Hypochlorite-oxidized low-density lipoprotein upregulates CD36 and PPARgamma mRNA expression and modulates SR-BI gene expression in murine macrophages.

The uptake of oxidized low-density lipoprotein (oxLDL) by scavenger receptors of macrophages with resulting foam cell formation is considered a critical event in atherogenesis. Since hypochlorite-oxidized LDL (HOCl-LDL) has been shown to be recognized by macrophages and evidence was provided that HOCl-LDL is internalized via class B scavenger receptors CD36 and SR-BI, the regulatory relationships between CD36, SR-BI, and the nuclear transcription factor PPARgamma in murine macrophages (RAW 264.7) on exposure to HOCl-LDL were examined. Using the highly sensitive real-time RT-PCR we could demonstrate that HOCl-LDL upregulated CD36 and PPARgamma levels dose- and time dependently while modulating SR-BI message levels differently in dependence on HOCl-LDL concentration and incubation time. On exposure of macrophages to HOCl-LDL but not native LDL in varying concentrations, a significant positive correlation between CD36 and PPARgamma (rho = 0.603, p = 0.001) was observed indicating the presence of a positive feedback mechanism by which HOCl-LDL could promote its own uptake. The transcriptional expression of SR-BI in macrophages was not significantly related to PPARgamma mRNA levels after treatment with HOCl-LDL suggesting a differential regulation of the two members of the scavenger receptor class B family in response to HOCl-LDL.