Oxidized low‐density lipoprotein promotes osteoblast differentiation in primary cultures of vascular smooth muscle cells by up‐regulating Osterix expression in an Msx2‐dependent manner

Abstract

We have previously shown that oxidized low-density lipoproteins (oxLDLs) act synergistically with β-glycerophosphate to induce the osteogenic differentiation of primary bovine aortic smooth muscle cells (BASMCs). In the present study, we attempt to resolve the mechanism responsible for this effect by examining the expression of several osteoblast-specific transcription factors. Thus, by culturing BASMCs in the absence or presence of β-glycerophosphate and/or oxLDL, we demonstrate that β-glycerophosphate induces both Runx2 and Osterix (Osx) expression. In contrast, oxLDL has no effect on Runx2 expression but rather it enhances β-glycerophosphate-induced osteoblast differentiation by further up-regulating Osx expression. In an attempt to elucidate the mechanism responsible for this latter effect, we examined the ability of oxLDL to affect Msh homeobox 2 (Msx2) expression. Similar to its effect on Osx expression, oxLDL was found to synergistically enhance β-glycerophosphate-induced Msx2 expression in an extracellular signal-regulated kinase 1 and 2 (Erk 1 and 2)-dependent manner. Furthermore, oxLDL's ability to enhance both β-glycerophosphate-induced Osx expression and alkaline phosphatase activity was prevented when the BASMCs were first transfected with Msx2-specific siRNA. Taken together, these findings suggest a plausible mechanism by which oxLDL may promote osteoblast differentiation and vascular calcification in vivo.

Ablation of Adenosine Monophosphate-Activated Protein Kinase α1 in Vascular Smooth Muscle Cells Promotes Diet-Induced Atherosclerotic Calcification In Vivo

“…29,30 We checked the effect of AMPK activation on Runx2 in human aortic VSMC. As expected, metformin supplementation significantly reduced ox-LDL-induced Runx2 upregulation ( Figure 5C).…”

Oxidized low-density lipoprotein and β-glycerophosphate synergistically induce endothelial progenitor cell ossification

“…The effect of ox-LDL on cell differentiation has been fully explained to different degrees [11,28] . Our study presents, for the first time, the effects of ox-LDL on transdifferentiation of BMEPCs.…”

“…After attachment, the primary passages were exposed to 5 µg/mL ox-LDL, 10 mmol/L β-GP, or 5 µg/mL ox-LDL plus 10 mmol/L β-GP. Historically, β-GP has been thought to act solely as a phosphate donor and as such was required for the mineralization of primary cell cultures in vitro [11] . Cells were maintained in normal growth medium as a control.…”

“…Ox-LDL stimuli can cause endothelial cells to lose their vaso-protective effect and damage EPCs by triggering apoptosis, accelerating senescence and inhibiting endothelialization [8][9][10] . Ox-LDL also induces vascular smooth muscle cells to express genes associated with bone formation by up-regulating osterix [11] , which is considered a risk factor for calcification.…”

Bone alkaline phosphatase isoforms in chronic kidney disease : mineral and bone disorder

“…As mentioned above, this involves the transition of VSMCs from a contractile to a synthetic phenotype, with the downregulation of muscle specific proteins, such as α-actin and the up-regulation of osteoblastspecific proteins (139,148). This transition is driven by osteoblast-specific transcription factors RUNX2 and muscle segment homeobox 2 (MSX2), which both seem to be stimulated synergistically by phosphate (149), but also can be activated independently of each other In addition to the osteoblastic transition, VSMCs can adapt a chondrocyte-like phenotype in both intimal and medial calcification (155,156). This endochondral ossification is initiated by the chondrocyte-specific transcription factor SOX9 in VSMCs and is associated with the synthesis of a typical cartilage matrix consisting of collagen II and proteoglycans (157).…”