Apoptosis induction by oxidized glycated LDL in human retinal capillary pericytes is independent of activation of MAPK signaling pathways.
BACKGROUND
Pericyte loss is a cardinal feature of early diabetic retinopathy. We previously reported that highly oxidized-glycated low density lipoprotein (HOG-LDL) induces pericyte apoptosis in vitro. In this study, we investigated the role of the mitogen-activated protein kinase (MAPK) signaling pathways in HOG-LDL-induced apoptosis in human pericytes.


METHODS
Human retinal capillary pericytes (HRCP) were exposed to native LDL (N-LDL) and HOG-LDL, and apoptosis was measured using flow cytometry. Time- and dose-dependent responses of extracellular signal-regulated kinase (ERK), p38, and Jun N-terminal kinase (JNK) following exposure to N-LDL or HOG-LDL were determined using western blotting. U0126 (ERK inhibitor), SB203580 (p38 inhibitor), and SP600125 (JNK inhibitor) were used to determine the role of MAPK signaling in HOG-LDL-induced apoptosis.


RESULTS
HOG-LDL induced apoptosis in HRCP in a dose-dependent manner at concentrations from 5 to 50 mg/l, with a constant effect from 50 to 200 mg/l. When compared to serum-free medium (SFM), this effect of HOG-LDL was found to be significant at all doses above 10 mg/l. In contrast, N-LDL at 200 mg/l did not induce apoptosis compared with SFM. Exposure to N-LDL versus HOG-LDL induced similar phosphorylation of ERK, p38, and JNK, peaking at 5 min, with similar dose-dependent responses up to 25 mg/l that were constant from 25 to 100 mg/l. Blocking of the ERK, p38, and JNK pathways did not inhibit pericyte apoptosis induced by HOG-LDL.


CONCLUSIONS
Our data suggest that apoptosis induced by HOG-LDL in HRCP is independent of the activation of MAPK signaling pathways.
Diffley
J Matthew
JM
Harold Hamm Oklahoma Diabetes Center and Section of Endocrinology and Diabetes, University of Oklahoma Health Sciences Center, Oklahoma City, OK 73104, USA.
Wu
Mingyuan
M
Sohn
Mimi
M
Song
Weiwei
W
Hammad
Samar M
SM
Lyons
Timothy J
TJ
D000873:Anthracenes / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects*; D002070:Butadienes / Q000494:pharmacology; D002196:Capillaries / Q000166:cytology / Q000187:drug effects / Q000201:enzymology; D048049:Extracellular Signal-Regulated MAP Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D017127:Glycation End Products, Advanced; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology; D048031:JNK Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D008077:Lipoproteins, LDL / Q000494:pharmacology*; D020935:MAP Kinase Signaling System / Q000187:drug effects; D009570:Nitriles / Q000494:pharmacology; D020286:Pericytes / Q000166:cytology* / Q000187:drug effects* / Q000201:enzymology; D010766:Phosphorylation; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011725:Pyridines / Q000494:pharmacology; D012171:Retinal Vessels / Q000166:cytology*; D013997:Time Factors; D048051:p38 Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D000093844:Glycated Proteins
D000873:Anthracenes; D002070:Butadienes; D048049:Extracellular Signal-Regulated MAP Kinases; D017127:Glycation End Products, Advanced; D007093:Imidazoles; D048031:JNK Mitogen-Activated Protein Kinases; D008077:Lipoproteins, LDL; D009570:Nitriles; D047428:Protein Kinase Inhibitors; D011725:Pyridines; D048051:p38 Mitogen-Activated Protein Kinases; C113580:U 0126; C031797:glycated lipoproteins, LDL; D000093844:Glycated Proteins; C099252:oxidized low density lipoprotein; C432165:pyrazolanthrone; C093642:SB 203580