In the body, neural stem cells are found near blood vessels in the subventricular zone, the hippocampus, and the songbird higher vocal center. The cells in the ventricular zone release vascular endothelial growth factor (VEGF). Because blood vessel growth is attracted to VEGF, the vascular cells are near the central nervous system germinal zones. Scientists have suggested these cells provide a neural stem cell niche.
In order to investigate the relationship between the neural stem cells and vascular cells, researchers in the Center for Neuropharmacology and Neuroscience, the Center for Cardiovascular Sciences, and the Center for Cell Biology and Cancer Research at Albany Medical College cocultured vascular cells and neural stem cells. In transwell plates, mouse neural stem cells were seeded in the well bases and vascular type cells were seeded in the upper compartment of the wells. Various types of vascular cells were studied, including primary bovine pulmonary artery endothelial (BPAE) cells, vascular smooth muscle (VSM) cells, mouse brain endothelial (MbEND) cells, and NIH3T3 fibroblasts. High-density, age-matched cortical cells (CTX) were used as controls.
When BPAE and MbEND cells were used in the upper compartments, the endothelial cells were not found in the lower cells because they could not fit and migrate through the pores. Within one day of cell seeding, the neural stem cells cultured with the control, CTX, started creating neurons. The neuron growth was mostly in glial lineages. However, cells cultured with BPAE or MbEND grew into sheets of flattened progeny. Stem cells cultured with endothelial cells produce fewer neurons and larger stem cells, as compared to cells grown with CTX. Researchers concluded that endothelial cells aid in expansion of neural stem cells, but inhibit cell differentiation. VSM and NIH3T3 cells were also found to promote stem cell proliferation.
After researchers removed the transwell inserts, endothelial-expanded stem cells proliferated and differentiated. Approximately 31% of the progeny produced were neurons, while only 9% of stem cells cultured with CTX were neurons. Neural stem cells cocultured with BPAE contained as much as 64% neurons. However, neurogenesis was reduced in the stem cells cultured with VSM or NIH3T3 cells. Therefore, endothelial cells’ affect on neurogenesis in neural stem cells depends on the cell type and is not universal across all endothelial cells.
Scientists also found that endothelial cells activate proliferation and neurogenesis of neural stem cells in a variety of areas in the central nervous system (CNS). Another type of stem cells, neurosphere-expanded stem cells, was also influenced by endothelial cells. When exposed to the endothelial cells, neurosphere-expanded stem cells created 22% neurons, compared to 2% neuron production in control cells and CTX.
In the body, most neurons are produced in the early embryonic stage, but interneurons and glia arrive later, typically in adult stem cells. Stem cells were cocultured with endothelial cells and stained for glutamic acid decarboxylase, an interneuron marker, or Tbr1, an early neuron marker that labels projection neurons. Endothelial cell coculture produced more projection neuron and interneuron markers than the controls. Additional signaling experiments also demonstrated that endothelial cell and neural stem cell coculture activated the signaling molecules, Notch and Hes1, which promote neural stem cell self-renewal.
Through this research, scientists demonstrated that endothelial cells release some type of factors that maintain central nervous system stem self renewal and neurogenesis. In the presence of these endothelial cells, neural stem cells undergo proliferation to produce sheets of undifferentiated stem cells that can generate neurons, astrocytes, and oligodendroctyes. The growth of stem cells in the presence of endothelial cells may be important for neuron replacement therapies. If researchers can isolate the secreted factors from endothelial cells that cause neurogenesis and capture it in a drug, patients that have lost nerve function may be able to regrow their own neurons through neural stem cell self-renewal and neurogenesis.
Other neural stem cell marker: MAP2, Brn2 ,PAX6