Impairment of the ubiquitin?proteasome system by truncated cardiac myosin binding protein C mutants

Sarikas, Antonio; Carrier, Lucie; Schenke, Carolus; Doll, Daniela; Flavigny, Jeanne; Lindenberg, Katrin S.; Eschenhagen, Thomas; Zolk, Oliver

doi:10.1016/j.cardiores.2005.01.004

Cited by 142 publications

(128 citation statements)

References 37 publications

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“…As we previously showed (20), long-term voluntary exercise increased the survival probability of CryAB R120G ×tTA mice to 50%, whereas the genetically identical nonexercised control group died from heart failure by 7 months. The data from this group closely matched that obtained with the nonexercised CryAB R120G ×Atg7×tTA control cohort; however, induction of autophagy by voluntary exerreported in different genetic models of cardiac disease induced by the expression of Tg Mst1, truncated Mybpc3, DesΔ7, PQ83, and CryAB R120G , but the prevalence of autophagic deficiency in a majority of these models is unclear (16,39,(46)(47)(48). Clearance of aggregation-prone proteins dependent upon autophagy has been reported for different cell-based models, in which either autophagy inhibitors were added (49,50) or Atg gene expression was decreased by siRNA transfection (51).…”

Section: Discussionsupporting

confidence: 76%

Enhanced autophagy ameliorates cardiac proteinopathy

et al. 2013

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Basal autophagy is a crucial mechanism in cellular homeostasis, underlying both normal cellular recycling and the clearance of damaged or misfolded proteins, organelles and aggregates. We showed here that enhanced levels of autophagy induced by either autophagic gene overexpression or voluntary exercise ameliorated desmin-related cardiomyopathy (DRC). To increase levels of basal autophagy, we generated an inducible Tg mouse expressing autophagy-related 7 (Atg7), a critical and rate-limiting autophagy protein. Hearts from these mice had enhanced autophagy, but normal morphology and function. We crossed these mice with CryAB R120G mice, a model of DRC in which autophagy is significantly attenuated in the heart, to test the functional significance of autophagy activation in a proteotoxic model of heart failure. Sustained Atg7-induced autophagy in the CryAB R120G hearts decreased interstitial fibrosis, ameliorated ventricular dysfunction, decreased cardiac hypertrophy, reduced intracellular aggregates and prolonged survival. To determine whether different methods of autophagy upregulation have additive or even synergistic benefits, we subjected the autophagy-deficient CryAB R120G mice and the Atg7-crossed CryAB R120G mice to voluntary exercise, which also upregulates autophagy. The entire exercised Atg7-crossed CryAB R120G cohort survived to 7 months. These findings suggest that activating autophagy may be a viable therapeutic strategy for improving cardiac performance under proteotoxic conditions.

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Section: Discussionsupporting

confidence: 76%

Enhanced autophagy ameliorates cardiac proteinopathy

et al. 2013

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“…First, the minigene splice assay may not identify the precise splice alteration that occurs in vivo. However, of the 53 splice-altering variants identified here, 16 variants were independently characterized by RT-PCR in patient tissues (15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25), alter splicing, and are pathogenic (Table S3). Moreover, the fact that 48 of 53 VUS were identified in patients with an AD cardiomyopathy provides a very strong likelihood that the aberrant splicing observed in the minigene assay occurs in vivo.…”

Section: Discussionmentioning

confidence: 99%

Identification of pathogenic gene mutations in LMNA and MYBPC3 that alter RNA splicing

Ito

Patel

Gorham

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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Genetic variants that cause haploinsufficiency account for many autosomal dominant (AD) disorders. Gene-based diagnosis classifies variants that alter canonical splice signals as pathogenic, but due to imperfect understanding of RNA splice signals other variants that may create or eliminate splice sites are often clinically classified as variants of unknown significance (VUS). To improve recognition of pathogenic splice-altering variants in AD disorders, we used computational tools to prioritize VUS and developed a cell-based minigene splicing assay to confirm aberrant splicing. Using this two-step procedure we evaluated all rare variants in two AD cardiomyopathy genes, lamin A/C (LMNA) and myosin binding protein C (MYBPC3). We demonstrate that 13 LMNA and 35 MYBPC3 variants identified in cardiomyopathy patients alter RNA splicing, representing a 50% increase in the numbers of established damaging splice variants in these genes. Over half of these variants are annotated as VUS by clinical diagnostic laboratories. Familial analyses of one variant, a synonymous LMNA VUS, demonstrated segregation with cardiomyopathy affection status and altered cardiac LMNA splicing. Application of this strategy should improve diagnostic accuracy and variant classification in other haploinsufficient AD disorders.D NA sequence analysis of patient DNA has been used to clinically diagnose associated inherited diseases, leading to the identification of thousands of rare sequence variants in affected and unaffected individuals. Interpreting the medical significance of these variants has proven to be a significant challenge. The annotation of nonsense, frameshift, insertion, and deletion variants that cause a highly predictable outcome [i.e., loss of function (LoF) of proteins encoded by disease genes] allows these to be clinically classified as pathogenic variants in more than 4,000 genes that cause disease by haploinsufficiency (1). Classification of rare synonymous and missense variants in these genes, however, has been more difficult. Although bioinformatic algorithms predict that some variants may damage the encoded protein, these annotations are imperfect, and many rare variants remain unclassified and are clinically designated as variants of unknown significance (VUS) (2).Splicing signals reside at all exon-intron junctions and include a 9-bp 5′ splice donor sequence with an invariant GT dinucleotide and a 23-bp 3′ splice acceptor sequence with an invariant AG dinucleotide (3) (Fig. 1A). Variants that alter the canonical GT and AG dinucleotides in haploinsufficient autosomal dominant (AD) genes are diagnostically classified as pathogenic, whereas substitutions of the remaining seven residues within the donor sequence, or the 21 residues within the acceptor sequence, are often classified as VUS (4). VUS that alter these sequences, however, have the potential to disrupt normal RNA splicing (5) (resulting in donor or acceptor loss; Fig. 1C). Similarly, variants within a nearby intron or exon may sufficiently mimic the consensus donor...

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“…***P < 0.01, n = 8-10 per group. (6,54,55). Elimination of the toxic misfolded protein is a legitimate therapeutic target for the proteotoxic phenotypes but, despite substantial efforts across multiple fields of study, no effective therapeutic intervention to reverse pathological protein aggregation has been found.…”

Section: Discussionmentioning

confidence: 99%

Tubulin hyperacetylation is adaptive in cardiac proteotoxicity by promoting autophagy

McLendon

Ferguson

Osińska

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

100

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Proteinopathy causes cardiac disease, remodeling, and heart failure but the pathological mechanisms remain obscure. Mutated αB-crystallin (CryAB R120G ), when expressed only in cardiomyocytes in transgenic (TG) mice, causes desmin-related cardiomyopathy, a protein conformational disorder. The disease is characterized by the accumulation of toxic misfolded protein species that present as perinuclear aggregates known as aggresomes. Previously, we have used the CryAB R120G model to determine the underlying processes that result in these pathologic accumulations and to explore potential therapeutic windows that might be used to decrease proteotoxicity. We noted that total ventricular protein is hypoacetylated while hyperacetylation of α-tubulin, a substrate of histone deacetylase 6 (HDAC6) occurs. HDAC6 has critical roles in protein trafficking and autophagy, but its function in the heart is obscure. Here, we test the hypothesis that tubulin acetylation is an adaptive process in cardiomyocytes. By modulating HDAC6 levels and/or activity genetically and pharmacologically, we determined the effects of tubulin acetylation on aggregate formation in CryAB R120G cardiomyocytes. Increasing HDAC6 accelerated aggregate formation, whereas siRNA-mediated knockdown or pharmacological inhibition ameliorated the process. HDAC inhibition in vivo induced tubulin hyperacetylation in CryAB R120G TG hearts, which prevented aggregate formation and significantly improved cardiac function. HDAC6 inhibition also increased autophagic flux in cardiomyocytes, and increased autophagy in the diseased heart correlated with increased tubulin acetylation, suggesting that autophagy induction might underlie the observed cardioprotection. Taken together, our data suggest a mechanistic link between tubulin hyperacetylation and autophagy induction and points to HDAC6 as a viable therapeutic target in cardiovascular disease.P roteotoxicity is an important yet understudied mechanism in cardiac pathobiology (1), as maintaining tight control of protein homeostasis is critical for proper cell function. This is especially important in the unique context of the heart, as it is under constant mechanical and oxidative stress, and cardiomyocytes appear to be largely postmitotic soon after birth and are unable to readily regenerate (2, 3). Cellular stress events, including normal physiologic stimuli, can lead to altered cardiomyocyte function if the pathways of protein quality control (PQC) are compromised. Pathological cardiac stress, including pressure overload-induced hypertrophy and ischemia-reperfusion (I/R) injury, can alter protein degradation pathways (4-6). Our laboratory has developed a model of cardiac proteotoxicity based upon transgenically mediated cardiomyocyte expression of a mutated αB-crystallin (CryAB R120G ), which causes desminrelated cardiomyopathy in humans (7-9).CryAB is a molecular chaperone for desmin, an intermediate filament protein expressed in myocytes. Desmin is a crucial cardiomyocyte protein with vital signaling and structural ro...

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Impairment of the ubiquitin?proteasome system by truncated cardiac myosin binding protein C mutants

Cited by 142 publications

References 37 publications

Enhanced autophagy ameliorates cardiac proteinopathy

Enhanced autophagy ameliorates cardiac proteinopathy

Identification of pathogenic gene mutations in LMNA and MYBPC3 that alter RNA splicing

Tubulin hyperacetylation is adaptive in cardiac proteotoxicity by promoting autophagy

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