Calcium-sensing receptors induce apoptosis in rat cardiomyocytes via the endo(sarco)plasmic reticulum pathway during hypoxia/reoxygenation.
The calcium-sensing receptor (CaR) is a G protein-coupled receptor. The CaR stimulation elicits phospholipase C-mediated inositol triphosphate formation, leading to an elevation in the level of intracellular calcium released from endoplasmic reticulum (ER). Depletion of ER Ca(2+) leads to ER stress, which is thought to induce apoptosis. Intracellular calcium overload-induced apoptosis in cardiac myocytes during hypoxia-reoxygenation (H/Re) has been demonstrated. However, the links between CaR, ER stress and apoptosis during H/Re are unclear. This study hypothesized that the CaR could induce apoptosis in neonatal rat cardiomyocytes during H/Re via the ER stress pathway. Neonatal rat cardiomyocytes were subjected to 3 hr of hypoxia, followed by 6 hr of reoxygenation. CaR expression was elevated and the number of apoptotic cells was significantly increased, as shown by transferase-mediated dUTP nick end-labelling, with exposure to CaCl(2), a CaR activator, during H/Re. The intracellular calcium concentration was significantly elevated and the Ca(2+) concentration in the ER was dramatically decreased during H/Re with CaCl(2); both intracellular and ER calcium concentrations were detected by laser confocal microscopy. Expression of GRP78 (glucose-regulated protein 78), the cleavage products of ATF6 (activating transcription factor 6), phospho-PERK [pancreatic ER kinase (PKR)-like ER kinase], the activated fragments of caspase-12, and phospho-JNK (c-Jun NH(2)-terminal kinase) were increased following exposure to CaCl(2) during H/Re. Our results confirmed that the activated CaR can induce cardiomyocyte apoptosis via ER stress-associated apoptotic pathways during H/Re.
Lu
Fanghao
F
Department of Pathophysiology, Harbin Medical University, Harbin, China.
Tian
Zhiliang
Z
Zhang
Weihua
W
Zhao
Yajun
Y
Bai
Shuzhi
S
Ren
Huan
H
Chen
He
H
Yu
Xue
X
Wang
Jingxiao
J
Wang
Lina
L
Li
Hong
H
Pan
Zhenwei
Z
Tian
Ye
Y
Yang
Baofeng
B
Wang
Rui
R
Xu
Changqing
C
D051702:Activating Transcription Factor 6 / Q000378:metabolism; D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D002118:Calcium / Q000378:metabolism; D053454:Caspase 12 / Q000378:metabolism; D015687:Cell Hypoxia; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D066298:In Vitro Techniques; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D008297:Male; D018613:Microscopy, Confocal; D015428:Myocardial Reperfusion Injury / Q000378:metabolism*; D032383:Myocytes, Cardiac / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D044169:Receptors, Calcium-Sensing / Q000378:metabolism*
D051702:Activating Transcription Factor 6; D044169:Receptors, Calcium-Sensing; D048031:JNK Mitogen-Activated Protein Kinases; D053454:Caspase 12; D002118:Calcium