Autophagy and p62 in Cardiac Proteinopathy

Abstract

Rationale Recent studies suggest an important role of autophagy in protection against αB-crystallin-based (CryABR120G) desmin-related cardiomyopathies (DRC) but this has not been demonstrated in a different model of cardiac proteinopathy. Mechanisms underlying the response of cardiomyocytes to proteotoxic stress remain incompletely understood. Objective First, to determine whether and how the autophagic activity is changed in a mouse model of desminopathy; second, to investigate the role of p62 in the protein quality control of cardiomyocytes. Methods and Results Using an autophagosome reporter and determining changes in LC3-II protein levels in response to lysosomal inhibition, we found significantly increased autophagic flux in mouse hearts with transgenic overexpression of a DRC-linked mutant desmin. Similarly, autophagic flux was increased in cultured neonatal rat ventricular myocytes (NRVMs) expressing a mutant desmin. Suppression of autophagy by 3-methyladenine increased, whereas enhancement of autophagy by rapamycin reduced, the ability of a comparable level of mutant desmin overexpression to accumulate ubiquitinated proteins in NRVMs. Furthermore, p62 mRNA and protein expression was significantly upregulated in cardiomyocytes by transgenic overexpression of the mutant desmin or CryABR120G both in intact mice and in vitro. p62 depletion impaired aggresome and autophagosome formation, exacerbated cell injury, and decreased cell viability in cultured NRVMs expressing the misfolded proteins. Conclusions Autophagic flux is increased in desminopathic hearts and, as previously suggested in CryABR120G-based DRC, this increased autophagic flux serves as an adaptive response to overexpression of misfolded proteins. p62 is upregulated in mouse proteinopathic hearts. p62 promotes aggresome formation and autophagy activation and protects cardiomyocytes against proteotoxic stress.

NEDD8 Ultimate Buster 1 Long (NUB1L) Protein Suppresses Atypical Neddylation and Promotes the Proteasomal Degradation of Misfolded Proteins

“…Cardiomyocyte Isolation, Adenovirus Infection, and siRNA Transfection-Neonatal rat ventricular myocytes (NRVMs) were isolated using the neonatal cardiomyocyte isolation system (Worthington) following the protocol of the manufacturer (29).…”

“…All gene knockdown assays were performed using siRNA (Qiagen) as described previously (29). The siRNAs used for NUB1L were 5Ј-CCGGAAACGATGCCTTACTTA-3Ј and 5Ј-TCCGAGGCTCCGGAAAGATAA-3Ј.…”

Aberrant Mitochondrial Fission Is Maladaptive in Desmin Mutation–Induced Cardiac Proteotoxicity

“…The mutant desmin transgenic mouse (D7‐Des Tg) carries a 7 amino acid deletion R172‐E178 in DES and provides a clinically relevant mouse model of cardiac proteotoxicity 9, 10, 11, 12. This model manifests a collapse of the desmin network, and accumulation of desmin aggregates, which contributes to cardiomyopathy 10.…”

Aggregate-Prone R120GCRYAB Triggers Multifaceted Modifications of the Thioredoxin System

“…Besides acting directly on the mechanisms involved in aggregate formation, another nonmutually exclusive possibility would be to alter the degradation processes of those three forms of R120GCRYAB (s, ins, agg). The proteasome would selectively handle the soluble form and insoluble small oligomers (34,66), while autophagy would be involved in aggregate destruction (42,59,64,67). In support of this later possibility, BAG3 has recently been shown to stimulate autophagy in a complex with the sHSP HspB8 (8).…”

“…Nrf2, nuclear factor, erythroid derived 2, like 2. To see this illustration in color, the reader is referred to the web version of this article at www.liebertpub.com/ars concentrates misfolded proteins and sets them apart from the cytoplasm (67). In particular, preamyloid oligomers, which appeared to exert toxic effects, were found to accumulate in R120GCRYAB aggregates so that preventing aggregate formation could have a deleterious effect by abolishing amyloid sequestration (53).…”