Using CXCR4 to Make Stem Cells Stay Put: Regenerating Intervertebral Discs

The migration of several different types of stem cells is regulated by a receptor called “CXCR4” and the molecule that binds to this receptor, SDF-1. SDF-1 is a powerful summoner of white blood cells. During early development, SDF-1 mediates the migration of hematopoietic cells from fetal liver to bone marrow and plays a role in the formation of large blood vessels. During adult hood, SDF-1 plays an important role in making new blood vessels by recruiting endothelial progenitor cells (EPCs) from the bone marrow. Consequently, SDF-1 has a role in tumor metastasis where cancer cells that express the receptor CXCR4 are attracted to metastasis target tissues that release SDF-1. SDF-1 also attracts mesenchymal stem cells and helps them suppress the breakdown of bone.

Hopefully, I have convinced you that SDF-1 and its receptor CXC4 are important molecules. Can overexpression the CXCR4 receptor improve the retention of stem cells within an injured tissue?

Xiao-Tao Wu and Feng Wang from Zhongda Hospital in Nanjing, China and their colleagues have used this CXCR4 receptor/SDF-1 system to test this question in the damaged spinal cord.  This work was published in the journal DNA and Cell Biology (doi:10.1089/dna.2015.3118).

Isolated MSCs were treated with genetically engineered viruses to so that would overexpress the CXCR4 receptor. In order to track these cells under medical imaging scans, the MSCs were also labeled with superparamagnetic iron oxide (SPIO). Next, rabbits that had suffered injuries to their intervertebral discs that lie between the vertebrae were given infusions of these labeled, genetically engineered MSCs. Images of the spine were taken at 0, 8, and 16 weeks after the surgery. The degeneration of the damaged intervertebral discs were also evaluated by disc height (damaged, degenerating intervertebral discs tend to shrink and lose height).

The SPIO-labeled CXCR4-MSC could be detected within the intervertebral discs by MRI 16 weeks post-transplantation. The MSCs that had been engineered to overexpress CXCR4 showed better retention within the discs, relative to implanted MSCs that had not been engineered to overexpress CXCR4.

Did the implanted MSCs affect the integrity of the intervertebral discs? Indeed they did. Compared to the control group, loss of disc height was slowed in the animals that received the CXCR4-overexpressing MSCs. Also, the genetically engineered MSCs seemed to make more cartilage-specific materials, like the giant molecule aggrecan and type II collagen. There is a caveat here, since there is no indication that measured protein directly; only mRNAs. Until the quantities of these molecules can be directly shown to increase in the disc, the increases in these cartilage-building molecules can be said to be presumptive, but not proven.

From these experiments, it seems reasonable to conclude that CXCR4 overexpression promoted MSC retention within the damaged intervertebral discs and the increased stem cell retention enhanced stem cell-based disc regeneration. Therefore this SDF-1/CXCR4 signaling pathway might be a way to drive stem cell migration and infiltration within degenerated intervertebral discs.

Hair Loss Cure Isn’t Here Yet, But Experimental Stem Cell Approach Looks Promising

While a cure for hair loss is some years away, a California research team has brought us much closer that such a treatment becoming a reality. Hair loss, a condition that affects 50 million men and 30 million women in the U.S. alone, might fall to stem cell treatments some day.

Dr. Alexey Terskikh led the team from the Sanford-Burnham Medical Research Institute in La Jolla, California that showed that stem cells derived from human skin can be used to grow hair in mice.

“The method is a marked improvement over current methods that rely on transplanting existing hair follicles from one part of the head to another,” Dr. Terskikh, who serves as an associate professor at the institute. “Our stem cell method provides an unlimited source of cells from the patient for transplantation and isn’t limited by the availability of existing hair follicles.”

Conventional hair transplantation and other hair restoration treatments that are presently in use must use whatever hair the patient has left. However a stem cell-based procedure could, in theory, grow all kinds of hair on the heads of completely bald men and women.

“If this approach is proven to work in humans, it will change existing treatments radically,” Dr. Nicole Rogers, a dermatologist and hair transplant surgeon in New Orleans, told The Huffington Post in an email.

Dr. Marie Jhin, a dermatologist in San Francisco and an adjunct clinical instructor at Stanford University, feels the same way about Terskikh’s results. If this treatment pans out, she said that it “absolutely would be a breakthrough.”

Rogers, however, tempered her excitement by advising caution and skepticism, since there have been many “fits and starts” over the years in the hair-restoration field. Rogers added that the Sanford-Burnham group must face many challenges in order to replicate their results in large-scale human trials.

The technique exploits the ability of human pluripotent stem cells to differentiate into almost any other adult cell type in the body. Terskikh and his collaborators differentiated induced pluripotent stem cells made from reprogrammed skin cells into the dermal papilla cells that regulate the formation and growth of hair follicles. Furthermore, when they injected these cells into the lower layers of the skin of mice, they grew hair.

Close-up photograph showing new hair growth | Sanford-Burnham Medical Research Institute
Close-up photograph showing new hair growth | Sanford-Burnham Medical Research Institute

Human dermal papilla cells are unsuitable for conventional hair transplants because quickly lose their hair-growing potency and cannot be obtained in necessary numbers for clinical purposes.

Terskikh wisely did not prognosticate when they would be able to extend their protocol to treat hairless humans. The next step, according to Terskikh is to secure a partner to fund future research into this area.

New Stem Cell Technology to Form Blood Vessels and Treat Peripheral Artery Disease

How to make new blood vessels for patients who need them? Researchers at the University of Indiana University School of Medicine have developed a new therapy for illnesses such as peripheral artery disease. Diseases such a peripheral artery disease can lead to skin problems, gangrene and sometimes amputation.

Our bodies have the ability to repair blood vessels and creating new ones, because of a cell type called “endothelial colony-forming cells.” Unfortunately, these cells tend to lose their ability to proliferate and form new blood vessels as patients age or develop diseases like peripheral arterial disease, according to Mervin C. Yoder Jr., M.D., who is the Richard and Pauline Klingler Professor of Pediatrics at IU and leader of the research team.

Physicians can prescribe drugs that improve blood flow to patients with peripheral artery disease, but if the blood vessels are reduced in number or function, the benefits from such drugs are minimal. A better treatment might be to introduce “younger,” more effective endothelial colony forming into the affected tissues. In this case, such a treatment would jump-start the creation of new blood vessels. Gathering such cells, however is rather difficult, since endothelial colony-forming cells are somewhat difficult to find in adults, especially in those with peripheral arterial disease. Fortunately, endothelial colony-forming cells are rather numerous in umbilical cord blood.

Yoder and his colleagues published their work in the journal Nature Biotechnology, and they have reported that they have developed a potential therapy by using patient-specific induced pluripotent stem cells (iPSCs). Induced pluripotent stem cells are pluripotent stem cells that are derived from normal adult cells by means of genetic engineering and cell culture techniques. Once an iPSC line has been derived from a patient, they can potentially be differentiated into any adult cells type, including endothelial colony-forming cells.

In this paper, Yoder and his research team developed a novel methodology to differentiate iPSCs into cells with the characteristics of the endothelial colony-forming cells that are found in umbilical cord blood. These laboratory-generated endothelial colony-forming cells were injected into mice, and they proliferated and generated human blood vessels that nicely restored blood flow to damaged tissues in mouse retinas and limbs

Another problem addressed in this paper was growing endothelial colony-forming cells from umbilical cord in culture so that they can achieve sufficient numbers for therapies. In this paper, Yoder and his team designed a cell culture system that was able to dramatically expand these iPSC-derived endothelial colony-forming cells in culture from one founding cell to 100 million new cells in a little less than three months.

“This is one of the first studies using induced pluripotent stem cells that has [sic] been able to produce new cells in clinically relevant numbers — enough to enable a clinical trial,” Dr. Yoder said. According to Yoder, the next steps will be to reach solidify an agreement with a facility approved to produce cells for use in human testing. Additionally, Yoder would like to treat more than just peripheral artery disease, since he and his colleagues are evaluating the potential uses of these cells to treat diseases of the eye and lungs that involve blood flow problems.

Stem Cell Treatment for Degenerative Disc Disease

A new analysis of stem cell trials that targeted degenerative disc disease of the spine in animals has shown that these treatments are effective in halting or even reversing this disease. Such results should facilitate the implementation of human clinical trials.

Our spinal cords are encased in a protective body of bone known as the vertebral column. The vertebral column consists of a stack of vertebral bodies that are positioned with one vertebra one on top of the other. Between each pair of vertebral bodies is a cushion-like structure known as the intervertebral disc. The intervertebral disc absorbs the stress and shock placed on the vertebral column when someone walks, runs, moves, bends, or twists. The discs prevent the vertebral bodies from grinding against each other.

Vertebral column

Structurally, the intervertebral discs are unique. They have no blood supply of their own, and are, as a matter of fact, the largest structures in the body without their own blood vessel system. Instead they absorb the nutrients they need from circulating blood by means of osmosis.

Each intervertebral disc is composed of two parts: an outer annulus fibrosus (fibrous ring) and the nucleus pulposus (pulpy interior). The annulus fibrosus is a ring-like structure that completely encases the nucleus pulposus. It is composed of water and strong elastic collagen fibers bound together by glue-like material called proteoglycan. The arrangement of these collagen fibers at varying angles relative to each other makes the annulus fibrosus a rather strong structure. The annulus fibrous stabilizes the intervertebral disc and helps the spine can rotate properly and resist compression or other stresses placed on the spine.

The center portion of the intervertebral disc that is protected by the annulus fibrosus is a gel-like elastic substance called nucleus pulposus. The nucleus pulposus transmits and transfers stress and weight placed on vertebrae during movement and activity. The nucleus pulposus is made of the same basic materials as the nucleus fibrosus: water, collagen, and proteoglycans. The main difference between the ring-like annulus fibrosus and the gel-like nucleus pulposus is the relative amounts of these substances. The nucleus pulposus contains more water than the annulus fibrosus.

Intervertebral disc structure

Recent developments in stem cell research have made it possible to measure the effects of stem cells treatments on intervertebral disc height. Researchers at the Mayo Clinic in Rochester, Minnesota have pioneered such techniques.

In preclinical animal studies, stem cell treatments have been used to treat animals with degenerative disc disease. Because degenerative disc disease can great affect someone’s quality of life and productivity, such a treatment has been highly sought after.

Wenchun Qu, MD, PhD, of the Mayo Clinic in Rochester, Minn said that stem cell injections into degenerating intervertebral discs not only increased disc height, but also increased disc water content and improved the expressed of particular genes. “These exciting developments place us in a position to prepare for translation of stem cell therapy for degenerative disc disease into clinical trials,” said Qu.

Animals that had received stem cell injections into their intervertebral discs had a disc structure that was large restored. The nucleus pulposus showed an increased water content and improved abilities to transfer shear forces.

In their analysis, Qu and his colleagues examined six preclinical trials and only examined those studies that were randomized and properly controlled. Because of various methodological differences between these studies, Qu and his gang used a random-effects model to analyze the data. Random-effects models, put simply, put all the animals in a group of studies together and assumes that they can be placed in a hierarchy of those who are the sickest to those who are the least sick. By placing the individuals in a hierarchy like this they can be classified accordingly and the effects of their treatments assessed fairly.

When properly and rigorously analyzed, the intervertebral disc height increases were significant in all six studies.  What they found was an over 23.6% increase in the disc height index in the transplant group compared with the placebo group (95% confidence interval [CI], 19.7-23.5; p < 0.001). None of the 6 studies showed a decrease of the disc height index in the transplant group. Increases in the disc height index were statistically significant in all individual studies.

On the strength of these preclinical studies, Qu and his colleagues think that it is time to determine the safety, feasibility, and efficacy of stem cell transplants for degenerative disc disease in human patients.

Because intervertebral discs show such poor regenerative capabilities, degenerative disc disease is an excellent candidate for stem cell treatments. Also, present treatments tend to be very invasive and often make the disc worse.