Abstract

Oxidized low density lipoprotein inhibits phosphate signaling and phosphate-induced mineralization in osteoblasts. Involvement of oxidative stress.

It is well admitted that oxidized LDL (OxLDL) plays a major role in the generation and progression of atherosclerosis. Since atherosclerosis is often accompanied by osteoporosis, the effects of OxLDL on phosphate-induced osteoblast mineralization were investigated.
Calcium deposition, expression of osteoblast markers and inorganic phosphate (Pi) signaling were determined under OxLDL treatment.
OxLDL, within the range of 10-50 μg protein/ml, inhibited Pi-induced UMR106 rat osteoblast mineralization. In parallel, the expression of Cbfa1/Runx2 transcription factor was decreased, and the intracellular level of the osteoblast marker osteopontin (OPN) was reduced. The extracellular level of another marker, receptor activator of nuclear factor kappa B ligand (RANKL), was also diminished. OxLDL inhibited Pi signaling via ERK/JNK kinases and AP1/CREB transcription factors. OxLDL triggered the generation of reactive oxygen species (ROS), either in the absence or presence of Pi. Furthermore, the effects of OxLDL on Pi-induced mineralization, generation of ROS and extracellular level OPN were reproduced by the lipid extract of the particle, whereas the antioxidant vitamin E prevented them.
This work demonstrates that OxLDL, by generation of an oxidative stress, inhibits of Pi signaling and impairs Pi-induced osteoblast differentiation.
This highlights the role of OxLDL in bone remodeling and in degenerative disorders other than atherosclerosis, especially in osteoporosis.

Mazière C, Savitsky V, Galmiche A, Gomila C…
Biochim. Biophys. Acta Nov 2010
PMID: 20667472