Spontaneous injuries, such as losing a limb or spinal cord damage, cannot be healed by humans. However, some animals possess remarkable abilities to regenerate after injuries, which relies on a specific sequence of cellular activities. Recent research has identified an important timing factor—specifically the duration for which cells respond to injury—that plays a role in regulating this regeneration process. This research not only enhances our understanding of the evolutionary aspects of regeneration but also opens doors for new therapeutic methods in regenerative medicine.
Injuries like losing a limb or spinal cord damage are things that humans cannot repair. On the other hand, certain animals can regenerate remarkably well after sustaining injuries, a process that depends on a precise series of cellular events. Recent research from the Stowers Institute for Medical Research has revealed an important timing factor – namely, how long cells actively respond to injury – that is significant for governing regeneration.
A study featured in iScience on September 20, 2024, aimed to investigate how an organism determines the extent of tissue loss due to injury. The study, led by former Predoctoral Researcher Augusto Ortega Granillo, Ph.D., in the lab of Stowers’ President and Chief Scientific Officer Alejandro Sánchez Alvarado, Ph.D., focused on the African killifish’s ability to effectively regrow its tail fin after it has been damaged. The researchers examined tissue dynamics as the fin regrew and discovered that beyond known factors, such as the number and location of contributing cells, the duration of time that cells engage in the repair process is also crucial.
“One of regeneration’s biggest mysteries is how organisms identify what has been lost after an injury,” remarked Sánchez Alvarado. “In essence, this research introduces a new variable into the regeneration equation. If we can manage the speed and duration of a tissue’s regenerative response, it may lead to therapies that can activate or potentially extend the regenerative capabilities of tissues that usually do not regenerate.”
After an injury to a killifish’s tail, the remaining tissue must quickly gauge the extent of the damage. Following this, it must recruit the appropriate number of repair cells for the necessary period. The processes of damage detection, cell recruitment, and appropriate timing need to work together for the tail to regrow successfully.
“When an animal capable of regenerating parts, like a tail, loses just a small section, how does it know to regenerate only that missing piece instead of a whole new tail?” Sánchez Alvarado asked. To explore this question, the research team analyzed various areas of injury on the killifish tail fin.
The study found that skin cells near the injury as well as those in far-off, unaffected regions activate a genetic program that gets the entire organism ready for a repair response. Subsequently, the skin cells at the injury site maintain this response and briefly alter their state to modify the surrounding structure known as the extracellular matrix. Ortega Granillo compares this matrix to a sponge that collects signals released by the injured tissue, guiding the repair cells to start their work. If these signals fail to be transmitted or understood properly, the tail may not regenerate to its original shape and size.
“We distinctly identified when and where – specifically at 24 hours after the injury and within the extracellular matrix – the temporary cell state operates in the fin tissue,” said Ortega Granillo. “Knowing exactly where and when to focus our efforts allowed us to make genetic modifications and improve our understanding of these cell states’ functions during regeneration.”
To determine if these unique cellular states transmit information to the extracellular matrix during the repair process, the researchers utilized the CRISPR-Cas9 gene editing technique. They specifically targeted a gene known to alter the extracellular matrix because they had noted its activation at the beginning of the regeneration response. By disrupting the functionality of this gene, the researchers sought to clarify its role in conveying information from the cells to the matrix during the regeneration phase.
“These altered animals lost the ability to gauge how much tissue was lost,” Ortega Granillo explained. “Although they still regenerated, the rate of tissue growth was inadequate. This implies that by altering the extracellular environment, skin cells communicate to the tissue how much has been lost and how quickly it should regenerate.”
The observed rate and amount of tissue regrowth in these genetically modified killifish increased whether the tail injury was minor or major. This suggests that the cell states affecting the matrix enhance the rejuvenation of tissue growth. If we could adjust these cell states, it might lead to stimulating a stronger regenerative response.
From an evolutionary standpoint, understanding why certain organisms are highly efficient at regeneration while others like humans have constrained regenerative abilities is a central focus in regenerative biology. Researchers aspire to extract general principles from organisms with robust regenerative capacities to potentially enhance regeneration in humans. This comparative approach not only illuminates the evolutionary components of regeneration but also presents opportunities for innovative therapeutic strategies in regenerative medicine.
“Our objective is to learn how to shape and develop tissues,” Ortega Granillo stated. “For individuals who suffer from injuries or organ failures, regenerative therapies could restore functionality that has been compromised due to illness or injury.”
Additional contributors to the study include Daniel Zamora, Robert Schnittker, Allison Scott, Alessia Spluga, Jonathon Russell, Carolyn Brewster, Eric Ross, Daniel Acheampong, Ning Zhang, Ph.D., Kevin Ferro, Ph.D., Jason Morrison, Boris Rubinstein, Ph.D., Anoja Perera, and Wei Wang, Ph.D.
This research was supported by institutional funding from the Stowers Institute for Medical Research and the Howard Hughes Medical Institute.
