Astrocyte Generation

Glial cells constitute approximately half of the cells in the human brain. As the largest population of glial cells, astrocytes are crucial for the survival and function of neurons. Defects in astrocyte generation are associated with severe neurological disorders including gliomas, the most common primary brain tumor. The rapid growth of the rodent brain during the early postnatal period is accompanied by a 4-fold increase in blood vessel density, in parallel with a 6- to 8-fold increase in glial cell population, which predominantly contains astrocytes.

So far, little is known about the cellular and molecular mechanisms of astrocyte generation in the postnatal brain. In the short term, we will study the molecular mechanisms that are responsible for the local generation of astrocytes in the postnatal brain.

Video 1. Local generation of astrocytes in postnatal cortex.
This video shows local division of astrocytes in an acutely isolated cortical slice (cortical layers I-IV) from a P3 hGFAP-GFP transgenic mouse. Total time of the full-length video is 2 hours, 46 minutes. This segment shows approximately 5 seconds of division activity, repeating to show the activity twice. Three astrocytes enter the cell cycle and divide. See details in Ge et al., Nature 484, 376-380. (PubMed). Click image to play video.

Formation of Gliovascular Interface

Astrocytic endfeet and brain vasculature form an intricate structure called the gliovascular interface, which is critical for the transport of glucose from the blood to neurons, the regulation of cerebral blood flow, and the maintenance of the blood-brain barrier. Detachment of astrocytic endfeet from the vascular membrane is responsible for brain edema and results in neurodegeneration. Thus, the ability to restore its function after stroke is of the utmost importance for improving functional brain recovery in patients.

Unfortunately, how the gliovascular interface forms and develops is unclear. We will study the cellular and molecular mechanisms for interactions between brain vasculature and astrocytes with genetic manipulation and time-lapse slice or in vivo imaging.

Fig. 1. Astrocytic endfeet.
Figure 2: An astrocyte forms endfeet with blood vessels (purple)
A single astrocyte (green, GFP fluorescence) forms two endfeet (white arrows) with blood vessels in the cerebral cortex. Blood vessels are labeled by antibodies against Laminin (purple). Click image to enlarge.
Fig. 2. Gliovascular interface formation.
Our model for gliovascular interface (endfoot) formation
Astrocytes are generated from radial glial cells in the ventricular zone (VZ), glial progenitors in the subventricular zone (SVZ). They can also be produced locally. We hypothesize that astrocytes from different sources will form endfeet with blood vessels via different mechanisms. Click image to enlarge.
Video 2. Endfoot formation.
This video shows that an astrocyte (green) forms an endfoot structure with a blood vessel. The image was taken from an acutely isolated cortical slice. Click image to play video.

Pericyte Subtypes and Their Interactions with Neurons/Astrocytes

Although pericytes are located along vessels in both the central nervous system and other organs, only the vasculature in the central nervous system is covered by astrocytic endfeet. It remains unclear whether there are subtypes of pericytes in blood vessels, and if so, what their functions are in the brain, and how different subtypes of pericytes interact with glial cells or neurons in the brain.

To answer these questions, we will introduce techniques including electrophysiology and in vivo imaging into the study of brain pericytes. The goal is to isolate pericytes from arteriole, pre-capillary, capillary, post-capillary and venule to characterize the molecular and cellular profile of pericytes from different locations.

Fig. 3. Pericytes in blood vessels.
Pericytes in blood vessels
Pericytes wrap around endothelial cells and can be found in all segments of blood vessels including capillaries (left), arterioles, and venules (right). Click image to enlarge.
Fig. 4. Whole-cell recording of pericytes.
Whole-cell recording of pericytes
We have established an electrophysiological technique to record from individual pericytes within different segments of blood vessels in acutely isolated brain slices. Click image to enlarge.

Development of New Tools

We believe that new techniques are critical for opening a new field in biomedical research. We are interested in developing new tools in the study of brain development, brain vasculature, and neurovascular/gliovascular interaction in live animals.

Video 3. Glial cells in the cerebral cortex.
This video shows migrating astrocytes (green) in acutely isolated cortical slices from an hGFAP-GFP transgenic mouse. Click image to play video.
Video 4. Glial cells in subventricular zone.
This video shows moving glial cells (green) in the subventricular zone from acutely isolated brain slices. Click image to play video.