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Abstract 466: Myopathy Causing Bag3
P209L
Protein Leads to Restrictive Cardiomyopathy Caused by Aggregate Formation and Sarcomere Disruption in Cardiomyocytes. Circ Res 2019. [DOI: 10.1161/res.125.suppl_1.466] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The co-chaperone BAG3 (Bcl-2 associated athanogene 3) is strongly expressed in cross-striated muscles and plays a key role in the turnover of muscle-proteins as a member of the CASA (chaperone-assisted selected autophagy) complex. An amino acid exchange (P209L) in the human BAG3 gene, caused by a single base mutation, gives rise to a severe dominant childhood muscular dystrophy, restrictive cardiomyopathy, and respiratory insufficiency. To get deeper insights into the pathophysiological mechanisms of the disease, we generated a transgenic mouse model of the human mutation BAG3
P209L
, in which a fusion protein consisting of the human BAG3
P209L
and the green fluorescent protein eGFP can be conditionally overexpressed. Ubiquitous overexpression of BAG3
P209L
-eGFP leads to a severe phenotype between the second and fourth week of life, including decreased body weight, skeletal muscle weakness, and heart failure. Echocardiography revealed that the BAG3
P209L
-mice suffer from restrictive cardiomyopathy and Sirius-red-staining of heart tissue showed extensive fibrosis. In cardiomyocytes, isolated from hearts of transgenic mice overexpressing BAG3
wt
-eGFP or BAG3
P209L
-eGFP, BAG3
wt
-eGFP stringently localizes to sarcomeres and intercalated discs, whereas cardiomyocytes from BAG3
P209L
-eGFP mice displayed formation of BAG3 containing aggregates and disruption of sarcomeres in
vivo
. While BAG3
P209L
-eGFP binding to á-Hsp70, Filamin C and á-HspB8 was unchanged it was less soluble than BAG3 and had a tendency to aggregate, thereby sequestering BAG3 and its clients. Depletion of the BAG3 pool leads to an impairment of CASA and accumulation of damaged proteins, causing sarcomere disintegration leading to restrictive cardiomyopathy.
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