Matrix GLA protein and BMP-2 regulate osteoinduction in calcifying vascular cells.
Expression of matrix GLA protein (MGP), an alleged calcification inhibitor, is increased in calcified arteries. We used calcifying vascular cells (CVC) that form calcified nodules in vitro to clarify the importance of MGP in vascular cell calcification and differentiation. Unexpectedly, MGP dose-dependently increased calcification in CVC. It also increased expression of the osteogenic marker Cbfal, while decreasing expression of the smooth muscle marker alpha-actin as assessed by immunoblotting. Bone morphogenetic protein-2 (BMP-2), a known osteoinductive factor also increased calcification and osteogenic differentiation in CVC. We hypothesized that the effect of MGP was linked to that of BMP-2 since previous studies show that MGP modulates BMP-2 activity. Therefore, we compared the effect of MGP at different levels of exogenous BMP-2. Results showed that high BMP-2 levels significantly increased the stimulatory effect of low levels of MGP. A relative inhibition of calcification was observed at intermediate levels of MGP and a trend towards renewed stimulation at high levels of MGP. Thus, addition of MGP either promoted or inhibited calcification, depending on the relative amounts of BMP-2 and MGP. This was confirmed in human CVC with different relative expression of BMP-2 and MGP. Calcification in CVC with high relative expression of BMP-2 was inhibited by MGP, while calcification in CVC with low relative expression of BMP-2 was stimulated by MGP. MGP and BMP-2 both accelerated nodule formation, but had opposite effects on nodule size; MGP decreased while BMP-2 increased nodule size. The effect of BMP-2 may partly be explained by a BMP-2 induced decrease in MGP expression. Together, our results suggest that the effect of MGP on calcification and osteogenic differentiation is determined by availability of BMP-2.
Zebboudj
Amina F
AF
Division of Cardiology, David Geffen School of Medicine at UCLA, Los Angeles, California 90095-1679, USA.
Shin
Victoria
V
Boström
Kristina
K
D000818:Animals; D055396:Bone Morphogenetic Protein 2; D019485:Bone Morphogenetic Proteins / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology*; D002113:Calcification, Physiologic / Q000502:physiology*; D002135:Calcium-Binding Proteins / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D002417:Cattle; D002452:Cell Count; D018929:Cell Culture Techniques; D002454:Cell Differentiation / Q000187:drug effects; D017077:Culture Media, Conditioned / Q000737:chemistry / Q000494:pharmacology; D016326:Extracellular Matrix Proteins; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D009131:Muscle, Smooth, Vascular / Q000166:cytology* / Q000187:drug effects*; D010006:Osteoblasts / Q000166:cytology* / Q000187:drug effects*; D016212:Transforming Growth Factor beta; D000097568:Matrix Gla Protein
D055396:Bone Morphogenetic Protein 2; D019485:Bone Morphogenetic Proteins; D002135:Calcium-Binding Proteins; D017077:Culture Media, Conditioned; D016326:Extracellular Matrix Proteins; D016212:Transforming Growth Factor beta; D000097568:Matrix Gla Protein; C525718:BMP2 protein, human