Intracellular VEGF regulates the balance between osteoblast and adipocyte differentiation
Yanqiu Liu, … , Napoleone Ferrara, Bjorn R. Olsen
Yanqiu Liu, … , Napoleone Ferrara, Bjorn R. Olsen
Published August 13, 2012
Citation Information: J Clin Invest. 2012;122(9):3101-3113. https://doi.org/10.1172/JCI61209.
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Research Article Bone biology Article has an altmetric score of 10

Intracellular VEGF regulates the balance between osteoblast and adipocyte differentiation

Abstract

Osteoporotic bones have reduced spongy bone mass, altered bone architecture, and increased marrow fat. Bone marrow stem cells from osteoporotic patients are more likely to differentiate into adipocytes than control cells, suggesting that adipocyte differentiation may play a role in osteoporosis. VEGF is highly expressed in osteoblastic precursor cells and is known to stimulate bone formation. Here we tested the hypothesis that VEGF is also an important regulator of cell fate, determining whether differentiation gives rise to osteoblasts or adipocytes. Mice with conditional VEGF deficiency in osteoblastic precursor cells exhibited an osteoporosis-like phenotype characterized by reduced bone mass and increased bone marrow fat. In addition, reduced VEGF expression in mesenchymal stem cells resulted in reduced osteoblast and increased adipocyte differentiation. Osteoblast differentiation was reduced when VEGF receptor 1 or 2 was knocked down but was unaffected by treatment with recombinant VEGF or neutralizing antibodies against VEGF. Our results suggested that VEGF controls differentiation in mesenchymal stem cells by regulating the transcription factors RUNX2 and PPARγ2 as well as through a reciprocal interaction with nuclear envelope proteins lamin A/C. Importantly, our data support a model whereby VEGF regulates differentiation through an intracrine mechanism that is distinct from the role of secreted VEGF and its receptors.

Authors

Yanqiu Liu, Agnes D. Berendsen, Shidong Jia, Sutada Lotinun, Roland Baron, Napoleone Ferrara, Bjorn R. Olsen

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Figure 7

Mechanisms by which VEGF controls osteoblast/adipocyte differentiation in BMSCs.

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Mechanisms by which VEGF controls osteoblast/adipocyte differentiation i...
(A) VEGF and VEGFR2 expression is detected in both nuclear and cytoplasmic regions of Osx-expressing cells, whereas VEGFR1 expression is primarily observed in the nuclear area similar to lamin A/C. Original magnification, ×250. (B) Reduced VEGF protein levels associated with WT and Lmna+/– cultures expressing VEGF-specific shRNA. *P < 0.05, **P < 0.01; n = 3. (C) Increased lamin A protein levels associated with WT and Lmna+/– cultures expressing VEGF-specific shRNA. Values above and below the blots represent relative lamin A and β-actin protein levels. (D) Reduced number of ALP-positive colonies in both WT and Lmna+/– cultures expressing VEGF shRNA. *P < 0.05, **P < 0.01; n = 3. (E) The number of colonies increased in Lmna+/– compared with WT cultures but was not affected by treatment with VEGF-specific shRNA. *P < 0.05; n = 3. (F) Increased number of adipogenic colonies in WT and Lmna+/– cultures expressing VEGF shRNA and Lmna+/– cultures expressing control shRNA. *P < 0.001; n = 4. (G) VEGF protein levels in culture medium prior to CFU-A assay are only slightly affected in WT and Lmna+/– cultures expressing VEGF-specific shRNA. *P < 0.05 and **P < 0.01. (H) VEGFR1 is mainly expressed as the soluble splice variant (sVEGFR1), whereas full-length (I) and phosphorylated (J) VEGFR2 is detected in WT and Lmna+/– cultures. (K) Reduced RUNX2 transcriptional activity in cultures expressing VEGF-specific shRNA and/or Lmna+/– cultures expressing control shRNA. *P < 0.05; n = 4. (L and N) RUNX2 protein levels are decreased in WT (L) and Lmna+/– (N) cultures expressing VEGF-specific shRNA under osteogenic conditions. (M and O) PPARγ2 protein levels are increased in WT (M) and Lmna+/– (O) cultures expressing VEGF-specific shRNA in the presence of adipogenic inducers.