The overall goal of this protocol is to establish primary mixed glial cultures from adult mouse spinal cords for in vitro studies. This method provides us an in vitro system to investigate the roles of glial cells in neurological diseases that involve pathological changes within the spinal cord, such as neuropathic pain and multiple sclerosis. The main advantage of this technique is that the glial cultures are prepared from adult mouse spinal cord, providing a system that is more accurately reflecting the in vivo conditions.
Demonstrating the procedure will be Jennifer Malon, a technician from my laboratory. Working in a tissue culture hood, transfer four mouse spinal cords into a petri dish of HBSS. Use sterile scissors and forceps to cut each of the spinal cords into small pieces.
Then, transfer the pieces to a 50 millimeter conical tube containing Papain DNAse enzyme mixture. Avoid transferring HBSS to the enzyme mixture, as this may result in decreased performance of the enzyme. It is crucial that tissue pieces are well digested to obtain a single cell suspension.
However, over digestion will result in fewer viable cells. Each lab needs to perform pilot tests to determine the exact digestion time based on what works best for their cells. Next, gently vortex the tube and then incubate at 37 degrees Celsius for one hour with orbital shaking at 150 rotations per minute.
Following the incubation, vortex the tube, and then vigorously triturate the tissue using a five milliliter pipet to promote further dissociation. Then, transfer the cell suspension into a 15 milliliter tube and centrifuge for 300 x g for five minutes at room temperature. During the centrifugation, at 300 microliters of reconstituted albumin ovomucoid inhibitor solution to 2.7 milliliters of ABSS in a sterile tube and mix well.
Then add 150 microliters of DNAse solution. Following the centifugation, remove the supernatant, and resuspend the cell pellet in the freshly prepared albumin ovomucoid inhibitor and DNAse solution. Vortex well to break the cell pellet.
Then, add three milliliters of reconstituted albumin ovomucoid inhibitor solution, without DNAse, to the cell suspension. Centrifuge the cells at 70 x g for six minutes at room temperature. After the spin, remove the supernatant, which contains membrane fragments, and retain the pellet.
To remove myelin from the dissociated spinal cord cells, first add eight milliliters of room temperature 20%gradient density medium into the tube containing the cell pellet and vortex gently. Next, centrifuge the cells at 800 x g for 30 minutes at room temperature without breaking. Following centrifugation, carefully aspirate the top layer of debris, which contains mostly myelin and the supernatant, leaving the pellet.
To remove any remaining density gradient, wash the cells by resuspending the pellet with eight milliliters of cDMEM diluted with HBSS. Centrifuge the cells at 400g for 10 minutes at four degrees Celsius. Remove the supernatant, and wash the cells with diluted cDMEM as before.
After removing the supernatant, the pellet can be stored on ice until seeding the cells. Once ready for plating, resuspend the cells in 14 milliliters of cDMEM, supplemented with 2-Mercaptoethanol. And add one milliliter of the cell suspension to each well in a 12 well plate.
Plate extra wells that can be used to determine the average cell number per well and the microglial content of the culture. Once the cells have been plated, incubate the cells at 35.9 degrees Celsius with 5%carbon dioxide. Change the medium on day 1, which is the day after plating.
Some cells are attached to the culture plate, but they are still mostly round. There are also many floating cells and significant debris. Repeat the media change three to four days thereafter until the cells are ready for treatment between days 12 and 14.
Mixed glial cells from adult C57 black six mice were cultured at either 37 degrees Celsius or 35.9 degrees Celsius and analyzed via flow cytometry. As you can see, there is no obvious difference in the total cell populations at these temperatures. These representative plots show the CD45 positive CD11b positive microglia populations isolated from the total cell populations previously shown.
This figure demonstrates that a higher microglial content can be obtained when mixed glia are cultured at 35.9 degrees Celsius, instead of 37 degrees Celsius. Adult spinal cord, mixed glial cultures were prepared from C67 black six mice. Representative images of the cultured cells at days one, four, eight, and 12 are shown.
Images showing the typical progress of the culture, as well as demonstrating the importance of media, change at day one post-culture establishment. Once mastered, the initial set up of mixed glia cell culture can be completed in about four hours, if performed properly. Following the establishment of mixed glia culture, microglia depleted, and microglia enriched cultures, can be obtained from this initial mixed population.
However, the yield of microglia enriched cells will be limited unless large number of spinal cords are used to establish cultures. This technique was initially designed to investigate the roles of glial cells during the development of neuropathic pain. However, it can be used to study other neurological diseases that involve pathological changes within the adult spinal cord.
