Nanometer Scaffolds Regulate Neural Stem Cells

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.

Collagen fibers
Collagen fibers

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.

Mesenchymal Stem Cells from Diabetic Patients Show Impaired Abilities

When using a patient’s own stem cells to treat their diseases, there is a caveat to such a treatment. Things like great age, diabetes mellitus, or a heart attack can seriously compromise the quality of the patient’s stem cells.

To determine if a patient’s stem cells can potentially work under certain circumstances, it is necessary that we test them. With that in mind, Huishan Wang’s laboratory from Shenyang Northern Hospital in Liaoning, China, has extracted mesenchymal stem cells from the bone marrow of patients with type II diabetes. These bone marrow stem cells were used to treat rats that had suffered heart attacks. As a comparison, Wang and his associates used mesenchymal stem cells from the bone marrow of patients diagnosed with coronary artery disease, but not diabetes mellitus.

In these experiments, all patients were between the ages of 50 to 60 years of age, had type II diabetes for at least 10 years, previously suffered a heart attack, and had no signs of liver, kidney or infectious diseases, and no cancer. Bone marrow samples were taken from the breastbone (sternum) during coronary bypass surgery, and the mesenchymal stem cells (MSCs) were extracted from the bone marrow and grown in culture for up to three passages. Ten diabetic patients were selected and two non-diabetic patients were used as a control group.

Male rats (Sprague-Dawley rats for those who are interested) were given heart attacks and then the MSCs were injected into the heart tissue in the area of the heart scar and in the areas adjacent to the heart scar. One group of rats received injections of MSCs from the patients that had type II diabetes, the second group with MSCs from the non-diabetic patients, and a third group rats received only injections of culture medium. The rats were given shots on the drug cyclosporine to ensure that none of the mice rejected their grafted cells. Heart function was assessed with echocardiography, and the tissue was examined, post-mortem, with a “TUNEL” assay, to determine the number of dead cells in the heart, and protein expression was also determined with Western blots.

The MSCs were tested for growth characteristics in culture and gene expression patterns were assayed with microarray studies.

Wang and others found that the MSCs from diabetic patients grew noticeably slower in culture than MSCs from non-diabetic patients. Also, the gene expression profiles a few significant examples; levels of the anti-cell death protein Bcl-2 were significantly lower in MSCs from diabetics.

When it came to the heart function of rats that had received MSC injections after a heart attack, those rats that had received MSCs from diabetic patients fared far worse than those that had received the MSCs from non-diabetics. Also, hearts that had received MSCs from diabetic patients had great amounts of cell death, and expressed significantly lower amounts of growth factors, and the anti-cell death protein Bcl-2.

These data show that MSCs from diabetic patients are impaired in the proliferative ability, and in their survival. This poor survival is due to lower levels of the anti-cell death protein Bcl-2.

Bcl2 activity
Bcl2 activity

A consequence of these experiments is that autologous or self stem cell transplantations in type I diabetics will probably be unsuccessful. This means that allogeneic transplantations or transplants that use stem cells from donors who are not diabetics are a better strategy for treating diabetics.