Abstract 10324: Sumo E2 Ligase is Required for Efficient Protein Quality Control of Cardiomyocytes
Background: Proper protein quality control is required to maintain normal cardiac function. Impairment of proteasomal function occurs and is pathogenic in a number of cardiac proteinopathies caused by genetic mutation or stress, eventually leading to heart failure. For example, patients suffering from Desmin Related Cardiomyopathy, accumulate cytosolic misfolded proteins that can form large aggregates termed aggresomes as a well as extremely cytotoxic soluble pre-amyloid oligomers. Impaired proteasomal function is thought to be a contributing factor to these pathogenic processes. The Ubiquitin Proteasome System (UPS) can be responsible for 90% of cellular protein degradation. A role for the ubiquitin pathway in proteasomal function is well studied but the function of an ancillary post-translational modification, SUMOylation, in protein quality control is not fully understood.
Objective: To determine the role of SUMO E2 ligase in protein quality control in cardiomyocytes, in order to improve and maintain normal proteasomal function in the proteinopathies.
Methods and Results: To define the role of UBC9, a SUMO-conjugating enzyme, on the UPS, gain- and loss-of-function approaches were taken. Overexpression of UBC9 enhanced proteasomal function in cardiomyocytes while knockdown of UBC9 by siRNA caused significant accumulations of aggregated protein. Proteasomal function was analyzed using an in vitro proteasomal assay as well as a proteasomal reporter assay. Further, the effects on proteasomal function of UBC-9 was tested in a proteotoxic model of desmin-related cardiomyopathy, caused by cardiomyocyte specific expression of a mutated alpha B crystallin, CryABR120G. CryABR120G expression leads to aggregate formation and decreased proteasomal function. Co-infection of UBC9-adenovirus with R120G virus specifically reduces the severity of this phenotype, decreasing overall aggregate concentrations. Conversely, knockdown of UBC9 significantly increased aggregate levels and decreased the proteasomal function.
Conclusions: UBC9 plays a significant role in protein quality control in cardiomyocytes and its activity can be exploited to reduce toxic levels of misfolded or aggregated proteins in cardiomyopathy.
- © 2013 by American Heart Association, Inc.