Expression of TGF-β1, TGF-β3 and bFGF in full-thickness dermal wounds of the horse

Abstract

Wounds on equine limbs often develop exuberant granulation tissue and subsequently heal in a delayed fashion, while body wounds generally heal uneventfully. Growth factors favor angiogenesis and the deposition of extracellular matrix. In other species, TGF-β1 levels are elevated in fibrotic disease and neutralization of this growth factor provides an antiscarring effect. Conversely, TGF-β3 is considered antifibrotic since application has been shown to reduce connective tissue deposition and subsequent scarring. To understand the pathogenesis of exuberant granulation tissue, I mapped the expression of various growth factors in normally healing equine limb and thoracic wounds, as well as in limb wounds healing exuberantly. Four horses had six wounds created on each metacarpus III and midthoracic areas. The wounds of one side of the body were sutured, while those of the other side were not. Another four horses had six wounds created on each metacarpus III area; one forelimb received no treatment whereas the other was bandaged (exuberant granulation tissue model). Wounds were assessed grossly and histologically at 12 and 24 hours, and two, five, ten and 14 days postoperatively. ELISAs were utilized to measure the protein levels of TGF-β1 and -3, and bFGF in tissue extracts of wound margin biopsies. Grossly, the quality and speed of healing were greater in thoracic wounds. Histologically, inflammation was greater and persisted longer in limb wounds whereas epithelial coverage was significantly accelerated in thoracic wounds. All bandaged wounds developed proud flesh which inhibited epithelialization. TGF-β1 expression was upregulated early in the study for all wounds. By the end of the study its levels were significantly reduced in thoracic wounds as compared to limb wounds. The expression of TGF-β3 differed with an overall pattern of gradual increase over time and peak levels attained after the proliferative phase of healing. This is the first study to map the expression of growth factors during normal wound repair in the horse. There appears to be a reciprocal regulation of TGF-β1 and -3 during equine wound healing. The persistent elevation of profibrotic TGF-β1 may be responsible for the development of proud flesh in the limb wounds of some horses.