder neck, and 8 times for the rectum. It was common for multiple at-risk organs to require adaptation for a single fraction within both cohorts. Although the percentage of patients requiring adaptation for rectal constraints was greater in the non-hydrogel patients (36.8% vs. 20%), this was not found to be statistically significant; p value greater than 0.1.

CONCLUSION

The presence of a rectal spacer did not significantly reduce the need for online plan adaptation of the rectum for stereotactic online adaptive MRgRT. Furthermore, patients with a rectal spacer continued to often require adaptation to meet other prescription constraints. Further work is necessary to better select patients who would benefit from hydrogel spacers in the setting of online adaptive MRgRT. Additionally, longer follow-up of this patient population coupled with a larger patient cohort overall remains needed to increase the power of this analysis and to further explore the clinical outcomes of this patient group.

Does a Dominant Intraprostatic Lesion Boost Require Daily Adaptation when Treated with Stereotactic Online Adaptive MR-Guided Therapy?

PURPOSE/OBJECTIVE(S)

Multiple trials have demonstrated a dose-response relationship for radiation therapy in the treatment of localized prostate cancer. Recent data has also demonstrated a benefit with whole gland stereotactic radiation therapy (SBRT) in conjunction with a simultaneous integrated boost to the dominant intraprostatic lesion (DIL). SBRT with a DIL boost can often increase dose to nearby organs at risk such as the rectum and online adaptive MR guided radiation therapy (MGgRT) may offer a dosimetric and toxicity benefit.

MATERIALS/METHODS

A prospective database of MRgRT patients was queried for intact prostate cancer patients who received SBRT with a SIB to the DIL. The guideline for adaptation for coverage was to ensure the PTV-prostate coverage at 95% of prescribed dose was greater than 92% or by discretion of the treating physician. Adaptions for organs at risk were made to meet prescription constraints. The number of fractions requiring adaptation to meet organs at risk constraints and/or adequate coverage were reviewed.

RESULTS

A total of 26 patients were treated with SBRT with a DIL boost using stereotactic online adaptive MRgRT from 2020 to 2022. 10 of 26 patients were treated for re-irradiation of intact prostate. Out of the 130 fractions delivered, 107 fractions required adaptation (82.3%). 59 fractions were adapted for urethra (45.2%), 48 fractions were adapted for bladder (36.9%), 36 fractions were adapted for rectum (27.7%), 23 fractions were adapted for bladder neck (17.7%), and 19 fractions were adapted for coverage (14.6%). For 53 fractions (40.8 %), adaptation was required for more than one organ at risk.

CONCLUSION

A total of 82.3% of fractions required adaptation for patients treated with SBRT with a DIL boost using stereotactic online adaptive MRgRT. Adaptation occurred most frequently for urethral (45.2%), bladder (36.9%), and rectal constraints (27.7%). Further studies are needed to elucidate if daily adaptive online MRgRT translates to reduced patient toxicity and improved quality of life.

Bag3 Regulates Mitochondrial Function and the Inflammasome Through Canonical and Noncanonical Pathways in the Heart

B-cell lymphoma 2-associated athanogene-3 (Bag3) is expressed in all animal species, with Bag3 levels being most prominent in the heart, the skeletal muscle, the central nervous system, and in many cancers. Preclinical studies of Bag3 biology have focused on animals that have developed compromised cardiac function; however, the present studies were performed to identify the pathways perturbed in the heart even before the occurrence of clinical signs of dilatation and failure of the heart. These studies show that hearts carrying variants that knockout one allele of BAG3 have significant alterations in multiple cellular pathways including apoptosis, autophagy, mitochondrial homeostasis, and the inflammasome.

BAG3: Nature's Quintessential Multi-Functional Protein Functions as a Ubiquitous Intra-Cellular Glue

BAG3 is a 575 amino acid protein that is found throughout the animal kingdom and homologs have been identified in plants. The protein is expressed ubiquitously but is most prominent in cardiac muscle, skeletal muscle, the brain and in many cancers. We describe BAG3 as a quintessential multi-functional protein. It supports autophagy of both misfolded proteins and damaged organelles, inhibits apoptosis, maintains the homeostasis of the mitochondria, and facilitates excitation contraction coupling through the L-type calcium channel and the beta-adrenergic receptor. High levels of BAG3 are associated with insensitivity to chemotherapy in malignant cells whereas both loss of function and gain of function variants are associated with cardiomyopathy.

Genetics of BAG3: A Paradigm for Developing Precision Therapies for Dilated Cardiomyopathies

Nonischemic dilated cardiomyopathy is a common form of heart muscle disease in which genetic factors play a critical etiological role. In this regard, both rare disease-causing mutations and common disease-susceptible variants, in the Bcl-2-associated athanogene 3 (BAG3) gene have been reported, highlighting the critical role of BAG3 in cardiomyocytes and in the development of dilated cardiomyopathy. The phenotypic effects of the BAG3 mutations help investigators understand the structure and function of the BAG3 gene. Indeed, we report herein that all of the known pathogenic/likely pathogenic variants affect at least 1 of 3 protein functional domains, ie, the WW domain, the second IPV (Ile-Pro-Val) domain, or the BAG domain, whereas none of the missense nontruncating pathogenic/likely pathogenic variants affect the proline-rich repeat (PXXP) domain. A common variant, p.Cys151Arg, associated with reduced susceptibility to dilated cardiomyopathy demonstrated a significant difference in allele frequencies among diverse human populations, suggesting evolutionary selective pressure. As BAG3-related therapies for heart failure move from the laboratory to the clinic, the ability to provide precision medicine will depend in large part on having a thorough understanding of the potential effects of both common and uncommon genetic variants on these target proteins. The current review article provides a roadmap that investigators can utilize to determine the potential interactions between a patient's genotype, their phenotype, and their response to therapeutic interventions with both gene delivery and small molecules.

The Effect of Cardiac Resynchronization without a Defibrillator on Morbidity and Mortality: An Individual-Patient-Data Meta-Analysis of COMPANION and CARE-HF

BACKGROUND

Cardiac resynchronization therapy (CRT) reduces morbidity and mortality for patients with heart failure, reduced left ventricular ejection fraction, QRS duration >130 ms and in sinus rhythm.

OBJECTIVES

To identify patient-characteristics that predict the effect, specifically, of CRT-pacemakers (CRT-P) on all-cause mortality or the composite of hospitalisation for heart failure or all-cause mortality.

METHODS

An individual patient-data meta-analysis of the Comparison of Medical Therapy, Pacing, and Defibrillation in Heart Failure (COMPANION) and Cardiac Resynchronization - Heart Failure (CARE-HF) trials. Only patients assigned to CRT-P or control (n = 1738) were included in order to avoid confounding from concomitant defibrillator therapy. The influence of baseline characteristics on treatment effects was investigated.

RESULTS

Median age was 67 (59-73) years, most patients were men (70%), 68% had a QRS duration of 150-199 ms and 80% had left bundle branch block (LBBB). Patients assigned to CRT-P had lower rates for all-cause mortality (HR 0.68 (95% CI 0.56 to 0.81; p < 0.0001) and the composite outcome (HR 0.67 (95% CI 0.58 to 0.78; p < 0.0001). No pre-specified characteristic, including sex, aetiology of ventricular dysfunction, QRS duration (within the studied range) or morphology or PR interval significantly influenced the effect of CRT-P on all-cause mortality or the composite outcome. However, CRT-P had a greater effect on the composite outcome for patients with lower body surface area (BSA) and those prescribed beta-blockers.

CONCLUSIONS

CRT-P reduces morbidity and mortality in appropriately selected patients with heart failure. Benefits may be greater in smaller patients and in those receiving beta-blockers. Neither QRS duration nor morphology independently predicted the benefit of CRT-P.

Therapeutic targeting of BAG3: considering its complexity in cancer and heart disease

Bcl2-associated athanogene-3 (BAG3) is expressed ubiquitously in humans, but its levels are highest in the heart, the skeletal muscle, and the central nervous system; it is also elevated in many cancers. BAG3's diverse functions are supported by its multiple protein-protein binding domains, which couple with small and large heat shock proteins, members of the Bcl2 family, other antiapoptotic proteins, and various sarcomere proteins. In the heart, BAG3 inhibits apoptosis, promotes autophagy, couples the β-adrenergic receptor with the L-type Ca2+ channel, and maintains the structure of the sarcomere. In cancer cells, BAG3 binds to and supports an identical array of prosurvival proteins, and it may represent a therapeutic target. However, the development of strategies to block BAG3 function in cancer cells may be challenging, as they are likely to interfere with the essential roles of BAG3 in the heart. In this Review, we present the current knowledge regarding the biology of this complex protein in the heart and in cancer and suggest several therapeutic options.

Cardiomyocyte contractile impairment in heart failure results from reduced BAG3-mediated sarcomeric protein turnover

The association between reduced myofilament force-generating capacity (F_max) and heart failure (HF) is clear, however the underlying molecular mechanisms are poorly understood. Here, we show impaired F_max arises from reduced BAG3-mediated sarcomere turnover. Myofilament BAG3 expression decreases in human HF and positively correlates with F_max. We confirm this relationship using BAG3 haploinsufficient mice, which display reduced F_max and increased myofilament ubiquitination, suggesting impaired protein turnover. We show cardiac BAG3 operates via chaperone-assisted selective autophagy (CASA), conserved from skeletal muscle, and confirm sarcomeric CASA complex localization is BAG3/proteotoxic stress-dependent. Using mass spectrometry, we characterize the myofilament CASA interactome in the human heart and identify eight clients of BAG3-mediated turnover. To determine if increasing BAG3 expression in HF can restore sarcomere proteostasis/F_max, HF mice were treated with rAAV9-BAG3. Gene therapy fully rescued F_max and CASA protein turnover after four weeks. Our findings indicate BAG3-mediated sarcomere turnover is fundamental for myofilament functional maintenance.

Decreased expression of BAG3 in the heart is associated with contractile dysfunction and heart failure. Here the authors show that this is due to decreased BAG3-dependent sarcomere protein turnover, which impairs mechanical function, and that sarcomere force-generating capacity is restored with BAG3 gene therapy.

The Addition of a Defibrillator to Resynchronization Therapy Decreases Mortality in Patients With Nonischemic Cardiomyopathy

OBJECTIVES

The aim of this study was to determine whether patients with heart failure with reduced ejection fraction (HFrEF) due to nonischemic etiology eligible for cardiac resynchronization therapy (CRT) benefit from an implantable cardioverter-defibrillator (ICD).

BACKGROUND

It is uncertain whether CRT with an ICD (CRT-D) compared to without an ICD (CRT-P) is associated with a survival benefit in patients with nonischemic etiologies of HFrEF.

METHODS

Analyses of the COMPANION (Comparison of Medical Therapy, Pacing, and Defibrillation in Heart Failure) trial were performed, using Cox proportional hazards modeling stratified by HFrEF etiology of nonischemic cardiomyopathy (NICM) or ischemic cardiomyopathy (ICM). The primary outcome was all-cause mortality (ACM), and secondary outcomes were the combination of cardiovascular mortality or heart failure hospitalization and sudden cardiac death.

RESULTS

Among patients randomized to CRT (n = 1,212), 236 (19.5%) died, 131 and 105 in the CRT-P and CRT-D arms, respectively. The unadjusted and adjusted hazard ratios (HRs) for CRT-D versus CRT-P were both 0.84 (95% confidence interval [CI]: 0.65 to 1.09) for ACM, with a significant device-etiology interaction (p_interaction = 0.015 adjusted; p_interaction = 0.040 unadjusted). In patients with NICM (n = 555), CRT-D versus CRT-P was associated with reduced ACM (adjusted HR: 0.54; 95% CI: 0.34 to 0.86), while patients with ICM (n = 657) did not exhibit a between-device reduction in ACM (adjusted HR: 1.05; 95% CI: 0.77 to 1.44). The effects of CRT-D versus CRT-P on sudden cardiac death (advantage CRT-D) and cardiovascular mortality or heart failure hospitalization (no difference between CRT-P and CRT-D) were similar between the 2 HFrEF etiologies.

CONCLUSIONS

COMPANION patients with NICM exhibited a decrease in ACM associated with CRT-D but not CRT-P treatment, whereas patients with ICM did not.

Novel BAG3 Variants in African American Patients With Cardiomyopathy: Reduced β-Adrenergic Responsiveness in Excitation-Contraction

BACKGROUND

We reported 3 novel nonsynonymous single nucleotide variants of Bcl2-associated athanogene 3 (BAG3) in African Americans with heart failure (HF) that are associated with a 2-fold increase in cardiac events (HF hospitalization, heart transplantation, or death).

METHODS AND RESULTS

We expressed BAG3 variants (P63A, P380S, and A479V) via adenovirus-mediated gene transfer in adult left ventricular myocytes isolated from either wild-type (WT) or cardiac-specific BAG3 haploinsufficient (cBAG3^+/-) mice: the latter to simulate the clinical situation in which BAG3 variants are only found on 1 allele. Compared with WT myocytes, cBAG3^+/- myocytes expressed approximately 50% of endogenous BAG3 levels and exhibited decreased [Ca²⁺]_i and contraction amplitudes after isoproterenol owing to decreased L-type Ca²⁺ current. BAG3 repletion with WT BAG3 but not P380S, A479V, or P63A/P380S variants restored contraction amplitudes in cBAG3^+/- myocytes to those measured in WT myocytes, suggesting excitation-contraction abnormalities partly account for HF in patients harboring these mutants. Because P63A is near the WW domain (residues 21-55) and A479V is in the BAG domain (residues 420-499), we expressed BAG3 deletion mutants (Δ1-61 and Δ421-575) in WT myocytes and demonstrated that the BAG but not the WW domain was involved in enhancement of excitation-contraction by isoproterenol.

CONCLUSIONS

The BAG3 variants contribute to HF in African American patients partly by decreasing myocyte excitation-contraction under stress, and that both the BAG and PXXP domains are involved in mediating β-adrenergic responsiveness in myocytes.

Abstract MP101: Functional Maintenance of the Sarcomere Requires Bag3-dependent Autophagy

Bcl2-associated athanogene-3 (BAG3) is a pro-autophagy co-chaperone highly expressed in the heart. Clinical studies show BAG3 haploinsufficiency and mutations are associated with heart failure (HF). However, these studies are largely observational and fail to go beyond the observed phenotype and study mechanism. One study in neonatal myocytes suggests a role for BAG3 in structural maintenance of the sarcomere. However, the structural and functional significance of BAG3 in adult myocytes is not known. We found that myofilament BAG3 expression decreases in human heart failure and is associated with impaired myofilament force-generating capacity (F max ). To assess whether rescuing BAG3 levels could restore function, we used a mouse model of HF and treated with BAG3 gene therapy via AAV9. Myofilament function was assessed in skinned cardiomyocytes by force-calcium relationship. HF mice experienced a reduction in F max , but this was fully restored to sham levels by BAG3 gene therapy.To explore mechanism, we used mass spectrometry to identify the BAG3-interactome at the myofilament and found heat shock proteins (HSP) 70 and B8 among the top hits. Immunofluorescence further showed that HSP70, B8, and BAG3 each localized to the sarcomere z-disk. This BAG3-Hsp complex had previously been described to promote ubiquitin-dependent autophagy in skeletal muscle. Notably, in both human HF samples and in the mouse HF model, myofilament ubiquitin levels increased significantly. However, BAG3 gene therapy in HF reduces ubiquitin levels and restores autophagy flux. This suggests that BAG3 serves a role in proteostasis for the sarcomere, which may explain the functional effect of BAG3 gene therapy.To further explore the impact of the BAG3/HSP complex on myofilament function, we used a mouse model with the P209L BAG3 mutation, which had previously been described to disrupt client processing by the complex. We found cardiomyocytes from P209L mice had significantly reduced F max and elevated myofilament ubiquitin levels, suggesting BAG3-dependent autophagy is required to maintain function. Together, our data identify a functional role for BAG3 at the sarcomere and indicate BAG3-mediated autophagy is an important mechanism for maintaining myofilament proteostasis.

Association of Variants in BAG3 With Cardiomyopathy Outcomes in African American Individuals

Importance

The prevalence of nonischemic dilated cardiomyopathy (DCM) is greater in individuals of African ancestry than in individuals of European ancestry. However, little is known about whether the difference in prevalence or outcomes is associated with functional genetic variants.

Objective

We hypothesized that Bcl2-associated anthanogene 3 (BAG3) genetic variants were associated with outcomes in individuals of African ancestry with DCM.

Design

This multicohort study of the BAG3 genotype in patients of African ancestry with dilated cardiomyopathy uses DNA obtained from African American individuals enrolled in 3 clinical studies: the Genetic Risk Assessment of African Americans With Heart Failure (GRAHF) study; the Intervention in Myocarditis and Acute Cardiomyopathy Trial-2 (IMAC-2) study; and the Genetic Risk Assessment of Cardiac Events (GRACE) study. Samples of DNA were also acquired from the left ventricular myocardium of patients of African ancestry who underwent heart transplant at the University of Colorado and University of Pittsburgh.

Main Outcomes and Measures

The primary end points were the prevalence of BAG3 mutations in African American individuals and event-free survival in participants harboring functional BAG3 mutations.

Results

Four BAG3 genetic variants were identified; these were expressed in 42 of 402 African American individuals (10.4%) with nonischemic heart failure and 9 of 107 African American individuals (8.4%) with ischemic heart failure but were not present in a reference population of European ancestry (P < .001). The variants included 2 nonsynonymous single-nucleotide variants; 1 three-nucleotide in-frame insertion; and 2 single-nucleotide variants that were linked in cis. The presence of BAG3 variants was associated with a nearly 2-fold (hazard ratio, 1.97 [95% CI, 1.19-3.24]; P = .01) increase in cardiac events in carriers compared with noncarriers. Transfection of transformed adult human ventricular myocytes with plasmids expressing the 4 variants demonstrated that each variant caused an increase in apoptosis and a decrease in autophagy when samples were subjected to the stress of hypoxia-reoxygenation.

Conclusions and Relevance

This study demonstrates that genetic variants in BAG3 found almost exclusively in individuals of African ancestry were not causative of disease but were associated with a negative outcome in patients with a dilated cardiomyopathy through modulation of the function of BAG3. The results emphasize the importance of biological differences in causing phenotypic variance across diverse patient populations, the need to include diverse populations in genetic cohorts, and the importance of determining the pathogenicity of genetic variants.

Trpm2 enhances physiological bioenergetics and protects against pathological oxidative cardiac injury: Role of Pyk2 phosphorylation

The mechanisms by which Trpm2 channels enhance mitochondrial bioenergetics and protect against oxidative stress-induced cardiac injury remain unclear. Here, the role of proline-rich tyrosine kinase 2 (Pyk2) in Trpm2 signaling is explored. Activation of Trpm2 in adult myocytes with H₂ O₂ resulted in 10- to 21-fold increases in Pyk2 phosphorylation in wild-type (WT) myocytes which was significantly lower (~40%) in Trpm2 knockout (KO) myocytes. Pyk2 phosphorylation was inhibited (~54%) by the Trpm2 blocker clotrimazole. Buffering Trpm2-mediated Ca²⁺ increase with 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA) resulted in significantly reduced pPyk2 in WT but not in KO myocytes, indicating Ca²⁺ influx through activated Trpm2 channels phosphorylated Pyk2. Part of phosphorylated Pyk2 translocated from cytosol to mitochondria which has been previously shown to augment mitochondrial Ca²⁺ uptake and enhance adenosine triphosphate generation. Although Trpm2-mediated Ca²⁺ influx phosphorylated Ca²⁺ -calmodulin kinase II (CaMKII), the CaMKII inhibitor KN93 did not significantly affect Pyk2 phosphorylation in H₂ O₂ -treated WT myocytes. After ischemia/reperfusion (I/R), Pyk2 phosphorylation and its downstream prosurvival signaling molecules (pERK1/2 and pAkt) were significantly lower in KO-I/R when compared with WT-I/R hearts. After hypoxia/reoxygenation, mitochondrial membrane potential was lower and superoxide level was higher in KO myocytes, and were restored to WT values by the mitochondria-targeted superoxide scavenger MitoTempo. Our results suggested that Ca²⁺ influx via tonically activated Trpm2 phosphorylated Pyk2, part of which translocated to mitochondria, resulting in better mitochondrial bioenergetics to maintain cardiac health. After I/R, Pyk2 activated prosurvival signaling molecules and prevented excessive increases in reactive oxygen species, thereby affording protection from I/R injury.

Evidence for the impact of BAG3 on electrophysiological activity of primary culture of neonatal cardiomyocytes

Homeostasis of proteins involved in contractility of individual cardiomyocytes and those coupling adjacent cells is of critical importance as any abnormalities in cardiac electrical conduction may result in cardiac irregular activity and heart failure. Bcl2-associated athanogene 3 (BAG3) is a stress-induced protein whose role in stabilizing myofibril proteins as well as protein quality control pathways, especially in the cardiac tissue, has captured much attention. Mutations of BAG3 have been implicated in the pathogenesis of cardiac complications such as dilated cardiomyopathy. In this study, we have used an in vitro model of neonatal rat ventricular cardiomyocytes to investigate potential impacts of BAG3 on electrophysiological activity by employing the microelectrode array (MEA) technology. Our MEA data showed that BAG3 plays an important role in the cardiac signal generation as reduced levels of BAG3 led to lower signal frequency and amplitude. Our analysis also revealed that BAG3 is essential to the signal propagation throughout the myocardium, as the MEA data-based conduction velocity, connectivity degree, activation time, and synchrony were adversely affected by BAG3 knockdown. Moreover, BAG3 deficiency was demonstrated to be connected with the emergence of independently beating clusters of cardiomyocytes. On the other hand, BAG3 overexpression improved the activity of cardiomyocytes in terms of electrical signal amplitude and connectivity degree. Overall, by providing more in-depth analyses and characterization of electrophysiological parameters, this study reveals that BAG3 is of critical importance for electrical activity of neonatal cardiomyocytes.

Role of Bcl2-associated Athanogene 3 in Turnover of Gap Junction Protein, Connexin 43, in Neonatal Cardiomyocytes

Any pathological stress that impairs expression, turnover and phosphorylation of connexin 43 (Cx43), one of the major proteins of gap junctions, can adversely impact myocardial cell behavior, thus leading to the development of cardiac arrhythmias and heart failure. Our results in primary neonatal rat ventricular cardiomyocytes (NRVCs) show that impairment of the autophagy-lysosome pathway dysregulates degradation of Cx43, either by inhibiting lysosomal activity or suppressing the level of Bcl2-associated athanogene 3 (BAG3), a stress-induced pleiotropic protein that is involved in protein quality control (PQC) via the autophagy pathway. Inhibition of lysosomal activity leads to the accumulation of Cx43 aggregates and suppression of BAG3 significantly diminished turnover of Cx43. In addition, knock-down of BAG3 reduced the levels of Cx43 by dysregulating Cx43 protein stability. Under stress conditions, expression of BAG3 affected the state of Cx43 phosphorylation and its degradation. Furthermore, we found that BAG3 co-localized with the cytoskeleton protein, α-Tubulin, and depolymerization of α-Tubulin led to the intracellular accumulation of Cx43. These observations ascribe a novel function for BAG3 that involves control of Cx43 turnover under normal and stress conditions and potentially for optimizing communication of cardiac muscle cells through gap junctions.

Adrenergic Polymorphisms and Survival in African Americans With Heart Failure: Results From A-HeFT

BACKGROUND

Polymorphisms in adrenergic signaling affect the molecular function of adrenergic receptors and related proteins. The β1 adrenergic receptor (ADRB1) Arg389Gly, G-protein receptor kinase type 5 (GRK5) Gln41Leu, G-protein β-3 subunit (GNB3) 825 C/T, and α2c deletion affect adrenergic tone, impact heart failure outcomes and differ in prevalence by ethnicity. Their combined effect within black cohorts remains unknown.

METHODS AND RESULTS

We analyzed subjects from the African American Heart Failure Trial (A-HeFT) by assessing event-free survival, quality of life, and gene coinheritance. Significant coinheritance effects on survival included GRK5 Leu41 among subjects co-inheriting GNB3 825 C alleles (n = 166, 90.4% vs 69.0%, P < 0.001). By contrast, the impact of ADRB1 Arg389Arg genotype was magnified among subjects with GNB3 825 TT genotype (n = 181, 66.3% vs 85.7%, P = .002). The lack of the α2c deletion (ie, insertion) led to a greater impact of the ARG389Arg genotype (n = 289, 76.4% vs 86.1%, P = .007).

CONCLUSIONS

Polymorphisms in adrenergic signaling affects outcomes in black subjects with heart failure. Coinheritance patterns in genetic variation may help determine heart failure survival.

Mitochondrial dysfunction in human immunodeficiency virus-1 transgenic mouse cardiac myocytes

The pathophysiology of human immunodeficiency virus (HIV)-associated cardiomyopathy remains uncertain. We used HIV-1 transgenic (Tg26) mice to explore mechanisms by which HIV-related proteins impacted on myocyte function. Compared to adult ventricular myocytes isolated from nontransgenic (wild type [WT]) littermates, Tg26 myocytes had similar mitochondrial membrane potential (ΔΨ _m ) under normoxic conditions but lower Δ Ψ _m after hypoxia/reoxygenation (H/R). In addition, Δ Ψ _m in Tg26 myocytes failed to recover after Ca ²⁺ challenge. Functionally, mitochondrial Ca ²⁺ uptake was severely impaired in Tg26 myocytes. Basal and maximal oxygen consumption rates (OCR) were lower in normoxic Tg26 myocytes, and further reduced after H/R. Complex I subunit and ATP levels were lower in Tg26 hearts. Post-H/R, mitochondrial superoxide (O ₂ ^•- ) levels were higher in Tg26 compared to WT myocytes. Overexpression of B-cell lymphoma 2-associated athanogene 3 (BAG3) reduced O ₂ ^•- levels in hypoxic WT and Tg26 myocytes back to normal. Under normoxic conditions, single myocyte contraction dynamics were similar between WT and Tg26 myocytes. Post-H/R and in the presence of isoproterenol, myocyte contraction amplitudes were lower in Tg26 myocytes. BAG3 overexpression restored Tg26 myocyte contraction amplitudes to those measured in WT myocytes post-H/R. Coimmunoprecipitation experiments demonstrated physical association of BAG3 and the HIV protein Tat. We conclude: (a) Under basal conditions, mitochondrial Ca ²⁺ uptake, OCR, and ATP levels were lower in Tg26 myocytes; (b) post-H/R, Δ Ψ _m was lower, mitochondrial O ₂ ^•- levels were higher, and contraction amplitudes were reduced in Tg26 myocytes; and (c) BAG3 overexpression decreased O ₂ ^•- levels and restored contraction amplitudes to normal in Tg26 myocytes post-H/R in the presence of isoproterenol.

Haplo-insufficiency of Bcl2-associated athanogene 3 in mice results in progressive left ventricular dysfunction, β-adrenergic insensitivity, and increased apoptosis

Bcl2-associated athanogene 3 (BAG3) is a 575 amino acid protein that is found predominantly in the heart, skeletal muscle, and many cancers. Deletions and truncations in BAG3 that result in haplo-insufficiency have been associated with the development of dilated cardiomyopathy. To study the cellular and molecular events attributable to BAG3 haplo-insufficiency we generated a mouse in which one allele of BAG3 was flanked by loxP recombination sites (BAG3^fl/+ ). Mice were crossed with α-MHC-Cre mice in order to generate mice with cardiac-specific haplo-insufficiency (cBAG3^+/-) and underwent bi-weekly echocardiography to assess their cardiac phenotype. By 10 weeks of age, cBAG3^+/- mice demonstrated increased heart size and diminished left ventricular ejection fraction when compared with non-transgenic littermates (Cre^-/- BAG3^fl/+ ). Contractility in adult myocytes isolated from cBAG3^+/- mice were similar to those isolated from control mice at baseline, but showed a significantly decreased response to adrenergic stimulation. Intracellular calcium ([Ca²⁺ ]_i ) transient amplitudes in myocytes isolated from cBAG3^+/- mice were also similar to myocytes isolated from control mice at baseline but were significantly lower than myocytes from control mice in their response to isoproterenol. BAG3 haplo-insufficiency was also associated with decreased autophagy flux and increased apoptosis. Taken together, these results suggest that mice in which BAG3 has been deleted from a single allele provide a model that mirrors the biology seen in patients with heart failure and BAG3 haplo-insufficiency.

A common variant alters SCN5A-miR-24 interaction and associates with heart failure mortality

SCN5A encodes the voltage-gated Na+ channel NaV1.5 that is responsible for depolarization of the cardiac action potential and rapid intercellular conduction. Mutations disrupting the SCN5A coding sequence cause inherited arrhythmias and cardiomyopathy, and single-nucleotide polymorphisms (SNPs) linked to SCN5A splicing, localization, and function associate with heart failure-related sudden cardiac death. However, the clinical relevance of SNPs that modulate SCN5A expression levels remains understudied. We recently generated a transcriptome-wide map of microRNA (miR) binding sites in human heart, evaluated their overlap with common SNPs, and identified a synonymous SNP (rs1805126) adjacent to a miR-24 site within the SCN5A coding sequence. This SNP was previously shown to reproducibly associate with cardiac electrophysiological parameters, but was not considered to be causal. Here, we show that miR-24 potently suppresses SCN5A expression and that rs1805126 modulates this regulation. We found that the rs1805126 minor allele associates with decreased cardiac SCN5A expression and that heart failure subjects homozygous for the minor allele have decreased ejection fraction and increased mortality, but not increased ventricular tachyarrhythmias. In mice, we identified a potential basis for this in discovering that decreased Scn5a expression leads to accumulation of myocardial reactive oxygen species. Together, these data reiterate the importance of considering the mechanistic significance of synonymous SNPs as they relate to miRs and disease, and highlight a surprising link between SCN5A expression and nonarrhythmic death in heart failure.

The Multifunctional Protein BAG3: A Novel Therapeutic Target in Cardiovascular Disease

The B-cell lymphoma 2–associated anthanogene (BAG3) protein is expressed most prominently in the heart, the skeletal muscle, and in many forms of cancer. In the heart, it serves as a co-chaperone with heat shock proteins in facilitating autophagy; binds to B-cell lymphoma 2, resulting in inhibition of apoptosis; attaches actin to the Z disk, providing structural support for the sarcomere; and links the α-adrenergic receptor with the L-type Ca²⁺ channel. When BAG3 is overexpressed in cancer cells, it facilitates prosurvival pathways that lead to insensitivity to chemotherapy, metastasis, cell migration, and invasiveness. In contrast, in the heart, mutations in BAG3 have been associated with a variety of phenotypes, including both hypertrophic/restrictive and dilated cardiomyopathy. In murine skeletal muscle and vasculature, a mutation in BAG3 leads to critical limb ischemia after femoral artery ligation. An understanding of the biology of BAG3 is relevant because it may provide a therapeutic target in patients with both cardiac and skeletal muscle disease.

HIV-1 Nef-induced cardiotoxicity through dysregulation of autophagy

Cardiovascular disease is a leading cause of co-morbidity in HIV-1 positive patients, even those in whom plasma virus levels are well-controlled. The pathogenic mechanism of HIV-1-associated cardiomyopathy is unknown, but has been presumed to be mediated indirectly, owing to the absence of productive HIV-1 replication in cardiomyocytes. We sought to investigate the effect of the HIV-1 auxiliary protein, Nef, which is suspected of extracellular release by infected CD4+ T cells on protein quality control and autophagy in cardiomyocytes. After detection of Nef in the serum of HIV-1 positive patients and the accumulation of this protein in human and primate heart tissue from HIV-1/SIV-infected cells we employed cell and molecular biology approaches to investigate the effect of Nef on cardiomyocyte-homeostasis by concentrating on protein quality control (PQC) pathway and autophagy. We found that HIV-1 Nef-mediated inhibition of autophagy flux leads to cytotoxicity and death of cardiomyocytes. Nef compromises autophagy at the maturation stage of autophagosomes by interacting with Beclin 1/Rab7 and dysregulating TFEB localization and cellular lysosome content. These effects were reversed by rapamycin treatment. Our results indicate that HIV-1 Nef-mediated inhibition of cellular PQC is one possible mechanism involved in the development of HIV-associated cardiomyopathy.

Dysregulation of mitochondrial bioenergetics and quality control by HIV-1 Tat in cardiomyocytes

Cardiovascular disease remains a leading cause of morbidity and mortality in HIV-positive patients, even in those whose viral loads are well controlled with antiretroviral therapy. However, the underlying molecular events responsible for the development of cardiac disease in the setting of HIV remain unknown. The HIV-encoded Tat protein plays a critical role in the activation of HIV gene expression and profoundly impacts homeostasis in both HIV-infected cells and uninfected cells that have taken up released Tat via a bystander effect. Since cardiomyocyte function, including excitation-contraction coupling, greatly depends on energy provided by the mitochondria, in this study, we performed a series of experiments to assess the impact of Tat on mitochondrial function and bioenergetics pathways in a primary cell culture model derived from neonatal rat ventricular cardiomyocytes (NRVCs). Our results show that the presence of Tat in cardiomyocytes is accompanied by a decrease in oxidative phosphorylation, a decline in the levels of ATP, and an accumulation of reactive oxygen species (ROS). Tat impairs the uptake of mitochondrial Ca²⁺ ([Ca²⁺ ]_m ) and the electrophysiological activity of cardiomyocytes. Tat also affects the protein clearance pathway and autophagy in cardiomyocytes under stress due to hypoxia-reoxygenation conditions. A reduction in the level of ubiquitin along with dysregulated degradation of autophagy proteins including SQSTM1/p62 and a reduction of LC3 II were detected in cardiomyocytes harboring Tat. These results suggest that, by targeting mitochondria and protein quality control, Tat significantly impacts bioenergetics and autophagy resulting in dysregulation of cardiomyocyte health and homeostasis.

Sudden Cardiac Death in Patients With Ischemic Heart Failure Undergoing Coronary Artery Bypass Grafting: Results From the STICH Randomized Clinical Trial (Surgical Treatment for Ischemic Heart Failure)

BACKGROUND

The risk of sudden cardiac death (SCD) in patients with heart failure after coronary artery bypass graft surgery (CABG) has not been examined in a contemporary clinical trial of surgical revascularization. This analysis describes the incidence, timing, and clinical predictors of SCD after CABG.

METHODS

Patients enrolled in the STICH trial (Surgical Treatment of Ischemic Heart Failure) who underwent CABG with or without surgical ventricular reconstruction were included. We excluded patients with prior implantable cardioverter-defibrillator and those randomized only to medical therapy. The primary outcome was SCD as adjudicated by a blinded committee. A Cox model was used to examine and identify predictors of SCD. The Fine and Gray method was used to estimate the incidence of SCD accounting for the competing risk of other deaths.

RESULTS

Over a median follow-up of 46 months, 113 of 1411 patients who received CABG without (n = 934) or with (n = 477) surgical ventricular reconstruction had SCD; 311 died of other causes. The mean left ventricular ejection fraction at enrollment was 28±9%. The 5-year cumulative incidence of SCD was 8.5%. Patients who had SCD and those who did not die were younger and had fewer comorbid conditions than did those who died of causes other than SCD. In the first 30 days after CABG, SCD (n=5) accounted for 7% of all deaths. The numerically greatest monthly rate of SCD was in the 31- to 90-day time period. In a multivariable analysis including baseline demographics, risk factors, coronary anatomy, and left ventricular function, end-systolic volume index and B-type natriuretic peptide were most strongly associated with SCD.

CONCLUSIONS

The monthly risk of SCD shortly after CABG among patients with a low left ventricular ejection fraction is highest between the first and third months, suggesting that risk stratification for SCD should occur early in the postoperative period, particularly in patients with increased preoperative end-systolic volume index or B-type natriuretic peptide.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov. Unique identifier: NCT0002359.

Adeno-associated Virus Serotype 9 - Driven Expression of BAG3 Improves Left Ventricular Function in Murine Hearts with Left Ventricular Dysfunction Secondary to a Myocardial Infarction

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BAG3 is a highly conserved protein having pleiotropic effects that is expressed at high levels in the heart, skeletal muscles, and many cancers.

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BAG3 levels are reduced in many forms of LV dysfunction including mice after ligation of the left coronary artery.

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Retro-orbital injection of mice with an adeno-associated virus coupled to murine BAG3 under the control of a CMV promoter (rAAV9-BAG3) increased myocardial levels of BAG3 by 7 days post-injection.

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Retro-orbital injection of rAAV9-BAG3 in mice post-myocardial infarction improved LV function, whereas rAAV9-BAG3 had no effect on LV function in the absence of an MI.

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BAG3 may prove to be a new therapeutic target in the treatment of heart failure.

Mutations in Bcl-2–associated athanogene 3 (BAG3) were associated with skeletal muscle dysfunction and dilated cardiomyopathy. Retro-orbital injection of an adeno-associated virus serotype 9 expressing BAG3 (rAAV9-BAG3) significantly (p < 0.0001) improved left ventricular ejection fraction, fractional shortening, and stroke volume 9 days post-injection in mice with cardiac dysfunction secondary to a myocardial infarction. Furthermore, myocytes isolated from mice 3 weeks after injection showed improved cell shortening, enhanced systolic [Ca²⁺]_i and increased [Ca²⁺]_i transient amplitudes, and increased maximal L-type Ca²⁺ current amplitude. These results suggest that BAG3 gene therapy may provide a novel therapeutic option for the treatment of heart failure.

Bcl-2-associated athanogene 3 protects the heart from ischemia/reperfusion injury

Bcl-2-associated athanogene 3 (BAG3) is an evolutionarily conserved protein expressed at high levels in the heart and the vasculature and in many cancers. While altered BAG3 expression has been associated with cardiac dysfunction, its role in ischemia/reperfusion (I/R) is unknown. To test the hypothesis that BAG3 protects the heart from reperfusion injury, in vivo cardiac function was measured in hearts infected with either recombinant adeno-associated virus serotype 9-expressing (rAAV9-expressing) BAG3 or GFP and subjected to I/R. To elucidate molecular mechanisms by which BAG3 protects against I/R injury, neonatal mouse ventricular cardiomyocytes (NMVCs) in which BAG3 levels were modified by adenovirus expressing (Ad-expressing) BAG3 or siBAG3 were exposed to hypoxia/reoxygenation (H/R). H/R significantly reduced NMVC BAG3 levels, which were associated with enhanced expression of apoptosis markers, decreased expression of autophagy markers, and reduced autophagy flux. The deleterious effects of H/R on apoptosis and autophagy were recapitulated by knockdown of BAG3 with Ad-siBAG3 and were rescued by Ad-BAG3. In vivo, treatment of mice with rAAV9-BAG3 prior to I/R significantly decreased infarct size and improved left ventricular function when compared with mice receiving rAAV9-GFP and improved markers of autophagy and apoptosis. These findings suggest that BAG3 may provide a therapeutic target in patients undergoing reperfusion after myocardial infarction.

Evidence for the Role of BAG3 in Mitochondrial Quality Control in Cardiomyocytes

Mitochondrial abnormalities impact the development of myofibrillar myopathies. Therefore, understanding the mechanisms underlying the removal of dysfunctional mitochondria from cells is of great importance toward understanding the molecular events involved in the genesis of cardiomyopathy. Earlier studies have ascribed a role for BAG3 in the development of cardiomyopathy in experimental animals leading to the identification of BAG3 mutations in patients with heart failure which may play a part in the onset of disease development and progression. BAG3 is co-chaperone of heat shock protein 70 (HSP70), which has been shown to modulate apoptosis and autophagy, in several cell models. In this study, we explore the potential role of BAG3 in mitochondrial quality control. We demonstrate that siRNA mediated suppression of BAG3 production in neonatal rat ventricular cardiomyocytes (NRVCs) significantly elevates the level of Parkin, a key component of mitophagy. We found that both BAG3 and Parkin are recruited to depolarized mitochondria and promote mitophagy. Suppression of BAG3 in NRVCs significantly reduces autophagy flux and eliminates clearance of Tom20, an essential import receptor for mitochondria proteins, after induction of mitophagy. These observations suggest that BAG3 is critical for the maintenance of mitochondrial homeostasis under stress conditions, and disruptions in BAG3 expression impact cardiomyocyte function. J. Cell. Physiol. 232: 797-805, 2017. © 2016 Wiley Periodicals, Inc.

Lessons Learned and Insights Gained in the Design, Analysis, and Outcomes of the COMPANION Trial

COMPANION (Comparison of Medical Therapy, Pacing and Defibrillation in Heart Failure), the first cardiac resynchronization therapy (CRT)-heart failure mortality and morbidity controlled clinical trial planned, conducted, and reported, was a randomized, 3-arm study that compared CRT delivered by a biventricular pacemaker (CRT-P) or a CRT defibrillator device (CRT-D) with optimal pharmacological therapy alone. The patient population had advanced chronic heart failure with QRS interval prolongation ≥120 ms and reduced left ventricular ejection fraction (heart failure with reduced ejection fraction). COMPANION had a composite hospitalization and mortality endpoint as the primary outcome measure but was also powered for mortality as the first secondary endpoint. The conduct of COMPANION was challenged by important issues that arose during the trial, the most important of which was U.S. Food and Drug Administration approval of CRT devices. Along with other challenges, this issue was appropriately dealt with by the Steering Committee and the Data and Safety Monitoring Committee and did not negatively affect trial results or conclusions. The authors report here updated analyses from the study, which are consistent with previously published results indicating that CRT-P or CRT-D has favorable effects on heart failure morbidity and mortality in a patient population "precision" selected by the surrogate marker of increased QRS interval duration. New analyses indicate that increasing the number of classes of neurohormonal inhibitor concurrent therapy has a positive effect on CRT mortality reduction. Hypothesis-generating new findings are that in patients receiving beta-blocker therapy, the mortality reduction advantage of CRT-D versus CRT-P may be minimized or eliminated and that there may be adverse effects of CRT-D defibrillator shocks on pump failure-related outcomes.

BAG3: a new player in the heart failure paradigm

BAG3 is a cellular protein that is expressed predominantly in skeletal and cardiac muscle but can also be found in the brain and in the peripheral nervous system. BAG3 functions in the cell include: serving as a co-chaperone with members of the heat-shock protein family of proteins to facilitate the removal of misfolded and degraded proteins, inhibiting apoptosis by interacting with Bcl2 and maintaining the structural integrity of the Z-disk in muscle by binding with CapZ. The importance of BAG3 in the homeostasis of myocytes and its role in the development of heart failure was evidenced by the finding that single allelic mutations in BAG3 were associated with familial dilated cardiomyopathy. Furthermore, significant decreases in the level of BAG3 have been found in end-stage failing human heart and in animal models of heart failure including mice with heart failure secondary to trans-aortic banding and in pigs after myocardial infarction. Thus, it becomes relevant to understand the cellular biology and molecular regulation of BAG3 expression in order to design new therapies for the treatment of patients with both hereditary and non-hereditary forms of dilated cardiomyopathy.

GRP78 Interacting Partner Bag5 Responds to ER Stress and Protects Cardiomyocytes From ER Stress-Induced Apoptosis

Bag5 is a member of the BAG family of molecular chaperone regulators and is unusual in that it consists of five BAG domains, which function as modulators of chaperone activity. Bag family proteins play a key role in cellular as well as in cardiac function and their differential expression is reported in heart failure. In this study, we examined the importance of a Bag family member protein, Bag5, in cardiomyocytes during endoplasmic reticulum (ER) stress. We found that expression of Bag5 in cardiomyocytes is significantly increased with the induction of ER stress in a time dependent manner. We have taken gain-in and loss-of functional approaches to characterize Bag5 protein function in cardiomyocytes. Adenoviral mediated expression of Bag5 significantly decreased cell death as well as improved cellular viability in ER stress. Along with this, ER stress-induced CHOP protein expression is significantly decreased in cells that overexpress Bag5. Conversely, we found that siRNA-mediated knockdown of Bag5 caused cell death, increased cytotoxicity, and decreased cellular viability in cardiomyocytes. Mechanistically, we found that Bag5 protein expression is significantly increased in the ER during ER stress and that this in turn modulates GRP78 protein stability and reduces ER stress. This study suggests that Bag5 is an important regulator of ER function and so could be exploited as a tool to improve cardiomyocyte function under stress conditions. J. Cell. Biochem. 117: 1813-1821, 2016. © 2016 Wiley Periodicals, Inc.

Paroxetine-mediated GRK2 inhibition reverses cardiac dysfunction and remodeling after myocardial infarction

Heart failure (HF) is a disease of epidemic proportion and is associated with exceedingly high health care costs. G protein (heterotrimeric guanine nucleotide-binding protein)-coupled receptor (GPCR) kinase 2 (GRK2), which is up-regulated in the failing human heart, appears to play a critical role in HF progression in part because enhanced GRK2 activity promotes dysfunctional adrenergic signaling and myocyte death. Recently, we found that the selective serotonin reuptake inhibitor (SSRI) paroxetine could inhibit GRK2 with selectivity over other GRKs. Wild-type mice were treated for 4 weeks with paroxetine starting at 2 weeks after myocardial infarction (MI). These mice were compared with mice treated with fluoxetine, which does not inhibit GRK2, to control for the SSRI effects of paroxetine. All mice exhibited similar left ventricular (LV) dysfunction before treatment; however, although the control and fluoxetine groups had continued degradation of function, the paroxetine group had considerably improved LV function and structure, and several hallmarks of HF were either inhibited or reversed. Use of genetically engineered mice indicated that paroxetine was working through GRK2 inhibition. The beneficial effects of paroxetine were markedly greater than those of β-blocker therapy, a current standard of care in human HF. These data demonstrate that paroxetine-mediated inhibition of GRK2 improves cardiac function after MI and represents a potential repurposing of this drug, as well as a starting point for innovative small-molecule GRK2 inhibitor development.