To determine the origin of the neoplastic cell in central nervous system (CNS) hemangioblastomas in von Hippel-Lindau disease (VHL) and its role in tumor formation and distribution, we characterized and differentiated neoplastic cells from hemangioblastomas removed from VHL patients.
Methods and Findings
A total of 31 CNS hemangioblastomas from 25 VHL patients were resected and analyzed. Tumor cells from the hemangioblastomas were characterized, grown, and differentiated into multiple lineages. Resected hemangioblastomas were located in the cerebellum (11 tumors), brainstem (five tumors), and spinal cord (15 tumors). Consistent with an embryologically derived hemangioblast, the neoplastic cells demonstrated coexpression of the mesodermal markers brachyury, Flk-1 (vascular endothelial growth factor-2), and stem cell leukemia (Scl). The neoplastic cells also expressed hematopoietic stem cell antigens and receptors including CD133, CD34, c-kit, Scl, erythropoietin, and erythropoietin receptor. Under specific microenvironments, neoplastic cells (hemangioblasts) were expanded and differentiated into erythrocytic, granulocytic, and endothelial progenitors. Deletion of the wild-type VHL allele in the hematopoietic and endothelial progeny confirmed their neoplastic origin.
The neoplastic cell of origin for CNS hemangioblastomas in VHL patients is the mesoderm-derived, embryologically arrested hemangioblast. The hematopoietic and endothelial differentiation potential of these cells can be reactivated under suitable conditions. These findings may also explain the unique tissue distribution of tumor involvement.
In this study, the neoplastic cell of origin for central nervous system hemangioblastomas in patients with von Hippel-Lindau disease is shown to be the mesoderm-derived, embryologically arrested hemangioblast.
von Hippel-Lindau (VHL) disease is a rare genetic condition characterized by the development of benign and malignant tumors in multiple organ systems. All the cells of people with this disorder contain one normal copy of the VHL gene and one altered copy. This gene encodes a tumor suppressor, a protein that stops tumors growing. One functioning copy of the VHL gene is sufficient to prevent any problems, but if the remaining normal copy becomes altered (mutated) in individual cells of patients with VHL disease, tumors result. These tumors are mainly benign (noncancerous growths that do not spread around the body) and form in parts of the body that are rich in blood vessels, in particular in the retina (the back of the eye), the cerebellum (the back of the brain), the brainstem (which links the cerebellum to the spinal cord), and the spinal cord. These central nervous system (CNS) tumors are called hemangioblastomas and look like little knots of capillaries (fine blood vessels). As they grow, they can cause problems through fluid leakage or by pressing on brain tissue. There is no cure for VHL disease, but patients can be monitored and their tumors dealt with before they get too large.
Why Was This Study Done?
It is not known what sort of cells hemangioblastomas develop from or why they occur only in specific parts of the CNS. This information could help researchers develop ways to prevent or treat these hemangioblastomas. One possibility is that hemangioblastomas develop from a special kind of embryonic cell called a hemangioblast. This multipotent stem cell—a continuously dividing cell that can develop (differentiate) into several nondividing cell types—is the source of blood cells and blood vessel cells in the embryo. In this study, the researchers have examined tumor cells (so-called neoplastic stromal cells) taken from hemangioblastomas to see whether this theory is correct.
What Did the Researchers Do and Find?
The researchers obtained several CNS hemangioblastomas from patients with VHL disease and stained slices of them with antibodies that stick to proteins made only by specific types of embryonic cells. This experiment showed that the neoplastic stromal cells in the tumors contained two proteins (brachyury and Flk-1) that mark hemangioblast cells in embryos and a protein called Scl that is required for blood cell formation. The neoplastic stromal cells also made several proteins expressed by the precursors of different blood cell types. When the researchers grew neoplastic stromal cells from the hemangioblastomas in different conditions, they found that the cells differentiated into the precursors of two types of blood cell (erythrocytes and granulocytes) and of the cells that line blood vessels (endothelial cells). The researchers confirmed that these precursors had arisen from the neoplastic cells in the hemangioblastomas by showing that they did not contain a normal copy of the VHL gene.
What Do These Findings Mean?
These findings indicate that the neoplastic stromal cells in CNS hemangioblastomas in patients with VHL disease are indeed hemangioblasts. Their expression of the protein brachyury, which is normally only expressed in early development, suggests that these hemangioblasts were arrested during embryogenesis, possibly when they lost their normal VHL gene. Because VHL-related tumors usually appear in adulthood, circulating factors such as hormones might promote the growth of these pre-existing but dormant tumor cells at specific stages of life. Furthermore, the expression of Scl in the neoplastic stromal cells suggests that the specific pattern of hemangioblastomas in VHL disease is determined during development since Scl is transiently expressed in hemangioblasts in the parts of the developing brain that subsequently harbor hemangioblastomas. Because the researchers only examined VHL-associated hemangioblastomas, their findings do not explain the origin of hemangioblastomas in patients without VHL disease or the origin of VHL-associated malignant tumors. However, the identification of hemangioblasts as the source of hemangioblastomas in VHL disease suggests that it might be possible to treat these tumors by persuading the hemangioblasts to differentiate or by using their unique proteins to target toxic drugs to hemangioblastomas.
Please access these Web sites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.0040060.
VHL Family Alliance has information for patients and physicians on VHL disease
The US National Institute of Neurological Disorders and Stroke Web site contains information on VHL disease
Wikipedia carries pages on VHL disease (note that Wikipedia is a free online encyclopedia that anyone can edit)
The Online Mendelian Inheritance in Man (OMIM) site has detailed scientific information on VHL disease