Increased Protein Expression May Improve Healing in Patients with Diabetes

A new study shows that activating bone stem cells can initiate fracture repair in mice models of diabetes.

Adding a protein to the fracture was found to increase signaling proteins, which resulted in more optimal healing, according to the study, published by Translational Medicine. These findings could have important implications for human patients with diabetes who also have slowed fracture healing.

The investigators discovered that applying the protein increased stem cell activity among mice models and in bone samples from human patients with diabetes.

“We’ve uncovered the reason why some patients with diabetes don’t heal well from fractures, and we’ve come up with a solution that can be locally applied during surgery to repair the break,” said senior author Michael Longaker, MD. “Diabetes is rampant worldwide, and any improvement in the ability of affected people to heal from fractures could have an enormously positive effect on their quality of life.”

In addition to poor blood glucose control, patients with diabetes experience slowed healing from soft tissue injuries and fractures. However, the mechanism behind this phenomenon is currently unknown.

The current study was based on prior research where the group of investigators discovered and assessed skeletal stem cells in the bones of mice. These stem cells can mature into bone, cartilage, and the stroma. The investigators found that fracture healing was slowed in mice whose stem cells were removed.

“We wanted to apply what we knew about skeletal stem cells to the problem of impaired bone healing in people with diabetes,” said senior author Charles Chan, PhD. “Does the disease affect fracture healing by somehow modulating the activity of these stem cells?”

In the current study, the researchers used a mouse model of type 2 diabetes. During pre-diabetes, mice were able to heal fractures similarly to wild-type mice, but once they developed diabetes, the repaired bone was weaker and less dense compared with the control group, according to the study.

After 7 days of healing, mice with diabetes had significantly less skeletal stem cells, compared with the control group. The researchers ruled out systemic reasons for this discovery, and hypothesized that cell signaling may be the issue.

When testing this hypothesis, the investigators found that mice with diabetes had significantly lower expression of the hedgehog family of proteins. This group of signaling proteins are known to play a critical role in biologic processes, including tissue regeneration, according to the study.

Upon further testing, the researchers discovered that control mice whose hedgehog signaling pathway was inhibited had weaker and brittle bone regrowth similar to mice with diabetes. The investigators then created a hydrogel that was laced with hedgehog signaling proteins.

“Next we had to test whether adding the hedgehog signaling proteins back into the local environment in diabetic animals restored their ability to heal fractures,” Dr Longaker said. “And these animals healed just like normal mice.”

Lastly, the researchers conducted a similar trial in human bone samples from patients with diabetes who underwent surgery for osteoarthritis. The expression of proteins in these samples were then compared with samples from patients without diabetes.

“What we saw in these human samples completely echoed what we saw in the mice,” Dr Chan said. “The bones from the diabetic patients displayed significantly reduced expression of these important signaling proteins.”

From these findings, the investigators hypothesized that the inhibition of this pathway is caused by inflammation that increased TNF-alpha expression, which is known to be high in humans, as well as mouse models of the disease.

The researchers found that increased TNF-alpha expression was attributed to the low expression of certain hedgehog proteins. However, inhibiting TNF-alpha may have severe biologic consequences, according to the study.

“Here we’ve devised a feasible strategy for reversing a tissue-specific pathology — the inability to heal skeletal fractures efficiently — in a complex metabolic disease like diabetes, through the local application of a compound to stimulate the activity of adult stem cells,” Dr Longaker said. “We anticipate that hedgehog-mediated molecular therapies that directly target stem cells in human patients could be therapeutic.”

Although additional research is necessary, the researchers believe that the local application of hedgehog proteins will be safe and effective in humans. These new findings also highlight the importance of stem cells in tissue regeneration, according to the study.

“This research represents a significant step forward toward realizing the promise of Proposition 71, which established the California Institute for Regenerative Medicine,” Dr Chan concluded. “We’ve looked to stem cells to learn why people with diabetes don’t heal bone fractures properly, and come up with an approach that we are excited to try in the clinic."