Abstract 14216: Mitochondrial Dysfunction in Aged Hearts: Role of Mitochondrial Calpain Activation

Abstract

Introduction: Mitochondrial function is impaired in aged hearts. Calpain 1 (CPN1) is a calcium-dependent cysteine protease located in cytosol (cCPN1) and mitochondria (mCPN1). Activation of CPN1 contributes to mitochondrial dysfunction during ischemia-reperfusion. Induction of acute ER (endoplasm reticulum) stress causes CPN1 activation in adult hearts. We find that aging leads to increased ER stress that may favor CPN1 activation. Hypothesis: ER stress induced CPN1 activation leads to mitochondrial dysfunction during aging. Methods: Male adult (3 mo.) and aged (24 mo.) mice were provided by NIA. 4-PBA (1g/kg/day) was dissolved in drinking water with sucrose (0.2 g/100 ml) as sweetener. Sucrose water was used as vehicle control. Mice were treated for two weeks with 4-PBA or vehicle followed by the isolation of cardiac cytosol, SSM (subsarcolemmal mitochondria) and IFM (interfibrillar mitochondria). Results: Oxidative phosphorylation was decreased in IFM from 24 mo. compared to 3 mo. when glutamate + malate was used as complex I substrate (Fig A). The 4-PBA treatment improved oxidative phosphorylation in aged IFM (Figure A). The cCPN1 was activated in 24 mo. as shown by increased spectrin cleavage (Figure B). The α1 subunit of pyruvate dehydrogenase (PDH) is a substrate of mCPN1. The content of the PDH α1 subunit was decreased in 24 mo. compared to 3 mo., indicating that the mCPN1 was activated during aging (Figure C). The 4-PBA treatment decreased the activation of cCPN1 and mCPN1 in aged mice. SSM function is also impaired during aging (data not shown). Conclusions: Aging increased the activation of both cCPN1 and mCPN1. Attenuation of ER stress in 24 mo. mice using 4-PBA decreased cCPN1 and mCPN1 activation. Decreased CPN1 activation was accompanied by improved mitochondrial function . The results support that activation of calpain 1, most likely mCPN1, is a likely cause of increased mitochondrial dysfunction during aging.