Native and modified LDL activate extracellular signal-regulated kinases in mesangial cells.
Glycation and/or oxidation of LDL may promote diabetic nephropathy. The mitogen-activated protein kinase (MAPK) cascade, which includes extracellular signal-regulated protein kinases (ERKs), modulates cell function. Therefore, we examined the effects of LDL on ERK phosphorylation in cultured rat mesangial cells. In cells exposed to 100 microg/ml native LDL or LDL modified by glycation, and/or mild or marked (copper-mediated) oxidation, ERK activation peaked at 5 min. Five minutes of exposure to 10-100 microg/ml native or modified LDL produced a concentration-dependent (up to sevenfold) increase in ERK activity. Also, 10 microg/ml native LDL and mildly modified LDL (glycated and/or mildly oxidized) produced significantly greater ERK activation than that induced by copper-oxidized LDL +/- glycation (P < 0.05). Pretreatment of cells with Src kinase and MAPK kinase inhibitors blocked ERK activation by 50-80% (P < 0.05). Native and mildly modified LDL, which are recognized by the native LDL receptor, induced a transient spike of intracellular calcium. Copper-oxidized (+/- glycation) LDL, recognized by the scavenger receptor, induced a sustained rise in intracellular calcium. The intracellular calcium chelator (EGTA/AM) further increased ERK activation by native and mildly modified LDL (P < 0.05). These findings demonstrate that native and modified LDL activate ERKs 1 and 2, an early mitogenic signal, in mesangial cells and provide evidence for a potential link between modified LDL and the development of glomerular injury in diabetes.
Jenkins
A J
AJ
Department of Medicine, Medical University of South Carolina, Charleston 29425, USA.
Velarde
V
V
Klein
R L
RL
Joyce
K C
KC
Phillips
K D
KD
Mayfield
R K
RK
Lyons
T J
TJ
Jaffa
A A
AA
D000818:Animals; D002118:Calcium / Q000502:physiology; D002478:Cells, Cultured; D004789:Enzyme Activation; D005920:Glomerular Mesangium / Q000166:cytology / Q000187:drug effects* / Q000201:enzymology*; D006031:Glycosylation; D006801:Humans; D008077:Lipoproteins, LDL / Q000378:metabolism / Q000494:pharmacology*; D008297:Male; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D009994:Osmolar Concentration; D010084:Oxidation-Reduction; D010766:Phosphorylation / Q000187:drug effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D013997:Time Factors; D019061:src-Family Kinases / Q000378:metabolism
D008077:Lipoproteins, LDL; D019061:src-Family Kinases; D020928:Mitogen-Activated Protein Kinases; D020929:Mitogen-Activated Protein Kinase Kinases; D002118:Calcium