Activation of lectin-like oxidized low-density lipoprotein receptor-1 induces apoptosis in cultured neonatal rat cardiac myocytes.
BACKGROUND
Lectin-like oxidized LDL receptor-1 (LOX-1) was originally identified as a receptor expressed predominantly in endothelial cells. LOX-1 can also be expressed in other cell types, and the activation of the LOX-1 pathway has been implicated in apoptosis. There have been no reports, however, about LOX-1 expression in cardiac myocytes or regulation of myocardial cell apoptosis by LOX-1.


RESULTS
In primary cardiac myocytes from neonatal rats, immunohistochemical analyses using a specific monoclonal antibody against LOX-1 demonstrated that LOX-1 expression was markedly induced by stimulation with norepinephrine and endothelin-1. LOX-1 expression was upregulated in cardiac myocytes as well as in vessel walls of failing rat hearts in vivo. In the presence of a low concentration of oxidized LDL that did not induce apoptosis by itself, artificial overexpression of LOX-1 in cardiac myocytes in culture resulted in apoptosis. LOX-1 overexpression induced activation of p38 mitogen-activated protein kinase (MAPK) and oxidative stress in cardiac myocytes, as demonstrated by an increase in positive immunostaining for 8-hydroxy-2'-deoxyguanosine. Inhibition of p38 MAPK by cotransfection of a dominant-negative form of MKK6 as well as by administration of a specific inhibitor, SB203580 or FR167653, almost completely blocked the induction of apoptosis by LOX-1 activation. Antioxidant catalase also blocked LOX-1-induced apoptosis as well as activation of p38 MAPK.


CONCLUSIONS
These findings demonstrate that LOX-1 expression in cardiac myocytes is induced by neurohormonal factors activated in heart failure and that LOX-1-dependent apoptosis in these cells requires p38 MAPK, a component of oxidant stress-sensitive signaling pathways.
Iwai-Kanai
E
E
Department of Cardiovascular Medicine, Graduate School of Medicine, Kyoto University, Kyoto, Japan.
Hasegawa
K
K
Sawamura
T
T
Fujita
M
M
Yanazume
T
T
Toyokuni
S
S
Adachi
S
S
Kihara
Y
Y
Sasayama
S
S
D000818:Animals; D000831:Animals, Newborn; D017209:Apoptosis / Q000502:physiology*; D002478:Cells, Cultured; D019332:Endothelin-1 / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006333:Heart Failure / Q000378:metabolism; D006352:Heart Ventricles / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D007093:Imidazoles / Q000494:pharmacology; D007150:Immunohistochemistry; D020287:In Situ Nick-End Labeling; D007425:Intracellular Membranes / Q000502:physiology; D008564:Membrane Potentials / Q000502:physiology; D008928:Mitochondria / Q000502:physiology; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D009638:Norepinephrine / Q000494:pharmacology; D018384:Oxidative Stress / Q000502:physiology; D011720:Pyrazoles / Q000494:pharmacology; D011725:Pyridines / Q000494:pharmacology; D051381:Rats; D020303:Rats, Inbred Dahl; D011973:Receptors, LDL / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D051131:Receptors, Oxidized LDL; D051127:Scavenger Receptors, Class E; D015398:Signal Transduction / Q000502:physiology; D014162:Transfection; D048051:p38 Mitogen-Activated Protein Kinases
D019332:Endothelin-1; D004791:Enzyme Inhibitors; C104334:FR 167653; D007093:Imidazoles; C495136:OLR1 protein, rat; D011720:Pyrazoles; D011725:Pyridines; D011973:Receptors, LDL; D051131:Receptors, Oxidized LDL; D051127:Scavenger Receptors, Class E; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; C093642:SB 203580; D009638:Norepinephrine