Elsevier

Brain Research

Volume 1288, 8 September 2009, Pages 125-134
Brain Research

Research Report
Glioma-induced remodeling of the neurovascular unit

https://doi.org/10.1016/j.brainres.2009.06.095Get rights and content

Abstract

The normal BBB (blood–brain barrier) consists of a series of structures collectively known as neurovascular units, or NVU, that are composed of endothelial cells and astrocyte endfeet separated by a basal lamina at their interface. The integrity of the BBB and specifically endothelial tight junctions is maintained by interactions between these different components and the local microenvironment of the NVU. Central nervous system cancers such as gliomas disrupt the integrity of the BBB and this compromise is associated with increased tumor growth and invasion of the surrounding brain parenchyma. Because the relationship between glioma-induced BBB breakdown and glioma invasion remains poorly understood, and the host microenvironment can influence tumor cell migration, we used immunohistochemical techniques to characterize tumor associated BBB remodeling. Using an orthotopic xenograft model of glioma, we demonstrate that tumor cells induce specific changes in the composition of the basal lamina and in astrocytic components of the NVU. We suggest that these changes may be essential to understand the capacity of gliomas to regulate BBB integrity and as such, glioma invasion into brain parenchyma.

Introduction

Gliomas are associated with aggressive invasion of the surrounding brain parenchyma. While resection reduces the primary tumor burden, extensive migration of glioma cells away from the primary tumor mass prevents the complete removal of tumor cells and represents a significant challenge in the treatment of glioma. In vivo experimental models of glioma have been used to demonstrate that tagging tumor cells can be used to monitor the infiltration of tumor cells in the parenchyma and/or perivascular spaces even at a single cell level (Lampson et al., 1993, Lund et al., 2006, Winkler et al., 2009, Zhang et al., 2002). However, the relationship between glioma-induced BBB dysregulation and glioma invasion remains poorly understood.

Gliomas disrupt the integrity of the blood–brain barrier (BBB), and this compromise is associated with increased glioma tumor growth and infiltration in human and rodents (Lund et al., 2006, Neuwelt and Rapoport, 1984). Whereas normally, the BBB consists of endothelial cells held together by tight junctions, it also contains a basal lamina surrounding the capillary walls and adjacent astrocyte endfeet that form a structure collectively known as the neurovascular unit, NVU (Iadecola, 2004, Simard and Nedergaard, 2004). The interactions between the different cell types of NVU are disrupted in the microenvironment of the glioma (Abbott et al., 2006, Abramsson et al., 2007, Virgintino et al., 2007).

While many studies with malignant glioma focus on the dysregulated signaling pathways in tumor cells as a potential target for therapeutics (Furnari et al., 2007), our previous studies have shown the importance of the host microenvironment to influence the migration of the tumor cells (Criscuoli et al., 2005, Lund et al., 2006). For example, the presence of specific host factors such as src in the brain endothelium is essential for tumor-mediated BBB breakdown and glioma invasion (Eliceiri et al., 1999, Lund et al., 2006). In this study, we compared tumor-induced changes in the NVU of primary vs secondary tumors (as defined by their distance from the primary tumor), and suggest that changes in basal lamina composition may mediate the capacity of gliomas to regulate BBB integrity.

Section snippets

Immunostaining of the astrocyte–endothelial interface of the BBB

In the normal brain, a subset of astrocytes extends projections to the basal lamina that surrounds the microvascular endothelium. Immunohistochemical staining with anti-glial fibrillary acidic protein (GFAP) demonstrates the difference between arterioles/venules and the capillary bed and highlights the specific association of GFAP-positive astrocytes with larger vessels that have a minimal role in regulating vascular permeability (Fig. 1A). Immunostaining of 60 μm thick tissue sections with an

Discussion

In this study, we show that tumor induces specific changes in endothelial cells, remodeling of the ECM and changes in endothelial-associated astrocytes. We observed a decrease in laminin and agrin, and an increase in tenascin in the primary tumor (Fig. 3). In secondary tumors, both astrocytes and blood vessels remain separated by a basal lamina that contains laminin and agrin (Fig. 3, Fig. 4). The changes in staining observed in the primary tumor are in general agreement with observations from

Mice

Rag2 knockout mice were used for xenograft studies based on previous studies using rag2−/−, src+/+ or rag2−/−, src+/− hosts (Eliceiri et al., 1999, Lund et al., 2006). All animal handling procedures were approved by the University of California San Diego Institutional Animal Care and Use Committee.

Glioma tumor cells

Early passages of patient-derived human glioma cells, DBTRG (a kind gift from Dr. C. Kruse) were used for xenograft studies. Cells were maintained in Dulbecco's modified Eagle's minimum essential

Acknowledgments

We acknowledge the expert technical assistance of Montha Pao. These studies were supported by grants from the NHLBI and NINDS (B.E.).

References (29)

  • CahoyJ.D. et al.

    A transcriptome database for astrocytes, neurons, and oligodendrocytes: a new resource for understanding brain development and function

    J. Neurosci.

    (2008)
  • ChekhoninV.P. et al.

    Modeling and immunohistochemical analysis of C6 glioma in vivo

    Bull. Exp. Biol. Med.

    (2007)
  • DeryuginaE.I. et al.

    Tenascin mediates human glioma cell migration and modulates cell migration on fibronectin

    J. Cell Sci.

    (1996)
  • FurnariF.B. et al.

    Malignant astrocytic glioma: genetics, biology, and paths to treatment

    Genes Dev.

    (2007)
  • Cited by (44)

    • Temporal lobe tumors modify local venous drainage

      2023, Clinical Neurology and Neurosurgery
    • The Problem of Neurovascular Uncoupling

      2021, Neuroimaging Clinics of North America
      Citation Excerpt :

      NVU may result from disruption of any component of the normal neurovascular coupling cascade (NCC), which is composed of a series of biochemical steps at the cellular level, including (proximally) neurotransmitters released from activated neurons to astrocytes and (distally) chemical mediators that directly act on vascular smooth muscle of arterioles that are responsible for regulating blood flow.7,33 Preclinical studies have suggested that tumors may induce remodeling of the extracellular matrix, changes in endothelial cells, and changes in endothelial-associated astrocytes that disrupt the NCC.34–37 Studies have suggested that the disruption of NCC in the vicinity of high-grade gliomas is primarily caused by tumor angiogenesis that results in compromise of normal cerebral autoregulatory capacity in the tumoral and peritumoral regions.29,30

    • Nanoparticles for Brain Tumor Delivery

      2019, Nervous System Drug Delivery: Principles and Practice
    • Limitations of Resting-State Functional MR Imaging in the Setting of Focal Brain Lesions

      2017, Neuroimaging Clinics of North America
      Citation Excerpt :

      Such NVU also may adversely affect other applications of task and rsfMR imaging in the setting of focal brain lesions that may alter regional hemodynamics or otherwise disrupt local networks. The mechanisms underlying brain tumor–induced neurovascular uncoupling are not yet completely understood, but preclinical studies have suggested that tumors induce a variety of physiologic changes in the microenvironment that may contribute to this phenomenon.30 Previous studies31–39 have demonstrated prevalence of NVU in high-grade gliomas as well as with low-grade gliomas.

    View all citing articles on Scopus
    View full text