LDL receptor-related protein mediates uptake of aggregated LDL in human vascular smooth muscle cells

Foam cell formation is a key event in the onset and progression of atherosc lerotic lesions. We have previously reported that internalization of aggreg ated low density lipoproteins (agLDLs) by vascular smooth muscle cells (VSM Cs) produces cholesteryl ester (CE) accumulation in these cells. The aim of this study was to analyze whether the low density lipoprotein receptor-rel ated protein (LRP) mediates the uptake of agLDL by VSMCs. First, immunocyto chemistry and fluorescence microscopic analysis with the use of anti-LRP an tibodies indicated that there was a high expression of LRP in VSMCs, Confoc al microscopic analysis with the use of agLDLs labeled with fluorochrome 1, 1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocycine and anti-LRP antibodies showed the colocalization of agLDL and LRP. The second approach was to ana lyze the effect of LRP ligands on agLDL internalization; lactoferrin strong ly inhibited CE accumulation from agLDLs (85.0+/-5.7% at 25 mu g/mL) by imp airing agLDL binding. Coincubation of agLDL with anti-LRP antibodies decrea sed in a dose-dependent manner agLDL-derived CE accumulation (from 20% at 1 2.5 mu g/mL to 80% at 50 mu g/mL). The third approach was to evaluate wheth er antisense LRP oligodeoxynucleotides were able to block agLDL internaliza tion. Treatment of VSMCs with 5 mu mol/L antisense LRP oligodeoxynucleotide s reduced agLDL-derived CE accumulation by 84+/-2%. In conclusion, these re sults from immunologic, biochemical, and molecular interventions demonstrat e that LRP mediates the binding and internalization of agLDL in human VSMCs . Because LRP is highly expressed in VSMCs and the uptake of 1 LDL aggregat e amounts to the deposition of several hundreds of LDL particles, the uptak e of agLDL through LRP could have a crucial role for lipid deposition in VS MCs.