Characterisation of the Binding of Low-Density Lipoproteins to Cultured Rat Mesangial Cells

Abstract

Mesangial cell lipid accumulation is a recognised feature of glomerular disease and has been implicated as a factor in the pathogenesis of renal injury. To investigate possible mechanisms of such accumulation, binding of 125I-labelled human low-density lipoprotein (LDL) to rat mesangial cells was studied in vitro. Experiments were performed at 4 degrees C to prevent ligand internalisation. LDL remained associated with the cells after repeated washing. Binding was time-dependent, was inhibited by addition of an excess of unlabelled LDL, but to a much lesser extent by apoprotein-A-rich high-density lipoprotein particles devoid of apoprotein E (HDL-A). Specific binding reached saturation at an LDL concentration of 21 micrograms/ml, required the presence of calcium, and was inhibited by heparin and dextran sulphate. Scatchard analysis suggested a single class of binding site (Kd 22.7 micrograms protein/ml). Higher binding affinities were obtained when rat LDL was substituted for human LDL (Kd 1.3 micrograms/ml) and when human fibroblasts were exposed to human LDL under identical experimental conditions (Kd 3.0 micrograms/ml). Further experiments at 37 degrees C demonstrated degradation of LDL by cells. These results suggest that mesangial cells possess apoprotein B, E receptors. Mesangial cell lipid accumulation may therefore result from receptor-mediated endocytosis of LDL particles.

Inflammatory stress increases unmodified LDL uptake via LDL receptor: an alternative pathway for macrophage foam-cell formation

“…Recent experimental and clinical evidence suggests that inflammation is an aggravating factor in lipid-mediated peripheral cell injury, such as atherogenesis and also glomerulosclerosis, which has many similarities to atherosclerosis, as described by our group [22][23][24] and others [25,26]. Cardiovascular risk is increased in chronic inflammatory states, up to 33-fold in patients with renal failure and allograft, and 50-fold in patients with immune dysregulation (e.g., systemic lupus erythematosus) [27,28].…”

Dyslipidemia in diabetic nephropathy

“…Finally, lipid-lowering therapy has been shown to improve glomerulosclerosis in the Zucker rat, a model of diabetes complicated with dyslipidemia [22]. Mesangial cells and glomerular epithelial cells (podocytes) have been shown to express receptors for TG-rich lipoproteins (TGRLs) [23][24][25][26]. TGRLs stimulate inflammatory pathways via the secretion of proinflammatory cytokines such as TNF-α, transforming growth factor (TGF)-β, and interleukin (IL)-6 [27], which results in the production of reactive oxygen species (ROS), leading to excessive ECM production.…”

VLDL and LDL Metabolism in Human and Rat Mesangial Cells

“…Although Sprague-Dawley and obese Zuckcr rats have mainly been used for studies of lipoprotein metabolism and glomerulosclerosis, only sporadic attempts have been made to use rat cells in stud ies of atherosclerosis in the past. Wheeler et al [8] showed in single experiments that the affinity of rat LDL towards the rat mesangial cell receptor is considerably higher com pared to human LDL. These data are supported by in vivo experiments in rat which showed clearance of human LDL to be slower than that of homologous rat LDL [20].…”

“…The relative abundance of apoE-containing highdensity lipoproteins (HDL) in the rat along with the rela tive deficiency of apoB-containing rat low-density lipo proteins (LDL) would suggest that in this species prefera bly apoE-containing lipoproteins may supply the extrahepatic tissues with cholesterol whereas LDL might be less important. Support for these observations came from studies demonstrating that rat mesangial cells have highaffinity receptors for rat lipoproteins but bind human LDL ineffectively [8], Therefore, the purpose of this study was to investigate the interaction of human apoB-and apoB.E-containing lipoproteins with receptors of rat and human mesangial cells. Furthermore, the value of using human lipoproteins in metabolic studies with rats was the subject of this investigation.…”