In the laboratory, stem cells can grow in liquid culture quite well in many cases, but this type of culture system, though convenient and rather inexpensive, does not recapitulate the milieu in which stem cells normally grow inside our bodies. Inside our bodies, stem cells stick to all kinds of surfaces and interact with and move over a host of complex molecules. Many of the molecules that stem cells contact have profound influences over their behaviors. Therefore, reconstituting or approximating these environments in the laboratory is important even though it is very difficult.
Fortunately nanotechnology is providing ways to build surfaces that approximate the kinds of surfaces stem cells encounter in our bodies. While this field is still in its infancy, stem cell-based nanotechnology may provide strategies to synthesize biologically relevant surfaces for stem cell growth, differentiation, and culture.
One recent contribution to this approach comes from Jihui Zhou and his team from the Fifth Hospital Affiliated to Qiqihar Medical University. Zhou and his co-workers prepared randomly oriented collagen nanofiber scaffolds by spinning them with an electronic device. Collagen is a long, fibrous protein that is found in tendons, ligaments, skin, basement membranes (the substratum upon which sheets of cells sit), bones, and is also abundant in cornea, blood vessels, cartilage, intervertebral disc, muscles, and the digestive tract. Collagen is extremely abundant in the human body; some 30% of all the proteins in our bodies are collagen. It is the main component in connective tissues.
There are many different types of collagen. Some types of collagen form fibers, while others for sheets. There are twenty-eight different types of collagen. Mutations in the genes that encode collagens cause several well-known genetic diseases. For example, mutations in collagen I cause osteogenesis imperfecta, the disease made famous by the Bruce Willis/Samuel T. Jackson movie, “Unbreakable.” Mutations in Collagen IV cause Alport syndrome, and mutations in either collagen III or V cause Ehlers-Danlos Syndrome.
Wen cells make fibrous collagen, they weave three collagen polypeptides together to form a triple helix protein that is also heavily crosslinked. This gives collagen its tremendous tensile strength.
In this experiment, electronic spinning technology made the collagen fibers and these fibers had a high swelling ratio when placed in water, high pore size, and very good mechanical properties.
Zhou grew neural stem cells from spinal cord on these nanofiber scaffolds and the proliferation of the neural stem cells was enhanced as was cell survival. Those genes that increase cell proliferation (cyclin D1 and cyclin-dependent kinase 2) were increased, as was those genes that prevent cells from dying (Bcl-2). Likewise, the expression of genes that cause cells to die (caspase-3 and Bax) decreased.
Thus novel nanofiber scaffolds could promote the proliferation of spinal cord-derived neural stem cells and inhibit programmed cell death without inducing differentiation of the stem cells. These scaffolds do this by inducing the expression of proliferation- and survival-promoting genes.