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Published on: September 12, 2017
Increased angiogenic response in aortic explants of collagen XVIII/endostatin-null mice
1Department of Cell Biology, Harvard Medical School, 240 Longwood Ave., Boston, MA 02115, USA.
Abstract:
Endostatin, a proteolytic fragment of basement membrane-associated collagen XVIII, has been shown to be a potent angiogenesis inhibitor both in vivo and in vitro when given at high concentrations. The precise molecular mechanisms by which it functions and whether or not it plays a role in physiological regulation of angiogenesis are not clear. In mice with targeted null alleles of Col18a1, there appears to be no major abnormality in vascular patterns or capillary density in most organs. Furthermore, the growth of experimental tumors is not increased. However, a detailed analysis of induced angiogenesis in these mice has not been performed. Therefore, we compared the angiogenic responses induced by in vitro culture of aortic explants from collagen XVIII/endostatin-null mice (ko) to wild-type (wt) littermates. We found a twofold increase in microvessel outgrowth in explants from ko mice, relative to wt explants. This increased angiogenesis was reduced to the wt level by the addition of low levels (0.1 microg/ml) of recombinant mouse or human endostatin during the culture period. To address cellular/molecular mechanisms underlying this difference in angiogenic response between ko and wt mice, we isolated endothelial cells from both strains and compared their biological behavior. Proliferation assays showed no difference between the two types of endothelial cells. In contrast, adhesion assays showed a striking difference in their ability to adhere to fibronectin suggesting that collagen XVIII/endostatin may regulate interactions between endothelial cells and underlying basement membrane-associated components, including fibronectin, such that in the absence of collagen XVIII/endostatin, endothelial cells are more adhesive to fibronectin. In the aortic explant assay, characterized by dynamic processes of microvessel elongation and regression, this may result in stabilization of newly formed vessels, reduced regression, and a net increase in microvessel outgrowth in explants from ko mice compared to the wt littermates.
Insights
Collagen XVIII/endostatin deficiency in mice significantly increases angiogenesis, suggesting its role in regulating blood vessel formation and endothelial cell adhesion to fibronectin.
Area of Science:
- Biochemistry
- Molecular Biology
- Vascular Biology
Background:
- Endostatin, derived from collagen XVIII, inhibits angiogenesis at high concentrations.
- The physiological role and molecular mechanisms of endostatin in angiogenesis remain unclear.
- Collagen XVIII-null mice show no gross vascular abnormalities, suggesting a need for detailed angiogenesis studies.
Purpose of the Study:
- To investigate the role of collagen XVIII/endostatin in physiological angiogenesis.
- To compare angiogenic responses in collagen XVIII/endostatin-null mice versus wild-type littermates.
- To elucidate the cellular and molecular mechanisms underlying differences in angiogenesis.
Main Methods:
- In vitro culture of aortic explants from collagen XVIII/endostatin-null and wild-type mice.
- Assessment of microvessel outgrowth in explant cultures.
- Addition of recombinant endostatin to cultures.
- Isolation and comparative analysis of endothelial cell proliferation and adhesion to fibronectin.
Main Results:
- A twofold increase in microvessel outgrowth was observed in explants from null mice compared to wild-type.
- Low concentrations of recombinant endostatin normalized the angiogenic response in null mouse explants.
- Endothelial cells from null mice exhibited significantly higher adhesion to fibronectin.
- No differences in endothelial cell proliferation were detected between the two groups.
Conclusions:
- Collagen XVIII/endostatin plays a crucial role in regulating physiological angiogenesis.
- The absence of collagen XVIII/endostatin enhances endothelial cell adhesion to fibronectin, potentially stabilizing new vessels.
- This suggests a mechanism where collagen XVIII/endostatin modulates endothelial cell interactions with the extracellular matrix to control angiogenesis.
