Cardiomyocyte degeneration with calpain deficiency reveals a critical role in protein homeostasis.
Regulating the balance between synthesis and proteasomal degradation of cellular proteins is essential for tissue growth and maintenance, but the critical pathways regulating protein ubiquitination and degradation are incompletely defined. Although participation of calpain calcium-activated proteases in post-necrotic myocardial autolysis is well characterized, their importance in homeostatic turnover of normal cardiac tissue is controversial. Hence, we evaluated the consequences of physiologic calpain (calcium-activated protease) activity in cultured cardiomyocytes and unstressed mouse hearts. Comparison of in vitro proteolytic activities of cardiac-expressed calpains 1 and 2 revealed calpain 1, but not calpain 2, activity at physiological calcium concentrations. Physiological calpain 1 activation was evident in adenoviral transfected cultured cardiomyocytes as proteolysis of specific substrates, generally increased protein ubiquitination, and accelerated protein turnover, that were each inhibited by coexpression of the inhibitor protein calpastatin. Conditional forced expression of calpain 1, but not calpain 2, in mouse hearts demonstrated substrate-specific proteolytic activity under basal conditions, with hyperubiquitination of cardiac proteins and increased 26S proteasome activity. Loss of myocardial calpain activity by forced expression of calpastatin diminished ubiquitination of 1 or more specific myocardial proteins, without affecting overall ubiquitination or proteasome activity, and resulted in a progressive dilated cardiomyopathy characterized by accumulation of intracellular protein aggregates, formation of autophagosomes, and degeneration of sarcomeres. Thus, calpain 1 is upstream of, and necessary for, ubiquitination and proteasomal degradation of a subset of myocardial proteins whose abnormal accumulation produces autophagosomes and degeneration of cardiomyocytes with functional decompensation.
Galvez
Anita S
AS
Center for Molecular Cardiovascular Research, University of Cincinnati, OH, USA.
Diwan
Abhinav
A
Odley
Amy M
AM
Hahn
Harvey S
HS
Osinska
Hanna
H
Melendez
Jaime G
JG
Robbins
Jeffrey
J
Lynch
Roy A
RA
Marreez
Yehia
Y
Dorn
Gerald W
GW
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000235:genetics / Q000378:metabolism; D002154:Calpain / Q000037:antagonists & inhibitors / Q000172:deficiency* / Q000235:genetics / Q000378:metabolism; D002311:Cardiomyopathy, Dilated / Q000139:chemically induced / Q000378:metabolism / Q000473:pathology; D002478:Cells, Cultured; D006333:Heart Failure / Q000209:etiology / Q000473:pathology; D006706:Homeostasis; D051379:Mice; D008822:Mice, Transgenic; D008854:Microscopy, Electron; D009206:Myocardium / Q000378:metabolism / Q000473:pathology; D032383:Myocytes, Cardiac / Q000378:metabolism* / Q000473:pathology*; D009994:Osmolar Concentration; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D020033:Protein Isoforms / Q000037:antagonists & inhibitors / Q000378:metabolism; D011506:Proteins / Q000378:metabolism*; D013379:Substrate Specificity; D014162:Transfection; D025801:Ubiquitin / Q000378:metabolism
D002135:Calcium-Binding Proteins; D020033:Protein Isoforms; D011506:Proteins; D025801:Ubiquitin; C033668:calpastatin; D002154:Calpain; D046988:Proteasome Endopeptidase Complex; C061553:ATP dependent 26S protease; D002118:Calcium