Skin flap-induced regression of granulation tissue correlates with reduced growth factor and increased metalloproteinase expression

• Published in: The Journal of pathology 2002-05, Vol.197 (1), p.117-127
• Main Authors: Darby, Ian A., Bisucci, Teresa, Pittet, Brigitte, Garbin, Stefania, Gabbiani, Giulio, Desmoulière, Alexis
• Format: Article
• Language: English
• Subjects: Animals; Apoptosis; Biological and medical sciences; Degeneration. Regeneration. Wound healing. Graft; Female; Fundamental and applied biological sciences. Psychology; Gene Expression; granulation tissue; Granulation Tissue - metabolism; Granulation Tissue - pathology; growth factor; Growth Substances - metabolism; In Situ Hybridization; Metalloendopeptidases - metabolism; metalloproteinase; myofibroblast; Nitric Oxide Synthase - metabolism; Rats; Rats, Wistar; RNA, Messenger - genetics; Skin Transplantation - pathology; Surgical Flaps - pathology; Tissue Inhibitor of Metalloproteinase-1 - genetics; Tissue Inhibitor of Metalloproteinase-1 - metabolism; Transforming Growth Factor beta - genetics; Transforming Growth Factor beta - metabolism; Transforming Growth Factor beta1; Vertebrates: anatomy and physiology, studies on body, several organs or systems
• ISSN: 0022-3417; 1096-9896
• DOI: 10.1002/path.1074

Previous studies have shown that covering granulation tissue of a full‐thickness skin wound by a vascularized skin flap induces tissue remodeling, with a rapid loss of granulation tissue cells by apoptosis. In the present study, in situ hybridization has been used to examine mRNA expression for several factors that may be implicated in the apoptosis seen in this tissue. Skin wounds were made on the dorsal skin of 8‐week‐old rats. Ten days after wounding, skin flaps were created surgically and sutured over the granulation tissue. Tissue sections of granulation tissue from various times after addition of the skin flap were hybridized with 33P‐labelled cRNA probes for transforming growth factor‐β1 (TGF‐β1), beta‐inducible gene H3 (β‐ig‐h3), α1 (I) procollagen, α‐smooth muscle actin, matrix metalloproteinase‐13 (MMP‐13) and ‐2 (MMP‐2), tissue inhibitor of metalloproteinase‐1 (TIMP‐1), and inducible nitric oxide synthase (iNOS). Control granulation tissue prior to addition of the skin flap showed high levels of TGF‐β1, β‐ig‐h3, α1 (I) procollagen, α‐smooth muscle actin, and TIMP‐1 expression. MMP‐13, MMP‐2, and iNOS mRNA were low in 10‐day granulation tissue. Addition of a skin flap resulted in a decrease in the expression of TGF‐β1, β‐ig‐h3, α1 (I) procollagen, α‐smooth muscle actin, and TIMP‐1, but increased expression of MMP‐13 and MMP‐2. Similarly, an increase in iNOS mRNA expression was observed in the granulation tissue after addition of the skin flap. Addition of a vascularized skin flap may result in rapid remodelling of granulation tissue due to a decrease in expression ofthe trophic growth factor TGF‐β1 and increased degradation of extracellular matrix due to an alteration in the balance between MMPs and their inhibitor, TIMP‐1. Additionally, increased iNOS expression may also favour apoptosis through the generation of free radicals. The additive effect of reduced growth factor expression, increased extracellular matrix turnover, and nitric oxide generation may result in the fibroblast and vascular cell apoptosis seen during the rapid remodelling of this tissue. Copyright © 2002 John Wiley & Sons, Ltd.