No abstract

Growth factors, transforming growth factor beta (TGF-beta), epidermal growth factor (EGF), platelet-derived growth factor (PDGF), insulin-like growth factor (IGF), basic fibroblast growth factor (bFGF), and vascular endothelial growth factor (VEGF), are critical components of the cutaneous wound healing process. Little is known, however, about the expression of these growth factors in normal flexor tendon healing. In this study, we wished to examine which of these growth factors are present at 10 days following tendon injury in a canine flexor tendon repair model. Using immunohistochemical analysis, we found positive staining for all growth factors in both timing groups. TGF-beta was detected around the repair site and proximal to it. PDGF-AA, PDGF-BB and VEGF appeared in the whole tendon section following repair. EGF, IGF and bFGF were not seen in tenocytes but were present in inflammatory cells surrounding the repair site. These findings provide evidence that TGF-beta, EGF, PDGF-AA, PDGF-BB, IGF, bFGF and VEGF are all expressed at 10 days after tendon injury but by different cell types and in different locations. The time course of growth factor expression is an important element in wound healing, and a better understanding of where and when such factors are expressed may help in the development of methods to manipulate this expression, accelerate healing, and reduce adhesions.

The purpose of this study is to investigate age-dependent changes in the architecture and mechanical properties of tendon in TGF-beta inducible early gene-1 (TIEG) knockout mice. Wild-type and TIEG knockout mice, aged 1, 2, and 15 mo, were used. The mechanical properties of tail tendons isolated from these mice were determined using uniaxial tensile ramp (0.05 mm/s) and relaxation (5 mm/s) tests, with a strain of 10%. Mechanical parameters (Young's modulus from the ramp test; fast and static stresses from the relaxation test) were measured and recorded. The structure of the tail tendon fascicle was characterized by transmission electron microscopy. The results of the mechanical testing revealed no significant difference between the knockout and wild-type groups at 1 or 15 mo of age. However, the fascicles of the knockout mice at 3 mo of age exhibited decreased fast and static stresses compared with those of the wild-type mice. Electron microscopy revealed an increase in fibril size in the knockout mouse tendons relative to wild-type controls at 1 and 3 mo of age. These data indicate an important role for TIEG in tendon microarchitecture and strength in adult mice.

The role of transforming growth factor b (TGF-b) in tendon healing is still not clearly established. TGF-b affects gene expression primarily through the activation of the Smad signaling pathway. The first step in the Smad pathway is the expression of TGF-b inducible early gene (TIEG). Recently, a TIEG knockout mouse has been developed. The purpose of this study was to examine the healing potential of flexor tendons in mice lacking the TIEG gene, and to further examine what role the TIEG pathway plays in flexor tendon repair. Twenty-two mice, consisting of 11 normal wild-type mice and 11 TIEG knockout mice, were euthanized at 8 to 12 weeks of age. The second through fifth FDL tendons of both hind feet were transected and repaired in zone 2. The repaired tendons were removed from the mice and placed into tissue culture. Tendons were then examined at days 3, 7, 14, 21, and 42 after surgery. Hematoxylin and eosin (HE) staining and immunohistochemical staining for TGF-b, collagen type I, and collagen type III were performed. Reverse transcriptase polymerase chain reaction (RT-PCR) was performed to examine expression of TGF-b1, b2, b3, and collagen type I and III. At 42 days after surgery, HE staining showed coaptation of lacerated tendon ends in both groups. Both groups showed healing of the lacerated tendon, but the chronologic expression pattern of TGF-b was different between the knockout and normal tendons. TIEG deficient tendons had delayed expression of TGF-b when compared with control tendons. The collagen mRNA expression pattern was similar with both groups, but the expression level was different, with TIEG knockout tendons having a lower expression of collagen type I mRNA (p < 0.001). TGF-b is thought to play a major role in tendon healing. Healing of tendons in the TIEG knockout mouse suggests the possibility of tendon healing in the absence of the Smad pathway. The knockout mouse model described in the present study provides a novel means for further understanding of the tendon healing process through isolated deletion of specific growth factors. ß