Timing of regenerative cues may be key to better healing from injury

For decades, medicine has chased a simple but elusive goal of delivering the right drug to the right place at the right time. New research from the University of Oregon suggests that when it comes to healing from injury, the timing of regenerative cues might be even more important than previously realized. 

The findings suggest a possible explanation for why some regenerative therapies underperform in the clinic despite success in the lab: They may be delivering the right regenerative cues in the wrong order. The research also demonstrates a way to precisely control the rate at which regenerative cues are released. That could someday help doctors better treat complex injuries that require multiple treatments delivered in a specific order to mimic the body's natural healing process.

In two studies published recently in Biomacromolecules and the Journal of Controlled Release, scientists at the Phil and Penny Knight Campus for Accelerating Scientific Impact showed that releasing specialized tissue repair signals in a staggered sequence led to better blood vessel regeneration, compared to releasing them all at once.

Through a staggered release, we've actually learned more about the order in which these signals act during the regeneration process, and how that timing contributes to better healing. This might help explain why some promising therapies haven't lived up to their potential in patients. For future patients, getting the timing right could be just as important as getting the biological signals right."

Marian Hettiaratchi, Lary Simpson Professor and associate professor in the department of bioengineering

The team's approach relies on affibodies, engineered proteins that work like antibodies but are roughly ten times smaller. Unlike natural antibodies, which evolve to recognize foreign invaders such as viruses, affibodies can be designed from scratch to bind nearly any target. In this case, they bind to the biological signals, or growth factors, that direct tissue repair.

Hettiaratchi's lab designed affibodies to hold onto specific regenerative cues, called growth factors, temporarily blocking their activity. Depending on how tightly an affibody grips its target, the growth factor is released at a different rate, and becomes biologically active anywhere from minutes to days later.

Building affibodies with precisely tuned binding strength fell to graduate student Justin Svendsen, a biochemist with a talent for computational modeling. Svendsen used computer models to design affibodies targeting growth factors involved in blood vessel formation, then validated their specificity in the lab. He then used the same computational approach to predict how small genetic mutations would change an affibody's release rate, screening hundreds of candidate designs on a computer before testing any of them at the bench.

"We're essentially creating molecular timers," Svendsen said. "By introducing a single mutation, we can program an affibody to release its target growth factor over minutes, hours, or even days."

That first study, published in Biomacromolecules, established that a single genetic mutation could shift an affibody's release timeline from minutes to as long as seven days, proof that computational design could reliably tune protein behavior before a single experiment was run in the lab.

The second study, published in the Journal of Controlled Release with co-author Chandler Asnes, scaled the approach from one growth factor to three, all involved in regenerating blood vessels. Through swapping in different affibodies, each tuned to release its target on a different schedule, the researchers could deliver the three growth factors in any order they chose.

Blood vessel regeneration was measurably worse when all three growth factors were released simultaneously than when they were released in a staggered sequence. The researchers suspect this is because growth factors are highly context-dependent, the same molecule can promote new blood vessel growth in one setting and trigger existing vessels to regress in another.

The approach could extend well beyond blood vessel repair, the researchers say. Because affibody design is largely computational, new candidates can be modeled and screened far faster than through lab-only methods, a pipeline the Hettiaratchi lab is now applying to bone healing, muscle repair, and spinal cord regeneration.

"It could revolutionize how we approach injuries that require multiple therapeutic interventions delivered with the precision," Hettiaratchi said.

Svendsen said the team sees potential across a wide range of injury types. "We're excited about applying this across tissue and cell types," he said. "We think the applications could stretch from sports injuries to far more serious medical conditions."