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

ABSTRACT: 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.

SUBMITTER: Martin TG

PROVIDER: S-EPMC8134551 | biostudies-literature | 2021 May

REPOSITORIES: biostudies-literature

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

Martin Thomas G TG Myers Valerie D VD Dubey Praveen P Dubey Shubham S Perez Edith E Moravec Christine S CS Willis Monte S MS Feldman Arthur M AM Kirk Jonathan A JA

Nature communications 20210519 1

The association between reduced myofilament force-generating capacity (Fmax) and heart failure (HF) is clear, however the underlying molecular mechanisms are poorly understood. Here, we show impaired Fmax arises from reduced BAG3-mediated sarcomere turnover. Myofilament BAG3 expression decreases in human HF and positively correlates with Fmax. We confirm this relationship using BAG3 haploinsufficient mice, which display reduced Fmax and increased myofi ...[more]

PMID: 34011988

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Project description:BackgroundWhereas heart failure with reduced ejection fraction (HFrEF) is associated with ventricular dilation and markedly reduced systolic function, heart failure with preserved ejection fraction (HFpEF) patients exhibit concentric hypertrophy and diastolic dysfunction. Impaired cardiomyocyte Ca2+ homeostasis in HFrEF has been linked to disruption of membrane invaginations called t-tubules, but it is unknown if such changes occur in HFpEF.ObjectivesThis study examined whether distinct cardiomyocyte phenotypes underlie the heart failure entities of HFrEF and HFpEF.MethodsT-tubule structure was investigated in left ventricular biopsies obtained from HFrEF and HFpEF patients, whereas cardiomyocyte Ca2+ homeostasis was studied in rat models of these conditions.ResultsHFpEF patients exhibited increased t-tubule density in comparison with control subjects. Super-resolution imaging revealed that higher t-tubule density resulted from both tubule dilation and proliferation. In contrast, t-tubule density was reduced in patients with HFrEF. Augmented collagen deposition within t-tubules was observed in HFrEF but not HFpEF hearts. A causative link between mechanical stress and t-tubule disruption was supported by markedly elevated ventricular wall stress in HFrEF patients. In HFrEF rats, t-tubule loss was linked to impaired systolic Ca2+ homeostasis, although diastolic Ca2+ removal was also reduced. In contrast, Ca2+ transient magnitude and release kinetics were largely maintained in HFpEF rats. However, diastolic Ca2+ impairments, including reduced sarco/endoplasmic reticulum Ca2+-ATPase activity, were specifically observed in diabetic HFpEF but not in ischemic or hypertensive models.ConclusionsAlthough t-tubule disruption and impaired cardiomyocyte Ca2+ release are hallmarks of HFrEF, such changes are not prominent in HFpEF. Impaired diastolic Ca2+ homeostasis occurs in both conditions, but in HFpEF, this mechanism for diastolic dysfunction is etiology-dependent.

Project description:Lifestyle and metabolic diseases influence the severity and pathogenesis of cardiovascular disease (CVD) through numerous mechanisms, including regulation via post-translational modifications (PTM). A specific PTM, the addition of O-linked β-N acetylglucosamine (O-GlcNAcylation), has been implicated in both physiological and pathological mechanisms. The current study aimed to test the hypothesis that protein O-GlcNAcylation contributes to cardiac adaptations, and its progression to pathophysiology when sustained in cardiomyocytes. Using an inducible cardiomyocyte-specific dominant-negative O-GlcNAcase (dnOGAh) overexpression transgenic mouse model, we induced dnOGA in 8-10-weeks-old mouse hearts. We examined the effects of 2-weeks (2wk) and 24-weeks (24wk) dnOGA overexpression, which progressed to a 1.8-fold increase in protein O-GlcNAcylation. 2wk increases in protein O-GlcNAc levels did not alter heart weight or function; however, 24wk increases in protein O-GlcNAcylation led to cardiac hypertrophy, reduced mitochondrial function, fibrosis, and diastolic dysfunction. Interestingly, systolic function was maintained in 24wk dnOGA overexpression, despite several changes in gene expression associated with CVD. Specifically, mRNA-seq analysis revealed several gene signatures, including reduction of mitochondrial oxidative phosphorylation, fatty acid and glucose metabolism pathways, and antioxidant response pathways at 24wk. In contrast, cardiac fibrosis pathway genes were induced at 24wk after dnOGA overexpression. Changes in mitochondrial function after 24wk induction were independent of changes in mitochondrial DNA copy number. This study indicates that moderate protein O-GlcNAcylation leads to a differential response with an initial reduction of metabolic pathways (2wk phase), which leads to cardiac remodeling (24wk phase) including cardiac hypertrophy, decreased oxidative phosphorylation pathways, and increased cardiac structural changes. This study shows that sustained exposure of elevated protein O-GlcNAcylation in cardiomyocytes alters gene expression and supports a switch to pathophysiological mechanisms of O-GlcNAcylation in adaptive versus maladaptive changes.

Project description:RationaleThe capacity for cardiomyocyte regeneration in the healthy adult human heart is fundamentally relevant for both myocardial homeostasis and cardiomyopathy therapeutics. However, estimates of cardiomyocyte turnover rates conflict greatly, with a study employing C14 pulse-chase methodology concluding 1% annual turnover in youth declining to 0.5% with aging and another using cell population dynamics indicating substantial, age-increasing turnover (4% increasing to 20%).ObjectiveCreate a hybrid mathematical model to critically examine rates of cardiomyocyte turnover derived from alternative methodologies.Methods and resultsExamined in isolation, the cell population analysis exhibited severe sensitivity to a stem cell expansion exponent (20% variation causing 2-fold turnover change) and apoptosis rate. Similarly, the pulse-chase model was acutely sensitive to assumptions of instantaneous incorporation of atmospheric C14 into the body (4-fold impact on turnover in young subjects) while numerical restrictions precluded otherwise viable solutions. Incorporating considerations of primary variable sensitivity and controversial model assumptions, an unbiased numerical solver identified a scenario of significant, age-increasing turnover (4-6% increasing to 15-22% with age) that was compatible with data from both studies, provided that successive generations of cardiomyocytes experienced higher attrition rates than predecessors.ConclusionsAssignment of histologically-observed stem/progenitor cells into discrete regenerative phenotypes in the cell population model strongly influenced turnover dynamics without being directly testable. Alternatively, C14 trafficking assumptions and restrictive models in the pulse-chase model artificially eliminated high-turnover solutions. Nevertheless, discrepancies among recent cell turnover estimates can be explained and reconciled. The hybrid mathematical model provided herein permits further examination of these and forthcoming datasets.

Project description:Background Lifestyle and metabolic diseases influence the severity and pathogenesis of cardiovascular disease through numerous mechanisms, including regulation via posttranslational modifications. A specific posttranslational modification, the addition of O-linked β-N acetylglucosamine (O-GlcNAcylation), has been implicated in molecular mechanisms of both physiological and pathologic adaptations. The current study aimed to test the hypothesis that in cardiomyocytes, sustained protein O-GlcNAcylation contributes to cardiac adaptations, and its progression to pathophysiology. Methods and Results Using a naturally occurring dominant-negative O-GlcNAcase (dnOGA) inducible cardiomyocyte-specific overexpression transgenic mouse model, we induced dnOGA in 8- to 10-week-old mouse hearts. We examined the effects of 2-week and 24-week dnOGA overexpression, which progressed to a 1.8-fold increase in protein O-GlcNAcylation. Two-week increases in protein O-GlcNAc levels did not alter heart weight or function; however, 24-week increases in protein O-GlcNAcylation led to cardiac hypertrophy, mitochondrial dysfunction, fibrosis, and diastolic dysfunction. Interestingly, systolic function was maintained in 24-week dnOGA overexpression, despite several changes in gene expression associated with cardiovascular disease. Specifically, mRNA-sequencing analysis revealed several gene signatures, including reduction of mitochondrial oxidative phosphorylation, fatty acid, and glucose metabolism pathways, and antioxidant response pathways after 24-week dnOGA overexpression. Conclusions This study indicates that moderate increases in cardiomyocyte protein O-GlcNAcylation leads to a differential response with an initial reduction of metabolic pathways (2-week), which leads to cardiac remodeling (24-week). Moreover, the mouse model showed evidence of diastolic dysfunction consistent with a heart failure with preserved ejection fraction. These findings provide insight into the adaptive versus maladaptive responses to increased O-GlcNAcylation in heart.

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

Publications

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

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