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Presence of intratumoral platelets is associated with tumor vessel structure and metastasis.

Li R, Ren M, Chen N, Luo M, Deng X, Xia J, Yu G, Liu J, He B, Zhang X, Zhang Z, Zhang X, Ran B, Wu J - BMC Cancer (2014)

Bottom Line: Vascular permeability was evaluated by determination of intratumoral Evans blue and Miles vascular permeability assay.Furthermore, microdialysis was used to examining the intratumoral extracellular angiogenic growth factors (VEGF, TGF-β) by ELISA.Platelet depletion led to reduced tumor hypoxia and Met receptor activation and was associated with a decreased release of MMP-2, 9, PAI-1, VEGF, and TGF-β.

View Article: PubMed Central - HTML - PubMed

Affiliation: Drug Discovery Research Center, Luzhou Medical College, Luzhou, Sichuan, People's Republic of China. wuji@missouri.edu.

ABSTRACT

Background: Platelets play a fundamental role in maintaining hemostasis and have been shown to participate in hematogenous dissemination of tumor cells. Abundant platelets were detected in the tumor microenvironment outside of the blood vessel, thus, platelet -tumor cell interaction outside of the bloodstream may play a role in regulating primary tumor growth and metastasis initiation. However, it is unclear that platelet depletion affects tumor vessel structure and dynamics.

Methods: Using thrombocytopenia induction in two different tumor-bearing mouse models, tumor tissues were performed by Westernblotting and immunohistochemical staining. Vascular permeability was evaluated by determination of intratumoral Evans blue and Miles vascular permeability assay. Furthermore, microdialysis was used to examining the intratumoral extracellular angiogenic growth factors (VEGF, TGF-β) by ELISA.

Results: Platelet depletion showed no change in tumor growth and reduced lung metastasis. Platelet depletion led to reduced tumor hypoxia and Met receptor activation and was associated with a decreased release of MMP-2, 9, PAI-1, VEGF, and TGF-β. Tumor vessels in platelet-depleted mice showed impaired vessel density and maturation.

Conclusions: Our findings demonstrate that platelets within the primary tumor microenvironment play a critical role in the induction of vascular permeability and initiation of tumor metastasis.

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Related in: MedlinePlus

Platelets changed intratumoral levels of angiogenic factors. (A), (B) Western blot analysis of Angiopoietin-1, 2 expression in tumors from control and PLT-depleted mice. Quantification of western blot analysis for each protein (normalized to β-actin). (C) Microdialysis was used to sample extracellular proteins in vivo. Extracellular VEGF level was measured by ELISA as described in Materials and Methods. The results are expressed as the mean ± SEM. * p < 0.05. (n = 6 for each group).
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Figure 5: Platelets changed intratumoral levels of angiogenic factors. (A), (B) Western blot analysis of Angiopoietin-1, 2 expression in tumors from control and PLT-depleted mice. Quantification of western blot analysis for each protein (normalized to β-actin). (C) Microdialysis was used to sample extracellular proteins in vivo. Extracellular VEGF level was measured by ELISA as described in Materials and Methods. The results are expressed as the mean ± SEM. * p < 0.05. (n = 6 for each group).

Mentions: Proangiogenic growth factors released from platelet granules can affect tumor cell survival, proliferation, or invasiveness. Because our data indicated decreased hypoxia in platelet-depleted tumors, we considered the possible involvement of growth factors known to regulate tumor growth and metastasis. Previous studies demonstrated that the angiogenic cascade of the Ang-Tie system is critical for controlling vessel assembly and maturation. We performed Western blotting to examine the expression of Ang-1, which induces Tie2 activation leading to vessel stabilization and maturation, and its antagonist Ang-2, which causes vessel destabilization [19,20]. We observed a significant reduction in Ang-1 in platelet-depleted tumors compared to control tumors (Figure 5A). In contrast, the Ang-2 level was significantly increased in platelet-depleted tumors compared to control tumors (Figure 5B). Since the VEGF protein is bioactive as soluble protein in the extracellular space [21], we next examined extracellular VEGF level of tumors. Microdialysis was performed at 24 days before sacrifice, and found a significant decrease of extracellular VEGF in platelet-depleted tumors compared to control tumors (p < 0.05) (Figure 5C). These data suggest that platelets play a role in the secretion of growth factors in the tumor microenvironment.


Presence of intratumoral platelets is associated with tumor vessel structure and metastasis.

Li R, Ren M, Chen N, Luo M, Deng X, Xia J, Yu G, Liu J, He B, Zhang X, Zhang Z, Zhang X, Ran B, Wu J - BMC Cancer (2014)

Platelets changed intratumoral levels of angiogenic factors. (A), (B) Western blot analysis of Angiopoietin-1, 2 expression in tumors from control and PLT-depleted mice. Quantification of western blot analysis for each protein (normalized to β-actin). (C) Microdialysis was used to sample extracellular proteins in vivo. Extracellular VEGF level was measured by ELISA as described in Materials and Methods. The results are expressed as the mean ± SEM. * p < 0.05. (n = 6 for each group).
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4016490&req=5

Figure 5: Platelets changed intratumoral levels of angiogenic factors. (A), (B) Western blot analysis of Angiopoietin-1, 2 expression in tumors from control and PLT-depleted mice. Quantification of western blot analysis for each protein (normalized to β-actin). (C) Microdialysis was used to sample extracellular proteins in vivo. Extracellular VEGF level was measured by ELISA as described in Materials and Methods. The results are expressed as the mean ± SEM. * p < 0.05. (n = 6 for each group).
Mentions: Proangiogenic growth factors released from platelet granules can affect tumor cell survival, proliferation, or invasiveness. Because our data indicated decreased hypoxia in platelet-depleted tumors, we considered the possible involvement of growth factors known to regulate tumor growth and metastasis. Previous studies demonstrated that the angiogenic cascade of the Ang-Tie system is critical for controlling vessel assembly and maturation. We performed Western blotting to examine the expression of Ang-1, which induces Tie2 activation leading to vessel stabilization and maturation, and its antagonist Ang-2, which causes vessel destabilization [19,20]. We observed a significant reduction in Ang-1 in platelet-depleted tumors compared to control tumors (Figure 5A). In contrast, the Ang-2 level was significantly increased in platelet-depleted tumors compared to control tumors (Figure 5B). Since the VEGF protein is bioactive as soluble protein in the extracellular space [21], we next examined extracellular VEGF level of tumors. Microdialysis was performed at 24 days before sacrifice, and found a significant decrease of extracellular VEGF in platelet-depleted tumors compared to control tumors (p < 0.05) (Figure 5C). These data suggest that platelets play a role in the secretion of growth factors in the tumor microenvironment.

Bottom Line: Vascular permeability was evaluated by determination of intratumoral Evans blue and Miles vascular permeability assay.Furthermore, microdialysis was used to examining the intratumoral extracellular angiogenic growth factors (VEGF, TGF-β) by ELISA.Platelet depletion led to reduced tumor hypoxia and Met receptor activation and was associated with a decreased release of MMP-2, 9, PAI-1, VEGF, and TGF-β.

View Article: PubMed Central - HTML - PubMed

Affiliation: Drug Discovery Research Center, Luzhou Medical College, Luzhou, Sichuan, People's Republic of China. wuji@missouri.edu.

ABSTRACT

Background: Platelets play a fundamental role in maintaining hemostasis and have been shown to participate in hematogenous dissemination of tumor cells. Abundant platelets were detected in the tumor microenvironment outside of the blood vessel, thus, platelet -tumor cell interaction outside of the bloodstream may play a role in regulating primary tumor growth and metastasis initiation. However, it is unclear that platelet depletion affects tumor vessel structure and dynamics.

Methods: Using thrombocytopenia induction in two different tumor-bearing mouse models, tumor tissues were performed by Westernblotting and immunohistochemical staining. Vascular permeability was evaluated by determination of intratumoral Evans blue and Miles vascular permeability assay. Furthermore, microdialysis was used to examining the intratumoral extracellular angiogenic growth factors (VEGF, TGF-β) by ELISA.

Results: Platelet depletion showed no change in tumor growth and reduced lung metastasis. Platelet depletion led to reduced tumor hypoxia and Met receptor activation and was associated with a decreased release of MMP-2, 9, PAI-1, VEGF, and TGF-β. Tumor vessels in platelet-depleted mice showed impaired vessel density and maturation.

Conclusions: Our findings demonstrate that platelets within the primary tumor microenvironment play a critical role in the induction of vascular permeability and initiation of tumor metastasis.

Show MeSH
Related in: MedlinePlus