Native and modified LDL activate extracellular signal-regulated kinases in mesangial cells.

Abstract

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 µg/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 µg/ml native or modified LDL produced a concentration-dependent (up to sevenfold) increase in ERK activity. Also, 10 µg/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. D iabetes is the most common cause of end-stage renal disease in the Western world (1). Features of diabetic nephropathy include an alteration in glomerular cellularity, with early hypercellularity and late hypocellularity, thickened basement membranes, and increased mesangial matrix (2). Associations between elevated cholesterol levels, atherosclerosis, and the progression of renal damage are recognized (3-7). There is an extensive amount of literature suggesting that qualitative as well as quantitative abnormalities of the major cholesterol carrier LDL may contribute to its atherogenicity (7-11). More recently, LDL has been implicated in diabetic microvascular complications (12,13). Qualitative abnormalities of LDL occurring in diabetes include enhanced glycation (9,14), oxidation (14,15), and glycoxidation (combined glycation and oxidation) (9,11).Modified lipoproteins may be involved in nephrosclerosis and glomerulosclerosis (15)(16)(17)(18)(19)(20)(21)(22)(23). Oxidized LDL has been demonstrated in renal glomeruli in vivo, and intravenous administration of in vitro-oxidized LDL results in renal injury and LDL accumulation (23). Diabetic nephropathy-like lesions have also been induced in a rat model by glycated and glycoxidized albumin (24-26). With use of cultured mesangial cells, cytotoxicity (23,27) and enhanced production of mesangial matrix (23) in response to LDL have been demonstrated. We previously demonstrated that a noncytotoxic dose of glycated LDL increases transforming growth factor (TGF)-␤ mRNA expression (28): TGF-␤ is a modulator of mesangial cell survival and matrix production (29,30).Mitogen-activated protein kinases (MAPKs) are serine threonine-specific kinases that are activated in response to extracellular stimuli by dual phosphorylation at conserved tyrosine and threonine residues. Activation of the MAPK signaling pathways has been associated with effects relevant to vascular pathology in cultured cells implicated in macrovascular disease (31-33) and, more recently, in renal disease (34-36). Effects include stimulation or inhibition of cell proliferation (34,35), induction of apoptosis (37), and matrix production (36). There are at least three parallel series of MAPK cascades: 1) p38 MAPK; 2) stress-...

Oxidised, glycated LDL selectively influences tissue inhibitor of metalloproteinase-3 gene expression and protein production in human retinal capillary pericytes

“…This is consistent with our earlier findings demonstrating that HOG-LDL is significantly more cytotoxic than G-LDL [13] and demonstrating a distinct pattern of global gene expression induced by HOG-LDL, but not by G-LDL, in human retinal pericytes [16]. Our group has reported that uptake of HOG-LDL in rat mesangial cells mainly occurs via scavenger receptors, whereas N-and G-LDL are taken up by the LDL receptors [18]. Whether the differential actions of HOG-and G-LDL can be explained by their separate receptor mechanisms is not known.…”

“…The protein content of LDL was determined using a bicinchoninic acid assay kit (Pierce, Rockford, IL, USA). Native and modified LDLs were characterised by agarose gel electrophoresis (LIPOEPG; Beckman, Fullerton, CA, USA), fluorescence at 360 nm excitation and 430 nm emission (Gilford Fluorimeter IV, Oberlin, OH, USA) and absorbance at 234 nm in a Beckman DU650 spectrophotometer, confirming that the products were of a quality comparable with that in previous reports [18].…”

“…Informed consent was obtained from all volunteers. N-LDL (d=1.019-1.063 g/ml) was prepared by sequential ultracentrifugation, pooled, and modified in vitro as described [18]. G-LDL was prepared by incubating N-LDL in freshly prepared 50 mmol/l glucose (72 h, 37°C) under antioxidant conditions (1 mmol/l diethylene triamine pentaacetic acid [DTPA], under nitrogen).…”

Adrenocortical LDL receptor function negatively influences glucocorticoid output

“…The small molecule sunitinib is a potent multi-targeted receptor tyrosine kinase inhibitor (O'Farrell et al 2003, Sun et al 2003, suggesting that changes in intracellular signaling pathways are able to modulate the HSD3B2 transcription rate. Studies in respectively cultured mesangial cells (Jenkins et al 2000) and osteoblasts (Klein et al 2006) have indicated that exposure to native LDL -the normal substrate of the LDLR -increases the activity (phosphorylation state) of MAPK and tuberin and lowers Src protein levels and Akt activity. These combined findings suggest that, by changing the activity of major intracellular signaling pathways, enhanced adrenal uptake of native LDL from the plasma compartment might ultimately decrease the HSD3B2 expression in this tissue.…”

Effect of glycated LDL on microvascular tone in mice: a comparative study with LDL modified in vitro or isolated from diabetic patients

“…Mildly glycated LDL cause injury to retinal capillary endothelial cells and pericytes [17]. In cultured mesangial cells, glycated LDL activate extracellular signal-regulated protein kinases 1 and 2, an early mitogenic signal [18]. However, the possible influence of glycated LDL, in vivo, at the level of microvessels remains unknown.…”