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Kristina Boström

Publications and source records attributed to Kristina Boström.

9 recordsLinked to original sources
PubMed2006

Activin-like kinase receptor 1 (ALK1) in atherosclerotic lesions and vascular mesenchymal cells.

OBJECTIVE: Activin-like kinase receptor 1 (ALK1) is a transforming growth factor (TGF)-beta type I receptor expressed in vascular mesenchyme, yet its function in vascular mesenchymal cells (VMC) is unclear. We examined ALK1 expression in human coronary atherosclerotic lesions and bovine and human VMC undergoing cellular condensation in vitro. We also examined the effect of activated ALK1 on cell proliferation and smooth muscle cell (SMC) differentiation. METHODS AND RESULTS: Our results showed that ALK1 was expressed in human coronary atherosclerotic lesions as determined by immunohistochemistry. ALK1 was also expressed in cellular condensations of bovine and human VMC as determined by real-time PCR and immunocytochemistry. Bone morphogenetic protein (BMP)-2, which is known to increase condensation size, increased ALK1 expression when induced from a BMP-2 adenoviral vector. In turn, activated ALK1 induced expression of matrix GLA protein (MGP), a BMP-2 inhibitor known to limit condensation size. Activated ALK1 enhanced proliferation of VMC as determined by 3H-thymidine incorporation, whereas MGP decreased proliferation. Activated ALK1 also enhanced expression of SMC lineage markers and ALK5, another TGF-beta type I receptor, as determined by immunoblotting, real-time PCR and immunocytochemistry. Anti-TGF-beta antibodies abolished expression of SMC markers in the presence of constitutively active ALK1, suggesting that ALK1 activation alone is not sufficient to promote SMC differentiation. CONCLUSIONS: We conclude that there is a balance between the actions of BMP-2 and MGP in the initiation of vascular mesenchymal cell condensation and SMC differentiation, and that targeting ALK1, BMP2 and/or MGP may lead to novel concepts of atherosclerosis treatment.

Activin Receptors, Type I↗
PubMed2006

Regulation of bone morphogenetic protein-4 by matrix GLA protein in vascular endothelial cells involves activin-like kinase receptor 1.

Matrix GLA protein (MGP) has previously been shown to enhance expression of vascular endothelial growth factor (VEGF) through the activin-like kinase receptor 1 (ALK1) in bovine aortic endothelial cells. MGP has also been identified as an inhibitor of bone morphogenetic protein-2 (BMP-2). This study showed that the effect of MGP on ALK1 signaling and VEGF expression in bovine aortic endothelial cells was dose-dependent, that a progressive increase of MGP levels ceased to be stimulatory and instead turned inhibitory. We identified a new regulatory pathway involving BMP that may explain this response. BMP-2 and BMP-4 induced expression of ALK1 in a dose-dependent fashion as determined by real-time PCR and immunoblotting. Activation of ALK1 signaling induced expression of MGP in addition to that of VEGF, allowing for negative feedback regulation of BMP by MGP. MGP inhibited BMP-4 activity similarly to that of BMP-2 and interacted with BMP-4 on a protein level as determined by co-immunoprecipitation. The dose-dependent effect on ALK1 expression and the stimulation of MGP and VEGF expression were dependent on signaling by transforming growth factor-beta (TGF-beta) and ALK1. Inhibition of TGF-beta by neutralizing antibodies abolished the inhibitory effect of high BMP-4 levels on ALK1 expression and the induction of MGP and VEGF. Depletion of ALK1 by small interfering RNA abolished the induction of MGP and VEGF. MGP promoter activity was also stimulated by BMP-4 in a TGF-beta-dependent fashion. The results suggest that the effects of BMP on endothelial cells occur in part through induction of ALK1, an effect that may be limited by ALK1-induced MGP.

Activin Receptors, Type II↗
PubMed2004

Matrix GLA protein stimulates VEGF expression through increased transforming growth factor-beta1 activity in endothelial cells.

Matrix GLA protein (MGP) is expressed in endothelial cells (EC), and MGP deficiency results in developmental defects suggesting involvement in EC function. To determine the role of MGP in EC, we cultured bovine aortic EC with increasing concentrations of human MGP (hMGP) for 24 h. The results showed increased proliferation, migration, tube formation, and increased release of vascular endothelial growth factor-A (VEGF-A) and basic fibroblast growth factor (bFGF). HMGP, added endogenously or transiently expressed, increased VEGF gene expression dose-dependently as determined by real-time PCR. To determine the mechanism by which hMGP increased VEGF expression, we studied the effect of MGP on the activity of transforming growth factor (TGF)-beta1 compared with that of bone morphogenetic protein (BMP)-2 using transfection assays with TGF-beta- and BMP-response element reporter genes. Our results showed a strong enhancement of TGF-beta1 activity by hMGP, which was paralleled by increased VEGF expression. BMP-2 activity, on the other hand, was inhibited by hMGP. Neutralizing antibodies to TGF-beta blocked the effect of MGP on VEGF expression. The enhanced TGF-beta1 activity specifically activated the Smad1/5 pathway indicating that the TGF-beta receptor activin-like kinase 1 (ALK1) had been stimulated. It occurred without changes in expression of TGF-beta1 or ALK1 and was mimicked by transfection of constitutively active ALK1, which increased VEGF expression. Expression of VEGF and MGP was induced by TGF-beta1, but the induction of MGP preceded that of VEGF, consistent with a promoting effect on VEGF expression. Together, the results suggest that MGP plays a role in EC function, altering the response to TGF-beta superfamily growth factors.

Animals↗
PubMed2004

Pattern formation by vascular mesenchymal cells.

In embryogenesis, immature mesenchymal cells aggregate and organize into patterned tissues. Later in life, a pathological recapitulation of this process takes place in atherosclerotic lesions, when vascular mesenchymal cells organize into trabecular bone tissue within the artery wall. Here we show that multipotential adult vascular mesenchymal cells self-organize in vitro into patterns that are predicted by a mathematical model based on molecular morphogens interacting in a reaction-diffusion process. We identify activator and inhibitor morphogens for stripe, spot, and labyrinthine patterns and confirm the model predictions in vitro. Thus, reaction-diffusion principles may play a significant role in morphogenetic processes in adult mesenchymal cells.

Animals↗
PubMed2004

Endothelial cells modulate osteogenesis in calcifying vascular cells.

The potential role of vascular endothelium in atherosclerotic calcification is unknown. Endothelial cells (EC) express bone morphogenetic proteins (BMP), and EC-conditioned medium is osteoinductive in marrow stromal cells. To test whether EC are osteoinductive in vascular cells, we used calcifying vascular cells (CVC) that form nodules and mineralize in vitro. We established a coculture model with EC grown opposite CVC on membranes coated with collagen I or collagen IV, both of which are expressed in atherosclerotic lesions. On collagen I, EC did not alter CVC nodule formation, calcification or expression of the osteogenic marker Cbfa1, the chondrogenic marker collagen IX or smooth muscle cell alpha-actin. However, on collagen IV, EC abolished nodule formation and calcification, and expression of cell markers decreased, suggesting dedifferentiation. Matrix GLA protein (MGP), also expressed in atherosclerotic lesions, was added to CVC in coculture. Unexpectedly, MGP enhanced Cbfa1 expression in CVC on both collagen I and IV. The enhancement was most apparent on collagen IV, where calcification also increased. However, MGP did not restore nodule formation on collagen IV, suggesting that nodule formation and cell differentiation are separate processes. The effect of EC on CVC calcification was suppressed by noggin, an inhibitor of BMP activity, and in part mimicked by replacement of EC by BMP-2. Our results support a role for endothelium in vascular calcification, modulated by collagens and MGP.

Animals↗
PubMed2003

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.

Animals↗
PubMed2003

Multilineage potential of cells from the artery wall.

BACKGROUND: In diabetes or atherosclerosis, ectopic bone, fat, cartilage, and marrow often develop in arteries. However the mechanism is unknown. We have previously identified a subpopulation of vascular cells (calcifying vascular cells, CVC), derived by dilutional cloning of bovine aortic medial cells, and showed that they undergo osteoblastic differentiation and mineralization. We now show that CVC have the potential to differentiate along other mesenchymal lineages. METHODS AND RESULTS: To determine the multilineage potential of CVC, molecular and functional markers of multiple mesenchymal lineages were assessed. Chondrogenic potential of CVC was evidenced by expression of types II and IX collagen and cytochemical staining for Alcian blue. Leiomyogenic potential of CVC was evidenced by the expression of smooth muscle-alpha actin, calponin, caldesmon, and myosin heavy chain. Stromogenic potential of CVC was evidenced by the ability to support growth of colony-forming units of hematopoietic progenitor cells from human CD34+ umbilical cord blood cells for a period of 5 weeks. Adipogenic potential was not observed. CVC were immunopositive to antigens to CD29 and CD44 but not to CD14 or CD45, consistent with other mesenchymal stem cells. CVC retained multipotentiality despite passaging and expansion through more than 20 to 25 population triplings, indicating a capacity for self-renewal. CONCLUSIONS: These results suggest that the artery wall contains cells that have the potential for multiple lineages similar to mesenchymal stem cells but with a unique differentiation repertoire.

Animals↗
PubMed2001

Matrix GLA protein, a regulatory protein for bone morphogenetic protein-2.

Matrix GLA protein (MGP) has been identified as a calcification inhibitor in cartilage and vasculature. Part of this effect may be attributed to its influence on osteoinductive activity of bone morphogenetic protein-2 (BMP-2). To detect binding between MGP and BMP-2, we performed immunoprecipitation using MGP and BMP-2 tagged with FLAG and c-Myc. The results showed co-precipitation of BMP-2 with MGP. To quantify the effect of MGP on BMP-2 activity, we assayed for alkaline phosphatase activity and showed a dose-dependent effect. Low levels of MGP relative to BMP-2 (<1-fold excess) resulted in mild enhancement of osteoinduction, whereas intermediate levels (1-15-fold excess) resulted in strong inhibition. High levels of MGP (>15-fold excess), however, resulted in pronounced enhancement of the osteoinductive effect of BMP-2. Cross-linking studies showed that inhibitory levels of MGP abolished BMP-2 receptor binding. Immunoblotting showed a corresponding decrease in activation of Smad1, part of the BMP signaling system. Enhancing levels of MGP resulted in increased Smad1 activation. To determine the cellular localization of BMP-2 in the presence of MGP, binding assays were performed on whole cells and cell-synthesized matrix. Inhibitory levels of MGP yielded increased matrix binding of BMP-2, suggesting that MGP inhibits BMP-2 in part via matrix association. These results suggest that MGP is a BMP-2 regulatory protein.

Animals↗