Abstract 14091: Cathepsin K Deficiency Attenuates Starvation-Induced Cardiac Autophagy and Apoptosis
Cathepsin K, a lysosomal cysteine protease, is up-regulated in the heart in response to pressure-overload and knockout of cathepsin K protects against cardiac dysfunction associated with obesity and hypertension, although the molecular mechanism involved in the process is unclear. Because the process of autophagy plays an important role in cardioprotection, we evaluated the effect of genetic ablation of cathepsin K on starvation-induced autophagy in the heart. Wild-type mice subjected to starvation displayed impaired cardiac function as evidenced by decreased fractional shortening and enlarged left ventricle end diastolic dimension which were reconciled in mice lacking cathepsin K. Additionally, starvation resulted in single cardiomyocyte contractile dysfunction and impaired intracellular Ca2+ handling in wild-type mice, both of which were alleviated by cathepsin K knockout. Furthermore, the aforementioned compromised contractile function was alleviated by treating the cardiomyocytes with 3-methyladenine, an autophagy inhibitor. Although autophagy was also activated in the starved cathepsin K knockout mice as evidenced by the dissociation of Beclin-1/Bcl-2 complex, the autophagic flux was disrupted, as indicated by the increase in accumulation of microtubule-associated protein 1 light chain 3 (LC3B-II) and unchanged levels of the autophagy substrate p62. Starvation also induced cardiomyocyte apoptosis, assessed as TUNEL-positive staining and upregulation of proapoptotic Bax and PARP and a reciprocal downregulation of antiapoptotic Bcl2, all of which were reconciled in the cathepsin K knockout mice. In cultured H9c2 cells, starvation (glucose-deprivation) induced autophagy was identified by the accumulation of green fluorescent protein (GFP)-LC3 puncta, which was accentuated on siRNA-mediated silencing of cathepsin K. In addition, p62 levels which were attenuated by glucose-deprivation remained unchanged following cathepsin K silencing. Furthermore, increased apoptosis consequent to starvation, was attenuated by silencing of cathepsin K. Taken together, the beneficial effects of cathepsin K knockout in the failing heart may be attributed to the disruption of autophagic flux and inhibition of apoptosis.
- © 2013 by American Heart Association, Inc.