Delivering CREB3L1 to the suture site improved tendon healing in aged rats
Delivering CREB3L1 to the suture site improved tendon healing in aged rats
In an Aging Cell article published on August 23, researchers described an experiment in 18-month-old rats. After suturing the tendon, they delivered the CREB3L1 gene to cells near the injury. Three weeks later, they measured how well the healed tendon glided, withstood loading, and resisted stretching.
A tendon transmits force from muscle to bone. After a rupture, surgeons suture the ends together, and cells must produce new collagen fibers. This process allows the digit to flex again and enables the repair to withstand loading.
The authors compared tendons from 8-week-old and 18-month-old rats. In the cells that build the tissue scaffold, the activity of three genes declined with age: CREB3L1, COL1A1, and SPARC. CREB3L1 encodes a protein that activates other genes. COL1A1 encodes one of the chains of collagen I, which forms load-bearing fibers. SPARC helps organize these fibers within the protein-rich environment between cells.
The researchers tested whether CREB3L1 could activate both genes. A computational search identified sites in the regulatory DNA regions of COL1A1 and SPARC where the protein might bind. The researchers linked these regions to a luminescent reporter. CREB3L1 increased the reporter signal, while changes to the regions eliminated this effect in all four SPARC variants tested and in three of the four COL1A1 variants. Adding CREB3L1 to tendon cells also increased the abundance of both proteins.
The researchers then tested this pathway during healing. They transected and sutured the tendon that flexes the digit, then injected a lentivirus into the suture site. The lentivirus was a modified virus designed to deliver the CREB3L1 gene. Separate groups underwent surgery alone or received the same virus without the gene. These controls allowed the authors to distinguish the effect of CREB3L1 from the effects of suturing and viral delivery.
Three weeks later, applying a load to the tendon produced greater digit flexion in both males and females. In males, the healed tissue reached a strength of 32.6 N, compared with 22.5 N after surgery alone and 23.6 N after delivery of the control virus. Its elastic modulus, a measure of resistance to stretching, increased to 11.7 N/mm, compared with 8.1 and 8.6 N. In females, the authors confirmed improvement only in the digit flexion angle.
The authors therefore linked the age-related decline in gene activity to the function of the repaired tendon. Local CREB3L1 delivery improved tendon gliding in both sexes and also improved mechanical properties in males.